exits, _exits, exitcode, atexit, atexitdont – terminate process, process cleanup

#include <u.h>
#include <libc.h>
void    _exits(char *msg)
void    exits(char *msg)
int    exitcode(char *msg)
int    atexit(void(*)(void))
void    atexitdont(void(*)(void))

Exits is the conventional way to terminate a process. _Exits also terminates a process but does not call the registered atexit handlers (q.v.). 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(3).
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.


fork(2), wait(3)

Because of limitations of Unix, the exit status of a process can only be an 8-bit integer. Exits and _exits treat null or empty exit status as exit code 0 and call exitcode to translate any other string into an exit code. By default, the library provides an exitcode that maps all messages to 1. Applications may find it useful to provide their own implementations of exitcode .
Exit codes 97 through 99 are used by the thread library to signal internal synchronization errors between the main program and a proxy process that implements backgrounding.
To avoid name conflicts with the underlying system, atexit and atexitdont are preprocessor macros defined as p9atexit and p9atexitdont; see intro(3).

Space Glenda