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cleaning after programs crash.

Posted on 2000-04-03
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Last Modified: 2013-12-26
Hi,

I have a c program that uses sem_open() to create a semaphore and releases it before it exits.  But when my program crashes in the middle, the semaphore is hanging there since the program didn't get to the point where it releases the semaphore.

Can someone please tell me how I can handle this? How do I release the semaphore(or other type of resources) when programs abnormally stops?

Thanks in advance.

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Question by:samantha
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by:jlevie
ID: 2682039
You might could reduce the incidence of hanging semaphores by installing signal handlers for the common crash events (SIGABRT, SIGSEGV, SIGPIPE, etc). If the crash isn't so bad as to have destroyed the handler code, it can release the semaphore. Take a look at the manpages for signal(2) & signal(7).
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ufolk123 earned 300 total points
ID: 2682435
You can not do that if program is killed using SIGSTOP.So there is not a 100% failsafe method available to ensure the cleanup of hanging resources as Unix resources are not process wide.Ther generally do not reference counting associated with them.
If resources like semaphore are in use by only your application may be you can do the following.

Create a cleanup function.
Include it in shared library startup routine for your app ( please lokk compiler help for specification about how to add shared library init routine in your code).
Now this cleanup routine will get called before entry func of your app ( generally main) and can do the cleanup for your prev instance( For this to work use a pre-defined key in semget).

This way you can delay the cleanup up to next invokation of your application.
Otherwise create a starter program for your application running only the cleanup func and use it like this.


Starter program
{
create the main application
wait for app to exit using waitpid
call semctl(delete semaphore).
}


Pls get back for futher clarification.
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