view tests/test-obsolete-changeset-exchange.t @ 44118:f81c17ec303c

hgdemandimport: apply lazy module loading to sys.meta_path finders

Python's `sys.meta_path` finders are the primary objects whose job it
is to find a module at import time. When `import` is called, Python
iterates objects in this list and calls `o.find_spec(...)` to find
a `ModuleSpec` (or None if the module couldn't be found by that
finder). If no meta path finder can find a module, import fails.

One of the default meta path finders is `PathFinder`. Its job is to
import modules from the filesystem and is probably the most important
importer. This finder looks at `sys.path` and `sys.path_hooks` to do
its job.

The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a
`loader` attribute, which defines the concrete module loader to use.
`sys.path_hooks` is a hook point for teaching `PathFinder` to
instantiate custom loader types.

Previously, we injected a custom `sys.path_hook` that told `PathFinder`
to wrap the default loaders with a loader that creates a module object
that is lazy.

This approach worked. But its main limitation was that it only applied
to the `PathFinder` meta path importer. There are other meta path
importers that are registered. And in the case of PyOxidizer loading
modules from memory, `PathFinder` doesn't come into play since
PyOxidizer's own meta path importer was handling all imports.

This commit changes our approach to lazy module loading by proxying
all meta path importers. Specifically, we overload the `find_spec()`
method to swap in a wrapped loader on the `ModuleSpec` before it
is returned. The end result of this is all meta path importers should
be lazy.

As much as I would have loved to utilize .__class__ manipulation to
achieve this, some meta path importers are implemented in C/Rust
in such a way that they cannot be monkeypatched. This is why we
use __getattribute__ to define a proxy.

Also, this change could theoretically open us up to regressions in
meta path importers whose loader is creating module objects which
can't be monkeypatched. But I'm not aware of any of these in the
wild. So I think we'll be safe.

According to hyperfine, this change yields a decent startup time win of
5-6ms:

```
Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version
  Time (mean ± σ):      86.8 ms ±   0.5 ms    [User: 78.0 ms, System: 8.7 ms]
  Range (min … max):    86.0 ms …  89.1 ms    50 runs

  Time (mean ± σ):      81.1 ms ±   2.7 ms    [User: 74.5 ms, System: 6.5 ms]
  Range (min … max):    77.8 ms …  90.5 ms    50 runs

Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version
  Time (mean ± σ):      78.9 ms ±   0.6 ms    [User: 70.2 ms, System: 8.7 ms]
  Range (min … max):    78.1 ms …  81.2 ms    50 runs

  Time (mean ± σ):      73.4 ms ±   0.6 ms    [User: 65.3 ms, System: 8.0 ms]
  Range (min … max):    72.4 ms …  75.7 ms    50 runs

Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version
  Time (mean ± σ):      78.1 ms ±   0.6 ms    [User: 70.2 ms, System: 7.9 ms]
  Range (min … max):    77.4 ms …  80.9 ms    50 runs

  Time (mean ± σ):      72.1 ms ±   0.4 ms    [User: 64.4 ms, System: 7.6 ms]
  Range (min … max):    71.4 ms …  74.1 ms    50 runs
```

Differential Revision: https://phab.mercurial-scm.org/D7954

Test changesets filtering during exchanges (some tests are still in
test-obsolete.t)

  $ cat >> $HGRCPATH << EOF
  > [experimental]
  > evolution.createmarkers=True
  > EOF

Push does not corrupt remote
----------------------------

Create a DAG where a changeset reuses a revision from a file first used in an
extinct changeset.

  $ hg init local
  $ cd local
  $ echo 'base' > base
  $ hg commit -Am base
  adding base
  $ echo 'A' > A
  $ hg commit -Am A
  adding A
  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg revert -ar 1
  adding A
  $ hg commit -Am "A'"
  created new head
  $ hg log -G --template='{desc} {node}'
  @  A' f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  |
  | o  A 9d73aac1b2ed7d53835eaeec212ed41ea47da53a
  |/
  o  base d20a80d4def38df63a4b330b7fb688f3d4cae1e3
  
  $ hg debugobsolete 9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  1 new obsolescence markers
  obsoleted 1 changesets

Push it. The bundle should not refer to the extinct changeset.

