Bob,

I had already implemented a rough class before I read your
message :-(. I have just filed in your class and it looks great.
I will post a revised events system incorporating
recursive semaphores in the next day or so. I just need to
check that it all runs robustly....

Cheers

Peter



On Fri, 28 May 1999 10:17:46 +0930 "Peter Smet" <peter.smet at flinders.edu.au>
wrote:
>It would be good to have a "smart semaphore" that forced
>outside callers to wait, but let self invoke multiple invocations
>of a message. I would appreciate it if someone could point
>out some code to identify if the invoker of the currently
>executing message is self or not.....

Hi Peter,

You could try something like the code below.

Cheers,
Bob

'From Squeak 2.3 of January 14, 1999 on 29 May 1999 at 1:53:30 pm'!
"Change Set: RecursiveSema
Date: 29 May 1999
Author: Bob Arning

I am a variation of the conventional Semaphore that allows consecutive waits
without intervening signals to proceed as long as the process which issues
the subsequent waits is the one which issued the first wait. This will
permit recursive (or other) routines to exclude other processes from a block
of code while allowing the current process to keep running. As soon as the
number of signals equals the number of waits, another process may proceed.

Test examples are included as class methods."!

Object subclass: #RecursiveSemaphore
instanceVariableNames: 'holdingProcess waitCount semaphore '
classVariableNames: ''
poolDictionaries: ''
category: 'Kernel-Processes'!

!RecursiveSemaphore commentStamp: '<historical>' prior: 0!
I am a variation of the conventional Semaphore that allows consecutive waits
without intervening signals to proceed as long as the process which issues
the subsequent waits is the one which issued the first wait. This will
permit recursive (or other) routines to exclude other processes from a block
of code while allowing the current process to keep running. As soon as the
number of signals equals the number of waits, another process may proceed.

Test examples are included as class methods.!

!RecursiveSemaphore methodsFor: 'as yet unclassified' stamp: 'RAA 5/29/1999
13:27'!
critical: mutuallyExcludedBlock
"Evaluate mutuallyExcludedBlock only if the receiver is not currently in
the process of running the critical: message. If the receiver is, evaluate
mutuallyExcludedBlock after the other critical: message is finished."

| blockValue |
self wait.
blockValue _ mutuallyExcludedBlock value.
self signal.
^blockValue! !

!RecursiveSemaphore methodsFor: 'as yet unclassified' stamp: 'RAA 5/29/1999
13:14'!
forMutualExclusion

semaphore _ Semaphore forMutualExclusion.
waitCount _ 0.! !

!RecursiveSemaphore methodsFor: 'as yet unclassified' stamp: 'RAA 5/29/1999
13:20'!
signal

waitCount _ waitCount - 1.
waitCount <= 0 ifTrue: [
holdingProcess _ nil.
waitCount _ 0.
semaphore signal
].
! !

!RecursiveSemaphore methodsFor: 'as yet unclassified' stamp: 'RAA 5/29/1999
13:12'!
wait

holdingProcess == Processor activeProcess ifFalse: [
semaphore wait.
waitCount _ 0.
holdingProcess _ Processor activeProcess.
].
waitCount _ waitCount + 1.
! !


!RecursiveSemaphore class reorganize!
('instance creation' forMutualExclusion)
('test example' reportAndWait: test test1: test2: test3: test4:)
!


!RecursiveSemaphore class methodsFor: 'instance creation' stamp: 'RAA
5/29/1999 13:14'!
forMutualExclusion

^self new forMutualExclusion! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:04'!
reportAndWait: aString

Transcript show: 'process = ',Processor activeProcess hash printString,
'  method = ',aString; cr.
(Delay forSeconds: 1) wait.
! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:34'!
test
"
RecursiveSemaphore test
"
| semaphore |
semaphore _ self forMutualExclusion.
3 timesRepeat: [self test1: semaphore].! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:34'!
test1: semaphore

[
self reportAndWait: 'test1'.
self test2: semaphore.
] fork.! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:35'!
test2: semaphore

semaphore critical: [
self reportAndWait: 'test2'.
self test3: semaphore.
].! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:35'!
test3: semaphore

semaphore critical: [
self reportAndWait: 'test3'.
self test4: semaphore.
].! !

!RecursiveSemaphore class methodsFor: 'test example' stamp: 'RAA 5/29/1999
13:35'!
test4: semaphore

semaphore critical: [
self reportAndWait: 'test4'.
].! !