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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/trunk@189 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
191 lines
3.6 KiB
HTML
191 lines
3.6 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.75 [en]C-gatewaynet (Win98; U) [Netscape]">
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<meta name="Author" content="Phil Burk">
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<meta name="Description" content="Internal docs. How a stream is started or stopped.">
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<meta name="KeyWords" content="audio, tutorial, library, portable, open-source, DirectSound,sound, music, JSyn, synthesis,">
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<title>PortAudio Implementation - Start/Stop</title>
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</head>
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<body>
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<center><table COLS=1 WIDTH="100%" BGCOLOR="#FADA7A" >
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<tr>
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<td>
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<center>
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<h1>
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PortAudio Implementation</h1></center>
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</td>
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</tr>
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</table></center>
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<h2>
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Starting and Stopping Streams</h2>
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PortAudio is generally executed in two "threads". The foreground thread
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is the application thread. The background "thread" may be implemented as
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an actual thread, an interrupt handler, or a callback from a timer thread.
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<p>There are three ways that PortAudio can stop a stream. In each case
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we look at the sequence of events and the messages sent between the two
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threads. The following variables are contained in the internalPortAudioStream.
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<blockquote><tt>int past_IsActive;
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/* Background is still playing. */</tt>
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<br><tt>int past_StopSoon; /* Stop
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when last buffer done. */</tt>
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<br><tt>int past_StopNow; /*
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Stop IMMEDIATELY. */</tt></blockquote>
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<h3>
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Pa_AbortStream()</h3>
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This function causes the background thread to terminate as soon as possible
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and audio I/O to stop abruptly.
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<br>
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<table BORDER COLS=2 WIDTH="60%" >
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<tr>
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<td><b>Foreground Thread</b></td>
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<td><b>Background Thread</b></td>
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</tr>
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<tr>
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<td>sets <tt>StopNow</tt></td>
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<td></td>
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</tr>
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<tr>
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<td></td>
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<td>sees <tt>StopNow</tt>, </td>
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</tr>
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<tr>
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<td></td>
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<td>clears IsActive, stops thread</td>
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</tr>
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<tr>
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<td>waits for thread to exit</td>
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<td></td>
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</tr>
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<tr>
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<td>turns off audio I/O</td>
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<td></td>
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</tr>
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</table>
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<h3>
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Pa_StopStream()</h3>
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This function stops the user callback function from being called and then
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waits for all audio data written to the output buffer to be played. In
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a system with very low latency, you may not hear any difference between
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<br>
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<table BORDER COLS=2 WIDTH="60%" >
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<tr>
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<td><b>Foreground Thread</b></td>
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<td><b>Background Thread</b></td>
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</tr>
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<tr>
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<td>sets StopSoon</td>
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<td></td>
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</tr>
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<tr>
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<td></td>
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<td>stops calling user callback</td>
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</tr>
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<tr>
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<td></td>
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<td>continues until output buffer empty</td>
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</tr>
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<tr>
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<td></td>
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<td>clears IsActive, stops thread</td>
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</tr>
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<tr>
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<td>waits for thread to exit</td>
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<td></td>
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</tr>
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<tr>
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<td>turns off audio I/O</td>
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<td></td>
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</tr>
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</table>
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<h3>
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User callback returns one.</h3>
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If the user callback returns one then the user callback function will no
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longer be called. Audio output will continue until all audio data written
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to the output buffer has been played. Then the audio I/O is stopped, the
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background thread terminates, and the stream becomes inactive.
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<br>
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<table BORDER COLS=2 WIDTH="60%" >
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<tr>
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<td><b>Foreground Thread</b></td>
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<td><b>Background Thread</b></td>
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</tr>
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<tr>
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<td></td>
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<td>callback returns 1</td>
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</tr>
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<tr>
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<td></td>
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<td>sets StopSoon</td>
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</tr>
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<tr>
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<td></td>
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<td>stops calling user callback</td>
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</tr>
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<tr>
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<td></td>
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<td>continues until output buffer empty</td>
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</tr>
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<tr>
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<td></td>
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<td>clears IsActive, stops thread</td>
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</tr>
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<tr>
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<td>waits for thread to exit</td>
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<td></td>
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</tr>
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<tr>
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<td>turns off audio I/O</td>
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<td></td>
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</tr>
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</table>
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<br>
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</body>
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</html>
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