System: Allow host to set async worker count

For regtest.

src/core/system.cpp

@@ -115,8 +115,6 @@ SystemBootParameters::~SystemBootParameters() = default;
 
 namespace System {
 
-static constexpr u32 NUM_ASYNC_WORKER_THREADS = 2;
-
 static constexpr float PRE_FRAME_SLEEP_UPDATE_INTERVAL = 1.0f;
 static constexpr const char FALLBACK_EXE_NAME[] = "PSX.EXE";
 static constexpr u32 MAX_SKIPPED_DUPLICATE_FRAME_COUNT = 2; // 20fps minimum
@@ -497,7 +495,7 @@ void System::ProcessShutdown()
   CPU::CodeCache::ProcessShutdown();
 }
 
-bool System::CPUThreadInitialize(Error* error)
+bool System::CPUThreadInitialize(Error* error, u32 async_worker_thread_count)
 {
 #ifdef _WIN32
   // On Win32, we have a bunch of things which use COM (e.g. SDL, Cubeb, etc).
@@ -516,7 +514,7 @@ bool System::CPUThreadInitialize(Error* error)
 
   LogStartupInformation();
 
-  s_state.async_task_queue.SetWorkerCount(NUM_ASYNC_WORKER_THREADS);
+  s_state.async_task_queue.SetWorkerCount(async_worker_thread_count);
 
   GPUThread::Internal::ProcessStartup();
 

src/core/system_private.h

@@ -60,7 +60,7 @@ bool ProcessStartup(Error* error);
 void ProcessShutdown();
 
 /// Called on CPU thread initialization.
-bool CPUThreadInitialize(Error* error);
+bool CPUThreadInitialize(Error* error, u32 async_worker_thread_count);
 
 /// Called on CPU thread shutdown.
 void CPUThreadShutdown();

src/duckstation-qt/qthost.cpp

@@ -77,6 +77,9 @@ LOG_CHANNEL(Host);
 static constexpr u32 SETTINGS_VERSION = 3;
 static constexpr u32 SETTINGS_SAVE_DELAY = 1000;
 
+/// Use two async worker threads, should be enough for most tasks.
+static constexpr u32 NUM_ASYNC_WORKER_THREADS = 2;
+
 /// Interval at which the controllers are polled when the system is not active.
 static constexpr u32 BACKGROUND_CONTROLLER_POLLING_INTERVAL = 100;
 
@@ -1844,7 +1847,7 @@ void EmuThread::run()
   // input source setup must happen on emu thread
   {
     Error startup_error;
-    if (!System::CPUThreadInitialize(&startup_error))
+    if (!System::CPUThreadInitialize(&startup_error, NUM_ASYNC_WORKER_THREADS))
     {
       moveToThread(m_ui_thread);
       Host::ReportFatalError("Fatal Startup Error", startup_error.GetDescription());

src/duckstation-regtest/regtest_host.cpp

@@ -813,7 +813,8 @@ int main(int argc, char* argv[])
   if (!RegTestHost::SetNewDataRoot(autoboot->filename))
     return EXIT_FAILURE;
 
-  if (!System::CPUThreadInitialize(&startup_error))
+  // Only one async worker.
+  if (!System::CPUThreadInitialize(&startup_error, 1))
   {
     ERROR_LOG("CPUThreadInitialize() failed: {}", startup_error.GetDescription());
     return EXIT_FAILURE;