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 The sem argument is no longer valid after a successful call to sem_destroy(3).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