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/WebServer.cpp

@@ -15,21 +15,23 @@
 // Official git repository and contact information can be found at
 // https://github.com/hrydgard/ppsspp and http://www.ppsspp.org/.
 
-#include <atomic>
-#include <condition_variable>
 #include <cstring>
-#include <mutex>
 #include <string_view>
-#include <thread>
 
+#include <retro_atomic.h>
+
+#include "Common/Net/Cancel.h"
 #include "Common/Net/HTTPServer.h"
 #include "Common/Net/Sinks.h"
+#include "Common/Thread/ParkingLot.h"
+#include "Common/Thread/Thread.h"
 #include "Common/Thread/ThreadUtil.h"
 #include "Common/Log.h"
 #include "Common/File/Path.h"
 #include "Common/File/VFS/VFS.h"
 #include "Common/StringUtils.h"
 #include "Core/Config.h"
+#include "Core/Core.h"
 #include "Core/WebServer.h"
 #include "Core/Debugger/WebSocket.h"
 
@@ -41,25 +43,24 @@ enum class ServerStatus {
 	FINISHED,
 };
 
-static std::thread serverThread;
-static ServerStatus serverStatus;
-static std::mutex serverStatusLock;
-static std::condition_variable serverStatusCond;
-// See WebServerSetRequireExactPort(). Atomic because it's set from whichever thread parsed the
-// command line, and read from the server thread.
-static std::atomic<bool> serverRequireExactPort;
+// serverThread and serverStop belong to the thread calling Start/ShutdownWebServer.
+static Thread serverThread;
+// Set by ShutdownWebServer(); wakes the accept loop and every connection. One per server run,
+// deleted only after the server thread (and with it every connection thread) is joined.
+static net::CancelToken *serverStop;
+static retro_atomic_int_t serverStatus{ (int)ServerStatus::STOPPED };
+// See WebServerSetRequireExactPort().
+static retro_atomic_int_t serverRequireExactPort{ 0 };
 
 static void UpdateStatus(ServerStatus s) {
-	{
-		std::lock_guard<std::mutex> guard(serverStatusLock);
-		serverStatus = s;
-	}
-	serverStatusCond.notify_all();
+	retro_atomic_store_release_int(&serverStatus, (int)s);
+	ParkingLotNotify(&serverStatus);
+	// ShutdownWebServer() may be waiting on the CPU thread's queue for this.
+	Core_WakeCPUThread();
 }
 
 static ServerStatus RetrieveStatus() {
-	std::lock_guard<std::mutex> guard(serverStatusLock);
-	return serverStatus;
+	return (ServerStatus)retro_atomic_load_acquire_int(&serverStatus);
 }
 
 static bool ServeAssetFile(const http::ServerRequest &request) {
@@ -143,7 +144,7 @@ static void ForwardDebuggerRequest(const http::ServerRequest &request) {
 
 	// Yes - proceed with the socket.
 	if (strcasecmp(upgrade.c_str(), "websocket") == 0) {
-		HandleDebuggerRequest(request);
+		HandleDebuggerRequest(request, serverStop);
 	} else {
 		RedirectToDebugger(request);
 	}
@@ -157,7 +158,7 @@ static void WebServerThread() {
 	http->RegisterHandler("/debugger", &ForwardDebuggerRequest);
 
 	if (!http->Listen(g_Config.iRemoteISOPort, "debugger-webserver")) {
-		if (serverRequireExactPort) {
+		if (retro_atomic_load_acquire_int(&serverRequireExactPort)) {
 			// Someone asked for this specific port (--debugger=PORT) - see
 			// WebServerSetRequireExactPort(). Coming up on a different one would just look like
 			// success while nothing can connect, so give up loudly instead.
@@ -182,14 +183,13 @@ static void WebServerThread() {
 	// line is the only way a client can find out which one it got.
 	NOTICE_LOG(Log::HTTP, "Entering web server loop. Listening on port %d", g_Config.iRemoteISOPort);
 
-	while (RetrieveStatus() == ServerStatus::RUNNING) {
-		constexpr double webServerSliceSeconds = 0.2f;
-		http->RunSlice(webServerSliceSeconds);
+	while (!serverStop->IsCancelled()) {
+		http->RunSlice(serverStop);
 	}
 	INFO_LOG(Log::HTTP, "Leaving web server loop.");
 
 	http->Stop();
-	StopAllDebuggers();
+	// Joins the connection threads, which see serverStop too.
 	delete http;
 
 	UpdateStatus(ServerStatus::FINISHED);
@@ -197,15 +197,17 @@ static void WebServerThread() {
 }
 
 bool StartWebServer() {
-	std::lock_guard<std::mutex> guard(serverStatusLock);
-	switch (serverStatus) {
+	switch (RetrieveStatus()) {
 	case ServerStatus::FINISHED:
 		serverThread.join();
+		delete serverStop;
+		serverStop = nullptr;
 		[[fallthrough]];
 
 	case ServerStatus::STOPPED:
-		serverStatus = ServerStatus::STARTING;
-		serverThread = std::thread(&WebServerThread);
+		serverStop = new net::CancelToken();
+		UpdateStatus(ServerStatus::STARTING);
+		serverThread = Thread(&WebServerThread);
 		return true;
 
 	default:
@@ -214,14 +216,28 @@ bool StartWebServer() {
 }
 
 void ShutdownWebServer() {
-	{
-		std::lock_guard<std::mutex> guard(serverStatusLock);
-		if (serverStatus == ServerStatus::RUNNING)
-			serverStatus = ServerStatus::STOPPING;
+	if (retro_atomic_cas_int(&serverStatus, (int)ServerStatus::RUNNING, (int)ServerStatus::STOPPING)) {
+		ParkingLotNotify(&serverStatus);
 	}
-	if (serverThread.joinable())
+	if (serverStop) {
+		serverStop->Cancel();
+	}
+	if (serverThread.joinable()) {
+		// Connections finishing up may still need the CPU thread (Core_RunOnCPUThread), and this
+		// is it, so keep serving them until the server thread is done.
+		for (;;) {
+			const int seen = Core_CPUWorkSeen();
+			Core_ProcessCPUQueue();
+			if (RetrieveStatus() == ServerStatus::FINISHED || RetrieveStatus() == ServerStatus::STOPPED) {
+				break;
+			}
+			Core_WaitForCPUWork(seen);
+		}
 		serverThread.join();
-	serverStatus = ServerStatus::STOPPED;
+	}
+	delete serverStop;
+	serverStop = nullptr;
+	UpdateStatus(ServerStatus::STOPPED);
 }
 
 bool WebServerRunning() {
@@ -233,11 +249,10 @@ int WebServerPort() {
 }
 
 void WebServerSetRequireExactPort(bool require) {
-	serverRequireExactPort = require;
+	retro_atomic_store_release_int(&serverRequireExactPort, require ? 1 : 0);
 }
 
 bool WebServerWaitForStartup() {
-	std::unique_lock<std::mutex> guard(serverStatusLock);
-	serverStatusCond.wait(guard, [] { return serverStatus != ServerStatus::STARTING; });
-	return serverStatus == ServerStatus::RUNNING;
+	ParkingLotWait(&serverStatus, [] { return RetrieveStatus() != ServerStatus::STARTING; });
+	return RetrieveStatus() == ServerStatus::RUNNING;
 }