Package org.jboss.weld.injection

Class ThreadLocalStack<T>

java.lang.Object

org.jboss.weld.injection.ThreadLocalStack<T>

Direct Known Subclasses:

CurrentEventMetadata, CurrentInjectionPoint

public class ThreadLocalStack<T>
extends Object

A stack that is kept in thread-local. Two operations were identified to be expensive in micro benchmarks:

• ThreadLocal.set()
• ThreadLocal.get() if the current value is null (because such get involves setting the initial value)

Therefore this implementation tries to optimize that. First of all we make use of RequestScopedCache for cleaning up the thread local. If RequestScopedCache is active we do not remove the stack from thread local immediately when it becomes empty but defer this to the point when RequestScopedCache is cleaned up. Secondly, we reduce the number of ThreadLocal.get() accesses by returning a ThreadLocalStack.ThreadLocalStackReference which a client uses to pop a value. Lastly, the ThreadLocal instance is configured to set a new initial value by default. This is safe when RequestScopedCache is used but may lead to ThreadLocal leak when it is not. Therefore, special care needs to be take to guarantee that each ThreadLocal.get() operation has a matching ThreadLocalStack.Stack.removeIfEmpty() call (see peek()) as an example.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	ThreadLocalStack.ThreadLocalStackReference<T>	Reference to a thread-local stack.

Constructor Summary

Constructors

Constructor	Description
ThreadLocalStack()

Method Summary

Modifier and Type	Method	Description
T	peek()
ThreadLocalStack.ThreadLocalStackReference<T>	push(T item)
ThreadLocalStack.ThreadLocalStackReference<T>	pushConditionally(T item, boolean condition)	Convenience method which only pushes something to stack if the condition evaluates to true.
ThreadLocalStack.ThreadLocalStackReference<T>	pushIfNotNull(T item)	Convenience method which also accepts null values.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ThreadLocalStack

public ThreadLocalStack()

Method Details

push

public ThreadLocalStack.ThreadLocalStackReference<T> push(T item)

peek

public T peek()

pushConditionally

public ThreadLocalStack.ThreadLocalStackReference<T> pushConditionally(T item,
 boolean condition)

Convenience method which only pushes something to stack if the condition evaluates to true. If the condition evaluates to true, this method behaves the same as push(Object). Otherwise, a special null ThreadLocalStack.ThreadLocalStackReference object is returned. ThreadLocalStack.ThreadLocalStackReference.pop() may be called on the returned object - it will not have any effect and always return null.

pushIfNotNull

public ThreadLocalStack.ThreadLocalStackReference<T> pushIfNotNull(T item)

Convenience method which also accepts null values. If the given parameter is non-null, this method behaves the same as push(Object). Otherwise, a special null ThreadLocalStack.ThreadLocalStackReference object is returned. ThreadLocalStack.ThreadLocalStackReference.pop() may be called on the returned object - it will not have any effect and always return null.