sem_init(3)						     Library Functions Manual						       sem_init(3)

NAME

       sem_init - Initializes an unnamed semaphore (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

       int sem_init (
       sem_t *sem,
       int pshared,
       unsigned int value);

PARAMETERS

       sem	   Specifies a location to receive the descriptor of the initialized semaphore.

       pshared Specifies a value indicating whether the semaphore should be sharable between processes (non-zero value) or not (zero).

       value   Specifies the initial value to be given to the semaphore.

DESCRIPTION

       The  sem_init function creates a new counting semaphore with a specific value.  A semaphore is used to limit access to a critical resource.
       When a process requires access to the resource without interference from other processes, it attempts to establish a  connection  with  the
       associated semaphore.  If the semaphore value is greater than zero, the connection is established and the semaphore value is decremented by
       one.  If the semaphore value is less than or equal to zero, the process attempting to access the resource is  blocked  and  must  wait  for
       another process to release the semaphore and increment the semaphore value.

       The  sem_init function establishes a connection between an unnamed semaphore and a process; the sem_wait and sem_trywait functions lock the
       semaphore; and the sem_post function unlocks the semaphore.  Use the sem_destroy function to deallocate system resources allocated  to  the
       process for use with the semaphore.  You can use the sem_getvalue function to obtain the value of a semaphore.

       A semaphore created by a call to the sem_init function remains valid until the semaphore is removed by a call to the sem_destroy function.

RETURN VALUES

       On  successful completion, the function returns the value 0 (zero); otherwise, the function returns the value -1 and sets errno to indicate
       the error.

ERRORS

       The sem_init function fails under the following conditions:

       [EINVAL] 	   The value argument exceeds {SEM_VALUE_MAX}.

       [ENOSPC] 	   A resource required to initialize the semaphore has been exhausted.	The limit on semaphores ({SEM_NSEMS_MAX}) has been
			   reached.

       [EPERM]		   The process lacks the appropriate privilege to initialize the semaphore.

RELATED INFORMATION

       Functions: sem_destroy(3), sem_post(3), sem_trywait(3),sem_wait(3)

       Guide to Realtime Programming delim off

																       sem_init(3)