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exit(2)
NAME
exit, atexit, _exit - Terminates a process
LIBRARY
Standard C Library (libc)
SYNOPSIS
#include <stdlib.h>
int atexit(
void (*function) (void));
void exit(
int status);
#include <unistd.h>
void _exit(
int status);
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
exit(), _exit(), atexit(): XSH4.2
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
status Indicates the status of the process.
function Points to a function that is called at normal process termination
for cleanup processing. The number of exit handlers that can be
specified with the atexit() function is limited by the amount of
available virtual memory.
DESCRIPTION
The atexit() function registers functions to be called at normal process
termination for cleanup processing. The function adds a single exit
handler to a list of handlers to be called at process termination. The
system calls the functions in reverse order, calling the function at the
top of the list first. Any function that is registered more than once will
be repeated.
The exit() function terminates the calling process after calling the
_cleanup() function to flush any buffered output. Then it calls any
functions registered previously for the process by the atexit() function,
in the reverse order to that in which they were registered. In addition,
the exit() function flushes all open output streams, closes all open
streams, and removes all files created by the tmpfile() function. Finally,
it calls the _exit() function, which completes process termination and does
not return.
The _exit() and exit() functions terminate the calling process and cause
the following to occur:
· All of the file descriptors and directory streams open in the calling
process are closed. Since the exit() function terminates the process,
any errors encountered during these close operations go unreported.
Message catalog descriptors and conversion descriptors opened in the
calling process are also closed with no reporting of errors.
· The parent process ID of all the calling process' existing child
processes and zombie processes is reset. The child processes continue
executing; however, their parent process ID is set to the process ID
of init. The init process thus adopts each of these processes,
catches the SIGCHLD signals that they generate, and calls the wait()
function for each of them.
· If the parent process of the calling process is running a wait() or
waitpid() function, that parent process is notified that the calling
process is being terminated. The low-order 8 bits (that is, bits 0377
or 0xFF) of the status parameter are made available to the parent
process.
[XSH4.2] This behavior also applies if the parent process is running
a wait3() or waitid() function. In addition, this behavior only
applies when the parent process of the calling process has neither set
its SA_NOCLDWAIT flag nor set SIGCHLD to SIG_IGN.
· If the parent process is not running a wait() or waitpid() function
when the child process terminates, the parent process receives a
SIGCHLD signal to notify it that the child process is terminating.
The child process is transformed into a zombie process.
Once the parent process calls the wait() or waitpid() routine, the
child process completes termination and the low-order 8 bits (that is,
bits 0377 or 0xFF) of the status parameter are made available to it.
[XSH4.2] This behavior also applies to the wait3() and waitid()
functions. In addition, this behavior only applies when the parent
process has not set its SA_NOCLDWAIT flag or set SIGCHLD to SIG_IGN.
· The parent process is sent a SIGCHLD signal when a child terminates;
however, since the default action for this signal is to ignore it, the
signal usually is not seen.
· If the process is a controlling process, the system sends a SIGHUP
signal to each process executing in the foreground on the terminal
that belongs to the calling process. The terminal is disassociated
from the session, allowing it to be acquired by a new controlling
process.
· If the termination of a process causes a process group to become
orphaned, and if any member of the newly orphaned process group is
stopped, a SIGHUP signal, followed by a SIGCONT signal, is sent to
each newly orphaned process.
· [XSH4.2] If the parent process has set its SA_NOCLDWAIT flag or set
SIGCHLD to SIG_IGN, the status is discarded, and the lifetime of the
calling process ends immediately.
· [XSH4.2] Each mapped memory object is unmapped.
· Each attached shared memory segment is detached and the value of
shm_nattach in the data structure associated with its shared memory
identifier is decremented by 1. (For more information about the data
structure, see shmget(2).)
· For each semaphore for which the calling process has set a semadj
value, that semadj value is added to the semval of the specified
semaphore. (The semop() function provides information about semaphore
operations.)
· [Tru64 UNIX] If the process has a process lock, text lock, or data
lock, an unlock is performed. (See the plock() function.)
· [Tru64 UNIX] An accounting record is written to the accounting file
if the system accounting routine is enabled. (The acct() function
provides information about enabling accounting routines.)
· [Tru64 UNIX] Locks set by the fcntl(), flock(), and lockf() functions
are removed.
[Tru64 UNIX] If a thread calls the _exit() function, the entire process
exits and all threads within the process are terminated.
NOTES
[XSH4.2] An application should call sysconf() to obtain the value of
{ATEXIT_MAX}, the number of handlers that can be registered. There is no
way for an application to tell how many functions have already been
registered with atexit().
To prematurely terminate atexit handler processing from within a handler,
_exit() can be called. It is not recommended to call exit() from within an
atexit handler.
RETURN VALUES
The exit() function and _exit() function do not return.
The atexit() function returns 0 (zero) if successful. The function fails if
an application attempts to register more process cleanup functions than
available virtual memory allows. In this case, the function returns a
nonzero value.
RELATED INFORMATION
Functions: acct(2), sigaction(2), sigvec(2), wait(2), ldr_atexit(3),
times(3)
Standards: standards(5)
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Index for
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Alphabetical
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