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From cmcc...@apache.org
Subject [3/5] incubator-htrace git commit: HTRACE-259. Rename htrace-core module to htrace-core4 to match the artifactId (stack via cmccabe)
Date Sun, 20 Sep 2015 04:12:55 GMT
http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core/src/test/java/org/apache/htrace/core/TraceCreator.java
----------------------------------------------------------------------
diff --git a/htrace-core/src/test/java/org/apache/htrace/core/TraceCreator.java b/htrace-core/src/test/java/org/apache/htrace/core/TraceCreator.java
deleted file mode 100644
index b843999..0000000
--- a/htrace-core/src/test/java/org/apache/htrace/core/TraceCreator.java
+++ /dev/null
@@ -1,141 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.htrace.core;
-
-import java.util.Random;
-import java.util.concurrent.ThreadLocalRandom;
-
-/**
- * Does some stuff and traces it.
- */
-public class TraceCreator {
-  public static final String RPC_TRACE_ROOT = "createSampleRpcTrace";
-  public static final String THREADED_TRACE_ROOT = "createThreadedTrace";
-  public static final String SIMPLE_TRACE_ROOT = "createSimpleTrace";
-
-  private final Tracer tracer;
-
-  public TraceCreator(Tracer tracer) {
-    this.tracer = tracer;
-  }
-
-  public void createSampleRpcTrace() {
-    TraceScope s = tracer.newScope(RPC_TRACE_ROOT);
-    try {
-      pretendRpcSend();
-    } finally {
-      s.close();
-    }
-  }
-
-  public void createSimpleTrace() {
-    TraceScope s = tracer.newScope(SIMPLE_TRACE_ROOT);
-    try {
-      importantWork1();
-    } finally {
-      s.close();
-    }
-  }
-
-  /**
-   * Creates the demo trace (will create different traces from call to call).
-   */
-  public void createThreadedTrace() {
-    TraceScope s = tracer.newScope(THREADED_TRACE_ROOT);
-    try {
-      Random r = ThreadLocalRandom.current();
-      int numThreads = r.nextInt(4) + 1;
-      Thread[] threads = new Thread[numThreads];
-
-      for (int i = 0; i < numThreads; i++) {
-        threads[i] = new Thread(tracer.wrap(new MyRunnable(), null));
-      }
-      for (int i = 0; i < numThreads; i++) {
-        threads[i].start();
-      }
-      for (int i = 0; i < numThreads; i++) {
-        try {
-          threads[i].join();
-        } catch (InterruptedException e) {
-        }
-      }
-      importantWork1();
-    } finally {
-      s.close();
-    }
-  }
-
-  private void importantWork1() {
-    TraceScope cur = tracer.newScope("important work 1");
-    try {
-      Thread.sleep((long) (2000 * Math.random()));
-      importantWork2();
-    } catch (InterruptedException e) {
-      Thread.currentThread().interrupt();
-    } finally {
-      cur.close();
-    }
-  }
-
-  private void importantWork2() {
-    TraceScope cur = tracer.newScope("important work 2");
-    try {
-      Thread.sleep((long) (2000 * Math.random()));
-    } catch (InterruptedException e) {
-      Thread.currentThread().interrupt();
-    } finally {
-      cur.close();
-    }
-  }
-
-  private class MyRunnable implements Runnable {
-    @Override
-    public void run() {
-      try {
-        Thread.sleep(750);
-        Random r = ThreadLocalRandom.current();
-        int importantNumber = 100 / r.nextInt(3);
-        System.out.println("Important number: " + importantNumber);
-      } catch (InterruptedException ie) {
-        Thread.currentThread().interrupt();
-      } catch (ArithmeticException ae) {
-        TraceScope c = tracer.newScope("dealing with arithmetic exception.");
-        try {
-          Thread.sleep((long) (3000 * Math.random()));
-        } catch (InterruptedException ie1) {
-          Thread.currentThread().interrupt();
-        } finally {
-          c.close();
-        }
-      }
-    }
-  }
-
-  public void pretendRpcSend() {
-    Span span = tracer.getCurrentSpan();
-    pretendRpcReceiveWithTraceInfo(span.getSpanId());
-  }
-
-  public void pretendRpcReceiveWithTraceInfo(SpanId parentId) {
-    TraceScope s = tracer.newScope("received RPC", parentId);
-    try {
-      importantWork1();
-    } finally {
-      s.close();
-    }
-  }
-}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core/src/test/java/org/apache/htrace/core/TraceGraph.java
----------------------------------------------------------------------
diff --git a/htrace-core/src/test/java/org/apache/htrace/core/TraceGraph.java b/htrace-core/src/test/java/org/apache/htrace/core/TraceGraph.java
deleted file mode 100644
index a06e620..0000000
--- a/htrace-core/src/test/java/org/apache/htrace/core/TraceGraph.java
+++ /dev/null
@@ -1,176 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.htrace.core;
-
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.Comparator;
-import java.util.HashMap;
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.TreeSet;
-
-/**
- * Used to create the graph formed by spans.
- */
-public class TraceGraph {
-  private static final Log LOG = LogFactory.getLog(Tracer.class);
-
-
-  public static class SpansByParent {
-    /**
-     * Compare two spans by span ID.
-     */
-    private static Comparator<Span> COMPARATOR =
-        new Comparator<Span>() {
-          @Override
-          public int compare(Span a, Span b) {
-            return a.getSpanId().compareTo(b.getSpanId());
-          }
-        };
-
-    private final TreeSet<Span> treeSet;
-
-    private final HashMap<SpanId, LinkedList<Span>> parentToSpans;
-
-    SpansByParent(Collection<Span> spans) {
-      TreeSet<Span> treeSet = new TreeSet<Span>(COMPARATOR);
-      parentToSpans = new HashMap<SpanId, LinkedList<Span>>();
-      for (Span span : spans) {
-        treeSet.add(span);
-        for (SpanId parent : span.getParents()) {
-          LinkedList<Span> list = parentToSpans.get(parent);
-          if (list == null) {
-            list = new LinkedList<Span>();
-            parentToSpans.put(parent, list);
-          }
-          list.add(span);
-        }
-        if (span.getParents().length == 0) {
-          LinkedList<Span> list = parentToSpans.get(SpanId.INVALID);
-          if (list == null) {
-            list = new LinkedList<Span>();
-            parentToSpans.put(SpanId.INVALID, list);
-          }
-          list.add(span);
-        }
-      }
-      this.treeSet = treeSet;
-    }
-
-    public List<Span> find(SpanId parentId) {
-      LinkedList<Span> spans = parentToSpans.get(parentId);
-      if (spans == null) {
-        return new LinkedList<Span>();
-      }
-      return spans;
-    }
-
-    public Iterator<Span> iterator() {
-      return Collections.unmodifiableSortedSet(treeSet).iterator();
-    }
-  }
-
-  public static class SpansByTracerId {
-    /**
-     * Compare two spans by process ID, and then by span ID.
-     */
-    private static Comparator<Span> COMPARATOR =
-        new Comparator<Span>() {
-          @Override
-          public int compare(Span a, Span b) {
-            int cmp = a.getTracerId().compareTo(b.getTracerId());
-            if (cmp != 0) {
-              return cmp;
-            }
-            return a.getSpanId().compareTo(b.getSpanId());
-          }
-        };
-
-    private final TreeSet<Span> treeSet;
-
-    SpansByTracerId(Collection<Span> spans) {
-      TreeSet<Span> treeSet = new TreeSet<Span>(COMPARATOR);
-      for (Span span : spans) {
-        treeSet.add(span);
-      }
-      this.treeSet = treeSet;
-    }
-
-    public List<Span> find(String tracerId) {
-      List<Span> spans = new ArrayList<Span>();
-      Span span = new MilliSpan.Builder().
-                    spanId(SpanId.INVALID).
-                    tracerId(tracerId).
