@node Inter-Process Communication, Job Control, Processes, Top
@c %MENU% All about inter-process communication
@chapter Inter-Process Communication
@cindex ipc

This chapter describes the @glibcadj{} inter-process communication primitives.

@menu
* Semaphores::	Support for creating and managing semaphores
@end menu

@node Semaphores
@section Semaphores

@Theglibc{} implements the semaphore APIs as defined in POSIX and
System V.  Semaphores can be used by multiple processes to coordinate shared
resources.  The following is a complete list of the semaphore functions provided
by @theglibc{}.

@c Need descriptions for all of these functions.

@subsection System V Semaphores
@deftypefun int semctl (int @var{semid}, int @var{semnum}, int @var{cmd})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{/linux}}}
@c syscall(ipc) ok
@c
@c AC-unsafe because we need to translate the new kernel
@c semid_ds buf into the userspace layout.  Cancellation
@c at that point results in an inconsistent userspace
@c semid_ds.
@end deftypefun

@deftypefun int semget (key_t @var{key}, int @var{nsems}, int @var{semflg})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c syscall(ipc) ok
@end deftypefun

@deftypefun int semop (int @var{semid}, struct sembuf *@var{sops}, size_t @var{nsops})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c syscall(ipc) ok
@end deftypefun

@deftypefun int semtimedop (int @var{semid}, struct sembuf *@var{sops}, size_t @var{nsops}, const struct timespec *@var{timeout})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c syscall(ipc) ok
@end deftypefun

@subsection POSIX Semaphores
@Theglibc{} provides POSIX semaphores as well.  These functions' names begin
with @code{sem_} and they are declared in @file{semaphore.h}.  @xref{POSIX
Semaphores}.