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concurrency : Object leak prematurely

 
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http://docs.oracle.com/javase/tutorial/essential/concurrency/syncmeth.html

When constructing an object that will be shared between threads, be very careful that a reference to the object does not "leak" prematurely. For example, suppose you want to maintain a List called instances containing every instance of class. You might be tempted to add the following line to your constructor:

instances.add(this);

But then other threads can use instances to access the object before construction of the object is complete.



Can someone please give an example explaining the above?

Thanks
Shivani
 
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In this code the new thread may grab either the first A or the second A from the list, depending on whether the second A was already added to the list by the time the thread started running. If the thread gets the second A, it may then find that initialized can be either true or false, it depends on whether initialized = true; ran before the thread tried to print it.
 
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