Make threading lock-free

The core and the headless tools no longer use mutexes, condition variables,
spinlocks, std::atomic, std::thread or volatile flags. Threads hand off through
libretro-common's retro_atomic and rthreads plus a few small pieces on top of
them in Common/Thread: Thread, MpscQueue, EventCounter, ParkingLot waits and
ReaderGate. Every wait blocks until it's woken; nothing polls on a timer.

State that only one thread touches just loses its lock. The PSP filesystem,
sceIo and the savedata dialog now belong to the emulation thread: async reads
and writes run when they're queued and complete later in emulated time, and
the IO and savedata threads are gone. The friend finder only talks to the
adhoc server and hands what it gets to the emulation thread. GPU init always
runs on the thread that starts the game.

The Vulkan render and compile queues, pipeline and render pass caches, delete
list and SPIR-V cache, the GL render queue, the software renderer's jit caches,
the file loader caches, the web debugger, UPnP, input, savestates, logging and
the GE debugger all hand off through queues and atomics. The IR jit's spinning
profiler thread goes.

A CPU thread with nothing to run now sleeps until work is queued instead of
spinning. Headless with --debugger waits for a client while stopped, and ends
the run once every client that connected has left. Web server shutdown keeps
servicing the CPU queue until the server has finished.

Core/EmuThread.cpp

@@ -1,8 +1,6 @@
 #include "ppsspp_config.h"
 
-#include <mutex>
-#include <atomic>
-#include <thread>
+#include <retro_atomic.h>
 
 #include "Common/System/System.h"
 #include "Common/System/Request.h"
@@ -13,6 +11,7 @@
 #include "Common/Log.h"
 #include "Common/StringUtils.h"
 #include "Common/GPU/GraphicsContext.h"
+#include "Common/Thread/Thread.h"
 #include "Common/Thread/ThreadUtil.h"
 
 #include "Core/EmuThread.h"
@@ -27,37 +26,38 @@ enum class EmuThreadState {
 	STOPPED,
 };
 
-static std::atomic<EmuThreadState> g_emuThreadState(EmuThreadState::STOPPED);
-static std::atomic<bool> g_inLoop;
+static retro_atomic_int_t g_emuThreadState{ (int)EmuThreadState::STOPPED };
 
-class GraphicsContext;
+static EmuThreadState GetEmuThreadState() {
+	return (EmuThreadState)retro_atomic_load_acquire_int(&g_emuThreadState);
+}
 
-bool MainThread_Ready() {
-	return g_inLoop;
+static void SetEmuThreadState(EmuThreadState state) {
+	retro_atomic_store_release_int(&g_emuThreadState, (int)state);
 }
 
 static void EmuThreadFunc(GraphicsContext *graphicsContext, Application *application, std::function<bool (GraphicsContext *)> frame) {
 	INFO_LOG(Log::G3D, "Entering separate emu thread");
 	SetCurrentThreadName("EmuThread");
 
-	g_emuThreadState = EmuThreadState::RUNNING;
+	SetEmuThreadState(EmuThreadState::RUNNING);
 
 
 	// This normally calls NativeInitGraphics()
 	if (!application->InitGraphics(graphicsContext)) {
 		_assert_msg_(false, "NativeInitGraphics failed, might as well bail");
 		// If this fails, which it normally shouldn't, let's bail.
-		g_emuThreadState = EmuThreadState::QUIT_REQUESTED;
+		SetEmuThreadState(EmuThreadState::QUIT_REQUESTED);
 	} else {
 		INFO_LOG(Log::G3D, "EmuThread: Entering loop");
 	}
 
-	while (g_emuThreadState != EmuThreadState::QUIT_REQUESTED) {
+	while (GetEmuThreadState() != EmuThreadState::QUIT_REQUESTED) {
 		// We're here again, so the game quit.  Restart Run() which controls the UI.
 		// This way they can load a new game.
 		// This normally calls NativeFrame()
 		if (!frame(graphicsContext)) {
-			g_emuThreadState = EmuThreadState::QUIT_REQUESTED;
+			SetEmuThreadState(EmuThreadState::QUIT_REQUESTED);
 		}
 	}
 
@@ -69,46 +69,43 @@ static void EmuThreadFunc(GraphicsContext *graphicsContext, Application *applica
 
