how to subscribe to speshevent and gcevent

gistfile1.txt

use nqp;
my $eventqueue;
class QueueType is repr<ConcBlockingQueue> {}
constant $evq = QueueType.new;

class GCEvent is array[int64] is repr<VMArray> is array_type(int64) {
    method gist {
        "GCEvent:\n  " ~ (<seqnum starttime vmtime duration is_major promoted promoted_ttl thread gen2roots> Z=> self.list).join("\n  ");
    }
}

class SpeshOverviewEvent is array[int64] is repr<VMArray> is array_type(int64) {
    method gist {
        "SpeshEvent:\n  " ~ (<seqnum starttime vmtime wait_before thread_id statstime new_frames updated_frames plantime certain_spesh observed_spesh osr_spesh speshtime frames_with_stats totaltime> Z=> self.list).join("\n  ");
    }
}

nqp::vmeventsubscribe($evq<>,
    nqp::hash(
        'gcevent', GCEvent,
        #'speshoverviewevent', SpeshOverviewEvent)
    )
    );

$eventqueue = $evq;

start {
    loop {
        my $thing = nqp::shift($eventqueue<>);
        if $thing.list[4] {
            say "---- ---- ---- ---- ----";
            say "GC EVENT";
            $thing.say;
            say "---- ---- ---- ---- ----";
        }
    }
}