Threads: Synchronised Methods

• Critical section: lost update; race condition; one or more threads accessing an object already accessed by another thread; potential error condition
• Locking: avoids race condition by not allowing other threads to access an object already accessed by a thread
• synchronized methods & blocks: Java locking mechanism; ensures that no other thread may access a synchronised method of the object; unsynchronised methods may still be accessed
• notify(): notifies a particular thread waiting for access of a locked object as the locking thread unlocks it before exiting
• notifyAll(): notifies all the threads waiting for access of a locked object as the locking thread unlocks it before exit
• wait(): waits for access of a synchronised method of an object locked by another thread
• Reentrant lock: A thread accessing synchronised methods (blocks) of an object already locked by itself
• Examples:
  • synchronized method:

      public synchronized int get(){
    

  • wait():

    	while (available == false){
    	  try{
    		wait();
    	  } catch (InterruptedException e){ }
    	}
    

  • notifyAll();: