discovery: use command executor interface We're trying to port all wire protocol code to use the new interface so we can implement wire protocol version 2 clients. Differential Revision: https://phab.mercurial-scm.org/D3288

discovery: don't redundantly call branchmap We were calling the remote command twice without mutation the remote in between. Derp. Differential Revision: https://phab.mercurial-scm.org/D3287

wireproto: convert legacy commands to command executor Calls to the legacy commands "changegroup" and "changegroupsubset" have been ported to the new command executor interface. Because we always pass arguments by name and not position, some inconsistent names throughout the code base have been unified. As part of this change, we no longer had any remaining callers of the legacy command methods {between, branches, changegroup, changegroupsubset}. So, these interfaces/methods have been dropped from peer interfaces. We still have an interface declaring these methods. But that interface is implemented on the concrete peer types and isn't part of the generic peer interface. (The implementations of the command executor continue to call these methods.) The ultimate goal is to remove the per-command methods from the generic peer interface: the only interface-conforming way to call a command will be with the new executor API. At some point, we may want to move the methods outside of the peer classes and change the executor implementations to not call methods directly on a peer instance. Differential Revision: https://phab.mercurial-scm.org/D3273

treediscovery: switch to command executor interface We now have a new interface for requesting that commands run. Switch to it. Differential Revision: https://phab.mercurial-scm.org/D3272

wireproto: remove iterbatch() from peer interface (API) Good riddance. Some tests have been ported to the new API. This probably should have been done in earlier commits. But duplicating the test coverage would have been difficult. It was easier this way. .. api:: The wire protocol peer's ``iterbatch()`` for bulk executing commands has been remove.d Use ``peer.commandexecutor()`` instead. Differential Revision: https://phab.mercurial-scm.org/D3271

largefiles: use command executor for batch operation This is the only other user of iterbatch() in core. Tests changed because the new command executor is smart enough to not send a "batch" command over the wire if only 1 command was requested. There is still coverage for the "batch" command in this test though. Differential Revision: https://phab.mercurial-scm.org/D3270

wireproto: implement batching on peer executor interface This is a bit more complicated than non-batch requests because we need to buffer sends until the last request arrives *and* we need to support resolving futures as data arrives from the remote. In a classical concurrent.futures executor model, the future "starts" as soon as it is submitted. However, we have nothing to start until the last command is submitted. If we did nothing, calling result() would deadlock, since the future hasn't "started." So in the case where we queue the command, we return a special future type whose result() will trigger sendcommands(). This eliminates the deadlock potential. It also serves as a check against callers who may be calling result() prematurely, as it will prevent any subsequent callcommands() from working. This behavior is slightly annoying and a bit restrictive. But it's the world that half duplex connections forces on us. In order to support streaming responses, we were previously using a generator. But with a futures-based API, we're using futures and not generators. So in order to get streaming, we need a background thread to read data from the server. The approach taken in this patch is to leverage the ThreadPoolExecutor from concurrent.futures for managing a background thread. We create an executor and future that resolves when all response data is processed (or an error occurs). When exiting the context manager, we wait on that background reading before returning. I was hoping we could manually spin up a threading.Thread and this would be simple. But I ran into a few deadlocks when implementing. After looking at the source code to concurrent.futures, I figured it would just be easier to use a ThreadPoolExecutor than implement all the code needed to manually manage a thread. To prove this works, a use of the batch API in discovery has been updated. Differential Revision: https://phab.mercurial-scm.org/D3269