Allow consumer methods to run while closing

[milindl]

See #1062
#901 (comment)

With #901, such flows were no longer working after the final Close().

rebalanceCb() {
   ...
   ...
   if (partitions_are_being_revoked) { 
     commit(some_offsets) 
   }

This was because the consumer would be counted as closed and commit would return an error.

it's based on the dev_go_flush_ignore_queue_buffering_time since I'm using the same file

[pranavrth]

Should this be just before returning? rd_kafka_destroy can stuck due to various reasons.

[milindl]

We're destroying an important queue below, which is necessary for most public API to run (it's the queue on which we're getting all the events from, from librdkafka side).

So most functions called after this point will panic due to segfault

[pranavrth]

I was just talking about atomic.StoreUint32(&c.isClosed, 1)

[milindl]

Yep, storing that will allow a small window of usage after the queue destruction - methods like Poll() can be called until that store is called.

[milindl]

It's merged but only in the other branch. I did it on top of that because of test file organization related changes.

[jdemeyer]

Is this by chance related to #1016 ?

[milindl]

I'm guessing it would not be. I saw the stack traces in those functions, we've already made it to the librdkafka functions and are waiting for those to return, the internal state of the Go consumer wouldn't come into the picture