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From bus...@apache.org
Subject accumulo git commit: ACCUMULO-3393 Follow-on work for per-table volume chooser.
Date Sat, 13 Dec 2014 05:57:38 GMT
Repository: accumulo
Updated Branches:
  refs/heads/master 5eb084cb5 -> bd4d190ee


ACCUMULO-3393 Follow-on work for per-table volume chooser.

* docs clean up + code guideline compliance.
* ensure RandomVolumeChoosers are independent when used per-table.
* make sure that per-table choosers can keep state the way that global choosers can
* make sure that a chooser can only pick from the options it is presented.
* reduce object creation in critical path for Tablet.split.


Project: http://git-wip-us.apache.org/repos/asf/accumulo/repo
Commit: http://git-wip-us.apache.org/repos/asf/accumulo/commit/bd4d190e
Tree: http://git-wip-us.apache.org/repos/asf/accumulo/tree/bd4d190e
Diff: http://git-wip-us.apache.org/repos/asf/accumulo/diff/bd4d190e

Branch: refs/heads/master
Commit: bd4d190eee16058097f4f439ed3b21696633cf9c
Parents: 5eb084c
Author: Sean Busbey <busbey@cloudera.com>
Authored: Tue Dec 9 15:55:06 2014 -0600
Committer: Sean Busbey <busbey@cloudera.com>
Committed: Fri Dec 12 23:00:50 2014 -0600

----------------------------------------------------------------------
 .../org/apache/accumulo/core/conf/Property.java |  2 +
 .../server/fs/PerTableVolumeChooser.java        | 47 ++++++++++--
 .../server/fs/PreferredVolumeChooser.java       | 75 ++++++++++++++------
 .../accumulo/server/fs/RandomVolumeChooser.java |  2 +-
 .../accumulo/server/fs/VolumeChooser.java       |  6 ++
 .../accumulo/server/fs/VolumeManager.java       |  1 +
 .../accumulo/server/fs/VolumeManagerImpl.java   | 16 ++++-
 .../apache/accumulo/server/fs/VolumeUtil.java   |  4 +-
 .../server/fs/VolumeManagerImplTest.java        | 26 +++++++
 9 files changed, 147 insertions(+), 32 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/core/src/main/java/org/apache/accumulo/core/conf/Property.java
----------------------------------------------------------------------
diff --git a/core/src/main/java/org/apache/accumulo/core/conf/Property.java b/core/src/main/java/org/apache/accumulo/core/conf/Property.java
index 4c2d0b4..e054a5f 100644
--- a/core/src/main/java/org/apache/accumulo/core/conf/Property.java
+++ b/core/src/main/java/org/apache/accumulo/core/conf/Property.java
@@ -164,6 +164,7 @@ public enum Property {
   GENERAL_MAX_MESSAGE_SIZE("general.server.message.size.max", "1G", PropertyType.MEMORY,
"The maximum size of a message that can be sent to a server."),
   GENERAL_SIMPLETIMER_THREADPOOL_SIZE("general.server.simpletimer.threadpool.size", "1",
PropertyType.COUNT, "The number of threads to use for "
       + "server-internal scheduled tasks"),
+  // If you update the default type, be sure to update the default used for initialization
failures in VolumeManagerImpl
   @Experimental
   GENERAL_VOLUME_CHOOSER("general.volume.chooser", "org.apache.accumulo.server.fs.PerTableVolumeChooser",
PropertyType.CLASSNAME,
       "The class that will be used to select which volume will be used to create new files."),
@@ -467,6 +468,7 @@ public enum Property {
   TABLE_REPLICATION_TARGET("table.replication.target.", null, PropertyType.PREFIX, "Enumerate
a mapping of other systems which this table should " +
       "replicate their data to. The key suffix is the identifying cluster name and the value
is an identifier for a location on the target system, " +
       "e.g. the ID of the table on the target to replicate to"),
+  @Experimental
   TABLE_VOLUME_CHOOSER("table.volume.chooser", "org.apache.accumulo.server.fs.RandomVolumeChooser",
PropertyType.CLASSNAME,
       "The class that will be used to select which volume will be used to create new files
for this table."),
 

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
b/server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
index 7a825c7..a579cc8 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
@@ -16,23 +16,58 @@
  */
 package org.apache.accumulo.server.fs;
 
