(svn r17776) -Codechange: [SDL] make "update the video card"-process asynchronious. Profiling with gprof etc. hasn't shown us that DrawSurfaceToScreen takes a significant amount of CPU; only using TIC/TOC it became apparant that it was a heavy CPU-cycle user or that it was waiting for something.

The benefit of making this function asynchronious ranges from 2%-25% (real time) during fast forward on dual core/hyperthreading-enabled CPUs; 8bpp improvements are, in my test cases, significantly smaller than 32bpp improvements.
On single core non-hyperthreading-enabled CPUs the extra locking/scheduling costs up to 1% extra realtime in fast forward. You can use -v sdl:no_threads to disable threading and undo this loss.
During normal non-fast-forwarded games the benefit/costs are negligable except when the gameloop takes more than about 90% of the time of a tick.
Note that allegro's performance does not improve with this system, likely due to their way of getting data to the video card. It is not implemented for the OS X/Windows video backends, unless (ofcourse) SDL is used there.
Funny is that the performance of the 32bpp(-anim) blitter is, at least in some test cases, significantly faster (more than 10%) than the 8bpp(-optimized) blitter when looking at real time in fast forward on a dual core CPU; it was slower.
The idea comes from a paper/report by Idar Borlaug and Knut Imar Hagen.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/thread/thread_win32.cpp b/src/thread/thread_win32.cpp
index e752de1ae..a3b2d3734 100644
--- a/src/thread/thread_win32.cpp
+++ b/src/thread/thread_win32.cpp
@@ -107,16 +107,19 @@ private:
 class ThreadMutex_Win32 : public ThreadMutex {
 private:
 	CRITICAL_SECTION critical_section;
+	HANDLE event;
 
 public:
 	ThreadMutex_Win32()
 	{
 		InitializeCriticalSection(&this->critical_section);
+		this->event = CreateEvent(NULL, FALSE, FALSE, NULL);
 	}
 
 	/* virtual */ ~ThreadMutex_Win32()
 	{
 		DeleteCriticalSection(&this->critical_section);
+		CloseHandle(this->event);
 	}
 
 	/* virtual */ void BeginCritical()
@@ -128,6 +131,18 @@ public:
 	{
 		LeaveCriticalSection(&this->critical_section);
 	}
+
+	/* virtual */ void WaitForSignal()
+	{
+		this->EndCritical();
+		WaitForSingleObject(this->event, INFINITE);
+		this->BeginCritical();
+	}
+
+	/* virtual */ void SendSignal()
+	{
+		SetEvent(this->event);
+	}
 };
 
 /* static */ ThreadMutex *ThreadMutex::New()