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
24namespace 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 */
34class WorkQueue {
35public:
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
88private:
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