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)

sem_init(2)							System Calls Manual						       sem_init(2)

NAME

       sem_init - initialize an unnamed POSIX semaphore

SYNOPSIS

DESCRIPTION

       is  used  to initialize an unnamed semaphore.  A successful call to will create a new unnamed semaphore referred to by sem, if one does not
       exist, initialize the unnamed semaphore descriptor, referred to by sem, to the non-negative value specified by value.  If the unnamed sema-
       phore  already exists, i.e. created by a previous call to it is re-initialized only if its current value is equal to its initial value (set
       by the last successful call to If so, the initial value of the unnamed semaphore is re-initialized to the value	argument.  Otherwise,  the
       call fails.

       The  argument  pshared specifies if the unnamed semaphore is sharable with other processes. If pshared is equal to 0, the unnamed semaphore
       is not shared with other processes.  If pshared is non-zero, the unnamed semaphore is sharable with any processes that can access sem.  The
       access  mode  specified for the unnamed semaphore allows read and write permissions to all processes.  If the calling process may attach to
       the shared structure, it is assumed it may operate on the semaphore.

       To use this function, link in the realtime library by specifying on the compiler or linker command line.

EXAMPLES

       The following call to will create a new unnamed semaphore referred to by sem, if one does  not  exist,  initialize  the	unnamed  semaphore
       descriptor, referred to by sem, to the non-negative value specified by value.

RETURN VALUE

       If the semaphore was created and initialized, returns 0 to the caller.

       If the semaphore could not be created/initialized, the call returns -1 and sets to indicate the error.

ERRORS

       fails and does not perform the requested operation if any of the following conditions are encountered:

	      [EPERM]	     The calling process does not have the privileges necessary to initialize the semaphore.

	      [EBUSY]	     There are threads currently blocked on the semaphore or there are outstanding locks held on the semaphore.

	      [EINVAL]	     The argument value is greater than

	      [ENOSPC]	     There are insufficient resources to perform the operation or the upper limit on the number of semaphores is reached.

SEE ALSO

       sem_destroy(2), sem_post(2), sem_trywait(2), sem_wait(2), <semaphore.h>.

STANDARDS CONFORMANCE

																       sem_init(2)