InheritableThreadLocal

AI-generated Key Takeaways

• InheritableThreadLocal allows child threads to inherit values from their parent threads for thread-local variables.

• It's primarily used for propagating per-thread attributes like User IDs or Transaction IDs to child threads automatically.

• Child values are typically identical to the parent's but can be customized by overriding the childValue method.

• This class extends ThreadLocal and provides additional inheritance functionality.

public class InheritableThreadLocal extends ThreadLocal<T>

This class extends ThreadLocal to provide inheritance of values from parent thread to child thread: when a child thread is created, the child receives initial values for all inheritable thread-local variables for which the parent has values. Normally the child's values will be identical to the parent's; however, the child's value can be made an arbitrary function of the parent's by overriding the childValue method in this class.

Inheritable thread-local variables are used in preference to ordinary thread-local variables when the per-thread-attribute being maintained in the variable (e.g., User ID, Transaction ID) must be automatically transmitted to any child threads that are created.

See Also

• ThreadLocal

Public Constructor Summary

InheritableThreadLocal()

Protected Method Summary

T	childValue(T parentValue) Computes the child's initial value for this inheritable thread-local variable as a function of the parent's value at the time the child thread is created.

Inherited Method Summary

From class java.lang.ThreadLocal

T	get() Returns the value in the current thread's copy of this thread-local variable.
T	initialValue() Returns the current thread's "initial value" for this thread-local variable.
void	remove() Removes the current thread's value for this thread-local variable.
void	set(T value) Sets the current thread's copy of this thread-local variable to the specified value.
static <S> ThreadLocal<S>	withInitial(Supplier<? extends S> supplier) Creates a thread local variable.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public InheritableThreadLocal ()

Protected Methods

protected T childValue (T parentValue)

Computes the child's initial value for this inheritable thread-local variable as a function of the parent's value at the time the child thread is created. This method is called from within the parent thread before the child is started.

This method merely returns its input argument, and should be overridden if a different behavior is desired.

Parameters

parentValue	the parent thread's value

Returns

• the child thread's initial value