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| | semget - get set of semaphores |
SYNOPSIS
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#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h> int semget(key_t key, int nsems, int semflg); |
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The semget() function
returns the semaphore identifier associated with key.
A semaphore identifier and associated data structure and set containing nsems semaphores (see intro(2)) are created for key if one of the
following is true:
-
key is equal to IPC_PRIVATE.
-
key does not already have a semaphore identifier associated with it, and (semflg&IPC_CREAT) is true.
On creation, the data structure associated with the new semaphore identifier is initialized as follows:
-
sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and sem_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the
calling process.
- The access permission bits of sem_perm.mode are set equal to the access permission bits of semflg.
-
sem_nsems is set equal to the value of nsems.
-
sem_otime is set equal to 0 and sem_ctime is set equal to the current time.
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Upon successful completion, a non-negative integer representing a semaphore identifier is returned. Otherwise, -1 is returned and errno is set to indicate the error.
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The semget() function will fail if:
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EACCES
- A semaphore identifier exists for key, but operation permission (see intro(2)) as specified by the low-order 9 bits of semflg would not be granted.
-
EEXIST
- A semaphore identifier exists for key but both (semflg&IPC_CREAT) and (semflg&IPC_EXCL) are both true.
-
EINVAL
- The nsems argument is either less than or equal to 0 or greater than the system-imposed limit; or a semaphore identifier exists for key, but the number of semaphores in the set associated
with it is less than nsems and nsems is not equal to 0.
-
ENOENT
- A semaphore identifier does not exist for key and (semflg&IPC_CREAT) is false.
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ENOSPC
- A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores or semaphore identifiers system-wide would be exceeded.
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