Examples with EventBatch org.apache.hadoop.hdfs.inotify.EventBatch used on opensource projects

Example 1 with EventBatch

use of org.apache.hadoop.hdfs.inotify.EventBatch in project hadoop by apache.

the class TestDFSInotifyEventInputStream method testReadEventsWithTimeout.

@Test(timeout = 120000)
public void testReadEventsWithTimeout() throws IOException, InterruptedException, MissingEventsException {
    Configuration conf = new HdfsConfiguration();
    MiniQJMHACluster cluster = new MiniQJMHACluster.Builder(conf).build();
    try {
        cluster.getDfsCluster().waitActive();
        cluster.getDfsCluster().transitionToActive(0);
        final DFSClient client = new DFSClient(cluster.getDfsCluster().getNameNode(0).getNameNodeAddress(), conf);
        DFSInotifyEventInputStream eis = client.getInotifyEventStream();
        ScheduledExecutorService ex = Executors.newSingleThreadScheduledExecutor();
        ex.schedule(new Runnable() {

            @Override
            public void run() {
                try {
                    client.mkdirs("/dir", null, false);
                } catch (IOException e) {
                    // test will fail
                    LOG.error("Unable to create /dir", e);
                }
            }
        }, 1, TimeUnit.SECONDS);
        // a very generous wait period -- the edit will definitely have been
        // processed by the time this is up
        EventBatch batch = eis.poll(5, TimeUnit.SECONDS);
        Assert.assertNotNull(batch);
        Assert.assertEquals(1, batch.getEvents().length);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CREATE);
        Assert.assertEquals("/dir", ((Event.CreateEvent) batch.getEvents()[0]).getPath());
    } finally {
        cluster.shutdown();
    }
}

Example 2 with EventBatch

use of org.apache.hadoop.hdfs.inotify.EventBatch in project hadoop by apache.

the class TestDFSInotifyEventInputStream method testBasic.

