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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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <time.h>
#include <utils/LinearTransform.h>
#include "NBAIO.h"
#include <media/SingleStateQueue.h>
namespace android {
typedef SingleStateQueue<AudioTimestamp> AudioTimestampSingleStateQueue;
// MonoPipe is similar to Pipe except:
// - supports only a single reader, called MonoPipeReader
// - write() cannot overrun; instead it will return a short actual count if insufficient space
// - write() can optionally block if the pipe is full
// Like Pipe, it is not multi-thread safe for either writer or reader
// but writer and reader can be different threads.
class MonoPipe : public NBAIO_Sink {
friend class MonoPipeReader;
// reqFrames will be rounded up to a power of 2, and all slots are available. Must be >= 2.
// Note: whatever shares this object with another thread needs to do so in an SMP-safe way (like
// creating it the object before creating the other thread, or storing the object with a
// release_store). Otherwise the other thread could see a partially-constructed object.
MonoPipe(size_t reqFrames, const NBAIO_Format& format, bool writeCanBlock = false);
virtual ~MonoPipe();
// NBAIO_Port interface
//virtual ssize_t negotiate(const NBAIO_Format offers[], size_t numOffers,
// NBAIO_Format counterOffers[], size_t& numCounterOffers);
//virtual NBAIO_Format format() const;
// NBAIO_Sink interface
//virtual size_t framesWritten() const;
//virtual size_t framesUnderrun() const;
//virtual size_t underruns() const;
virtual ssize_t availableToWrite() const;
virtual ssize_t write(const void *buffer, size_t count);
//virtual ssize_t writeVia(writeVia_t via, size_t total, void *user, size_t block);
// MonoPipe's implementation of getNextWriteTimestamp works in conjunction
// with MonoPipeReader. Every time a MonoPipeReader reads from the pipe, it
// receives a "readPTS" indicating the point in time for which the reader
// would like to read data. This "last read PTS" is offset by the amt of
// data the reader is currently mixing and then cached cached along with the
// updated read pointer. This cached value is the local time for which the
// reader is going to request data next time it reads data (assuming we are
// in steady state and operating with no underflows). Writers to the
// MonoPipe who would like to know when their next write operation will hit
// the speakers can call getNextWriteTimestamp which will return the value
// of the last read PTS plus the duration of the amt of data waiting to be
// read in the MonoPipe.
virtual status_t getNextWriteTimestamp(int64_t *timestamp);
// average number of frames present in the pipe under normal conditions.
// See throttling mechanism in MonoPipe::write()
size_t getAvgFrames() const { return mSetpoint; }
void setAvgFrames(size_t setpoint);
size_t maxFrames() const { return mMaxFrames; }
// Set the shutdown state for the write side of a pipe.
// This may be called by an unrelated thread. When shutdown state is 'true',
// a write that would otherwise block instead returns a short transfer count.
// There is no guarantee how long it will take for the shutdown to be recognized,
// but it will not be an unbounded amount of time.
// The state can be restored to normal by calling shutdown(false).
void shutdown(bool newState = true);
// Return true if the write side of a pipe is currently shutdown.
bool isShutdown();
// Return NO_ERROR if there is a timestamp available
status_t getTimestamp(AudioTimestamp& timestamp);
// A pair of methods and a helper variable which allows the reader and the
// writer to update and observe the values of mFront and mNextRdPTS in an
// atomic lock-less fashion.
// :: Important ::
// Two assumptions must be true in order for this lock-less approach to
// function properly on all systems. First, there may only be one updater
// thread in the system. Second, the updater thread must be running at a
// strictly higher priority than the observer threads. Currently, both of
// these assumptions are true. The only updater is always a single
// FastMixer thread (which runs with SCHED_FIFO/RT priority while the only
// observer is always an AudioFlinger::PlaybackThread running with
// traditional (non-RT) audio priority.
void updateFrontAndNRPTS(int32_t newFront, int64_t newNextRdPTS);
void observeFrontAndNRPTS(int32_t *outFront, int64_t *outNextRdPTS);
volatile int32_t mUpdateSeq;
const size_t mReqFrames; // as requested in constructor, unrounded
const size_t mMaxFrames; // always a power of 2
void * const mBuffer;
// mFront and mRear will never be separated by more than mMaxFrames.
// 32-bit overflow is possible if the pipe is active for a long time, but if that happens it's
// safe because we "&" with (mMaxFrames-1) at end of computations to calculate a buffer index.
volatile int32_t mFront; // written by the reader with updateFrontAndNRPTS, observed by
// the writer with observeFrontAndNRPTS
volatile int32_t mRear; // written by writer with android_atomic_release_store,
// read by reader with android_atomic_acquire_load
volatile int64_t mNextRdPTS; // written by the reader with updateFrontAndNRPTS, observed by
// the writer with observeFrontAndNRPTS
bool mWriteTsValid; // whether mWriteTs is valid
struct timespec mWriteTs; // time that the previous write() completed
size_t mSetpoint; // target value for pipe fill depth
const bool mWriteCanBlock; // whether write() should block if the pipe is full
int64_t offsetTimestampByAudioFrames(int64_t ts, size_t audFrames);
LinearTransform mSamplesToLocalTime;
bool mIsShutdown; // whether shutdown(true) was called, no barriers are needed
AudioTimestampSingleStateQueue::Shared mTimestampShared;
AudioTimestampSingleStateQueue::Mutator mTimestampMutator;
AudioTimestampSingleStateQueue::Observer mTimestampObserver;
} // namespace android