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/*
* Copyright (C) 2010, Google Inc. and others
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0 which is available at
* https://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.eclipse.jgit.lib;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
/**
* Wrapper around the general {@link org.eclipse.jgit.lib.ProgressMonitor} to
* make it thread safe.
*
* Updates to the underlying ProgressMonitor are made only from the thread that
* allocated this wrapper. Callers are responsible for ensuring the allocating
* thread uses {@link #pollForUpdates()} or {@link #waitForCompletion()} to
* update the underlying ProgressMonitor.
*
* Only {@link #update(int)}, {@link #isCancelled()}, and {@link #endWorker()}
* may be invoked from a worker thread. All other methods of the ProgressMonitor
* interface can only be called from the thread that allocates this wrapper.
*/
public class ThreadSafeProgressMonitor implements ProgressMonitor {
private final ProgressMonitor pm;
private final ReentrantLock lock;
private final Thread mainThread;
private final AtomicInteger workers;
private final AtomicInteger pendingUpdates;
private final Semaphore process;
/**
* Wrap a ProgressMonitor to be thread safe.
*
* @param pm
* the underlying monitor to receive events.
*/
public ThreadSafeProgressMonitor(ProgressMonitor pm) {
this.pm = pm;
this.lock = new ReentrantLock();
this.mainThread = Thread.currentThread();
this.workers = new AtomicInteger(0);
this.pendingUpdates = new AtomicInteger(0);
this.process = new Semaphore(0);
}
/** {@inheritDoc} */
@Override
public void start(int totalTasks) {
if (!isMainThread())
throw new IllegalStateException();
pm.start(totalTasks);
}
/** {@inheritDoc} */
@Override
public void beginTask(String title, int totalWork) {
if (!isMainThread())
throw new IllegalStateException();
pm.beginTask(title, totalWork);
}
/**
* Notify the monitor a worker is starting.
*/
public void startWorker() {
startWorkers(1);
}
/**
* Notify the monitor of workers starting.
*
* @param count
* the number of worker threads that are starting.
*/
public void startWorkers(int count) {
workers.addAndGet(count);
}
/**
* Notify the monitor a worker is finished.
*/
public void endWorker() {
if (workers.decrementAndGet() == 0)
process.release();
}
/**
* Non-blocking poll for pending updates.
*
* This method can only be invoked by the same thread that allocated this
* ThreadSafeProgressMonior.
*/
public void pollForUpdates() {
assert isMainThread();
doUpdates();
}
/**
* Process pending updates and wait for workers to finish.
*
* This method can only be invoked by the same thread that allocated this
* ThreadSafeProgressMonior.
*
* @throws java.lang.InterruptedException
* if the main thread is interrupted while waiting for
* completion of workers.
*/
public void waitForCompletion() throws InterruptedException {
assert isMainThread();
while (0 < workers.get()) {
doUpdates();
process.acquire();
}
doUpdates();
}
private void doUpdates() {
int cnt = pendingUpdates.getAndSet(0);
if (0 < cnt)
pm.update(cnt);
}
/** {@inheritDoc} */
@Override
public void update(int completed) {
if (0 == pendingUpdates.getAndAdd(completed))
process.release();
}
/** {@inheritDoc} */
@Override
public boolean isCancelled() {
lock.lock();
try {
return pm.isCancelled();
} finally {
lock.unlock();
}
}
/** {@inheritDoc} */
@Override
public void endTask() {
if (!isMainThread())
throw new IllegalStateException();
pm.endTask();
}
private boolean isMainThread() {
return Thread.currentThread() == mainThread;
}
}
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