Changeset 2296

Timestamp:

Sep 19, 2008 1:28:40 PM (16 years ago)

Author:

nanang

Message:

More ticket #633: Fixed DirectSound? implementation to avoid playback buffer read & write cursor race.

File:

• pjproject/trunk/pjmedia/src/pjmedia/dsound.c (modified) (6 diffs)

pjproject/trunk/pjmedia/src/pjmedia/dsound.c

@@ -26 +26 @@
 #if PJMEDIA_SOUND_IMPLEMENTATION == PJMEDIA_SOUND_WIN32_DIRECT_SOUND
 
+#define PJ_MIN(x, y)    ((x < y) ? (x) : (y))
+
 #ifdef _MSC_VER
 #   pragma warning(push, 3)
@@ -150 +152 @@
     DSBPOSITIONNOTIFY dsPosNotify[MAX_PACKET_BUFFER_COUNT];
     unsigned bytes_per_frame;
+    unsigned max_latency;
     unsigned i;
 
@@ -239 +242 @@
     ds_strm->dwDsBufferSize = buffer_count * bytes_per_frame;
     ds_strm->timestamp.u64 = 0;
-    ds_strm->latency = buffer_count * samples_per_frame * 1000 / clock_rate / 
-                       channel_count;
+    /*
+     * Play latency does not need to be on a frame boundry, it is just how far
+     * ahead of the read pointer we set the write pointer.  So we should just
+     * use the user configured latency.  However, if the latency measured in
+     * bytes causes more buffers than we are allowed, we must cap the latency
+     * at the time contained in 1-buffer_count.
+     */
+    max_latency = (1 - buffer_count) * samples_per_frame * 1000 / clock_rate /
+        channel_count;
+    ds_strm->latency = PJ_MIN(max_latency, snd_output_latency);
 
     /* Done setting up play device. */
@@ -346 +357 @@
     ds_strm->timestamp.u64 = 0;
     ds_strm->dwDsBufferSize = buffer_count * bytes_per_frame;
+    /*
+     * Capture latency must always be on a frame boundry,
+     * so compute it based off the calculated buffer_count.
+     */
     ds_strm->latency = buffer_count * samples_per_frame * 1000 / clock_rate / 
                        channel_count;
@@ -812 +827 @@
         buffer_count = clock_rate * snd_output_latency / samples_per_frame /
                        1000;
+        /* There must always be one more buffer than required for the latency */
+        buffer_count += 1;
         if (buffer_count < MIN_PACKET_BUFFER_COUNT)
             buffer_count = MIN_PACKET_BUFFER_COUNT;
@@ -959 +976 @@
             return PJ_RETURN_OS_ERROR(hr);
         
-        stream->play_strm.dwBytePos = 0;
+        /* Set the write pointer ahead of the read pointer by latency bytes */
+        stream->play_strm.dwBytePos = BYTES_PER_SAMPLE * stream->clock_rate *
+                stream->channel_count * stream->play_strm.latency / 1000;
 
         hr = IDirectSoundBuffer_Play(stream->play_strm.ds.play.lpDsBuffer,