 	INFO_LOG(Log::System, "Leaving separate emu thread");
 
-	g_emuThreadState = EmuThreadState::STOPPED;
+	SetEmuThreadState(EmuThreadState::STOPPED);
 }
 
-std::thread EmuThread_Start(GraphicsContext *graphicsContext, Application *application, std::function<bool(GraphicsContext *)> frame) {
+static Thread EmuThread_Start(GraphicsContext *graphicsContext, Application *application, std::function<bool(GraphicsContext *)> frame) {
 	INFO_LOG(Log::System, "EmuTread_Start");
-	_dbg_assert_(g_emuThreadState == EmuThreadState::STOPPED);
-	std::thread emuThread = std::thread(&EmuThreadFunc, graphicsContext, application, frame);
+	_dbg_assert_(GetEmuThreadState() == EmuThreadState::STOPPED);
+	Thread emuThread(&EmuThreadFunc, graphicsContext, application, frame);
 	graphicsContext->ThreadStart();
 	return emuThread;
 }
 
 // This is useful when the render thread is in control.
-void EmuThread_RequestExit() {
+static void EmuThread_RequestExit() {
 	INFO_LOG(Log::System, "EmuTread_RequestExit");
-	if (g_emuThreadState == EmuThreadState::RUNNING) {
-		g_emuThreadState = EmuThreadState::QUIT_REQUESTED;
+	if (GetEmuThreadState() == EmuThreadState::RUNNING) {
+		SetEmuThreadState(EmuThreadState::QUIT_REQUESTED);
 	} else {
 		INFO_LOG(Log::System, "EmuTread_RequestExit: g_emuThreadState was not RUNNING, so not requesting exit.");
 	}
 }
 
-void EmuThread_Join(GraphicsContext *graphicsContext, std::thread &emuThread) {
+static void EmuThread_Join(GraphicsContext *graphicsContext, Thread &emuThread) {
 	INFO_LOG(Log::System, "EmuTread_Join");
 	if (graphicsContext->NeedsSeparateEmuThread()) {
 		EmuThread_RequestExit();
 		while (graphicsContext->ThreadFrame()) {}
 	}
 	emuThread.join();
-	emuThread = std::thread();
 	graphicsContext->ThreadEnd();
 }
 
-bool RunMainLoop(GraphicsContext *graphicsContext, Application *application, std::function<bool(GraphicsContext *)> frame) {
+static bool RunMainLoop(GraphicsContext *graphicsContext, Application *application, std::function<bool(GraphicsContext *)> frame) {
 	// This is the main loop for graphics context that handle their own threading.
 	// InitFromRenderThread/ShutdownFromRenderThread are not used.
 
 	application->InitGraphics(graphicsContext);
 
-	g_inLoop = true;
-
 	while (frame(graphicsContext)) {}
 
 	// NOTE: Don't call stuff like Core_Stop here. On Android, we fully shut down graphics when you switch away from the app,
@@ -117,8 +114,6 @@ bool RunMainLoop(GraphicsContext *graphicsContext, Application *application, std
 	// Process the shutdown.  Without this, non-GL delays 800ms on shutdown. TODO: is this still an issue?
 	Core_StateProcessed();
 
-	g_inLoop = false;
-
 	application->ShutdownGraphics(graphicsContext);
 	delete application;
 	return true;
@@ -135,15 +130,12 @@ bool MainThreadFunc(GraphicsContext *graphicsContext, Application *application,
 	if (graphicsContext->NeedsSeparateEmuThread()) {
 		SetCurrentThreadName("RenderThread");
 
-		g_inLoop = true;
-		std::thread emuThread = EmuThread_Start(graphicsContext, application, frame);
+		Thread emuThread = EmuThread_Start(graphicsContext, application, frame);
 		graphicsContext->ThreadStart();
 		// This thread becomes the render thread. EmuThread will tell it when to quit by sending a message.
 		while (graphicsContext->ThreadFrame()) {}
 		EmuThread_Join(graphicsContext, emuThread);
-		g_inLoop = false;
-
-		graphicsContext->ThreadEnd();
+			graphicsContext->ThreadEnd();
 
 		INFO_LOG(Log::System, "RenderThread - joined");