Synchronize DVDInterface::ChangeDisc with the CPU thread properly.

This addresses a bit of thread unsafety mentioned in a comment, and
fixes a 'ScheduleEvent_Threadsafe from main thread' message.

To make this work nicely, make PauseAndLock call DeclareAsCPUThread -
i.e. while you have the CPU thread locked, you can consider yourself the
CPU thread.

Source/Core/Core/Core.cpp

@@ -276,7 +276,7 @@ void Stop()  // - Hammertime!
 	}
 }
 
-static void DeclareAsCPUThread()
+void DeclareAsCPUThread()
 {
 #ifdef ThreadLocalStorage
 	tls_is_cpu_thread = true;
@@ -288,7 +288,7 @@ static void DeclareAsCPUThread()
 #endif
 }
 
-static void UndeclareAsCPUThread()
+void UndeclareAsCPUThread()
 {
 #ifdef ThreadLocalStorage
 	tls_is_cpu_thread = false;
@@ -715,6 +715,7 @@ bool PauseAndLock(bool doLock, bool unpauseOnUnlock)
 
 	// video has to come after CPU, because CPU thread can wait for video thread (s_efbAccessRequested).
 	g_video_backend->PauseAndLock(doLock, unpauseOnUnlock);
+
 	return wasUnpaused;
 }
 

Source/Core/Core/Core.h

@@ -41,6 +41,9 @@ bool Init();
 void Stop();
 void Shutdown();
 
+void DeclareAsCPUThread();
+void UndeclareAsCPUThread();
+
 std::string StopMessage(bool, const std::string&);
 
 bool IsRunning();

Source/Core/Core/HW/CPU.cpp

@@ -149,13 +149,22 @@ void Break()
 
 bool PauseAndLock(bool do_lock, bool unpause_on_unlock)
 {
+	static bool s_have_fake_cpu_thread;
 	bool wasUnpaused = !IsStepping();
 	if (do_lock)
 	{
 		// we can't use EnableStepping, that would causes deadlocks with both audio and video
 		PowerPC::Pause();
 		if (!Core::IsCPUThread())
+		{
 			m_csCpuOccupied.lock();
+			s_have_fake_cpu_thread = true;
+			Core::DeclareAsCPUThread();
+		}
+		else
+		{
+			s_have_fake_cpu_thread = false;
+		}
 	}
 	else
 	{
@@ -165,8 +174,12 @@ bool PauseAndLock(bool do_lock, bool unpause_on_unlock)
 			m_StepEvent.Set();
 		}
 
-		if (!Core::IsCPUThread())
+		if (s_have_fake_cpu_thread)
+		{
+			Core::UndeclareAsCPUThread();
 			m_csCpuOccupied.unlock();
+			s_have_fake_cpu_thread = false;
+		}
 	}
 	return wasUnpaused;
 }

Source/Core/Core/HW/DVDInterface.cpp

@@ -14,6 +14,7 @@
 #include "Common/MathUtil.h"
 
 #include "Core/ConfigManager.h"
+#include "Core/Core.h"
 #include "Core/CoreTiming.h"
 #include "Core/Movie.h"
 #include "Core/HW/AudioInterface.h"
@@ -522,10 +523,11 @@ void InsertDiscCallback(u64 userdata, int cyclesLate)
 
 void ChangeDisc(const std::string& newFileName)
 {
+	bool is_cpu = Core::IsCPUThread();
+	bool was_unpaused = is_cpu ? false : Core::PauseAndLock(true);
 	std::string* _FileName = new std::string(newFileName);
-	CoreTiming::ScheduleEvent_Threadsafe(0, ejectDisc);
-	CoreTiming::ScheduleEvent_Threadsafe(500000000, insertDisc, (u64)_FileName);
-	// TODO: We shouldn't be modifying movie state from the GUI thread.
+	CoreTiming::ScheduleEvent(0, ejectDisc);
+	CoreTiming::ScheduleEvent(500000000, insertDisc, (u64)_FileName);
 	if (Movie::IsRecordingInput())
 	{
 		Movie::g_bDiscChange = true;
@@ -538,6 +540,8 @@ void ChangeDisc(const std::string& newFileName)
 		}
 		Movie::g_discChange = fileName.substr(sizeofpath);
 	}
+	if (!is_cpu)
+		Core::PauseAndLock(false, was_unpaused);
 }
 
 void SetLidOpen(bool _bOpen)