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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-6345) NetworkClient.inFlightRequestCount() is not thread safe, causing ConcurrentModificationExceptions when sensors are read
Date Tue, 30 Jan 2018 18:22:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-6345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16345558#comment-16345558
] 

ASF GitHub Bot commented on KAFKA-6345:
---------------------------------------

becketqin closed pull request #4460: KAFKA-6345: Keep a separate count of in-flight requests
to avoid ConcurrentModificationException.
URL: https://github.com/apache/kafka/pull/4460
 
 
   

This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:

As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):

diff --git a/clients/src/main/java/org/apache/kafka/clients/InFlightRequests.java b/clients/src/main/java/org/apache/kafka/clients/InFlightRequests.java
index 3689a09a117..a062818e3b2 100644
--- a/clients/src/main/java/org/apache/kafka/clients/InFlightRequests.java
+++ b/clients/src/main/java/org/apache/kafka/clients/InFlightRequests.java
@@ -23,6 +23,8 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
+
 
 /**
  * The set of requests which have been sent or are being sent but haven't yet received a
response
@@ -31,6 +33,8 @@
 
     private final int maxInFlightRequestsPerConnection;
     private final Map<String, Deque<NetworkClient.InFlightRequest>> requests
= new HashMap<>();
+    /** Thread safe total number of in flight requests. */
+    private final AtomicInteger inFlightRequestCount = new AtomicInteger(0);
 
     public InFlightRequests(int maxInFlightRequestsPerConnection) {
         this.maxInFlightRequestsPerConnection = maxInFlightRequestsPerConnection;
@@ -47,6 +51,7 @@ public void add(NetworkClient.InFlightRequest request) {
             this.requests.put(destination, reqs);
         }
         reqs.addFirst(request);
+        inFlightRequestCount.incrementAndGet();
     }
 
     /**
@@ -63,7 +68,9 @@ public void add(NetworkClient.InFlightRequest request) {
      * Get the oldest request (the one that will be completed next) for the given node
      */
     public NetworkClient.InFlightRequest completeNext(String node) {
-        return requestQueue(node).pollLast();
+        NetworkClient.InFlightRequest inFlightRequest = requestQueue(node).pollLast();
+        inFlightRequestCount.decrementAndGet();
+        return inFlightRequest;
     }
 
     /**
@@ -80,7 +87,9 @@ public void add(NetworkClient.InFlightRequest request) {
      * @return The request
      */
     public NetworkClient.InFlightRequest completeLastSent(String node) {
-        return requestQueue(node).pollFirst();
+        NetworkClient.InFlightRequest inFlightRequest = requestQueue(node).pollFirst();
+        inFlightRequestCount.decrementAndGet();
+        return inFlightRequest;
     }
 
     /**
@@ -114,13 +123,10 @@ public boolean isEmpty(String node) {
     }
 
     /**
-     * Count all in-flight requests for all nodes
+     * Count all in-flight requests for all nodes. This method is thread safe, but may lag
the actual count.
      */
     public int count() {
-        int total = 0;
-        for (Deque<NetworkClient.InFlightRequest> deque : this.requests.values())
-            total += deque.size();
-        return total;
+        return inFlightRequestCount.get();
     }
 
     /**
@@ -141,8 +147,14 @@ public boolean isEmpty() {
      * @return All the in-flight requests for that node that have been removed
      */
     public Iterable<NetworkClient.InFlightRequest> clearAll(String node) {
-        Deque<NetworkClient.InFlightRequest> reqs = requests.remove(node);
-        return (reqs == null) ? Collections.<NetworkClient.InFlightRequest>emptyList()
: reqs;
+        Deque<NetworkClient.InFlightRequest> reqs = requests.get(node);
+        if (reqs == null) {
+            return Collections.emptyList();
+        } else {
+            Deque<NetworkClient.InFlightRequest> clearedRequests = requests.remove(node);
+            inFlightRequestCount.getAndAdd(-clearedRequests.size());
+            return clearedRequests;
+        }
     }
 
