How to achieve exclusive writing but non-exclusive reading?

Look at the Java5 parallel api:

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/locks/ReadWriteLock.html

This will satisfy your requirement, as you can allow multiple threads to read without locking and locking only when writing.

Here's an interesting post comparing this api with a traditional synchronous read: ReentrantReadWriteLock vs synchronized

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