Make HttpPostEmitter more robust in the face of serious errors (like OutOfMemoryError) during onSealExclusive() (#5386)

java-util/src/main/java/io/druid/java/util/emitter/core/Batch.java

@@ -90,8 +90,12 @@ class Batch extends AbstractQueuedLongSynchronizer
 
   /**
    * Ordering number of this batch, as they filled & emitted in {@link HttpPostEmitter} serially, starting from 0.
+   * It's a boxed Integer rather than int, because we want to minimize the number of allocations done in
+   * {@link HttpPostEmitter#onSealExclusive} and so the probability of {@link OutOfMemoryError}.
+   * @see HttpPostEmitter#onSealExclusive
+   * @see HttpPostEmitter#concurrentBatch
    */
-  final int batchNumber;
+  final Integer batchNumber;
 
   /**
    * The number of events in this batch, needed for event count-based batch emitting.

java-util/src/main/java/io/druid/java/util/emitter/core/HttpPostEmitter.java

@@ -110,9 +110,12 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
   private final AtomicInteger approximateBuffersToReuseCount = new AtomicInteger();
 
   /**
-   * concurrentBatch.get() == null means the service is closed.
+   * concurrentBatch.get() == null means the service is closed. concurrentBatch.get() is the instance of Integer,
+   * it means that some thread has failed with a serious error during {@link #onSealExclusive} (with the batch number
+   * corresponding to the Integer object) and {@link #tryRecoverCurrentBatch} needs to be called. Otherwise (i. e.
+   * normally), an instance of {@link Batch} is stored in this atomic reference.
    */
-  private final AtomicReference<Batch> concurrentBatch = new AtomicReference<>();
+  private final AtomicReference<Object> concurrentBatch = new AtomicReference<>();
 
   private final ConcurrentLinkedDeque<Batch> buffersToEmit = new ConcurrentLinkedDeque<>();
   /**
@@ -247,10 +250,15 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
     }
 
     while (true) {
-      Batch batch = concurrentBatch.get();
-      if (batch == null) {
+      Object batchObj = concurrentBatch.get();
+      if (batchObj instanceof Integer) {
+        tryRecoverCurrentBatch((Integer) batchObj);
+        continue;
+      }
+      if (batchObj == null) {
         throw new RejectedExecutionException("Service is closed.");
       }
+      Batch batch = (Batch) batchObj;
       if (batch.tryAddEvent(eventBytes)) {
         return batch;
       } else {
@@ -294,6 +302,25 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
    * Called from {@link Batch} only once for each Batch in existence.
    */
   void onSealExclusive(Batch batch, long elapsedTimeMillis)
+  {
+    try {
+      doOnSealExclusive(batch, elapsedTimeMillis);
+    }
+    catch (Throwable t) {
+      try {
+        if (!concurrentBatch.compareAndSet(batch, batch.batchNumber)) {
+          log.error("Unexpected failure to set currentBatch to the failed Batch.batchNumber");
+        }
+        log.error(t, "Serious error during onSealExclusive(), set currentBatch to the failed Batch.batchNumber");
+      }
+      catch (Throwable t2) {
+        t.addSuppressed(t2);
+      }
+      throw t;
+    }
+  }
+
+  private void doOnSealExclusive(Batch batch, long elapsedTimeMillis)
   {
     batchFillingTimeCounter.add((int) Math.max(elapsedTimeMillis, 0));
     if (elapsedTimeMillis > 0) {
@@ -305,13 +332,29 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
     wakeUpEmittingThread();
     if (!isTerminated()) {
       int nextBatchNumber = EmittedBatchCounter.nextBatchNumber(batch.batchNumber);
-      if (!concurrentBatch.compareAndSet(batch, new Batch(this, acquireBuffer(), nextBatchNumber))) {
-        // If compareAndSet failed, the service is closed concurrently.
+      byte[] newBuffer = acquireBuffer();
+      if (!concurrentBatch.compareAndSet(batch, new Batch(this, newBuffer, nextBatchNumber))) {
+        buffersToReuse.add(newBuffer);
+        // If compareAndSet failed, the service should be closed concurrently, i. e. we expect isTerminated() = true.
+        // If we don't see this, there should be some bug in HttpPostEmitter.
         Preconditions.checkState(isTerminated());
       }
     }
   }
 
+  private void tryRecoverCurrentBatch(Integer failedBatchNumber)
+  {
+    log.info("Trying to recover currentBatch");
+    int nextBatchNumber = EmittedBatchCounter.nextBatchNumber(failedBatchNumber);
+    byte[] newBuffer = acquireBuffer();
+    if (concurrentBatch.compareAndSet(failedBatchNumber, new Batch(this, newBuffer, nextBatchNumber))) {
+      log.info("Successfully recovered currentBatch");
+    } else {
+      // It's normal, a concurrent thread could succeed to recover first.
+      buffersToReuse.add(newBuffer);
+    }
+  }
+
   private void addBatchToEmitQueue(Batch batch)
   {
     limitBuffersToEmitSize();
@@ -363,7 +406,10 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
   public void flush() throws IOException
   {
     awaitStarted();
-    flush(concurrentBatch.get());
+    Object batchObj = concurrentBatch.get();
+    if (batchObj instanceof Batch) {
+      flush((Batch) batchObj);
+    }
   }
 
   private void flush(Batch batch) throws IOException
@@ -396,8 +442,10 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
     synchronized (startLock) {
       if (running) {
         running = false;
-        Batch lastBatch = concurrentBatch.getAndSet(null);
-        flush(lastBatch);
+        Object lastBatch = concurrentBatch.getAndSet(null);
+        if (lastBatch instanceof Batch) {
+          flush((Batch) lastBatch);
+        }
         emittingThread.shuttingDown = true;
         // EmittingThread is interrupted after the last batch is flushed.
         emittingThread.interrupt();
@@ -478,16 +526,19 @@ public class HttpPostEmitter implements Flushable, Closeable, Emitter
     {
       boolean needsToShutdown = Thread.interrupted() || shuttingDown;
       if (needsToShutdown) {
-        Batch lastBatch = concurrentBatch.getAndSet(null);
-        if (lastBatch != null) {
-          lastBatch.seal();
+        Object lastBatch = concurrentBatch.getAndSet(null);
+        if (lastBatch instanceof Batch) {
+          ((Batch) lastBatch).seal();
         }
       } else {
-        Batch batch = concurrentBatch.get();
-        if (batch != null) {
-          batch.sealIfFlushNeeded();
+        Object batch = concurrentBatch.get();
+        if (batch instanceof Batch) {
+          ((Batch) batch).sealIfFlushNeeded();
         } else {
-          needsToShutdown = true;
+          // batch == null means that HttpPostEmitter is terminated. Batch object could also be Integer, if some
+          // thread just failed with a serious error in onSealExclusive(), in this case we don't want to shutdown
+          // the emitter thread.
+          needsToShutdown = batch == null;
         }
       }
       return needsToShutdown;