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)

Check Out this Related Man Page

sem_wait(3)						     Library Functions Manual						       sem_wait(3)

NAME

       sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

       int sem_wait (
       sem_t *sem);

       int sem_trywait (
       sem_t *sem);

PARAMETERS

       sem	 Specifies a pointer to the semaphore to be locked.

DESCRIPTION

       The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero,
       the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.

       The sem_trywait function locks a semaphore only if the semaphore is currently not locked.  If the semaphore value is zero, the  sem_trywait
       function returns without locking the semaphore.

       These  functions  help ensure that the resource associated with the semaphore cannot be accessed by other processes.  The semaphore remains
       locked until the process unlocks it with a call to the sem_post function.

       Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.

RETURN VALUES

       If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore  lock
       operation.

       On  an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains
       unchanged.

ERRORS

       The sem_wait and sem_trywait functions fail under the following conditions:

       [EAGAIN]       The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only).

       [EINTR]	      A signal interrupted this function.

       [EINVAL]       The sem argument does not refer to a valid semaphore.

RELATED INFORMATION

       Functions: sem_post(3)

       Guide to Realtime Programming delim off

																       sem_wait(3)

Linux and UNIX Man Pages

msem_init(3) [osf1 man page]

Check Out this Related Man Page