100 lines
3 KiB
C++
100 lines
3 KiB
C++
/*
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* Copyright (C) 2012 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "PipeReader"
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//#define LOG_NDEBUG 0
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#include <cutils/compiler.h>
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#include <utils/Log.h>
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#include <media/nbaio/PipeReader.h>
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namespace android {
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PipeReader::PipeReader(Pipe& pipe) :
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NBAIO_Source(pipe.mFormat),
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mPipe(pipe),
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// any data already in the pipe is not visible to this PipeReader
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mFront(android_atomic_acquire_load(&pipe.mRear)),
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mFramesOverrun(0),
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mOverruns(0)
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{
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android_atomic_inc(&pipe.mReaders);
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}
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PipeReader::~PipeReader()
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{
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#if !LOG_NDEBUG
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int32_t readers =
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#else
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(void)
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#endif
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android_atomic_dec(&mPipe.mReaders);
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ALOG_ASSERT(readers > 0);
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}
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ssize_t PipeReader::availableToRead()
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{
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if (CC_UNLIKELY(!mNegotiated)) {
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return NEGOTIATE;
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}
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int32_t rear = android_atomic_acquire_load(&mPipe.mRear);
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// read() is not multi-thread safe w.r.t. itself, so no mutex or atomic op needed to read mFront
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size_t avail = rear - mFront;
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if (CC_UNLIKELY(avail > mPipe.mMaxFrames)) {
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// Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
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int32_t oldFront = mFront;
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mFront = rear - mPipe.mMaxFrames + (mPipe.mMaxFrames >> 4);
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mFramesOverrun += (size_t) (mFront - oldFront);
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++mOverruns;
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return OVERRUN;
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}
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return avail;
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}
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ssize_t PipeReader::read(void *buffer, size_t count)
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{
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ssize_t avail = availableToRead();
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if (CC_UNLIKELY(avail <= 0)) {
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return avail;
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}
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// An overrun can occur from here on and be silently ignored,
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// but it will be caught at next read()
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if (CC_LIKELY(count > (size_t) avail)) {
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count = avail;
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}
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size_t front = mFront & (mPipe.mMaxFrames - 1);
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size_t red = mPipe.mMaxFrames - front;
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if (CC_LIKELY(red > count)) {
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red = count;
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}
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// In particular, an overrun during the memcpy will result in reading corrupt data
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memcpy(buffer, (char *) mPipe.mBuffer + (front * mFrameSize), red * mFrameSize);
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// We could re-read the rear pointer here to detect the corruption, but why bother?
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if (CC_UNLIKELY(front + red == mPipe.mMaxFrames)) {
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if (CC_UNLIKELY((count -= red) > front)) {
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count = front;
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}
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if (CC_LIKELY(count > 0)) {
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memcpy((char *) buffer + (red * mFrameSize), mPipe.mBuffer, count * mFrameSize);
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red += count;
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}
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}
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mFront += red;
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mFramesRead += red;
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return red;
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}
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} // namespace android
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