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#if !LOG_NDEBUG
40    int32_t readers =
41#else
42    (void)
43#endif
44            android_atomic_dec(&mPipe.mReaders);
45    ALOG_ASSERT(readers > 0);
46}
47
48ssize_t PipeReader::availableToRead()
49{
50    if (CC_UNLIKELY(!mNegotiated)) {
51        return NEGOTIATE;
52    }
53    int32_t rear = android_atomic_acquire_load(&mPipe.mRear);
54    // read() is not multi-thread safe w.r.t. itself, so no mutex or atomic op needed to read mFront
55    size_t avail = rear - mFront;
56    if (CC_UNLIKELY(avail > mPipe.mMaxFrames)) {
57        // Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
58        int32_t oldFront = mFront;
59        mFront = rear - mPipe.mMaxFrames + (mPipe.mMaxFrames >> 4);
60        mFramesOverrun += (size_t) (mFront - oldFront);
61        ++mOverruns;
62        return OVERRUN;
63    }
64    return avail;
65}
66
67ssize_t PipeReader::read(void *buffer, size_t count)
68{
69    ssize_t avail = availableToRead();
70    if (CC_UNLIKELY(avail <= 0)) {
71        return avail;
72    }
73    // An overrun can occur from here on and be silently ignored,
74    // but it will be caught at next read()
75    if (CC_LIKELY(count > (size_t) avail)) {
76        count = avail;
77    }
78    size_t front = mFront & (mPipe.mMaxFrames - 1);
79    size_t red = mPipe.mMaxFrames - front;
80    if (CC_LIKELY(red > count)) {
81        red = count;
82    }
83    // In particular, an overrun during the memcpy will result in reading corrupt data
84    memcpy(buffer, (char *) mPipe.mBuffer + (front * mFrameSize), red * mFrameSize);
85    // We could re-read the rear pointer here to detect the corruption, but why bother?
86    if (CC_UNLIKELY(front + red == mPipe.mMaxFrames)) {
87        if (CC_UNLIKELY((count -= red) > front)) {
88            count = front;
89        }
90        if (CC_LIKELY(count > 0)) {
91            memcpy((char *) buffer + (red * mFrameSize), mPipe.mBuffer, count * mFrameSize);
92            red += count;
93        }
94    }
95    mFront += red;
96    mFramesRead += red;
97    return red;
98}
99
100}   // namespace android
101