From 5e2d802e29f0a8f81de297f9a3e3922f2d6cd6c0 Mon Sep 17 00:00:00 2001
From: Raimo Niskanen <raimo@erlang.org>
Date: Fri, 14 Oct 2016 10:08:49 +0200
Subject: Fix race condition in cancel_timer/1

---
 lib/stdlib/src/gen_statem.erl | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lib/stdlib/src/gen_statem.erl b/lib/stdlib/src/gen_statem.erl
index 5c750cb93d..17d1ebecec 100644
--- a/lib/stdlib/src/gen_statem.erl
+++ b/lib/stdlib/src/gen_statem.erl
@@ -1609,13 +1609,14 @@ cancel_timer(undefined) ->
     ok;
 cancel_timer(TRef) ->
     case erlang:cancel_timer(TRef) of
-	TimeLeft when is_integer(TimeLeft) ->
-	    ok;
 	false ->
+	    %% We have to assume that TRef is the ref of a running timer
+	    %% and if so the timer has expired
+	    %% hence we must wait for the timeout message
 	    receive
 		{timeout,TRef,_} ->
 		    ok
-	    after 0 ->
-		    ok
-	    end
+	    end;
+	_TimeLeft ->
+	    ok
     end.
-- 
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