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* Copyright (C) 2012 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <utils/Errors.h>
#include <utils/Vector.h>
#include <utils/threads.h>
namespace android {
* A threaded work queue.
* This class is designed to make it easy to run a bunch of isolated work
* units in parallel, using up to the specified number of threads.
* To use it, write a loop to post work units to the work queue, then synchronize
* on the queue at the end.
class WorkQueue {
class WorkUnit {
WorkUnit() { }
virtual ~WorkUnit() { }
* Runs the work unit.
* If the result is 'true' then the work queue continues scheduling work as usual.
* If the result is 'false' then the work queue is canceled.
virtual bool run() = 0;
/* Creates a work queue with the specified maximum number of work threads. */
WorkQueue(size_t maxThreads, bool canCallJava = true);
/* Destroys the work queue.
* Cancels pending work and waits for all remaining threads to complete.
/* Posts a work unit to run later.
* If the work queue has been canceled or is already finished, returns INVALID_OPERATION
* and does not take ownership of the work unit (caller must destroy it itself).
* Otherwise, returns OK and takes ownership of the work unit (the work queue will
* destroy it automatically).
* For flow control, this method blocks when the size of the pending work queue is more
* 'backlog' times the number of threads. This condition reduces the rate of entry into
* the pending work queue and prevents it from growing much more rapidly than the
* work threads can actually handle.
* If 'backlog' is 0, then no throttle is applied.
status_t schedule(WorkUnit* workUnit, size_t backlog = 2);
/* Cancels all pending work.
* If the work queue is already finished, returns INVALID_OPERATION.
* If the work queue is already canceled, returns OK and does nothing else.
* Otherwise, returns OK, discards all pending work units and prevents additional
* work units from being scheduled.
* Call finish() after cancel() to wait for all remaining work to complete.
status_t cancel();
/* Waits for all work to complete.
* If the work queue is already finished, returns INVALID_OPERATION.
* Otherwise, waits for all work to complete and returns OK.
status_t finish();
class WorkThread : public Thread {
WorkThread(WorkQueue* workQueue, bool canCallJava);
virtual ~WorkThread();
virtual bool threadLoop();
WorkQueue* const mWorkQueue;
status_t cancelLocked();
bool threadLoop(); // called from each work thread
const size_t mMaxThreads;
const bool mCanCallJava;
Mutex mLock;
Condition mWorkChangedCondition;
Condition mWorkDequeuedCondition;
bool mCanceled;
bool mFinished;
size_t mIdleThreads;
Vector<sp<WorkThread> > mWorkThreads;
Vector<WorkUnit*> mWorkUnits;
}; // namespace android