-                    build();
-      while (true) {
-        span = treeSet.higher(span);
-        if (span == null) {
-          break;
-        }
-        if (span.getTracerId().equals(tracerId)) {
-          break;
-        }
-        spans.add(span);
-      }
-      return spans;
-    }
-
-    public Iterator<Span> iterator() {
-      return Collections.unmodifiableSortedSet(treeSet).iterator();
-    }
-  }
-
-  private final SpansByParent spansByParent;
-  private final SpansByTracerId spansByTracerId;
-
-  /**
-   * Create a new TraceGraph
-   *
-   * @param spans The collection of spans to use to create this TraceGraph. Should
-   *              have at least one root span.
-   */
-  public TraceGraph(Collection<Span> spans) {
-    this.spansByParent = new SpansByParent(spans);
-    this.spansByTracerId = new SpansByTracerId(spans);
-  }
-
-  public SpansByParent getSpansByParent() {
-    return spansByParent;
-  }
-
-  public SpansByTracerId getSpansByTracerId() {
-    return spansByTracerId;
-  }
-
-  @Override
-  public String toString() {
-    StringBuilder bld = new StringBuilder();
-    String prefix = "";
-    for (Iterator<Span> iter = spansByParent.iterator(); iter.hasNext();) {
-      Span span = iter.next();
-      bld.append(prefix).append(span.toString());
-      prefix = "\n";
-    }
-    return bld.toString();
-  }
-}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core/src/test/java/org/apache/htrace/util/TestUtil.java
----------------------------------------------------------------------
diff --git a/htrace-core/src/test/java/org/apache/htrace/util/TestUtil.java b/htrace-core/src/test/java/org/apache/htrace/util/TestUtil.java
deleted file mode 100644
index 7cb4aed..0000000
--- a/htrace-core/src/test/java/org/apache/htrace/util/TestUtil.java
+++ /dev/null
@@ -1,91 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.apache.htrace.util;
-
-import java.io.File;
-import java.util.Map;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.TimeoutException;
-
-/**
- * Utilities for writing unit tests.
- */
-public class TestUtil {
-  /**
-   * Get a dump of the stack traces of all threads.
-   */
-  public static String threadDump() {
-    StringBuilder dump = new StringBuilder();
-    Map<Thread, StackTraceElement[]> stackTraces = Thread.getAllStackTraces();
-    for (Map.Entry<Thread, StackTraceElement[]> e : stackTraces.entrySet()) {
-      Thread thread = e.getKey();
-      dump.append(String.format(
-          "\"%s\" %s prio=%d tid=%d %s\njava.lang.Thread.State: %s",
-          thread.getName(),
-          (thread.isDaemon() ? "daemon" : ""),
-          thread.getPriority(),
-          thread.getId(),
-          Thread.State.WAITING.equals(thread.getState()) ?
-              "in Object.wait()" : thread.getState().name().toLowerCase(),
-          Thread.State.WAITING.equals(thread.getState()) ?
-              "WAITING (on object monitor)" : thread.getState()));
-      for (StackTraceElement stackTraceElement : e.getValue()) {
-        dump.append("\n        at ");
-        dump.append(stackTraceElement);
-      }
-      dump.append("\n");
-    }
-    return dump.toString();
-  }
-
-  /**
-   * A callback which returns a value of type T.
-   *
-   * TODO: remove this when we're on Java 8, in favor of
-   * java.util.function.Supplier.
-   */
-  public interface Supplier<T> {
-    T get();
-  }
-
-  /**
-   * Wait for a condition to become true for a configurable amount of time.
-   *
-   * @param check           The condition to wait for.
-   * @param periodMs        How often to check the condition, in milliseconds.
-   * @param timeoutMs       How long to wait in total, in milliseconds.
-   */
-  public static void waitFor(Supplier<Boolean> check, 
-      long periodMs, long timeoutMs)
-          throws TimeoutException, InterruptedException
-  {
-    long endNs = System.nanoTime() +
-        TimeUnit.NANOSECONDS.convert(timeoutMs, TimeUnit.MILLISECONDS);
-    while (true) {
-      boolean result = check.get();
-      if (result) {
-        return;
-      }
-      long nowNs = System.nanoTime();
-      if (nowNs >= endNs) {
-        throw new TimeoutException("Timed out waiting for test condition. " +
-            "Thread dump:\n" + threadDump());
-      }
-      Thread.sleep(periodMs);
-    }
-  }
-}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/pom.xml
----------------------------------------------------------------------
diff --git a/htrace-core4/pom.xml b/htrace-core4/pom.xml
new file mode 100644
index 0000000..efaaf65
--- /dev/null
+++ b/htrace-core4/pom.xml
@@ -0,0 +1,125 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor
+license agreements. See the NOTICE file distributed with this work for additional
+information regarding copyright ownership. The ASF licenses this file to
+You under the Apache License, Version 2.0 (the "License"); you may not use
+this file except in compliance with the License. You may obtain a copy of
+the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required
+by applicable law or agreed to in writing, software distributed under the
+License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS
+OF ANY KIND, either express or implied. See the License for the specific
+language governing permissions and limitations under the License. -->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <artifactId>htrace-core4</artifactId>
+  <packaging>jar</packaging>
+
+  <parent>
+    <artifactId>htrace</artifactId>
+    <groupId>org.apache.htrace</groupId>
+    <version>4.0.1-incubating</version>
+    <relativePath>..</relativePath>
+  </parent>
+
+  <name>htrace-core4</name>
+  <url>http://incubator.apache.org/projects/htrace.html</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-source-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <artifactId>maven-javadoc-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-shade-plugin</artifactId>
+        <executions>
+          <execution>
+            <phase>package</phase>
+            <configuration>
+              <relocations>
+                <relocation>
+                  <pattern>org.apache.commons.logging</pattern>
+                  <shadedPattern>org.apache.htrace.commons.logging</shadedPattern>
+                </relocation>
+                <relocation>
+                  <pattern>com.fasterxml.jackson</pattern>
+                  <shadedPattern>org.apache.htrace.fasterxml.jackson</shadedPattern>
+                </relocation>
+              </relocations>
+            </configuration>
+            <goals>
+              <goal>shade</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-gpg-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.rat</groupId>
+        <artifactId>apache-rat-plugin</artifactId>
+      </plugin>
+      <plugin>
+        <!-- explicitly define maven-deploy-plugin after other to force exec order -->
+        <artifactId>maven-deploy-plugin</artifactId>
+      </plugin>
+    </plugins>
+  </build>
+
+  <dependencies>
+    <!-- Global deps. -->
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-core</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-databind</artifactId>
+    </dependency>
+    <!-- core specific deps. -->
+    <dependency>
+      <groupId>commons-logging</groupId>
+      <artifactId>commons-logging</artifactId>
+    </dependency>
+  </dependencies>
+
+  <profiles>
+    <profile>
+      <id>dist</id>
+      <build>
+        <plugins>
+          <plugin>
+            <!--Make it so assembly:single does nothing in here-->
+            <artifactId>maven-assembly-plugin</artifactId>
+            <configuration>
+              <skipAssembly>true</skipAssembly>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
+  </profiles>
+</project>

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/AlwaysSampler.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/AlwaysSampler.java b/htrace-core4/src/main/java/org/apache/htrace/core/AlwaysSampler.java
new file mode 100644
index 0000000..8d5a296
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/AlwaysSampler.java
@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+/**
+ * A Sampler that always returns true.
+ */
+public final class AlwaysSampler extends Sampler {
+  public static final AlwaysSampler INSTANCE = new AlwaysSampler(null);
+
+  public AlwaysSampler(HTraceConfiguration conf) {
+  }
+
+  @Override
+  public boolean next() {
+    return true;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/CountSampler.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/CountSampler.java b/htrace-core4/src/main/java/org/apache/htrace/core/CountSampler.java
new file mode 100644
index 0000000..5a838c7
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/CountSampler.java
@@ -0,0 +1,39 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+/**
+ * Sampler that returns true every N calls. Specify the frequency interval by configuring a
+ * {@code long} value for {@link #SAMPLER_FREQUENCY_CONF_KEY}.