+import java.util.concurrent.ConcurrentHashMap;
+
 import org.apache.accumulo.core.conf.Property;
 import org.apache.accumulo.server.client.HdfsZooInstance;
 import org.apache.accumulo.server.conf.ServerConfigurationFactory;
 import org.apache.accumulo.server.conf.TableConfiguration;
 
+/**
+ * A {@link VolumeChooser} that delegates to another volume chooser based on the presence
of an experimental table
+ * property, {@link Property#TABLE_VOLUME_CHOOSER}. If it isn't found, defaults back to {@link
RandomVolumeChooser}.
+ */
 public class PerTableVolumeChooser implements VolumeChooser {
 
-  private static final VolumeChooser fallbackVolumeChooser = new RandomVolumeChooser();
-
-  public PerTableVolumeChooser() {}
+  private final VolumeChooser fallbackVolumeChooser = new RandomVolumeChooser();
+  // TODO Add hint of expected size to construction, see ACCUMULO-3410
+  /* Track VolumeChooser instances so they can keep state. */
+  private final ConcurrentHashMap<String, VolumeChooser> tableSpecificChooser = new
ConcurrentHashMap<String, VolumeChooser>();
+  // TODO has to be lazily initialized currently because of the reliance on HdfsZooInstance.
see ACCUMULO-3411
+  private volatile ServerConfigurationFactory serverConfs;
 
   @Override
   public String choose(VolumeChooserEnvironment env, String[] options) {
-    VolumeChooser chooser;
+    VolumeChooser chooser = null;
     if (env.hasTableId()) {
-      TableConfiguration conf = new ServerConfigurationFactory(HdfsZooInstance.getInstance()).getTableConfiguration(env.getTableId());
-      chooser = Property.createTableInstanceFromPropertyName(conf, Property.TABLE_VOLUME_CHOOSER,
VolumeChooser.class, fallbackVolumeChooser);
+      // This local variable is an intentional component of the single-check idiom.
+      ServerConfigurationFactory localConf = serverConfs;
+      if (localConf == null) {
+        // If we're under contention when first getting here we'll throw away some initializations.
+        localConf = new ServerConfigurationFactory(HdfsZooInstance.getInstance());
+        serverConfs = localConf;
+      }
+      final TableConfiguration tableConf = localConf.getTableConfiguration(env.getTableId());
+      chooser = tableSpecificChooser.get(env.getTableId());
+      if (chooser == null) {
+        VolumeChooser temp = Property.createTableInstanceFromPropertyName(tableConf, Property.TABLE_VOLUME_CHOOSER,
VolumeChooser.class, fallbackVolumeChooser);
+        chooser = tableSpecificChooser.putIfAbsent(env.getTableId(), temp);
+        if (chooser == null) {
+          chooser = temp;
+          // Otherwise, someone else beat us to initializing; use theirs.
+        }
+      } else if (!(chooser.getClass().getName().equals(tableConf.get(Property.TABLE_VOLUME_CHOOSER))))
{
+        // the configuration for this table's chooser has been updated. In the case of failure
to instantiate we'll repeat here next call.
+        // TODO stricter definition of when the updated property is used, ref ACCUMULO-3412
+        VolumeChooser temp = Property.createTableInstanceFromPropertyName(tableConf, Property.TABLE_VOLUME_CHOOSER,
VolumeChooser.class, fallbackVolumeChooser);
+        VolumeChooser last  = tableSpecificChooser.replace(env.getTableId(), temp);
+        if (chooser.equals(last)) {
+          chooser = temp;
+        } else {
+          // Someone else beat us to updating; use theirs.
+          chooser = last;
+        }
+      }
     } else {
       chooser = fallbackVolumeChooser;
     }

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/PreferredVolumeChooser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/PreferredVolumeChooser.java
b/server/base/src/main/java/org/apache/accumulo/server/fs/PreferredVolumeChooser.java
index 7ed7bba..4ddf9bb 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/PreferredVolumeChooser.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/PreferredVolumeChooser.java
@@ -16,24 +16,48 @@
  */
 package org.apache.accumulo.server.fs;
 
+import static org.apache.commons.lang.ArrayUtils.EMPTY_STRING_ARRAY;
+
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 
 import org.apache.accumulo.core.conf.AccumuloConfiguration.PropertyFilter;
 import org.apache.accumulo.core.conf.Property;
+import org.apache.accumulo.core.volume.Volume;
 import org.apache.accumulo.server.client.HdfsZooInstance;
 import org.apache.accumulo.server.conf.ServerConfigurationFactory;
 import org.apache.accumulo.server.conf.TableConfiguration;
+import org.apache.commons.collections.map.LRUMap;
+import org.apache.commons.lang.StringUtils;
 import org.apache.log4j.Logger;
 
