Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

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 The sem argument is no longer valid after a successful call to sem_destroy(3).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

Check Out this Related Man Page

sem_init(3RT)						    Realtime Library Functions						     sem_init(3RT)

NAME
sem_init - initialize an unnamed semaphore SYNOPSIS
cc [ flag... ] file... -lrt [ library... ] #include <semaphore.h> int sem_init(sem_t *sem, int pshared, unsigned int value); DESCRIPTION
The sem_init() function is used to initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore is value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT). This semaphore remains usable until the semaphore is destroyed. If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore sem can use sem for performing sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT) operations. Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(3RT), sem_try- wait(3RT), sem_post(3RT), and sem_destroy(3RT), is undefined. If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can use sem for performing sem_wait(3RT), sem_trywait(3RT), sem_post(3RT), and sem_destroy(3RT) operations. The use of the semaphore by threads other than those created in the same process is undefined. Attempting to initialize an already initialized semaphore results in undefined behavior. RETURN VALUES
Upon successful completion, the function initializes the semaphore in sem. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The sem_init() function will fail if: EINVAL The value argument exceeds SEM_VALUE_MAX. ENOSPC A resource required to initialize the semaphore has been exhausted, or the resources have reached the limit on semaphores (SEM_NSEMS_MAX). ENOSYS The sem_init() function is not supported by the system. EPERM The process lacks the appropriate privileges to initialize the semaphore. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
sem_destroy(3RT), sem_post(3RT), sem_wait(3RT), attributes(5), standards(5) SunOS 5.10 28 Jun 2002 sem_init(3RT)
Man Page