/**
   * Tests all FsEditLogOps that are converted to inotify events.
   */
@Test(timeout = 120000)
@SuppressWarnings("deprecation")
public void testBasic() throws IOException, URISyntaxException, InterruptedException, MissingEventsException {
    Configuration conf = new HdfsConfiguration();
    conf.setLong(DFSConfigKeys.DFS_BLOCK_SIZE_KEY, BLOCK_SIZE);
    conf.setBoolean(DFSConfigKeys.DFS_NAMENODE_ACLS_ENABLED_KEY, true);
    // so that we can get an atime change
    conf.setLong(DFSConfigKeys.DFS_NAMENODE_ACCESSTIME_PRECISION_KEY, 1);
    MiniQJMHACluster.Builder builder = new MiniQJMHACluster.Builder(conf);
    builder.getDfsBuilder().numDataNodes(2);
    MiniQJMHACluster cluster = builder.build();
    try {
        cluster.getDfsCluster().waitActive();
        cluster.getDfsCluster().transitionToActive(0);
        DFSClient client = new DFSClient(cluster.getDfsCluster().getNameNode(0).getNameNodeAddress(), conf);
        FileSystem fs = cluster.getDfsCluster().getFileSystem(0);
        DFSTestUtil.createFile(fs, new Path("/file"), BLOCK_SIZE, (short) 1, 0L);
        DFSTestUtil.createFile(fs, new Path("/file3"), BLOCK_SIZE, (short) 1, 0L);
        DFSTestUtil.createFile(fs, new Path("/file5"), BLOCK_SIZE, (short) 1, 0L);
        DFSTestUtil.createFile(fs, new Path("/truncate_file"), BLOCK_SIZE * 2, (short) 1, 0L);
        DFSInotifyEventInputStream eis = client.getInotifyEventStream();
        // RenameOp -> RenameEvent
        client.rename("/file", "/file4", null);
        // RenameOldOp -> RenameEvent
        client.rename("/file4", "/file2");
        // DeleteOp, AddOp -> UnlinkEvent, CreateEvent
        OutputStream os = client.create("/file2", true, (short) 2, BLOCK_SIZE);
        os.write(new byte[BLOCK_SIZE]);
        // CloseOp -> CloseEvent
        os.close();
        // AddOp -> AppendEvent
        os = client.append("/file2", BLOCK_SIZE, EnumSet.of(CreateFlag.APPEND), null, null);
        os.write(new byte[BLOCK_SIZE]);
        // CloseOp -> CloseEvent
        os.close();
        // so that the atime will get updated on the next line
        Thread.sleep(10);
        // TimesOp -> MetadataUpdateEvent
        client.open("/file2").read(new byte[1]);
        // SetReplicationOp -> MetadataUpdateEvent
        client.setReplication("/file2", (short) 1);
        // ConcatDeleteOp -> AppendEvent, UnlinkEvent, CloseEvent
        client.concat("/file2", new String[] { "/file3" });
        // DeleteOp -> UnlinkEvent
        client.delete("/file2", false);
        // MkdirOp -> CreateEvent
        client.mkdirs("/dir", null, false);
        // SetPermissionsOp -> MetadataUpdateEvent
        client.setPermission("/dir", FsPermission.valueOf("-rw-rw-rw-"));
        // SetOwnerOp -> MetadataUpdateEvent
        client.setOwner("/dir", "username", "groupname");
        // SymlinkOp -> CreateEvent
        client.createSymlink("/dir", "/dir2", false);
        client.setXAttr("/file5", "user.field", "value".getBytes(), EnumSet.of(// SetXAttrOp -> MetadataUpdateEvent
        XAttrSetFlag.CREATE));
        // RemoveXAttrOp -> MetadataUpdateEvent
        client.removeXAttr("/file5", "user.field");
        // SetAclOp -> MetadataUpdateEvent
        client.setAcl("/file5", AclEntry.parseAclSpec("user::rwx,user:foo:rw-,group::r--,other::---", true));
        // SetAclOp -> MetadataUpdateEvent
        client.removeAcl("/file5");
        // RenameOldOp -> RenameEvent
        client.rename("/file5", "/dir");
        //TruncateOp -> TruncateEvent
        client.truncate("/truncate_file", BLOCK_SIZE);
        EventBatch batch = null;
        // RenameOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        long txid = batch.getTxid();
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.RENAME);
        Event.RenameEvent re = (Event.RenameEvent) batch.getEvents()[0];
        Assert.assertEquals("/file4", re.getDstPath());
        Assert.assertEquals("/file", re.getSrcPath());
        Assert.assertTrue(re.getTimestamp() > 0);
        LOG.info(re.toString());
        Assert.assertTrue(re.toString().startsWith("RenameEvent [srcPath="));
        long eventsBehind = eis.getTxidsBehindEstimate();
        // RenameOldOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.RENAME);
        Event.RenameEvent re2 = (Event.RenameEvent) batch.getEvents()[0];
        Assert.assertTrue(re2.getDstPath().equals("/file2"));
