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:
WorkUnit()38         WorkUnit() { }
~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     explicit 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