sem_open(3)						     Library Functions Manual						       sem_open(3)

NAME

       sem_open - Opens/creates a named semaphore for use by a process (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

       sem_t *sem_open (
       const char *name,
       int oflag,
       mode_t mode,
       unsigned int value);

PARAMETERS

       name    Points to a string naming the semaphore object.

       oflag   Specifies  whether  the	semaphore  is to be created (O_CREAT flag bit set) or only opened (O_CREAT flag bit clear).  If O_CREAT is
	       set, the O_EXCL flag bit may additionally be set to specify that the call should fail if a  semaphore  of  the  same  name  already
	       exists.	The O_CREAT and O_EXCL flags are defined in the <fcntl.h> header file.

       mode    Specifies the semaphore's permission bits.  This argument is used only when the semaphore is being created.

       value   Specifies the initial value to be given to the semaphore.  This argument is used only when the semaphore is being created.

DESCRIPTION

       Use  the sem_open function to establish the connection between a named semaphore and a process.	Subsequently, the calling process can ref-
       erence the semaphore by using the address returned from the call.  The semaphore is available in subsequent calls to sem_wait, sem_trywait,
       sem_post,  and  sem_getvalue  functions.  The semaphore remains usable by the process until the semaphore is closed by a successful call to
       the sem_close function.

       The O_CREAT flag bit in the oflag parameter controls whether the semaphore is created or only opened by the call to sem_open.

       A created semaphore's user ID is set to the user ID of the calling process and its group ID is set to a system  default	group  or  to  the
       group  ID of the process.  The semaphore's permission bits are set to the value of the mode argument, except for those set in the file mode
       creation mask of the process.

       After a semaphore is created, other processes can open the semaphore by calling sem_open with the same value for the name argument.

RETURN VALUES

       On successful completion, this function opens the semaphore and returns the semaphore's descriptor.  Otherwise, the function returns -1 and
       sets errno to indicate the error.

ERRORS

       The sem_open function fails under the following conditions:

       [EACCES] 	   The named semaphore exists and the permissions specified by oflag are denied, or the named semaphore does not exist and
			   the permissions specified by oflag are denied.

       [EEXIST] 	   O_CREAT and O_EXCL are set and the named semaphore already exists.

       [EINTR]		   The sem_open operation was interrupted by a signal.

       [EINVAL] 	   The sem_open operation is not supported for the given name.	Or, O_CREAT was specified in oflag and value  was  greater
			   than {SEM_VALUE_MAX}.

       [EMFILE] 	   Too many semaphore descriptors or file descriptors are currently in use by this process.

       [ENAMETOOLONG]	   The	length	of  the  name  string  exceeds	{PATH_MAX},  or  a  pathname  component  is  longer  than {NAME_MAX} while
			   {_POSIX_NO_TRUNC} is in effect.

       [ENFILE] 	   Too many semaphores are currently open in the system.

       [ENOENT] 	   O_CREAT is not set and the named semaphore does not exist.

       [ENOSPC] 	   Insufficient space exists for the creation of a new named semaphore.

RELATED INFORMATION

       Functions: sem_close(3), sem_post(3), sem_trywait(3), sem_unlink(3), sem_wait(3)

       Guide to Realtime Programming delim off

																       sem_open(3)