python4

Synchronizing Threads

 A new lock is created by calling the Lock() method

The release() method of the new lock object is used to release the lock

• run(): The run() method is the entry point for a thread.
• start(): The start() method starts a thread by calling the run method.
• join([time]): The join() waits for threads to terminate.

  #!/usr/bin/python
  
  import threading
  import time
  
  exitFlag = 0
  
  class myThread (threading.Thread):
      def __init__(self, threadID, name, counter):
          threading.Thread.__init__(self)
          self.threadID = threadID
          self.name = name
          self.counter = counter
      def run(self):
          print "Starting " + self.name
          print_time(self.name, self.counter, 5)
          print "Exiting " + self.name
  
  def print_time(threadName, delay, counter):
      while counter:
          if exitFlag:
              threadName.exit()
          time.sleep(delay)
          print "%s: %s" % (threadName, time.ctime(time.time()))
          counter -= 1
  
  # Create new threads
  thread1 = myThread(1, "Thread-1", 1)
  thread2 = myThread(2, "Thread-2", 2)
  
  # Start new Threads
  thread1.start()
  thread2.start()
  
  print "Exiting Main Thread"

  When the above code is executed, it produces the following result −

  Starting Thread-1
  Starting Thread-2
  Exiting Main Thread
  Thread-1: Thu Mar 21 09:10:03 2013
  Thread-1: Thu Mar 21 09:10:04 2013
  Thread-2: Thu Mar 21 09:10:04 2013
  Thread-1: Thu Mar 21 09:10:05 2013
  Thread-1: Thu Mar 21 09:10:06 2013
  Thread-2: Thu Mar 21 09:10:06 2013
  Thread-1: Thu Mar 21 09:10:07 2013
  Exiting Thread-1
  Thread-2: Thu Mar 21 09:10:08 2013
  Thread-2: Thu Mar 21 09:10:10 2013
  Thread-2: Thu Mar 21 09:10:12 2013
  Exiting Thread-2

   Now, Syncronize the threads,

  #!/usr/bin/python
  
  import threading
  import time
  
  class myThread (threading.Thread):
      def __init__(self, threadID, name, counter):
          threading.Thread.__init__(self)
          self.threadID = threadID
          self.name = name
          self.counter = counter
      def run(self):
          print "Starting " + self.name
          # Get lock to synchronize threads
          threadLock.acquire()
          print_time(self.name, self.counter, 3)
          # Free lock to release next thread
          threadLock.release()
  
  def print_time(threadName, delay, counter):
      while counter:
          time.sleep(delay)
          print "%s: %s" % (threadName, time.ctime(time.time()))
          counter -= 1
  
  threadLock = threading.Lock()
  threads = []
  
  # Create new threads
  thread1 = myThread(1, "Thread-1", 1)
  thread2 = myThread(2, "Thread-2", 2)
  
  # Start new Threads
  thread1.start()
  thread2.start()
  
  # Add threads to thread list
  threads.append(thread1)
  threads.append(thread2)
  
  # Wait for all threads to complete
  for t in threads:
      t.join()
  print "Exiting Main Thread"

  When the above code is executed, it produces the following result −

  Starting Thread-1
  Starting Thread-2
  Thread-1: Thu Mar 21 09:11:28 2013
  Thread-1: Thu Mar 21 09:11:29 2013
  Thread-1: Thu Mar 21 09:11:30 2013
  Thread-2: Thu Mar 21 09:11:32 2013
  Thread-2: Thu Mar 21 09:11:34 2013
  Thread-2: Thu Mar 21 09:11:36 2013
  Exiting Main Thread