sem(3head) [sunos man page]
sem.h(3HEAD) Headers sem.h(3HEAD) NAME
sem.h, sem - semaphore facility SYNOPSIS
#include <sys/sem.h> DESCRIPTION
The <sys/sem.h> header defines the following constants and structures. Semaphore operation flags: SEM_UNDO Set up adjust on exit entry. Command definitions for the semctl() function are provided as listed below. See semctl(2). GETNCNT Get semncnt. GETPID Get sempid. GETVAL Get semval. GETALL Get all cases of semval. GETZCNT Get semzcnt. SETVAL Set semval. SETALL Set all cases of semval. The semid_ds structure contains the following members: struct ipc_perm sem_perm /* operation permission structure */ unsigned short sem_nsems /* number of semaphores in set */ time_t sem_otime /* last semop() time */ time_t sem_ctime /* last time changed by semctl() */ The pid_t, time_t, key_t, and size_t types are defined as described in <sys/types.h>. See types.h(3HEAD). A semaphore is represented by an anonymous structure containing the following members: unsigned short semval /* semaphore value */ pid_t sempid /* process ID of last operation */ unsigned short semncnt /* number of processes waiting for semval /* to become greater than current value */ unsigned short semzcnt /* number of processes waiting for semval to become 0 */ The sembuf structure contains the following members: unsigned short sem_num /* semaphore number */ short sem_op /* semaphore operation */ short sem_flg /* operation flags */ All of the symbols from <sys/ipc.h> are defined when this header is included. See ipc.h(3HEAD). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
semctl(2), semget(2), semop(2), ipc.h(3HEAD), types.h(3HEAD), attributes(5), standards(5) SunOS 5.10 10 Sep 2004 sem.h(3HEAD)
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semctl(2) System Calls Manual semctl(2) Name semctl - semaphore control operations Syntax #include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> int semctl (semid, semnum, cmd, arg) int semid, cmd; int semnum; union semun { int val; struct semid_ds *buf; ushort array[]; } arg; Description The system call provides a variety of semaphore control operations as specified by cmd. The following cmds are executed with respect to the semaphore specified by semid and semnum: GETVAL Return the value of semval. For further information, see SETVAL Set the value of semval to arg.val. When this command is successfully executed, the semadj value corresponding to the spec- ified semaphore in all processes is cleared. GETPID Return the value of sempid. GETNCNT Return the value of semncnt. GETZCNT Return the value of semzcnt. The following cmds return and set every semval in the set of semaphores: GETALL Place semvals into array pointed to by arg.array. SETALL Set semvals according to the array pointed to by arg.array When this command is successfully executed, the semadj values corresponding to each specified semaphore in all processes are cleared. The following cmds are also available: IPC_STAT Place the current value of each member of the data structure associated with semid into the structure pointed to by arg.buf. The contents of this structure are defined in IPC_SET Set the value of the following members of the data structure associated with semid to the corresponding value found in the structure pointed to by arg.buf: sem_perm.uid sem_perm.gid sem_perm.mode /* only low 9 bits */ This command can only be executed by a process that has an effective user ID equal to superuser or to the values of sem_perm.uid or sem_perm.cuid in the data structure associated with semid. IPC_RMID Remove the semaphore identifier specified by semid from the system and destroy the set of semaphores and data structure associated with it. This cmd can only be executed by a process that has an effective user ID equal to either that of supe- ruser or to the value of sem_perm.uid in the data structure associated with semid. Return Values Upon successful completion, the value returned depends on cmd, as follows: GETVAL The value of semval. GETPID The value of sempid. GETNCNT The value of semncnt. GETZCNT The value of semzcnt. All other A value of 0. Otherwise, a value of -1 is returned and errno is set to indicate the error. Diagnostics The system call fails if any of the following is true: [EINVAL] The semid is not a valid semaphore identifier. [EINVAL] The semnum is less than zero or greater than sem_nsems. [EINVAL] The cmd is not a valid command. [EACCES] Operation permission is denied to the calling process. For further information, see [ERANGE] The cmd is SETVAL or SETALL, and the value to which semval is to be set is greater than the system imposed maximum. [EPERM] The cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that of superuser nor to the value of sem_perm.uid in the data structure associated with semid. [EFAULT] The arg.buf points to an illegal address. See Also errno(2), intro(2), semget(2), semop(2) semctl(2)