ThrottledSource.cpp revision a15ed9529e70caaf42aae78f9fe530abe38bcc1b 
1/*
2 * Copyright (C) 2010 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#include "include/ThrottledSource.h"
18
19#include <media/stagefright/foundation/ADebug.h>
20#include <media/stagefright/foundation/ALooper.h>
21
22namespace android {
23
24ThrottledSource::ThrottledSource(
25        const sp<DataSource> &source,
26        int32_t bandwidthLimitBytesPerSecond)
27    : mSource(source),
28      mBandwidthLimitBytesPerSecond(bandwidthLimitBytesPerSecond),
29      mStartTimeUs(-1),
30      mTotalTransferred(0) {
31    CHECK(mBandwidthLimitBytesPerSecond > 0);
32}
33
34ssize_t ThrottledSource::readAt(off64_t offset, void *data, size_t size) {
35    Mutex::Autolock autoLock(mLock);
36
37    ssize_t n = mSource->readAt(offset, data, size);
38
39    if (n <= 0) {
40        return n;
41    }
42
43    mTotalTransferred += n;
44
45    int64_t nowUs = ALooper::GetNowUs();
46
47    if (mStartTimeUs < 0) {
48        mStartTimeUs = nowUs;
49    }
50
51    // How long would it have taken to transfer everything we ever
52    // transferred given the limited bandwidth.
53    int64_t durationUs =
54        mTotalTransferred * 1000000ll / mBandwidthLimitBytesPerSecond;
55
56    int64_t whenUs = mStartTimeUs + durationUs;
57
58    if (whenUs > nowUs) {
59        usleep(whenUs - nowUs);
60    }
61    return n;
62}
63
64
65}  // namespace android
66
67