[Python-checkins] r45902 - stackless/Python-2.4.3/dev/Stackless/module/taskletobject.c

[richard.tew]

Author: richard.tew
Date: Thu May  4 19:08:03 2006
New Revision: 45902

Modified:
   stackless/Python-2.4.3/dev/Stackless/module/taskletobject.c
Log:
There is a unpickling race condition.  While it is rare,
sometimes tasklets get their setstate call after the
channel they are blocked on.  If this happens and we
do not account for it, they will be left in a broken
state where they are on the channels chain, but have
cleared their blocked flag.

We will assume that the presence of a chain, can only
mean that the chain is that of a channel, rather than
that of the main tasklet/scheduler.  And therefore
they can leave their blocked flag in place because the
channel would have set it.


Modified: stackless/Python-2.4.3/dev/Stackless/module/taskletobject.c
==============================================================================
--- stackless/Python-2.4.3/dev/Stackless/module/taskletobject.c	(original)
+++ stackless/Python-2.4.3/dev/Stackless/module/taskletobject.c	Thu May  4 19:08:03 2006
@@ -315,9 +315,28 @@
 
 	nframes = PyList_GET_SIZE(lis);
 	TASKLET_SETVAL(t, tempval);
+
+	/* There is a unpickling race condition.  While it is rare,
+	 * sometimes tasklets get their setstate call after the
+	 * channel they are blocked on.  If this happens and we
+	 * do not account for it, they will be left in a broken
+	 * state where they are on the channels chain, but have
+	 * cleared their blocked flag.
+	 *
+	 * We will assume that the presence of a chain, can only
+	 * mean that the chain is that of a channel, rather than
+	 * that of the main tasklet/scheduler. And therefore
+	 * they can leave their blocked flag in place because the
+	 * channel would have set it.
+	 */
+	i = t->flags.blocked;
 	*(int *)&t->flags = flags;
-	/* we cannot restore blocked, must be done by a channel */
-	t->flags.blocked = 0;
+	if (t->next == NULL) {
+		t->flags.blocked = 0;
+	} else {
+		t->flags.blocked = i;
+	}
+
 	/* t->nesting_level = nesting_level;
 	   XXX how do we handle this?
 	   XXX to be done: pickle the cstate without a ref to the task.