msem_init(3) [osf1 man page]

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 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.

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 following 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)

msem_init(2)							System Calls Manual						      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 semaphore.  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 inter-
       preted 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  ini-
			     tial_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)