+ */
+public class CountSampler extends Sampler {
+  public final static String SAMPLER_FREQUENCY_CONF_KEY = "sampler.frequency";
+
+  final long frequency;
+  long count = ThreadLocalRandom.current().nextLong();
+
+  public CountSampler(HTraceConfiguration conf) {
+    this.frequency = Long.parseLong(conf.get(SAMPLER_FREQUENCY_CONF_KEY), 10);
+  }
+
+  @Override
+  public boolean next() {
+    return (count++ % frequency) == 0;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/HTraceConfiguration.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/HTraceConfiguration.java b/htrace-core4/src/main/java/org/apache/htrace/core/HTraceConfiguration.java
new file mode 100644
index 0000000..c6e445b
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/HTraceConfiguration.java
@@ -0,0 +1,109 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Wrapper which integrating applications should implement in order
+ * to provide tracing configuration.
+ */
+public abstract class HTraceConfiguration {
+
+  private static final Log LOG = LogFactory.getLog(HTraceConfiguration.class);
+
+  private static final Map<String, String> EMPTY_MAP = new HashMap<String, String>(1);
+
+  /**
+   * An empty HTrace configuration.
+   */
+  public static final HTraceConfiguration EMPTY = fromMap(EMPTY_MAP);
+
+  /**
+   * Create an HTrace configuration from a map.
+   *
+   * @param conf    The map to create the configuration from.
+   * @return        The new configuration.
+   */
+  public static HTraceConfiguration fromMap(Map<String, String> conf) {
+    return new MapConf(conf);
+  }
+
+  public static HTraceConfiguration fromKeyValuePairs(String... pairs) {
+    if ((pairs.length % 2) != 0) {
+      throw new RuntimeException("You must specify an equal number of keys " +
+          "and values.");
+    }
+    Map<String, String> conf = new HashMap<String, String>();
+    for (int i = 0; i < pairs.length; i+=2) {
+      conf.put(pairs[i], pairs[i + 1]);
+    }
+    return new MapConf(conf);
+  }
+
+  public abstract String get(String key);
+
+  public abstract String get(String key, String defaultValue);
+
+  public boolean getBoolean(String key, boolean defaultValue) {
+    String value = get(key, String.valueOf(defaultValue)).trim().toLowerCase();
+
+    if ("true".equals(value)) {
+      return true;
+    } else if ("false".equals(value)) {
+      return false;
+    }
+
+    LOG.warn("Expected boolean for key [" + key + "] instead got [" + value + "].");
+    return defaultValue;
+  }
+
+  public int getInt(String key, int defaultVal) {
+    String val = get(key);
+    if (val == null || val.trim().isEmpty()) {
+      return defaultVal;
+    }
+    try {
+      return Integer.parseInt(val);
+    } catch (NumberFormatException nfe) {
+      throw new IllegalArgumentException("Bad value for '" + key + "': should be int");
+    }
+  }
+
+  private static class MapConf extends HTraceConfiguration {
+    private final Map<String, String> conf;
+
+    public MapConf(Map<String, String> conf) {
+      this.conf = new HashMap<String, String>(conf);
+    }
+
+    @Override
+    public String get(String key) {
+      return conf.get(key);
+    }
+
+    @Override
+    public String get(String key, String defaultValue) {
+      String value = get(key);
+      return value == null ? defaultValue : value;
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/LocalFileSpanReceiver.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/LocalFileSpanReceiver.java b/htrace-core4/src/main/java/org/apache/htrace/core/LocalFileSpanReceiver.java
new file mode 100644
index 0000000..69a43b1
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/LocalFileSpanReceiver.java
@@ -0,0 +1,257 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.EOFException;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.FileSystems;
+import java.nio.file.StandardOpenOption;
+import java.util.UUID;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Writes the spans it receives to a local file.
+ */
+public class LocalFileSpanReceiver extends SpanReceiver {
+  private static final Log LOG = LogFactory.getLog(LocalFileSpanReceiver.class);
+  public static final String PATH_KEY = "local.file.span.receiver.path";
+  public static final String CAPACITY_KEY = "local.file.span.receiver.capacity";
+  public static final int CAPACITY_DEFAULT = 5000;
+  private static ObjectWriter JSON_WRITER = new ObjectMapper().writer();
+  private final String path;
+
+  private byte[][] bufferedSpans;
+  private int bufferedSpansIndex;
+  private final ReentrantLock bufferLock = new ReentrantLock();
+
+  private final FileOutputStream stream;
+  private final FileChannel channel;
+  private final ReentrantLock channelLock = new ReentrantLock();
+
+  public LocalFileSpanReceiver(HTraceConfiguration conf) {
+    int capacity = conf.getInt(CAPACITY_KEY, CAPACITY_DEFAULT);
+    if (capacity < 1) {
+      throw new IllegalArgumentException(CAPACITY_KEY + " must not be " +
+          "less than 1.");
+    }
+    String pathStr = conf.get(PATH_KEY);
+    if (pathStr == null || pathStr.isEmpty()) {
+      path = getUniqueLocalTraceFileName();
+    } else {
+      path = pathStr;
+    }
+    boolean success = false;
+    try {
+      this.stream = new FileOutputStream(path, true);
+    } catch (IOException ioe) {
+      LOG.error("Error opening " + path + ": " + ioe.getMessage());
+      throw new RuntimeException(ioe);
+    }
+    this.channel = stream.getChannel();
+    if (this.channel == null) {
+      try {
+        this.stream.close();
+      } catch (IOException e) {
+        LOG.error("Error closing " + path, e);
+      }
+      LOG.error("Failed to get channel for " + path);
+      throw new RuntimeException("Failed to get channel for " + path);
+    }
+    this.bufferedSpans = new byte[capacity][];
+    this.bufferedSpansIndex = 0;
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Created new LocalFileSpanReceiver with path = " + path +
+                ", capacity = " + capacity);
+    }
+  }
+
+  /**
+   * Number of buffers to use in FileChannel#write.
+   *
+   * On UNIX, FileChannel#write uses writev-- a kernel interface that allows
+   * us to send multiple buffers at once.  This is more efficient than making a
+   * separate write call for each buffer, since it minimizes the number of
+   * transitions from userspace to kernel space.
+   */
+  private final int WRITEV_SIZE = 20;
+
+  private final static ByteBuffer newlineBuf = 
+      ByteBuffer.wrap(new byte[] { (byte)0xa });
+
+  /**
+   * Flushes a bufferedSpans array.
+   */
+  private void doFlush(byte[][] toFlush, int len) throws IOException {
+    int bidx = 0, widx = 0;
+    ByteBuffer writevBufs[] = new ByteBuffer[2 * WRITEV_SIZE];
+
+    while (true) {
+      if (widx == writevBufs.length) {
+        channel.write(writevBufs);
+        widx = 0;
+      }
+      if (bidx == len) {
+        break;
+      }
+      writevBufs[widx] = ByteBuffer.wrap(toFlush[bidx]);
+      writevBufs[widx + 1] = newlineBuf;
+      bidx++;
+      widx+=2;
+    }
+    if (widx > 0) {
+      channel.write(writevBufs, 0, widx);
+    }
+  }
+
+  @Override
+  public void receiveSpan(Span span) {
+    // Serialize the span data into a byte[].  Note that we're not holding the
+    // lock here, to improve concurrency.
+    byte jsonBuf[] = null;
+    try {
+      jsonBuf = JSON_WRITER.writeValueAsBytes(span);
+    } catch (JsonProcessingException e) {
+        LOG.error("receiveSpan(path=" + path + ", span=" + span + "): " +
+                  "Json processing error: " + e.getMessage());
+      return;
+    }
+
+    // Grab the bufferLock and put our jsonBuf into the list of buffers to
+    // flush. 
