sem_open - initialize and open a named semaphore
#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);
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).
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
value are ignored.
The semaphore exists, but the caller does not have permission to open it.
Both O_CREAT and O_EXCL were specified in
oflag, but a semaphore with this
name already exists.
value was greater than SEM_VALUE_MAX.
name consists of just "/", followed by no other characters.
The per-process limit on the number of open file descriptors has been reached.
name was too long.
The system-wide limit on the total number of open files has been reached.
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.
For an explanation of the terms used in this section, see attributes(7).
sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)
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