Re: WRKJOB ?

A thread is a smaller unit of "work" than a job.  It is very common in
the Windows and Unix worlds.

The good thing about threads is you can very easily share data and
communicate between threads.  Much easier than between Processes
(equivalent to a Job on the AS/400).

They are especially handy when you are doing a "server" type job.

The bad part of threads is that since it is so easy to share data
between threads of the same process (job)...it is also very easy to
corrupt that data.

Say thread 1 sets the value of an integer to 12....at the exact same
time (easy to do on a multi processor box), thread 2 reads that data.
What will it get?  Garbage.

Mutex's come to the rescue.  They allow threads to "synchronize".  In
the above scenario, thread 1 would first lock the mutex.  Thread 2
would attempt to lock the mutex but would not be able to until thread 1
released the mutex (after it had finished updating the data), thread 2
would then get the lock and the data.

Mutex's can also be used between processes.  Right now, you can do an
ALCOBJ on a file or data area.  Mutex's allow the same sort of thing
without an actual object on disk.

The main reason (but not the only) for Threads and Mutex's on the
AS/400 is to make porting code from the Unix and Windows world.

Hope this clears it up a little bit.

Bob

-----Original Message-----
From: Shen <ipacsjj@public.sta.net.cn>
To: midrange-l@midrange.com <midrange-l@midrange.com>
Date: Sunday, April 25, 1999 10:03 AM
Subject: WRKJOB ?


>
>When we use WRKJOB command, we often see two below
>selection.
>
>19. Work with mutexes, if active
>20. Work with threads, if active
>
>What it means about the mutex & thread?
>
>Thanks.
>
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