+    byte toFlush[][] = null;
+    bufferLock.lock();
+    try {
+      if (bufferedSpans == null) {
+        LOG.debug("receiveSpan(path=" + path + ", span=" + span + "): " +
+                  "LocalFileSpanReceiver for " + path + " is closed.");
+        return;
+      }
+      bufferedSpans[bufferedSpansIndex] = jsonBuf;
+      bufferedSpansIndex++;
+      if (bufferedSpansIndex == bufferedSpans.length) {
+        // If we've hit the limit for the number of buffers to flush, 
+        // swap out the existing bufferedSpans array for a new array, and
+        // prepare to flush those spans to disk.
+        toFlush = bufferedSpans;
+        bufferedSpansIndex = 0;
+        bufferedSpans = new byte[bufferedSpans.length][];
+      }
+    } finally {
+      bufferLock.unlock();
+    }
+    if (toFlush != null) {
+      // We released the bufferLock above, to avoid blocking concurrent
+      // receiveSpan calls.  But now, we must take the channelLock, to make
+      // sure that we have sole access to the output channel.  If we did not do
+      // this, we might get interleaved output.
+      //
+      // There is a small chance that another thread doing a flush of more
+      // recent spans could get ahead of us here, and take the lock before we
+      // do.  This is ok, since spans don't have to be written out in order.
+      channelLock.lock();
+      try {
+        doFlush(toFlush, toFlush.length);
+      } catch (IOException ioe) {
+        LOG.error("Error flushing buffers to " + path + ": " +
+            ioe.getMessage());
+      } finally {
+        channelLock.unlock();
+      }
+    }
+  }
+
+  @Override
+  public void close() throws IOException {
+    byte toFlush[][] = null;
+    int numToFlush = 0;
+    bufferLock.lock();
+    try {
+      if (bufferedSpans == null) {
+        LOG.info("LocalFileSpanReceiver for " + path + " was already closed.");
+        return;
+      }
+      numToFlush = bufferedSpansIndex;
+      bufferedSpansIndex = 0;
+      toFlush = bufferedSpans;
+      bufferedSpans = null;
+    } finally {
+      bufferLock.unlock();
+    }
+    channelLock.lock();
+    try {
+      doFlush(toFlush, numToFlush);
+    } catch (IOException ioe) {
+      LOG.error("Error flushing buffers to " + path + ": " +
+          ioe.getMessage());
+    } finally {
+      try {
+        stream.close();
+      } catch (IOException e) {
+        LOG.error("Error closing stream for " + path, e);
+      }
+      channelLock.unlock();
+    }
+  }
+
+  public static String getUniqueLocalTraceFileName() {
+    String tmp = System.getProperty("java.io.tmpdir", "/tmp");
+    String nonce = null;
+    BufferedReader reader = null;
+    try {
+      // On Linux we can get a unique local file name by reading the process id
+      // out of /proc/self/stat.  (There isn't any portable way to get the
+      // process ID from Java.)
+      reader = new BufferedReader(
+          new InputStreamReader(new FileInputStream("/proc/self/stat"),
+                                "UTF-8"));
+      String line = reader.readLine();
+      if (line == null) {
+        throw new EOFException();
+      }
+      nonce = line.split(" ")[0];
+    } catch (IOException e) {
+    } finally {
+      if (reader != null) {
+        try {
+          reader.close();
+        } catch(IOException e) {
+          LOG.warn("Exception in closing " + reader, e);
+        }
+      }
+    }
+    if (nonce == null) {
+      // If we can't use the process ID, use a random nonce.
+      nonce = UUID.randomUUID().toString();
+    }
+    return new File(tmp, nonce).getAbsolutePath();
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/MilliSpan.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/MilliSpan.java b/htrace-core4/src/main/java/org/apache/htrace/core/MilliSpan.java
new file mode 100644
index 0000000..5dd6bdb
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/MilliSpan.java
@@ -0,0 +1,347 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.UnsupportedEncodingException;
+import java.math.BigInteger;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A Span implementation that stores its information in milliseconds since the
+ * epoch.
+ */
+@JsonDeserialize(using = MilliSpan.MilliSpanDeserializer.class)
+public class MilliSpan implements Span {
+  private static ObjectMapper OBJECT_MAPPER = new ObjectMapper();
+  private static ObjectReader JSON_READER = OBJECT_MAPPER.reader(MilliSpan.class);
+  private static ObjectWriter JSON_WRITER = OBJECT_MAPPER.writer();
+  private static final SpanId EMPTY_PARENT_ARRAY[] = new SpanId[0];
+  private static final String EMPTY_STRING = "";
+
+  private long begin;
+  private long end;
+  private final String description;
+  private SpanId parents[];
+  private final SpanId spanId;
+  private Map<String, String> traceInfo = null;
+  private String tracerId;
+  private List<TimelineAnnotation> timeline = null;
+
+  @Override
+  public Span child(String childDescription) {
+    return new MilliSpan.Builder().
+      begin(System.currentTimeMillis()).
+      end(0).
+      description(childDescription).
+      parents(new SpanId[] {spanId}).
+      spanId(spanId.newChildId()).
+      tracerId(tracerId).
+      build();
+  }
+
+  /**
+   * The public interface for constructing a MilliSpan.
+   */
+  public static class Builder {
+    private long begin;
+    private long end;
+    private String description = EMPTY_STRING;
+    private SpanId parents[] = EMPTY_PARENT_ARRAY;
+    private SpanId spanId = SpanId.INVALID;
+    private Map<String, String> traceInfo = null;
+    private String tracerId = EMPTY_STRING;
+    private List<TimelineAnnotation> timeline = null;
+
+    public Builder() {
+    }
+
+    public Builder begin(long begin) {
+      this.begin = begin;
+      return this;
+    }
+
+    public Builder end(long end) {
+      this.end = end;
+      return this;
+    }
+
+    public Builder description(String description) {
+      this.description = description;
+      return this;
+    }
+
+    public Builder parents(SpanId parents[]) {
+      this.parents = parents;
+      return this;
+    }
+
+    public Builder parents(List<SpanId> parentList) {
+      SpanId[] parents = new SpanId[parentList.size()];
+      for (int i = 0; i < parentList.size(); i++) {
+        parents[i] = parentList.get(i);
+      }
+      this.parents = parents;
+      return this;
+    }
+
+    public Builder spanId(SpanId spanId) {
+      this.spanId = spanId;
+      return this;
+    }
+
+    public Builder traceInfo(Map<String, String> traceInfo) {
+      this.traceInfo = traceInfo.isEmpty() ? null : traceInfo;
+      return this;
+    }
+
+    public Builder tracerId(String tracerId) {
+      this.tracerId = tracerId;
+      return this;
+    }
+
+    public Builder timeline(List<TimelineAnnotation> timeline) {
+      this.timeline = timeline.isEmpty() ? null : timeline;
+      return this;
+    }
+
+    public MilliSpan build() {
+      return new MilliSpan(this);
+    }
+  }
+
+  public MilliSpan() {
+    this.begin = 0;
+    this.end = 0;
+    this.description = EMPTY_STRING;
+    this.parents = EMPTY_PARENT_ARRAY;
+    this.spanId = SpanId.INVALID;
+    this.traceInfo = null;
+    this.tracerId = EMPTY_STRING;
+    this.timeline = null;
+  }
+
+  private MilliSpan(Builder builder) {
+    this.begin = builder.begin;
+    this.end = builder.end;
+    this.description = builder.description;
+    this.parents = builder.parents;
+    this.spanId = builder.spanId;
+    this.traceInfo = builder.traceInfo;
+    this.tracerId = builder.tracerId;
+    this.timeline = builder.timeline;
+  }
+
+  @Override
+  public synchronized void stop() {
+    if (end == 0) {
+      if (begin == 0)
+        throw new IllegalStateException("Span for " + description
+            + " has not been started");
+      end = System.currentTimeMillis();
+    }
+  }
+
+  protected long currentTimeMillis() {
+    return System.currentTimeMillis();
+  }
+
+  @Override
+  public synchronized boolean isRunning() {
+    return begin != 0 && end == 0;
+  }
+
+  @Override
+  public synchronized long getAccumulatedMillis() {
+    if (begin == 0)
+      return 0;
+    if (end > 0)
+      return end - begin;
+    return currentTimeMillis() - begin;
+  }
+
+  @Override
+  public String toString() {
+    return toJson();
+  }
+
+  @Override
+  public String getDescription() {
+    return description;
+  }
+
+  @Override
+  public SpanId getSpanId() {
+    return spanId;
+  }
+
+  @Override
+  public SpanId[] getParents() {
+    return parents;
+  }
+
+  @Override
+  public void setParents(SpanId[] parents) {
+    this.parents = parents;
+  }
+
+  @Override
+  public long getStartTimeMillis() {
+    return begin;
+  }
+
+  @Override
+  public long getStopTimeMillis() {
+    return end;
+  }
+
+  @Override
+  public void addKVAnnotation(String key, String value) {
+    if (traceInfo == null)
+      traceInfo = new HashMap<String, String>();
+    traceInfo.put(key, value);
+  }
+
+  @Override
+  public void addTimelineAnnotation(String msg) {
+    if (timeline == null) {
+      timeline = new ArrayList<TimelineAnnotation>();
+    }
+    timeline.add(new TimelineAnnotation(System.currentTimeMillis(), msg));
+  }
+
+  @Override
+  public Map<String, String> getKVAnnotations() {
+    if (traceInfo == null)
+      return Collections.emptyMap();
+    return Collections.unmodifiableMap(traceInfo);
+  }
+
+  @Override
+  public List<TimelineAnnotation> getTimelineAnnotations() {
+    if (timeline == null) {
+      return Collections.emptyList();
+    }
+    return Collections.unmodifiableList(timeline);
+  }
+
+  @Override
+  public String getTracerId() {
+    return tracerId;
+  }
+
+  @Override
+  public void setTracerId(String tracerId) {
+    this.tracerId = tracerId;
+  }
+
+  @Override
+  public String toJson() {
+    StringWriter writer = new StringWriter();
+    try {
+      JSON_WRITER.writeValue(writer, this);
+    } catch (IOException e) {
+      // An IOException should not be possible when writing to a string.
