Originální popis anglicky:
wait3, wait4 - wait for process termination, BSD style
Návod, kniha: Linux Programmer's Manual
#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);
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 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.
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.
- 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.
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>.)
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).
SVr4, POSIX.1
getrusage(2),
signal(2),
wait(2),
signal(7)
