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msem_init(2)							  msem_init(2)

NAME
       msem_init - initialize a semaphore in a mapped file or anonymous memory
       region

SYNOPSIS
DESCRIPTION
       allocates a new binary semaphore and initializes the state of  the  new
       semaphore.

       sem points to an structure in which the state of the semaphore is to be
       stored.

       If initial_value is the new semaphore  is  initialized  in  the	locked
       state.	If  initial_value  is  the new semaphore is initialized in the
       unlocked state.

       The structure must be located within a mapped file or anonymous	memory
       region  created	by  a  successful call to and have both read and write
       access.

       If a semaphore is created in a mapped file region, any reference	 by  a
       process that has mapped the same file, using a pointer that resolves to
       the same file offset is interpreted as a reference to  the  same	 sema‐
       phore.	If  a  semaphore is created in an anonymous memory region, any
       reference by a process sharing the same region by use of a pointer that
       resolves to the same offset from the start of the region is interpreted
       as a reference to the same semaphore.

       Any previous semaphore state stored in the structure  will  be  ignored
       and overwritten.

   Implementation Notes
       In  order to ensure that an structure is entirely contained in a single
       memory page, sem must be at an address that is an exact multiple of The
       size  of	 the  structure is guaranteed to prevent semaphores that cross
       page boundaries given the above restriction.

       For a memory mapped file region, the  system  deallocates  memory  that
       corresponds to a range of the file that has been truncated with or If a
       semaphore is located in memory so deallocated, the effect is equivalent
       to an on the semaphore.

RETURN VALUE
       returns the address of the initialized structure; otherwise, it returns
       NULL and sets to indicate the error.

ERRORS
       fails if any of the following conditions are encountered:

	      sem	     points to an structure that is not located	 in  a
			     mapped  region created by and with read and write
			     access, or initial_value is not valid.

	      A new semaphore could not be created.

	      sem	     is an invalid pointer.

AUTHOR
       was developed by HP and OSF.

SEE ALSO
       mmap(2), msem_lock(2), msem_remove(2), msem_unlock(2), mman(5).

STANDARDS CONFORMANCE
								  msem_init(2)

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