Don't call RunAsCPUThread in config callbacks

In theory, our config system supports calling Set from any thread. But
because we have config callbacks that call RunAsCPUThread, it's a lot
more restricted in practice. Calling Set from any thread other than the
host thread or the CPU thread is formally thread unsafe, and calling Set
on the host thread while the CPU thread is showing a panic alert causes
a deadlock. This is especially a problem because 04072f0 made the
"Ignore for this session" button in panic alerts call Set.

Because so many of our config callbacks want their code to run on the
CPU thread, I thought it would make sense to have a centralized way to
move execution to the CPU thread for config callbacks. To solve the
deadlock problem, this new way is non-blocking. This means that threads
other than the CPU thread might continue executing before the CPU thread
is informed of the new config, but I don't think there's any problem
with that.

Intends to fix https://bugs.dolphin-emu.org/issues/13108.

Source/Core/Common/Config/Config.h

@@ -22,7 +22,8 @@ void AddLayer(std::unique_ptr<ConfigLayerLoader> loader);
 std::shared_ptr<Layer> GetLayer(LayerType layer);
 void RemoveLayer(LayerType layer);
 
-// returns an ID that can be passed to RemoveConfigChangedCallback()
+// Returns an ID that can be passed to RemoveConfigChangedCallback().
+// The callback may be called from any thread.
 size_t AddConfigChangedCallback(ConfigChangedCallback func);
 void RemoveConfigChangedCallback(size_t callback_id);
 void OnConfigChanged();

Source/Core/Core/CMakeLists.txt

@@ -59,6 +59,8 @@ add_library(core
   Core.h
   CoreTiming.cpp
   CoreTiming.h
+  CPUThreadConfigCallback.cpp
+  CPUThreadConfigCallback.h
   Debugger/CodeTrace.cpp
   Debugger/CodeTrace.h
   Debugger/DebugInterface.h

Source/Core/Core/CPUThreadConfigCallback.cpp

@@ -0,0 +1,76 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "Core/CPUThreadConfigCallback.h"
+
+#include <atomic>
+
+#include "Common/Assert.h"
+#include "Common/Config/Config.h"
+#include "Core/Core.h"
+
+namespace
+{
+std::atomic<bool> s_should_run_callbacks = false;
+
+static std::vector<std::pair<size_t, Config::ConfigChangedCallback>> s_callbacks;
+static size_t s_next_callback_id = 0;
+
+void RunCallbacks()
+{
+  for (const auto& callback : s_callbacks)
+    callback.second();
+}
+
+void OnConfigChanged()
+{
+  if (Core::IsCPUThread())
+  {
+    s_should_run_callbacks.store(false, std::memory_order_relaxed);
+    RunCallbacks();
+  }
+  else
+  {
+    s_should_run_callbacks.store(true, std::memory_order_relaxed);
+  }
+}
+
+};  // namespace
+
+namespace CPUThreadConfigCallback
+{
+size_t AddConfigChangedCallback(Config::ConfigChangedCallback func)
+{
+  DEBUG_ASSERT(Core::IsCPUThread());
+
+  static size_t s_config_changed_callback_id = Config::AddConfigChangedCallback(&OnConfigChanged);
+
+  const size_t callback_id = s_next_callback_id;
+  ++s_next_callback_id;
+  s_callbacks.emplace_back(std::make_pair(callback_id, std::move(func)));
+  return callback_id;
+}
+
+void RemoveConfigChangedCallback(size_t callback_id)
+{
+  DEBUG_ASSERT(Core::IsCPUThread());
+
+  for (auto it = s_callbacks.begin(); it != s_callbacks.end(); ++it)
+  {
+    if (it->first == callback_id)
+    {
+      s_callbacks.erase(it);
+      return;
+    }
+  }
+}
+
+void CheckForConfigChanges()
+{
+  DEBUG_ASSERT(Core::IsCPUThread());
+
+  if (s_should_run_callbacks.exchange(false, std::memory_order_relaxed))
+    RunCallbacks();
+}
+
+};  // namespace CPUThreadConfigCallback

