EXITS(3)                                                 EXITS(3)

          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 reg-
          istered 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 pro-
          cess id of the exiting process, when the parent does a

          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 argu-
          ment 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

          Atexitdont cancels a previous registration of an exit func-


     EXITS(3)                                                 EXITS(3)


          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 pro-
          gram 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).