wait3, wait4 - wait for process termination, BSD style
SYNOPSIS
#define _USE_BSD
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>
pid_t wait3(int *status, int options,
struct rusage *rusage)
pid_t wait4(pid_t pid, int *status, int options,
struct rusage *rusage)
DESCRIPTION
The wait3 function suspends execution of the current pro
cess until a child has exited, or until a signal is deliv
ered whose action is to terminate the current process or
to call a signal handling function. If a child has
already exited by the time of the call (a so-called "zom
bie" process), the function returns immediately. Any sys
tem resources used by the child are freed.
The wait4 function suspends execution of the current pro
cess until a child as specified by the pid argument has
exited, or until a signal is delivered whose action is to
terminate the current process or to call a signal handling
function. If a child as requested by pid has already
exited by the time of the call (a so-called "zombie" pro
cess), the function returns immediately. Any system
resources used by the child are freed.
The value of pid can be one of:
< -1 which means to wait for any child process whose
process group ID is equal to the absolute value of
pid.
-1 which means to wait for any child process; this is
equivalent to calling wait3.
0 which means to wait for any child process whose
process group ID is equal to that of the calling
process.
> 0 which means to wait for the child whose process ID
is equal to the value of pid.
The value of options is a bitwise OR of zero or more of
the following constants:
which means to return immediately if no child is
there to be waited for.
WUNTRACED
which means to also return for children which are
stopped, and whose status has not been reported.
If status is not NULL, wait3 or wait4 store status infor
mation in the location pointed to by status.
This status can be evaluated with the following macros
(these macros take the stat buffer (an int) as an argument
-- not a pointer to the buffer!):
WIFEXITED(status)
is non-zero if the child exited normally.
WEXITSTATUS(status)
evaluates to the least significant eight bits of
the return code of the child which terminated,
which may have been set as the argument to a call
to exit() or as the argument for a return statement
in the main program. This macro can only be evalu
ated if WIFEXITED returned non-zero.
WIFSIGNALED(status)
returns true if the child process exited because of
a signal which was not caught.
WTERMSIG(status)
returns the number of the signal that caused the
child process to terminate. This macro can only be
evaluated if WIFSIGNALED returned non-zero.
WIFSTOPPED(status)
returns true if the child process which caused the
return is currently stopped; this is only possible
if the call was done using WUNTRACED.
WSTOPSIG(status)
returns the number of the signal which caused the
child to stop. This macro can only be evaluated if
WIFSTOPPED returned non-zero.
If rusage is not NULL, the struct rusage as defined in
<sys/resource.h> it points to will be filled with account
ing information. See getrusage(2) for details.
RETURN VALUE
The process ID of the child which exited, -1 on error (in
particular, when no unwaited-for child processes of the
specified kind exist) or zero if WNOHANG was used and no
child was available yet. In the latter two cases errno
ERRORS
ECHILD No unwaited-for child process as specified does
exist.
ERESTARTSYS
if WNOHANG was not set and an unblocked signal or a
SIGCHLD was caught. This error is returned by the
system call. The library interface is not allowed
to return ERESTARTSYS, but will return EINTR.
NOTE
Including <sys/time.h> is not required these days, but
increases portability. (Indeed, <sys/resource.h> defines
the rusage structure with fields of type struct timeval
defined in <sys/time.h>.)
CONFORMING TO
SVr4, POSIX.1
SEE ALSO
signal(2), getrusage(2), wait(2), signal(7)
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