wcarlson5 commented on a change in pull request #9695:
URL: https://github.com/apache/kafka/pull/9695#discussion_r553004791
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File path: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java
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@@ -947,24 +948,65 @@ 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 {
+ }
+ 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()));
+ log.warn("Cannot add a stream thread in state " + state());
+ return Optional.empty();
+ }
+ }
+ }
+ log.warn("Cannot add a stream thread in state " + state());
+ 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()) {
+ synchronized (changeThreadCount) {
+ for (final StreamThread streamThread : threads) {
+ if (streamThread.isAlive()) {
streamThread.shutdown();
+ if
(!streamThread.getName().equals(Thread.currentThread().getName())) {
Review comment:
We want to avoid removing the calling thread because the idea is that
the call will block until thread is gone. This is best for the cache resizing
too. However I do not like the idea of not letting a thread remove itself
because, if we have one stream thread left not letting that thread remove it
self (maybe leaving a global thread) this seems incomplete. If we need to make
this more structured maybe we only remove itself if is the only thread running?
that should make the cache and blocking issue less of a problem. How does that
sound?
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