Tried to come up with a text for the documentation for the EventSemaphore class.
Please check the raildiagrams and descriptions for the methods.
Also please note that the example got simplified in the formatting somewhat
(e.g. the date portion
is not used anymore, making the output better legible and also will not "age"
because in five years
the dates look "outdated").
Any errors and/or bad English are mine only!
;)
Please let me know whether this is helpful or not. If so, I will try to come up
with the text for
the MutexSemaphore class in the next days.
Here it goes:
===============================================================================
5.4.x EventSemaphore Class
Semaphores get used in multithreaded scenarios.
An "event semaphore" allows one thread "A" to synchronize multiple threads
(like "B", "C", ...) with whom the event semaphore gets shared. Thread
"A" creates the event semaphore and sends it the "reset" message. Then
thread "A" supplies the event semaphore to the threads "B", "C", ...,
which each send the received event semaphore a "wait" message. This will
block the threads "B", "C", ..., until thread "A" sends the "post" message
to the event semaphore. At this time all threads waiting on the event
semaphore get released and can run in parallel on their threads.
5.4.x.1 close
>>--- close ---><
Closes the event semaphore.
5.4.x.2 isPosted
>>--- isPosted ---><
Returns .true if the event semaphore is in the "posted" state, such that
sending the "wait" message to this event semaphore would return
immediately. A return value of .false indicates that the event semaphore
is not in the "posted" state, such that a "wait" message will block.
5.4.x.2 post
>>--- post ---><
Sets the event semaphore to the "posted" state, signalling that the event
that other threads are waiting on has occurred, such that all threads
waiting on this event semaphore will be released and start to run again.
5.4.x.3 reset
>>--- reset ---><
Resets (clears) the event semaphore to the non-"posted" state, such that
"wait"
messages to this event semaphore will block.
5.4.x.4 uninit
>>--- uninit ---><
This method cleans up the object when it is garbage collected. It should
not be invoked directly except via an uninit method of a subclass of the
EventSemaphore class.
5.4.x.5 wait
>>--- wait(--+-------------+--)---><
| |
+-- timeout --+
Waits (blocks) on the event semaphore until it gets "posted". If
"timeout" was supplied it must be a whole number that represents the
milliseconds to wait on the event semaphore before returning.
If no "timeout" value was supplied or its value is negative, the wait will
be forever, ie. until the event semaphore gets posted.
If the "timeout" value is zero the method returns immediately with the
same value that the method "isPosted" would return if sent to the event
semaphore instead.
The method returns .true if the event semaphore got "posted", .false if
the method returns prematurely because the given timeout has occurred.
Example 5.xxx
The following example will fetch the routine object "WORKER" and in a loop
will send the routine object the message "start" (defined in the ooRexx
root class "Object") supplying the message name ("call") to be sent on a
new (asynchroneous) thread, and as arguments the event semaphore to wait
on and the number of the loop for the respective asynchroneous message.
The main program creates an event semaphore and sends the message "reset"
to it. Then it sends the "start" message three times to the routine
object in the loop, causing the routine "worker" to run on three different
threads, where in each thread the executed routine then waits on the event
semaphore ("wait" message to the event semaphore). The main program then
sleeps for five seconds, before sending the "post" message to the event
semaphore, which will awake the routines on the three threads, ie. they
return from the wait message and execute on their threads in parallel,
causing each to sleep for two seconds before returning from the routine
invocation.
<code>
eventSem=.eventSemaphore~new -- create an event semaphore, will be
in posted state
dt=.dateTime~new -- a .DateTime object to allow measuring
elapsed time
say "/main\ " pp(dt~elapsed) "currently 'eventSem~isPosted':"
pp(eventSem~isPosted)
eventSem~reset -- reset event semaphore, such that "wait"
will block
say "/main\ " pp(dt~elapsed) "after 'eventSem~reset',
'eventSem~isPosted':" pp(eventSem~isPosted)
w=.routines~waiter -- get routine 'WAITER' as a routine object
do i=1 to 3
say "/main\ " pp(dt~elapsed) "running routine 'WAITER' #"
pp(i) "asynchroneously"
w~start("call", eventSem, i) -- call (run) the routine object
on a separate thread
end
say
sleepTime=5
say "/main\ " pp(dt~elapsed) "sleeping" pp(sleepTime)
"seconds ..."
call sysSleep sleepTime -- sleep five seconds
say "/main\ " pp(dt~elapsed) "awoke, about doing an
'eventSem~post' ..."
say
eventSem~post -- wake up all threads waiting on this event
semaphore
say "\main/ " pp(dt~elapsed) "--> leaving main, other threads
may still be active!"
::routine waiter -- this routine will be called on a separate
thread
use arg eventSem, nr
s=.dateTime~new -- we use our own .DateTime object to measure
elapsed time on this thread
say .context~name" #" nr":" pp(s~elapsed) "arrived,
eventSem~isPosted="pp(eventSem~isPosted)", waiting..."
eventSem~wait -- wait until main program posts this event
semaphore
sleepTime=2
say .context~name" #" nr":" pp(s~elapsed) "wait over,
'eventSem~isPosted':" pp(eventSem~isPosted)
say .context~name" #" nr":" pp(s~elapsed) "now sleeping"
pp(sleepTime) "second(s)"
call syssleep sleeptime -- sleep a second
o=.dateTime~new
say .context~name" #" nr":" pp(s~elapsed) "sleep over"
::routine pp -- "pretty print" ;) (encloses argument in
square brackets)
return "["arg(1)"]"
</code>
Running this program may yield the following output:
<code>
/main\ [00:00:00.000000] currently 'eventSem~isPosted': [1]
/main\ [00:00:00.015000] after 'eventSem~reset',
'eventSem~isPosted': [0]
/main\ [00:00:00.015000] running routine 'WAITER' # [1]
asynchroneously
/main\ [00:00:00.015000] running routine 'WAITER' # [2]
asynchroneously
WAITER # 1: [00:00:00.000000] arrived, eventSem~isPosted=[0],
waiting...
/main\ [00:00:00.015000] running routine 'WAITER' # [3]
asynchroneously
WAITER # 2: [00:00:00.016000] arrived, eventSem~isPosted=[0],
waiting...
WAITER # 3: [00:00:00.000000] arrived, eventSem~isPosted=[0],
waiting...
/main\ [00:00:00.047000] sleeping [5] seconds ...
/main\ [00:00:05.054000] awoke, about doing an 'eventSem~post'
...
\main/ [00:00:05.054000] --> leaving main, other threads may
still be active!
WAITER # 2: [00:00:05.039000] wait over, 'eventSem~isPosted': [1]
WAITER # 1: [00:00:05.039000] wait over, 'eventSem~isPosted': [1]
WAITER # 3: [00:00:05.023000] wait over, 'eventSem~isPosted': [1]
WAITER # 2: [00:00:05.055000] now sleeping [2] second(s)
WAITER # 1: [00:00:05.055000] now sleeping [2] second(s)
WAITER # 3: [00:00:05.039000] now sleeping [2] second(s)
WAITER # 3: [00:00:07.067000] sleep over
WAITER # 1: [00:00:07.083000] sleep over
WAITER # 2: [00:00:07.083000] sleep over
</code>
---rony
_______________________________________________
Oorexx-devel mailing list
Oorexx-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/oorexx-devel