+      throw new RuntimeException(e);
+    }
+    return writer.toString();
+  }
+
+  public static class MilliSpanDeserializer
+        extends JsonDeserializer<MilliSpan> {
+    @Override
+    public MilliSpan deserialize(JsonParser jp, DeserializationContext ctxt)
+          throws IOException, JsonProcessingException {
+      JsonNode root = jp.getCodec().readTree(jp);
+      Builder builder = new Builder();
+      JsonNode bNode = root.get("b");
+      if (bNode != null) {
+        builder.begin(bNode.asLong());
+      }
+      JsonNode eNode = root.get("e");
+      if (eNode != null) {
+        builder.end(eNode.asLong());
+      }
+      JsonNode dNode = root.get("d");
+      if (dNode != null) {
+        builder.description(dNode.asText());
+      }
+      JsonNode sNode = root.get("a");
+      if (sNode != null) {
+        builder.spanId(SpanId.fromString(sNode.asText()));
+      }
+      JsonNode rNode = root.get("r");
+      if (rNode != null) {
+        builder.tracerId(rNode.asText());
+      }
+      JsonNode parentsNode = root.get("p");
+      LinkedList<SpanId> parents = new LinkedList<SpanId>();
+      if (parentsNode != null) {
+        for (Iterator<JsonNode> iter = parentsNode.elements();
+             iter.hasNext(); ) {
+          JsonNode parentIdNode = iter.next();
+          parents.add(SpanId.fromString(parentIdNode.asText()));
+        }
+      }
+      builder.parents(parents);
+      JsonNode traceInfoNode = root.get("n");
+      if (traceInfoNode != null) {
+        HashMap<String, String> traceInfo = new HashMap<String, String>();
+        for (Iterator<String> iter = traceInfoNode.fieldNames();
+             iter.hasNext(); ) {
+          String field = iter.next();
+          traceInfo.put(field, traceInfoNode.get(field).asText());
+        }
+        builder.traceInfo(traceInfo);
+      }
+      JsonNode timelineNode = root.get("t");
+      if (timelineNode != null) {
+        LinkedList<TimelineAnnotation> timeline =
+            new LinkedList<TimelineAnnotation>();
+        for (Iterator<JsonNode> iter = timelineNode.elements();
+             iter.hasNext(); ) {
+          JsonNode ann = iter.next();
+          timeline.add(new TimelineAnnotation(ann.get("t").asLong(),
+              ann.get("m").asText()));
+        }
+        builder.timeline(timeline);
+      }
+      return builder.build();
+    }
+  }
+
+  public static MilliSpan fromJson(String json) throws IOException {
+    return JSON_READER.readValue(json);
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/NeverSampler.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/NeverSampler.java b/htrace-core4/src/main/java/org/apache/htrace/core/NeverSampler.java
new file mode 100644
index 0000000..60cc7d2
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/NeverSampler.java
@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+/**
+ * A Sampler that never returns true.
+ */
+public final class NeverSampler extends Sampler {
+  public static final NeverSampler INSTANCE = new NeverSampler(null);
+
+  public NeverSampler(HTraceConfiguration conf) {
+  }
+
+  @Override
+  public boolean next() {
+    return false;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/NullScope.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/NullScope.java b/htrace-core4/src/main/java/org/apache/htrace/core/NullScope.java
new file mode 100644
index 0000000..fe76e46
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/NullScope.java
@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+/**
+ * An empty {@link TraceScope}.
+ */
+class NullScope extends TraceScope {
+  NullScope(Tracer tracer) {
+    super(tracer, null, null);
+  }
+
+  @Override
+  public SpanId getSpanId() {
+    return SpanId.INVALID;
+  }
+
+  @Override
+  public void detach() {
+    if (detached) {
+      Tracer.throwClientError("Can't detach this TraceScope  because " +
+          "it is already detached.");
+    }
+    detached = true;
+  }
+
+  @Override
+  public void reattach() {
+    if (!detached) {
+      Tracer.throwClientError("Can't reattach this TraceScope  because " +
+          "it is not detached.");
+    }
+    detached = false;
+  }
+
+  @Override
+  public void close() {
+    tracer.popNullScope();
+  }
+
+  @Override
+  public String toString() {
+    return "NullScope";
+  }
+
+  @Override
+  public void addKVAnnotation(String key, String value) {
+    // do nothing
+  }
+
+  @Override
+  public void addTimelineAnnotation(String msg) {
+    // do nothing
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/POJOSpanReceiver.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/POJOSpanReceiver.java b/htrace-core4/src/main/java/org/apache/htrace/core/POJOSpanReceiver.java
new file mode 100644
index 0000000..34322fa
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/POJOSpanReceiver.java
@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.HashSet;
+
+/**
+ * SpanReceiver for testing only that just collects the Span objects it
+ * receives. The spans it receives can be accessed with getSpans();
+ */
+public class POJOSpanReceiver extends SpanReceiver {
+  private final Collection<Span> spans;
+
+  public POJOSpanReceiver(HTraceConfiguration conf) {
+    this.spans = new HashSet<Span>();
+  }
+
+  /**
+   * @return The spans this POJOSpanReceiver has received.
+   */
+  public Collection<Span> getSpans() {
+    return spans;
+  }
+
+  @Override
+  public void close() throws IOException {
+  }
+
+  @Override
+  public void receiveSpan(Span span) {
+    spans.add(span);
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/ProbabilitySampler.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/ProbabilitySampler.java b/htrace-core4/src/main/java/org/apache/htrace/core/ProbabilitySampler.java
new file mode 100644
index 0000000..c0bb16c
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/ProbabilitySampler.java
@@ -0,0 +1,45 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * Sampler that returns true a certain percentage of the time. Specify the frequency interval by
+ * configuring a {@code double} value for {@link #SAMPLER_FRACTION_CONF_KEY}.
