[Issue 11493] Fix #11493. Simple implementation of getting number of references from C++ client

[Sunny-Island]

Fixes #11493

Master Issue: #11493

Motivation

In Pulsar, we use a single client to create multiple producers/consumers/readers. Is there any method/attribute that can give information on number of producers/readers/consumers connected to the given pulsar client instance at the given point of time?

Say there is a single pulsar client instance. Multiple consumers and readers are created from the given client instance. This client needs to be cleaned up when all the references are closed. In this case, it would be of help, to get information on the number of the consumers/readers/ getPartitionsForTopic calls are active on the given client. Ie, having the number of references for the given client can provide information on whether it is fine to clean up the client instance at the given point of time.

Explain here the context, and why you're making that change. What is the problem you're trying to solve.

Modifications

Add these method to Client.h, Client.cc, ClientImpl.h, CliemtImpl.cc :

uint64_t getNumberOfProducer()
uint64_t getNumberOfConsumer()
uint64_t getNumberOfReader() (May not be used)

To count alive producers, I get each producer by weak point and check if it is connected.

Verifying this change

This change added tests and can be verified as follows:

Add unit test to check if these functions can return correct references number. Test file is ClientTest.cc. Test function is TEST(ClientTest, testGetNumberOfReferences).

Documentation

For this PR, do we need to update docs?

I will add doc to C++ client part in follow-up issue.

[Sunny-Island]

There are two questions:

1. For PartitionedProducer/PartitionedConsumer/MultiTopicConsumer which consist of more than one consumer/producer. They should be counted as one or more reference？
2. When created reader from client, client add reader's consumer to its consumer list. Should we remove getNumberOfReader()? I haven't implemented this function yet.

[BewareMyPower]

For PartitionedProducer/PartitionedConsumer/MultiTopicConsumer which consist of more than one consumer/producer. They should be counted as one or more reference？

I think it should be counted as multiple references. For example, if you created a producer of a 3 partitions topic, there're actually 3 TCP connections.

When created reader from client, client add reader's consumer to its consumer list. Should we remove getNumberOfReader()? I haven't implemented this function yet.

Reader is just treated as a Consumer, so I think we can remove the getNumberOfReader() method.

[Anonymitaet]

@Sunny-Island you can take this as references when adding docs.

[BewareMyPower]

@Anonymitaet I changed the label from doc-required to no-need-doc because the documents are already added to the C++ header so that the related documents will be generated by Doxygen.

[Anonymitaet]

@BewareMyPower many thanks for providing doc info! Since this PR modifies docs (it adds some descriptions in .h files and they are "docs"), I label this PR with doc.