Switch to spinning on SID thread synchronisation.

ClockReceiver/JustInTime.hpp

@@ -325,7 +325,7 @@ public:
 	/// Flushes all accumulated time.
 	inline void flush() {
 		if(!is_flushed_) {
-			task_queue_.flush();
+			task_queue_.lock_flush();
 			object_.run_for(time_since_update_.template flush<TargetTimeScale>());
 			is_flushed_ = true;
 		}

Components/6560/6560.hpp

@@ -75,7 +75,7 @@ public:
 	}
 
 	~MOS6560() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_clock_rate(const double clock_rate) {

Components/SID/SID.cpp

@@ -142,7 +142,7 @@ uint8_t SID::read(const Numeric::SizedInt<5> address) {
 		case 0x1b:
 		case 0x1c:
 			// Ensure all channels are entirely up to date.
-			audio_queue_.flush();
+			audio_queue_.spin_flush();
 			return (address == 0x1c) ? voices_[2].adsr.envelope : uint8_t(voices_[2].output(voices_[1]) >> 4);
 	}
 }

Concurrency/AsyncTaskQueue.hpp

@@ -137,7 +137,7 @@ public:
 
 	/// Schedules any remaining unscheduled work, then blocks synchronously
 	/// until all scheduled work has been performed.
-	void flush() {
+	void lock_flush() {
 		std::mutex flush_mutex;
 		std::condition_variable flush_condition;
 		bool has_run = false;
@@ -156,6 +156,22 @@ public:
 		flush_condition.wait(lock, [&has_run] { return has_run; });
 	}
 
+	/// Schedules any remaining unscheduled work, then spins
+	/// until all scheduled work has been performed.
+	void spin_flush() {
+		std::atomic<bool> has_run = false;
+
+		enqueue([&has_run] () {
+			has_run.store(true, std::memory_order::release);
+		});
+
+		if constexpr (!perform_automatically) {
+			perform();
+		}
+
+		while(!has_run.load(std::memory_order::acquire));
+	}
+
 	~AsyncTaskQueue() {
 		stop();
 	}

Machines/Acorn/BBCMicro/BBCMicro.cpp

@@ -138,7 +138,7 @@ public:
 	}
 
 	~Audio() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	template <typename TargetT>

Machines/Acorn/Electron/Electron.cpp

@@ -143,7 +143,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_key_state(uint16_t key, bool isPressed) final {

Machines/AmstradCPC/AmstradCPC.cpp

@@ -127,7 +127,7 @@ public:
 	}
 
 	~AYDeferrer() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	/// Adds @c half_cycles half cycles to the amount of time that has passed.

Machines/Apple/AppleII/AppleII.cpp

@@ -678,7 +678,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/Apple/AppleIIgs/AppleIIgs.cpp

@@ -210,7 +210,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void run_for(const Cycles cycles) override {

Machines/Apple/Macintosh/Macintosh.cpp

@@ -172,7 +172,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_.queue.flush();
+		audio_.queue.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/Atari/2600/Bus.hpp

@@ -26,7 +26,7 @@ public:
 		speaker_(tia_sound_) {}
 
 	virtual ~Bus() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	virtual void run_for(const Cycles cycles) = 0;

Machines/Atari/ST/AtariST.cpp

@@ -144,7 +144,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// MARK: CRTMachine::Machine

Machines/ColecoVision/ColecoVision.cpp

@@ -168,7 +168,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	const std::vector<std::unique_ptr<Inputs::Joystick>> &get_joysticks() final {

Machines/Commodore/Plus4/Plus4.cpp

@@ -236,7 +236,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// HACK. NOCOMMIT.

Machines/Enterprise/Enterprise.cpp

@@ -257,7 +257,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	// MARK: - Z80::BusHandler.

Machines/MSX/MSX.cpp

@@ -360,7 +360,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		speaker_.audio_queue.flush();
+		speaker_.audio_queue.lock_flush();
 	}
 
 	void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/MasterSystem/MasterSystem.cpp

@@ -178,7 +178,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	ChangeEffect effect_for_file_did_change(const std::string &) const final {

Machines/Oric/Oric.cpp

@@ -406,7 +406,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	void set_key_state(uint16_t key, bool is_pressed) final {

Machines/PCCompatible/PCCompatible.cpp

@@ -817,7 +817,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		speaker_.queue.flush();
+		speaker_.queue.lock_flush();
 	}
 
 	// MARK: - TimedMachine.

Machines/Sinclair/ZX8081/ZX8081.cpp

@@ -114,7 +114,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	forceinline HalfCycles perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {

Machines/Sinclair/ZXSpectrum/ZXSpectrum.cpp

@@ -213,7 +213,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.flush();
+		audio_queue_.lock_flush();
 	}
 
 	static constexpr unsigned int clock_rate() {

Storage/Disk/DiskImage/DiskImageImplementation.hpp

@@ -75,7 +75,7 @@ Track *DiskImageHolder<T>::track_at_position(Track::Address address) const {
 
 template <typename T>
 DiskImageHolder<T>::~DiskImageHolder() {
-	if(update_queue_) update_queue_->flush();
+	if(update_queue_) update_queue_->lock_flush();
 }
 
 template <typename T>