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/Debugger/WebSocket/GPUStatsSubscriber.cpp

@@ -15,10 +15,13 @@
 // Official git repository and contact information can be found at
 // https://github.com/hrydgard/ppsspp and http://www.ppsspp.org/.
 
-#include <mutex>
+#include <cstring>
 #include <vector>
 
+#include <retro_atomic.h>
+
 #include "Common/Data/Text/StringWriter.h"
+#include "Common/Thread/MpscQueue.h"
 #include "Core/Debugger/WebSocket/GPUStatsSubscriber.h"
 #include "Core/Core.h"
 #include "Core/HW/Display.h"
@@ -81,13 +84,14 @@ struct WebSocketGPUStatsState : public DebuggerSubscriber {
 	void FlipListener();
 
 protected:
+	// The WebSocket thread's.
 	bool forced_ = false;
-	bool sendNext_ = false;
-	bool sendFeed_ = false;
-
 	std::string lastTicket_;
-	std::mutex pendingLock_;
-	std::vector<CollectedStats> pendingStats_;
+	// Set by the WebSocket thread, read on the emu thread at each flip.
+	retro_atomic_int_t sendNext_{ 0 };
+	retro_atomic_int_t sendFeed_{ 0 };
+	// Collected on the emu thread, sent from the WebSocket thread.
+	MpscQueue<CollectedStats> pendingStats_;
 };
 
 DebuggerSubscriber *WebSocketGPUStatsInit(DebuggerEventHandlerMap &map) {
@@ -99,15 +103,20 @@ DebuggerSubscriber *WebSocketGPUStatsInit(DebuggerEventHandlerMap &map) {
 }
 
 WebSocketGPUStatsState::WebSocketGPUStatsState() {
-	__DisplayListenFlip(&WebSocketGPUStatsState::FlipForwarder, this);
+	// The flip listeners belong to the CPU thread.
+	Core_RunOnCPUThread([this] { __DisplayListenFlip(&WebSocketGPUStatsState::FlipForwarder, this); });
 }
 
 WebSocketGPUStatsState::~WebSocketGPUStatsState() {
 	// PSP_ForceDebugStats bumps a plain counter, so do it on the CPU thread that owns it - see
 	// Core_RunOnCPUThread() in Core.h.
-	if (forced_)
-		Core_RunOnCPUThread([] { PSP_ForceDebugStats(false); });
-	__DisplayForgetFlip(&WebSocketGPUStatsState::FlipForwarder, this);
+	const bool forced = forced_;
+	Core_RunOnCPUThread([this, forced] {
+		if (forced) {
+			PSP_ForceDebugStats(false);
+		}
+		__DisplayForgetFlip(&WebSocketGPUStatsState::FlipForwarder, this);
+	});
 }
 
 void WebSocketGPUStatsState::FlipForwarder(void *thiz) {
@@ -116,13 +125,11 @@ void WebSocketGPUStatsState::FlipForwarder(void *thiz) {
 }
 
 void WebSocketGPUStatsState::FlipListener() {
-	if (!sendNext_ && !sendFeed_)
+	if (!retro_atomic_load_acquire_int(&sendNext_) && !retro_atomic_load_acquire_int(&sendFeed_))
 		return;
 
 	// Okay, collect the data (we'll actually send at next Broadcast.)
-	std::lock_guard<std::mutex> guard(pendingLock_);
-	pendingStats_.resize(pendingStats_.size() + 1);
-	CollectedStats &stats = pendingStats_[pendingStats_.size() - 1];
+	CollectedStats stats;
 
 	__DisplayGetFPS(&stats.vps, &stats.fps, &stats.actual_fps);
 
@@ -140,7 +147,9 @@ void WebSocketGPUStatsState::FlipListener() {
 		memcpy(&stats.sleepTimes[0], sleepHistory, sizeof(float) * valid);
 	}
 
-	sendNext_ = false;
+	pendingStats_.Push(std::move(stats));
+	retro_atomic_store_release_int(&sendNext_, 0);
+	mailbox->Wake();
 }
 
 // Get next GPU stats (gpu.stats.get)
@@ -163,11 +172,9 @@ void WebSocketGPUStatsState::Get(DebuggerRequest &req) {
 	if (PSP_GetBootState() != BootState::Complete)
 		return req.Fail("CPU not started");
 
-	std::lock_guard<std::mutex> guard(pendingLock_);
-	sendNext_ = true;
-
 	const JsonNode *value = req.data.get("ticket");
 	lastTicket_ = value ? json_stringify(value) : "";
+	retro_atomic_store_release_int(&sendNext_, 1);
 }
 
 // Setup GPU stats feed (gpu.stats.feed)
@@ -186,8 +193,7 @@ void WebSocketGPUStatsState::Feed(DebuggerRequest &req) {
 	if (!req.ParamBool("enable", &enable, DebuggerParamType::OPTIONAL))
 		return;
 
-	std::lock_guard<std::mutex> guard(pendingLock_);
-	sendFeed_ = enable;
+	retro_atomic_store_release_int(&sendFeed_, enable ? 1 : 0);
 	if (forced_ != enable) {
 		Core_RunOnCPUThread([enable] { PSP_ForceDebugStats(enable); });
 		forced_ = enable;
@@ -195,19 +201,25 @@ void WebSocketGPUStatsState::Feed(DebuggerRequest &req) {
 }
 
 void WebSocketGPUStatsState::Broadcast(net::WebSocketServer *ws) {
-	std::lock_guard<std::mutex> guard(pendingLock_);
-	if (lastTicket_.empty() && !sendFeed_) {
-		pendingStats_.clear();
+	if (pendingStats_.Empty()) {
+		return;
+	}
+	std::vector<CollectedStats> pending;
+	pendingStats_.Drain([&](CollectedStats &&stats) {
+		pending.push_back(std::move(stats));
+	});
+
+	const bool sendFeed = retro_atomic_load_acquire_int(&sendFeed_) != 0;
+	if (lastTicket_.empty() && !sendFeed) {
 		return;
 	}
 
 	// To be safe, make sure we only send one if we're doing a get.
-	if (!sendFeed_ && pendingStats_.size() > 1)
-		pendingStats_.resize(1);
+	if (!sendFeed && pending.size() > 1)
+		pending.resize(1);
 
-	for (size_t i = 0; i < pendingStats_.size(); ++i) {
-		ws->Send(DebuggerGPUStatsEvent{ pendingStats_[i], lastTicket_ });
+	for (size_t i = 0; i < pending.size(); ++i) {
+		ws->Send(DebuggerGPUStatsEvent{ pending[i], lastTicket_ });
 		lastTicket_.clear();
 	}
-	pendingStats_.clear();
 }