Insufficient locking in ResteasyProviderFactory.getInstance()...?

[ThomasLorenzAGFA]

There is some locking in the ResteasyProviderFactory.getInstance() to prevent concurrent access to the instance:

resteasy/resteasy-core-spi/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java

Lines 99 to 117 in a304b9c

	public static ResteasyProviderFactory getInstance() {
	ResteasyProviderFactory result = instance;
	if (result == null) { // First check (no locking)
	synchronized (RD_LOCK) {
	result = instance;
	if (result == null) { // Second check (with locking)
	RuntimeDelegate runtimeDelegate = RuntimeDelegate.getInstance();
	if (runtimeDelegate instanceof ResteasyProviderFactory) {
	instance = result = (ResteasyProviderFactory) runtimeDelegate;
	} else {
	instance = result = newInstance(); //TODO use reflection directly, to avoid circular dependency
	}
	if (registerBuiltinByDefault)
	result.registerBuiltin();
	}
	}
	}
	return result;
	}

However it appears to be insufficient as the instance field is already set, and can be accessed by another thread without acquiring the lock, before the registerBuiltin() method is called (and has finished).