SIS in "real time"

[Heinz Junkes]

Hello Joel,
thanks for the program, but it doesn't change the (mis-) behavior under RTEMS?

I add a 3 seconds delay (sleep 3).

 clock_gettime( CLOCK_REALTIME, &now );
 printf("\nnow tv_sec = %d, tv_nsec = %d\n", now.tv_sec, now.tv_nsec);
 printf(" sleep 3 sec \n");
 sleep(3);
 clock_gettime( CLOCK_REALTIME, &now );
 printf("\nnow tv_sec = %d, tv_nsec = %d\n", now.tv_sec, now.tv_nsec);

The issue is related to the clock_gettime()

it "sorts" the values incorrectly:

now tv_sec = 6683109, tv_nsec = 567993600
 sleep 3 sec
now tv_sec = 10978989, tv_nsec = 567993603

on Unix:

now tv_sec = 1618027860, tv_nsec = 240887959
 sleep 3 sec

now tv_sec = 1618027863, tv_nsec = 241181294

Heinz


> On 9. Apr 2021, at 20:19, Joel Sherrill <joel at rtems.org> wrote:
> 
> Hi
> 
> I  made some changes to test3.c so it can be compiled for RTEMS or
> any "normal" POSIX host like Linux. I avoided the rtems timespec
> addition method.
> 
> I think this does what you expect on Linux but didn't try it on RTEMS.
> 
> FWIW this is a good minimal example of how a program can support
> being built for Linux and RTEMS. For bigger examples, I prefer the RTEMS
> configuration and Init thread to be in a separate file. I think the psx reporting
> examples do that.
> 
> --joel
> 
> On Fri, Apr 9, 2021 at 12:45 PM Heinz Junkes <junkes at fhi-berlin.mpg.de> wrote:
> Jiri, Joel, thanks for your answers.
> 
> @Joel: I was wondering that rtems-examples in psx_example_3 does not wait 3 seconds.
> 
> I made a curious observation:
> 
> in the original code:
> 
>    clock_gettime( CLOCK_REALTIME, &timeout );
>    timeout.tv_sec += 3;
>    timeout.tv_nsec = 0;
>    printf("The task is coming to enter in a timed wait\n");
>    pthread_cond_timedwait(&cond, &mutex, &timeout);
> 
> 
> I then inserted some printfs and found that the "3" is added to the nsec’s.
> 
> Then I added the rtems-timespec-helpers routines, but get the same behavior:
> 
> 
> void * print_hello(void * arg)
> {
>   struct timespec now, timeout;
>   rtems_timespec_set(&timeout, 3, 0);
> 
>   printf("<child>: Hello World! task with max priority \n");
>   clock_gettime( CLOCK_REALTIME, &now );
> printf("now tv_sec = %d, tv_nsec = %d\n", now.tv_sec, now.tv_nsec);
>   rtems_timespec_add_to(&timeout, &now);
> printf("timeout tv_sec = %d, tv_nsec = %d\n", timeout.tv_sec, timeout.tv_nsec);
>   printf("The task is coming to enter in a timed wait\n");
>   pthread_cond_timedwait(&cond, &mutex, &timeout);
>   printf("The task is coming out from the timed wait \n");
>   return NULL;
> }
> 
> program output:
> 
> <main> Enter in the main
> Creating first task
> <child>: Hello World! task with max priority
> now tv_sec = 4766459, tv_nsec = 567993600
> timeout tv_sec = 4766459, tv_nsec = 567993603
> The task is coming to enter in a timed wait
> The task is coming out from the timed wait
> First Task created
> Creating second task
>  <child>: Hello World! Task with lowest priority Second task created
> <main> Out of the main
> 
> If I now swap the arguments in the set-function , i.e. instead of
>  rtems_timespec_set(&timeout, 3, 0);
> 
>  rtems_timespec_set(&timeout, 0, 3);
> 
> it looks as it should
> 
> <child>: Hello World! task with max priority
> now tv_sec = 10766729, tv_nsec = 567993600
> timeout tv_sec = 10766732, tv_nsec = 567993600
> The task is coming to enter in a timed wait
> The task is coming out from the timed wait
> First Task created
> Creating second task
>  <child>: Hello World! Task with lowest priority Second task created
> <main> Out of the main
> 
> But still no timed wait  recognizable :-(
> 
> Heinz
> 
> 
> 
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> <test3.c>

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