wcarlson5 commented on a change in pull request #9695:
URL: https://github.com/apache/kafka/pull/9695#discussion_r538938550
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File path: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java
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@@ -924,28 +924,69 @@ 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.
+ *
+ * The removed stream thread is gracefully shut down. This method does not
specify which stream
+ * thread is shut down.
+ *
+ * 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 {@code cache.max.bytes.buffering}.
+ *
+ * @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) {
+ if (streamThread.isAlive()) {
+ streamThread.shutdown();
+ while (streamThread.state() != StreamThread.State.DEAD &&
!streamThread.getName().equals(Thread.currentThread().getName())) {
Review comment:
I think we have to put the thread id back on the menu. Otherwise when we
replace the thread we will not be able to use the same id. In the tests for
`REPLACE_THREAD` there has been no problems with having the thread that is
shutting down have the same name as the thread that is starting. But for a call
to `removeThread` it is probably best to not resize until shutdown is complete
i think the OOM risk is acceptable. The thread shutdown is much simpler than
a client one and should not be using more space and the new thread should not
have any tasks assigned until the old thread leaves the group.
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