tempest@csuchico.uucp (Kenneth Lui) (04/28/89)
I'm just getting the feel of Occam 2 on TDS2. I"ve written some simple SEQtype programs and some ALTtype programs. I'm having some problems with PAR structures. Specifically, I want to write a section of code that would allow two or more parallel processes to output to the screen concurrently. I wanted to see if the output of one process within of a PAR structure would be intermixed with another process. I used the following code fragment: ... PAR SEQ write.full.string(screen,"String from 'a'") newline(screen) SEQ write.full.string(screen,"String from 'b'") newline(screen) ... Needless to say, it doesn't work. All I got was a big blank from the VDT, except one carriagereturn or linefeed. I looked through the example programs in the c:\tdsxampl subdirectory and it uses other predefined functions in c:\tdsiolib\interf.tsr. Hunting through the documentation (which I have limited access to), I read the section that talked about interf.tsr; but it's all greek to me. I kludged around with the functions mentioned, but all my experiments went down the drain... Can somebody offer some hints as to how I might accomplish the above using either userio.tsr, or both userio.tsr and interf.tsr? Thanks very much, Ken tempest@csuchico.EDU
Link_-_APO@cup.portal.com (04/29/89)
One way to solve your problem is to create a multiplexor. As the name implied,
the multiplexor will "ALT"ternate between two or more input screen channels
and writes the output to the "real" screen channel one at a time. This
prevents processes from overriding data to the screen channel.
You can write the multiplexor using the ALT construct,such as,
SEQ
WHILE continue
PRI ALT
quit ? any
SEQ
continue :=FALSE
ALT i=0 FOR n
... process input screen channels
Or you could use the scrstream.multiplexor PROC from INMOS-TDS by including:
"#USE interf" statement in your occam program.
Ahn Nuzen
Link Flight Simulation
link_apo@cup.portal.comian@uowcsa.cs.uow.oz (Ian Gorton) (05/01/89)
In article <1989Apr27.120625.5348@csuchico.uucp>, tempest@csuchico.uucp (Kenneth Lui) writes: > I'm just getting the feel of Occam 2 on TDS2. I"ve written some simple > SEQtype programs and some ALTtype programs. I'm having some problems > with PAR structures. Specifically, I want to write a section of code that [deleted] > I used the following code fragment: > ... > PAR > SEQ > write.full.string(screen,"String from 'a'") > newline(screen) > SEQ > write.full.string(screen,"String from 'b'") > newline(screen) > ... > > Needless to say, it doesn't work. All I got was a big blank from the VDT, > except one carriagereturn or linefeed. I looked through the example Yeah, the reason is that you're breaking one of the fundamental laws of occam channels. You are attempting to write to the screen channel from TWO processes simultaneously. This is not allowed, as each channel may only have one process outputting to it, and one inputting from it. A library routine is your solution, it's documented in the PROGRAMMING INTERFACE section of the TDS manuals. The library process you need is called 'scrstream.multiplexor': it essentially multiplexes output from a number of channels onto the 'real' screen channel. This sort of process is frequently required in occam programs. So, to solve your problem you need, [2]CHAN OF ANY scr: CHAN OF INT stop: -- to terminate multiplexor PAR scrstream.multiplexor(scr, screen, stop) SEQ PAR SEQ write.full.string(scr[0], " whatever") newline(scr[0]) SEQ write.full.string(scr[1], "something else") newline(scr[0]) stop ! 22 -- send any value to terminate multiplexor The added complications come about because it's necessary to terminate the multiplexor process, and the signal to do this ( stop ! 22 ) must be sent after EVERYTHING has been sent to the screen. It should work! Don't forget to include the libraries. Good luck, Ian Gorton