childWait

fn childWait(userdata: ?*anyopaque, child: *process.Child) process.Child.WaitError!process.Child.Term {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    defer ev.childCleanup(child);
    const pid = child.id.?;
    const source = c.dispatch.source_create(
        .PROC,
        @bitCast(@as(isize, pid)),
        .{ .PROC = .{ .EXIT = true } },
        ev.queue,
    ) orelse return error.Unexpected;
    source.as_object().set_context(Thread.current().currentFiber());
    source.set_event_handler(&Fiber.@"resume");
    ev.yield(.{ .activate = source.as_object() });
    source.as_object().release();
    var status: c_int = undefined;
    var ru: c.rusage = undefined;
    const ru_ptr = if (child.request_resource_usage_statistics) &ru else null;
    while (true) switch (c.errno(c.wait4(pid, &status, 0, ru_ptr))) {
        .SUCCESS => {
            if (ru_ptr) |p| child.resource_usage_statistics.rusage = p.*;
            return statusToTerm(@bitCast(status));
        },
        .INTR => {},
        .CHILD => |err| return errnoBug(err), // Double-free.
        else => |err| return unexpectedErrno(err),
    };
}