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📌 TransmittableThreadLocal(TTL) 📌

Build Status Windows Build Status Coverage Status Maintainability
License Javadocs Maven Central GitHub release
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📖 English Documentation | 📖 中文文档

🔧 Functions

👉 The missing Java™ std lib(simple & 0-dependency) for framework/middleware, provide an enhanced InheritableThreadLocal that transmits ThreadLocal value between threads even using thread pooling components. Support Java 15/14/13/12/11/10/9/8/7/6.

Class InheritableThreadLocal in JDK can transmit value to child thread from parent thread.

But when use thread pool, thread is cached up and used repeatedly. Transmitting value from parent thread to child thread has no meaning. Application need transmit value from the time task is created to the time task is executed.

If you have problem or question, please submit Issue or play fork and pull request dance.

🎨 Requirements

The Requirements listed below is also why I sort out TransmittableThreadLocal in my work.

  • Application container or high layer framework transmit information to low layer sdk.
  • Transmit context to logging without application code aware.

👥 User Guide

1. Simple usage

// set in parent thread
TransmittableThreadLocal<String> context = new TransmittableThreadLocal<String>();
context.set("value-set-in-parent");

// =====================================================

// read in child thread, value is "value-set-in-parent"
String value = context.get();

# See the executable demo SimpleDemo.kt with full source code.

This is the function of class InheritableThreadLocal, should use class InheritableThreadLocal instead.

But when use thread pool, thread is cached up and used repeatedly. Transmitting value from parent thread to child thread has no meaning. Application need transmit value from the time task is created to the point task is executed.

The solution is below usage.

2. Transmit value even using thread pool

2.1 Decorate Runnable and Callable

Decorate input Runnable and Callable by TtlRunnable and TtlCallable.

Sample code:

TransmittableThreadLocal<String> parent = new TransmittableThreadLocal<String>();
parent.set("value-set-in-parent");

Runnable task = new RunnableTask();
// extra work, create decorated ttlRunnable object
Runnable ttlRunnable = TtlRunnable.get(task);
executorService.submit(ttlRunnable);

// =====================================================

// read in task, value is "value-set-in-parent"
String value = parent.get();

above code show how to dealing with Runnable, Callable is similar:

TransmittableThreadLocal<String> parent = new TransmittableThreadLocal<String>();
parent.set("value-set-in-parent");

Callable call = new CallableTask();
// extra work, create decorated ttlCallable object
Callable ttlCallable = TtlCallable.get(call);
executorService.submit(ttlCallable);

// =====================================================

// read in call, value is "value-set-in-parent"
String value = parent.get();

# See the executable demo TtlWrapperDemo.kt with full source code.

2.2 Decorate thread pool

Eliminating the work of Runnable and Callable Decoration every time it is submitted to thread pool. This work can completed in the thread pool.

Use util class com.alibaba.ttl.threadpool.TtlExecutors to decorate thread pool.

Util class com.alibaba.ttl.threadpool.TtlExecutors has below methods:

  • getTtlExecutor: decorate interface Executor
  • getTtlExecutorService: decorate interface ExecutorService
  • getTtlScheduledExecutorService: decorate interface ScheduledExecutorService

Sample code:

ExecutorService executorService = ...
// extra work, create decorated executorService object
executorService = TtlExecutors.getTtlExecutorService(executorService);

TransmittableThreadLocal<String> parent = new TransmittableThreadLocal<String>();
parent.set("value-set-in-parent");

Runnable task = new RunnableTask();
Callable call = new CallableTask();
executorService.submit(task);
executorService.submit(call);

// =====================================================

// read in Task or Callable, value is "value-set-in-parent"
String value = parent.get();

# See the executable demo TtlExecutorWrapperDemo.kt with full source code.

2.3 Use Java Agent to decorate thread pool implementation class

In this usage, transmission is transparent(no decoration operation).

Sample code:

// ## 1. upper layer logic of framework ##
TransmittableThreadLocal<String> context = new TransmittableThreadLocal<String>();
context.set("value-set-in-parent");

// ## 2. biz logic ##
ExecutorService executorService = Executors.newFixedThreadPool(3);

Runnable task = new RunnableTask();
Callable call = new CallableTask();
executorService.submit(task);
executorService.submit(call);

// ## 3. underlayer logic of framework ##
// read in Task or Callable, value is "value-set-in-parent"
String value = context.get();

# See the executable demo AgentDemo.kt with full source code, run demo by the script scripts/run-agent-demo.sh.

At present, TTL agent has decorated below JDK execution components(aka. thread pool) implementation:

