Re: [PATCH 18/19] index-helper: autorun

On Tue, 2016-03-15 at 15:26 +0100, Johannes Schindelin wrote:

Hi Duy,

On Tue, 15 Mar 2016, Duy Nguyen wrote:

quoted

On Thu, Mar 10, 2016 at 1:36 AM, David Turner <
dturner@twopensource.com> wrote:

quoted

Introduce a new config option, indexhelper.autorun, to
automatically
run git index-helper before starting up a builtin git command. 
 This
enables users to keep index-helper running without manual
intervention.

This could be a problem on Windows because "index-helper --detach"
does not work there. I have no idea how "daemons" are managed on
Windows and not sure if our design is still good when such a
"daemon"
is added on Windows. So I'm pulling Johannes in for his opinions.

Background for Johannes. We're adding "git index-helper" daemon
(one
per repo) to cache the index in memory to speed up index load time
(and in future probably name-hash too, I think it's also more often
used on Windows because of case-insensitive fs). It also enables
watchman (on Windows) for faster refresh. This patch allows to
start
the daemon automatically if it's not running. But I don't know it
will
work ok on Windows.

Assuming that "index-helper" service has to be installed and
started
from system, there can only be one service running right? This
clashes
with the per-repo daemon design... I think it can stilf work, if
the
main service just spawns new process, one for each repo. But again
I'm
not sure.

If we want to run the process as a Windows service, you are correct,
there
really can only be one. Worse: it runs with admin privileges.

But why not just keep it running as a detached process? We can run
those
on Windows, and if we're opening a named pipe whose name reveals the
one-to-one mapping with the index in question, I think we are fine
(read:
we can detect whether the process is running already).

We can even tell those processes to have a timeout, or to react to
other
system events.

Please note that I am *very* interested in this feature (speeding up
index
operations).

I don't understand what a "detached process" is on Windows (I have
never done any real Windows programming). Does that mean "call
daemonize() and it'll take care of it?"  Or something else?  Or should
I just not worry about it and let you take care of it?

Also, I'll figure out how to switch to named pipes.