Ensured GL context is active when destructing CRTOpenGL.

Machines/Atari2600/Atari2600.cpp

@@ -42,10 +42,16 @@ void Machine::setup_output(float aspect_ratio)
 	_crt->set_output_device(Outputs::CRT::Television);
 }
 
+void Machine::close_output()
+{
+	delete _crt;
+	_crt = nullptr;
+}
+
 Machine::~Machine()
 {
 	delete[] _rom;
-	delete _crt;
+	close_output();
 }
 
 void Machine::switch_region()

Machines/Atari2600/Atari2600.hpp

@@ -31,6 +31,7 @@ class Machine: public CPU6502::Processor<Machine> {
 
 		Outputs::CRT::CRT *get_crt() { return _crt; }
 		void setup_output(float aspect_ratio);
+		void close_output();
 
 	private:
 		uint8_t *_rom, *_romPages[4], _ram[128];

Machines/Electron/Electron.cpp

@@ -77,6 +77,11 @@ void Machine::setup_output(float aspect_ratio)
 	_speaker.set_input_rate(2000000 / clock_rate_audio_divider);
 }
 
+void Machine::close_output()
+{
+	_crt = nullptr;
+}
+
 unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
 {
 	unsigned int cycles = 1;

Machines/Electron/Electron.hpp

@@ -157,6 +157,7 @@ class Machine: public CPU6502::Processor<Machine>, Tape::Delegate {
 		void clear_all_keys();
 
 		void setup_output(float aspect_ratio);
+		void close_output();
 		Outputs::CRT::CRT *get_crt() { return _crt.get(); }
 		Outputs::Speaker *get_speaker() { return &_speaker; }
 

OSBindings/Mac/Clock Signal/Wrappers/CSAtari2600.mm

@@ -83,4 +83,10 @@ struct CRTDelegate: public Outputs::CRT::Delegate {
 	}
 }
 
+- (void)closeOutput {
+	@synchronized(self) {
+		_atari2600.close_output();
+	}
+}
+
 @end

OSBindings/Mac/Clock Signal/Wrappers/CSElectron.mm

@@ -171,4 +171,10 @@
 	}
 }
 
+- (void)closeOutput {
+	@synchronized(self) {
+		_electron.close_output();
+	}
+}
+
 @end

OSBindings/Mac/Clock Signal/Wrappers/CSMachine+Subclassing.h

@@ -17,5 +17,6 @@
 - (void)performAsync:(dispatch_block_t)action;
 - (void)performSync:(dispatch_block_t)action;
 - (void)setupOutputWithAspectRatio:(float)aspectRatio;
+- (void)closeOutput;
 
 @end

OSBindings/Mac/Clock Signal/Wrappers/CSMachine.h

@@ -16,5 +16,6 @@
 - (void)setView:(CSOpenGLView *)view aspectRatio:(float)aspectRatio;
 
 @property (nonatomic, weak) AudioQueue *audioQueue;
+@property (nonatomic, readonly) CSOpenGLView *view;
 
 @end

OSBindings/Mac/Clock Signal/Wrappers/CSMachine.mm

@@ -37,6 +37,12 @@ struct SpeakerDelegate: public Outputs::Speaker::Delegate {
 	return self;
 }
 
+- (void)dealloc {
+	[_view performWithGLContext:^{
+		[self closeOutput];
+	}];
+}
+
 - (BOOL)setSpeakerDelegate:(Outputs::Speaker::Delegate *)delegate sampleRate:(int)sampleRate {
 	return NO;
 }
@@ -53,7 +59,10 @@ struct SpeakerDelegate: public Outputs::Speaker::Delegate {
 
 - (void)setupOutputWithAspectRatio:(float)aspectRatio {}
 
+- (void)closeOutput {}
+
 - (void)setView:(CSOpenGLView *)view aspectRatio:(float)aspectRatio {
+	_view = view;
 	[view performWithGLContext:^{
 		[self setupOutputWithAspectRatio:aspectRatio];
 	}];

Outputs/CRT/Internals/Shader.cpp

@@ -80,8 +80,7 @@ Shader::Shader(const char *vertex_shader, const char *fragment_shader, const Att
 
 Shader::~Shader()
 {
-	// TODO: ensure this is destructed within the correct context.
-//	glDeleteProgram(_shader_program);
+	glDeleteProgram(_shader_program);
 }
 
 void Shader::bind()