sem_open.2 (2010 09)

ManualsBrandsHP ManualsSoftwareHP-UX Manpages

sem_open(2) sem_open(2)

NAME

sem_open - create/open a named POSIX semaphore

SYNOPSIS

#include <sys/semaphore.h>

sem_t * sem_open(const char *name, int oflag, mode_t mode,

unsigned int value);

DESCRIPTION

sem_open() is used to open or create a named semaphore. A successful call to

sem_open() will

create a descriptor for the semaphore speciﬁed by name . The pointer to the semaphore returned by

sem_open() can be used to access the semaphore associated with name in subsequent operations. The

name argument points to a string referring to a semaphore. It should begin with a "/" and shall conform to

pathname rules except that no path component should be "." or "..".

The oﬂag argument speciﬁes whether a semaphore is to be created or not. The following bits in it may be

set:

O_CREAT If this ﬂag is set, a new semaphore is created if it does not already exist. If this ﬂag

is not set, the semaphore should already exist.

O_EXCL If this ﬂag is set, the call fails if the semaphore already exists. This ﬂag is valid

only when O_CREAT is also set; otherwise, it is ignored.

The mode and value arguments are provided to supply the permissions and the initial value information

necessary for creating a new semaphore.

To use this function, link in the realtime library by specifying

-lrt on the compiler or linker command

line.

EXAMPLES

The following call to

sem_open() will create a new named semaphore if one does not exist, which

depends on the ﬂags speciﬁed in oﬂag, has the permissions speciﬁed in mode and has an initial value of

value .

sem_open(name, oflag, mode, value);

RETURN VALUE

If the semaphore was created and initialized, sem_open() returns a pointer to a sem_t structure con-

taining the index of the new descriptor.

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

errno to indicate the error.

If the named semaphore is already opened by the calling process, a descriptor and a

sem_t

structure for

the named semaphore already exists for the calling process. A new descriptor is not created and a pointer

to the existing

sem_t structure is returned for this call.

ERRORS

sem_open() fails and does not perform the requested operation if any of the following conditions are

encountered:

[EACCES] The named semaphore exists and the process does not have the permissions to open

the semaphore as described by oﬂag, or the named semaphore does not exist and

the process does not have the permission to open it.

[EEXIST] The ﬂags

O_CREAT and O_EXCL are set in oﬂag and the named semaphore exists.

[EINTR] A signal interrupted the

sem_open() operation.

[EINVAL] The argument value is greater than

{_POSIX_SEM_VALUE_MAX} and the

O_CREAT ﬂag was speciﬁed in oﬂag.

[EINVAL] The name argument does not begin with "/" or contains "." or ".." as a pathname com-

ponent.

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

[ENAMETOOLONG]

The name string is longer than

{PATH_MAX}.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (2 pages)

PAGE 1
sem_open(2) sem_open(2) NAME sem_open - create/open a named POSIX semaphore SYNOPSIS #include sem_t * sem_open(const char *name, int oflag, mode_t mode, unsigned int value); DESCRIPTION sem_open() is used to open or create a named semaphore. A successful call to sem_open() will create a descriptor for the semaphore specified by name. The pointer to the semaphore returned by sem_open() can be used to access the semaphore associated with name in subsequent operations.
PAGE 2
sem_open(2) sem_open(2) [ENFILE] There are too many semaphores in the system. [ENOENT] The flag O_CREAT is not set in oflag and the named semaphore does not exist. [ENOSPC] There are insufficient resources for the creation of a new named semaphore. SEE ALSO sem_close(2), sem_post(2), sem_wait(2), sem_unlink(2), privileges(5), .