Source/Core/Core/CPUThreadConfigCallback.h

@@ -0,0 +1,22 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/Config/Config.h"
+
+// This file lets you register callbacks like in Common/Config/Config.h, with the difference that
+// callbacks registered here are guaranteed to run on the CPU thread. Callbacks registered here may
+// run with a slight delay compared to regular config callbacks.
+
+namespace CPUThreadConfigCallback
+{
+// returns an ID that can be passed to RemoveConfigChangedCallback()
+size_t AddConfigChangedCallback(Config::ConfigChangedCallback func);
+
+void RemoveConfigChangedCallback(size_t callback_id);
+
+// Should be called regularly from the CPU thread
+void CheckForConfigChanges();
+
+};  // namespace CPUThreadConfigCallback

Source/Core/Core/Core.cpp

@@ -41,6 +41,7 @@
 #include "Core/AchievementManager.h"
 #include "Core/Boot/Boot.h"
 #include "Core/BootManager.h"
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/MainSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/CoreTiming.h"
@@ -511,6 +512,9 @@ static void EmuThread(std::unique_ptr<BootParameters> boot, WindowSystemInfo wsi
   DeclareAsCPUThread();
   s_frame_step = false;
 
+  // If settings have changed since the previous run, notify callbacks.
+  CPUThreadConfigCallback::CheckForConfigChanges();
+
   // Switch the window used for inputs to the render window. This way, the cursor position
   // is relative to the render window, instead of the main window.
   ASSERT(g_controller_interface.IsInit());

Source/Core/Core/CoreTiming.cpp

@@ -16,6 +16,7 @@
 #include "Common/Logging/Log.h"
 #include "Common/SPSCQueue.h"
 
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/MainSettings.h"
 #include "Core/Core.h"
 #include "Core/PowerPC/PowerPC.h"
@@ -88,8 +89,8 @@ void CoreTimingManager::UnregisterAllEvents()
 
 void CoreTimingManager::Init()
 {
-  m_registered_config_callback_id = Config::AddConfigChangedCallback(
-      [this]() { Core::RunAsCPUThread([this]() { RefreshConfig(); }); });
+  m_registered_config_callback_id =
+      CPUThreadConfigCallback::AddConfigChangedCallback([this]() { RefreshConfig(); });
   RefreshConfig();
 
   m_last_oc_factor = m_config_oc_factor;
@@ -118,7 +119,7 @@ void CoreTimingManager::Shutdown()
   MoveEvents();
   ClearPendingEvents();
   UnregisterAllEvents();
-  Config::RemoveConfigChangedCallback(m_registered_config_callback_id);
+  CPUThreadConfigCallback::RemoveConfigChangedCallback(m_registered_config_callback_id);
 }
 
 void CoreTimingManager::RefreshConfig()
@@ -311,11 +312,13 @@ void CoreTimingManager::MoveEvents()
 
 void CoreTimingManager::Advance()
 {
-  auto& power_pc = m_system.GetPowerPC();
-  auto& ppc_state = power_pc.GetPPCState();
+  CPUThreadConfigCallback::CheckForConfigChanges();
 
   MoveEvents();
 
+  auto& power_pc = m_system.GetPowerPC();
+  auto& ppc_state = power_pc.GetPPCState();
+
   int cyclesExecuted = m_globals.slice_length - DowncountToCycles(ppc_state.downcount);
   m_globals.global_timer += cyclesExecuted;
   m_last_oc_factor = m_config_oc_factor;

