What happens when multiple threads ask for the same class to be loaded at same time?

Question

In a multi-threaded environment, when multiple threads refer to a class at the same time, does the JVM end up loading the class multiple times?

If not, how does synchronization happen?

Answer 1

The class will be loaded once. See jls 12.4.2

For each class or interface C, there is a unique initialization lock LC. The mapping from C to LC is left to the discretion of the Java Virtual Machine implementation. The procedure for initializing C is then as follows:

1. Synchronize on the initialization lock, LC, for C. This involves waiting until the current thread can acquire LC.

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