WAIT(2) WAIT(2)
NAME
wait - wait for child process to exit
SYNOPSIS
wait := load Wait Wait->PATH;
Wait: module
{
init: fn();
read: fn(fd: ref Sys->FD): (int, string, string);
monitor: fn(fd: ref Sys->FD): (int, chan of (int, string, string));
parse: fn(status: string): (int, string, string);
};
DESCRIPTION
Wait helps use the wait file of prog(3).
Init must be called to initialise the module before invoking
any other function.
Read reads a single wait record from file descriptor fd,
which must be open on some process p's wait file, and
returns a tuple (pid, module, status) where pid is the pro-
cess ID of a child of p that has exited, module is the name
of the module that caused p to exit, and status is nil if
pid ended without error or a status message otherwise. If
reading the wait file resulted in end of file or error, pid
is 0 (for end of file) or -1 on error (and status is the
system error string for the error).
Monitor provides a channel interface to the wait file open
on fd; it allows, for instance, a process to use alt to
exchange data with a process but also see it exit (for good
or ill). It starts a monitor process that applies read to
fd and sends each resulting tuple on a channel. It returns
a tuple (pid, c) where pid is the process ID of the monitor
process (which can be used to kill it when done with it),
and c is the channel on which the process sends each value
it reads. The tuple has the format described above for
read. The monitor process exits when the wait file fd
yields end of file or error, after sending the corresponding
tuple on c.
Parse takes a complete status string as read from a wait
file and returns a tuple (pid, module, status) as described
for read above.
SEE ALSO
sh(1), prog(3)
Page 1 Plan 9 (printed 12/22/24)