backport blockchain stats plugin 0.16.5

[kotbegemot]

blockchain stats plugin
see issue:
#112
#209

[AKorpusenko]

Let me describe the problem a little bit in more detail.

• First of all, in first implementation I've used libcds lock-free flat combining queue. Btw I had a pain in the neck connected with cmake configuring libcds. After all I've finally done it, but after merging we've had some troubles with building libcds and we've figured out that we shouldn't use libcds, because its large thing to build and we don't need it mostly. So I've just removed the queue and made the statistics sender without any queue anymore.
  Now I do understand, that this statistics sender can slow (and its actually does so) the daemons work. If you look to the current source code of blockchain_statistics plugin you will see that sender sends a string with evaluator's delta via udp to all statsD agregators, so if we stably make the daemon spam to all agregators. And the data sending process is in the same thread, so daemon's work stops till it finish to send statistics change to all statsD endpoints. Thats why we have to write some small thread safe queue (maybe using mutex) for storing statistics changes as integrating libcds lock-free queue is so hard.
• Second problem in blockchain_statistics plugin is that not all the evaluators are handled. Also the handling is written in bad place. The good one place for that is blockchain_statistics_plugin_impl::on_block method, because it is called only about every 3 seconds.

[AKorpusenko]

As softfork 16.5 has to be implemented as soon as possible, we decided just to backport data sending feature.

[VIM-Arcange]

@AKorpusenko can we have an official statement on:

• what is the purpose of softfork 16.5?
• what will be included in it?
• why suddenly it has to be implemented has soon as possible?
• when it will be implemented?

Thank you

[nemothenoone]

@VIM-Arcange The purpose of version 0.16.5 is to backport some Steemit blockchain platform changes to Golos until version 0.17.0 got fully tested and well documented. An example of backported feature - steemit#1265.