diff --git a/3rdparty/w32pthreads/cleanup.c b/3rdparty/w32pthreads/cleanup.c
index 9cbf3cfdb8..4b88d011aa 100644
--- a/3rdparty/w32pthreads/cleanup.c
+++ b/3rdparty/w32pthreads/cleanup.c
@@ -44,6 +44,8 @@
  * SEH or C++ destructor support. 
  */
 
+#ifdef __CLEANUP_C
+
 ptw32_cleanup_t *
 ptw32_pop_cleanup (int execute)
      /*
@@ -144,3 +146,5 @@ ptw32_push_cleanup (ptw32_cleanup_t * cleanup,
   pthread_setspecific (ptw32_cleanupKey, (void *) cleanup);
 
 }				/* ptw32_push_cleanup */
+
+#endif
\ No newline at end of file
diff --git a/3rdparty/w32pthreads/dll.c b/3rdparty/w32pthreads/dll.c
index 50f09d0742..88b495b91d 100644
--- a/3rdparty/w32pthreads/dll.c
+++ b/3rdparty/w32pthreads/dll.c
@@ -35,6 +35,7 @@
  */
 
 #include "ptw32pch.h"
+#include <assert.h>
 
 #ifndef PTW32_STATIC_LIB
 
@@ -81,6 +82,10 @@ DllMain (HINSTANCE hinstDll, DWORD fdwReason, LPVOID lpvReserved)
     case DLL_PROCESS_DETACH:
       (void) pthread_win32_thread_detach_np ();
       result = pthread_win32_process_detach_np ();
+
+	  if( ptw32_testcancel_enable != 0 )
+		assert(0);
+
       break;
     }
 
diff --git a/3rdparty/w32pthreads/include/pthread.h b/3rdparty/w32pthreads/include/pthread.h
index 37c0f90bbc..92b52da529 100644
--- a/3rdparty/w32pthreads/include/pthread.h
+++ b/3rdparty/w32pthreads/include/pthread.h
@@ -970,7 +970,7 @@ extern void PTW32_CDECL pthread_testcancel (void);
 PTW32_DLLPORT int PTW32_CDECL pthread_once (pthread_once_t * once_control,
                           void (*init_routine) (void));
 
-#if PTW32_LEVEL >= PTW32_LEVEL_MAX
+#if PTW32_LEVEL >= PTW32_LEVEL_MAX && defined(__CLEANUP_C)
 PTW32_DLLPORT ptw32_cleanup_t * PTW32_CDECL ptw32_pop_cleanup (int execute);
 
 PTW32_DLLPORT void PTW32_CDECL ptw32_push_cleanup (ptw32_cleanup_t * cleanup,
diff --git a/3rdparty/w32pthreads/pthread_cancel.c b/3rdparty/w32pthreads/pthread_cancel.c
index af3ac74463..afcf000453 100644
--- a/3rdparty/w32pthreads/pthread_cancel.c
+++ b/3rdparty/w32pthreads/pthread_cancel.c
@@ -94,10 +94,6 @@ pthread_cancel (pthread_t thread)
   cancel_self = pthread_equal (thread, self);
   tp = (ptw32_thread_t *) thread.p;
 
-  // enables full cancel testing in pthread_testcancel, which is normally
-  // disabled because 
-  _InterlockedIncrement( &ptw32_testcancel_enable );
-  
   /*
    * Lock for async-cancel safety.
    */
@@ -127,8 +123,18 @@ pthread_cancel (pthread_t thread)
       /*
        * Set for deferred cancellation.
        */
+
       if (tp->state < PThreadStateCancelPending)
 	{
+		// enables full cancel testing in pthread_testcancel, which is normally disabled because
+		// the full test requires a DLL function invocation and TLS lookup.  This provides an
+		// inlinable first-step shortcut for much speedier testing. :)
+		
+		// Increment is performed here such that a thread that is already canceling won't get
+		// counted multiple times.
+		
+		_InterlockedIncrement( &ptw32_testcancel_enable );
+
 	  tp->state = PThreadStateCancelPending;
 	  if (!SetEvent (tp->cancelEvent))
 	    {
diff --git a/3rdparty/w32pthreads/pthread_testcancel.c b/3rdparty/w32pthreads/pthread_testcancel.c
index 1270eeb167..89ad26fd23 100644
--- a/3rdparty/w32pthreads/pthread_testcancel.c
+++ b/3rdparty/w32pthreads/pthread_testcancel.c
@@ -90,8 +90,6 @@ pthread_testcancel (void)
       return;
     }
 
-  _InterlockedDecrement( &ptw32_testcancel_enable );
-
   (void) pthread_mutex_lock (&sp->cancelLock);
 
   if (sp->cancelState != PTHREAD_CANCEL_DISABLE)
diff --git a/3rdparty/w32pthreads/ptw32_threadStart.c b/3rdparty/w32pthreads/ptw32_threadStart.c
index 0569fea3f8..5c86c22428 100644
--- a/3rdparty/w32pthreads/ptw32_threadStart.c
+++ b/3rdparty/w32pthreads/ptw32_threadStart.c
@@ -36,6 +36,27 @@
  */
 
 #include "ptw32pch.h"
+#include <assert.h>
+
+// This is a "safe" cleanup handler for the cancel optimization.  It ensures
+// the testcancel_enable flag gets cleared even when threads commit grotesque
+// exceptions.
+
+static void
+_cleanup_testcancel_optimization( void* specific )
+{
+	ptw32_thread_t * sp = (ptw32_thread_t*)specific; //(ptw32_thread_t *)pthread_getspecific (ptw32_selfThreadKey);
+	if( (sp != NULL) &&
+		(sp->cancelType == PTHREAD_CANCEL_DEFERRED) &&
+		(sp->state >= PThreadStateCancelPending)
+		)
+	{
+		assert( ptw32_testcancel_enable > 0 );
+
+		if( ptw32_testcancel_enable > 0 )
+			(void) _InterlockedDecrement( &ptw32_testcancel_enable );
+	}
+}
 
 #ifdef __CLEANUP_SEH
 
@@ -175,7 +196,9 @@ ptw32_threadStart (void *vthreadParms)
     /*
      * Run the caller's routine;
      */
+     pthread_cleanup_push( _cleanup_testcancel_optimization, sp );
     status = sp->exitStatus = (*start) (arg);
+	 pthread_cleanup_pop( 1 );
 
 #ifdef _UWIN
     if (--pthread_count <= 0)
@@ -324,6 +347,8 @@ ptw32_threadStart (void *vthreadParms)
 #endif /* __CLEANUP_C */
 #endif /* __CLEANUP_SEH */
 
+  //_cleanup_testcancel_optimization();
+
 #if defined(PTW32_STATIC_LIB)
   /*
    * We need to cleanup the pthread now if we have
diff --git a/3rdparty/w32pthreads/ptw32_throw.c b/3rdparty/w32pthreads/ptw32_throw.c
index 8349cab8af..f7bb5b602e 100644
--- a/3rdparty/w32pthreads/ptw32_throw.c
+++ b/3rdparty/w32pthreads/ptw32_throw.c
@@ -142,6 +142,7 @@ ptw32_throw (DWORD exception)
 }
 
 
+#ifdef __CLEANUP_C
 void
 ptw32_pop_cleanup_all (int execute)
 {
@@ -149,7 +150,7 @@ ptw32_pop_cleanup_all (int execute)
     {
     }
 }
-
+#endif
 
 DWORD
 ptw32_get_exception_services_code (void)