From 624ec168ecde5fbdbe83e4e7c558805b408fabcc Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Thu, 16 Jun 2016 17:06:25 +0000
Subject: [16828b3744] [vwait] *must* successfully undo its variable trace, or
 else it risks corrupting memory.  Namespace teardown complexities were giving
 the traces an opportunity to survive.  Added another (arguably better)
 Tcl_UntraceVar() call to be sure we avoid this problem.

---
 generic/tclEvent.c | 2 ++
 tests/event.test   | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/generic/tclEvent.c b/generic/tclEvent.c
index c664b38..4db524c 100644
--- a/generic/tclEvent.c
+++ b/generic/tclEvent.c
@@ -1379,6 +1379,8 @@ VwaitVarProc(
     int *donePtr = (int *) clientData;
 
     *donePtr = 1;
+    Tcl_UntraceVar(interp, name1, TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
+	    VwaitVarProc, clientData);
     return NULL;
 }
 
diff --git a/tests/event.test b/tests/event.test
index a7122f9..4996b97 100644
--- a/tests/event.test
+++ b/tests/event.test
@@ -559,6 +559,15 @@ test event-11.6 {Tcl_VwaitCmd procedure: round robin scheduling, same source} {
     removeFile $test2file
     list $x $y $z
 } {3 3 done}
+test event-11.7 {Bug 16828b3744} {
+    after idle {
+	set ::t::v 1
+	namespace delete ::t
+    }
+    namespace eval ::t {
+	vwait ::t::v
+    }
+} {}
 
 
 test event-12.1 {Tcl_UpdateCmd procedure} {
-- 
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