wcarlson5 commented on a change in pull request #9615:
URL: https://github.com/apache/kafka/pull/9615#discussion_r535503453
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File path: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java
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@@ -870,43 +900,75 @@ private KafkaStreams(final InternalTopologyBuilder
internalTopologyBuilder,
cacheSizePerThread,
stateDirectory,
delegatingStateRestoreListener,
- i + 1,
+ threadIdx,
KafkaStreams.this::closeToError,
- this::defaultStreamsUncaughtExceptionHandler
- );
- threads.add(streamThread);
- threadState.put(streamThread.getId(), streamThread.state());
- storeProviders.add(new
StreamThreadStateStoreProvider(streamThread));
- }
+ streamsUncaughtExceptionHandler
+ );
+ streamThread.setStateListener(streamStateListener);
+ threads.add(streamThread);
+ threadState.put(streamThread.getId(), streamThread.state());
+ storeProviders.add(new StreamThreadStateStoreProvider(streamThread));
+ return streamThread;
+ }
- ClientMetrics.addNumAliveStreamThreadMetric(streamsMetrics,
(metricsConfig, now) ->
- Math.toIntExact(threads.stream().filter(thread ->
thread.state().isAlive()).count()));
+ /**
+ * Adds and starts a stream thread in addition to the stream threads that
are already running in this
+ * Kafka Streams client.
+ * <p>
+ * Since the number of stream threads increases, the sizes of the caches
in the new stream thread
+ * and the existing stream threads are adapted so that the sum of the
cache sizes over all stream
+ * threads does not exceed the total cache size specified in configuration
+ * {@link StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG}.
+ * <p>
+ * Stream threads can only be added if this Kafka Streams client is in
state RUNNING or REBALANCING.
+ *
+ * @return name of the added stream thread or empty if a new stream thread
could not be added
+ */
+ public Optional<String> addStreamThread() {
+ synchronized (newThread) {
+ if (isRunningOrRebalancing()) {
+ final int threadIdx = getNextThreadIndex();
+ final long cacheSizePerThread =
getCacheSizePerThread(threads.size() + 1);
+ resizeThreadCache(cacheSizePerThread);
+ final StreamThread streamThread =
createStreamThread(cacheSizePerThread, threadIdx);
+ synchronized (stateLock) {
Review comment:
Expanding on this, the problem in the shutdown thread. When the join
only waits for alive threads, and to be alive the thread needs to be started.
So if in between the check and the start thread another thread transitions
the state to NOT_RUNNING the thread will not join in the shutdown thread. Then
when it continues it will start as it passed the check and we will have a
thread running after the client is shutdown.
This would be extremely though race condition to find or reproduce so best
to just avoid it.
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