+ */
+public class ProbabilitySampler extends Sampler {
+  private static final Log LOG = LogFactory.getLog(ProbabilitySampler.class);
+  public final double threshold;
+  public final static String SAMPLER_FRACTION_CONF_KEY = "sampler.fraction";
+
+  public ProbabilitySampler(HTraceConfiguration conf) {
+    this.threshold = Double.parseDouble(conf.get(SAMPLER_FRACTION_CONF_KEY));
+    if (LOG.isTraceEnabled()) {
+      LOG.trace("Created new ProbabilitySampler with threshold = " +
+                threshold + ".");
+    }
+  }
+
+  @Override
+  public boolean next() {
+    return ThreadLocalRandom.current().nextDouble() < threshold;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/Sampler.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/Sampler.java b/htrace-core4/src/main/java/org/apache/htrace/core/Sampler.java
new file mode 100644
index 0000000..af0165c
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/Sampler.java
@@ -0,0 +1,131 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.lang.reflect.Constructor;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * Extremely simple callback to determine the frequency that an action should be
+ * performed.
+ * <p/>
+ * For example, the next() function may look like this:
+ * <p/>
+ * <pre>
+ * <code>
+ * public boolean next() {
+ *   return Math.random() &gt; 0.5;
+ * }
+ * </code>
+ * </pre>
+ * This would trace 50% of all gets, 75% of all puts and would not trace any other requests.
+ */
+public abstract class Sampler {
+  /**
+   * A {@link Sampler} builder. It takes a {@link Sampler} class name and
+   * constructs an instance of that class, with the provided configuration.
+   */
+  public static class Builder {
+    private static final Log LOG = LogFactory.getLog(Builder.class);
+
+    private final static String DEFAULT_PACKAGE = "org.apache.htrace.core";
+    private final HTraceConfiguration conf;
+    private String className;
+    private ClassLoader classLoader = Builder.class.getClassLoader();
+
+    public Builder(HTraceConfiguration conf) {
+      this.conf = conf;
+      reset();
+    }
+
+    public Builder reset() {
+      this.className = null;
+      return this;
+    }
+
+    public Builder className(String className) {
+      this.className = className;
+      return this;
+    }
+
+    public Builder classLoader(ClassLoader classLoader) {
+      this.classLoader = classLoader;
+      return this;
+    }
+
+    private void throwError(String errorStr) {
+      LOG.error(errorStr);
+      throw new RuntimeException(errorStr);
+    }
+
+    private void throwError(String errorStr, Throwable e) {
+      LOG.error(errorStr, e);
+      throw new RuntimeException(errorStr, e);
+    }
+
+    public Sampler build() {
+      Sampler sampler = newSampler();
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("Created new sampler of type " +
+            sampler.getClass().getName(), new Exception());
+      }
+      return sampler;
+    }
+
+    private Sampler newSampler() {
+      if (className == null || className.isEmpty()) {
+        throwError("No sampler class specified.");
+      }
+      String str = className;
+      if (!str.contains(".")) {
+        str = DEFAULT_PACKAGE + "." + str;
+      }
+      Class cls = null;
+      try {
+        cls = classLoader.loadClass(str);
+      } catch (ClassNotFoundException e) {
+        throwError("Cannot find Sampler class " + str);
+      }
+      Constructor<Sampler> ctor = null;
+      try {
+        ctor = cls.getConstructor(HTraceConfiguration.class);
+      } catch (NoSuchMethodException e) {
+        throwError("Cannot find a constructor for class " +
+            str + "which takes an HTraceConfiguration.");
+      }
+      Sampler sampler = null;
+      try {
+        LOG.debug("Creating new instance of " + str + "...");
+        sampler = ctor.newInstance(conf);
+      } catch (ReflectiveOperationException e) {
+        throwError("Reflection error when constructing " +
+            str + ".", e);
+      } catch (Throwable t) {
+        throwError("NewInstance error when constructing " +
+            str + ".", t);
+      }
+      return sampler;
+    }
+  }
+
+  public static final Sampler ALWAYS = AlwaysSampler.INSTANCE;
+  public static final Sampler NEVER = NeverSampler.INSTANCE;
+
+  public abstract boolean next();
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/Span.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/Span.java b/htrace-core4/src/main/java/org/apache/htrace/core/Span.java
new file mode 100644
index 0000000..e63d414
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/Span.java
@@ -0,0 +1,193 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+
+/**
+ * Base interface for gathering and reporting statistics about a block of
+ * execution.
+ * <p/>
+ * Spans should form a directed acyclic graph structure.  It should be possible
+ * to keep following the parents of a span until you arrive at a span with no
+ * parents.<p/>
+ */
+@JsonSerialize(using = Span.SpanSerializer.class)
+public interface Span {
+  /**
+   * The block has completed, stop the clock
+   */
+  void stop();
+
+  /**
+   * Get the start time, in milliseconds
+   */
+  long getStartTimeMillis();
+
+  /**
+   * Get the stop time, in milliseconds
+   */
+  long getStopTimeMillis();
+
+  /**
+   * Return the total amount of time elapsed since start was called, if running,
+   * or difference between stop and start
+   */
+  long getAccumulatedMillis();
+
+  /**
+   * Has the span been started and not yet stopped?
+   */
+  boolean isRunning();
+
+  /**
+   * Return a textual description of this span.<p/>
+   *
+   * Will never be null.
+   */
+  String getDescription();
+
+  /**
+   * A pseudo-unique (random) number assigned to this span instance.<p/>
+   *
+   * The spanId is immutable and cannot be changed.  It is safe to access this
+   * from multiple threads.
+   */
+  SpanId getSpanId();
+
+  /**
+   * Create a child span of this span with the given description
+   * @deprecated Since 4.0.0. Use {@link MilliSpan.Builder}
+   */
+  @Deprecated
+  Span child(String description);
+
+  @Override
+  String toString();
+
+  /**
+   * Returns the parent IDs of the span.<p/>
+   *
+   * The array will be empty if there are no parents.
+   */
+  SpanId[] getParents();
+
+  /**
+   * Set the parents of this span.<p/>
+   *
+   * Any existing parents will be cleared by this call.
+   */
+  void setParents(SpanId[] parents);
+
+  /**
+   * Add a data annotation associated with this span
+   */
+  void addKVAnnotation(String key, String value);
+
+  /**
+   * Add a timeline annotation associated with this span
+   */
+  void addTimelineAnnotation(String msg);
+
+  /**
+   * Get data associated with this span (read only)<p/>
+   *
+   * Will never be null.
+   */
+  Map<String, String> getKVAnnotations();
+
+  /**
+   * Get any timeline annotations (read only)<p/>
+   *
+   * Will never be null.
+   */
+  List<TimelineAnnotation> getTimelineAnnotations();
+
+  /**
+   * Return a unique id for the process from which this Span originated.<p/>
+   *
+   * Will never be null.
+   */
+  String getTracerId();
+
+  /**
+   * Set the process id of a span.
