Package com.netflix.hystrix.strategy.concurrency

Class HystrixRequestVariableDefault<T>

java.lang.Object

com.netflix.hystrix.strategy.concurrency.HystrixRequestVariableDefault<T>

Type Parameters:

T - Type to be stored on the HystrixRequestVariable

Example 1: HystrixRequestVariable<ConcurrentHashMap<String, DataObject>>

Example 2: HystrixRequestVariable<PojoThatIsThreadSafe>

All Implemented Interfaces:

HystrixRequestVariable<T>, HystrixRequestVariableLifecycle<T>

Direct Known Subclasses:

HystrixLifecycleForwardingRequestVariable

public class HystrixRequestVariableDefault<T>
extends java.lang.Object
implements HystrixRequestVariable<T>

Default implementation of HystrixRequestVariable. Similar to ThreadLocal but scoped at the user request level. Context is managed via HystrixRequestContext.

All statements below assume that child threads are spawned and initialized with the use of HystrixContextCallable or HystrixContextRunnable which capture state from a parent thread and propagate to the child thread.

Characteristics that differ from ThreadLocal:

• HystrixRequestVariable context must be initialized at the beginning of every request by HystrixRequestContext.initializeContext()
• HystrixRequestVariables attached to a thread will be cleared at the end of every user request by HystrixRequestContext.shutdown() which execute remove() for each HystrixRequestVariable
• HystrixRequestVariables have a shutdown(T) lifecycle method that gets called at the end of every user request (invoked when HystrixRequestContext.shutdown() is called) to allow for resource cleanup.
• HystrixRequestVariables are copied (by reference) to child threads via the HystrixRequestContext.getContextForCurrentThread() and HystrixRequestContext.setContextOnCurrentThread(com.netflix.hystrix.strategy.concurrency.HystrixRequestContext) functionality.
• HystrixRequestVariables created on a child thread are available on sibling and parent threads.
• HystrixRequestVariables created on a child thread will be cleaned up by the parent thread via the shutdown(T) method.

Note on thread-safety: By design a HystrixRequestVariables is intended to be accessed by all threads in a user request, thus anything stored in a HystrixRequestVariables must be thread-safe and plan on being accessed/mutated concurrently.

For example, a HashMap would likely not be a good choice for a RequestVariable value, but ConcurrentHashMap would.

Constructor Summary

Constructors

Constructor and Description
HystrixRequestVariableDefault() Creates a new HystrixRequestVariable that will exist across all threads within a HystrixRequestContext

Method Summary

Modifier and Type	Method and Description
T	get() Get the current value for this variable for the current request context.
T	initialValue() Computes the initial value of the HystrixRequestVariable in a request.
void	remove() Removes the value of the HystrixRequestVariable from the current request.
void	set(T value) Sets the value of the HystrixRequestVariable for the current request context.
void	shutdown(T value) Provide life-cycle hook for a HystrixRequestVariable implementation to perform cleanup before the HystrixRequestVariable is removed from the current thread.

Methods inherited from class java.lang.Object

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

Constructor Detail

HystrixRequestVariableDefault

public HystrixRequestVariableDefault()

Creates a new HystrixRequestVariable that will exist across all threads within a HystrixRequestContext

Method Detail

get

public T get()

Get the current value for this variable for the current request context.

Specified by:

get in interface HystrixRequestVariable<T>

Returns:

the value of the variable for the current request, or null if no value has been set and there is no initial value

initialValue

public T initialValue()

Computes the initial value of the HystrixRequestVariable in a request.

This is called the first time the value of the HystrixRequestVariable is fetched in a request. Override this to provide an initial value for a HystrixRequestVariable on each request on which it is used. The default implementation returns null.

Specified by:

initialValue in interface HystrixRequestVariableLifecycle<T>

Returns:

initial value of the HystrixRequestVariable to use for the instance being constructed

set

public void set(T value)

Sets the value of the HystrixRequestVariable for the current request context.

Note, if a value already exists, the set will result in overwriting that value. It is up to the caller to ensure the existing value is cleaned up. The shutdown(T) method will not be called

Parameters:

value - the value to set

remove

public void remove()

Removes the value of the HystrixRequestVariable from the current request.

This will invoke shutdown(T) if implemented.

If the value is subsequently fetched in the thread, the initialValue() method will be called again.

shutdown

public void shutdown(T value)

Provide life-cycle hook for a HystrixRequestVariable implementation to perform cleanup before the HystrixRequestVariable is removed from the current thread.

This is executed at the end of each user request when HystrixRequestContext.shutdown() is called or whenever remove() is invoked.

By default does nothing.

NOTE: Do not call get() from within this method or initialValue() will be invoked again. The current value is passed in as an argument.

Specified by:

shutdown in interface HystrixRequestVariableLifecycle<T>

Parameters:

value - the value of the HystrixRequestVariable being removed