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) 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 << mBitShift), red << mBitShift); 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 << mBitShift), mPipe.mBuffer, count << mBitShift); 87 red += count; 88 } 89 } 90 mFront += red; 91 mFramesRead += red; 92 return red; 93} 94 95} // namespace android 96