Double-Checked Locking

[QiAnXinCodeSafe]

Jprotobuf-rpc-socket/jprotobuf-rpc-core-spring/src/main/java/com/baidu/jprotobuf/pbrpc/spring/annotation/CommonAnnotationBeanPostProcessor.java

Lines 250 to 261 in bab1e2f

	if (metadata == null) {
	synchronized (this.injectionMetadataCache) {
	metadata = this.injectionMetadataCache.get(clazz);
	if (metadata == null) {
	LinkedList<InjectionMetadata.InjectedElement> elements;
	elements = new LinkedList<InjectionMetadata.InjectedElement>();
	parseFields(clazz, annotion, elements);
	parseMethods(clazz, annotion, elements);
	metadata = new InjectionMetadata(clazz, elements);
	this.injectionMetadataCache.put(clazz, metadata);
	}

Double-Checked Locking is widely cited and used as an efficient method for implementing lazy initialization in a multithreaded environment.
Unfortunately, it will not work reliably in a platform independent way when implemented in Java, without additional synchronization.
Declare a volatile local variable metadata offers a much more elegant solution