TINKERPOP-2546 Gremlin-Python Client Transport Layer to use AIOHTTP

[lyndonbauto]

https://issues.apache.org/jira/browse/TINKERPOP-2546

Motivation

The current Tornado implementation of gremlin-python has a number of issues including heartbeat timeout, multithreading issues with DriverRemoteConnection, errors in the build due to the IOLoop, and issues with being unable to use the asyncio event loop when using the driver.

Because Python 2 support is dropped for Tinkerpop 3.5, this is a good time to switch to another implementation and do a clean cut of all these issues. This implementation uses AIOHTTP, this will also put gremlin-python one step closer to having a fully asyncio compatible solution that properly leverages the async/await syntax.

See more on the discussion here https://lists.apache.org/thread.html/rc4d047ba0245fde3261bad0ea156a0f35db1ab0f92c8e80d4fb1b815%40%3Cdev.tinkerpop.apache.org%3E

Changes

The following changes were made:

• Removed Tornado
• Added AIOHTTP implementation
• Added dependency on AIOHTTP and removed dependency on Tornado
• Added max_content_length and heartbeat parameters to transport
• Removed compression_options parameter from transport
• Added some unit tests
• Switched transport.closed to abc.abstractmethod/@property from @abstractproperty since the latter is deprecated

Applicable Tickets

Ticket for change to be made https://issues.apache.org/jira/browse/TINKERPOP-2546

The following issues are fixed with these changes:

• Heartbeat timeout issue: https://issues.apache.org/jira/browse/TINKERPOP-1886
• DriverRemoteConnection multithreading issue: https://issues.apache.org/jira/browse/TINKERPOP-2388
• IOLoop close build errors: https://issues.apache.org/jira/browse/TINKERPOP-2484

Testing Consideration

The following tests were done

• Builds with mvn clean install -pl gremlin-python
• Manually tested that if idleConnectionTimeout is set and a heartbeat is provided, connection does not drop
• Manually tested that if idleConnectionTimeout is set and a heartbeat is NOT provided, connection does drop
• Observed that the build output no longer prints IOLoop errors

[spmallette]

There are a few places in the documentation that make mention of tornado - they all seem to be in the "Python" section here:

https://github.com/apache/tinkerpop/blob/master/docs/src/reference/gremlin-variants.asciidoc#gremlin-python

If you could find those and make adjustments as necessary that would be great.

Also, this sort of change is the kind of thing we like to callout in our Upgrade Documentation, where we let folks know about major sorts of changes in new versions. If you'd like to draft something there in this PR that would be nice otherwise I can just take care of it after merge:

https://github.com/apache/tinkerpop/blob/master/docs/src/upgrade/release-3.5.x.asciidoc

[lyndonbauto]

There are a few places in the documentation that make mention of tornado - they all seem to be in the "Python" section here:

https://github.com/apache/tinkerpop/blob/master/docs/src/reference/gremlin-variants.asciidoc#gremlin-python

If you could find those and make adjustments as necessary that would be great.

Also, this sort of change is the kind of thing we like to callout in our Upgrade Documentation, where we let folks know about major sorts of changes in new versions. If you'd like to draft something there in this PR that would be nice otherwise I can just take care of it after merge:

https://github.com/apache/tinkerpop/blob/master/docs/src/upgrade/release-3.5.x.asciidoc

Thanks for the feedback @spmallette, sorry I missed those references on the first pass. I have corrected them. Also I added the upgrade documentation, if you want me to add any more or less on it, please let me know!

[spmallette]

This is good - two things:

1. please include the "See: " to link to the JIRA
2. i think we should clearly state that Tornado support has been removed.

[lyndonbauto]

Closing this because I made a new pull request with cleaned up git history:
#1416