msemaphore *msem_init (
int initial_value );
The msem_init() function allocates a new binary semaphore and initializes 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 memory region created by a successful call to the mmap() function and having 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 ignored and overwritten.
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.
If the msem_init() function fails, errno may be set to one of the following values: The initial_value parameter is not valid. A new semaphore could not be created.
Functions: mmap(2), msem_lock(3), msem_remove(3), msem_unlock(3) delim off