wcarlson5 commented on a change in pull request #9695:
URL: https://github.com/apache/kafka/pull/9695#discussion_r551597471
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File path: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java
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@@ -924,22 +924,64 @@ private StreamThread createStreamThread(final long
cacheSizePerThread, final int
* @return name of the added stream thread or empty if a new stream thread
could not be added
*/
public Optional<String> addStreamThread() {
- synchronized (changeThreadCount) {
- if (isRunningOrRebalancing()) {
- final int threadIdx = getNextThreadIndex();
- final long cacheSizePerThread =
getCacheSizePerThread(threads.size() + 1);
+ if (isRunningOrRebalancing()) {
+ final int threadIdx;
+ final long cacheSizePerThread;
+ synchronized (changeThreadCount) {
+ threadIdx = getNextThreadIndex();
+ cacheSizePerThread = getCacheSizePerThread(threads.size() + 1);
resizeThreadCache(cacheSizePerThread);
- final StreamThread streamThread =
createStreamThread(cacheSizePerThread, threadIdx);
- synchronized (stateLock) {
- if (isRunningOrRebalancing()) {
- streamThread.start();
- return Optional.of(streamThread.getName());
- } else {
- streamThread.shutdown();
+ }
+ final StreamThread streamThread =
createStreamThread(cacheSizePerThread, threadIdx);
+
+ synchronized (stateLock) {
+ if (isRunningOrRebalancing()) {
+ streamThread.start();
+ return Optional.of(streamThread.getName());
+ } else {
+ streamThread.shutdown();
+ threads.remove(streamThread);
+ resizeThreadCache(getCacheSizePerThread(threads.size()));
+ return Optional.empty();
+ }
+ }
+ }
+ return Optional.empty();
+ }
+
+ /**
+ * Removes one stream thread out of the running stream threads from this
Kafka Streams client.
+ * <p>
+ * The removed stream thread is gracefully shut down. This method does not
specify which stream
+ * thread is shut down.
+ * <p>
+ * Since the number of stream threads decreases, the sizes of the caches
in the remaining stream
+ * threads are adapted so that the sum of the cache sizes over all stream
threads equals the total
+ * cache size specified in configuration {@link
StreamsConfig#CACHE_MAX_BYTES_BUFFERING_CONFIG}.
+ *
+ * @return name of the removed stream thread or empty if a stream thread
could not be removed because
+ * no stream threads are alive
+ */
+ public Optional<String> removeStreamThread() {
+ if (isRunningOrRebalancing()) {
+ for (final StreamThread streamThread : threads) {
Review comment:
Okay we won't get a concurrent modification but the result won't be
deterministic, I think we can just synchronize the iterator in remove thread as
that is the only time were we are iterating and making changes. The other
places concurrent access should not be a problem.
I've added tests for the remove and add, there does not seem to be a problem
but it is hard to guarantee that the race condition hit each time.
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