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msem_init(3) Library Functions Manual msem_init(3) NAME msem_init - Initializes a semaphore in a mapped file or shared memory region LIBRARY Standard C Library (libc.a) SYNOPSIS #include <sys/mman.h> msemaphore *msem_init ( msemaphore *sem, int initial_value ); PARAMETERS Points to an msemaphore structure in which the state of the semaphore is stored. Determines whether the semaphore is locked or unlocked at allocation. DESCRIPTION The msem_init() function allocates a new binary semaphore and initial- izes the state of the new semaphore. If the initial_value parameter is MSEM_LOCKED, the new semaphore is initialized in the locked state. If the initial_value parameter is MSEM_UNLOCKED, the new semaphore is initialized in the unlocked state. The msemaphore structure is located within a mapped file or shared mem- ory region created by a successful call to the mmap() function and hav- ing both read and write access. If a semaphore is created in a mapped file region, any reference by a process which has mapped the same file, using a (struct msemaphore *) pointer which resolves to the same file offset, is taken as a reference to the same semaphore. If a semaphore is created in an anonymous shared memory region, any reference by a process which shares the same region, using a (struct msemaphore *) pointer which resolves to the same offset from the start of the region, is taken as a reference to the same semaphore. Any previous semaphore state stored in the msemaphore structure is ig- nored and overwritten. NOTES Trial use RETURN VALUES Upon successful completion, the msem_init() function returns a pointer to the initialized msemaphore structure. On error, the msem_init() function returns null and sets errno to indicate the error. ERRORS If the msem_init() function fails, errno may be set to one of the fol- lowing values: The initial_value parameter is not valid. A new sema- phore could not be created. RELATED INFORMATION Functions: mmap(2), msem_lock(3), msem_remove(3), msem_unlock(3) delim off msem_init(3)