[PATCH 3 of 4 V2] chgcache: implement the background preloading thread

[Yuya Nishihara]

On Wed, 22 Feb 2017 18:16:10 -0800, Jun Wu wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1487813979 28800
> #      Wed Feb 22 17:39:39 2017 -0800
> # Node ID 28571825744fb4f4b424385f55afa9484532ef43
> # Parent  630457e88fa0485bce7822345ea640b5cdcb9b8e
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r 28571825744f
> chgcache: implement the background preloading thread
> 
> The background preloading thread is meant to used by chg master, and it sets
> up the IPC channel.

> +    def _preloadloop(self, interval=0.5):
> +        while not self._shouldexit.is_set():
> +            try:
> +                atimestr, path = self._ipc.recv().split(' ', 1)
> +                atime = float(atimestr)
> +            except Exception: # ignore errors
> +                pass
> +            else:
> +                if path in _repocaches and _repocaches[path][0] >= atime:
> +                    # this repocache is up-to-date, no need to update
> +                    continue
> +                now = time.time()
> +                # TODO update repocache properly

Another concern just came up. Do you know what will happen if the process
is fork()ed while the preloader thread is actively loading cache?

Only the main thread (which called fork()) would be copied, so the preloader
would stop. That should be okay, but the other resources such as files and
mutexes (if any) would be copied.