+   */
+  void setTracerId(String s);
+
+  /**
+   * Serialize to Json
+   */
+  String toJson();
+
+  public static class SpanSerializer extends JsonSerializer<Span> {
+    @Override
+    public void serialize(Span span, JsonGenerator jgen, SerializerProvider provider)
+        throws IOException {
+      jgen.writeStartObject();
+      if (span.getSpanId().isValid()) {
+        jgen.writeStringField("a", span.getSpanId().toString());
+      }
+      if (span.getStartTimeMillis() != 0) {
+        jgen.writeNumberField("b", span.getStartTimeMillis());
+      }
+      if (span.getStopTimeMillis() != 0) {
+        jgen.writeNumberField("e", span.getStopTimeMillis());
+      }
+      if (!span.getDescription().isEmpty()) {
+        jgen.writeStringField("d", span.getDescription());
+      }
+      String tracerId = span.getTracerId();
+      if (!tracerId.isEmpty()) {
+        jgen.writeStringField("r", tracerId);
+      }
+      jgen.writeArrayFieldStart("p");
+      for (SpanId parent : span.getParents()) {
+        jgen.writeString(parent.toString());
+      }
+      jgen.writeEndArray();
+      Map<String, String> traceInfoMap = span.getKVAnnotations();
+      if (!traceInfoMap.isEmpty()) {
+        jgen.writeObjectFieldStart("n");
+        for (Map.Entry<String, String> e : traceInfoMap.entrySet()) {
+          jgen.writeStringField(e.getKey(), e.getValue());
+        }
+        jgen.writeEndObject();
+      }
+      List<TimelineAnnotation> timelineAnnotations =
+          span.getTimelineAnnotations();
+      if (!timelineAnnotations.isEmpty()) {
+        jgen.writeArrayFieldStart("t");
+        for (TimelineAnnotation tl : timelineAnnotations) {
+          jgen.writeStartObject();
+          jgen.writeNumberField("t", tl.getTime());
+          jgen.writeStringField("m", tl.getMessage());
+          jgen.writeEndObject();
+        }
+        jgen.writeEndArray();
+      }
+      jgen.writeEndObject();
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/SpanId.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/SpanId.java b/htrace-core4/src/main/java/org/apache/htrace/core/SpanId.java
new file mode 100644
index 0000000..ed31ad3
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/SpanId.java
@@ -0,0 +1,146 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+/**
+ * Uniquely identifies an HTrace span.
+ *
+ * Span IDs are 128 bits in total.  The upper 64 bits of a span ID is the same
+ * as the upper 64 bits of the parent span, if there is one.  The lower 64 bits
+ * are always random.
+ */
+public final class SpanId implements Comparable<SpanId> {
+  private static final int SPAN_ID_STRING_LENGTH = 32;
+  private final long high;
+  private final long low;
+
+  /**
+   * The invalid span ID, which is all zeroes.
+   *
+   * It is also the "least" span ID in the sense that it is considered
+   * smaller than any other span ID.
+   */
+  public static SpanId INVALID = new SpanId(0, 0);
+
+  private static long nonZeroRand64() {
+    while (true) {
+      long r = ThreadLocalRandom.current().nextLong();
+      if (r != 0) {
+        return r;
+      }
+    }
+  }
+
+  public static SpanId fromRandom() {
+    return new SpanId(nonZeroRand64(), nonZeroRand64());
+  }
+
+  public static SpanId fromString(String str) {
+    if (str.length() != SPAN_ID_STRING_LENGTH) {
+      throw new RuntimeException("Invalid SpanID string: length was not " +
+          SPAN_ID_STRING_LENGTH);
+    }
+    long high =
+      ((Long.parseLong(str.substring(0, 8), 16)) << 32) |
+      (Long.parseLong(str.substring(8, 16), 16));
+    long low =
+      ((Long.parseLong(str.substring(16, 24), 16)) << 32) |
+      (Long.parseLong(str.substring(24, 32), 16));
+    return new SpanId(high, low);
+  }
+
+  public SpanId(long high, long low) {
+    this.high = high;
+    this.low = low;
+  }
+
+  public long getHigh() {
+    return high;
+  }
+
+  public long getLow() {
+    return low;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof SpanId)) {
+      return false;
+    }
+    SpanId other = (SpanId)o;
+    return ((other.high == high) && (other.low == low));
+  }
+
+  @Override
+  public int compareTo(SpanId other) {
+    int cmp = compareAsUnsigned(high, other.high);
+    if (cmp != 0) {
+      return cmp;
+    }
+    return compareAsUnsigned(low, other.low);
+  }
+
+  private static int compareAsUnsigned(long a, long b) {
+    boolean aSign = a < 0;
+    boolean bSign = b < 0;
+    if (aSign != bSign) {
+      if (aSign) {
+        return 1;
+      } else {
+        return -1;
+      }
+    }
+    if (aSign) {
+      a = -a;
+      b = -b;
+    }
+    if (a < b) {
+      return -1;
+    } else if (a > b) {
+      return 1;
+    } else {
+      return 0;
+    }
+  }
+
+  @Override
+  public int hashCode() {
+    return (int)((0xffffffff & (high >> 32))) ^
+           (int)((0xffffffff & (high >> 0))) ^
+           (int)((0xffffffff & (low >> 32))) ^
+           (int)((0xffffffff & (low >> 0)));
+  }
+
+  @Override
+  public String toString() {
+    return String.format("%08x%08x%08x%08x",
+        (0x00000000ffffffffL & (high >> 32)),
+        (0x00000000ffffffffL & high),
+        (0x00000000ffffffffL & (low >> 32)),
+        (0x00000000ffffffffL & low));
+  }
+
+  public boolean isValid() {
+    return (high != 0)  || (low != 0);
+  }
+
+  public SpanId newChildId() {
+    return new SpanId(high, nonZeroRand64());
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/SpanReceiver.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/SpanReceiver.java b/htrace-core4/src/main/java/org/apache/htrace/core/SpanReceiver.java
new file mode 100644
index 0000000..a955ddf
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/SpanReceiver.java
@@ -0,0 +1,164 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.io.Closeable;
+import java.lang.reflect.Constructor;
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * The collector within a process that is the destination of Spans when a trace is running.
+ * {@code SpanReceiver} implementations are expected to provide a constructor with the signature
+ * <p>
+ * <pre>
+ * <code>public SpanReceiverImpl(HTraceConfiguration)</code>
+ * </pre>
+ */
+public abstract class SpanReceiver implements Closeable {
+  /**
+   * A {@link SpanReceiver} builder. It takes a {@link SpanReceiver} class name
+   * and constructs an instance of that class, with the provided configuration.
+   */
+  public static class Builder {
+    private static final Log LOG = LogFactory.getLog(Builder.class);
+
+    private final static String DEFAULT_PACKAGE = "org.apache.htrace.core";
+    private final HTraceConfiguration conf;
+    private boolean logErrors;
+    private String className;
+    private ClassLoader classLoader = Builder.class.getClassLoader();
+
+    public Builder(HTraceConfiguration conf) {
+      this.conf = conf;
+      reset();
+    }
+
+    /**
+     * Set this builder back to defaults.
+     *
+     * @return this instance.
+     */
+    public Builder reset() {
+      this.logErrors = true;
+      this.className = null;
+      return this;
+    }
+
+    public Builder className(final String className) {
+      this.className = className;
+      return this;
+    }
+
+    /**
+     * Configure whether we should log errors during build().
+     * @return This instance
+     */
+    public Builder logErrors(boolean logErrors) {
+      this.logErrors = logErrors;
+      return this;
+    }
+
+    public Builder classLoader(ClassLoader classLoader) {
+      this.classLoader = classLoader;
+      return this;
+    }
+
+    private void throwError(String errorStr) {
+      if (logErrors) {
+        LOG.error(errorStr);
+      }
+      throw new RuntimeException(errorStr);
+    }
+
+    private void throwError(String errorStr, Throwable e) {
+      if (logErrors) {
+        LOG.error(errorStr, e);
+      }
+      throw new RuntimeException(errorStr, e);
+    }
+
+    public SpanReceiver build() {
+      SpanReceiver spanReceiver = newSpanReceiver();
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("Created new span receiver of type " +
+                  spanReceiver.getClass().getName());
+      }
+      return spanReceiver;
+    }
+
+    private SpanReceiver newSpanReceiver() {
+      if ((className == null) || className.isEmpty()) {
+        throwError("No span receiver class specified.");
+      }
+      String str = className;
+      if (!str.contains(".")) {
+        str = DEFAULT_PACKAGE + "." + str;
+      }
+      Class cls = null;
+      try {
+        cls = classLoader.loadClass(str);
+      } catch (ClassNotFoundException e) {
+        throwError("Cannot find SpanReceiver class " + str);
+      }
+      Constructor<SpanReceiver> ctor = null;
+      try {
+        ctor = cls.getConstructor(HTraceConfiguration.class);
+      } catch (NoSuchMethodException e) {
+        throwError("Cannot find a constructor for class " +
+            str + "which takes an HTraceConfiguration.");
+      }
+      SpanReceiver receiver = null;
+      try {
+        LOG.debug("Creating new instance of " + str + "...");
+        receiver = ctor.newInstance(conf);
+      } catch (ReflectiveOperationException e) {
+        throwError("Reflection error when constructing " +
+            str + ".", e);
+      } catch (Throwable t) {
+        throwError("NewInstance error when constructing " +
+            str + ".", t);
+      }
+      return receiver;
+    }
+  }
+
+  /**
+   * An ID which uniquely identifies this SpanReceiver.
