== Vert.x gRPC Context Storage

Vert.x gRPC Context Storage overrides the default `io.grpc.Context.Storage` implementation.

The default implementation always stores the gRPC context in a _thread-local_ variable.
This implementation stores the gRPC context the same way as Vert.x core stores request tracing data.

This means, for example, that when you implement a service method, the gRPC context is propagated across Vert.x async API calls:

[source,java]
----
Context grpcCtx1 = Context.current();

vertx.<String>executeBlocking(prom -> {

  // Same as grpcCtx1
  Context grpcCtx2 = Context.current();

  String result = doSomething();
  prom.complete(result);

}, ar -> {

  // Same as grpcCtx1 and grpcCtx2
  Context grpcCtx3 = Context.current();

});
----

[CAUTION]
====
The gRPC context is propagated across Vert.x async API calls only when the current Vert.x `link:../../apidocs/io/vertx/core/Context.html[Context]` is bound to a Vert.x HTTP server request.

It is not propagated if, for example, you invoke a stub on a non-Vert.x thread or from a verticle `link:../../apidocs/io/vertx/core/Verticle.html#start-io.vertx.core.Promise-[start]` method.
====

=== Using Vert.x gRPC Context Storage

To use Vert.x gRPC Context Storage, add the following dependency to the _dependencies_ section of your build descriptor:

* Maven (in your `pom.xml`):

[source,xml,subs="+attributes"]
----
<dependency>
 <groupId>io.vertx</groupId>
 <artifactId>vertx-grpc-context-storage</artifactId>
 <version>4.4.4</version>
</dependency>
----

* Gradle (in your `build.gradle` file):

[source,groovy,subs="+attributes"]
----
dependencies {
 compile 'io.vertx:vertx-grpc-context-storage:4.4.4'
}
----