/*
 * 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 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 pollForUpdates() or waitForCompletion() to update the underlying ProgressMonitor. Only update(int), isCancelled(), and 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. /**
 * 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.
Params:
pm – 
           the underlying monitor to receive events./**
	 * 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} /** {@inheritDoc} */
	@Override
	public void start(int totalTasks) {
		if (!isMainThread())
			throw new IllegalStateException();
		pm.start(totalTasks);
	}

	
{@inheritDoc} /** {@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.
/**
	 * Notify the monitor a worker is starting.
	 */
	public void startWorker() {
		startWorkers(1);
	}

	
Notify the monitor of workers starting.
Params:
count – 
           the number of worker threads that are starting./**
	 * 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.
/**
	 * 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.
/**
	 * 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:
InterruptedException – 
            if the main thread is interrupted while waiting for
            completion of workers./**
	 * 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} /** {@inheritDoc} */
	@Override
	public void update(int completed) {
		if (0 == pendingUpdates.getAndAdd(completed))
			process.release();
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean isCancelled() {
		lock.lock();
		try {
			return pm.isCancelled();
		} finally {
			lock.unlock();
		}
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void endTask() {
		if (!isMainThread())
			throw new IllegalStateException();
		pm.endTask();
	}

	private boolean isMainThread() {
		return Thread.currentThread() == mainThread;
	}
}