Content-type: text/html Man page of msem_init

msem_init

Section: C Library Functions (3)
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NAME

msem_init - Initializes a semaphore in a mapped file or shared memory region  

LIBRARY

Standard C Library (libc.a)  

SYNOPSIS

#include <sys/mman.h>

msemaphore *msem_init (        msemaphore *sem,
       int initial_value );
 

PARAMETERS

Points to an msemaphore structure in which the state of the semaphore is stored. Determines whether the semaphore is locked or unlocked at allocation.  

DESCRIPTION

The msem_init() function allocates a new binary semaphore and initializes the state of the new semaphore.

If the initial_value parameter is MSEM_LOCKED, the new semaphore is initialized in the locked state. If the initial_value parameter is MSEM_UNLOCKED, the new semaphore is initialized in the unlocked state.

The msemaphore structure is located within a mapped file or shared memory region created by a successful call to the mmap() function and having both read and write access.

If a semaphore is created in a mapped file region, any reference by a process which has mapped the same file, using a (struct msemaphore *) pointer which resolves to the same file offset, is taken as a reference to the same semaphore. If a semaphore is created in an anonymous shared memory region, any reference by a process which shares the same region, using a (struct msemaphore *) pointer which resolves to the same offset from the start of the region, is taken as a reference to the same semaphore.

Any previous semaphore state stored in the msemaphore structure is ignored and overwritten.  

NOTES

Trial use  

RETURN VALUES

Upon successful completion, the msem_init() function returns a pointer to the initialized msemaphore structure. On error, the msem_init() function returns null and sets errno to indicate the error.  

ERRORS

If the msem_init() function fails, errno may be set to one of the following values: The initial_value parameter is not valid. A new semaphore could not be created.  

RELATED INFORMATION

Functions: mmap(2), msem_lock(3), msem_remove(3), msem_unlock(3) delim off


 

Index

NAME
LIBRARY
SYNOPSIS
PARAMETERS
DESCRIPTION
NOTES
RETURN VALUES
ERRORS
RELATED INFORMATION

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Time: 02:42:08 GMT, October 02, 2010