When doing multithread programming, it is a best practice that a program should not finish its processing until all of its threads are finished as well.
In this article we provide a sample logic of how to check that all the threads started by a program are finished.
The first step is that when you call a thread, you add the thread handle of that call to a dynamic array similar to the following:
call thread "progA"
handle in W-Th
*> using... would go here
display "main: progA not found"
not on overflow
add 1 to max-progs
move W-Th to Prog-H-Thread(max-progs)
move "progA" to Prog-Name(max-progs)
Do the same for any thread started by the main program.
Then, the paragraph to wait for all the threads to finish will have an infinite loop where it keeps sending status messages to the threads to check if they are still alive, when the status returned is "10", it means the thread is no longer running.
Something like the following:
perform until 1 = 2
move 0 to ws-threads-running
perform varying idx-prog from 1> by 1
until idx-prog > max-progs
if Prog-H-Thread(idx-prog) not = null
wait for Prog-H-Thread(idx-prog)
status in StatusWait
if StatusWait = "10" |*> The thread does not exist anymore, it's not running
move spaces to Prog-Name(idx-prog)
move 0 to Prog-H-Thread(idx-prog)
add 1 to ws-threads-running |*> Thread's still running, count it as running
if ws-threads-running = 0
Please download the Zip file with a full sample of this.
That sample shows a main program starting 3 threads. Each program being called in a thread performs a very simple arithmetic operations a few hundred times. Each program will delay few seconds to finish.
Each program will perform during a different length of time.
Using an isCOBOL Shell command prompt window, compile and run the test with the is_test.bat batch script.
When you run the test, you should get a console output like the following:
> iscc *.cbl
> iscrun MAIN
main: Waiting for threads to finish ...
main: thread finished, program: progB
main: thread finished, program: progC
main: thread finished, program: progA
main: All threads are done, program finished !