[PATCH] hgweb: make refresh interval configurable

[Anton Shestakov]

> # HG changeset patch
> # User Gregory Szorc <gregory.szorc at gmail.com>
> # Date 1440270190 25200
> #      Sat Aug 22 12:03:10 2015 -0700
> # Node ID 9b6d9cb5630fe4dcc5b2c32222ef0fd467976900
> # Parent  d9d3d49c4cf77049d12920980e91bf8e4a4ecda2
> hgweb: make refresh interval configurable

I don't have much experience reviewing patches here, but since it's
hgweb, I can give it a try.

> hgwebdir refreshes the set of known repositories periodically. This
> is necessary because refreshing on every request could add significant
> request latency.
> 
> More than once I've found myself wanting to tweak this interval at
> Mozilla. I've also wanted the ability to always refresh (often when
> writing tests for our replication setup).
> 
> This patch makes the refresh interval configurable. Negative values
> indicate to always refresh. The default is left unchanged.
> 
> diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
> --- a/mercurial/help/config.txt
> +++ b/mercurial/help/config.txt
> @@ -1751,8 +1751,16 @@ The full set of options is:
>  ``push_ssl``
>      Whether to require that inbound pushes be transported over SSL to
>      prevent password sniffing. Default is True.
>  
> +``refreshinterval``
> +    How frequently directory listings re-scan the filesystem for new
> +    repositories, in seconds. This is relevant when wildcards are
> used
> +    to define paths. Depending on how much filesystem traversal is
> +    required, refreshing may negatively impact performance.
> +
> +    Default is 30. Negative values mean to always refresh.

Is the +50% change from 20 to 30 a performance improvement? It's not
clear why must the default change to make the interval configurable.

This bug http://bz.selenic.com/show_bug.cgi?id=4266 would benefit from
a lower refreshinterval, but only if people read 3.6 release notes,
otherwise the situation will only get worse for them.

> +
>  ``staticurl``
>      Base URL to use for static files. If unset, static files (e.g.
> the hgicon.png favicon) will be served by the CGI script itself. Use
>      this setting to serve them directly with the HTTP server.
> diff --git a/mercurial/hgweb/hgwebdir_mod.py
> b/mercurial/hgweb/hgwebdir_mod.py ---
> a/mercurial/hgweb/hgwebdir_mod.py +++
> b/mercurial/hgweb/hgwebdir_mod.py @@ -78,19 +78,25 @@ def
> geturlcgivars(baseurl, port): 
>      return name, str(port), path
>  
>  class hgwebdir(object):
> -    refreshinterval = 20
> -
>      def __init__(self, conf, baseui=None):
>          self.conf = conf
>          self.baseui = baseui
> +        self.ui = None
>          self.lastrefresh = 0
>          self.motd = None
>          self.refresh()
>  
>      def refresh(self):
> -        if self.lastrefresh + self.refreshinterval > time.time():
> +        refreshinterval = 30
> +        if self.ui:
> +            refreshinterval = self.ui.configint('web',
> 'refreshinterval',
> +                                                refreshinterval)
> +
> +        # refreshinterval < 0 means to always refresh.
> +        if (refreshinterval >= 0 and
> +            self.lastrefresh + refreshinterval > time.time()):
>              return

It says that < 0 is always refresh, but what about 0? Looks like it
also always refreshes, unless system clock goes backwards.

For me 0 is special enough to think that 'refreshinterval = 0' also
means a special case: either always refresh or never refresh. If the
latter doesn't sound like a great idea (?), then I think it's good to
make 0 mean the former.