Hi All: Here is the question: Which of the following statements about threading are true 1) You can only obtain a mutually exclusive lock on methods in a class that extends Thread or implements runnable 2) You can obtain a mutually exclusive lock on any object 3) A thread can obtain a mutually exclusive lock on a method declared with the keyword synchronized 4) Thread scheduling algorithms are platform dependent I think only 2, 4 are correct, but the ans are 2, 3, 4. Is there any lock on a method ? Can somebody explain this ? Thanks in advance ! Yi Dong
Only oblects and classes have locks, methods don't. JLS, Chapter 17.13:
There is a lock associated with every object. The synchronized statement (�14.18) computes a reference to an object; it then attempts to perform a lock action on that object and does not proceed further until the lock action has successfully completed.
JLS, Chapter 18.104.22.168:
22.214.171.124 synchronized Methods A synchronized method acquires a lock (�17.1) before it executes. For a class (static) method, the lock associated with the Class object for the method�s class is used. For an instance method, the lock associated with this (the object for which the method was invoked) is used.
The code segments within a program that access the same object from separate, concurrent threads are called critical sections. In the Java language, a critical section can be a block or a method and are identified with the synchronized keyword. The Java platform then associates a lock with every object that has synchronized code.
[ November 24, 2003: Message edited by: Vad Fogel ] [ November 24, 2003: Message edited by: Vad Fogel ]