Fix chunk sizing in QPulseAudioSink

QPulseAudioSink:write() takes a length parameter which is set to the
qMin of itself and the return value of pa_stream_writable_size().

This method returns the number of bytes requested by the server,
but not yet written. Unless data is buffered, the value is 0.
That leads to length being set to 0 and no data being sent.

In PulseOutputPrivate::writeData(), a loop was implemented calling
QPulseAudioSink::write() up to 10 times for each data chunk.
That forced data buffering and subsequently the return value of
pa_stream_writable_size() to be > 0.

This patch replaces the query of pa_stream_writable_size() with the
nbytes value modified by pa_stream_begin_write(). It represents the
maximum amount of bytes the pulseaudio server is ready to accept.

The patch also removes the loop calling write up to 10 times as it
becomes unnecessary.

Fixes: QTBUG-60575
Change-Id: I316a5ac610c8540ab8f7fff4a3b0b1ee3d7e7ad5
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit f1829a24d4c9a393f95d55c415daa80275a90b93)

1 files changed, 17 insertions, 17 deletions

diff --git a/src/multimedia/platform/pulseaudio/qpulseaudiosink.cpp b/src/multimedia/platform/pulseaudio/qpulseaudiosink.cpp
index 0521a5670..716bfa9a9 100644
--- a/src/multimedia/platform/pulseaudio/qpulseaudiosink.cpp
+++ b/src/multimedia/platform/pulseaudio/qpulseaudiosink.cpp
@@ -512,26 +512,29 @@ qint64 QPulseAudioSink::write(const char *data, qint64 len)
 
     pulseEngine->lock();
 
-    len = qMin(len, static_cast<qint64>(pa_stream_writable_size(m_stream)));
+    size_t nbytes = len;
+    void *dest = nullptr;
+
+    if (pa_stream_begin_write(m_stream, &dest, &nbytes) < 0) {
+        qWarning("QAudioSink(pulseaudio): pa_stream_begin_write, error = %s",
+                 pa_strerror(pa_context_errno(pulseEngine->context())));
+        setError(QAudio::IOError);
+        return 0;
+    }
+
+    len = qMin(len, qint64(nbytes));
 
     if (m_volume < 1.0f) {
         // Don't use PulseAudio volume, as it might affect all other streams of the same category
         // or even affect the system volume if flat volumes are enabled
-        void *dest = nullptr;
-        size_t nbytes = len;
-        if (pa_stream_begin_write(m_stream, &dest, &nbytes) < 0) {
-            qWarning("QAudioSink(pulseaudio): pa_stream_begin_write, error = %s",
-                     pa_strerror(pa_context_errno(pulseEngine->context())));
-            setError(QAudio::IOError);
-            return 0;
-        }
-
-        len = int(nbytes);
         QAudioHelperInternal::qMultiplySamples(m_volume, m_format, data, dest, len);
-        data = reinterpret_cast<char *>(dest);
+    } else {
+        memcpy(dest, data, len);
     }
 
-    if (pa_stream_write(m_stream, data, len, nullptr, 0, PA_SEEK_RELATIVE) < 0) {
+    data = reinterpret_cast<char *>(dest);
+
+    if ((pa_stream_write(m_stream, data, len, nullptr, 0, PA_SEEK_RELATIVE)) < 0) {
         qWarning("QAudioSink(pulseaudio): pa_stream_write, error = %s",
                  pa_strerror(pa_context_errno(pulseEngine->context())));
         setError(QAudio::IOError);
@@ -672,7 +675,6 @@ qint64 PulseOutputPrivate::readData(char *data, qint64 len)
 
 qint64 PulseOutputPrivate::writeData(const char *data, qint64 len)
 {
-    int retry = 0;
     qint64 written = 0;
 
     if ((m_audioDevice->m_deviceState == QAudio::ActiveState
@@ -680,10 +682,8 @@ qint64 PulseOutputPrivate::writeData(const char *data, qint64 len)
          while(written < len) {
             int chunk = m_audioDevice->write(data+written, (len-written));
             if (chunk <= 0)
-                retry++;
-            written+=chunk;
-            if (retry > 10)
                 return written;
+            written+=chunk;
         }
     }