repository: define new interface for running commands Today, the peer interface exposes methods for each command that can be executed. In addition, there is an iterbatch() API that allows commands to be issued in batches and provides an iterator over the results. This is a glorified wrapper around the "batch" wire command. Wire protocol version 2 supports nicer things (such as batching any command and out-of-order replies). It will require a more flexible API for executing commands. This commit introduces a new peer interface for making command requests. In the new world, you can't simply call a method on the peer to execute a command: you need to obtain an object to be used for executing commands. That object can be used to issue a single command or it can batch multiple requests. In the case of full duplex peers, the command may even be sent out over the wire immediately. There are no per-command methods. Instead, there is a generic method to call a command. The implementation can then perform domain specific processing for specific commands. This includes passing data via a specially named argument. Arguments are also passed as a dictionary instead of using **kwargs. While **kwargs is nicer to use, we've historically gotten into trouble using it because there will inevitably be a conflict between the name of an argument to a wire protocol command and an argument we want to pass into a function. Instead of a command returning a value, it returns a future which will resolve to a value. This opens the door for out-of-order response handling and concurrent response handling in the version 2 protocol. Differential Revision: https://phab.mercurial-scm.org/D3267

pycompat: export a handle on concurrent.futures On Python 3, we use the built-in version in the standard library. Else we use our vendored backport. Differential Revision: https://phab.mercurial-scm.org/D3266

setup: add packages for concurrent.futures We conceivably don't need to distribute this package on Python 3 since we will use the version in the standard library. However, we want installs to be usable of multiple versions of Python. So it is best to always have it. Differential Revision: https://phab.mercurial-scm.org/D3265

futures: switch to absolute and relative imports This makes the package conform with our importing policy, silencing a number of warnings. It also makes the package usable when it isn't named "concurrent.futures." Differential Revision: https://phab.mercurial-scm.org/D3264

tests: silence pyflakes for thirdparty/concurrent It is complaining about unused imports. Differential Revision: https://phab.mercurial-scm.org/D3263

futures: get rid of extend_path This is used so mutliple directories can provide a package. We don't need it when vendoring. Differential Revision: https://phab.mercurial-scm.org/D3262

thirdparty: vendor futures 3.2.0 Python 3 has a concurrent.futures package in the standard library for representing futures. The "futures" package on PyPI is a backport of this package to work with Python 2. The wire protocol code today has its own future concept for handling of "batch" requests. The frame-based protocol will also want to use futures. I've heavily used the "futures" package on Python 2 in other projects and it is pretty nice. It even has a built-in thread and process pool for running functions in parallel. I've used this heavily for concurrent I/O and other GIL-less activities. The existing futures API in the wire protocol code is not as nice as concurrent.futures. Since concurrent.futures is in the Python standard library and will presumably be the long-term future for futures in our code base, let's vendor the backport so we can use proper futures today. # no-check-commit because of style violations Differential Revision: https://phab.mercurial-scm.org/D3261

py3: make sure decode() first argument is str Uses pycompat.sysstr() to make sure we uses bytes on Python 2 and unicodes on Python 3. Differential Revision: https://phab.mercurial-scm.org/D3279