org.elasticsearch.common.util.CancellableThreads Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of elasticsearch Show documentation
Show all versions of elasticsearch Show documentation
Elasticsearch subproject :server
/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.common.util;
import org.apache.lucene.util.SetOnce;
import org.apache.lucene.util.ThreadInterruptedException;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.core.Nullable;
import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
/**
* A utility class for multi threaded operation that needs to be cancellable via interrupts. Every cancellable operation should be
* executed via {@link #execute(Interruptible)}, which will capture the executing thread and make sure it is interrupted in the case
* of cancellation.
*
* Cancellation policy: This class does not support external interruption via Thread#interrupt(). Always use #cancel() instead.
*/
public class CancellableThreads {
private final Set threads = new HashSet<>();
// needs to be volatile as it is also read outside of synchronized blocks.
private volatile boolean cancelled = false;
private final SetOnce onCancel = new SetOnce<>();
private String reason;
public synchronized boolean isCancelled() {
return cancelled;
}
public void checkForCancel() {
checkForCancel(null);
}
private void checkForCancel(Exception beforeCancelException) {
if (isCancelled()) {
final String reason;
final OnCancel onCancel;
synchronized (this) {
reason = this.reason;
onCancel = this.onCancel.get();
}
if (onCancel != null) {
onCancel.onCancel(reason, beforeCancelException);
}
// fallback to the default exception
final RuntimeException cancelExp = new ExecutionCancelledException("operation was cancelled reason [" + reason + "]");
if (beforeCancelException != null) {
cancelExp.addSuppressed(beforeCancelException);
}
throw cancelExp;
}
}
private synchronized boolean add() {
checkForCancel();
threads.add(Thread.currentThread());
// capture and clean the interrupted thread before we start, so we can identify
// our own interrupt. we do so under lock so we know we don't clear our own.
return Thread.interrupted();
}
/**
* run the Interruptible, capturing the executing thread. Concurrent calls to {@link #cancel(String)} will interrupt this thread
* causing the call to prematurely return.
*
* @param interruptible code to run
*/
public void execute(Interruptible interruptible) {
boolean wasInterrupted = add();
boolean cancelledByExternalInterrupt = false;
RuntimeException runtimeException = null;
try {
interruptible.run();
} catch (InterruptedException | ThreadInterruptedException e) {
// ignore, this interrupt has been triggered by us in #cancel()...
assert cancelled : "Interruption via Thread#interrupt() is unsupported. Use CancellableThreads#cancel() instead";
// we can only reach here if assertions are disabled. If we reach this code and cancelled is false, this means that we've
// been interrupted externally (which we don't support).
cancelledByExternalInterrupt = cancelled == false;
} catch (RuntimeException t) {
runtimeException = t;
} finally {
remove();
}
// we are now out of threads collection so we can't be interrupted any more by this class
// restore old flag and see if we need to fail
if (wasInterrupted) {
Thread.currentThread().interrupt();
} else {
// clear the flag interrupted flag as we are checking for failure..
Thread.interrupted();
}
checkForCancel(runtimeException);
if (runtimeException != null) {
// if we're not canceling, we throw the original exception
throw runtimeException;
}
if (cancelledByExternalInterrupt) {
// restore interrupt flag to at least adhere to expected behavior
Thread.currentThread().interrupt();
throw new RuntimeException("Interruption via Thread#interrupt() is unsupported. Use CancellableThreads#cancel() instead");
}
}
private synchronized void remove() {
threads.remove(Thread.currentThread());
}
/** cancel all current running operations. Future calls to {@link #checkForCancel()} will be failed with the given reason */
public synchronized void cancel(String reason) {
if (cancelled) {
// we were already cancelled, make sure we don't interrupt threads twice
// this is important in order to make sure that we don't mark
// Thread.interrupted without handling it
return;
}
cancelled = true;
this.reason = reason;
for (Thread thread : threads) {
thread.interrupt();
}
threads.clear();
}
public interface Interruptible {
void run() throws InterruptedException;
}
public static class ExecutionCancelledException extends ElasticsearchException {
public ExecutionCancelledException(String msg) {
super(msg);
}
public ExecutionCancelledException(StreamInput in) throws IOException {
super(in);
}
}
/**
* Registers a callback that will be invoked when some running operations are cancelled or {@link #checkForCancel()} is called.
*/
public synchronized void setOnCancel(OnCancel onCancel) {
this.onCancel.set(onCancel);
}
@FunctionalInterface
public interface OnCancel {
/**
* Called when some running operations are cancelled or {@link #checkForCancel()} is explicitly called.
* If this method throws an exception, cancelling tasks will fail with that exception; otherwise they
* will fail with the default exception {@link ExecutionCancelledException}.
*
* @param reason the reason of the cancellation
* @param beforeCancelException any error that was encountered during the execution before the operations were cancelled.
* @see #checkForCancel()
* @see #setOnCancel(OnCancel)
*/
void onCancel(String reason, @Nullable Exception beforeCancelException);
}
}