winxp threads: fix some condition variable races

There are some races in the condition variable emulation code for
Windows XP with respect to timeouts while waiting.

First, in the event of a timeout, we never remove the waiter from the
condition variable.  This can cause crashes later.  That problem was
found by Rodrigo Rivas Costa.

Second, if the waiting thread times out and exits just as we were about
to call SetEvent() on its waiter event, we could end up trying to access
the waiter after it was closed/freed.  We need to hold on to the lock a
little bit longer to ensure that that's not possible.

https://bugzilla.gnome.org/show_bug.cgi?id=666551

diff --git a/glib/gthread-win32.c b/glib/gthread-win32.c
index 29065b5..3ec908d 100644 (file)
--- a/glib/gthread-win32.c
+++ b/glib/gthread-win32.c
@@ -520,8 +520,9 @@ static DWORD            g_thread_xp_waiter_tls;
 typedef struct _GThreadXpWaiter GThreadXpWaiter;
 struct _GThreadXpWaiter
 {
-  HANDLE                    event;
-  volatile GThreadXpWaiter *next;
+  HANDLE                     event;
+  volatile GThreadXpWaiter  *next;
+  volatile GThreadXpWaiter **my_owner;
 };
 
 static GThreadXpWaiter *
@@ -539,6 +540,7 @@ g_thread_xp_waiter_get (void)
       waiter->event = CreateEvent (0, FALSE, FALSE, NULL);
       if (waiter->event == NULL)
         g_thread_abort (GetLastError (), "CreateEvent");
+      waiter->my_owner = NULL;
 
       TlsSetValue (g_thread_xp_waiter_tls, waiter);
     }
@@ -848,6 +850,7 @@ g_thread_xp_SleepConditionVariableSRW (gpointer cond,
   waiter->next = NULL;
 
   EnterCriticalSection (&g_thread_xp_lock);
+  waiter->my_owner = cv->last_ptr;
   *cv->last_ptr = waiter;
   cv->last_ptr = &waiter->next;
   LeaveCriticalSection (&g_thread_xp_lock);
@@ -857,9 +860,19 @@ g_thread_xp_SleepConditionVariableSRW (gpointer cond,
 
   if (status != WAIT_TIMEOUT && status != WAIT_OBJECT_0)
     g_thread_abort (GetLastError (), "WaitForSingleObject");
-
   g_mutex_lock (mutex);
 
+  if (status == WAIT_TIMEOUT)
+    {
+      EnterCriticalSection (&g_thread_xp_lock);
+      if (waiter->my_owner)
+        {
+          *waiter->my_owner = waiter->next;
+          waiter->my_owner = NULL;
+        }
+      LeaveCriticalSection (&g_thread_xp_lock);
+    }
+
   return status == WAIT_OBJECT_0;
 }
 
@@ -870,17 +883,21 @@ g_thread_xp_WakeConditionVariable (gpointer cond)
   volatile GThreadXpWaiter *waiter;
 
   EnterCriticalSection (&g_thread_xp_lock);
+
   waiter = cv->first;
   if (waiter != NULL)
     {
       cv->first = waiter->next;
-      if (cv->first == NULL)
+      if (cv->first != NULL)
+        cv->first->my_owner = &cv->first;
+      else
         cv->last_ptr = &cv->first;
     }
-  LeaveCriticalSection (&g_thread_xp_lock);
 
   if (waiter != NULL)
     SetEvent (waiter->event);
+
+  LeaveCriticalSection (&g_thread_xp_lock);
 }
 
 static void __stdcall
@@ -890,10 +907,10 @@ g_thread_xp_WakeAllConditionVariable (gpointer cond)
   volatile GThreadXpWaiter *waiter;
 
   EnterCriticalSection (&g_thread_xp_lock);
+
   waiter = cv->first;
   cv->first = NULL;
   cv->last_ptr = &cv->first;
-  LeaveCriticalSection (&g_thread_xp_lock);
 
   while (waiter != NULL)
     {
@@ -901,8 +918,11 @@ g_thread_xp_WakeAllConditionVariable (gpointer cond)
 
       next = waiter->next;
       SetEvent (waiter->event);
+      waiter->my_owner = NULL;
       waiter = next;
     }
+
+  LeaveCriticalSection (&g_thread_xp_lock);
 }
 
 /* {{{2 XP Setup */