topic Re: Problems with simple threaded program in Operating System - OpenVMS

Problems with simple threaded program

Alex Chupahin — Sun, 09 Nov 2008 16:20:08 GMT

Hello!
Please help to point me to my error:

This is simple code:

#include
#include
#define NUM 5

main()
{
pthread_t t1,t2;

void *print_msg(void *);

pthread_create(&t1,NULL, print_msg, (void *)"hello");
pthread_create(&t2,NULL, print_msg, (void *)"world\n");
pthread_join(t1,NULL);
printf("end1\n");
pthread_join(t2,NULL);
}

void *print_msg(void *m)
{
char *s = (char *)m;

printf("%s",s);
fflush(stdout);
sleep(1);

printf("%s",s);
fflush(stdout);
sleep(1);

printf("%s",s);
fflush(stdout);
sleep(1);

printf("%s",s);
fflush(stdout);
sleep(1);

printf("%s",s);
fflush(stdout);
sleep(1);

return NULL;
}

Re: Problems with simple threaded program

Alex Chupahin — Sun, 09 Nov 2008 16:34:29 GMT

When I start it:
$ru simple

helloworld
helloworld
world
helloworld
helloworld
hello

and then program freezes. I can exit via ctrl-C only.
What I forget or doing wrong?

Re: Problems with simple threaded program

Jim_McKinney — Sun, 09 Nov 2008 17:10:21 GMT

I don't currently have access to a system to test but, from memory, I think you may need to call

pthread_exit(0);

just prior to your

return NULL;

in print_msg().

Re: Problems with simple threaded program

Alex Chupahin — Sun, 09 Nov 2008 17:36:56 GMT

Thank you, but during experimentation, I have added pthread_exit function before return. Without success.

Re: Problems with simple threaded program

John Gillings — Sun, 09 Nov 2008 20:19:25 GMT

Alex,

what are you expecting the main program to do while the threads are running? I wouldn't expect this program to hang, I'd expect it to just exit (like the code says). Maybe you need a sleep before the end? First cut I'd add sleep(10) after the second pthread_join so you know the main thread will still be around when the threads complete. Better would be to use the pthread routine to synchronize with the completions of each executing thread.

What about the printf in main? Should that have an fflush too?

Re: Problems with simple threaded program

Alex Chupahin — Sun, 09 Nov 2008 20:24:38 GMT

John I expect my program will be successfully finished and exit. But it doesnt. I should press ctrl-C to exit. printf() in main() between pthread_join is not working.

Re: Problems with simple threaded program

Hoff — Sun, 09 Nov 2008 23:23:51 GMT

LINK /THREAD=UP

Re: Problems with simple threaded program

Alex Chupahin — Mon, 10 Nov 2008 07:14:43 GMT

Thank you, Hoff!

Re: Problems with simple threaded program

Ruslan R. Laishev — Mon, 10 Nov 2008 09:40:39 GMT

Hi, Alex!

First at all you need to be ensure that the treads has been created with JOINABLE attributes (a default JOINABLE/DETACHED attribute depends frov OS version and platform).

I suggest to check threads state with SDA:
ana/sys
SDA>set proc /id=
SDA>pthread thread [-f]

sleep() - is not reenterable routine, you should use pthread_delay_np()

Re: Problems with simple threaded program

EdgarZamora_1 — Mon, 10 Nov 2008 14:26:17 GMT

Hoff that was your shortest reply ever and it was worth 10 points a character! lol

Re: Problems with simple threaded program

Alex Chupahin — Tue, 11 Nov 2008 06:11:44 GMT

Spasibo, Ruslan!
Eto tozhe vazhno.

Re: Problems with simple threaded program

Ruslan R. Laishev — Tue, 11 Nov 2008 07:29:09 GMT

Hi, Alex!

Using link/thread=(upcalls[,mult]) is not essential for normal behaviour of threads. :-)

Re: Problems with simple threaded program

Hoff — Tue, 11 Nov 2008 14:48:40 GMT

If we're exchanging aphorisms, remember that thread-safe is an oxymoron. And that per-thread security probably isn't.

And slightly more seriously, having $hiber and $wake flying around in any application can snarl an AST-driven or a thread-based program.

Re: Problems with simple threaded program

Ruslan R. Laishev — Tue, 11 Nov 2008 14:50:36 GMT

Agreed. :-)

Re: Problems with simple threaded program

GuentherF — Tue, 11 Nov 2008 23:25:34 GMT

Without the LINK/THREAD=UPCALLS the the threads interfere with each others sleep(). Eventually one $WAKE is lost and the process hange in HIB. Check the return value from sleep(). It's not always 0 meaning the sleep() returned earlier. That's the $WAKE (part of the sleep() implementation) that finally is missing.

/Guenther

Re: Problems with simple threaded program

Hoff — Tue, 11 Nov 2008 23:54:56 GMT

Back when I was more regularly tossing $hiber and $wake calls and ASTs around (and this was back in the era when the debugger itself would interfere with $hiber and $wake), a periodic $schdwk was a handy thing to have chugging along in the background. This was a deliberately-induced spurious wake-up, and it did tend to unwedge things until you could figure out what really happened.

(This all seems so primitive now. Ah, well.)

Re: Problems with simple threaded program

Willem Grooters — Wed, 12 Nov 2008 11:09:04 GMT

$HIBER / $WAKE in a multi-threaded program: Isn't that asking for trouble? IIRC, it used to be discouraged; but things may have chnaged in the years...