sem(4) [freebsd man page]

SEM(4)							   BSD Kernel Interfaces Manual 						    SEM(4)

NAME

     sem -- POSIX semaphores

SYNOPSIS

     To compile this driver into the kernel, place the following line in your kernel configuration file:

	   options P1003_1B_SEMAPHORES

     Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

	   sem_load="YES"

     To load the driver as a module at run-time, run the following command as root:

	   kldload sem

DESCRIPTION

     The sem facility provides system calls used by the standard C library (libc) to implement POSIX semaphores.  This facility offers support for
     such functions as sem_init() and sem_wait().  It is available both as a kernel option for static inclusion and as a dynamic kernel module.

SEE ALSO

     sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3), sem_wait(3), config(8), kldload(8), kldunload(8)

HISTORY

     The sem facility appeared in FreeBSD 5.0.

BSD
								 February 7, 2014							       BSD

SEM_INIT(3)						   BSD Library Functions Manual 					       SEM_INIT(3)

NAME

     sem_init -- initialize an unnamed semaphore

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <semaphore.h>

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

DESCRIPTION

     The sem_init() function initializes the unnamed semaphore pointed to by sem to have the value value.

     A non-zero value for pshared specifies a shared semaphore that can be used by multiple processes, the semaphore should be located in shared
     memory region (see mmap(2), shm_open(2), and shmget(2)), any process having read and write access to address sem can perform semaphore opera-
     tions on sem.

     Following a successful call to sem_init(), sem can be used as an argument in subsequent calls to sem_wait(3), sem_trywait(3), sem_post(3),
     and sem_destroy(3).  The sem argument is no longer valid after a successful call to sem_destroy(3).

RETURN VALUES

     The sem_init() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi-
     cate the error.

ERRORS

     The sem_init() function will fail if:

     [EINVAL]		The value argument exceeds SEM_VALUE_MAX.

     [ENOSPC]		Memory allocation error.

SEE ALSO

     sem_destroy(3), sem_getvalue(3), sem_post(3), sem_trywait(3), sem_wait(3)

STANDARDS

     The sem_init() function conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').

BSD
								  January 9, 2010							       BSD