Re-use of user-defined stacks for threads

[Wolfram Gloger <wmglo at dent dot med dot uni-muenchen dot de>]

Hello,

When providing a user-defined stack, e.g. one allocated with malloc(),
for a thread T, I understand I can re-use this stack immediately after
pthread_join(T) has returned successfully.  (This is not explicit in
the spec, but I consider it quite obvious.)

LinuxThreads breaks this, because the actual freeing of the thread
resources within the stack can occur _after_ pthread_join() has
returned.  Below is a fix.

Regards,
Wolfram.

2000-11-25  Wolfram Gloger  <wg@malloc.de>

	* join.c (pthread_join): For a user-defined stack, wait until the
	thread resources have actually been freed by the manager thread
	before returning.

	* manager.c (pthread_free): Wake up the joining thread if the
	stack is user-defined.

--- linuxthreads/join.c.orig	Wed Jun 21 20:11:00 2000
+++ linuxthreads/join.c	Sat Nov 25 11:45:52 2000
@@ -111,6 +111,7 @@
   pthread_descr th;
   pthread_extricate_if extr;
   int already_canceled = 0;
+  int userstack;
 
   /* Set up extrication interface */
   extr.pu_object = handle;
@@ -161,6 +162,8 @@
   }
   /* Get return value */
   if (thread_return != NULL) *thread_return = th->p_retval;
+  userstack = th->p_userstack;
+  th->p_joining = userstack ? self : NULL;
   __pthread_unlock(&handle->h_lock);
   /* Send notification to thread manager */
   if (__pthread_manager_request >= 0) {
@@ -169,6 +172,12 @@
     request.req_args.free.thread_id = thread_id;
     __libc_write(__pthread_manager_request,
 		 (char *) &request, sizeof(request));
+    if (userstack) {
+      /* Must wait for pthread_free() to actually have completed,
+	 because the stack can be reused immediately after
+	 pthread_join() returns.  */
+      suspend(self);
+    }
   }
   return 0;
 }
--- linuxthreads/manager.c.orig	Thu Sep  7 20:56:28 2000
+++ linuxthreads/manager.c	Sat Nov 25 11:59:25 2000
@@ -715,6 +715,13 @@
       munmap (guardaddr, stacksize + guardsize);
 #endif
     }
+  else
+    {
+      /* pthread_join() may be waiting for the stack to have been actually
+	 freed.  */
+      if (th->p_joining)
+	restart(th->p_joining);
+    }
 }
 
 /* Handle threads that have exited */