thread_pool_save_example.py

import Queue  
import threading  

# This is the current version of the database.
rows = {
    1: {
        "version": 2,
        "postcode": 111111,
        "id": 1
    },
    2: {
        "version": 8,
        "postcode": 222222,
        "id": 2
    },
    3: {
        "version": 10,
        "postcode": 333333,
        "id": 3
    },
    4: {
        "version": 5,
        "postcode": 444444,
        "id": 4
    }
}


class UpdateDataThread(threading.Thread):  
  def __init__(self, queue):  
        threading.Thread.__init__(self)  
        self.queue = queue  
  def run(self):  
        while True:  
            print "waiting for message"  
            client_data = self.queue.get()
            pk = client_data['id']
            db_data = rows[pk]
            if client_data['version'] < db_data['version']:
                print 'Ignoring ', client_data
                continue
            else:
                print 'Saving ', client_data
                rows[pk] = client_data
        

def run():
    # We have 2 threads in the thread pool. Primary keys 1 and 3 will be mapped to first thread
    # Primary keys 2 and 4 will be mapped to the second thread
    THREAD_POOL_SIZE = 2
    threads = []
    queues = []
    for i in range(THREAD_POOL_SIZE):
        queue = Queue.Queue()  
        thread = UpdateDataThread(queue)
        threads.append(thread)
        queues.append(queue)
        thread.start()

    #Now threads are ready to process messages

    #Start sending requests
    requests = {
        1: {
            "version": 5,
            "postcode": 123456,
            "id": 1
        },
        2: {
            "version": 4,
            "postcode": 222,
            "id": 2
        },
        3: {
            "version": 2,
            "postcode": 33,
            "id": 3
        },
        4: {
            "version": 10,
            "postcode": 123456,
            "id": 4
        }
    }
    
    for key, value in requests.items():
        queue = queues[key % THREAD_POOL_SIZE]
        queue.put(value)

    # Keep the main thread alive.
    for thread in threads:
        thread.join()

if __name__ == "__main__":
    run()