From 6451d35e929c80fe4249761959186b382c7c5558 Mon Sep 17 00:00:00 2001
From: David Chisnall <theraven@theravensnest.org>
Date: Mon, 27 Nov 2017 16:32:54 +0000
Subject: [PATCH] Fix block refcounts to use saturating arithmetic.

---
 blocks_runtime.m | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/blocks_runtime.m b/blocks_runtime.m
index 844d487..74e2163 100644
--- a/blocks_runtime.m
+++ b/blocks_runtime.m
@@ -60,8 +60,10 @@ static int increment24(int *ref)
 {
 	int old = *ref;
 	int val = old & BLOCK_REFCOUNT_MASK;
-	// FIXME: We should gracefully handle refcount overflow, but for now we
-	// just give up
+	if (val == BLOCK_REFCOUNT_MASK)
+	{
+		return val;
+	}
 	assert(val < BLOCK_REFCOUNT_MASK);
 	if (!__sync_bool_compare_and_swap(ref, old, old+1))
 	{
@@ -74,8 +76,10 @@ static int decrement24(int *ref)
 {
 	int old = *ref;
 	int val = old & BLOCK_REFCOUNT_MASK;
-	// FIXME: We should gracefully handle refcount overflow, but for now we
-	// just give up
+	if (val == BLOCK_REFCOUNT_MASK)
+	{
+		return val;
+	}
 	assert(val > 0);
 	if (!__sync_bool_compare_and_swap(ref, old, old-1))
 	{