     /**
diff --git a/clients/src/test/java/org/apache/kafka/clients/InFlightRequestsTest.java b/clients/src/test/java/org/apache/kafka/clients/InFlightRequestsTest.java
new file mode 100644
index 00000000000..e00ca086106
--- /dev/null
+++ b/clients/src/test/java/org/apache/kafka/clients/InFlightRequestsTest.java
@@ -0,0 +1,60 @@
+/*
+ * 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.kafka.clients;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class InFlightRequestsTest {
+
+    private InFlightRequests inFlightRequests;
+    @Before
+    public void setup() {
+        inFlightRequests = new InFlightRequests(12);
+        NetworkClient.InFlightRequest ifr =
+                new NetworkClient.InFlightRequest(null, 0, "dest", null, false, false, null,
null, 0);
+        inFlightRequests.add(ifr);
+    }
+
+    @Test
+    public void checkIncrementAndDecrementOnLastSent() {
+        assertEquals(1, inFlightRequests.count());
+
+        inFlightRequests.completeLastSent("dest");
+        assertEquals(0, inFlightRequests.count());
+    }
+
+    @Test
+    public void checkDecrementOnClear() {
+        inFlightRequests.clearAll("dest");
+        assertEquals(0, inFlightRequests.count());
+    }
+
+    @Test
+    public void checkDecrementOnCompleteNext() {
+        inFlightRequests.completeNext("dest");
+        assertEquals(0, inFlightRequests.count());
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void throwExceptionOnNeverBeforeSeenNode() {
+        inFlightRequests.completeNext("not-added");
+    }
+}


 

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> NetworkClient.inFlightRequestCount() is not thread safe, causing ConcurrentModificationExceptions
when sensors are read
> -----------------------------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-6345
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6345
>             Project: Kafka
>          Issue Type: Bug
>          Components: clients
>    Affects Versions: 1.0.0
>            Reporter: radai rosenblatt
>            Priority: Major
>
> example stack trace (code is ~0.10.2.*)
> {code}
> java.util.ConcurrentModificationException: java.util.ConcurrentModificationException
> 	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
> 	at java.util.HashMap$ValueIterator.next(HashMap.java:1458)
> 	at org.apache.kafka.clients.InFlightRequests.inFlightRequestCount(InFlightRequests.java:109)
> 	at org.apache.kafka.clients.NetworkClient.inFlightRequestCount(NetworkClient.java:382)
> 	at org.apache.kafka.clients.producer.internals.Sender$SenderMetrics$1.measure(Sender.java:480)
> 	at org.apache.kafka.common.metrics.KafkaMetric.value(KafkaMetric.java:61)
> 	at org.apache.kafka.common.metrics.KafkaMetric.value(KafkaMetric.java:52)
> 	at org.apache.kafka.common.metrics.JmxReporter$KafkaMbean.getAttribute(JmxReporter.java:183)
> 	at org.apache.kafka.common.metrics.JmxReporter$KafkaMbean.getAttributes(JmxReporter.java:193)
> 	at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.getAttributes(DefaultMBeanServerInterceptor.java:709)
> 	at com.sun.jmx.mbeanserver.JmxMBeanServer.getAttributes(JmxMBeanServer.java:705)
> {code}
> looking at latest trunk, the code is still vulnerable:
> # NetworkClient.inFlightRequestCount() eventually iterates over InFlightRequests.requests.values(),
which is backed by a (non-thread-safe) HashMap
> # this will be called from the "requests-in-flight" sensor's measure() method (Sender.java
line  ~765 in SenderMetrics ctr), which would be driven by some thread reading JMX values
> # HashMap in question would also be updated by some client io thread calling NetworkClient.doSend()
- which calls into InFlightRequests.add())
> i guess the only upside is that this exception will always happen on the thread reading
the JMX values and never on the actual client io thread ...



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