README.md

Wingtips - wingtips-java8

Wingtips is a distributed tracing solution for Java based on the Google Dapper paper.

This module is a plugin extension module of the core Wingtips library and contains support for distributed tracing in a Java 8 environment, in particular providing easy ways to support tracing in asynchronous scenarios. The features it provides are:

• AsyncWingtipsHelper - An interface full of helper methods for dealing with asynchronous scenarios. You can use AsyncWingtipsHelper.DEFAULT_IMPL if you just want the default behavior, or you can create a custom implementation and override anything you need different behavior for.
• AsyncWingtipsHelperStatic - The static version of AsyncWingtipsHelper - it has static methods with the same method signatures as AsyncWingtipsHelper, allowing you to do static method imports to keep your code more readable at the expense of flexibility if you ever want to use a non-default implementation.
• All the *WithTracing classes, e.g. RunnableWithTracing, FunctionWithTracing, BiConsumerWithTracing, etc. - These classes wrap their associated functional interface from the Java 8 JDK java.util.function package. They are what AsyncWingtipsHelper uses to provide its functionality under the hood, and allow you to easily wrap the functional interfaces (and/or lambdas) so that they have the tracing info attached to the thread when they are executed. Most of the common functional interfaces are included, but if you run into a use case where you need some that are missing you are encouraged to submit a pull request to include them. Note that each of these classes has static factory methods named withTracing(...) so you can do static method imports to keep your code as clean and readable as possible. The AsyncWingtipsHelper* classes contain disambiguated versions of these factory methods in case you need multiple in the same class, e.g. runnableWithTracing(...) and functionWithTracing(...).

Please make sure you have read the base project README.md. This readme assumes you understand the principles and usage instructions described there.

NOTE

This module builds on the wingtips-core library. See that library's documentation for more detailed information on distributed tracing in general and this implementation in particular.

Usage Examples

(NOTE: Full usage details can be found in the javadocs for AsyncWingtipsHelper and the various *WithTracing classes)

The following examples of common scenarios show how you can easily use Wingtips in an asynchronous way without a lot of hassle with thread local gunk:

• An example of making the current thread's tracing and MDC info hop to a thread executed by an Executor:

import static com.nike.wingtips.util.asynchelperwrapper.RunnableWithTracing.withTracing;

// ...

// Just an example - please use an appropriate Executor for your use case.
Executor executor = Executors.newSingleThreadExecutor(); 

executor.execute(withTracing(() -> {
    // Code that needs tracing/MDC wrapping goes here
}));

• A similar example using CompletableFuture:

import static com.nike.wingtips.util.asynchelperwrapper.SupplierWithTracing.withTracing;

// ...

CompletableFuture.supplyAsync(withTracing(() -> {
    // Supplier code that needs tracing/MDC wrapping goes here.
    return foo;
}));

• This example shows how you might accomplish tasks in an environment where the tracing information is attached to some request context, and you need to temporarily attach the tracing info in order to do something (e.g. log some messages with tracing info automatically added using MDC):

import static com.nike.wingtips.util.AsyncWingtipsHelperStatic.runnableWithTracing;

// ...

TracingState tracingInfo = requestContext.getTracingInfo();
runnableWithTracing(
    () -> {
        // Code that needs tracing/MDC wrapping goes here
    },
    tracingInfo
).run();

• If you want to use the link and unlink methods manually to wrap some chunk of code, the general procedure looks like this:

import static com.nike.wingtips.util.AsyncWingtipsHelperStatic.linkTracingToCurrentThread;
import static com.nike.wingtips.util.AsyncWingtipsHelperStatic.unlinkTracingFromCurrentThread;

// ...

TracingState originalThreadInfo = null;
try {
    originalThreadInfo = linkTracingToCurrentThread(...);
    // Code that needs tracing/MDC wrapping goes here
}
finally {
    unlinkTracingFromCurrentThread(originalThreadInfo);
}

NOTE: Be careful with the last example (manual linking/unlinking). If you fail to guarantee the associated unlink at the end then you risk having traces stomp on each other or having other weird interactions occur that you wouldn't expect or predict. This can mess up your tracing, so before you use the manual linking/unlinking procedure make sure you know what you're doing and test thoroughly in a multi-threaded way under load, and with failure scenarios. For this reason it's recommended that you use the *WithTracing(...) methods whenever possible instead of manual linking/unlinking.

ALSO NOTE: You may have noticed in the examples above that you can import a static factory method named withTracing(...) for each individual class type, e.g. import static com.nike.wingtips.util.asynchelperwrapper.RunnableWithTracing.withTracing;, but that there's also a similar helper method in the AsyncWingtipsHelper* classes, e.g. runnableWithTracing(...) from import static com.nike.wingtips.util.AsyncWingtipsHelperStatic.runnableWithTracing;. They ultimately do the exact same thing - which one you choose is personal preference for readability, although if your class required both RunnableWithTracing and CallableWithTracing for example then using the runnableWithTracing(...) and callableWithTracing(...) methods from the AsyncWingtipsHelper* helper class would disambiguate the calls and keep their meaning clear at the cost of a slight increase in verbosity.