[Client] Support passing existing executor providers to the client

[lhotari]

Motivation

In load and performance testing, there's a need to simulate production use cases and production workloads.
For this purpose, it would be useful to be able to share the thread pools used by Pulsar client instances in order to be able to run a large amount of Pulsar clients in a single JVM without the overhead of a lot of threads.
In the current solution, it's already possible to share the EventLoopGroup and HashedWheelTimer instances.
The solution for sharing the thread pools for the external / internal executors was missing. This PR adds support for that.

Example usage:

// shared thread pool related resources
ExecutorProvider internalExecutorProvider = new ExecutorProvider(8, "shared-internal-executor");
ExecutorProvider externalExecutorProvider = new ExecutorProvider(8, "shared-external-executor");
Timer sharedTimer = new HashedWheelTimer(getThreadFactory("shared-pulsar-timer"), 1, TimeUnit.MILLISECONDS);
EventLoopGroup sharedEventLoopGroup = new EpollEventLoopGroup();

// example of creating a client which uses the shared thread pools
PulsarClientImpl client = PulsarClientImpl.builder().conf(conf)
                .internalExecutorProvider(internalExecutorProvider)
                .externalExecutorProvider(externalExecutorProvider)
                .timer(sharedTimer)
                .eventLoopGroup(sharedEventLoopGroup)
                .build();

It seems that this would also improve the performance of the Pulsar Proxy since new thread pools for every client connection.

That happens in the Pulsar Proxy currently:

pulsar/pulsar-proxy/src/main/java/org/apache/pulsar/proxy/server/ProxyConnection.java

Lines 445 to 451 in af63e96

	private PulsarClientImpl createClient(final ClientConfigurationData clientConf, final AuthData clientAuthData,
	final String clientAuthMethod, final int protocolVersion) throws PulsarClientException {
	this.connectionPool = new ProxyConnectionPool(clientConf, service.getWorkerGroup(),
	() -> new ProxyClientCnx(clientConf, service.getWorkerGroup(), clientAuthRole, clientAuthData,
	clientAuthMethod, protocolVersion));
	return new PulsarClientImpl(clientConf, service.getWorkerGroup(), connectionPool, service.getTimer());
	}

An optimization was added in #9802 for sharing the timer, but it would be useful to also share the internal / external executors.

Modifications

Refactor the code to add an internal builder class so that more constructors don't have to be added for advanced initialization of the PulsarClientImpl class.

[eolivelli]

While I appreciate the feature and I see the benefits,
it looks like we are adding a new "official" way to build a Pulsar Client, that is not via the public API.

Do you want to use this only inside internal Pulsar tools ? the Proxy, Pulsar perf, Pulsar CLI tools ?

Why can't we add this support using the regular PulsarClient Builder API ?

[lhotari]

Do you want to use this only inside internal Pulsar tools ? the Proxy, Pulsar perf, Pulsar CLI tools ?

yes, mainly an internal, unsupported API. Pulsar Proxy and Pulsar perf are the main internal use cases.

Why can't we add this support using the regular PulsarClient Builder API ?

It seems that this would just add unnecessary complexity and extra baggage in the public API.
I'd assume that there are very few use cases where there would be a need to specify the thread pools to use.

My use case is in improving nosqlbench's Pulsar driver. This would allow to emulate thousands of isolated Pulsar clients within a single JVM. When a Pulsar client is shared, it doesn't properly emulate real production work loads.

[Anonymitaet]

@lhotari Thanks for your contribution. For this PR, do we need to update docs?

(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[codelipenghui]

@lhotari Could you please help resolve the conflicts? It's a nice have in 2.10.

[lhotari]

@lhotari Could you please help resolve the conflicts? It's a nice have in 2.10.

@codelipenghui I have rebased the changes and addressed the review comments. PTAL

[lhotari]

@codelipenghui This PR is now ready for final review