[DE-535] Provide the capability to reuse an existing Vertx instance

[jamesnetherton]

My project is based on a Framework (Quarkus) that uses Vert.x.

When I use the ArangoDB Java Driver to connect to a server I see:

WARN  [io.ver.cor.imp.VertxImpl] (executor-thread-1) You're already on a Vert.x context, are you sure you want to create a new Vertx instance?

It happens because HttpConnection, creates its own Vertx:

arangodb-java-driver/http/src/main/java/com/arangodb/http/HttpConnection.java

Line 111 in 3c5d8be

vertx = Vertx.vertx(new VertxOptions().setPreferNativeTransport(true).setEventLoopPoolSize(1));

In my case, there's already an existing Vertx instance managed by Quarkus. So it'd be useful if there were some way to reuse it in the ArangoDB Java Driver.

[rashtao]

@jamesnetherton
Thanks for reporting this.
In the next release, the driver can be configured with the Vert.x instance to use, see related PR.

[andtur]

Hi,

i have project that uses Vertx as framework. In one of the verticles I create a connection to arangoDB with java driver. With a configuration:
ArangoDB arango = new ArangoDB.Builder().host("localhost", 8529).user("some").password("some").build();
I get as expected:
WARNUNG: Found an existing Vert.x instance, you can reuse it by setting:
new ArangoDB.Builder()
// ...
.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build())
.build();**

if I add .protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build()) to the build call, then my request:
arango.db("myDB").exists()
hangs without returning back.
What could be the problem?
Thank you

[rashtao]

Hi,
note that arango.db("myDB").exists() uses the blocking driver API.

Are you invoking it from a Vert.x thread? In such case, you would block the Vert.x thread at the calling site and the driver would have no executor thread available to perform the request.

Instead, from within Vert.x threads you need to use the async driver API:

ArangoDBAsync arango = new ArangoDB.Builder()
// ...
.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build())
.build()
.async();

// ...

CompletableFuture<Boolean> existsCF = arango.db("myDB").exists();
// ...

Furthermore beware of the caveats of using CompletableFuture from within Vert.x threads, see https://github.com/cescoffier/vertx-completable-future

Or convert the CompletableFuture to Vert.x Future:

Future<Boolean> existsF = Future.fromCompletionStage(existsCF);
// ...

[andtur]

Hi,

Thank you very much for your answer, but that does not explain why does it work, when you are creating a new vertx instance inside of HTTPConnection.

Regards,
Andrey

[rashtao]

The Vert.x instance created inside HTTPConnection is used exclusively from the driver connection and it is never blocked. In such case, you would have multiple Vert.x instances in your applications, each one using different threads. So if you use the blocking API in your Vert.x threads you do not prevent the driver from executing the request, which is executed on different threads. Note that even in this case, you would block Vert.x threads, thus preventing execution of other Vert.x tasks (not from the driver, but related to other components of your application).

On the other side, when reusing the existing Vert.x instance, the driver does not create new Vert.x instaces or new threads, but reuses the existing ones.

[andtur]

Thank you very much for clarification. But that generally means, that if i use now the driver inside of my Vertx application and reuse the existing context, for each call to db (query, create, update) i need now create a Future? Before in my application I got a request, sent it over eventBus to DB vertical and there directly did a query.

[andtur]

So if i have a simple application like:

public class MainVerticle extends AbstractVerticle {

@Override
public void start(Promise<Void> startPromise) throws Exception {
	ArangoDB arango = new ArangoDB.Builder().host("localhost", 8529).user("user").password("pwd")

.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build()).build();
System.out.println(arango.db("myDB").exists());
}
}
I will have to pack now each execution of DB in blocking or Future?
That is not really practical, as the driver still returns boolean and not futures, so this:
CompletableFuture existsCF = arango.db("myDB").exists();
will not work.
And even this
ArangoDB arango = new ArangoDB.Builder().host("localhost", 8529).user("user").password("pwd").maxConnections(1)
.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build())
.build();
ArangoDBAsync adbAsync = arango.async();
CompletableFuture version = adbAsync.db("myDB").exists();
hangs in the exists call.

Thank you,
Andrey

[rashtao]

I will have to pack now each execution of DB in blocking or Future?

No, using the async API of the driver you get CompletableFuture back.

ArangoDB arango = new ArangoDB.Builder().host("localhost", 8529).user("user").password("pwd").maxConnections(1)
.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build())
.build();
ArangoDBAsync adbAsync = arango.async();
CompletableFuture version = adbAsync.db("myDB").exists();

this should work and not hang.
Are you sure it is hanging because the Vert.x thread is blocked? Can you please report the related thread dump or provide a code snippet to reproduce the issue?

[andtur]

Yes, i am, as i get the following:
WARNUNG: Thread Thread[vert.x-eventloop-thread-1,5,main] has been blocked for 5620 ms, time limit is 2000 ms
io.vertx.core.VertxException: Thread blocked

Sure, i start it now directly from IDE with io.vertx.core.Launcher run var.verticles.MainVerticle
MainVerticle:
public class MainVerticle extends AbstractVerticle {

@Override
public void start(Promise<Void> startPromise) throws Exception {
	ArangoDB arango = new ArangoDB.Builder().host("localhost", 8529).user("user").password("pwd").maxConnections(1)
			.protocolConfig(HttpProtocolConfig.builder().vertx(Vertx.currentContext().owner()).build())
			.build();
	ArangoDBAsync adbAsync = arango.async();
	CompletableFuture ex = adbAsync.db("myDB").exists();
	// This works
	ex.whenComplete((res, exp)->{
		System.out.println(res);
	});
	// This, the same as you use in CommunicationProtocol, hangs
	ex.get();
	System.out.println("Done");
}

}

[rashtao]

You are blocking the thread in your code:

ex.get();

Note that CommunicationProtocol invokes .get() only if you are using the sync API.
When using the async API CommunicationProtocol#executeAsync() is used.