mshtml: Use TLS_OUT_OF_INDEXES as invalid TLS value.

dlls/mshtml/main.c

@@ -44,7 +44,7 @@
 WINE_DEFAULT_DEBUG_CHANNEL(mshtml);
 
 HINSTANCE hInst;
-DWORD mshtml_tls = 0;
+DWORD mshtml_tls = TLS_OUT_OF_INDEXES;
 
 static HINSTANCE shdoclc = NULL;
 
@@ -69,7 +69,7 @@ static void process_detach(void)
 
     if(shdoclc)
         FreeLibrary(shdoclc);
-    if(mshtml_tls)
+    if(mshtml_tls != TLS_OUT_OF_INDEXES)
         TlsFree(mshtml_tls);
 }
 

dlls/mshtml/task.c

@@ -478,11 +478,19 @@ thread_data_t *get_thread_data(BOOL create)
 {
     thread_data_t *thread_data;
 
-    if(!mshtml_tls) {
-        if(create)
-            mshtml_tls = TlsAlloc();
-        else
+    if(mshtml_tls == TLS_OUT_OF_INDEXES) {
+        DWORD tls;
+
+        if(!create)
             return NULL;
+
+        tls = TlsAlloc();
+        if(tls == TLS_OUT_OF_INDEXES)
+            return NULL;
+
+        tls = InterlockedCompareExchange((LONG*)&mshtml_tls, tls, TLS_OUT_OF_INDEXES);
+        if(tls != mshtml_tls)
+            TlsFree(tls);
     }
 
     thread_data = TlsGetValue(mshtml_tls);