(__objc_thread_detach_function): Clear thread storage.

Call the thread hook function when first becoming multi-threaded.
(objc_set_thread_callback): New function.

From-SVN: r12261

gcc/objc/thr.c

@@ -32,10 +32,34 @@ Boston, MA 02111-1307, USA.  */
  */
 int     __objc_thread_exit_status = 0;          /* Global exit status.      */
 
+/* Flag which lets us know if we ever became multi threaded */
+int __objc_is_multi_threaded = 0;
+/* The hook function called when the runtime becomes multi threaded */
+objc_thread_callback _objc_became_multi_threaded = NULL;
+
 /*****************************************************************************
  *  Universal Functionality
  */
 
+/*
+  Use this to set the hook function that will be called when the 
+  runtime initially becomes multi threaded.
+  The hook function is only called once, meaning only when the 
+  2nd thread is spawned, not for each and every thread.
+
+  It returns the previous hook function or NULL if there is none.
+
+  A program outside of the runtime could set this to some function so
+  it can be informed; for example, the GNUstep Base Library sets it 
+  so it can implement the NSBecomingMultiThreaded notification.
+  */
+objc_thread_callback objc_set_thread_callback(objc_thread_callback func)
+{
+  objc_thread_callback temp = _objc_became_multi_threaded;
+  _objc_became_multi_threaded = func;
+  return temp;
+}
+
 /********
  *  First function called in a thread, starts everything else.
  */
@@ -57,6 +81,18 @@ __objc_thread_detach_function(struct __objc_thread_start_state *istate)
 
         free(istate);
 
+	/* Clear out the thread local storage */
+	objc_thread_set_data(NULL);
+
+	/* Check to see if we just became multi threaded */
+	if (!__objc_is_multi_threaded) {
+	  __objc_is_multi_threaded = 1;
+
+	  /* Call the hook function */
+	  if (_objc_became_multi_threaded != NULL)
+	    (*_objc_became_multi_threaded)();
+	}
+
         if ((imp = (id(*)(id, SEL, id))objc_msg_lookup(object, selector))) {
             (*imp)(object, selector, argument);
         }
@@ -93,6 +129,7 @@ objc_thread_detach(SEL selector, id object, id argument)
     free(istate);                           /* Release state if failed.   */
     return thread_id;
   }
+
   return thread_id;
 }