semaphore concept Post: 302134159

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Top Forums UNIX for Advanced & Expert Users semaphore concept Post 302134159 by maverix on Wednesday 29th of August 2007 07:02:38 AM

08-29-2007

Registered User

Hi Jim and Neo,

Thank you for your replies...

I am using RHEL 4.
I have used lockf() and flock() system calls and it seems to work fine.

However, I want to use semaphores to get the same effect. FYI...I am doing these just to understand and learn the concepts. Its not a live/industry project.

Using lockf() and flock(), I was able to lock certain sections of files depending on the file position we provide. Say, for example, the application is a simple banking application and the database I use is a simple file which has number of records which contains account information. Using lockf(), I was able to lock a certain record by obtaining the account number from the user so that another process wanting to access a different record didn't have any issues in reading/writing to a different record.

My question was how to get the same effect using semaphores. If the number of concurrent processes are more, then each process will be waiting to obtain the semaphore to enter the critical section of code, isn't that so?

regards
maverix

maverix

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LEARN ABOUT SUNOS

semaphore.h

semaphore.h(3HEAD)						      Headers							semaphore.h(3HEAD)

NAME

       semaphore.h, semaphore - semaphores

SYNOPSIS

       #include <semaphore.h>

DESCRIPTION

       The  <semaphore.h>  header  defines  the sem_t type, used in performing semaphore operations. The semaphore can be implemented using a file
       descriptor, in which case applications are able to open up at least a total of {OPEN_MAX} files and semaphores. The  symbol  SEM_FAILED	is
       defined (see sem_open(3RT)).

       Inclusion  of  the <semaphore.h> header can make visible symbols defined in the headers <fcntl.h> and <sys/types.h>. See fcntl.h(3HEAD) and
       types.h(3HEAD).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fcntl.h(3HEAD), types.h(3HEAD),	sem_destroy(3RT),  sem_getvalue(3RT),  sem_init(3RT),  sem_open(3RT),  sem_post(3RT),  sem_timedwait(3RT),
       sem_unlink(3RT), sem_wait(3RT), attributes(5), standards(5)

SunOS 5.10							    10 Sep 2004 						semaphore.h(3HEAD)