view tests/test-hgweb-descend-empties.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

#require serve

Test chains of near empty directories, terminating 3 different ways:
- a1: file at level 4 (deepest)
- b1: two dirs at level 3
- d1: file at level 2

Set up the repo

  $ hg init test
  $ cd test
  $ mkdir -p a1/a2/a3/a4
  $ mkdir -p b1/b2/b3/b4
  $ mkdir -p b1/b2/b3/c4
  $ mkdir -p d1/d2/d3/d4
  $ echo foo > a1/a2/a3/a4/foo
  $ echo foo > b1/b2/b3/b4/foo
  $ echo foo > b1/b2/b3/c4/foo
  $ echo foo > d1/d2/d3/d4/foo
  $ echo foo > d1/d2/foo
  $ hg ci -Ama
  adding a1/a2/a3/a4/foo
  adding b1/b2/b3/b4/foo
  adding b1/b2/b3/c4/foo
  adding d1/d2/d3/d4/foo
  adding d1/d2/foo
  $ hg serve -n test -p $HGPORT -d --pid-file=hg.pid -E errors.log
  $ cat hg.pid >> $DAEMON_PIDS

manifest with descending (paper)

  $ get-with-headers.py $LOCALIP:$HGPORT 'file'
  200 Script output follows
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png" />
  <meta name="robots" content="index, nofollow" />
  <link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>test: c9f45f7a1659 /</title>
  </head>
  <body>
  
  <div class="container">
  <div class="menu">
  <div class="logo">
  <a href="https://mercurial-scm.org/">
  <img src="/static/hglogo.png" alt="mercurial" /></a>
  </div>
  <ul>
  <li><a href="/shortlog/tip">log</a></li>
  <li><a href="/graph/tip">graph</a></li>
  <li><a href="/tags">tags</a></li>
  <li><a href="/bookmarks">bookmarks</a></li>
  <li><a href="/branches">branches</a></li>
  </ul>
  <ul>
  <li><a href="/rev/tip">changeset</a></li>
  <li class="active">browse</li>
  </ul>
  <ul>
  
  </ul>
  <ul>
   <li><a href="/help">help</a></li>
  </ul>
  </div>
  
  <div class="main">
  <h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
  <h3>
   directory / @ 0:<a href="/rev/c9f45f7a1659">c9f45f7a1659</a>
   <span class="phase">draft</span> <span class="branchhead">default</span> <span class="tag">tip</span> 
  </h3>
  
  
  <form class="search" action="/log">
  
  <p><input name="rev" id="search1" type="text" size="30" value="" /></p>
  <div id="hint">Find changesets by keywords (author, files, the commit message), revision
  number or hash, or <a href="/help/revsets">revset expression</a>.</div>
  </form>
  
  <table class="bigtable">
  <thead>
  <tr>
    <th class="name">name</th>
    <th class="size">size</th>
    <th class="permissions">permissions</th>
  </tr>
  </thead>
  <tbody class="stripes2">
  
  
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/a1">
  <img src="/static/coal-folder.png" alt="dir."/> a1/
  </a>
  <a href="/file/tip/a1/a2/a3/a4">
  a2/a3/a4
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/b1">
  <img src="/static/coal-folder.png" alt="dir."/> b1/
  </a>
  <a href="/file/tip/b1/b2/b3">
  b2/b3
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/d1">
  <img src="/static/coal-folder.png" alt="dir."/> d1/
  </a>
  <a href="/file/tip/d1/d2">
  d2
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  
  </tbody>
  </table>
  </div>
  </div>
  
  
  </body>
  </html>
  

manifest with descending (coal)

  $ get-with-headers.py $LOCALIP:$HGPORT 'file?style=coal'
  200 Script output follows
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US">
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png" />
  <meta name="robots" content="index, nofollow" />
  <link rel="stylesheet" href="/static/style-paper.css" type="text/css" />
  <link rel="stylesheet" href="/static/style-extra-coal.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>test: c9f45f7a1659 /</title>
  </head>
  <body>
  
