WAIT(3) WAIT(3)
NAME
await, awaitnohang, awaitfor, wait, waitnohang, waitfor,
waitpid - wait for a process to exit
SYNOPSIS
#include <u.h>
#include <libc.h>
Waitmsg* wait(void)
Waitmsg* waitnohang(void)
Waitmsg* waitfor(int pid)
int waitpid(void)
int await(char *s, int n)
int awaitnohang(char *s, int n)
int awaitfor(int pid, char *s, int n)
DESCRIPTION
Wait causes a process to wait for any child process (see
fork(2) and rfork(3)) to exit. It returns a Waitmsg holding
information about the exited child. A Waitmsg has this
structure:
typedef
struct Waitmsg
{
int pid; /* of loved one */
ulong time[3]; /* of loved one & descendants */
char *msg;
} Waitmsg;
Pid is the child's process id. The time array contains the
time the child and its descendants spent in user code, the
time spent in system calls, and the child's elapsed real
time, all in units of milliseconds. Msg contains the mes-
sage that the child specified in exits(3). For a normal
exit, msg[0] is zero, otherwise msg is the exit string pre-
fixed by the process name, a blank, the process id, and a
colon.
If there are no more children to wait for, wait returns
immediately, with return value nil.
The Waitmsg structure is allocated by malloc(3) and should
be freed after use. For programs that only need the pid of
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WAIT(3) WAIT(3)
the exiting program, waitpid returns just the pid and dis-
cards the rest of the information.
Waitnohang is like wait but does not block if there are no
more children to wait for. Instead it returns immediately
and sets errstr.
Waitfor is like wait but waits for a particular pid.
The underlying calls are await, awaitnohang, and awaitfor,
which fill in the n-byte buffer s with a textual representa-
tion of the pid, times, and exit string. There is no termi-
nal NUL. The return value is the length, in bytes, of the
data.
The filled-in buffer may be parsed (after appending a NUL)
using tokenize (see getfields(3)); the resulting fields are,
in order, pid, the three times, and the exit string, which
will be '' for normal exit. If the representation is longer
than n bytes, it is truncated but, if possible, properly
formatted. The information that does not fit in the buffer
is discarded, so a subsequent call to await will return the
information about the next exiting child, not the remainder
of the truncated message. In other words, each call to
await returns the information about one child, blocking if
necessary if no child has exited. If the calling process
has no living children, await returns -1.
SOURCE
/usr/local/plan9/src/lib9/wait.c
/usr/local/plan9/src/lib9/await.c
SEE ALSO
rfork(3), exits(3),
DIAGNOSTICS
These routines set errstr.
BUGS
To avoid name conflicts with the underlying system, wait,
waitpid, and waitfor are preprocessor macros defined as
p9wait, p9waitpid, and p9waitfor; see intro(3).
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