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#ifndef ANDROID_AUDIO_MONO_PIPE_H
18#define ANDROID_AUDIO_MONO_PIPE_H
19
20#include <time.h>
21#include "NBAIO.h"
22
23namespace android {
24
25// MonoPipe is similar to Pipe except:
26//  - supports only a single reader, called MonoPipeReader
27//  - write() cannot overrun; instead it will return a short actual count if insufficient space
28//  - write() can optionally block if the pipe is full
29// Like Pipe, it is not multi-thread safe for either writer or reader
30// but writer and reader can be different threads.
31class MonoPipe : public NBAIO_Sink {
32
33    friend class MonoPipeReader;
34
35public:
36    // reqFrames will be rounded up to a power of 2, and all slots are available. Must be >= 2.
37    // Note: whatever shares this object with another thread needs to do so in an SMP-safe way (like
38    // creating it the object before creating the other thread, or storing the object with a
39    // release_store). Otherwise the other thread could see a partially-constructed object.
40    MonoPipe(size_t reqFrames, NBAIO_Format format, bool writeCanBlock = false);
41    virtual ~MonoPipe();
42
43    // NBAIO_Port interface
44
45    //virtual ssize_t negotiate(const NBAIO_Format offers[], size_t numOffers,
46    //                          NBAIO_Format counterOffers[], size_t& numCounterOffers);
47    //virtual NBAIO_Format format() const;
48
49    // NBAIO_Sink interface
50
51    //virtual size_t framesWritten() const;
52    //virtual size_t framesUnderrun() const;
53    //virtual size_t underruns() const;
54
55    virtual ssize_t availableToWrite() const;
56    virtual ssize_t write(const void *buffer, size_t count);
57    //virtual ssize_t writeVia(writeVia_t via, size_t total, void *user, size_t block);
58
59            // average number of frames present in the pipe under normal conditions.
60            // See throttling mechanism in MonoPipe::write()
61            size_t  getAvgFrames() const { return mSetpoint; }
62            void    setAvgFrames(size_t setpoint);
63            size_t  maxFrames() const { return mMaxFrames; }
64
65private:
66    const size_t    mReqFrames;     // as requested in constructor, unrounded
67    const size_t    mMaxFrames;     // always a power of 2
68    void * const    mBuffer;
69    // mFront and mRear will never be separated by more than mMaxFrames.
70    // 32-bit overflow is possible if the pipe is active for a long time, but if that happens it's
71    // safe because we "&" with (mMaxFrames-1) at end of computations to calculate a buffer index.
72    volatile int32_t mFront;        // written by reader with android_atomic_release_store,
73                                    // read by writer with android_atomic_acquire_load
74    volatile int32_t mRear;         // written by writer with android_atomic_release_store,
75                                    // read by reader with android_atomic_acquire_load
76    bool            mWriteTsValid;  // whether mWriteTs is valid
77    struct timespec mWriteTs;       // time that the previous write() completed
78    size_t          mSetpoint;      // target value for pipe fill depth
79    const bool      mWriteCanBlock; // whether write() should block if the pipe is full
80};
81
82}   // namespace android
83
84#endif  // ANDROID_AUDIO_MONO_PIPE_H
85