Source/Core/Core/FreeLookConfig.cpp

@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include "Core/FreeLookConfig.h"
+
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/FreeLookSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
@@ -37,7 +39,7 @@ void Config::Refresh()
 {
   if (!s_has_registered_callback)
   {
-    ::Config::AddConfigChangedCallback([] { Core::RunAsCPUThread([] { s_config.Refresh(); }); });
+    CPUThreadConfigCallback::AddConfigChangedCallback([] { s_config.Refresh(); });
     s_has_registered_callback = true;
   }
 

Source/Core/Core/HW/CPU.cpp

@@ -10,6 +10,7 @@
 #include "AudioCommon/AudioCommon.h"
 #include "Common/CommonTypes.h"
 #include "Common/Event.h"
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Core.h"
 #include "Core/Host.h"
 #include "Core/PowerPC/GDBStub.h"
@@ -75,6 +76,7 @@ void CPUManager::Run()
   {
     m_state_cpu_cvar.wait(state_lock, [this] { return !m_state_paused_and_locked; });
     ExecutePendingJobs(state_lock);
+    CPUThreadConfigCallback::CheckForConfigChanges();
 
     Common::Event gdb_step_sync_event;
     switch (m_state)
@@ -113,6 +115,7 @@ void CPUManager::Run()
       // Wait for step command.
       m_state_cpu_cvar.wait(state_lock, [this, &state_lock, &gdb_step_sync_event] {
         ExecutePendingJobs(state_lock);
+        CPUThreadConfigCallback::CheckForConfigChanges();
         state_lock.unlock();
         if (GDBStub::IsActive() && GDBStub::HasControl())
         {

Source/Core/Core/IOS/SDIO/SDIOSlot0.cpp

@@ -15,6 +15,7 @@
 #include "Common/Logging/Log.h"
 #include "Common/SDCardUtil.h"
 
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/MainSettings.h"
 #include "Core/Config/SessionSettings.h"
 #include "Core/Core.h"
@@ -32,27 +33,23 @@ SDIOSlot0Device::SDIOSlot0Device(EmulationKernel& ios, const std::string& device
   if (!Config::Get(Config::MAIN_ALLOW_SD_WRITES))
     INFO_LOG_FMT(IOS_SD, "Writes to SD card disabled by user");
 
-  m_config_callback_id = Config::AddConfigChangedCallback([this] { RefreshConfig(); });
+  m_config_callback_id =
+      CPUThreadConfigCallback::AddConfigChangedCallback([this] { RefreshConfig(); });
   m_sd_card_inserted = Config::Get(Config::MAIN_WII_SD_CARD);
 }
 
 SDIOSlot0Device::~SDIOSlot0Device()
 {
-  Config::RemoveConfigChangedCallback(m_config_callback_id);
+  CPUThreadConfigCallback::RemoveConfigChangedCallback(m_config_callback_id);
 }
 
 void SDIOSlot0Device::RefreshConfig()
 {
-  if (m_sd_card_inserted != Config::Get(Config::MAIN_WII_SD_CARD))
+  const bool sd_card_inserted = Config::Get(Config::MAIN_WII_SD_CARD);
+  if (m_sd_card_inserted != sd_card_inserted)
   {
-    Core::RunAsCPUThread([this] {
-      const bool sd_card_inserted = Config::Get(Config::MAIN_WII_SD_CARD);
-      if (m_sd_card_inserted != sd_card_inserted)
-      {
-        m_sd_card_inserted = sd_card_inserted;
-        EventNotify();
-      }
-    });
+    m_sd_card_inserted = sd_card_inserted;
+    EventNotify();
   }
 }
 

Source/Core/Core/PowerPC/JitCommon/JitBase.cpp

@@ -7,6 +7,8 @@
 #include "Common/CommonTypes.h"
 #include "Common/MemoryUtil.h"
 #include "Common/Thread.h"
+
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/MainSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
@@ -64,14 +66,14 @@ JitBase::JitBase(Core::System& system)
     : m_code_buffer(code_buffer_size), m_system(system), m_ppc_state(system.GetPPCState()),
       m_mmu(system.GetMMU())
 {
-  m_registered_config_callback_id = Config::AddConfigChangedCallback(
-      [this] { Core::RunAsCPUThread([this] { RefreshConfig(); }); });
+  m_registered_config_callback_id =
+      CPUThreadConfigCallback::AddConfigChangedCallback([this] { RefreshConfig(); });
   RefreshConfig();
 }
 
