07event.py

# Fig. 19.15: fig19_15.py
# Event objects.

import threading
import random
import time


class VehicleThread(threading.Thread):
    """Class representing a motor vehicle at an intersection"""

    def __init__(self, threadName, event):
        """Initializes thread"""

        threading.Thread.__init__(self, name=threadName)

        # ensures that each vehicle waits for a green light
        self.threadEvent = event

    def run(self):
        """Vehicle waits unless/until light is green"""

        # stagger arrival times
        time.sleep(random.randrange(1, 10))

    # prints arrival time of car at intersection
        print("%s arrived at %s" %
              (self.getName(), time.ctime(time.time()))
              )
        # flag is false until light is green
        self.threadEvent.wait()

        # displays time that car departs intersection
        print("%s passes through intersection at %s" %
              (self.getName(), time.ctime(time.time())))


greenLight = threading.Event()
vehicleThreads = []

# creates and starts ten Vehicle threads
for i in range(1, 11):
    vehicleThreads.append(VehicleThread("Vehicle" + str(i),
                                        greenLight))

for vehicle in vehicleThreads:
    vehicle.start()

while threading.activeCount() > 1:

    # sets the Event's flag to false -- block all incoming vehicles
    greenLight.clear()
    print("RED LIGHT! at", time.ctime(time.time()))
    time.sleep(3)

    # sets the Event's flag to true -- awaken all waiting vehicles
    print("GREEN LIGHT! at", time.ctime(time.time()))
    greenLight.set()
    time.sleep(1)