|EXIT(3)||Linux Programmer's Manual||EXIT(3)|
noreturn void exit(int status);
All functions registered with atexit(3) and on_exit(3) are called, in the reverse order of their registration. (It is possible for one of these functions to use atexit(3) or on_exit(3) to register an additional function to be executed during exit processing; the new registration is added to the front of the list of functions that remain to be called.) If one of these functions does not return (e.g., it calls _exit(2), or kills itself with a signal), then none of the remaining functions is called, and further exit processing (in particular, flushing of stdio(3) streams) is abandoned. If a function has been registered multiple times using atexit(3) or on_exit(3), then it is called as many times as it was registered.
The C standard specifies two constants, EXIT_SUCCESS and EXIT_FAILURE, that may be passed to exit() to indicate successful or unsuccessful termination, respectively.
|exit ()||Thread safety||MT-Unsafe race:exit|
The exit() function uses a global variable that is not protected, so it is not thread-safe.
The use of EXIT_SUCCESS and EXIT_FAILURE is slightly more portable (to non-UNIX environments) than the use of 0 and some nonzero value like 1 or -1. In particular, VMS uses a different convention.
BSD has attempted to standardize exit codes (which some C libraries such as the GNU C library have also adopted); see the file <sysexits.h>.
After exit(), the exit status must be transmitted to the parent process. There are three cases:
- If the parent has set SA_NOCLDWAIT, or has set the SIGCHLD handler to SIG_IGN, the status is discarded and the child dies immediately.
- If the parent was waiting on the child, it is notified of the exit status and the child dies immediately.
- Otherwise, the child becomes a "zombie" process: most of the process resources are recycled, but a slot containing minimal information about the child process (termination status, resource usage statistics) is retained in process table. This allows the parent to subsequently use waitpid(2) (or similar) to learn the termination status of the child; at that point the zombie process slot is released.
If the implementation supports the SIGCHLD signal, this signal is sent to the parent. If the parent has set SA_NOCLDWAIT, it is undefined whether a SIGCHLD signal is sent.
If the exit of the process causes a process group to become orphaned, and if any member of the newly orphaned process group is stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent to each process in this process group. See setpgid(2) for an explanation of orphaned process groups.
Except in the above cases, where the signalled processes may be children of the terminating process, termination of a process does not in general cause a signal to be sent to children of that process. However, a process can use the prctl(2) PR_SET_PDEATHSIG operation to arrange that it receives a signal if its parent terminates.