core: adjust playing_for and underrun_for at rewind

A rewind may erase data that sink_input counted in playing_for or
underrun_for earlier. Add code adjusting those values after a rewind.

One visible symptom of this bug was problems recovering from an
underrun. When a client calls pa_stream_write() with a large block of
memory, the function can split that into smaller pieces before sending
it to the server. When receiving new data for a stream that had
silence queued due to underrun, the server would do a rewind to
replace the queued-but-not-played silence with the new data. Because
of the bug, this rewind itself would not change underrun_for. It's
possible for multiple rewinds to be done without filling the sink
buffer in between (which is what would eventually reset underrun_for).
In this case, the server rapidly processing the split packets would
rewind the stream for _each_ of them (as underrun_for would stay set),
erasing valid audio as a result.

1 files changed, 22 insertions, 4 deletions

diff --git a/src/pulsecore/sink-input.c b/src/pulsecore/sink-input.c
index 7a7575a98..1eb47511f 100644
--- a/src/pulsecore/sink-input.c
+++ b/src/pulsecore/sink-input.c
@@ -970,6 +970,15 @@ void pa_sink_input_drop(pa_sink_input *i, size_t nbytes /* in sink sample spec *
     pa_memblockq_drop(i->thread_info.render_memblockq, nbytes);
 }
 
+static void subtract_helper(size_t *p, size_t amount)
+{
+    if (*p == (size_t) -1)
+        return;
+    if (*p < amount)
+        *p = 0;
+    *p -= amount;
+}
+
 /* Called from thread context */
 void pa_sink_input_process_rewind(pa_sink_input *i, size_t nbytes /* in sink sample spec */) {
     size_t lbq;
@@ -996,8 +1005,12 @@ void pa_sink_input_process_rewind(pa_sink_input *i, size_t nbytes /* in sink sam
         /* We were asked to drop all buffered data, and rerequest new
          * data from implementor the next time peek() is called */
 
+        size_t s = pa_memblockq_get_length(i->thread_info.render_memblockq);
+        if (i->thread_info.resampler)
+            s = pa_resampler_request(i->thread_info.resampler, s);
         pa_memblockq_flush_write(i->thread_info.render_memblockq, TRUE);
-
+        subtract_helper(&i->thread_info.underrun_for, s);
+        subtract_helper(&i->thread_info.playing_for, s);
     } else if (i->thread_info.rewrite_nbytes > 0) {
         size_t max_rewrite, amount;
 
@@ -1012,6 +1025,8 @@ void pa_sink_input_process_rewind(pa_sink_input *i, size_t nbytes /* in sink sam
         amount = PA_MIN(i->thread_info.rewrite_nbytes, max_rewrite);
 
         if (amount > 0) {
+            size_t samount = amount;
+
             pa_log_debug("Have to rewind %lu bytes on implementor.", (unsigned long) amount);
 
             /* Tell the implementor */
@@ -1021,11 +1036,14 @@ void pa_sink_input_process_rewind(pa_sink_input *i, size_t nbytes /* in sink sam
 
             /* Convert back to to sink domain */
             if (i->thread_info.resampler)
-                amount = pa_resampler_result(i->thread_info.resampler, amount);
+                samount = pa_resampler_result(i->thread_info.resampler, amount);
 
-            if (amount > 0)
+            if (samount > 0) {
                 /* Ok, now update the write pointer */
-                pa_memblockq_seek(i->thread_info.render_memblockq, - ((int64_t) amount), PA_SEEK_RELATIVE, TRUE);
+                pa_memblockq_seek(i->thread_info.render_memblockq, - ((int64_t) samount), PA_SEEK_RELATIVE, TRUE);
+                subtract_helper(&i->thread_info.underrun_for, amount);
+                subtract_helper(&i->thread_info.playing_for, amount);
+            }
 
             if (i->thread_info.rewrite_flush)
                 pa_memblockq_silence(i->thread_info.render_memblockq);