+   */
+  private final long id;
+
+  private static final AtomicLong HIGHEST_SPAN_RECEIVER_ID = new AtomicLong(0);
+
+  /**
+   * Get an ID uniquely identifying this SpanReceiver.
+   */
+  public final long getId() {
+    return id;
+  }
+
+  protected SpanReceiver() {
+    this.id = HIGHEST_SPAN_RECEIVER_ID.incrementAndGet();
+  }
+
+  /**
+   * Called when a Span is stopped and can now be stored.
+   */
+  public abstract void receiveSpan(Span span);
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/StandardOutSpanReceiver.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/StandardOutSpanReceiver.java b/htrace-core4/src/main/java/org/apache/htrace/core/StandardOutSpanReceiver.java
new file mode 100644
index 0000000..f443ec6
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/StandardOutSpanReceiver.java
@@ -0,0 +1,42 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import java.io.IOException;
+
+/**
+ * Used for testing. Simply prints to standard out any spans it receives.
+ */
+public class StandardOutSpanReceiver extends SpanReceiver {
+  private static final Log LOG = LogFactory.getLog(StandardOutSpanReceiver.class);
+
+  public StandardOutSpanReceiver(HTraceConfiguration conf) {
+    LOG.trace("Created new StandardOutSpanReceiver.");
+  }
+
+  @Override
+  public void receiveSpan(Span span) {
+    System.out.println(span);
+  }
+
+  @Override
+  public void close() throws IOException {
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/TimelineAnnotation.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/TimelineAnnotation.java b/htrace-core4/src/main/java/org/apache/htrace/core/TimelineAnnotation.java
new file mode 100644
index 0000000..18de061
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/TimelineAnnotation.java
@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+public class TimelineAnnotation {
+  private final long time;
+  private final String msg;
+
+  public TimelineAnnotation(long time, String msg) {
+    this.time = time;
+    this.msg = msg;
+  }
+
+  public long getTime() {
+    return time;
+  }
+
+  public String getMessage() {
+    return msg;
+  }
+
+  @Override
+  public String toString() {
+    return "@" + time + ": " + msg;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/TraceCallable.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/TraceCallable.java b/htrace-core4/src/main/java/org/apache/htrace/core/TraceCallable.java
new file mode 100644
index 0000000..a0fec17
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/TraceCallable.java
@@ -0,0 +1,56 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.util.concurrent.Callable;
+
+/**
+ * Wrap a Callable with a Span that survives a change in threads.
+ */
+public class TraceCallable<V> implements Callable<V> {
+  private final Tracer tracer;
+  private final Callable<V> impl;
+  private final TraceScope parent;
+  private final String description;
+
+  TraceCallable(Tracer tracer, TraceScope parent, Callable<V> impl,
+      String description) {
+    this.tracer = tracer;
+    this.impl = impl;
+    this.parent = parent;
+    if (description == null) {
+      this.description = Thread.currentThread().getName();
+    } else {
+      this.description = description;
+    }
+  }
+
+  @Override
+  public V call() throws Exception {
+    TraceScope chunk = tracer.newScope(description,
+        parent.getSpan().getSpanId());
+    try {
+      return impl.call();
+    } finally {
+      chunk.close();
+    }
+  }
+
+  public Callable<V> getImpl() {
+    return impl;
+  }
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/TraceExecutorService.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/TraceExecutorService.java b/htrace-core4/src/main/java/org/apache/htrace/core/TraceExecutorService.java
new file mode 100644
index 0000000..81e31ea
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/TraceExecutorService.java
@@ -0,0 +1,121 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+public class TraceExecutorService implements ExecutorService {
+  private final Tracer tracer;
+  private final String scopeName;
+  private final ExecutorService impl;
+
+  TraceExecutorService(Tracer tracer, String scopeName,
+                       ExecutorService impl) {
+    this.tracer = tracer;
+    this.scopeName = scopeName;
+    this.impl = impl;
+  }
+
+  @Override
+  public void execute(Runnable command) {
+    impl.execute(tracer.wrap(command, scopeName));
+  }
+
+  @Override
+  public void shutdown() {
+    impl.shutdown();
+  }
+
+  @Override
+  public List<Runnable> shutdownNow() {
+    return impl.shutdownNow();
+  }
+
+  @Override
+  public boolean isShutdown() {
+    return impl.isShutdown();
+  }
+
+  @Override
+  public boolean isTerminated() {
+    return impl.isTerminated();
+  }
+
+  @Override
+  public boolean awaitTermination(long timeout, TimeUnit unit)
+      throws InterruptedException {
+    return impl.awaitTermination(timeout, unit);
+  }
+
+  @Override
+  public <T> Future<T> submit(Callable<T> task) {
+    return impl.submit(tracer.wrap(task, scopeName));
+  }
+
+  @Override
+  public <T> Future<T> submit(Runnable task, T result) {
+    return impl.submit(tracer.wrap(task, scopeName), result);
+  }
+
+  @Override
+  public Future<?> submit(Runnable task) {
+    return impl.submit(tracer.wrap(task, scopeName));
+  }
+
+  private <T> Collection<? extends Callable<T>> wrapCollection(
+      Collection<? extends Callable<T>> tasks) {
+    List<Callable<T>> result = new ArrayList<Callable<T>>();
+    for (Callable<T> task : tasks) {
+      result.add(tracer.wrap(task, scopeName));
+    }
+    return result;
+  }
+
+  @Override
+  public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
+      throws InterruptedException {
+    return impl.invokeAll(wrapCollection(tasks));
+  }
+
+  @Override
+  public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
+                                       long timeout, TimeUnit unit) throws InterruptedException {
+    return impl.invokeAll(wrapCollection(tasks), timeout, unit);
+  }
+
+  @Override
+  public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
+      throws InterruptedException, ExecutionException {
+    return impl.invokeAny(wrapCollection(tasks));
+  }
+
+  @Override
+  public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout,
+                         TimeUnit unit) throws InterruptedException, ExecutionException,
+      TimeoutException {
+    return impl.invokeAny(wrapCollection(tasks), timeout, unit);
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/incubator-htrace/blob/26f2c79f/htrace-core4/src/main/java/org/apache/htrace/core/TraceRunnable.java
----------------------------------------------------------------------
diff --git a/htrace-core4/src/main/java/org/apache/htrace/core/TraceRunnable.java b/htrace-core4/src/main/java/org/apache/htrace/core/TraceRunnable.java
new file mode 100644
index 0000000..8f98708
--- /dev/null
+++ b/htrace-core4/src/main/java/org/apache/htrace/core/TraceRunnable.java
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.htrace.core;
+
+/**
+ * Wrap a Runnable with a Span that survives a change in threads.
+ */
+public class TraceRunnable implements Runnable {
+  private final Tracer tracer;
+  private final TraceScope parent;
+  private final Runnable runnable;
+  private final String description;
+
+  public TraceRunnable(Tracer tracer, TraceScope parent,
+      Runnable runnable, String description) {
+    this.tracer = tracer;
+    this.parent = parent;
+    this.runnable = runnable;
+    if (description == null) {
+      this.description = Thread.currentThread().getName();
+    } else {
+      this.description = description;
+    }
+  }
+
+  @Override
+  public void run() {
+    TraceScope chunk = tracer.newScope(description,
+        parent.getSpan().getSpanId());
+    try {
+      runnable.run();
+    } finally {
+      chunk.close();
+    }
+  }
+
+  public Runnable getRunnable() {
+    return runnable;
+  }
+}



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