Question about Java synchronized

by

No; synchronized only prevents multiple threads from simultaneously executing the method in the same instance. If you have n instances, there could be n threads, each executing the method in one of the instances.

If you need to ensure that only one thread may execute the method across all instances, you should make the method static, or make the method non-synchronized and rather use a synchronized block inside the method to lock on a private static field.

Edit: Note that synchronizing on a private instance variable is preferrable to having a synchronized method or to synchronize on this, and that locking on a private static instance variable is preferrable to having a static synchronized method or an instance method that synchronizes on this.getClass(). The reason is that this and this.getClass() are object references that are accessible throughout the program, so anybody may synchronize on these objects, and thereby block threads that want to call your method.

Edit: Also, see @Cowan’s comment below – summary: if you really want to lock on the class, you might want to use synchronized (Worker.class) rather than synchronized (this.getClass()), depending on what effect you want in the case of subclassing.

More Related Contents:

  1. How can I get my threaded program to print specific output
  2. Loop doesn’t see value changed by other thread without a print statement
  3. Avoid synchronized(this) in Java?
  4. Is multi-thread output from System.out.println interleaved
  5. Synchronizing on String objects in Java
  6. Synchronization vs Lock
  7. What is the difference between atomic / volatile / synchronized?
  8. How to synchronize a static variable among threads running different instances of a class in Java?
  9. How do I make my ArrayList Thread-Safe? Another approach to problem in Java?
  10. How do synchronized static methods work in Java and can I use it for loading Hibernate entities?
  11. Are Java static initializers thread safe?
  12. Java double checked locking
  13. Synchronizing on an Integer value [duplicate]
  14. Java Synchronized Block for .class
  15. Waiting on multiple threads to complete in Java
  16. Concurrent threads adding to ArrayList at same time – what happens?
  17. What is the difference between a synchronized method and synchronized block in Java? [duplicate]
  18. Collections.synchronizedList and synchronized
  19. Java synchronized block vs. Collections.synchronizedMap
  20. Correct way to synchronize ArrayList in java
  21. Ensure that Spring Quartz job execution doesn’t overlap
  22. Sharing a variable between multiple different threads
  23. Should you synchronize the run method? Why or why not?
  24. How to acquire a lock by a key
  25. synchronized block for an Integer object
  26. difference between synchronizing a static method and a non static method
  27. Is synchronization within an HttpSession feasible?
  28. Why do I need to synchronize a list returned by Collections.synchronizedList
  29. Race between System.out and System.err in java [duplicate]
  30. How to synchronize or lock upon variables in Java?

Leave a Comment