sem_open - initialize and open a named semaphore
oflag argument specifies flags that control the
operation of the call. (Definitions of the flags values can be obtained
<fcntl.h>.) If O_CREAT is
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
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
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
oflag, but a semaphore with this
value was greater than SEM_VALUE_MAX.
name consists of just "/", followed by no other
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
and no semaphore with this
name exists; or,
O_CREAT was specified, but
name wasn't well
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