  <div class="container">
  <div class="menu">
  <div class="logo">
  <a href="https://mercurial-scm.org/">
  <img src="/static/hglogo.png" alt="mercurial" /></a>
  </div>
  <ul>
  <li><a href="/shortlog/tip?style=coal">log</a></li>
  <li><a href="/graph/tip?style=coal">graph</a></li>
  <li><a href="/tags?style=coal">tags</a></li>
  <li><a href="/bookmarks?style=coal">bookmarks</a></li>
  <li><a href="/branches?style=coal">branches</a></li>
  </ul>
  <ul>
  <li><a href="/rev/tip?style=coal">changeset</a></li>
  <li class="active">browse</li>
  </ul>
  <ul>
  
  </ul>
  <ul>
   <li><a href="/help?style=coal">help</a></li>
  </ul>
  </div>
  
  <div class="main">
  <h2 class="breadcrumb"><a href="/">Mercurial</a> </h2>
  <h3>
   directory / @ 0:<a href="/rev/c9f45f7a1659?style=coal">c9f45f7a1659</a>
   <span class="phase">draft</span> <span class="branchhead">default</span> <span class="tag">tip</span> 
  </h3>
  
  
  <form class="search" action="/log">
  <input type="hidden" name="style" value="coal" />
  <p><input name="rev" id="search1" type="text" size="30" value="" /></p>
  <div id="hint">Find changesets by keywords (author, files, the commit message), revision
  number or hash, or <a href="/help/revsets">revset expression</a>.</div>
  </form>
  
  <table class="bigtable">
  <thead>
  <tr>
    <th class="name">name</th>
    <th class="size">size</th>
    <th class="permissions">permissions</th>
  </tr>
  </thead>
  <tbody class="stripes2">
  
  
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/a1?style=coal">
  <img src="/static/coal-folder.png" alt="dir."/> a1/
  </a>
  <a href="/file/tip/a1/a2/a3/a4?style=coal">
  a2/a3/a4
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/b1?style=coal">
  <img src="/static/coal-folder.png" alt="dir."/> b1/
  </a>
  <a href="/file/tip/b1/b2/b3?style=coal">
  b2/b3
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  <tr class="fileline">
  <td class="name">
  <a href="/file/tip/d1?style=coal">
  <img src="/static/coal-folder.png" alt="dir."/> d1/
  </a>
  <a href="/file/tip/d1/d2?style=coal">
  d2
  </a>
  </td>
  <td class="size"></td>
  <td class="permissions">drwxr-xr-x</td>
  </tr>
  
  </tbody>
  </table>
  </div>
  </div>
  
  
  </body>
  </html>
  

manifest with descending (monoblue)

  $ get-with-headers.py $LOCALIP:$HGPORT 'file?style=monoblue'
  200 Script output follows
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  <head>
      <link rel="icon" href="/static/hgicon.png" type="image/png" />
      <meta name="robots" content="index, nofollow"/>
      <link rel="stylesheet" href="/static/style-monoblue.css" type="text/css" />
      <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>test: files</title>
      <link rel="alternate" type="application/atom+xml" href="/atom-log" title="Atom feed for test"/>
      <link rel="alternate" type="application/rss+xml" href="/rss-log" title="RSS feed for test"/>
  </head>
  
  <body>
  <div id="container">
      <div class="page-header">
          <h1 class="breadcrumb"><a href="/">Mercurial</a>  / files</h1>
  
          
  <form action="/log">
  <input type="hidden" name="style" value="monoblue" />
  <dl class="search">
  <dt><label>Search: </label></dt>
  <dd><input type="text" name="rev" value="" /></dd>
  </dl>
  </form>
  
          <ul class="page-nav">
              <li><a href="/summary?style=monoblue">summary</a></li>
              <li><a href="/shortlog?style=monoblue">shortlog</a></li>
              <li><a href="/changelog?style=monoblue">changelog</a></li>
              <li><a href="/graph/tip?style=monoblue">graph</a></li>
              <li><a href="/tags?style=monoblue">tags</a></li>
              <li><a href="/bookmarks?style=monoblue">bookmarks</a></li>
              <li><a href="/branches?style=monoblue">branches</a></li>
              <li class="current">files</li>
              <li><a href="/help?style=monoblue">help</a></li>
          </ul>
      </div>
  
      <ul class="submenu">
          <li><a href="/rev/tip?style=monoblue">changeset</a></li>
          
