NAME

msem_init − Initialize a semaphore in a mapped file or shared memory region

SYNOPSIS

#include <sys/mman.h>
msemaphore ∗msem_init(
        msemaphore ∗sem ,
        int initial_value );

LIBRARY

Standard C Library (libc)

PARAMETERS

semPoints to an msemaphore structure in which the state of the semaphore is stored. 

initial_value
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

AES Support Level:
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:

[EINVAL]
The initial_value parameter is not valid. 

[ENOMEM]
A new semaphore could not be created.

SEE ALSO

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