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#define LOG_TAG "PipeReader"
18//#define LOG_NDEBUG 0
19
20#include <cutils/compiler.h>
21#include <utils/Log.h>
22#include <media/nbaio/PipeReader.h>
23
24namespace android {
25
26PipeReader::PipeReader(Pipe& pipe) :
27        NBAIO_Source(pipe.mFormat),
28        mPipe(pipe),
29        // any data already in the pipe is not visible to this PipeReader
30        mFront(android_atomic_acquire_load(&pipe.mRear)),
31        mFramesOverrun(0),
32        mOverruns(0)
33{
34    android_atomic_inc(&pipe.mReaders);
35}
36
37PipeReader::~PipeReader()
38{
39    int32_t readers = android_atomic_dec(&mPipe.mReaders);
40    ALOG_ASSERT(readers > 0);
41}
42
43ssize_t PipeReader::availableToRead()
44{
45    if (CC_UNLIKELY(!mNegotiated)) {
46        return NEGOTIATE;
47    }
48    int32_t rear = android_atomic_acquire_load(&mPipe.mRear);
49    // read() is not multi-thread safe w.r.t. itself, so no mutex or atomic op needed to read mFront
50    size_t avail = rear - mFront;
51    if (CC_UNLIKELY(avail > mPipe.mMaxFrames)) {
52        // Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
53        int32_t oldFront = mFront;
54        mFront = rear - mPipe.mMaxFrames + (mPipe.mMaxFrames >> 4);
55        mFramesOverrun += (size_t) (mFront - oldFront);
56        ++mOverruns;
57        return OVERRUN;
58    }
59    return avail;
60}
61
62ssize_t PipeReader::read(void *buffer, size_t count, int64_t readPTS __unused)
63{
64    ssize_t avail = availableToRead();
65    if (CC_UNLIKELY(avail <= 0)) {
66        return avail;
67    }
68    // An overrun can occur from here on and be silently ignored,
69    // but it will be caught at next read()
70    if (CC_LIKELY(count > (size_t) avail)) {
71        count = avail;
72    }
73    size_t front = mFront & (mPipe.mMaxFrames - 1);
74    size_t red = mPipe.mMaxFrames - front;
75    if (CC_LIKELY(red > count)) {
76        red = count;
77    }
78    // In particular, an overrun during the memcpy will result in reading corrupt data
79    memcpy(buffer, (char *) mPipe.mBuffer + (front * mFrameSize), red * mFrameSize);
80    // We could re-read the rear pointer here to detect the corruption, but why bother?
81    if (CC_UNLIKELY(front + red == mPipe.mMaxFrames)) {
82        if (CC_UNLIKELY((count -= red) > front)) {
83            count = front;
84        }
85        if (CC_LIKELY(count > 0)) {
86            memcpy((char *) buffer + (red * mFrameSize), mPipe.mBuffer, count * mFrameSize);
87            red += count;
88        }
89    }
90    mFront += red;
91    mFramesRead += red;
92    return red;
93}
94
95}   // namespace android
96