sem_open(3) — Linux manual page

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 5.13 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                          2021-03-22                    SEM_OPEN(3)

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