Merge branch 'master' into jgrpp

# Conflicts:
#	.github/workflows/release-windows.yml
#	src/autoreplace_gui.cpp
#	src/cargotype.cpp
#	src/company_base.h
#	src/company_cmd.cpp
#	src/company_gui.cpp
#	src/currency.h
#	src/date_gui.cpp
#	src/dropdown.cpp
#	src/dropdown_func.h
#	src/dropdown_type.h
#	src/game/game_gui.cpp
#	src/genworld.cpp
#	src/genworld_gui.cpp
#	src/ground_vehicle.hpp
#	src/group_gui.cpp
#	src/house.h
#	src/industry_gui.cpp
#	src/network/network_client.cpp
#	src/network/network_server.cpp
#	src/network/network_type.h
#	src/newgrf_class_func.h
#	src/newgrf_house.cpp
#	src/newgrf_roadstop.h
#	src/openttd.cpp
#	src/order_gui.cpp
#	src/saveload/saveload.cpp
#	src/saveload/saveload.h
#	src/screenshot_gui.cpp
#	src/settings_gui.cpp
#	src/settings_type.h
#	src/slider.cpp
#	src/smallmap_gui.cpp
#	src/station_cmd.cpp
#	src/stdafx.h
#	src/survey.cpp
#	src/tile_map.h
#	src/town_cmd.cpp
#	src/town_gui.cpp
#	src/vehicle.cpp
#	src/vehicle_gui.cpp
#	src/vehicle_gui_base.h

src/mixer.cpp

@@ -38,6 +38,7 @@ struct MixerChannel {
 };
 
 static std::atomic<uint8_t> _active_channels;
+static std::atomic<uint8_t> _stop_channels;
 static MixerChannel _channels[8];
 static uint32_t _play_rate = 11025;
 static uint32_t _max_size = UINT_MAX;
@@ -111,6 +112,16 @@ static void MxCloseChannel(uint8_t channel_index)
 	_active_channels.fetch_and(~(1 << channel_index), std::memory_order_release);
 }
 
+/**
+ * Close all mixer channels.
+ * This signals to the mixer that each channel should be closed even if it has not played all remaining samples.
+ * This is safe (and designed) to be called from the main thread.
+ */
+void MxCloseAllChannels()
+{
+	_stop_channels.fetch_or(~0, std::memory_order_release);
+}
+
 void MxMixSamples(void *buffer, uint samples)
 {
 	PerformanceMeasurer framerate(PFE_SOUND);
@@ -129,6 +140,12 @@ void MxMixSamples(void *buffer, uint samples)
 		if (_music_stream) _music_stream((int16_t*)buffer, samples);
 	}
 
+	/* Check if any channels should be stopped. */
+	uint8_t stop = _stop_channels.load(std::memory_order_acquire);
+	for (uint8_t idx : SetBitIterator(stop)) {
+		MxCloseChannel(idx);
+	}
+
 	/* Apply simple x^3 scaling to master effect volume. This increases the
 	 * perceived difference in loudness to better match expectations. effect_vol
 	 * is expected to be in the range 0-127 hence the division by 127 * 127 to
@@ -203,6 +220,7 @@ void MxSetChannelVolume(MixerChannel *mc, uint volume, float pan)
 void MxActivateChannel(MixerChannel *mc)
 {
 	uint8_t channel_index = mc - _channels;
+	_stop_channels.fetch_and(~(1 << channel_index), std::memory_order_release);
 	_active_channels.fetch_or((1 << channel_index), std::memory_order_release);
 }