[Issue 8311][pulsar-client-cpp] In C shim, free message ID pointer after hitting callback

[bschofield]

Fixes #8311

Motivation

The C/C++ glue code in c_Producer.cc:handle_producer_send() has a memory leak. Specifically, a pulsar_message_id_t is created but never freed. This leaks one object for every asynchronous message send, which adds up to a big problem if sending lots of messages.

Modifications

After calling the C callback, delete the memory allocated for the pulsar_message_id_t.

Verifying this change

I have manually verified that this change fixes the leak, using valgrind.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no
• The rest endpoints: no
• The admin cli options: no
• Anything that affects deployment: no

Documentation

• Does this pull request introduce a new feature? no

[bschofield]

Actually the new and delete aren't required

[merlimat]

@bschofield I agree that this is very unintuitive (and wrong from a perspective of ownership), but the problem was when this change was introduced.

Right now, there is code depending on this (bad) API. If we change that, it will segfault in these apps.

[bschofield]

OK -- closing this PR in favor of a fix to the cgo interface instead.