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      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_PIPE_H
     18 #define ANDROID_AUDIO_PIPE_H
     19 
     20 #include "NBAIO.h"
     21 
     22 namespace android {
     23 
     24 // Pipe is multi-thread safe for readers (see PipeReader), but safe for only a single writer thread.
     25 // It cannot UNDERRUN on write, unless we allow designation of a master reader that provides the
     26 // time-base. Readers can be added and removed dynamically, and it's OK to have no readers.
     27 class Pipe : public NBAIO_Sink {
     28 
     29     friend class PipeReader;
     30 
     31 public:
     32     // maxFrames will be rounded up to a power of 2, and all slots are available. Must be >= 2.
     33     Pipe(size_t maxFrames, NBAIO_Format format);
     34     virtual ~Pipe();
     35 
     36     // NBAIO_Port interface
     37 
     38     //virtual ssize_t negotiate(const NBAIO_Format offers[], size_t numOffers,
     39     //                          NBAIO_Format counterOffers[], size_t& numCounterOffers);
     40     //virtual NBAIO_Format format() const;
     41 
     42     // NBAIO_Sink interface
     43 
     44     //virtual size_t framesWritten() const;
     45     //virtual size_t framesUnderrun() const;
     46     //virtual size_t underruns() const;
     47 
     48     // The write side of a pipe permits overruns; flow control is the caller's responsibility.
     49     // It doesn't return +infinity because that would guarantee an overrun.
     50     virtual ssize_t availableToWrite() const { return mMaxFrames; }
     51 
     52     virtual ssize_t write(const void *buffer, size_t count);
     53     //virtual ssize_t writeVia(writeVia_t via, size_t total, void *user, size_t block);
     54 
     55 private:
     56     const size_t    mMaxFrames;     // always a power of 2
     57     void * const    mBuffer;
     58     volatile int32_t mRear;         // written by android_atomic_release_store
     59     volatile int32_t mReaders;      // number of PipeReader clients currently attached to this Pipe
     60 };
     61 
     62 }   // namespace android
     63 
     64 #endif  // ANDROID_AUDIO_PIPE_H
     65