Semaphore example (Windows Regina)

[Arthur T.]

Earlier, I had asked for any examples of using semaphores. None were
forthcoming. As suggested, I e-mailed Mr. McPhee. He sent me very useful
sample code, but didn't specifically say I could publicly post his samples.

Using his samples, though, I was able to determine what I was doing
wrong. So that the next person to search will find something, here is the
code I came up with. They don't do anything particularly useful except to
prove that the semaphore code works correctly.

SemServ.rex:

/*REXX exec to play around with semaphores before doing it for real */

/* Standard entry code */
arg temp1
do while temp1 \= ''
parse var temp1 temp2 temp1
if right(temp2,1) = ')' then
temp2 = translate(temp2,'= ','()')
if pos('=',temp2) = 0 then temp2 = temp2 || '= ""'
interpret temp2
end
drop temp1
drop temp2
if debug = 'TRACE' then trace ?i
else if debug \= "DEBUG" then trace i
/* */

call rxfuncadd 'sysloadfuncs','RexxUtil','sysloadfuncs'
call sysloadfuncs

numCli = 10 /* number of clients to start */

mutexHandle = syscreatemutexsem('semtest')
if mutexhandle = '' then
do
say 'Error creating Mutex semaphore'
exit 8
end

do i = 1 to numcli
eventHandle.i = syscreateeventsem(i)
if eventhandle = '' then
do
say 'Error creating Event semaphore' i
exit 8
end

"start /B semcli" i
end

do i = numcli to 1 by -1 /* wait for them in reverse order of starting */
x = syswaiteventsem(eventhandle.i,15000)
if x <> 0 then say 'Event' i 'did not finish.'
end

say 'End of Serv'
exit 0

SemCli.rex:

/*REXX exec to play around with semaphores before doing it for real */

/* Standard modified entry code */
arg cli# temp1
do while temp1 \= ''
parse var temp1 temp2 temp1
if right(temp2,1) = ')' then
temp2 = translate(temp2,'= ','()')
if pos('=',temp2) = 0 then temp2 = temp2 || '= ""'
interpret temp2
end
drop temp1
drop temp2
if debug = 'TRACE' then trace ?i
else if debug \= "DEBUG" then trace i
/* */

call rxfuncadd 'sysloadfuncs','RexxUtil','sysloadfuncs'
call sysloadfuncs

datafile = 'f:\semtest.dat'

mutexHandle = sysopenmutexsem('semtest')
if mutexhandle = '' then
do
say 'Error Opening Mutex semaphore in client #' cli#
exit 8
end

eventHandle = sysopeneventsem(cli#)
if eventhandle = '' then
do
say 'Error creating Event semaphore in client #' cli#
exit 8
end

n = random(1,10)
x = sleep(n) /* simulate doing 1 to 10 seconds worth of work */

/*
deliberately choose a wait time low enough that at least one
will fail, usually. This IS for testing, after all.
*/
x = sysrequestmutexsem(mutexhandle, 1000)
if x = 0 then
do
do i = 1 to 5
call lineout datafile, right(i,3) 'From client' right(cli#,3)
end
call stream datafile, 'c', 'close'
x = sleep(1)
x = sysreleasemutexsem(mutexhandle)
end
else
do
say 'Could not get exclusive use in client #' cli#
end

x = sysposteventsem(eventhandle)
say 'End of Client #' cli#
exit 0

--
Arthur T. - ar23hur "at" intergate "dot" com
Looking for a z/OS (IBM mainframe) systems programmer position