+/**
+ * A {@link RandomVolumeChooser} that limits its choices from a given set of options to the
subset of those options preferred for a
+ * particular table. Defaults to selecting from all of the options presented. Can be customized
via the table property
+ * {@value #PREFERRED_VOLUMES_CUSTOM_KEY}, which should contain a comma separated list of
{@link Volume} URIs. Note that both the property
+ * name and the format of its value are specific to this particular implementation.
+ */
 public class PreferredVolumeChooser extends RandomVolumeChooser implements VolumeChooser
{
   private static final Logger log = Logger.getLogger(PreferredVolumeChooser.class);
 
   public static final String PREFERRED_VOLUMES_CUSTOM_KEY = Property.TABLE_ARBITRARY_PROP_PREFIX.getKey()
+ "preferredVolumes";
+  // TODO ACCUMULO-3417 replace this with the ability to retrieve by String key.
+  private static final PropertyFilter PREFERRED_VOLUMES_FILTER = new PropertyFilter() {
+    @Override
+    public boolean accept(String key) {
+      return PREFERRED_VOLUMES_CUSTOM_KEY.equals(key);
+    }
+  };
 
-  public PreferredVolumeChooser() {}
+  @SuppressWarnings("unchecked")
+  private final Map<String, Set<String>> parsedPreferredVolumes = Collections.synchronizedMap(new
LRUMap(1000));
+  // TODO has to be lazily initialized currently because of the reliance on HdfsZooInstance.
see ACCUMULO-3411
+  private volatile ServerConfigurationFactory serverConfs;
 
   @Override
   public String choose(VolumeChooserEnvironment env, String[] options) {
@@ -41,40 +65,49 @@ public class PreferredVolumeChooser extends RandomVolumeChooser implements
Volum
       return super.choose(env, options);
 
     // Get the current table's properties, and find the preferred volumes property
-    TableConfiguration config = new ServerConfigurationFactory(HdfsZooInstance.getInstance()).getTableConfiguration(env.getTableId());
-    PropertyFilter filter = new PropertyFilter() {
-      @Override
-      public boolean accept(String key) {
-        return PREFERRED_VOLUMES_CUSTOM_KEY.equals(key);
-      }
-    };
-    Map<String,String> props = new HashMap<>();
-    config.getProperties(props, filter);
+    // This local variable is an intentional component of the single-check idiom.
+    ServerConfigurationFactory localConf = serverConfs;
+    if (localConf == null) {
+      // If we're under contention when first getting here we'll throw away some initializations.
+      localConf = new ServerConfigurationFactory(HdfsZooInstance.getInstance());
+      serverConfs = localConf;
+    }
+    TableConfiguration tableConf = localConf.getTableConfiguration(env.getTableId());
+    final Map<String,String> props = new HashMap<String, String>();
+    tableConf.getProperties(props, PREFERRED_VOLUMES_FILTER);
     if (props.isEmpty()) {
       log.warn("No preferred volumes specified. Defaulting to randomly choosing from instance
volumes");
       return super.choose(env, options);
     }
     String volumes = props.get(PREFERRED_VOLUMES_CUSTOM_KEY);
-    log.trace("In custom chooser");
-    log.trace("Volumes: " + volumes);
-    log.trace("TableID: " + env.getTableId());
 
-    ArrayList<String> prefVol = new ArrayList<String>();
-    // If the preferred volumes property is specified, split the returned string by the comma
and add them to a preferred volumes list
-    prefVol.addAll(Arrays.asList(volumes.split(",")));
+    if (log.isTraceEnabled()) {
+      log.trace("In custom chooser");
+      log.trace("Volumes: " + volumes);
+      log.trace("TableID: " + env.getTableId());
+    }
+    // If the preferred volumes property was specified, split the returned string by the
comma and add use it to filter the given options.
+    Set<String> preferred = parsedPreferredVolumes.get(volumes);
+    if (preferred == null) {
+      preferred = new HashSet<String>(Arrays.asList(StringUtils.split(volumes, ',')));
+      parsedPreferredVolumes.put(volumes, preferred);
+    }
 
