Re: PATCH: Improve performance of gthr-win32

[Wu Yongwei <adah at netstd dot com>]

I have finally got the notification that my gcc assignment has been 
received by the GNU copyright clerk. So I am reposting the updated patch 
here.

Hope it is OK.

Best regards,

Wu Yongwei
Index: gcc/gthr-win32.h
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/gthr-win32.h,v
retrieving revision 1.21
diff -u -p -r1.21 gthr-win32.h
--- gcc/gthr-win32.h	21 May 2003 22:16:03 -0000	1.21
+++ gcc/gthr-win32.h	23 Mar 2004 11:41:13 -0000
@@ -54,10 +54,9 @@ Software Foundation, 59 Temple Place - S
       This may cause incorrect error return due to truncation values on
       hw where sizeof (DWORD) > sizeof (int).
 
-   3. We might consider using Critical Sections instead of Windows32
-      mutexes for better performance, but emulating __gthread_mutex_trylock
-      interface becomes more complicated (Win9x does not support
-      TryEnterCriticalSectioni, while NT does).
+   3. We are currently using a special mutex instead of the Critical
+      Sections, since Win9x does not support TryEnterCriticalSection
+      (while NT does).
 
    The basic framework should work well enough. In the long term, GCC
    needs to use Structured Exception Handling on Windows32.  */
@@ -339,11 +338,14 @@ typedef struct {
   long started;
 } __gthread_once_t;
 
-typedef void* __gthread_mutex_t;
+typedef struct {
+  long counter;
+  void *sema;
+} __gthread_mutex_t;
 
 #define __GTHREAD_ONCE_INIT {0, -1}
 #define __GTHREAD_MUTEX_INIT_FUNCTION __gthread_mutex_init_function
-#define __GTHREAD_MUTEX_INIT_DEFAULT 0
+#define __GTHREAD_MUTEX_INIT_DEFAULT {0, 0}
 
 #if __MINGW32_MAJOR_VERSION >= 1 || \
   (__MINGW32_MAJOR_VERSION == 0 && __MINGW32_MINOR_VERSION > 2)
@@ -534,8 +536,8 @@ __gthread_setspecific (__gthread_key_t k
 static inline void
 __gthread_mutex_init_function (__gthread_mutex_t *mutex)
 {
-  /* Create unnamed mutex with default security attr and no initial owner.  */
-  *mutex = CreateMutex (NULL, 0, NULL);
+  mutex->counter = 0;
+  mutex->sema = CreateSemaphore (NULL, 0, 65535, NULL);
 }
 
 static inline int
@@ -545,10 +547,16 @@ __gthread_mutex_lock (__gthread_mutex_t 
 
   if (__gthread_active_p ())
     {
-      if (WaitForSingleObject (*mutex, INFINITE) == WAIT_OBJECT_0)
+      if (InterlockedIncrement (&mutex->counter) == 1 ||
+	  WaitForSingleObject (mutex->sema, INFINITE) == WAIT_OBJECT_0)
 	status = 0;
       else
-	status = 1;
+	{
+	  // WaitForSingleObject returns WAIT_FAILED, and we can only do
+	  // some best-effort cleanup here.
+	  InterlockedDecrement (&mutex->counter);
+	  status = 1;
+	}
     }
   return status;
 }
@@ -560,7 +568,7 @@ __gthread_mutex_trylock (__gthread_mutex
 
   if (__gthread_active_p ())
     {
-      if (WaitForSingleObject (*mutex, 0) == WAIT_OBJECT_0)
+      if (InterlockedCompareExchange (&mutex->counter, 1, 0 ) == 0)
 	status = 0;
       else
 	status = 1;
@@ -572,9 +580,11 @@ static inline int
 __gthread_mutex_unlock (__gthread_mutex_t *mutex)
 {
   if (__gthread_active_p ())
-    return (ReleaseMutex (*mutex) != 0) ? 0 : 1;
-  else
-    return 0;
+    {
+      if (InterlockedDecrement (&mutex->counter))
+	return ReleaseSemaphore (mutex->sema, 1, NULL) ? 0 : 1;
+    }
+  return 0;
 }
 
 #endif /*  __GTHREAD_HIDE_WIN32API */
Index: gcc/config/i386/gthr-win32.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/config/i386/gthr-win32.c,v
retrieving revision 1.5
diff -u -p -r1.5 gthr-win32.c
--- gcc/config/i386/gthr-win32.c	31 Jan 2004 02:06:57 -0000	1.5
+++ gcc/config/i386/gthr-win32.c	23 Mar 2004 11:41:13 -0000
@@ -61,10 +61,9 @@ Software Foundation, 59 Temple Place - S
       This may cause incorrect error return due to truncation values on 
       hw where sizeof (DWORD) > sizeof (int).
    
-   3. We might consider using Critical Sections instead of Windows32 
-      mutexes for better performance, but emulating __gthread_mutex_trylock 
-      interface becomes more complicated (Win9x does not support
-      TryEnterCriticalSectioni, while NT does).
+   3. We are currently using a special mutex instead of the Critical
+      Sections, since Win9x does not support TryEnterCriticalSection
+      (while NT does).
   
    The basic framework should work well enough. In the long term, GCC
    needs to use Structured Exception Handling on Windows32.  */
@@ -145,23 +144,29 @@ __gthr_win32_setspecific (__gthread_key_
 void
 __gthr_win32_mutex_init_function (__gthread_mutex_t *mutex)
 {
-  /* Create unnamed mutex with default security attr and no initial owner.  */ 
-  *mutex = CreateMutex (NULL, 0, NULL);
+  mutex->counter = 0;
+  mutex->sema = CreateSemaphore (NULL, 0, 65535, NULL);
 }
 
 int
 __gthr_win32_mutex_lock (__gthread_mutex_t *mutex)
 {
-  if (WaitForSingleObject (*mutex, INFINITE) == WAIT_OBJECT_0)
+  if (InterlockedIncrement (&mutex->counter) == 1 ||
+      WaitForSingleObject (mutex->sema, INFINITE) == WAIT_OBJECT_0)
     return 0;
   else
-    return 1;
+    {
+      // WaitForSingleObject returns WAIT_FAILED, and we can only do
+      // some best-effort cleanup here.
+      InterlockedDecrement (&mutex->counter);
+      return 1;
+    }
 }
 
 int
 __gthr_win32_mutex_trylock (__gthread_mutex_t *mutex)
 {
-  if (WaitForSingleObject (*mutex, 0) == WAIT_OBJECT_0)
+  if (InterlockedCompareExchange (&mutex->counter, 1, 0 ) == 0)
     return 0;
   else
     return 1;
@@ -170,5 +175,8 @@ __gthr_win32_mutex_trylock (__gthread_mu
 int
 __gthr_win32_mutex_unlock (__gthread_mutex_t *mutex)
 {
-    return (ReleaseMutex (*mutex) != 0) ? 0 : 1;
+  if (InterlockedDecrement (&mutex->counter))
+    return ReleaseSemaphore (mutex->sema, 1, NULL) ? 0 : 1;
+  else
+    return 0;
 }