Job Queue Desing Ideas?

[Michael Mattias]

In an an application I am developing (win/32, PB/DLL 6.0, SDK-style), I have a need to run a "batch" job, during which other work needs to be done.

My basic program structure is quite elementary:

Thread One = User interface (get file names, options, etc).
Thread Two = The "worker" thread, where all the batch work gets done; started when requested from thread one, posts messages back to thread one for progress bars and an 'all done' message.

But...

Because of data conflicts and dependencies, I can only run one "worker" thread at a time; consequently, I disable the ability of the user to submit a second job until the first job is completed. What I want to do now is allow the user to send multiple batch job requests and have them queue up, running one after the other.

I also want to be able to react to a "cancel jobs in queue" command by allowing the currently running batch job to complete, but not allowing any more to start.

I had a couple of thoughts about this, but they all seem kind of clunky . Example: my latest 'really good idea' involved starting a thread, which itself starts a third thread and waits for the third thread to conplete. That just seems weird to me - that is, NOT a 'really good idea.'

I worked with Mr Florent Heyworth's code from April 22, 2001 using the QueueUserAPC API function; that works really well, except I can't figure out how to "cancel" or "unqueue" a job once queued. (That code uses something like a callback to itself too; that is really confusing to me).

I'd like to avoid using a separate process because the 'worker' thread code is already set up to post those messages to Thread One. (Using a separate process was another one of my 'really good ideas' which flopped when I got to the part about the messages).

I was wondering if anyone had a ideas, notes, jottings, (psuedo-) code examples or just some thoughts as to where to look for a good way to queue up jobs. (I would not be surprised if I am missing the something really obvious, so don't be shy).

Thanks,


------------------
Michael Mattias
Racine WI USA
[email protected]

[Don Dickinson]

You could use a criticalsection to protect the entire thread ...

function worker_thread (whatever)

entercriticalsection CS
if g_AbortAllThreads then exit function

'- do the work

leavecriticalsection CS

end function


This would make it so only one thread would be "active" at one time. If after enteriing the critical section, the abort flag is set, it can just bail out - effectively cancelling all "waiting" threads.

Best Regards,
Don

------------------
dickinson.basicguru.com

[Florent Heyworth]

hi michael

for the nt/w2k platforms this example is an effective job queue -
have a look at http://www.powerbasic.com/support/pb...ad.php?t=23286

cheers

florent

------------------

[Michael Mattias]

I already tried your nice code; but I could not figure out if/how I could "unqueue" a job.

By the way, it works under Win 98 (Ist edition), too

MCM

[Michael Mattias]

Don, I had forgotten about Critical Sections as a synchronization object. (For some reason I thought they were only used for data protection).

I also took a call from a client this AM, and since I knew he did some multi-threaded stuff, I asked him. He suggested using a callback.

So...

I combined a critical section with a callback, and got this to work.

There is a PB/CC demo program in the source code section posted earlier today.

MCM