  • java.util.concurrent.ThreadPoolExecutor and java.util.concurrent.ScheduledThreadPoolExecutor
  • java.util.concurrent.ForkJoinTask（corresponding execution component is java.util.concurrent.ForkJoinPool）
    • decoration implementation code is in TtlForkJoinTransformlet.java, supports since version 2.5.1.
    • NOTE: CompletableFuture and (parallel) Stream introduced in Java 8 is executed through ForkJoinPool underneath, so after supporting ForkJoinPool, TTL also supports CompletableFuture and Stream transparently. 🎉
  • java.util.TimerTask（corresponding execution component is java.util.Timer）
    • decoration implementation code is in TtlTimerTaskTransformlet.java, supports since version 2.7.0.
    • NOTE: Since version 2.11.2 decoration for TimerTask default is enable (because correctness is first concern, not the best practice like "It is not recommended to use TimerTask" :); before version 2.11.1 default is disable.
    • enabled/disable by agent argument ttl.agent.enable.timer.task:
      • -javaagent:path/to/transmittable-thread-local-2.x.x.jar=ttl.agent.enable.timer.task:true
      • -javaagent:path/to/transmittable-thread-local-2.x.x.jar=ttl.agent.enable.timer.task:false
    • more info about TTL agent arguments, see the javadoc of TtlAgent.java.

Add start options on Java command:

  • -javaagent:path/to/transmittable-thread-local-2.x.x.jar

NOTE：

  • Because TTL agent modified the JDK std lib classes, make code refer from std lib class to the TTL classes, so the TTL Agent jar must be added to boot classpath.
  • Since v2.6.0, TTL agent jar will auto add self to boot classpath. But you should NOT modify the downloaded TTL jar file name in the maven repo(eg: transmittable-thread-local-2.x.x.jar).
    • if you modified the downloaded TTL jar file name(eg: ttl-foo-name-changed.jar), you must add TTL agent jar to boot classpath manually by java option -Xbootclasspath/a:path/to/ttl-foo-name-changed.jar.

The implementation of auto adding self agent jar to boot classpath use the Boot-Class-Path property of manifest file(META-INF/MANIFEST.MF) in the TTL Java Agent Jar:

Boot-Class-Path

A list of paths to be searched by the bootstrap class loader. Paths represent directories or libraries (commonly referred to as JAR or zip libraries on many platforms). These paths are searched by the bootstrap class loader after the platform specific mechanisms of locating a class have failed. Paths are searched in the order listed.

More info:

Java command example:

java -javaagent:transmittable-thread-local-2.x.x.jar \
    -cp classes \
    com.alibaba.demo.ttl.agent.AgentDemo

or

# if changed the TTL jar file name or the TTL version is before 2.6.0,
# should set argument -Xbootclasspath explicitly.
java -javaagent:path/to/ttl-foo-name-changed.jar \
    -Xbootclasspath/a:path/to/ttl-foo-name-changed.jar \
    -cp classes \
    com.alibaba.demo.ttl.agent.AgentDemo

Run the script scripts/run-agent-demo.sh to start demo of "Use Java Agent to decorate thread pool implementation class".

🔌 Java API Docs

The current version Java API documentation: https://alibaba.github.io/transmittable-thread-local/apidocs/

🍪 Maven Dependency

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>transmittable-thread-local</artifactId>
    <version>2.11.5</version>
</dependency>

Check available version at search.maven.org.

🔨 About compilation, build and dev

How to compile and build

Compilation/build environment require JDK 8~11; Compilation can be performed in the normal way of Maven.

# The project already contains Maven that satisfied the required version, directly run mvnw in the project root directory; there is no need to manually install Maven by yourself.

# Run test case
./mvnw test
# Compile and package
./mvnw package
# Run test case, compile and package, install TTL library to local Maven
./mvnw install

##################################################
# If you use `Maven` installed by yourself, the version requirement: maven 3.3.9+

mvn install

How to development by IDE

If you use IDE to develop (such as IntelliJ IDEA), note that: open the pom4ide.xml file in the root directory of the project instead of pom.xml via IDE; To avoid IDE complain using JDK 8 standard library classes not found.

The reason that IDE support is not good / have to change a POM file, is:
The code implementation of TTL uses the JDK 8 standard library class, but it is compiled into a Java 6 version class files.

🗿 More Documentation

📚 Related Resources

JDK Core Classes

👷 Contributors

  • Jerry Lee <oldratlee at gmail dot com> @oldratlee
  • Yang Fang <snoop.fy at gmail dot com> @driventokill
  • Zava Xu <zava.kid at gmail dot com> @zavakid
  • wuwen <wuwen.55 at aliyun dot com> @wuwen5
  • Xiaowei Shi <179969622 at qq dot com> @xwshiustc
  • David Dai <351450944 at qq dot com> @LNAmp
  • Your name here :-)