WAIT4 (2)
wait for process termination, BSD style
SYNOPSIS
#define _USE_BSD
#include <sys/types.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 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:
which means to wait for any child process whose process group ID is
equal to the absolute value of
pid .
which means to wait for any child process; this is equivalent to
calling
wait3 .
which means to wait for any child process whose process group ID is
equal to that of the calling process.
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 evaluated 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 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.
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 .
CONFORMING TO
SEE ALSO
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