        Assert.assertTrue(re2.getSrcPath().equals("/file4"));
        Assert.assertTrue(re2.getTimestamp() > 0);
        LOG.info(re2.toString());
        // AddOp with overwrite
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CREATE);
        Event.CreateEvent ce = (Event.CreateEvent) batch.getEvents()[0];
        Assert.assertTrue(ce.getiNodeType() == Event.CreateEvent.INodeType.FILE);
        Assert.assertTrue(ce.getPath().equals("/file2"));
        Assert.assertTrue(ce.getCtime() > 0);
        Assert.assertTrue(ce.getReplication() > 0);
        Assert.assertTrue(ce.getSymlinkTarget() == null);
        Assert.assertTrue(ce.getOverwrite());
        Assert.assertEquals(BLOCK_SIZE, ce.getDefaultBlockSize());
        LOG.info(ce.toString());
        Assert.assertTrue(ce.toString().startsWith("CreateEvent [INodeType="));
        // CloseOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CLOSE);
        Event.CloseEvent ce2 = (Event.CloseEvent) batch.getEvents()[0];
        Assert.assertTrue(ce2.getPath().equals("/file2"));
        Assert.assertTrue(ce2.getFileSize() > 0);
        Assert.assertTrue(ce2.getTimestamp() > 0);
        LOG.info(ce2.toString());
        Assert.assertTrue(ce2.toString().startsWith("CloseEvent [path="));
        // AppendOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.APPEND);
        Event.AppendEvent append2 = (Event.AppendEvent) batch.getEvents()[0];
        Assert.assertEquals("/file2", append2.getPath());
        Assert.assertFalse(append2.toNewBlock());
        LOG.info(append2.toString());
        Assert.assertTrue(append2.toString().startsWith("AppendEvent [path="));
        // CloseOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CLOSE);
        Assert.assertTrue(((Event.CloseEvent) batch.getEvents()[0]).getPath().equals("/file2"));
        // TimesOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue.getPath().equals("/file2"));
        Assert.assertTrue(mue.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.TIMES);
        LOG.info(mue.toString());
        Assert.assertTrue(mue.toString().startsWith("MetadataUpdateEvent [path="));
        // SetReplicationOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue2 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue2.getPath().equals("/file2"));
        Assert.assertTrue(mue2.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.REPLICATION);
        Assert.assertTrue(mue2.getReplication() == 1);
        LOG.info(mue2.toString());
        // ConcatDeleteOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(3, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.APPEND);
        Assert.assertTrue(((Event.AppendEvent) batch.getEvents()[0]).getPath().equals("/file2"));
        Assert.assertTrue(batch.getEvents()[1].getEventType() == Event.EventType.UNLINK);
        Event.UnlinkEvent ue2 = (Event.UnlinkEvent) batch.getEvents()[1];
        Assert.assertTrue(ue2.getPath().equals("/file3"));
        Assert.assertTrue(ue2.getTimestamp() > 0);
        LOG.info(ue2.toString());
        Assert.assertTrue(ue2.toString().startsWith("UnlinkEvent [path="));
        Assert.assertTrue(batch.getEvents()[2].getEventType() == Event.EventType.CLOSE);
        Event.CloseEvent ce3 = (Event.CloseEvent) batch.getEvents()[2];
        Assert.assertTrue(ce3.getPath().equals("/file2"));
        Assert.assertTrue(ce3.getTimestamp() > 0);
        // DeleteOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.UNLINK);
        Event.UnlinkEvent ue = (Event.UnlinkEvent) batch.getEvents()[0];
        Assert.assertTrue(ue.getPath().equals("/file2"));
        Assert.assertTrue(ue.getTimestamp() > 0);
        LOG.info(ue.toString());
        // MkdirOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CREATE);
        Event.CreateEvent ce4 = (Event.CreateEvent) batch.getEvents()[0];
        Assert.assertTrue(ce4.getiNodeType() == Event.CreateEvent.INodeType.DIRECTORY);
        Assert.assertTrue(ce4.getPath().equals("/dir"));
        Assert.assertTrue(ce4.getCtime() > 0);
        Assert.assertTrue(ce4.getReplication() == 0);
        Assert.assertTrue(ce4.getSymlinkTarget() == null);
        LOG.info(ce4.toString());
        // SetPermissionsOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue3 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue3.getPath().equals("/dir"));
        Assert.assertTrue(mue3.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.PERMS);
