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