About POSIX timer

scanner · 04-25-2007, 12:26 AM

For POSIX timer, we can get a timer ID by calling timer_create. After checked man, timer ID may be any value including zero. But when our guy mistake to call timer_delete with zero as timer ID, crash happen with timer_delete, as core dump file. Can anyone confirm the issue? In addition, we are using tool-chain v4.1.

jim mcnamara · 04-25-2007, 06:39 AM

The kernel uses an integer value to uniquely identify each new timer.
It starts counting and goes on. It is theoretically possible for the number to rollover, ie., 0xffffffff -> 0. I do not know if Linux kernels support this. Plus, this would require using a LOT of timers on a system that was up for a very long time.

If your code tries to access a non-existent timer, it will dump core. Is that what you're asking? You do realize that what you describe is a coding error, not a kernel problem.

scanner · 04-26-2007, 12:53 AM

Quote:

Originally Posted by jim mcnamara

The kernel uses an integer value to uniquely identify each new timer.
It starts counting and goes on. It is theoretically possible for the number to rollover, ie., 0xffffffff -> 0. I do not know if Linux kernels support this. Plus, this would require using a LOT of timers on a system that was up for a very long time.

If your code tries to access a non-existent timer, it will dump core. Is that what you're asking? You do realize that what you describe is a coding error, not a kernel problem.

First thanks for your reply.

In addition, as your reply, zero may be a timer ID. Am I right?

So, as man timer_delete, if a invalid timer ID is inputted like my case, a error code should be returned instead of crash. Actually I mistook to input zero as timer ID to timer_delete, i.e. I used a invalid timer ID, so a error code should be returned in such case. Is my understanding correct?

Kristofer · 04-26-2007, 01:54 AM

Hi scanner

Lets look at the following to start with:

int timer_create(clockid_t clockid, struct sigevent *restrict evp, timer_t *restrict timerid);

"If the call succeeds, timer_create() shall return zero and update the location referenced by timerid to a timer_t, which can be passed to the per-process timer calls. If an error occurs, the function shall return a value of -1 and set errno to indicate the error. The value of timerid is undefined if an error occurs."

It's the return value of timer_create you have to check before you try to use the timerid in timer_delete(), because if you pass an invalid timer id to timer_delete it might/will crash, not return an error.

Code:

pseudocode
int retvalue timer_create(..., ..., &timerid);
if(retvalue == -1)
{
   print the error
   maybe exit
}
else
{
  do something with the timer
  ...
  time to delete the timer
  retvalue = timer_delete(timerid);
  if(retval == -1)
  {
    print error message, e.g "Failed to delete timer"
  }
}

/Kristofer

scanner · 04-26-2007, 02:24 AM

So when EINVAL will be returned by timer_delete???

EINVAL : The timer ID specified by timerid is not a valid timer ID.

Kristofer · 04-26-2007, 03:37 AM

Yes according to man, timer_delete should return EINVAL, not crash (did you try to do anything else than timer_delete with the invalid timer?), (note: I haven't tried it myself).

Here is a good example of how to interface with the timer_* functions
http://www.google.com/codesearch?hl=...elete/1-2.c#a0

/Kristofer