Package com.alibaba.ttl

Class TransmittableThreadLocal<T>

java.lang.Object

java.lang.ThreadLocal<T>

java.lang.InheritableThreadLocal<T>

com.alibaba.ttl.TransmittableThreadLocal<T>

public class TransmittableThreadLocal<T>
extends InheritableThreadLocal<T>

TransmittableThreadLocal can transmit value from the thread of submitting task to the thread of executing task.

Note:
TransmittableThreadLocal extends InheritableThreadLocal, so TransmittableThreadLocal first is a InheritableThreadLocal.
If the inheritable ability from InheritableThreadLocal has potential leaking problem, you can disable the inheritable ability:

❶ by wrapping thread factory using method TtlExecutors.getDisableInheritableThreadFactory(java.util.concurrent.ThreadFactory) / TtlForkJoinPoolHelper.getDefaultDisableInheritableForkJoinWorkerThreadFactory() for thread pooling components(ThreadPoolExecutor, ForkJoinPool). Inheritable feature in thread pooling components should never happen, because threads in thread pooling components is pre-created and pooled, these threads is neutral for biz logic/data.
You can turn on "disable inheritable for thread pool" by TtlAgent so as to wrap thread factory for thread pooling components (ThreadPoolExecutor, ForkJoinPool) automatically and transparently.

❷ or by overriding method InheritableThreadLocal.childValue(Object). Whether the value should be inheritable or not can be controlled by the data owner, disable it carefully when data owner have a clear idea.

 TransmittableThreadLocal<String> transmittableThreadLocal = new TransmittableThreadLocal<String>() {
     protected String childValue(String parentValue) {
         return initialValue();
     }
 }

More discussion about "disable the inheritable ability" see issue #100: disable Inheritable when it's not necessary and buggy.

Since:

0.10.0

Author:

Jerry Lee (oldratlee at gmail dot com), Yang Fang (snoop dot fy at gmail dot com)

See Also:

TtlRunnable, TtlCallable, TtlExecutors.getDefaultDisableInheritableThreadFactory(), TtlExecutors.getDisableInheritableThreadFactory(java.util.concurrent.ThreadFactory), TtlForkJoinPoolHelper.getDefaultDisableInheritableForkJoinWorkerThreadFactory(), TtlForkJoinPoolHelper.getDisableInheritableForkJoinWorkerThreadFactory(java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory)

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	TransmittableThreadLocal.Transmitter	TransmittableThreadLocal.Transmitter transmit all TransmittableThreadLocal values of current thread to other thread by static methods TransmittableThreadLocal.Transmitter.capture() => TransmittableThreadLocal.Transmitter.replay(Object) => TransmittableThreadLocal.Transmitter.restore(Object) (aka CRR operation).

Constructor Summary

Constructors

Constructor	Description
TransmittableThreadLocal()

Method Summary

Modifier and Type	Method	Description
protected void	afterExecute()	Callback method after task object(TtlRunnable/TtlCallable) execute.
protected void	beforeExecute()	Callback method before task object(TtlRunnable/TtlCallable) execute.
protected T	copy(T parentValue)	Computes the value for this transmittable thread-local variable as a function of the source thread's value at the time the task Object is created.
T	get()	see ThreadLocal.get()
void	remove()	see ThreadLocal.remove()
void	set(T value)	see ThreadLocal.set(T)

Methods inherited from class java.lang.InheritableThreadLocal

childValue

Methods inherited from class java.lang.ThreadLocal

initialValue, withInitial

Methods inherited from class java.lang.Object

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

Constructor Detail

TransmittableThreadLocal

public TransmittableThreadLocal()

Method Detail

copy

protected T copy(T parentValue)

Computes the value for this transmittable thread-local variable as a function of the source thread's value at the time the task Object is created. This method is called from TtlRunnable or TtlCallable when it create, before the task is started.

This method merely returns reference of its source thread value, and should be overridden if a different behavior is desired.

Since:

1.0.0

beforeExecute

protected void beforeExecute()

Callback method before task object(TtlRunnable/TtlCallable) execute.

Default behavior is do nothing, and should be overridden if a different behavior is desired.

Do not throw any exception, just ignored.

Since:

1.2.0

afterExecute

protected void afterExecute()

Callback method after task object(TtlRunnable/TtlCallable) execute.

Default behavior is do nothing, and should be overridden if a different behavior is desired.

Do not throw any exception, just ignored.

Since:

1.2.0

get

public final T get()

see ThreadLocal.get()

Overrides:

get in class ThreadLocal<T>

set

public final void set(T value)

see ThreadLocal.set(T)

Overrides:

set in class ThreadLocal<T>

remove

public final void remove()

see ThreadLocal.remove()

Overrides:

remove in class ThreadLocal<T>