-    // Change the given array to a List and only keep the preferred volumes that are in the
given array.
-    prefVol.retainAll(Arrays.asList(options));
+    // Only keep the options that are in the preferred set
+    final ArrayList<String> filteredOptions = new ArrayList<String>(Arrays.asList(options));
+    filteredOptions.retainAll(preferred);
 
     // If there are no preferred volumes left, then warn the user and choose randomly from
the instance volumes
-    if (prefVol.isEmpty()) {
+    if (filteredOptions.isEmpty()) {
       log.warn("Preferred volumes are not instance volumes. Defaulting to randomly choosing
from instance volumes");
       return super.choose(env, options);
     }
 
     // Randomly choose the volume from the preferred volumes
-    String choice = prefVol.get(random.nextInt(prefVol.size()));
-    log.trace("Choice = " + choice);
+    String choice = super.choose(env, filteredOptions.toArray(EMPTY_STRING_ARRAY));
+    if (log.isTraceEnabled()) {
+      log.trace("Choice = " + choice);
+    }
     return choice;
   }
 }

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/RandomVolumeChooser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/RandomVolumeChooser.java
b/server/base/src/main/java/org/apache/accumulo/server/fs/RandomVolumeChooser.java
index f2eb211..766d4c7 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/RandomVolumeChooser.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/RandomVolumeChooser.java
@@ -19,7 +19,7 @@ package org.apache.accumulo.server.fs;
 import java.util.Random;
 
 public class RandomVolumeChooser implements VolumeChooser {
-  protected static Random random = new Random();
+  private final Random random = new Random();
 
   @Override
   public String choose(VolumeChooserEnvironment env, String[] options) {

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeChooser.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeChooser.java b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeChooser.java
index f523057..9865512 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeChooser.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeChooser.java
@@ -16,6 +16,12 @@
  */
 package org.apache.accumulo.server.fs;
 
+import org.apache.accumulo.core.volume.Volume;
+
+/**
+ * Helper used by {@link VolumeManager}s to select from a set of {@link Volume} URIs.
+ * N.B. implemenations must be threadsafe. VolumeChooser.equals will be used for internal
caching.
+ */
 public interface VolumeChooser {
   String choose(VolumeChooserEnvironment env, String[] options);
 }

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManager.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManager.java b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManager.java
index 890651e..e2353d4 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManager.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManager.java
@@ -33,6 +33,7 @@ import com.google.common.base.Optional;
 /**
  * A wrapper around multiple hadoop FileSystem objects, which are assumed to be different
volumes. This also concentrates a bunch of meta-operations like
  * waiting for SAFE_MODE, and closing WALs.
+ * N.B. implementations must be thread safe.
  */
 public interface VolumeManager {
 

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManagerImpl.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManagerImpl.java
b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManagerImpl.java
index dc1be73..8202d27 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManagerImpl.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeManagerImpl.java
@@ -44,6 +44,7 @@ import org.apache.accumulo.core.util.CachedConfiguration;
 import org.apache.accumulo.core.volume.NonConfiguredVolume;
 import org.apache.accumulo.core.volume.Volume;
 import org.apache.accumulo.core.volume.VolumeConfiguration;
+import org.apache.commons.lang.ArrayUtils;
 import org.apache.commons.lang.NotImplementedException;
 import org.apache.commons.lang.StringUtils;
 import org.apache.hadoop.conf.Configuration;
@@ -84,7 +85,8 @@ public class VolumeManagerImpl implements VolumeManager {
     invertVolumesByFileSystem(volumesByName, volumesByFileSystemUri);
     this.conf = conf;
     ensureSyncIsEnabled();
-    chooser = Property.createInstanceFromPropertyName(conf, Property.GENERAL_VOLUME_CHOOSER,
VolumeChooser.class, new RandomVolumeChooser());
+    // Keep in sync with default type in the property definition.
+    chooser = Property.createInstanceFromPropertyName(conf, Property.GENERAL_VOLUME_CHOOSER,
VolumeChooser.class, new PerTableVolumeChooser());
   }
 
   private void invertVolumesByFileSystem(Map<String,Volume> forward, Multimap<URI,Volume>
inverted) {
@@ -572,9 +574,19 @@ public class VolumeManagerImpl implements VolumeManager {
     return getVolumeByPath(dir).getFileSystem().getContentSummary(dir);
   }
 
