From dfc768542017d1a89dfefe65cfe9fd4da4ab1ed5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C8=98tefan=20Talpalaru?= <stefantalpalaru@yahoo.com>
Date: Wed, 15 May 2019 08:42:30 +0200
Subject: [PATCH] fixes #11250 (#11251)

---
 lib/pure/concurrency/threadpool.nim | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/lib/pure/concurrency/threadpool.nim b/lib/pure/concurrency/threadpool.nim
index 15dbb10de5..04be704be8 100644
--- a/lib/pure/concurrency/threadpool.nim
+++ b/lib/pure/concurrency/threadpool.nim
@@ -18,7 +18,7 @@
 when not compileOption("threads"):
   {.error: "Threadpool requires --threads:on option.".}
 
-import cpuinfo, cpuload, locks
+import cpuinfo, cpuload, locks, os
 
 {.push stackTrace:off.}
 
@@ -570,17 +570,15 @@ proc sync*() =
   ## A simple barrier to wait for all ``spawn``'ed tasks.
   ##
   ## If you need more elaborate waiting, you have to use an explicit barrier.
-  var toRelease = 0
   while true:
     var allReady = true
     for i in 0 ..< currentPoolSize:
       if not allReady: break
       allReady = allReady and workersData[i].ready
     if allReady: break
-    blockUntil(gSomeReady)
-    inc toRelease
-
-  for i in 0 ..< toRelease:
-    signal(gSomeReady)
+    sleep(100)
+    # We cannot "blockUntil(gSomeReady)" because workers may be shut down between
+    # the time we establish that some are not "ready" and the time we wait for a
+    # "signal(gSomeReady)" from inside "slave()" that can never come.
 
 setup()