import heapq
import time
import threading
import Queue


class Sched:

    def __init__(self):
        self.heap = []
        self.running = True
        self.wait_event = threading.Event()

    def add(self, delay, queue):
        """Add new execution queue"""
        heapq.heappush(self.heap, (time.time() + delay, delay, queue))
        self.wait_event.set()

    def stop(self):
        self.running = False
        self.wait_event.set()

    def tasks(self):
        """Produce events until stopped"""
        self.running = True

        while self.running:
            self.wait_event.clear()
            runtime, delay, queue = checked_event = self.heap[0]
            now = time.time()
            if now < runtime:
                self.wait(runtime)
            else :
                runtime, delay, queue = event = heapq.heappop(self.heap)
                # assure event was not removed or altered after last look at self.heap[0]
                if event is checked_event:
                    try :
                        task = queue.get_nowait()
                    except Queue.Empty:
                        pass #XXX
                    else :
                        yield task
                self.add(delay, queue)

    def wait(self, timestamp):
        """Wait until time, may return earlier if internal event occurs (stop, add)"""
        self.wait_event.wait(timestamp - time.time())
        self.wait_event.clear()


if __name__ == '__main__':
    s = Sched()
    one_sec_q = Queue.Queue()
    one_sec_q.put('foo')
    one_sec_q.put('bar')
    s.add(1, one_sec_q)
    five_sec_q = Queue.Queue()
    five_sec_q.put('baz')
    s.add(5, five_sec_q)

    print time.time()
    for value in s.tasks():
        print time.time(), value