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     // buffer is an optional parameter specifying the virtual address of the pipe buffer,
34     // which must be of size roundup(maxFrames) * Format_frameSize(format) bytes.
35     Pipe(size_t maxFrames, const NBAIO_Format& format, void *buffer = NULL);
36 
37     // If a buffer was specified in the constructor, it is not automatically freed by destructor.
38     virtual ~Pipe();
39 
40     // NBAIO_Port interface
41 
42     //virtual ssize_t negotiate(const NBAIO_Format offers[], size_t numOffers,
43     //                          NBAIO_Format counterOffers[], size_t& numCounterOffers);
44     //virtual NBAIO_Format format() const;
45 
46     // NBAIO_Sink interface
47 
48     //virtual size_t framesWritten() const;
49     //virtual size_t framesUnderrun() const;
50     //virtual size_t underruns() const;
51 
52     // The write side of a pipe permits overruns; flow control is the caller's responsibility.
53     // It doesn't return +infinity because that would guarantee an overrun.
availableToWrite()54     virtual ssize_t availableToWrite() const { return mMaxFrames; }
55 
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 private:
60     const size_t    mMaxFrames;     // always a power of 2
61     void * const    mBuffer;
62     volatile int32_t mRear;         // written by android_atomic_release_store
63     volatile int32_t mReaders;      // number of PipeReader clients currently attached to this Pipe
64     const bool      mFreeBufferInDestructor;
65 };
66 
67 }   // namespace android
68 
69 #endif  // ANDROID_AUDIO_PIPE_H
70