sem_init(3) [freebsd man page]

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  The sem argument is no longer valid after a successful call to sem_destroy(3).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

SEM_INIT(3)						     Linux Programmer's Manual						       SEM_INIT(3)

NAME

       sem_init - initialize an unnamed semaphore

SYNOPSIS

       #include <semaphore.h>

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

       Link with -lrt or -pthread.

DESCRIPTION

       sem_init() initializes the unnamed semaphore at the address pointed to by sem.  The value argument specifies the initial value for the sem-
       aphore.

       The pshared argument indicates whether this semaphore is to be shared between the threads of a process, or between processes.

       If pshared has the value 0, then the semaphore is shared between the threads of a process, and should be located at some  address  that	is
       visible to all threads (e.g., a global variable, or a variable allocated dynamically on the heap).

       If pshared is nonzero, then the semaphore is shared between processes, and should be located in a region of shared memory (see shm_open(3),
       mmap(2), and shmget(2)).  (Since a child created by fork(2) inherits its parent's memory mappings, it can also access the semaphore.)   Any
       process that can access the shared memory region can operate on the semaphore using sem_post(3), sem_wait(3), etc.

       Initializing a semaphore that has already been initialized results in undefined behavior.

RETURN VALUE

       sem_init() returns 0 on success; on error, -1 is returned, and errno is set to indicate the error.

ERRORS

       EINVAL value exceeds SEM_VALUE_MAX.

       ENOSYS pshared is nonzero, but the system does not support process-shared semaphores (see sem_overview(7)).

CONFORMING TO

       POSIX.1-2001.

NOTES

       Bizarrely,  POSIX.1-2001  does  not  specify  the value that should be returned by a successful call to sem_init().  POSIX.1-2008 rectifies
       this, specifying the zero return on success.

SEE ALSO

       sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-07-27							       SEM_INIT(3)