From f2be90484850def90ca0caf11969a3ade2227446 Mon Sep 17 00:00:00 2001
From: Holger Hans Peter Freyther <holger@moiji-mobile.com>
Date: Sun, 27 Jul 2014 10:19:25 +0200
Subject: [PATCH] timer: Prevent a potential race with the loop process
 resumption

It is possible that the "loop" has determined there are no pending
timers but then the insertion application is executing and is
inserting a timer. Once the loop is executing again it will sleep
as there was no timer and we will miss the wake-up until there is
another timer.
---
 Timer.st             | 28 ++++++++++++++++------------
 changes_for_pharo.st |  3 ++-
 2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/Timer.st b/Timer.st
index b2acac0..d491053 100644
--- a/Timer.st
+++ b/Timer.st
@@ -73,7 +73,7 @@ Object subclass: Timer [
 ]
 
 Object subclass: TimerScheduler [
-    | queue sem loop quit processExited delay |
+    | queue sem loop quit processExited delay loopSem |
     <category: 'OsmoCore-Timer'>
     <comment: 'I can help to fire things at the right time. Right now I
 only work on seconds granularity because Time has no direct access to
@@ -108,7 +108,8 @@ bit difficult to do this race free.'>
         "Nothing for GST"
         loop ifNil: [^self].
         quit := true.
-        loop isSuspended ifTrue: [loop resume].
+        sem critical: [
+            loopSem ifNotNil: [loopSem signal]].
         delay ifNotNil: [:the_delay | the_delay signal].
         processExited wait.
         Transcript nextPutAll: 'Stopped the TimerScheduler process'; cr
@@ -158,15 +159,14 @@ bit difficult to do this race free.'>
         sem critical: [
             currentFirst := queue isEmpty ifFalse: [queue first].
             queue add: timer.
-            loop isSuspended
-                ifTrue: [loop resume]
-                ifFalse:  [
-                    "if the first item in the queue has changed we need to readjust the delay
-                     to wait for. Signalling the waiting delay will enter the recalculation of a new
-                     expire time"
 
-                    currentFirst == queue first
-                        ifFalse: [self signalDelay]]].
+            "Make sure the loopSem is waking up at least once."
+            loopSem ifNotNil: [loopSem signal].
+            "if the first item in the queue has changed we need to readjust the delay
+             to wait for. Signalling the waiting delay will enter the recalculation of
+             a new expire time"
+            currentFirst == queue first
+                ifFalse: [self signalDelay]].
 	^timer
     ]
 
@@ -180,7 +180,11 @@ bit difficult to do this race free.'>
 
         [quit] whileFalse: [
             | timer |
-            sem critical: [queue isEmpty ifFalse: [timer := queue first]].
+            sem critical: [
+                queue isEmpty ifFalse: [timer := queue first].
+                loopSem := Semaphore new.
+            ].
+
             timer isNil
                 ifTrue: [
                     "nothing to do. No need to poll an empty queue. Remove delay to get rid of
@@ -189,7 +193,7 @@ bit difficult to do this race free.'>
                      hold here."
 
                     delay := nil.
-                    loop suspend]
+                    loopSem wait]
                 ifFalse: [
                     "either a timer has expired and we process it or we wait for the first item in
                     the queue to expire"
diff --git a/changes_for_pharo.st b/changes_for_pharo.st
index 3f43e61..c452aad 100644
--- a/changes_for_pharo.st
+++ b/changes_for_pharo.st
@@ -19,7 +19,8 @@ TimerScheduler extend [
         <category: 'PharoHacks'>
         loop ifNil: [^self].
         quit := true.
-        loop isSuspended ifTrue: [loop resume].
+        sem critical: [
+            loopSem ifNotNil: [loopSem signal]].
         delay ifNotNil: [:the_delay | the_delay signalWaitingProcess].
         processExited wait.
         Transcript