NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON

SEM_OPEN(3)               Linux Programmer's Manual              SEM_OPEN(3)

NAME         top

       sem_open - initialize and open a named semaphore

SYNOPSIS         top

       #include <fcntl.h>           /* For O_* constants */
       #include <sys/stat.h>        /* For mode constants */
       #include <semaphore.h>

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

       Link with -pthread.

DESCRIPTION         top

       sem_open() creates a new POSIX semaphore or opens an existing
       semaphore.  The semaphore is identified by name.  For details of the
       construction of name, see sem_overview(7).

       The oflag argument specifies flags that control the operation of the
       call.  (Definitions of the flags values can be obtained by including
       <fcntl.h>.)  If O_CREAT is specified in oflag, then the semaphore is
       created if it does not already exist.  The owner (user ID) of the
       semaphore is set to the effective user ID of the calling process.
       The group ownership (group ID) is set to the effective group ID of
       the calling process.  If both O_CREAT and O_EXCL are specified in
       oflag, then an error is returned if a semaphore with the given name
       already exists.

       If O_CREAT is specified in oflag, then two additional arguments must
       be supplied.  The mode argument specifies the permissions to be
       placed on the new semaphore, as for open(2).  (Symbolic definitions
       for the permissions bits can be obtained by including <sys/stat.h>.)
       The permissions settings are masked against the process umask.  Both
       read and write permission should be granted to each class of user
       that will access the semaphore.  The value argument specifies the
       initial value for the new semaphore.  If O_CREAT is specified, and a
       semaphore with the given name already exists, then mode and value are
       ignored.

RETURN VALUE         top

       On success, sem_open() returns the address of the new semaphore; this
       address is used when calling other semaphore-related functions.  On
       error, sem_open() returns SEM_FAILED, with errno set to indicate the
       error.

ERRORS         top

       EACCES The semaphore exists, but the caller does not have permission
              to open it.

       EEXIST Both O_CREAT and O_EXCL were specified in oflag, but a
              semaphore with this name already exists.

       EINVAL value was greater than SEM_VALUE_MAX.

       EINVAL name consists of just "/", followed by no other characters.

       EMFILE The per-process limit on the number of open file descriptors
              has been reached.

       ENAMETOOLONG
              name was too long.

       ENFILE The system-wide limit on the total number of open files has
              been reached.

       ENOENT The O_CREAT flag was not specified in oflag and no semaphore
              with this name exists; or, O_CREAT was specified, but name
              wasn't well formed.

       ENOMEM Insufficient memory.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────┬───────────────┬─────────┐
       │Interface  Attribute     Value   │
       ├───────────┼───────────────┼─────────┤
       │sem_open() │ Thread safety │ MT-Safe │
       └───────────┴───────────────┴─────────┘

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

SEE ALSO         top

       sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3),
       sem_wait(3), sem_overview(7)

COLOPHON         top

       This page is part of release 4.11 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                            2015-12-28                      SEM_OPEN(3)

Pages that refer to this page: umask(2)sem_close(3)sem_unlink(3)sem_overview(7)