  $ hg init ../other
  $ hg push ../other
  pushing to ../other
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files
  $ hg -R ../other verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 2 changes to 2 files

Adding a changeset going extinct locally
------------------------------------------

Pull a changeset that will immediatly goes extinct (because you already have a
marker to obsolete him)
(test resolution of issue3788)

  $ hg phase --draft --force f89bcc95eba5
  $ hg phase -R ../other --draft --force f89bcc95eba5
  $ hg commit --amend -m "A''"
  $ hg --hidden --config extensions.mq= strip  --no-backup f89bcc95eba5
  $ hg pull ../other
  pulling from ../other
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 1 files (+1 heads)
  1 new phase-divergent changesets
  new changesets f89bcc95eba5
  (run 'hg heads' to see heads, 'hg merge' to merge)

check that bundle is not affected

  $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5.hg
  1 changesets found
  $ hg --hidden --config extensions.mq= strip --no-backup f89bcc95eba5
  $ hg unbundle ../f89bcc95eba5.hg
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 1 files (+1 heads)
  (1 other changesets obsolete on arrival)
  (run 'hg heads' to see heads)

check-that bundle can contain markers:

  $ hg bundle --hidden --rev f89bcc95eba5 --base "f89bcc95eba5^" ../f89bcc95eba5-obs.hg --config experimental.evolution.bundle-obsmarker=1
  1 changesets found
  $ hg debugbundle ../f89bcc95eba5.hg
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  cache:rev-branch-cache -- {} (mandatory: False)
  $ hg debugbundle ../f89bcc95eba5-obs.hg
  Stream params: {Compression: BZ}
  changegroup -- {nbchanges: 1, version: 02} (mandatory: True)
      f89bcc95eba5174b1ccc3e33a82e84c96e8338ee
  cache:rev-branch-cache -- {} (mandatory: False)
  obsmarkers -- {} (mandatory: True)
      version: 1 (70 bytes)
      9d73aac1b2ed7d53835eaeec212ed41ea47da53a f89bcc95eba5174b1ccc3e33a82e84c96e8338ee 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}

  $ cd ..

pull does not fetch excessive changesets when common node is hidden (issue4982)
-------------------------------------------------------------------------------

initial repo with server and client matching

  $ hg init pull-hidden-common
  $ cd pull-hidden-common
  $ touch foo
  $ hg -q commit -A -m initial
  $ echo 1 > foo
  $ hg commit -m 1
  $ echo 2a > foo
  $ hg commit -m 2a
  $ cd ..
  $ hg clone --pull pull-hidden-common pull-hidden-common-client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 1 files
  new changesets 96ee1d7354c4:6a29ed9c68de
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

server obsoletes the old head

  $ cd pull-hidden-common
  $ hg -q up -r 1
  $ echo 2b > foo
  $ hg -q commit -m 2b
  $ hg debugobsolete 6a29ed9c68defff1a139e5c6fa9696fb1a75783d bec0734cd68e84477ba7fc1d13e6cff53ab70129
  1 new obsolescence markers
  obsoleted 1 changesets
  $ cd ..

client only pulls down 1 changeset

  $ cd pull-hidden-common-client
  $ hg pull --debug
  pulling from $TESTTMP/pull-hidden-common
  query 1; heads
  searching for changes
  taking quick initial sample
  query 2; still undecided: 2, sample size is: 2
  2 total queries in *.????s (glob)
  1 changesets found
  list of changesets:
  bec0734cd68e84477ba7fc1d13e6cff53ab70129
  listing keys for "bookmarks"
  bundle2-output-bundle: "HG20", 4 parts total
  bundle2-output-part: "changegroup" (params: 1 mandatory 1 advisory) streamed payload
  bundle2-output-part: "listkeys" (params: 1 mandatory) empty payload
  bundle2-output-part: "phase-heads" 24 bytes payload
  bundle2-output-part: "cache:rev-branch-cache" (advisory) streamed payload
  bundle2-input-bundle: with-transaction
  bundle2-input-part: "changegroup" (params: 1 mandatory 1 advisory) supported
  adding changesets
  add changeset bec0734cd68e
  adding manifests
  adding file changes
  adding foo revisions
  bundle2-input-part: total payload size 476
  bundle2-input-part: "listkeys" (params: 1 mandatory) supported
  bundle2-input-part: "phase-heads" supported
  bundle2-input-part: total payload size 24
  bundle2-input-part: "cache:rev-branch-cache" (advisory) supported
  bundle2-input-part: total payload size 39
  bundle2-input-bundle: 4 parts total
  checking for updated bookmarks
  updating the branch cache
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets bec0734cd68e
  (run 'hg heads' to see heads, 'hg merge' to merge)