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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.gallery3d.util;
import com.android.gallery3d.common.Utils;
import com.android.gallery3d.util.ThreadPool.Job;
import com.android.gallery3d.util.ThreadPool.JobContext;
import java.util.LinkedList;
// Limit the number of concurrent jobs that has been submitted into a ThreadPool
@SuppressWarnings("rawtypes")
public class JobLimiter implements FutureListener {
private static final String TAG = "JobLimiter";
// State Transition:
// INIT -> DONE, CANCELLED
// DONE -> CANCELLED
private static final int STATE_INIT = 0;
private static final int STATE_DONE = 1;
private static final int STATE_CANCELLED = 2;
private final LinkedList<JobWrapper<?>> mJobs = new LinkedList<JobWrapper<?>>();
private final ThreadPool mPool;
private int mLimit;
private static class JobWrapper<T> implements Future<T>, Job<T> {
private int mState = STATE_INIT;
private Job<T> mJob;
private Future<T> mDelegate;
private FutureListener<T> mListener;
private T mResult;
public JobWrapper(Job<T> job, FutureListener<T> listener) {
mJob = job;
mListener = listener;
}
public synchronized void setFuture(Future<T> future) {
if (mState != STATE_INIT) return;
mDelegate = future;
}
@Override
public void cancel() {
FutureListener<T> listener = null;
synchronized (this) {
if (mState != STATE_DONE) {
listener = mListener;
mJob = null;
mListener = null;
if (mDelegate != null) {
mDelegate.cancel();
mDelegate = null;
}
}
mState = STATE_CANCELLED;
mResult = null;
notifyAll();
}
if (listener != null) listener.onFutureDone(this);
}
@Override
public synchronized boolean isCancelled() {
return mState == STATE_CANCELLED;
}
@Override
public boolean isDone() {
// Both CANCELLED AND DONE is considered as done
return mState != STATE_INIT;
}
@Override
public synchronized T get() {
while (mState == STATE_INIT) {
// handle the interrupted exception of wait()
Utils.waitWithoutInterrupt(this);
}
return mResult;
}
@Override
public void waitDone() {
get();
}
@Override
public T run(JobContext jc) {
Job<T> job = null;
synchronized (this) {
if (mState == STATE_CANCELLED) return null;
job = mJob;
}
T result = null;
try {
result = job.run(jc);
} catch (Throwable t) {
Log.w(TAG, "error executing job: " + job, t);
}
FutureListener<T> listener = null;
synchronized (this) {
if (mState == STATE_CANCELLED) return null;
mState = STATE_DONE;
listener = mListener;
mListener = null;
mJob = null;
mResult = result;
notifyAll();
}
if (listener != null) listener.onFutureDone(this);
return result;
}
}
public JobLimiter(ThreadPool pool, int limit) {
mPool = Utils.checkNotNull(pool);
mLimit = limit;
}
public synchronized <T> Future<T> submit(Job<T> job, FutureListener<T> listener) {
JobWrapper<T> future = new JobWrapper<T>(Utils.checkNotNull(job), listener);
mJobs.addLast(future);
submitTasksIfAllowed();
return future;
}
@SuppressWarnings({"rawtypes", "unchecked"})
private void submitTasksIfAllowed() {
while (mLimit > 0 && !mJobs.isEmpty()) {
JobWrapper wrapper = mJobs.removeFirst();
if (!wrapper.isCancelled()) {
--mLimit;
wrapper.setFuture(mPool.submit(wrapper, this));
}
}
}
@Override
public synchronized void onFutureDone(Future future) {
++mLimit;
submitTasksIfAllowed();
}
}
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