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