        Assert.assertTrue(mue3.getPerms().toString().contains("rw-rw-rw-"));
        LOG.info(mue3.toString());
        // SetOwnerOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue4 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue4.getPath().equals("/dir"));
        Assert.assertTrue(mue4.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.OWNER);
        Assert.assertTrue(mue4.getOwnerName().equals("username"));
        Assert.assertTrue(mue4.getGroupName().equals("groupname"));
        LOG.info(mue4.toString());
        // SymlinkOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CREATE);
        Event.CreateEvent ce5 = (Event.CreateEvent) batch.getEvents()[0];
        Assert.assertTrue(ce5.getiNodeType() == Event.CreateEvent.INodeType.SYMLINK);
        Assert.assertTrue(ce5.getPath().equals("/dir2"));
        Assert.assertTrue(ce5.getCtime() > 0);
        Assert.assertTrue(ce5.getReplication() == 0);
        Assert.assertTrue(ce5.getSymlinkTarget().equals("/dir"));
        LOG.info(ce5.toString());
        // SetXAttrOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue5 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue5.getPath().equals("/file5"));
        Assert.assertTrue(mue5.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.XATTRS);
        Assert.assertTrue(mue5.getxAttrs().size() == 1);
        Assert.assertTrue(mue5.getxAttrs().get(0).getName().contains("field"));
        Assert.assertTrue(!mue5.isxAttrsRemoved());
        LOG.info(mue5.toString());
        // RemoveXAttrOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue6 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue6.getPath().equals("/file5"));
        Assert.assertTrue(mue6.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.XATTRS);
        Assert.assertTrue(mue6.getxAttrs().size() == 1);
        Assert.assertTrue(mue6.getxAttrs().get(0).getName().contains("field"));
        Assert.assertTrue(mue6.isxAttrsRemoved());
        LOG.info(mue6.toString());
        // SetAclOp (1)
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue7 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue7.getPath().equals("/file5"));
        Assert.assertTrue(mue7.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.ACLS);
        Assert.assertTrue(mue7.getAcls().contains(AclEntry.parseAclEntry("user::rwx", true)));
        LOG.info(mue7.toString());
        // SetAclOp (2)
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.METADATA);
        Event.MetadataUpdateEvent mue8 = (Event.MetadataUpdateEvent) batch.getEvents()[0];
        Assert.assertTrue(mue8.getPath().equals("/file5"));
        Assert.assertTrue(mue8.getMetadataType() == Event.MetadataUpdateEvent.MetadataType.ACLS);
        Assert.assertTrue(mue8.getAcls() == null);
        LOG.info(mue8.toString());
        // RenameOp (2)
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.RENAME);
        Event.RenameEvent re3 = (Event.RenameEvent) batch.getEvents()[0];
        Assert.assertTrue(re3.getDstPath().equals("/dir/file5"));
        Assert.assertTrue(re3.getSrcPath().equals("/file5"));
        Assert.assertTrue(re3.getTimestamp() > 0);
        LOG.info(re3.toString());
        // TruncateOp
        batch = waitForNextEvents(eis);
        Assert.assertEquals(1, batch.getEvents().length);
        txid = checkTxid(batch, txid);
        Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.TRUNCATE);
        Event.TruncateEvent et = ((Event.TruncateEvent) batch.getEvents()[0]);
        Assert.assertTrue(et.getPath().equals("/truncate_file"));
        Assert.assertTrue(et.getFileSize() == BLOCK_SIZE);
        Assert.assertTrue(et.getTimestamp() > 0);
        LOG.info(et.toString());
        Assert.assertTrue(et.toString().startsWith("TruncateEvent [path="));
        // Returns null when there are no further events
        Assert.assertTrue(eis.poll() == null);
        // make sure the estimate hasn't changed since the above assertion
        // tells us that we are fully caught up to the current namesystem state
        // and we should not have been behind at all when eventsBehind was set
        // either, since there were few enough events that they should have all
        // been read to the client during the first poll() call
        Assert.assertTrue(eis.getTxidsBehindEstimate() == eventsBehind);
    } finally {
        cluster.shutdown();
    }
}

