IsolatedOutputStream.java
/*
* Copyright (C) 2016, Google Inc.
* and other copyright owners as documented in the project's IP log.
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* This program and the accompanying materials are made available
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* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
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package org.eclipse.jgit.util.io;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;
import org.eclipse.jgit.internal.JGitText;
/**
* OutputStream isolated from interrupts.
* <p>
* Wraps an OutputStream to prevent interrupts during writes from being made
* visible to that stream instance. This works around buggy or difficult
* OutputStream implementations like JSch that cannot gracefully handle an
* interrupt during write.
* <p>
* Every write (or flush) requires a context switch to another thread. Callers
* should wrap this stream with {@code BufferedOutputStream} using a suitable
* buffer size to amortize the cost of context switches.
*
* @since 4.6
*/
public class IsolatedOutputStream extends OutputStream {
private final OutputStream dst;
private final ExecutorService copier;
private Future<Void> pending;
/**
* Wraps an OutputStream.
*
* @param out
* stream to send all writes to.
*/
public IsolatedOutputStream(OutputStream out) {
dst = out;
copier = new ThreadPoolExecutor(1, 1, 0, TimeUnit.MILLISECONDS,
new ArrayBlockingQueue<Runnable>(1), new NamedThreadFactory());
}
/** {@inheritDoc} */
@Override
public void write(int ch) throws IOException {
write(new byte[] { (byte) ch }, 0, 1);
}
/** {@inheritDoc} */
@Override
public void write(byte[] buf, int pos, int cnt)
throws IOException {
checkClosed();
execute(new Callable<Void>() {
@Override
public Void call() throws IOException {
dst.write(buf, pos, cnt);
return null;
}
});
}
/** {@inheritDoc} */
@Override
public void flush() throws IOException {
checkClosed();
execute(new Callable<Void>() {
@Override
public Void call() throws IOException {
dst.flush();
return null;
}
});
}
/** {@inheritDoc} */
@Override
public void close() throws IOException {
if (!copier.isShutdown()) {
try {
if (pending == null || tryCleanClose()) {
cleanClose();
} else {
dirtyClose();
}
} finally {
copier.shutdown();
}
}
}
private boolean tryCleanClose() {
/*
* If the caller stopped waiting for a prior write or flush, they could
* be trying to close a stream that is still in-use. Check if the prior
* operation ended in a predictable way.
*/
try {
pending.get(0, TimeUnit.MILLISECONDS);
pending = null;
return true;
} catch (TimeoutException | InterruptedException e) {
return false;
} catch (ExecutionException e) {
pending = null;
return true;
}
}
private void cleanClose() throws IOException {
execute(new Callable<Void>() {
@Override
public Void call() throws IOException {
dst.close();
return null;
}
});
}
private void dirtyClose() throws IOException {
/*
* Interrupt any still pending write or flush operation. This may cause
* massive failures inside of the stream, but its going to be closed as
* the next step.
*/
pending.cancel(true);
Future<Void> close;
try {
close = copier.submit(new Callable<Void>() {
@Override
public Void call() throws IOException {
dst.close();
return null;
}
});
} catch (RejectedExecutionException e) {
throw new IOException(e);
}
try {
close.get(200, TimeUnit.MILLISECONDS);
} catch (InterruptedException | TimeoutException e) {
close.cancel(true);
throw new IOException(e);
} catch (ExecutionException e) {
throw new IOException(e.getCause());
}
}
private void checkClosed() throws IOException {
if (copier.isShutdown()) {
throw new IOException(JGitText.get().closed);
}
}
private void execute(Callable<Void> task) throws IOException {
if (pending != null) {
// Check (and rethrow) any prior failed operation.
checkedGet(pending);
}
try {
pending = copier.submit(task);
} catch (RejectedExecutionException e) {
throw new IOException(e);
}
checkedGet(pending);
pending = null;
}
private static void checkedGet(Future<Void> future) throws IOException {
try {
future.get();
} catch (InterruptedException e) {
throw interrupted(e);
} catch (ExecutionException e) {
throw new IOException(e.getCause());
}
}
private static InterruptedIOException interrupted(InterruptedException c) {
InterruptedIOException e = new InterruptedIOException();
e.initCause(c);
return e;
}
private static class NamedThreadFactory implements ThreadFactory {
private static final AtomicInteger cnt = new AtomicInteger();
@Override
public Thread newThread(Runnable r) {
int n = cnt.incrementAndGet();
String name = IsolatedOutputStream.class.getSimpleName() + '-' + n;
return new Thread(r, name);
}
}
}