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      1 /*]
      2  * Copyright (C) 2012 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef AAPT_WORK_QUEUE_H
     18 #define AAPT_WORK_QUEUE_H
     19 
     20 #include <utils/Errors.h>
     21 #include <utils/Vector.h>
     22 #include <utils/threads.h>
     23 
     24 namespace android {
     25 
     26 /*
     27  * A threaded work queue.
     28  *
     29  * This class is designed to make it easy to run a bunch of isolated work
     30  * units in parallel, using up to the specified number of threads.
     31  * To use it, write a loop to post work units to the work queue, then synchronize
     32  * on the queue at the end.
     33  */
     34 class WorkQueue {
     35 public:
     36     class WorkUnit {
     37     public:
     38         WorkUnit() { }
     39         virtual ~WorkUnit() { }
     40 
     41         /*
     42          * Runs the work unit.
     43          * If the result is 'true' then the work queue continues scheduling work as usual.
     44          * If the result is 'false' then the work queue is canceled.
     45          */
     46         virtual bool run() = 0;
     47     };
     48 
     49     /* Creates a work queue with the specified maximum number of work threads. */
     50     WorkQueue(size_t maxThreads, bool canCallJava = true);
     51 
     52     /* Destroys the work queue.
     53      * Cancels pending work and waits for all remaining threads to complete.
     54      */
     55     ~WorkQueue();
     56 
     57     /* Posts a work unit to run later.
     58      * If the work queue has been canceled or is already finished, returns INVALID_OPERATION
     59      * and does not take ownership of the work unit (caller must destroy it itself).
     60      * Otherwise, returns OK and takes ownership of the work unit (the work queue will
     61      * destroy it automatically).
     62      *
     63      * For flow control, this method blocks when the size of the pending work queue is more
     64      * 'backlog' times the number of threads.  This condition reduces the rate of entry into
     65      * the pending work queue and prevents it from growing much more rapidly than the
     66      * work threads can actually handle.
     67      *
     68      * If 'backlog' is 0, then no throttle is applied.
     69      */
     70     status_t schedule(WorkUnit* workUnit, size_t backlog = 2);
     71 
     72     /* Cancels all pending work.
     73      * If the work queue is already finished, returns INVALID_OPERATION.
     74      * If the work queue is already canceled, returns OK and does nothing else.
     75      * Otherwise, returns OK, discards all pending work units and prevents additional
     76      * work units from being scheduled.
     77      *
     78      * Call finish() after cancel() to wait for all remaining work to complete.
     79      */
     80     status_t cancel();
     81 
     82     /* Waits for all work to complete.
     83      * If the work queue is already finished, returns INVALID_OPERATION.
     84      * Otherwise, waits for all work to complete and returns OK.
     85      */
     86     status_t finish();
     87 
     88 private:
     89     class WorkThread : public Thread {
     90     public:
     91         WorkThread(WorkQueue* workQueue, bool canCallJava);
     92         virtual ~WorkThread();
     93 
     94     private:
     95         virtual bool threadLoop();
     96 
     97         WorkQueue* const mWorkQueue;
     98     };
     99 
    100     status_t cancelLocked();
    101     bool threadLoop(); // called from each work thread
    102 
    103     const size_t mMaxThreads;
    104     const bool mCanCallJava;
    105 
    106     Mutex mLock;
    107     Condition mWorkChangedCondition;
    108     Condition mWorkDequeuedCondition;
    109 
    110     bool mCanceled;
    111     bool mFinished;
    112     size_t mIdleThreads;
    113     Vector<sp<WorkThread> > mWorkThreads;
    114     Vector<WorkUnit*> mWorkUnits;
    115 };
    116 
    117 }; // namespace android
    118 
    119 #endif // AAPT_WORK_QUEUE_H
    120