java.lang.Object
- java.lang.ThreadLocal<T>
- - java.lang.InheritableThreadLocal<T>
  - - com.alibaba.ttl.TransmittableThreadLocal<T>

All Implemented Interfaces:

TtlCopier<T>
```
public class TransmittableThreadLocal<T>
extends InheritableThreadLocal<T>
implements TtlCopier<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, TtlExecutors.getTtlExecutor(java.util.concurrent.Executor), TtlExecutors.getTtlExecutorService(java.util.concurrent.ExecutorService), TtlExecutors.getTtlScheduledExecutorService(java.util.concurrent.ScheduledExecutorService), TtlExecutors.getDefaultDisableInheritableThreadFactory(), TtlExecutors.getDisableInheritableThreadFactory(java.util.concurrent.ThreadFactory), TtlForkJoinPoolHelper, TtlForkJoinPoolHelper.getDefaultDisableInheritableForkJoinWorkerThreadFactory(), TtlForkJoinPoolHelper.getDisableInheritableForkJoinWorkerThreadFactory(java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory), TtlAgent

Nested Class Summary

Nested Classes
Modifier and Type	Class	Description
`static class`	`TransmittableThreadLocal.Transmitter`	`TransmittableThreadLocal.Transmitter` transmit all `TransmittableThreadLocal` and registered `ThreadLocal`(registered by `TransmittableThreadLocal.Transmitter.registerThreadLocal(java.lang.ThreadLocal<T>, com.alibaba.ttl.TtlCopier<T>)`) values of the 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()`	Default constructor.
`TransmittableThreadLocal(boolean disableIgnoreNullValueSemantics)`	Constructor, create a `TransmittableThreadLocal` with parameter `disableIgnoreNullValueSemantics` to control "Ignore-Null-Value Semantics".

Method Summary

All Methods Instance Methods Concrete Methods
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.
`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()
```
    Default constructor.
    Create a TransmittableThreadLocal instance with "Ignore-Null-Value Semantics". About "Ignore-Null-Value Semantics":
    
    If value is null(check by get() method), do NOT transmit this ThreadLocal.
    
    If set null value, also remove value(invoke remove() method).
    
    This is a pragmatic design decision:
    
    use explicit value type rather than null to biz intent.
    
    more safe(avoid NPE) and gc friendly.
    
    So it's not recommended to use null value.
    But the behavior of "Ignore-Null-Value Semantics" is NOT compatible with ThreadLocal and InheritableThreadLocal, you can disable this behavior/semantics via using constructor TransmittableThreadLocal(boolean) and set parameter disableIgnoreNullValueSemantics instead.
    More info see Issue #157.
    See Also:
    
    TransmittableThreadLocal(boolean)
  - TransmittableThreadLocal
```
public TransmittableThreadLocal(boolean disableIgnoreNullValueSemantics)
```
    Constructor, create a TransmittableThreadLocal with parameter disableIgnoreNullValueSemantics to control "Ignore-Null-Value Semantics".
    
    Parameters:
    
    disableIgnoreNullValueSemantics - disable "Ignore-Null-Value Semantics"
    
    Since:
    
    2.11.3
    
    See Also:
    
    TransmittableThreadLocal()
- Method Detail
  - copy
```
public 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(the shadow copy), and should be overridden if a different behavior is desired.
    
    Specified by:
    
    copy in interface TtlCopier<T>
    
    Since:
    
    1.0.0
    
    See Also:
    
    TransmittableThreadLocal.Transmitter.registerThreadLocal(ThreadLocal, TtlCopier), TransmittableThreadLocal.Transmitter.registerThreadLocalWithShadowCopier(ThreadLocal), TransmittableThreadLocal.Transmitter.unregisterThreadLocal(java.lang.ThreadLocal<T>)
  - beforeExecute
```
protected void beforeExecute()
```
    Callback method before task object(TtlRunnable/TtlCallable) execute.
    Default behavior is to 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 to 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>

Class TransmittableThreadLocal<T>

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.InheritableThreadLocal

Methods inherited from class java.lang.ThreadLocal

Methods inherited from class java.lang.Object

Constructor Detail

TransmittableThreadLocal

TransmittableThreadLocal

Method Detail

copy

beforeExecute

afterExecute

get

set

remove