From 055512590fc6fbeb138aa81677452d14ff8bd80a Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Thu, 25 Jul 2013 08:47:28 -0600
Subject: [PATCH] place: fix finalizaiton of place channels stuck in a GC'ed
 channel

Lack of ordering on finalization requires some care for explicit
clean-up actions in a finalizer.

Back-port of commit a5f26013ab.
---
 src/racket/src/place.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/racket/src/place.c b/src/racket/src/place.c
index 27cdb555a7..7a017f0382 100644
--- a/src/racket/src/place.c
+++ b/src/racket/src/place.c
@@ -2957,6 +2957,11 @@ Scheme_Place_Async_Channel *place_async_channel_create() {
 
 static void async_channel_refcount(Scheme_Place_Async_Channel *ch, int for_send, int delta)
 {
+  if (!ch->lock) {
+    /* can happen via finalization, where the channel is already finalized
+       (due to the lack of ordering on finalization) */
+    return;
+  }
   mzrt_mutex_lock(ch->lock);
   if (for_send)
     ch->wr_ref += delta;