output/pipewire: call libpipewire only while holding the lock

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1210

src/lib/pipewire/ThreadLoop.hxx

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2003-2021 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+/* oh no, libspa likes to cast away "const"! */
+#pragma GCC diagnostic ignored "-Wcast-qual"
+/* suppress more annoying warnings */
+#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+#endif
+
+#include <pipewire/thread-loop.h>
+
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
+
+namespace PipeWire {
+
+class ThreadLoopLock {
+	struct pw_thread_loop *const loop;
+
+public:
+	explicit ThreadLoopLock(struct pw_thread_loop *_loop) noexcept
+		:loop(_loop)
+	{
+		pw_thread_loop_lock(loop);
+	}
+
+	~ThreadLoopLock() noexcept {
+		pw_thread_loop_unlock(loop);
+	}
+
+	ThreadLoopLock(const ThreadLoopLock &) = delete;
+	ThreadLoopLock &operator=(const ThreadLoopLock &) = delete;
+};
+
+} // namespace PipeWire

src/output/plugins/PipeWireOutputPlugin.cxx

@@ -18,7 +18,7 @@
  */
 
 #include "PipeWireOutputPlugin.hxx"
-//#include "lib/pipewire/MainLoop.hxx"
+#include "lib/pipewire/ThreadLoop.hxx"
 #include "../OutputAPI.hxx"
 #include "../Error.hxx"
 
@@ -212,6 +212,7 @@ PipeWireOutput::Open(AudioFormat &audio_format)
 	params[0] = spa_format_audio_raw_build(&pod_builder,
 					       SPA_PARAM_EnumFormat, &raw);
 
+	const PipeWire::ThreadLoopLock lock(thread_loop);
 	pw_stream_connect(stream,
 			  PW_DIRECTION_OUTPUT,
 			  target_id,
@@ -224,7 +225,10 @@ PipeWireOutput::Open(AudioFormat &audio_format)
 void
 PipeWireOutput::Close() noexcept
 {
+	{
+		const PipeWire::ThreadLoopLock lock(thread_loop);
 		pw_stream_destroy(stream);
+	}
 
 	// TODO synchronize with Process()?
 	delete ring_buffer;