 JitBase::~JitBase()
 {
-  Config::RemoveConfigChangedCallback(m_registered_config_callback_id);
+  CPUThreadConfigCallback::RemoveConfigChangedCallback(m_registered_config_callback_id);
 }
 
 void JitBase::RefreshConfig()

Source/Core/DolphinLib.props

@@ -190,6 +190,7 @@
     <ClInclude Include="Core\ConfigManager.h" />
     <ClInclude Include="Core\Core.h" />
     <ClInclude Include="Core\CoreTiming.h" />
+    <ClInclude Include="Core\CPUThreadConfigCallback.h" />
     <ClInclude Include="Core\Debugger\CodeTrace.h" />
     <ClInclude Include="Core\Debugger\DebugInterface.h" />
     <ClInclude Include="Core\Debugger\Debugger_SymbolMap.h" />
@@ -833,6 +834,7 @@
     <ClCompile Include="Core\ConfigManager.cpp" />
     <ClCompile Include="Core\Core.cpp" />
     <ClCompile Include="Core\CoreTiming.cpp" />
+    <ClCompile Include="Core\CPUThreadConfigCallback.cpp" />
     <ClCompile Include="Core\Debugger\CodeTrace.cpp" />
     <ClCompile Include="Core\Debugger\Debugger_SymbolMap.cpp" />
     <ClCompile Include="Core\Debugger\Dump.cpp" />

Source/Core/VideoCommon/VideoConfig.cpp

@@ -9,6 +9,7 @@
 #include "Common/CommonTypes.h"
 #include "Common/StringUtil.h"
 
+#include "Core/CPUThreadConfigCallback.h"
 #include "Core/Config/GraphicsSettings.h"
 #include "Core/Config/MainSettings.h"
 #include "Core/ConfigManager.h"
@@ -19,6 +20,7 @@
 #include "VideoCommon/AbstractGfx.h"
 #include "VideoCommon/BPFunctions.h"
 #include "VideoCommon/DriverDetails.h"
+#include "VideoCommon/Fifo.h"
 #include "VideoCommon/FramebufferManager.h"
 #include "VideoCommon/FreeLookCamera.h"
 #include "VideoCommon/GraphicsModSystem/Config/GraphicsMod.h"
@@ -57,14 +59,21 @@ void VideoConfig::Refresh()
   {
     // There was a race condition between the video thread and the host thread here, if
     // corrections need to be made by VerifyValidity(). Briefly, the config will contain
-    // invalid values. Instead, pause emulation first, which will flush the video thread,
-    // update the config and correct it, then resume emulation, after which the video
-    // thread will detect the config has changed and act accordingly.
-    Config::AddConfigChangedCallback([]() {
-      Core::RunAsCPUThread([]() {
-        g_Config.Refresh();
-        g_Config.VerifyValidity();
-      });
+    // invalid values. Instead, pause the video thread first, update the config and correct
+    // it, then resume emulation, after which the video thread will detect the config has
+    // changed and act accordingly.
+    CPUThreadConfigCallback::AddConfigChangedCallback([]() {
+      auto& system = Core::System::GetInstance();
+
+      const bool lock_gpu_thread = Core::IsRunningAndStarted();
+      if (lock_gpu_thread)
+        system.GetFifo().PauseAndLock(system, true, false);
+
+      g_Config.Refresh();
+      g_Config.VerifyValidity();
+
+      if (lock_gpu_thread)
+        system.GetFifo().PauseAndLock(system, false, true);
     });
     s_has_registered_callback = true;
   }