Example 3 with EventBatch

use of org.apache.hadoop.hdfs.inotify.EventBatch in project hadoop by apache.

the class TestDFSInotifyEventInputStream method testNNFailover.

@Test(timeout = 120000)
public void testNNFailover() throws IOException, URISyntaxException, MissingEventsException {
    Configuration conf = new HdfsConfiguration();
    MiniQJMHACluster cluster = new MiniQJMHACluster.Builder(conf).build();
    try {
        cluster.getDfsCluster().waitActive();
        cluster.getDfsCluster().transitionToActive(0);
        DFSClient client = ((DistributedFileSystem) HATestUtil.configureFailoverFs(cluster.getDfsCluster(), conf)).dfs;
        DFSInotifyEventInputStream eis = client.getInotifyEventStream();
        for (int i = 0; i < 10; i++) {
            client.mkdirs("/dir" + i, null, false);
        }
        cluster.getDfsCluster().shutdownNameNode(0);
        cluster.getDfsCluster().transitionToActive(1);
        EventBatch batch = null;
        // active
        for (int i = 0; i < 10; i++) {
            batch = waitForNextEvents(eis);
            Assert.assertEquals(1, batch.getEvents().length);
            Assert.assertTrue(batch.getEvents()[0].getEventType() == Event.EventType.CREATE);
            Assert.assertTrue(((Event.CreateEvent) batch.getEvents()[0]).getPath().equals("/dir" + i));
        }
        Assert.assertTrue(eis.poll() == null);
    } finally {
        cluster.shutdown();
    }
}

Example 4 with EventBatch

use of org.apache.hadoop.hdfs.inotify.EventBatch in project hadoop by apache.

the class DFSInotifyEventInputStream method poll.

/**
   * Returns the next event batch in the stream, waiting up to the specified
   * amount of time for a new batch. Returns null if one is not available at the
   * end of the specified amount of time. The time before the method returns may
   * exceed the specified amount of time by up to the time required for an RPC
   * to the NameNode.
   *
   * @param time number of units of the given TimeUnit to wait
   * @param tu the desired TimeUnit
   * @throws IOException see {@link DFSInotifyEventInputStream#poll()}
   * @throws MissingEventsException
   * see {@link DFSInotifyEventInputStream#poll()}
   * @throws InterruptedException if the calling thread is interrupted
   */
public EventBatch poll(long time, TimeUnit tu) throws IOException, InterruptedException, MissingEventsException {
    EventBatch next;
    try (TraceScope ignored = tracer.newScope("inotifyPollWithTimeout")) {
        long initialTime = Time.monotonicNow();
        long totalWait = TimeUnit.MILLISECONDS.convert(time, tu);
        long nextWait = INITIAL_WAIT_MS;
        while ((next = poll()) == null) {
            long timeLeft = totalWait - (Time.monotonicNow() - initialTime);
            if (timeLeft <= 0) {
                LOG.debug("timed poll(): timed out");
                break;
            } else if (timeLeft < nextWait * 2) {
                nextWait = timeLeft;
            } else {
                nextWait *= 2;
            }
            LOG.debug("timed poll(): poll() returned null, sleeping for {} ms", nextWait);
            Thread.sleep(nextWait);
        }
    }
    return next;
}

Example 5 with EventBatch

use of org.apache.hadoop.hdfs.inotify.EventBatch in project hadoop by apache.

the class DFSInotifyEventInputStream method take.

/**
   * Returns the next batch of events in the stream, waiting indefinitely if
   * a new batch  is not immediately available.
   *
   * @throws IOException see {@link DFSInotifyEventInputStream#poll()}
   * @throws MissingEventsException see
   * {@link DFSInotifyEventInputStream#poll()}
   * @throws InterruptedException if the calling thread is interrupted
   */
public EventBatch take() throws IOException, InterruptedException, MissingEventsException {
    EventBatch next;
    try (TraceScope ignored = tracer.newScope("inotifyTake")) {
        int nextWaitMin = INITIAL_WAIT_MS;
        while ((next = poll()) == null) {
            // sleep for a random period between nextWaitMin and nextWaitMin * 2
            // to avoid stampedes at the NN if there are multiple clients
            int sleepTime = nextWaitMin + rng.nextInt(nextWaitMin);
            LOG.debug("take(): poll() returned null, sleeping for {} ms", sleepTime);
            Thread.sleep(sleepTime);
            // the maximum sleep is 2 minutes
            nextWaitMin = Math.min(60000, nextWaitMin * 2);
        }
    }
    return next;
}