yRe: [Patch] Fix gethwnd race

Brian Ford ford@vss.fsi.com
Fri May 14 00:35:00 GMT 2004


On Thu, 13 May 2004, Brian Ford wrote:

> On Thu, 13 May 2004, Christopher Faylor wrote:
> > If it does exist, just return it.  No locking required.
>
> Ok, add:
>
> if (ourhwnd)
>   return ourhwnd;
>
> to the beginning of my patch if your worried about the interlocked
> overhead and don't mind a double test.

Revised patch attached that does this; in case it matters.  ChangeLog
unchanged.

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained pilot...
-------------- next part --------------
Index: window.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/window.cc,v
retrieving revision 1.30
diff -u -p -r1.30 window.cc
--- window.cc	9 Feb 2004 04:04:24 -0000	1.30
+++ window.cc	14 May 2004 00:29:09 -0000
@@ -73,7 +73,13 @@ WndProc (HWND hwnd, UINT uMsg, WPARAM wP
     }
 }
 
-static HANDLE window_started;
+static NO_COPY HANDLE window_started;
+
+void
+window_init ()
+{
+    window_started = CreateEvent (&sec_none_nih, TRUE, FALSE, NULL);
+}
 
 static DWORD WINAPI
 Winmain (VOID *)
@@ -126,18 +132,34 @@ Winmain (VOID *)
 HWND __stdcall
 gethwnd ()
 {
-  if (ourhwnd != NULL)
-    return ourhwnd;
+  HWND hwnd = ourhwnd;
+
+  if (hwnd)
+    return hwnd;
+
+  static NO_COPY long window_waiters;
+  long waiters = InterlockedIncrement (&window_waiters);
+
+  hwnd = ourhwnd;
+  if (hwnd == NULL)
+    {
+      if (waiters == 1)
+	{
+	  cygthread *h = new cygthread (Winmain, NULL, "win");
+	  h->zap_h ();
+	}
+
+      WaitForSingleObject (window_started, INFINITE);
+      hwnd = ourhwnd;
+    }
+
+  HANDLE ws;
 
-  cygthread *h;
+  if (InterlockedDecrement (&window_waiters) == 0 && hwnd
+      && (ws = (HANDLE) InterlockedExchange ((long *) &window_started, 0)))
+    CloseHandle (ws);
 
-  window_started = CreateEvent (&sec_none_nih, TRUE, FALSE, NULL);
-  h = new cygthread (Winmain, NULL, "win");
-  h->SetThreadPriority (THREAD_PRIORITY_HIGHEST);
-  WaitForSingleObject (window_started, INFINITE);
-  CloseHandle (window_started);
-  h->zap_h ();
-  return ourhwnd;
+  return hwnd;
 }
 
 extern "C" int
Index: winsup.h
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/winsup.h,v
retrieving revision 1.143
diff -u -p -r1.143 winsup.h
--- winsup.h	3 May 2004 11:53:07 -0000	1.143
+++ winsup.h	14 May 2004 00:29:09 -0000
@@ -218,6 +218,7 @@ void events_terminate (void);
 void __stdcall close_all_files ();
 
 /* Invisible window initialization/termination. */
+void window_init (void);
 HWND __stdcall gethwnd (void);
 /* Check if running in a visible window station. */
 extern bool has_visible_window_station (void);
Index: dcrt0.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/dcrt0.cc,v
retrieving revision 1.218
diff -u -p -r1.218 dcrt0.cc
--- dcrt0.cc	12 Mar 2004 03:09:28 -0000	1.218
+++ dcrt0.cc	14 May 2004 00:29:10 -0000
@@ -799,6 +799,9 @@ dll_crt0_1 (char *)
   /* Connect to tty. */
   tty_init ();
 
+  /* Initialize hidden window for itimers/sockets. */
+  window_init ();
+
   if (!__argc)
     {
       char *line = GetCommandLineA ();


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