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sem(4) [netbsd man page]

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

sem -- POSIX semaphores SYNOPSIS
To link into the kernel: options P1003_1B_SEMAPHORE DESCRIPTION
The sem facility provides system calls used by the standard C library (libc) to implement POSIX semaphores. SEE ALSO
config(1), sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3), sem_wait(3), options(4) HISTORY
The sem facility appeared as a kernel option in NetBSD 2.0. BUGS
The current implementation does not support shared, unnamed semaphores. BSD
January 21, 2005 BSD

Check Out this Related Man Page

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

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 The sem argument is no longer valid after a successful call to sem_destroy(3).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