Help Needed : Race condition while removing semaphore(sysvsem semaphore)

[techi_C]

Hi
I'm getting a problem while removing semaphore from system.

Before removing semaphore I'm checking the usage count of a smaphore.

// checking usage count
usage_count = semctl(sem_ptr->semid, 1, GETVAL, NULL);
if( usage_count > 1 )
// return don't remove semaphore
else
// remove semaphore

If usage count is more than 1 then I'm not removing it.It means that at
this time there are more than one threads waiting for resource.

The problem is coming when after checking the usage_count = 1 if
usage_count becomes 2.
then problem is coming.This operation is not atomic.the usage_count
should not be 2 while removing semaphore.

Please anybody can tell me that How to avoid this problem.

Regards,
Pawan

 

[zhao.kaiyong]

Hi
I'm getting a problem while removing semaphore from system.

Before removing semaphore I'm checking the usage count of a smaphore.

// checking usage count
usage_count = semctl(sem_ptr->semid, 1, GETVAL, NULL);
if( usage_count > 1 )
// return don't remove semaphore
else
// remove semaphore

If usage count is more than 1 then I'm not removing it.It means that at
this time there are more than one threads waiting for resource.

The problem is coming when after checking the usage_count = 1 if
usage_count becomes 2.
then problem is coming.This operation is not atomic.the usage_count
should not be 2 while removing semaphore.

Please anybody can tell me that How to avoid this problem.

Regards,
Pawan

Can you tell me how do you use the semphore and the threads. I think
it's the problem about the thread.

 

[Richard Bos]

I'm getting a problem while removing semaphore from system.

Please anybody can tell me that How to avoid this problem.

Yes. Anybody in a newsgroup where semaphores are on topic can. They're
not ISO C, so they're off topic here.

Richard