      </ul>
  
      <h2 class="no-link no-border">files</h2>
      <p class="files">/ <span class="logtags"><span class="phasetag" title="draft">draft</span> <span class="branchtag" title="default">default</span> <span class="tagtag" title="tip">tip</span> </span></p>
  
      <table>
          
          
  <tr class="parity1">
  <td>drwxr-xr-x</td>
  <td></td>
  <td></td>
  <td>
  <a href="/file/tip/a1?style=monoblue">a1</a>
  <a href="/file/tip/a1/a2/a3/a4?style=monoblue">a2/a3/a4</a>
  </td>
  <td><a href="/file/tip/a1?style=monoblue">files</a></td>
  </tr>
  <tr class="parity0">
  <td>drwxr-xr-x</td>
  <td></td>
  <td></td>
  <td>
  <a href="/file/tip/b1?style=monoblue">b1</a>
  <a href="/file/tip/b1/b2/b3?style=monoblue">b2/b3</a>
  </td>
  <td><a href="/file/tip/b1?style=monoblue">files</a></td>
  </tr>
  <tr class="parity1">
  <td>drwxr-xr-x</td>
  <td></td>
  <td></td>
  <td>
  <a href="/file/tip/d1?style=monoblue">d1</a>
  <a href="/file/tip/d1/d2?style=monoblue">d2</a>
  </td>
  <td><a href="/file/tip/d1?style=monoblue">files</a></td>
  </tr>
          
      </table>
  
      <div class="page-footer">
          <p>Mercurial Repository: test</p>
          <ul class="rss-logo">
              <li><a href="/rss-log">RSS</a></li>
              <li><a href="/atom-log">Atom</a></li>
          </ul>
          
      </div>
  
      <div id="powered-by">
          <p><a href="https://mercurial-scm.org/" title="Mercurial"><img src="/static/hglogo.png" width=75 height=90 border=0 alt="mercurial" /></a></p>
      </div>
  
  </div>
  
  </body>
  </html>
  

manifest with descending (gitweb)

  $ get-with-headers.py $LOCALIP:$HGPORT 'file?style=gitweb'
  200 Script output follows
  
  <?xml version="1.0" encoding="ascii"?>
  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US" lang="en-US">
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png" />
  <meta name="robots" content="index, nofollow"/>
  <link rel="stylesheet" href="/static/style-gitweb.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>test: files</title>
  <link rel="alternate" type="application/atom+xml"
     href="/atom-log" title="Atom feed for test"/>
  <link rel="alternate" type="application/rss+xml"
     href="/rss-log" title="RSS feed for test"/>
  </head>
  <body>
  
  <div class="page_header">
  <a href="https://mercurial-scm.org/" title="Mercurial" style="float: right;">Mercurial</a>
  <a href="/">Mercurial</a>  / files
  </div>
  
  <div class="page_nav">
  <div>
  <a href="/summary?style=gitweb">summary</a> |
  <a href="/shortlog?style=gitweb">shortlog</a> |
  <a href="/log?style=gitweb">changelog</a> |
  <a href="/graph?style=gitweb">graph</a> |
  <a href="/tags?style=gitweb">tags</a> |
  <a href="/bookmarks?style=gitweb">bookmarks</a> |
  <a href="/branches?style=gitweb">branches</a> |
  files |
  <a href="/rev/tip?style=gitweb">changeset</a>  |
  <a href="/help?style=gitweb">help</a>
  </div>
  
  <div class="search">
  <form id="searchform" action="/log">
  <input type="hidden" name="style" value="gitweb" />
  <input name="rev" type="text" value="" size="40" />
  <div id="hint">Find changesets by keywords (author, files, the commit message), revision
  number or hash, or <a href="/help/revsets">revset expression</a>.</div>
  </form>
  </div>
  </div>
  
  <div class="title">/ <span class="logtags"><span class="phasetag" title="draft">draft</span> <span class="branchtag" title="default">default</span> <span class="tagtag" title="tip">tip</span> </span></div>
  <table cellspacing="0">
  
