ThreadLocal JDK 1.6)

Description

public class ThreadLocal

This class provides thread-local variables.

This class provides thread-local variables. These variables differ from their normal counterparts in that each thread that accesses one (via its get or set method) has its own, independently initialized copy of the variable. ThreadLocal instances are typically private static fields in classes that wish to associate state with a thread (e.g., a user ID or Transaction ID).

For example, the class below generates unique identifiers local to each thread. A thread's id is assigned the first time it invokes UniqueThreadIdGenerator.getCurrentThreadId() and remains unchanged on subsequent calls.

 import java.util.concurrent.atomic.AtomicInteger;

 public class UniqueThreadIdGenerator {

     private static final AtomicInteger uniqueId = new AtomicInteger(0);

     private static final ThreadLocal < Integer > uniqueNum = 
         new ThreadLocal < Integer > () {
             @Override protected Integer initialValue() {
                 return uniqueId.getAndIncrement();
         }
     };
 
     public static int getCurrentThreadId() {
         return uniqueId.get();
     }
 } // UniqueThreadIdGenerator

Each thread holds an implicit reference to its copy of a thread-local variable as long as the thread is alive and the ThreadLocal instance is accessible; after a thread goes away, all of its copies of thread-local instances are subject to garbage collection (unless other references to these copies exist).

See also:

Methods

Hide/Show inherited methods

pack-private T childValue ( T parentValue)

Method childValue is visibly defined in subclass InheritableThreadLocal, but is internally defined here for the sake of providing createInheritedMap factory method without needing to subclass the map class in InheritableThreadLocal.

pack-privatestatic ThreadLocalMap createInheritedMap (ThreadLocalMap parentMap)

Factory method to create map of inherited thread locals.

pack-private void createMap (Thread t, T firstValue)

Create the map associated with a ThreadLocal.

public T get ()

Returns the value in the current thread's copy of this thread-local variable.

pack-private ThreadLocalMap getMap (Thread t)

Get the map associated with a ThreadLocal.

protected T initialValue ()

Returns the current thread's "initial value" for this thread-local variable.

public void remove ()

Removes the current thread's value for this thread-local variable.

public void set ( T value)

Sets the current thread's copy of this thread-local variable to the specified value.