org.eclipse.jetty.util.BlockingCallback Maven / Gradle / Ivy
//
// ========================================================================
// Copyright (c) 1995-2013 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.IOException;
import java.io.InterruptedIOException;
import java.util.concurrent.CancellationException;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicBoolean;
/* ------------------------------------------------------------ */
/**
* A Callback for simple reusable conversion of an
* asynchronous API to blocking.
*
* To avoid late redundant calls to {@link #succeeded()} or {@link #failed(Throwable)} from
* interfering with later reuses of this class, the callback context is used to hold pass a phase indicated
* and only a single callback per phase is allowed.
*
* A typical usage pattern is:
*
* public class MyClass
* {
* BlockingCallback cb = new BlockingCallback();
*
* public void blockingMethod(Object args) throws Exception
* {
* asyncMethod(args,cb);
* cb.block();
* }
*
* public void asyncMethod(Object args, Callback callback)
* {
* ...
* }
* }
*/
public class BlockingCallback implements Callback
{
private static Throwable COMPLETED=new Throwable();
private final AtomicBoolean _done=new AtomicBoolean(false);
private final Semaphore _semaphore = new Semaphore(0);
private Throwable _cause;
public BlockingCallback()
{}
@Override
public void succeeded()
{
if (_done.compareAndSet(false,true))
{
_cause=COMPLETED;
_semaphore.release();
}
}
@Override
public void failed(Throwable cause)
{
if (_done.compareAndSet(false,true))
{
_cause=cause;
_semaphore.release();
}
}
/** Block until the FutureCallback is done or cancelled and
* after the return leave in the state as if a {@link #reset()} had been
* done.
* This is useful for code that wants to repeatable use a FutureCallback to convert
* an asynchronous API to a blocking API.
* @return
* @throws IOException
*/
public void block() throws IOException
{
try
{
_semaphore.acquire();
if (_cause==COMPLETED)
return;
if (_cause instanceof IOException)
throw (IOException) _cause;
if (_cause instanceof CancellationException)
throw (CancellationException) _cause;
throw new IOException(_cause);
}
catch (final InterruptedException e)
{
throw new InterruptedIOException(){{initCause(e);}};
}
finally
{
_done.set(false);
_cause=null;
}
}
@Override
public String toString()
{
return String.format("%s@%x{%b,%b}",BlockingCallback.class.getSimpleName(),hashCode(),_done.get(),_cause==COMPLETED);
}
}