tests/test-lfs-bundle.t

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

In this test, we want to test LFS bundle application on both LFS and non-LFS
repos.

To make it more interesting, the file revisions will contain hg filelog
metadata ('\1\n'). The bundle will have 1 file revision overlapping with the
destination repo.

#  rev      1          2         3
#  repo:    yes        yes       no
#  bundle:  no (base)  yes       yes (deltabase: 2 if possible)

It is interesting because rev 2 could have been stored as LFS in the repo, and
non-LFS in the bundle; or vice-versa.

Init

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > lfs=
  > drawdag=$TESTDIR/drawdag.py
  > [lfs]
  > url=file:$TESTTMP/lfs-remote
  > EOF

Helper functions

  $ commitxy() {
  > hg debugdrawdag "$@" <<'EOS'
  >  Y  # Y/X=\1\nAAAA\nE\nF
  >  |  # Y/Y=\1\nAAAA\nG\nH
  >  X  # X/X=\1\nAAAA\nC\n
  >     # X/Y=\1\nAAAA\nD\n
  > EOS
  > }

  $ commitz() {
  > hg debugdrawdag "$@" <<'EOS'
  >  Z  # Z/X=\1\nAAAA\nI\n
  >  |  # Z/Y=\1\nAAAA\nJ\n
  >  |  # Z/Z=\1\nZ
  >  Y
  > EOS
  > }

  $ enablelfs() {
  >   cat >> .hg/hgrc <<EOF
  > [lfs]
  > track=all()
  > EOF
  > }

Generate bundles

  $ for i in normal lfs; do
  >   NAME=src-$i
  >   hg init $TESTTMP/$NAME
  >   cd $TESTTMP/$NAME
  >   [ $i = lfs ] && enablelfs
  >   commitxy
  >   commitz
  >   hg bundle -q --base X -r Y+Z $TESTTMP/$NAME.bundle
  >   SRCNAMES="$SRCNAMES $NAME"
  > done

Prepare destination repos

  $ for i in normal lfs; do
  >   NAME=dst-$i
  >   hg init $TESTTMP/$NAME
  >   cd $TESTTMP/$NAME
  >   [ $i = lfs ] && enablelfs
  >   commitxy
  >   DSTNAMES="$DSTNAMES $NAME"
  > done

Apply bundles

  $ for i in $SRCNAMES; do
  >   for j in $DSTNAMES; do
  >     echo ---- Applying $i.bundle to $j ----
  >     cp -R $TESTTMP/$j $TESTTMP/tmp-$i-$j
  >     cd $TESTTMP/tmp-$i-$j
  >     if hg unbundle $TESTTMP/$i.bundle -q 2>/dev/null; then
  >       hg verify -q && echo OK
  >     else
  >       echo CRASHED
  >     fi
  >   done
  > done
  ---- Applying src-normal.bundle to dst-normal ----
  OK
  ---- Applying src-normal.bundle to dst-lfs ----
  OK
  ---- Applying src-lfs.bundle to dst-normal ----
  OK
  ---- Applying src-lfs.bundle to dst-lfs ----
  OK