+  // Only used as a fall back if the configured chooser misbehaves.
+  private final VolumeChooser failsafeChooser = new RandomVolumeChooser();
+
   @Override
   public String choose(Optional<String> tableId, String[] options) {
-    return chooser.choose(new VolumeChooserEnvironment(tableId), options);
+    final VolumeChooserEnvironment env = new VolumeChooserEnvironment(tableId);
+    final String choice = chooser.choose(env, options);
+    if (!(ArrayUtils.contains(options, choice))) {
+      log.error("The configured volume chooser, '" +  chooser.getClass() + "', or one of
its delegates returned a volume not in the set of options provided; " +
+          "will continue by relying on a RandomVolumeChooser. You should investigate and
correct the named chooser.");
+      return failsafeChooser.choose(env, options);
+    }
+    return choice;
   }
 
   @Override

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeUtil.java
----------------------------------------------------------------------
diff --git a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeUtil.java b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeUtil.java
index 877d01c..e229209 100644
--- a/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeUtil.java
+++ b/server/base/src/main/java/org/apache/accumulo/server/fs/VolumeUtil.java
@@ -265,8 +265,8 @@ public class VolumeUtil {
       throw new IllegalArgumentException("Unexpected table dir " + dir);
     }
 
-    Path newDir = new Path(vm.choose(Optional.of(extent.getTableId().toString()), ServerConstants.getBaseUris())
+ Path.SEPARATOR + ServerConstants.TABLE_DIR + Path.SEPARATOR + dir.getParent().getName()
-        + Path.SEPARATOR + dir.getName());
+    Path newDir = new Path(vm.choose(Optional.of(extent.getTableId().toString()), ServerConstants.getBaseUris())
+ Path.SEPARATOR + ServerConstants.TABLE_DIR +
+        Path.SEPARATOR + dir.getParent().getName() + Path.SEPARATOR + dir.getName());
 
     log.info("Updating directory for " + extent + " from " + dir + " to " + newDir);
     if (extent.isRootTablet()) {

http://git-wip-us.apache.org/repos/asf/accumulo/blob/bd4d190e/server/base/src/test/java/org/apache/accumulo/server/fs/VolumeManagerImplTest.java
----------------------------------------------------------------------
diff --git a/server/base/src/test/java/org/apache/accumulo/server/fs/VolumeManagerImplTest.java
b/server/base/src/test/java/org/apache/accumulo/server/fs/VolumeManagerImplTest.java
index 582822a..23829d1 100644
--- a/server/base/src/test/java/org/apache/accumulo/server/fs/VolumeManagerImplTest.java
+++ b/server/base/src/test/java/org/apache/accumulo/server/fs/VolumeManagerImplTest.java
@@ -21,12 +21,16 @@ import java.util.List;
 
 import org.apache.accumulo.core.conf.ConfigurationCopy;
 import org.apache.accumulo.core.conf.Property;
+import org.apache.accumulo.server.fs.VolumeChooserEnvironment;
 import org.apache.accumulo.server.fs.VolumeManager.FileType;
+import org.apache.commons.lang.StringUtils;
 import org.apache.hadoop.fs.Path;
 import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 
+import com.google.common.base.Optional;
+
 /**
  *
  */
@@ -91,4 +95,26 @@ public class VolumeManagerImplTest {
     conf.set(Property.INSTANCE_VOLUMES, "viewfs://dummy");
     VolumeManagerImpl.get(conf);
   }
+
+  public static class WrongVolumeChooser implements VolumeChooser {
+    @Override
+    public String choose(VolumeChooserEnvironment env, String[] options) {
+      return "file://totally-not-given/";
+    }
+  }
+
+  @SuppressWarnings("deprecation")
+  private static final Property INSTANCE_DFS_URI = Property.INSTANCE_DFS_URI;
+
+  @Test
+  public void chooseFromOptions() throws Exception {
+    List<String> volumes = Arrays.asList("file://one/", "file://two/", "file://three/");
+    ConfigurationCopy conf = new ConfigurationCopy();
+    conf.set(INSTANCE_DFS_URI, volumes.get(0));
+    conf.set(Property.INSTANCE_VOLUMES, StringUtils.join(volumes,","));
+    conf.set(Property.GENERAL_VOLUME_CHOOSER, WrongVolumeChooser.class.getName());
+    VolumeManager vm = VolumeManagerImpl.get(conf);
+    String choice = vm.choose(Optional.of("sometable"), volumes.toArray(new String[0]));
+    Assert.assertTrue("shouldn't see invalid options from misbehaving chooser.", volumes.contains(choice));
+  }
 }


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