org.eclipse.jetty.util.SharedBlockingCallback Maven / Gradle / Ivy
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//
// ========================================================================
// Copyright (c) 1995-2018 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util;
import java.io.Closeable;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.concurrent.CancellationException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
/**
* 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 = Log.getLogger(SharedBlockingCallback.class);
private static Throwable IDLE = new ConstantThrowable("IDLE");
private static Throwable SUCCEEDED = new ConstantThrowable("SUCCEEDED");
private static 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();
@Deprecated
protected long getIdleTimeout()
{
return -1;
}
public Blocker acquire() throws IOException
{
long idle = getIdleTimeout();
_lock.lock();
try
{
while (_blocker._state != IDLE)
{
if (idle>0 && (idle < Long.MAX_VALUE/2))
{
// Wait a little bit longer than the blocker might block
if (!_idle.await(idle*2,TimeUnit.MILLISECONDS))
throw new IOException(new TimeoutException());
}
else
_idle.await();
}
_blocker._state = null;
return _blocker;
}
catch (InterruptedException x)
{
throw new InterruptedIOException();
}
finally
{
_lock.unlock();
}
}
protected void notComplete(Blocker blocker)
{
LOG.warn("Blocker not complete {}",blocker);
if (LOG.isDebugEnabled())
LOG.debug(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);
}
}
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)
{
// Failure arrived late, block() already
// modified the state, nothing more to do.
}
else
{
LOG.warn("Failed after {}: {}", _state, cause);
if (LOG.isDebugEnabled())
{
LOG.debug(_state);
LOG.debug(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
{
long idle = getIdleTimeout();
_lock.lock();
try
{
while (_state == null)
{
if (idle > 0)
{
// Waiting here may compete with the idle timeout mechanism,
// so here we wait a little bit longer to favor the normal
// idle timeout mechanism that will call failed(Throwable).
long excess = Math.min(idle / 2, 1000);
if (!_complete.await(idle + excess, TimeUnit.MILLISECONDS))
{
// Method failed(Throwable) has not been called yet,
// so we will synthesize a special TimeoutException.
_state = new BlockerTimeoutException();
}
}
else
{
_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
{
}
}