| /* |
| * 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 <media/nbaio/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() |
| { |
| #if !LOG_NDEBUG |
| int32_t readers = |
| #else |
| (void) |
| #endif |
| 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 * mFrameSize), red * mFrameSize); |
| // 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 * mFrameSize), mPipe.mBuffer, count * mFrameSize); |
| red += count; |
| } |
| } |
| mFront += red; |
| mFramesRead += red; |
| return red; |
| } |
| |
| } // namespace android |