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);
};

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 process 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.