/**
* Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
*
* You are hereby granted a non-exclusive, worldwide, royalty-free license to use,
* copy, modify, and distribute this software in source code or binary form for use
* in connection with the web services and APIs provided by Facebook.
*
* As with any software that integrates with the Facebook platform, your use of
* this software is subject to the Facebook Developer Principles and Policies
* [http://developers.facebook.com/policy/]. This copyright notice shall be
* included in all copies or substantial portions of the software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package com.facebook.internal;
import com.facebook.FacebookSdk;
import java.util.concurrent.Executor;
/**
* com.facebook.internal is solely for the use of other packages within the Facebook SDK for
* Android. Use of any of the classes in this package is unsupported, and they may be modified or
* removed without warning at any time.
*/
public class WorkQueue {
public static final int DEFAULT_MAX_CONCURRENT = 8;
private final Object workLock = new Object();
private WorkNode pendingJobs;
private final int maxConcurrent;
private final Executor executor;
private WorkNode runningJobs = null;
private int runningCount = 0;
public WorkQueue() {
this(DEFAULT_MAX_CONCURRENT);
}
public WorkQueue(int maxConcurrent) {
this(maxConcurrent, FacebookSdk.getExecutor());
}
public WorkQueue(int maxConcurrent, Executor executor) {
this.maxConcurrent = maxConcurrent;
this.executor = executor;
}
public WorkItem addActiveWorkItem(Runnable callback) {
return addActiveWorkItem(callback, true);
}
public WorkItem addActiveWorkItem(Runnable callback, boolean addToFront) {
WorkNode node = new WorkNode(callback);
synchronized (workLock) {
pendingJobs = node.addToList(pendingJobs, addToFront);
}
startItem();
return node;
}
public void validate() {
synchronized (workLock) {
// Verify that all running items know they are running, and counts match
int count = 0;
if (runningJobs != null) {
WorkNode walk = runningJobs;
do {
walk.verify(true);
count++;
walk = walk.getNext();
} while (walk != runningJobs);
}
assert runningCount == count;
}
}
private void startItem() {
finishItemAndStartNew(null);
}
private void finishItemAndStartNew(WorkNode finished) {
WorkNode ready = null;
synchronized (workLock) {
if (finished != null) {
runningJobs = finished.removeFromList(runningJobs);
runningCount--;
}
if (runningCount < maxConcurrent) {
ready = pendingJobs; // Head of the pendingJobs queue
if (ready != null) {
// The Queue reassignments are necessary since 'ready' might have been
// added / removed from the front of either queue, which changes its
// respective head.
pendingJobs = ready.removeFromList(pendingJobs);
runningJobs = ready.addToList(runningJobs, false);
runningCount++;
ready.setIsRunning(true);
}
}
}
if (ready != null) {
execute(ready);
}
}
private void execute(final WorkNode node) {
executor.execute(new Runnable() {
@Override
public void run() {
try {
node.getCallback().run();
} finally {
finishItemAndStartNew(node);
}
}
});
}
private class WorkNode implements WorkItem {
private final Runnable callback;
private WorkNode next;
private WorkNode prev;
private boolean isRunning;
WorkNode(Runnable callback) {
this.callback = callback;
}
@Override
public boolean cancel() {
synchronized (workLock) {
if (!isRunning()) {
pendingJobs = removeFromList(pendingJobs);
return true;
}
}
return false;
}
@Override
public void moveToFront() {
synchronized (workLock) {
if (!isRunning()) {
pendingJobs = removeFromList(pendingJobs);
pendingJobs = addToList(pendingJobs, true);
}
}
}
@Override
public boolean isRunning() {
return isRunning;
}
Runnable getCallback() {
return callback;
}
WorkNode getNext() {
return next;
}
void setIsRunning(boolean isRunning) {
this.isRunning = isRunning;
}
WorkNode addToList(WorkNode list, boolean addToFront) {
assert next == null;
assert prev == null;
if (list == null) {
list = next = prev = this;
} else {
next = list;
prev = list.prev;
next.prev = prev.next = this;
}
return addToFront ? this : list;
}
WorkNode removeFromList(WorkNode list) {
assert next != null;
assert prev != null;
if (list == this) {
if (next == this) {
list = null;
} else {
list = next;
}
}
next.prev = prev;
prev.next = next;
next = prev = null;
return list;
}
void verify(boolean shouldBeRunning) {
assert prev.next == this;
assert next.prev == this;
assert isRunning() == shouldBeRunning;
}
}
interface WorkItem {
boolean cancel();
boolean isRunning();
void moveToFront();
}
}