MAINT-3703 Suspected thread race crasher in fmodex library

Two problems found in DLL involving threads.  First, DllMain
was reinitializing a critical section for all entry reasons
(process attach, detach and thread attach, detach).  Should
only be done on process attach.  Second, static container
object was being modified and accessed without serialization.
Added some double-check locking to the initialization path
to reduce the total number of serialization calls made while
making the code thread safe.

indra/media_plugins/winmmshim/winmm_shim.cpp

@@ -4,7 +4,7 @@
  *
  * $LicenseInfo:firstyear=2010&license=viewerlgpl$
  * Second Life Viewer Source Code
- * Copyright (C) 2010, Linden Research, Inc.
+ * Copyright (C) 2010-2014, Linden Research, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -30,8 +30,8 @@
 
 using std::wstring;
 
-static float sVolumeLevel = 1.f;
-static bool sMute = false;
+static float sVolumeLevel = 1.f;		// Could be covered by critical section,
+static bool sMute = false;				// not needed with atomicity and alignment.
 static CRITICAL_SECTION sCriticalSection;
 
 BOOL APIENTRY DllMain( HMODULE hModule,
@@ -39,37 +39,44 @@ BOOL APIENTRY DllMain( HMODULE hModule,
                        LPVOID lpReserved
 					 )
 {
-	InitializeCriticalSection(&sCriticalSection);
+	if (DLL_PROCESS_ATTACH == ul_reason_for_call)
+	{
+		InitializeCriticalSection(&sCriticalSection);
+	}
 	return TRUE;
 }
 
 void ll_winmm_shim_initialize(){
-	static bool initialized = false;
-	// do this only once
-	EnterCriticalSection(&sCriticalSection);
+	static volatile bool initialized = false;
+
+	// do this only once using double-check locking
 	if (!initialized)
-	{	// bind to original winmm.dll
-		TCHAR system_path[MAX_PATH];
-		TCHAR dll_path[MAX_PATH];
-		::GetSystemDirectory(system_path, MAX_PATH);
-
-		// grab winmm.dll from system path, where it should live
-		wsprintf(dll_path, "%s\\winmm.dll", system_path);
-		HMODULE winmm_handle = ::LoadLibrary(dll_path);
-
-		if (winmm_handle != NULL)
-		{	// we have a dll, let's get out pointers!
-			initialized = true;
-			init_function_pointers(winmm_handle);
-			::OutputDebugStringA("WINMM_SHIM.DLL: real winmm.dll initialized successfully\n");
-		}
-		else
-		{
-			// failed to initialize real winmm.dll
-			::OutputDebugStringA("WINMM_SHIM.DLL: Failed to initialize real winmm.dll\n");
+	{
+		EnterCriticalSection(&sCriticalSection);
+		if (!initialized)
+		{	// bind to original winmm.dll
+			TCHAR system_path[MAX_PATH];
+			TCHAR dll_path[MAX_PATH];
+			::GetSystemDirectory(system_path, MAX_PATH);
+
+			// grab winmm.dll from system path, where it should live
+			wsprintf(dll_path, "%s\\winmm.dll", system_path);
+			HMODULE winmm_handle = ::LoadLibrary(dll_path);
+
+			if (winmm_handle != NULL)
+			{	// we have a dll, let's get out pointers!
+				init_function_pointers(winmm_handle);
+				::OutputDebugStringA("WINMM_SHIM.DLL: real winmm.dll initialized successfully\n");
+				initialized = true;		// Last thing after completing setup
+			}
+			else
+			{
+				// failed to initialize real winmm.dll
+				::OutputDebugStringA("WINMM_SHIM.DLL: Failed to initialize real winmm.dll\n");
+			}
 		}
+		LeaveCriticalSection(&sCriticalSection);
 	}
-	LeaveCriticalSection(&sCriticalSection);
 }
 
 
@@ -84,7 +91,7 @@ extern "C"
 		int	mBitsPerSample;
 	};
 	typedef std::map<HWAVEOUT, WaveOutFormat*> wave_out_map_t;
-	static wave_out_map_t sWaveOuts;
+	static wave_out_map_t sWaveOuts;						// Covered by sCriticalSection
 
 	MMRESULT WINAPI waveOutOpen( LPHWAVEOUT phwo, UINT uDeviceID, LPCWAVEFORMATEX pwfx, DWORD_PTR dwCallback, DWORD_PTR dwInstance, DWORD fdwOpen)
 	{
@@ -100,7 +107,9 @@ extern "C"
 			&& ((fdwOpen & WAVE_FORMAT_QUERY) == 0)) // not just querying for format support
 		{	// remember the requested bits per sample, and associate with the given handle
 			WaveOutFormat* wave_outp = new WaveOutFormat(pwfx->wBitsPerSample);
+			EnterCriticalSection(&sCriticalSection);
 			sWaveOuts.insert(std::make_pair(*phwo, wave_outp));
+			LeaveCriticalSection(&sCriticalSection);
 		}
 		return result;
 	}
@@ -108,13 +117,15 @@ extern "C"
 	MMRESULT WINAPI waveOutClose( HWAVEOUT hwo)
 	{
 		ll_winmm_shim_initialize();
+		EnterCriticalSection(&sCriticalSection);
 		wave_out_map_t::iterator found_it = sWaveOuts.find(hwo);
 		if (found_it != sWaveOuts.end())
 		{	// forget what we know about this handle
 			delete found_it->second;
 			sWaveOuts.erase(found_it);
 		}
-		return waveOutClose_orig( hwo);
+		LeaveCriticalSection(&sCriticalSection);
+		return waveOutClose_orig(hwo);
 	}
 
 	MMRESULT WINAPI waveOutWrite( HWAVEOUT hwo, LPWAVEHDR pwh, UINT cbwh)
@@ -128,11 +139,19 @@ extern "C"
 		}
 		else if (sVolumeLevel != 1.f) 
 		{ // need to apply volume level
+			int bits_per_sample(0);
+			
+			EnterCriticalSection(&sCriticalSection);
 			wave_out_map_t::iterator found_it = sWaveOuts.find(hwo);
 			if (found_it != sWaveOuts.end())
 			{
-				WaveOutFormat* formatp = found_it->second;
-				switch (formatp->mBitsPerSample){
+				bits_per_sample = found_it->second->mBitsPerSample;
+			}
+			LeaveCriticalSection(&sCriticalSection);
+			if (bits_per_sample)
+			{
+				switch (bits_per_sample)
+				{
 				case 8:
 					{
 						char volume = (char)(sVolumeLevel * 127.f);