Manpage of SEM_OPEN
SEM_OPENSection: Linux Programmer's Manual (3)
NAMEsem_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);
DESCRIPTIONsem_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 oflagargument specifies flags that control the operation of the call. (Definitions of the flags values can be obtained by including <fcntl.h>.) If O_CREATis 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_CREATand O_EXCLare specified in oflag, then an error is returned if a semaphore with the given namealready exists.
If O_CREATis specified in oflag, then two additional arguments must be supplied. The modeargument 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 valueargument specifies the initial value for the new semaphore. If O_CREATis specified, and a semaphore with the given namealready exists, then modeand valueare ignored.
RETURN VALUEOn 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 errnoset to indicate the error.
- The semaphore exists, but the caller does not have permission to open it.
- Both O_CREATand O_EXCLwere specified in oflag, but a semaphore with this namealready exists.
- valuewas greater than SEM_VALUE_MAX.
- nameconsists of just "/", followed by no other characters.
- The per-process limit on the number of open file descriptors has been reached.
- namewas too long.
- The system-wide limit on the total number of open files has been reached.
- The O_CREATflag was not specified in oflagand no semaphore with this nameexists; or, O_CREATwas specified, but namewasn't well formed.
- Insufficient memory.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.1-2001, POSIX.1-2008.
SEE ALSOsem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)
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