Repository: apache/kafka
File: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java (Java)

Code before:
     * 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#STATESTORE_CACHE_MAX_BYTES_CONFIG}.
     *
     * @param timeout The length of time to wait for the thread to shut down
     * @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(final Duration timeout) {
        final String msgPrefix = prepareMillisCheckFailMsgPrefix(timeout, "timeout");
        final long timeoutMs = validateMillisecondDuration(timeout, msgPrefix);
        return removeStreamThread(timeoutMs);
    }

    private Optional<String> removeStreamThread(final long timeoutMs) throws TimeoutException {
        final long startMs = time.milliseconds();

        if (isRunningOrRebalancing()) {
            synchronized (changeThreadCount) {
                // make a copy of threads to avoid holding lock
                for (final StreamThread streamThread : new ArrayList<>(threads)) {
                    final boolean callingThreadIsNotCurrentStreamThread = !streamThread.getName().equals(Thread.currentThread().getName());
                    if (streamThread.isThreadAlive() && (callingThreadIsNotCurrentStreamThread || numLiveStreamThreads() == 1)) {
                        log.info("Removing StreamThread {}", streamThread.getName());
                        streamThread.shutdown(true);
                        if (!streamThread.getName().equals(Thread.currentThread().getName())) {
                            final long remainingTimeMs = timeoutMs - (time.milliseconds() - startMs);
                            if (remainingTimeMs <= 0 || !streamThread.waitOnThreadState(StreamThread.State.DEAD, remainingTimeMs)) {
                                log.warn("{} did not shutdown in the allotted time.", streamThread.getName());
                                // Don't remove from threads until shutdown is complete. We will trim it from the
                                // list once it reaches DEAD, and if for some reason it's hanging indefinitely in the
                                // shutdown then we should just consider this thread.id to be burned
                            } else {
                                log.info("Successfully removed {} in {}ms", streamThread.getName(), time.milliseconds() - startMs);
                                threads.remove(streamThread);
                                queryableStoreProvider.removeStoreProviderForThread(streamThread.getName());
                            }
                        } else {
                            log.info("{} is the last remaining thread and must remove itself, therefore we cannot wait "
                                + "for it to complete shutdown as this will result in deadlock.", streamThread.getName());
                        }

                        final long cacheSizePerThread = cacheSizePerThread(numLiveStreamThreads());
                        log.info("Resizing thread cache due to thread removal, new cache size per thread is {}", cacheSizePerThread);
                        resizeThreadCache(cacheSizePerThread);
                        final long remainingTimeMs = timeoutMs - (time.milliseconds() - startMs);
                        if (remainingTimeMs <= 0) {
                            throw new TimeoutException("Thread " + streamThread.getName() + " did not stop in the allotted time");
                        }
                        return Optional.of(streamThread.getName());
                    }

Review comment (suggestion):
As you are updating this file, please replace `!streamThread.getName().equals(Thread.currentThread().getName())` with `callingThreadIsNotCurrentStreamThread`.

Code after:
     * The removed stream thread is gracefully shut down. This method does not specify which stream
     * thread is shut down.
     * <p>
     * The consumer associated with the stream thread is closed using consumer.close() during the shutdown process.
     * Note that this method does not guarantee immediate removal of the consumer from the consumer group.
     * The consumer is only kicked off from the group after the stream thread completes its run function.
     * <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#STATESTORE_CACHE_MAX_BYTES_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() {
        return removeStreamThread(Long.MAX_VALUE);
    }

    /**
     * The consumer associated with the stream thread is closed using consumer.close() during the shutdown process.
     * Note that this method does not guarantee immediate removal of the consumer from the consumer group.
     * The consumer is only kicked off from the group after the stream thread completes its run function.
     * <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#STATESTORE_CACHE_MAX_BYTES_CONFIG}.
     *
     * @param timeout The length of time to wait for the thread to shut down
     * @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(final Duration timeout) {
        final String msgPrefix = prepareMillisCheckFailMsgPrefix(timeout, "timeout");
        final long timeoutMs = validateMillisecondDuration(timeout, msgPrefix);
        return removeStreamThread(timeoutMs);
    }

    private Optional<String> removeStreamThread(final long timeoutMs) throws TimeoutException {
        final long startMs = time.milliseconds();

        if (isRunningOrRebalancing()) {
            synchronized (changeThreadCount) {
                // make a copy of threads to avoid holding lock
                for (final StreamThread streamThread : new ArrayList<>(threads)) {
                    final boolean callingThreadIsNotCurrentStreamThread = !streamThread.getName().equals(Thread.currentThread().getName());
                    if (streamThread.isThreadAlive() && (callingThreadIsNotCurrentStreamThread || numLiveStreamThreads() == 1)) {
                        log.info("Removing StreamThread {}", streamThread.getName());
                        streamThread.shutdown(true);
                        if (callingThreadIsNotCurrentStreamThread) {
                            final long remainingTimeMs = timeoutMs - (time.milliseconds() - startMs);
                            if (remainingTimeMs <= 0 || !streamThread.waitOnThreadState(StreamThread.State.DEAD, remainingTimeMs)) {