  
  <tr class="parity1">
  <td style="font-family:monospace">drwxr-xr-x</td>
  <td style="font-family:monospace"></td>
  <td style="font-family:monospace"></td>
  <td>
  <a href="/file/tip/a1?style=gitweb">a1</a>
  <a href="/file/tip/a1/a2/a3/a4?style=gitweb">a2/a3/a4</a>
  </td>
  <td class="link">
  <a href="/file/tip/a1?style=gitweb">files</a>
  </td>
  </tr>
  <tr class="parity0">
  <td style="font-family:monospace">drwxr-xr-x</td>
  <td style="font-family:monospace"></td>
  <td style="font-family:monospace"></td>
  <td>
  <a href="/file/tip/b1?style=gitweb">b1</a>
  <a href="/file/tip/b1/b2/b3?style=gitweb">b2/b3</a>
  </td>
  <td class="link">
  <a href="/file/tip/b1?style=gitweb">files</a>
  </td>
  </tr>
  <tr class="parity1">
  <td style="font-family:monospace">drwxr-xr-x</td>
  <td style="font-family:monospace"></td>
  <td style="font-family:monospace"></td>
  <td>
  <a href="/file/tip/d1?style=gitweb">d1</a>
  <a href="/file/tip/d1/d2?style=gitweb">d2</a>
  </td>
  <td class="link">
  <a href="/file/tip/d1?style=gitweb">files</a>
  </td>
  </tr>
  
  </table>
  
  <div class="page_footer">
  <div class="page_footer_text">test</div>
  <div class="rss_logo">
  <a href="/rss-log">RSS</a>
  <a href="/atom-log">Atom</a>
  </div>
  <br />
  
  </div>
  </body>
  </html>
  

manifest with descending (spartan)

  $ get-with-headers.py $LOCALIP:$HGPORT 'file?style=spartan'
  200 Script output follows
  
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
  <html>
  <head>
  <link rel="icon" href="/static/hgicon.png" type="image/png">
  <meta name="robots" content="index, nofollow" />
  <link rel="stylesheet" href="/static/style.css" type="text/css" />
  <script type="text/javascript" src="/static/mercurial.js"></script>
  
  <title>test: files for changeset c9f45f7a1659</title>
  </head>
  <body>
  
  <div class="buttons">
  <a href="/log/tip?style=spartan">changelog</a>
  <a href="/shortlog/tip?style=spartan">shortlog</a>
  <a href="/graph/tip?style=spartan">graph</a>
  <a href="/tags?style=spartan">tags</a>
  <a href="/branches?style=spartan">branches</a>
  <a href="/rev/tip?style=spartan">changeset</a>
  
  <a href="/help?style=spartan">help</a>
  </div>
  
  <h2><a href="/">Mercurial</a>  / files for changeset <a href="/rev/c9f45f7a1659">c9f45f7a1659</a>: /</h2>
  
  <table cellpadding="0" cellspacing="0">
  
  
  <tr class="parity1">
  <td><tt>drwxr-xr-x</tt>&nbsp;</td>
  <td>&nbsp;</td>
  <td>&nbsp;</td>
  <td>
  <a href="/file/tip/a1?style=spartan">a1/</a>
  <a href="/file/tip/a1/a2/a3/a4?style=spartan">
  a2/a3/a4
  </a>
  </td>
  </tr>
  <tr class="parity0">
  <td><tt>drwxr-xr-x</tt>&nbsp;</td>
  <td>&nbsp;</td>
  <td>&nbsp;</td>
  <td>
  <a href="/file/tip/b1?style=spartan">b1/</a>
  <a href="/file/tip/b1/b2/b3?style=spartan">
  b2/b3
  </a>
  </td>
  </tr>
  <tr class="parity1">
  <td><tt>drwxr-xr-x</tt>&nbsp;</td>
  <td>&nbsp;</td>
  <td>&nbsp;</td>
  <td>
  <a href="/file/tip/d1?style=spartan">d1/</a>
  <a href="/file/tip/d1/d2?style=spartan">
  d2
  </a>
  </td>
  </tr>
  
  </table>
  
  <div class="logo">
  <a href="https://mercurial-scm.org/">
  <img src="/static/hglogo.png" width=75 height=90 border=0 alt="mercurial"></a>
  </div>
  
  </body>
  </html>
  

  $ cat errors.log

  $ cd ..