--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/EventSemaphore.st	Mon Dec 26 17:02:18 2016 +0100
@@ -0,0 +1,170 @@
+"
+ COPYRIGHT (c) 2016 by eXept Sofware AG
+              All Rights Reserved
+
+ This software is furnished under a license and may be used
+ only in accordance with the terms of that license and with the
+ inclusion of the above copyright notice.  This software may not
+ be provided or otherwise made available to, or used by, any
+ other person.  No title to or ownership of the software is
+ hereby transferred.
+"
+"{ Package: 'stx:libbasic' }"
+
+"{ NameSpace: Smalltalk }"
+
+Semaphore subclass:#EventSemaphore
+	instanceVariableNames:''
+	classVariableNames:''
+	poolDictionaries:''
+	category:'Kernel-Processes'
+!
+
+!EventSemaphore class methodsFor:'documentation'!
+
+copyright
+"
+ COPYRIGHT (c) 2016 by eXept Sofware AG
+              All Rights Reserved
+
+ This software is furnished under a license and may be used
+ only in accordance with the terms of that license and with the
+ inclusion of the above copyright notice.  This software may not
+ be provided or otherwise made available to, or used by, any
+ other person.  No title to or ownership of the software is
+ hereby transferred.
+"
+!
+
+documentation
+"
+    Processes wait for an EventSemaphores until it is signaled.
+    The EventSemaphore is not consumed and remains signaled until manually reset.
+
+    [author:]
+        Stefan Vogel
+
+    [see also:]
+        Semaphore
+"
+!
+
+example
+"
+    Create an event and signal it.
+    After being signaled waiter on the event return immediately.
+
+                                [exBegin]
+    |event|
+
+    event := EventSemaphore new.
+    [ event wait. Transcript showCR:'Process 1 continued' ] forkAt:9.
+    [ event wait. Transcript showCR:'Process 2 continued' ] forkAt:9.
+    event signal.
+    event wait.
+    event wait.
+                                [exEnd]
+"
+! !
+
+!EventSemaphore class methodsFor:'signaling'!
+
+new:n
+    "count must be 0 or 1"
+
+    (n == 0 or:[n == 1]) ifTrue:[
+        self new:n.
+    ].
+    ^ self error:'invalid count'.
+! !
+
+!EventSemaphore methodsFor:'blocked'!
+
+signalForAll
+    "blocked, since it would only set the event if there was anyone waiting"
+
+    ^ self shouldNotImplement.
+!
+
+signalIf
+    "blocked, since it would only set the event if there was anyone waiting"
+
+    ^ self shouldNotImplement.
+!
+
+waitWithTimeoutMs:milliSeconds state:waitStateSymbol
+    "blocked, since we had to re-implement it here"
+
+   ^ self shouldNotImplement
+! !
+
+!EventSemaphore methodsFor:'misc'!
+
+reset
+    "reset the event to the non-signaled state"
+
+    count := 0
+! !
+
+!EventSemaphore methodsFor:'semaphoreSet interface'!
+
+checkAndAddWaitingProcess:process
+    "interface for SemaphoreSet.
+     If the semaphore is available, return true.
+     Otherwise register our process to be wakened up once the semaphore is available
+     and return false.
+     ATTENTION: this must be invoked with OperatingSystem-interrupts-blocked.
+    "
+
+    count > 0 ifTrue:[
+        ^ true
+    ].
+    (waitingProcesses notNil and:[(waitingProcesses includesIdentical:process)]) ifFalse:[
+        self addWaitingProcess:process.
+    ].
+    ^ false
+
+    "Modified: / 14-12-1995 / 10:32:17 / stefan"
+    "Modified: / 11-08-2011 / 14:36:20 / cg"
+! !
+
+!EventSemaphore methodsFor:'signaling'!
+
+signal
+    "redefined to limit count to 1"
+
+    self signalOnce.
+! !
+
+!EventSemaphore methodsFor:'waiting'!
+
+wait
+    "once signaled, do not decrement the count"
+
+    self waitUncounted
+!
+
+waitWithTimeoutMs:milliSeconds
+    "wait for the semaphore, but abort the wait after some time.
+     return the receiver if the semaphore triggered normal, nil if we return
+     due to a timeout.
+     With zero timeout, this can be used to poll a semaphore (returning
+     the receiver if the semaphore is available, nil if not).
+     However, polling is not the intended use of semaphores, though.
+     If milliSeconds is nil, wait without timeout.
+
+     Redefined: once signaled, do not decrement the count"
+
+    ^ self waitUncountedWithTimeoutMs:milliSeconds.
+! !
+
+!EventSemaphore class methodsFor:'documentation'!
+
+version
+    ^ '$Header$'
+!
+
+version_CVS
+    ^ '$Header$'
+! !
+