[GitHub] [kafka] cadonna commented on a change in pull request #9615: KAFKA-10500: Add thread option

[GitBox <gi...@apache.org>]

cadonna commented on a change in pull request #9615:
URL: https://github.com/apache/kafka/pull/9615#discussion_r533675429



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File path: streams/src/main/java/org/apache/kafka/streams/KafkaStreams.java
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@@ -894,19 +885,88 @@ private KafkaStreams(final InternalTopologyBuilder internalTopologyBuilder,
         queryableStoreProvider = new QueryableStoreProvider(storeProviders, globalStateStoreProvider);
 
         stateDirCleaner = setupStateDirCleaner();
-        oldHandler = false;
         maybeWarnAboutCodeInRocksDBConfigSetter(log, config);
         rocksDBMetricsRecordingService = maybeCreateRocksDBMetricsRecordingService(clientId, config);
     }
 
+    private StreamThread createStreamThread(final long cacheSizePerThread, final int threadIdx) {
+        final StreamThread streamThread = StreamThread.create(
+                internalTopologyBuilder,
+                config,
+                clientSupplier,
+                adminClient,
+                processId,
+                clientId,
+                streamsMetrics,
+                time,
+                streamsMetadataState,
+                cacheSizePerThread,
+                stateDirectory,
+                delegatingStateRestoreListener,
+                threadIdx,
+                KafkaStreams.this::closeToError,
+                streamsUncaughtExceptionHandler
+        );
+        threads.add(streamThread);
+        threadState.put(streamThread.getId(), streamThread.state());
+        storeProviders.add(new StreamThreadStateStoreProvider(streamThread));
+        return streamThread;
+    }
+
+    /**
+     * Adds and starts a stream thread in addition to the stream threads that are already running in this
+     * Kafka Streams client.
+     *
+     * 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
+     * {@code cache.max.bytes.buffering}.
+     *
+     * 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() {
+        if (isRunningOrRebalancing()) {
+            final int threadIdx = getNextThreadIndex();
+            final long cacheSizePerThread = getCacheSizePerThread(threads.size() + 1);
+            resizeThreadCache(cacheSizePerThread);
+            final StreamThread streamThread = createStreamThread(cacheSizePerThread, threadIdx);
+            streamThread.setStateListener(streamStateListener);
+            synchronized (stateLock) {
+                if (isRunningOrRebalancing()) {
+                    streamThread.start();

Review comment:
       What about checking for the state and do the clean-up only if the state is not `PENDING_SHUTDOWN` and not `ERROR` and not `NOT_RUNNING`? In this way we are safe for future changes that break our assumption on state transitions and we make sure not to do unnecessary stuff when we are shutting down.   




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