Example for use of kernel semaphore Post: 101897

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Top Forums Programming Example for use of kernel semaphore Post 101897 by Rakesh Ranjan on Tuesday 14th of March 2006 06:02:05 AM

03-14-2006

Registered User

Example for use of kernel semaphore

Hi friends I'm doing a project and in that I need to use kernel semaphore but I'm not very clear about how to use it. I've used system V semaphore.
What I find difficult to understand is that in system V semaphore, a semaphore set is registered to the system (the semid returned from semget call is unique and can identify the semaphore set) allowing synchronisation between processes as against this in kernel semaphore it seems to me only a instance of structure semaphore needs to be created and up() and down() called upon it for synchronisation. But how can an instance of structure declared in one program be known in other program.

May be I'm thinking wrong way plz. rectify me if so and plz. show me an example how to use kernel semaphore.
Thanks in advance

Last edited by Rakesh Ranjan; 03-16-2006 at 05:01 AM..

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SEM_POST(3)						     Linux Programmer's Manual						       SEM_POST(3)

NAME

       sem_post - unlock a semaphore

SYNOPSIS

       #include <semaphore.h>

       int sem_post(sem_t *sem);

       Link with -pthread.

DESCRIPTION

       sem_post()  increments  (unlocks)  the  semaphore pointed to by sem.  If the semaphore's value consequently becomes greater than zero, then
       another process or thread blocked in a sem_wait(3) call will be woken up and proceed to lock the semaphore.

RETURN VALUE

       sem_post() returns 0 on success; on error, the value of the semaphore is left unchanged, -1 is returned, and errno is set to  indicate  the
       error.

ERRORS

       EINVAL sem is not a valid semaphore.

       EOVERFLOW
	      The maximum allowable value for a semaphore would be exceeded.

CONFORMING TO

       POSIX.1-2001.

NOTES

       sem_post() is async-signal-safe: it may be safely called within a signal handler.

EXAMPLE

       See sem_wait(3).

SEE ALSO

       sem_getvalue(3), sem_wait(3), sem_overview(7)

COLOPHON

       This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-05-13							       SEM_POST(3)

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