From: Richard Kettlewell <rjk@greenend.org.uk>
Date: Fri, 13 Mar 2009 21:05:44 +0000 (+0000)
Subject: disorder-playrtp now releases its lock around activate/deactivate
X-Git-Tag: 5.0~178^2~3
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~mdw/git/disorder/commitdiff_plain/d4170ca70fd4f87f77fa2213219eb30f89d3d0d0

disorder-playrtp now releases its lock around activate/deactivate
calls.  This necessary since deactivate may block if a sample
collection callback is still running (in this case it will be blocked
indefinitely).  It actually happens with the Core Audio backend but it
could apply to other APIs too.
---

diff --git a/clients/playrtp.c b/clients/playrtp.c
index 9647437..92cbb75 100644
--- a/clients/playrtp.c
+++ b/clients/playrtp.c
@@ -763,7 +763,9 @@ int main(int argc, char **argv) {
     info("Playing...");
     next_timestamp = pheap_first(&packets)->timestamp;
     active = 1;
+    pthread_mutex_unlock(&lock);
     backend->activate();
+    pthread_mutex_lock(&lock);
     /* Wait until the buffer empties out */
     while(nsamples >= minbuffer
 	  || (nsamples > 0
@@ -771,7 +773,9 @@ int main(int argc, char **argv) {
       pthread_cond_wait(&cond, &lock);
     }
     /* Stop playing for a bit until the buffer re-fills */
+    pthread_mutex_unlock(&lock);
     backend->deactivate();
+    pthread_mutex_lock(&lock);
     active = 0;
     /* Go back round */
   }
diff --git a/lib/uaudio.h b/lib/uaudio.h
index aa686d0..e796393 100644
--- a/lib/uaudio.h
+++ b/lib/uaudio.h
@@ -34,6 +34,15 @@ extern size_t uaudio_sample_size;
  * @param max_samples How many samples to supply
  * @param userdata As passed to uaudio_open()
  * @return Number of samples filled
+ *
+ * This function should not block if possible (better to fill the buffer with
+ * 0s) and should definitely not block indefinitely.  This great caution with
+ * any locks or syscalls!  In particular avoid it taking a lock that may be
+ * held while any of the @ref uaudio members are called.
+ *
+ * If it's more convenient, it's OK to return less than the maximum number of
+ * samples (including 0) provided you expect to be called again for more
+ * samples immediately.
  */
 typedef size_t uaudio_callback(void *buffer,
                                size_t max_samples,