From f17d549093a9653285f81ff5a14f4a41d395fbce Mon Sep 17 00:00:00 2001
From: Phil Burk <philburk@mobileer.com>
Date: Wed, 14 Sep 2016 08:50:33 -0700
Subject: [PATCH] pa_linux_alsa: fix hang in callback caused by abort

The author of this patch is Alan Horstmann.

Fixes ticket #251
---
 src/hostapi/alsa/pa_linux_alsa.c | 35 ++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/src/hostapi/alsa/pa_linux_alsa.c b/src/hostapi/alsa/pa_linux_alsa.c
index f286591..584cde8 100644
--- a/src/hostapi/alsa/pa_linux_alsa.c
+++ b/src/hostapi/alsa/pa_linux_alsa.c
@@ -3805,8 +3805,23 @@ static PaError PaAlsaStream_WaitForFrames( PaAlsaStream *self, unsigned long *fr
             totalFds += self->playback.nfds;
         }
 
+#ifdef PTHREAD_CANCELED
+        if( self->callbackMode )
+        {
+            /* To allow 'Abort' to terminate the callback thread, enable cancelability just for poll() (& disable after) */
+            pthread_setcancelstate( PTHREAD_CANCEL_ENABLE, NULL );
+        }
+#endif
+
         pollResults = poll( self->pfds, totalFds, pollTimeout );
 
+#ifdef PTHREAD_CANCELED
+        if( self->callbackMode )
+        {
+            pthread_setcancelstate( PTHREAD_CANCEL_DISABLE, NULL );
+        }
+#endif
+
         if( pollResults < 0 )
         {
             /*  XXX: Depend on preprocessor condition? */
@@ -4175,12 +4190,18 @@ static void *CallbackThreadFunc( void *userData )
     int streamStarted = 0;
 
     assert( stream );
+    /* Not implemented */
+    assert( !stream->primeBuffers );
 
     /* Execute OnExit when exiting */
     pthread_cleanup_push( &OnExit, stream );
-
-    /* Not implemented */
-    assert( !stream->primeBuffers );
+#ifdef PTHREAD_CANCELED
+    /* 'Abort' will use thread cancellation to terminate the callback thread, but the Alsa-lib functions
+     * are NOT cancel-safe, (and can end up in an inconsistent state).  So, disable cancelability for
+     * the thread here, and just re-enable it for the poll() in PaAlsaStream_WaitForFrames(). */
+    pthread_testcancel();
+    pthread_setcancelstate( PTHREAD_CANCEL_DISABLE, NULL );
+#endif
 
     /* @concern StreamStart If the output is being primed the output pcm needs to be prepared, otherwise the
      * stream is started immediately. The latter involves signaling the waiting main thread.
@@ -4265,10 +4286,6 @@ static void *CallbackThreadFunc( void *userData )
         {
             xrun = 0;
 
-#ifdef PTHREAD_CANCELED
-           pthread_testcancel();
-#endif
-
             /** @concern Xruns Under/overflows are to be reported to the callback */
             if( stream->underrun > 0.0 )
             {
@@ -4299,11 +4316,12 @@ static void *CallbackThreadFunc( void *userData )
 #if 0
             CallbackUpdate( &stream->threading );
 #endif
+
             CalculateTimeInfo( stream, &timeInfo );
             PaUtil_BeginBufferProcessing( &stream->bufferProcessor, &timeInfo, cbFlags );
             cbFlags = 0;
 
-            /* CPU load measurement should include processing activivity external to the stream callback */
+            /* CPU load measurement should include processing activity external to the stream callback */
             PaUtil_BeginCpuLoadMeasurement( &stream->cpuLoadMeasurer );
 
             framesGot = framesAvail;
@@ -4334,7 +4352,6 @@ static void *CallbackThreadFunc( void *userData )
             {
                 /* Go back to polling for more frames */
                 break;
-
             }
 
             if( paContinue != callbackResult )
-- 
2.43.0