outputThread: optimize Command::OPEN

Try harder to skip steps (reopen filter, reopen output) if the
AudioOutput is already open.

src/output/Internal.hxx

@@ -171,6 +171,14 @@ struct AudioOutput {
 	 */
 	AudioFormat in_audio_format;
 
+	/**
+	 * The #AudioFormat which is emitted by the #Filter, with
+	 * #config_audio_format already applied.  This is used to
+	 * decide whether this object needs to be closed and reopened
+	 * upon #AudioFormat changes.
+	 */
+	AudioFormat filter_audio_format;
+
 	/**
 	 * The audio_format which is really sent to the device.  This
 	 * is basically config_audio_format (if configured) or
@@ -445,15 +453,6 @@ private:
 
 	void Open();
 
-	/**
-	 * Open the #ChainFilter and call OpenOutputAndConvert().
-	 *
-	 * Caller must not lock the mutex.
-	 *
-	 * @return true on success
-	 */
-	bool OpenFilterAndOutput();
-
 	/**
 	 * Invoke OutputPlugin::open() and configure the
 	 * #ConvertFilter.
@@ -465,7 +464,6 @@ private:
 	bool OpenOutputAndConvert(AudioFormat audio_format);
 
 	void Close(bool drain);
-	void Reopen();
 
 	/**
 	 * Close the output plugin.
@@ -486,8 +484,6 @@ private:
 	 */
 	void CloseFilter();
 
-	void ReopenFilter();
-
 	/**
 	 * Wait until the output's delay reaches zero.
 	 *

src/output/OutputThread.cxx

@@ -133,54 +133,61 @@ AudioOutput::CloseFilter()
 inline void
 AudioOutput::Open()
 {
-	assert(!open);
 	assert(request.audio_format.IsValid());
 
 	fail_timer.Reset();
 
 	/* enable the device (just in case the last enable has failed) */
-
+	if (!Enable()) {
-	if (!Enable())
 		/* still no luck */
-		return;
-
-	in_audio_format = request.audio_format;
-	pipe.Init(*request.pipe);
-
-	bool success;
-
-	{
-		const ScopeUnlock unlock(mutex);
-		success = OpenFilterAndOutput();
-	}
-
-	if (success)
-		open = true;
-	else
 		fail_timer.Update();
-}
+		return;
-
-bool
-AudioOutput::OpenFilterAndOutput()
-{
-	AudioFormat filter_audio_format;
-	try {
-		filter_audio_format = OpenFilter(in_audio_format);
-	} catch (const std::runtime_error &e) {
-		FormatError(e, "Failed to open filter for \"%s\" [%s]",
-			    name, plugin.name);
-		return false;
 	}
 
-	assert(filter_audio_format.IsValid());
+	if (!open || request.pipe != &pipe.GetPipe())
+		pipe.Init(*request.pipe);
 
-	const auto audio_format =
+	/* (re)open the filter */
-		filter_audio_format.WithMask(config_audio_format);
+
-	bool success = OpenOutputAndConvert(audio_format);
+	if (filter_instance != nullptr &&
-	if (!success)
+	    request.audio_format != in_audio_format)
+		/* the filter must be reopened on all input format
+		   changes */
 		CloseFilter();
 
-	return success;
+	if (filter_instance == nullptr) {
+		/* open the filter */
+		AudioFormat f;
+		try {
+			f = OpenFilter(request.audio_format)
+				.WithMask(config_audio_format);
+		} catch (const std::runtime_error &e) {
+			FormatError(e, "Failed to open filter for \"%s\" [%s]",
+				    name, plugin.name);
+			fail_timer.Update();
+			return;
+		}
+
+		if (open && f != filter_audio_format) {
+			/* if the filter's output format changes, the
+			   outpuit must be reopened as well */
+			CloseOutput(true);
+			open = false;
+		}
+
+		filter_audio_format = f;
+	}
+
+	in_audio_format = request.audio_format;
+
+	if (!open) {
+		if (OpenOutputAndConvert(filter_audio_format)) {
+			open = true;
+		} else {
+			CloseFilter();
+			fail_timer.Update();
+		}
+	}
 }
 
 bool
@@ -263,41 +270,6 @@ AudioOutput::CloseOutput(bool drain)
 	ao_plugin_close(this);
 }
 
-void
-AudioOutput::ReopenFilter()
-{
-	try {
-		const ScopeUnlock unlock(mutex);
-		CloseFilter();
-		OpenFilter(in_audio_format);
-		convert_filter_set(convert_filter.Get(), out_audio_format);
-	} catch (const std::runtime_error &e) {
-		FormatError(e,
-			    "Failed to open filter for \"%s\" [%s]",
-			    name, plugin.name);
-
-		Close(false);
-	}
-}
-
-void
-AudioOutput::Reopen()
-{
-	assert(open);
-
-	if ((request.audio_format != in_audio_format &&
-	     !config_audio_format.IsFullyDefined()) ||
-	    request.pipe != &pipe.GetPipe()) {
-		Close(true);
-		Open();
-	} else {
-		/* the audio format has changed, and all filters have
-		   to be reconfigured */
-		in_audio_format = request.audio_format;
-		ReopenFilter();
-	}
-}
-
 /**
  * Wait until the output's delay reaches zero.
  *
@@ -578,10 +550,7 @@ AudioOutput::Task()
 			break;
 
 		case Command::OPEN:
-			if (open)
+			Open();
-				Reopen();
-			else
-				Open();
 			CommandFinished();
 			break;