exits(2) [plan9 man page]

EXITS(2)							System Calls Manual							  EXITS(2)

NAME

       exits, _exits, atexit, atexitdont, terminate - terminate process, process cleanup

SYNOPSIS

       #include <u.h>
       #include <libc.h>

       void _exits(char *msg)
       void exits(char *msg)

       int  atexit(void(*)(void))

       void atexitdont(void(*)(void))

       /* Alef only */

       void _exits(byte *msg)

       void exits(byte *msg)

       void terminate(byte *msg)

DESCRIPTION

       Exits is the conventional way to terminate a process.  _Exits is the underlying system call.  They can never return.

       Msg  conventionally  includes  a  brief (maximum length ERRLEN) explanation of the reason for exiting, or a null pointer or empty string to
       indicate normal termination.  The string is passed to the parent process, prefixed by the name and process id of the exiting process,  when
       the parent does a wait(2).

       Before calling _exits with msg as an argument, exits calls in reverse order all the functions recorded by atexit.

       Atexit  records	fn  as a function to be called by exits.  It returns zero if it failed, nonzero otherwise.  A typical use is to register a
       cleanup routine for an I/O package.  To simplify programs that fork or share memory, exits only	calls  those  atexit-registered  functions
       that were registered by the same process as that calling exits.

       Calling atexit twice (or more) with the same function argument causes exits to invoke the function twice (or more).

       There is a limit to the number of exit functions that will be recorded; atexit returns 0 if that limit has been reached.

       Atexitdont cancels a previous registration of an exit function.

Alef
       In  Alef,  the system call _exits is the same, but its use is discouraged because the run-time system needs to maintain consistency; termi-
       nate and exits are the recommended routines.  Terminate is called automatically when a task or proc returns from its main function; it  may
       also  be  called  explicitly.  In either case, it frees resources private to the task (which may be the implicit main task within the proc)
       and terminates that task.  If that task is the last one in the proc, resources private to the proc are then freed.  If  that  proc  is  the
       last  one in the program, it calls exits.  Exits should only be called in the last proc of a program; it calls any atexit functions (regis-
       tered by any proc) and then calls _exits.

       In Alef, atexit and atexitdont behave the same as in C.

SOURCE

       /sys/src/libc/port/atexit.c

SEE ALSO

       fork(2), wait(2)

																	  EXITS(2)

ATEXIT(3)						     Linux Programmer's Manual							 ATEXIT(3)

NAME

       atexit - register a function to be called at normal process termination

SYNOPSIS

       #include <stdlib.h>

       int atexit(void (*function)(void));

DESCRIPTION

       The  atexit()  function	registers the given function to be called at normal process termination, either via exit(3) or via return from the
       program's main().  Functions so registered are called in the reverse order of their registration; no arguments are passed.

       The same function may be registered multiple times: it is called once for each registration.

       POSIX.1 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered.	The actual limit supported  by	an
       implementation can be obtained using sysconf(3).

       When  a	child  process	is  created  via  fork(2), it inherits copies of its parent's registrations.  Upon a successful call to one of the
       exec(3) functions, all registrations are removed.

RETURN VALUE

       The atexit() function returns the value 0 if successful; otherwise it returns a nonzero value.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute	  | Value   |
       +----------+---------------+---------+
       |atexit()  | Thread safety | MT-Safe |
       +----------+---------------+---------+

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES

       Functions registered using atexit() (and on_exit(3)) are not called if a process terminates abnormally because of the delivery of a signal.

       If one of the functions registered functions calls _exit(2), then any remaining functions are not invoked, and the other  process  termina-
       tion steps performed by exit(3) are not performed.

       POSIX.1 says that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered using atexit()) is unde-
       fined.  On some systems (but not Linux), this can result in an infinite recursion; portable programs should not	invoke	exit(3)  inside  a
       function registered using atexit().

       The  atexit()  and  on_exit(3)  functions  register functions on the same list: at normal process termination, the registered functions are
       invoked in reverse order of their registration by these two functions.

       According to POSIX.1, the result is undefined if longjmp(3) is used to terminate  execution  of	one  of  the  functions  registered  using
       atexit().

   Linux notes
       Since  glibc  2.2.3,  atexit()  (and on_exit(3)) can be used within a shared library to establish functions that are called when the shared
       library is unloaded.

EXAMPLE

       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       void
       bye(void)
       {
	   printf("That was all, folks
");
       }

       int
       main(void)
       {
	   long a;
	   int i;

	   a = sysconf(_SC_ATEXIT_MAX);
	   printf("ATEXIT_MAX = %ld
", a);

	   i = atexit(bye);
	   if (i != 0) {
	       fprintf(stderr, "cannot set exit function
");
	       exit(EXIT_FAILURE);
	   }

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       _exit(2), dlopen(3), exit(3), on_exit(3)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15								 ATEXIT(3)