Class: EventSemaphore

• Inheritance
• Description
• Class protocol
  • signaling
• Instance protocol
  • blocked
  • misc
  • semaphoreSet interface
  • signaling
  • waiting

Inheritance:

   Object
   |
   +--AbstractLock
      |
      +--Semaphore
         |
         +--EventSemaphore

Package:

stx:libbasic

Category:

Kernel-Processes

Version:

rev: 1.9 date: 2021/01/20 12:58:21

user: cg

file: EventSemaphore.st directory: libbasic

module: stx stc-classLibrary: libbasic

Description:

Processes wait for an EventSemaphores until it is signaled.
The EventSemaphore is not consumed and remains signaled until manually reset.

copyright
COPYRIGHT (c) 2016 by eXept Software 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.

example
Create an event and signal it.
After being signaled, the waiter on the event returns 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]

Class protocol:

 new: n

count must be 0 or 1

Instance protocol:

 signalForAll

blocked, since it would only set the event if there was anyone waiting

 signalIf

blocked, since it would only set the event if there was anyone waiting

 reset

reset the event to the non-signaled state

 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.

 signal

redefined to limit count to 1

 wait

once signaled, do not decrement the count

 waitWithTimeoutMs: milliSeconds state: newState

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