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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.index;
import java.util.IdentityHashMap;
import java.util.Map;
import org.apache.lucene.util.ThreadInterruptedException;
/**
* Controls the health status of a {@link DocumentsWriter} sessions. This class used to block
* incoming indexing threads if flushing significantly slower than indexing to ensure the {@link
* DocumentsWriter}s healthiness. If flushing is significantly slower than indexing the net memory
* used within an {@link IndexWriter} session can increase very quickly and easily exceed the JVM's
* available memory.
*
* To prevent OOM Errors and ensure IndexWriter's stability this class blocks incoming threads
* from indexing once 2 x number of available {@link DocumentsWriterPerThread}s in {@link
* DocumentsWriterPerThreadPool} is exceeded. Once flushing catches up and the number of flushing
* DWPT is equal or lower than the number of active {@link DocumentsWriterPerThread}s threads are
* released and can continue indexing.
*/
final class DocumentsWriterStallControl {
private volatile boolean stalled;
private int numWaiting; // only with assert
private boolean wasStalled; // only with assert
private final Map waiting = new IdentityHashMap<>(); // only with assert
/**
* Update the stalled flag status. This method will set the stalled flag to true iff
* the number of flushing {@link DocumentsWriterPerThread} is greater than the number of active
* {@link DocumentsWriterPerThread}. Otherwise it will reset the {@link
* DocumentsWriterStallControl} to healthy and release all threads waiting on {@link
* #waitIfStalled()}
*/
synchronized void updateStalled(boolean stalled) {
if (this.stalled != stalled) {
this.stalled = stalled;
if (stalled) {
wasStalled = true;
}
notifyAll();
}
}
/** Blocks if documents writing is currently in a stalled state. */
void waitIfStalled() {
if (stalled) {
synchronized (this) {
if (stalled) { // react on the first wakeup call!
// don't loop here, higher level logic will re-stall!
try {
incWaiters();
// Defensive, in case we have a concurrency bug that fails to .notify/All our thread:
// just wait for up to 1 second here, and let caller re-stall if it's still needed:
wait(1000);
decrWaiters();
} catch (InterruptedException e) {
throw new ThreadInterruptedException(e);
}
}
}
}
}
boolean anyStalledThreads() {
return stalled;
}
private void incWaiters() {
numWaiting++;
assert waiting.put(Thread.currentThread(), Boolean.TRUE) == null;
assert numWaiting > 0;
}
private void decrWaiters() {
numWaiting--;
assert waiting.remove(Thread.currentThread()) != null;
assert numWaiting >= 0;
}
synchronized boolean hasBlocked() { // for tests
return numWaiting > 0;
}
synchronized int getNumWaiting() { // for tests
return numWaiting;
}
boolean isHealthy() { // for tests
return !stalled; // volatile read!
}
synchronized boolean isThreadQueued(Thread t) { // for tests
return waiting.containsKey(t);
}
synchronized boolean wasStalled() { // for tests
return wasStalled;
}
}