[PATCH 3 of 3 RFC] chgserve: preimport enabled extensions

[Jun Wu]

This is the first 3 patches of the chg re-arch series. They may look simpler
than expected at first sight, but locally I have 7 more patches, and the
handling of "ui" is still not done yet.

I have chosen these 3 to start the discussion, as they reveal the plan to
some extent, and seem to be most relevant to the next steps.

  - Should we hack "hg" / "dispatch" instead so they become aware of chg?
    This leads to simpler code but since chg is experimental, I guess the
    answer is no for now. But we may move chg to dispatch eventually.
  - "chgserve" as an executable, will couple with "hgext/chgserver.py".
    With the current direction, "chgserver" will make less sense as an
    extension. I'm not sure if moving it out is a good idea or not.


Excerpts from Jun Wu's message of 2016-10-03 07:11:20 +0100:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1475463449 -3600
> #      Mon Oct 03 03:57:29 2016 +0100
> # Node ID 6f38a7d259add12c44040535681c4b3ceef0a791
> # Parent  7d106c3386e17746c9b49ab9c788535634b3e8f6
> # Available At https://bitbucket.org/quark-zju/hg-draft 
> #              hg pull https://bitbucket.org/quark-zju/hg-draft  -r 6f38a7d259ad
> chgserve: preimport enabled extensions
> 
> This patch pre-imports enabled extensions, so performance improvement is
> visible. It's about 0.01 seconds slower than the old chg, which seems to be
> acceptable.
> 
> diff --git a/contrib/chg/chgserve b/contrib/chg/chgserve
> --- a/contrib/chg/chgserve
> +++ b/contrib/chg/chgserve
> @@ -11,4 +11,5 @@ from mercurial import (
>      commandserver,
>      dispatch,
> +    extensions,
>      fancyopts,
>      ui as uimod,
> @@ -24,4 +25,27 @@ def _confighash(ui):
>      return envhash[:12]
>  
> +_preimported = {} # {(name, path): mod}
> +
> +def _importext(orig, name, path=None, reportfunc=None):
> +    mod = _preimported.get((name, path))
> +    if mod:
> +        return mod
> +    else:
> +        return orig(name, path, reportfunc)
> +
> +def _preimportextensions(ui):
> +    for name, path in ui.configitems("extensions"):
> +        # only enabled extensions are pre-imported - assuming importing an
> +        # extension is side-effect free.
> +        if path.startswith('!'):
> +            continue
> +        try:
> +            mod = extensions._importext(name, path)
> +        except ImportError:
> +            pass
> +        else:
> +            _preimported[(name, path)] = mod
> +            ui.debug('chg: preimported %s\n' % name)
> +
>  def _startchgservice():
>      # patch chgserver's confighash to only hash environment variables
> @@ -35,4 +59,7 @@ def _startchgservice():
>      fancyopts.fancyopts(args, commands.table['^serve'][1], opts)
>  
> +    _preimportextensions(ui)
> +    extensions.wrapfunction(extensions, '_importext', _importext)
> +
>      service = chgserver.chgunixservice(ui, repo, opts)
>      cmdutil.service(opts, initfn=service.init, runfn=service.run)