org.eclipse.jetty.util.SharedBlockingCallback Maven / Gradle / Ivy
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//
// ========================================================================
// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//
package org.eclipse.jetty.util;
import java.io.Closeable;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.Objects;
import java.util.concurrent.CancellationException;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Provides a reusable {@link Callback} that can block the thread
* while waiting to be completed.
*
* A typical usage pattern is:
*
* void someBlockingCall(Object... args) throws IOException
* {
* try(Blocker blocker = sharedBlockingCallback.acquire())
* {
* someAsyncCall(args, blocker);
* blocker.block();
* }
* }
*
*/
public class SharedBlockingCallback
{
private static final Logger LOG = LoggerFactory.getLogger(SharedBlockingCallback.class);
private static final Throwable IDLE = new ConstantThrowable("IDLE");
private static final Throwable SUCCEEDED = new ConstantThrowable("SUCCEEDED");
private static final Throwable FAILED = new ConstantThrowable("FAILED");
private final ReentrantLock _lock = new ReentrantLock();
private final Condition _idle = _lock.newCondition();
private final Condition _complete = _lock.newCondition();
private Blocker _blocker = new Blocker();
public Blocker acquire() throws IOException
{
_lock.lock();
try
{
while (_blocker._state != IDLE)
{
_idle.await();
}
_blocker._state = null;
return _blocker;
}
catch (InterruptedException x)
{
throw new InterruptedIOException();
}
finally
{
_lock.unlock();
}
}
public boolean fail(Throwable cause)
{
Objects.requireNonNull(cause);
_lock.lock();
try
{
if (_blocker._state == null)
{
_blocker._state = new BlockerFailedException(cause);
_complete.signalAll();
return true;
}
}
finally
{
_lock.unlock();
}
return false;
}
protected void notComplete(Blocker blocker)
{
LOG.warn("Blocker not complete {}", blocker);
if (LOG.isDebugEnabled())
LOG.debug("Blocker not complete stacktrace", new Throwable());
}
/**
* A Closeable Callback.
* Uses the auto close mechanism to check block has been called OK.
* Implements {@link Callback} because calls to this
* callback do not blocak, rather they wakeup the thread that is blocked
* in {@link #block()}
*/
public class Blocker implements Callback, Closeable
{
private Throwable _state = IDLE;
protected Blocker()
{
}
@Override
public InvocationType getInvocationType()
{
return InvocationType.NON_BLOCKING;
}
@Override
public void succeeded()
{
_lock.lock();
try
{
if (_state == null)
{
_state = SUCCEEDED;
_complete.signalAll();
}
else
{
LOG.warn("Succeeded after {}", _state.toString());
if (LOG.isDebugEnabled())
LOG.debug("State", _state);
}
}
finally
{
_lock.unlock();
}
}
@Override
public void failed(Throwable cause)
{
_lock.lock();
try
{
if (_state == null)
{
if (cause == null)
_state = FAILED;
else if (cause instanceof BlockerTimeoutException)
// Not this blockers timeout
_state = new IOException(cause);
else
_state = cause;
_complete.signalAll();
}
else if (_state instanceof BlockerTimeoutException || _state instanceof BlockerFailedException)
{
// Failure arrived late, block() already
// modified the state, nothing more to do.
if (LOG.isDebugEnabled())
LOG.debug("Failed after {}", _state);
}
else
{
String msg = String.format("Failed after %s: %s", _state, cause);
LOG.warn(msg);
if (LOG.isDebugEnabled())
{
LOG.debug(msg, _state);
LOG.debug(msg, cause);
}
}
}
finally
{
_lock.unlock();
}
}
/**
* Block until the Callback has succeeded or failed and after the return leave in the state to allow reuse. This is useful for code that wants to
* repeatable use a FutureCallback to convert an asynchronous API to a blocking API.
*
* @throws IOException if exception was caught during blocking, or callback was cancelled
*/
public void block() throws IOException
{
_lock.lock();
try
{
while (_state == null)
{
_complete.await();
}
if (_state == SUCCEEDED)
return;
if (_state == IDLE)
throw new IllegalStateException("IDLE");
if (_state instanceof IOException)
throw (IOException)_state;
if (_state instanceof CancellationException)
throw (CancellationException)_state;
if (_state instanceof RuntimeException)
throw (RuntimeException)_state;
if (_state instanceof Error)
throw (Error)_state;
throw new IOException(_state);
}
catch (final InterruptedException e)
{
_state = e;
throw new InterruptedIOException();
}
finally
{
_lock.unlock();
}
}
/**
* Check the Callback has succeeded or failed and after the return leave in the state to allow reuse.
*/
@Override
public void close()
{
_lock.lock();
try
{
if (_state == IDLE)
throw new IllegalStateException("IDLE");
if (_state == null)
notComplete(this);
}
finally
{
try
{
// If we have a failure
if (_state != null && _state != SUCCEEDED)
// create a new Blocker
_blocker = new Blocker();
else
// else reuse Blocker
_state = IDLE;
_idle.signalAll();
_complete.signalAll();
}
finally
{
_lock.unlock();
}
}
}
@Override
public String toString()
{
_lock.lock();
try
{
return String.format("%s@%x{%s}", Blocker.class.getSimpleName(), hashCode(), _state);
}
finally
{
_lock.unlock();
}
}
}
private static class BlockerTimeoutException extends TimeoutException
{
}
private static class BlockerFailedException extends Exception
{
public BlockerFailedException(Throwable cause)
{
super(cause);
}
}
}