"
 COPYRIGHT (c) 1995 by Stefan Vogel / Claus Gittinger
              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.
"


IdentitySet subclass:#SemaphoreSet
	instanceVariableNames:''
	classVariableNames:''
	poolDictionaries:''
	category:'Kernel-Processes'
!

!SemaphoreSet class methodsFor:'documentation'!

copyright
"
 COPYRIGHT (c) 1995 by Stefan Vogel / Claus Gittinger
              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
"
    SemaphoreSets allow waiting until one of several semaphores becomes available.
    They provide a waiting protocol which is compatible to Semaphore, 
    i.e. #wait and #waitWithTimeOut.

    [see also:]
        Semaphore
        Process ProcessorScheduler

    [author:]
        Stefan Vogel
"
!

examples
"
 the following example forks a process which waits on any
 of sema1, sema2 to be signalled. The main thread signals those.
 ---------------------------------------------------------------
                                                                        [exBegin]
    |sema1 sema2 semaSet proc|

    sema1 := Semaphore new.
    sema2 := Semaphore new.
    semaSet := SemaphoreSet with:sema1 with:sema2.

    proc := [
        [
            |ret name|

            ret := semaSet wait.
            ret == sema1 ifTrue:[
                name := 'sema1'
            ] ifFalse:[ 
                ret == sema2 ifTrue:[
                    name := 'sema2'
                ]
            ].
            Transcript showCR: name, ' raised'.
            ret == sema2 ifTrue:[
                proc terminate
            ]
        ] loop
    ] fork.

    (Delay forSeconds:3) wait.
    sema1 signal.
    (Delay forSeconds:3) wait.
    sema2 signal.
                                                                        [exEnd]


 the following example forks a process which waits on any
 of sema1, sema2 to be signalled, or a timeout to occur.
 ---------------------------------------------------------------
                                                                        [exBegin]
    |sema1 sema2 semaSet proc|

    sema1 := Semaphore new.
    sema2 := Semaphore new.
    semaSet := SemaphoreSet with:sema1 with:sema2.

    proc := [
        [
            |ret name|

            ret := semaSet waitWithTimeout:5.
            ret == sema1 ifTrue:[
                name := 'sema1'
            ] ifFalse:[ 
                ret == sema2 ifTrue:[
                    name := 'sema2'
                ] ifFalse:[
                    name := ret printString
                ]
            ].
            Transcript showCR: name, ' raised'.
            ret isNil ifTrue:[
                proc terminate
            ]
        ] loop
    ] fork.

    (Delay forSeconds:3) wait.
    sema1 signal.
    (Delay forSeconds:3) wait.
    sema2 signal.
                                                                        [exEnd]



 the following example forks a process which waits on input
 to arrive on any of 2 sharedQueues (with timeout)
 The main thread writes data into those queues.
 ---------------------------------------------------------------
                                                                        [exBegin]
    |q1 q2 semaSet proc|

    q1 := SharedQueue new.
    q2 := SharedQueue new.
    semaSet := SemaphoreSet with:(q1 readSemaphore) with:(q2 readSemaphore).

    proc := [
        [
            |ret whatHappened|

            ret := semaSet waitWithTimeout:5.
            ret == q1 readSemaphore ifTrue:[
                Transcript show:'q1 has data: '; show:q1 next; cr.
            ] ifFalse:[ 
                ret == q2 readSemaphore ifTrue:[
                    Transcript show:'q2 has data: '; show:q2 next; cr.
                ] ifFalse:[
                    Transcript showCR:'timeout'
                ]
            ].
        ] loop
    ] fork.

    (Delay forSeconds:3) wait.
    q1 nextPut:'one'.
    (Delay forSeconds:2) wait.
    q1 nextPut:'two'.
    (Delay forSeconds:2) wait.
    q1 nextPut:'three'.
    (Delay forSeconds:6) wait.
    proc terminate.
                                                                        [exEnd]
"
! !

!SemaphoreSet methodsFor:'wait'!

wait
    "wait for any of the semaphores in the set to be signalled.
     Return the (first) semaphore which is triggered."

    |currentProcess gotSema wasBlocked registeredAllSemas|

    currentProcess := Processor activeProcess.
    registeredAllSemas := false.

    wasBlocked := OperatingSystem blockInterrupts.
    [
        [
            gotSema := self detect:[:sema|
                sema checkAndRegisterProcess:currentProcess
            ] ifNone:[
                registeredAllSemas := true.
                currentProcess suspendWithState:#wait.
                nil
            ].
        ] doWhile:[gotSema isNil].

        "
          we finaly got at least one of our semaphores.
          Now unregister from any semaphore, we are registered on.
        "
        self detect:[:sema|
            (sema == gotSema) ifTrue:[
                registeredAllSemas not        
            ] ifFalse:[        
                sema unregisterProcess:currentProcess.
                false
            ]
        ] ifNone:[].
    ] valueNowOrOnUnwindDo:[
        wasBlocked ifFalse:[OperatingSystem unblockInterrupts].
        self do:[:aSema |
            aSema unregisterProcess:currentProcess.
        ]
    ].

    ^ gotSema

    "Modified: 15.12.1995 / 23:10:07 / stefan"
    "Modified: 20.8.1997 / 18:33:09 / cg"
!

waitWithTimeout:seconds
    "wait for any of the the semaphore, but abort the wait after some time.
     Return the (first) triggered semaphore if any, nil if we return due to a timeout."

    |currentProcess gotSema wasBlocked now endTime unblock timeoutOccured registeredAllSemas|

    currentProcess := Processor activeProcess.
    timeoutOccured := false.
    registeredAllSemas := false.

    wasBlocked := OperatingSystem blockInterrupts.
    [
        seconds notNil ifTrue:[
            "
             calculate the end-time
            "
            now := OperatingSystem getMillisecondTime.
            endTime := OperatingSystem millisecondTimeAdd:now and:(seconds * 1000).

            unblock := [timeoutOccured := true. Processor resume:currentProcess].
            Processor addTimedBlock:unblock for:currentProcess atMilliseconds:endTime.
        ].

        [
            gotSema := self detect:[:sema|
                sema checkAndRegisterProcess:currentProcess
            ] ifNone:[
                registeredAllSemas := true.
                currentProcess suspendWithState:#wait.
                nil
            ].
        ] doWhile:[gotSema isNil and:[timeoutOccured not]].

        (timeoutOccured not and:[unblock notNil]) ifTrue:[
            Processor removeTimedBlock:unblock.
        ].

        "
          we finaly got at least one of our semaphores.
          Now unregister from any semaphore, we are registered on.
        "
        self detect:[:sema|
            (sema == gotSema) ifTrue:[
                registeredAllSemas not        
            ] ifFalse:[        
                sema unregisterProcess:currentProcess.
                false
            ]
        ] ifNone:[].
    ] valueNowOrOnUnwindDo:[
        wasBlocked ifFalse:[OperatingSystem unblockInterrupts].
        self do:[:aSema |
            aSema unregisterProcess:currentProcess.
        ]
    ].
    ^ gotSema

    "Modified: 15.12.1995 / 23:10:54 / stefan"
    "Modified: 20.8.1997 / 18:33:23 / cg"
! !

!SemaphoreSet class methodsFor:'documentation'!

version
    ^ '$Header: /cvs/stx/stx/libbasic/SemaphoreSet.st,v 1.11 1997-08-20 16:39:12 cg Exp $'
! !