WAIT4(2) Linux Programmer's Manual WAIT4(2)
NAME
wait3, wait4 - wait for process termination, BSD style
SYNOPSIS
#include
#include
#include
#include
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 process until a child 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 has already exited by the time of the call (a
so-called "zombie" process), the function returns immediately. Any system resources used
by the child are freed.
The wait4 function suspends execution of the current process 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" process), 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:
WNOHANG
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 information 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 it points to will
be filled with accounting 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 will be set appropriately.
ERRORS
ECHILD No unwaited-for child process as specified does exist.
EINTR if WNOHANG was not set and an unblocked signal or a SIGCHLD was caught.
EINVAL Invalid value for options given for wait4.
NOTES
Including is not required these days, but increases portability. (Indeed,
defines the rusage structure with fields of type struct timeval defined
in .)
The prototype for these functions is only available if _BSD_SOURCE is defined (either
explicitly, or implicitly, by not defining _POSIX_SOURCE or compiling with the -ansi
flag).
CONFORMING TO
SVr4, POSIX.1
SEE ALSO
signal(2), getrusage(2), wait(2), signal(7)
Linux 1997-06-23 WAIT4(2)
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