sleepPosix

fn sleepPosix(timeout: Io.Timeout) Io.Cancelable!void {
    const clock_id: posix.clockid_t = clockToPosix(switch (timeout) {
        .none => .awake,
        .duration => |d| d.clock,
        .deadline => |d| d.clock,
    });
    const deadline_nanoseconds: i96 = switch (timeout) {
        .none => std.math.maxInt(i96),
        .duration => |duration| duration.raw.nanoseconds,
        .deadline => |deadline| deadline.raw.nanoseconds,
    };
    var timespec: posix.timespec = timestampToPosix(deadline_nanoseconds);
    const syscall: Syscall = try .start();
    while (true) {
        const rc = posix.system.clock_nanosleep(clock_id, .{ .ABSTIME = switch (timeout) {
            .none, .duration => false,
            .deadline => true,
        } }, &timespec, &timespec);
        // POSIX-standard libc clock_nanosleep() returns *positive* errno values directly
        switch (if (builtin.link_libc) @as(posix.E, @fromBackingInt(@intCast(rc))) else posix.errno(rc)) {
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            // Handles SUCCESS as well as clock not available and unexpected
            // errors. The user had a chance to check clock resolution before
            // getting here, which would have reported 0, making this a legal
            // amount of time to sleep.
            else => {
                syscall.finish();
                return;
            },
        }
    }
}