[PATCH 20 of 22] obsstore: make markerindex support serialization

[Augie Fackler]

On Sun, Jun 04, 2017 at 04:59:32PM -0700, Jun Wu wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1496615642 25200
> #      Sun Jun 04 15:34:02 2017 -0700
> # Node ID edae716e97c441aff52688f3be4750b34b199901
> # Parent  160567b62f74e8e02fa2e9a7b2cb4076b105e528
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r edae716e97c4
> obsstore: make markerindex support serialization
>
> This allows us to load and save index state to disk.
>
> Note this is the first user of .hg/store/cache. The indexes are purely
> depending on .hg/store/obsstore and .hg/store/cache looks reasonable - if
> store is shared, the indexes won't need to be duplicated.

I'm kind of sort of -0 on adding another cache dir, but I don't feel
strongly enough to want a change. Hold for opinions from other
reviewers though.

>
> diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
> --- a/mercurial/obsolete.py
> +++ b/mercurial/obsolete.py
> @@ -532,9 +532,11 @@ class markerindex(radixlink.radixlink):
>      def __init__(self, obsstore, name, keyfunc):
>          """keyfunc: rawmarker -> [key]"""
> -        super(markerindex, self).__init__()
> +        path = 'cache/obsindex-%s' % name
> +        data = obsstore.svfs.tryread(path)
> +        super(markerindex, self).__init__(data)
> +        self._path = path
>          self._keyfunc = keyfunc
>          self._obsstore = weakref.proxy(obsstore)
>          self.name = name
> -        self.sourceoftruthsize = 0
>          self._readmarker = formats[obsstore._version][0]
>          self.update()
> @@ -567,4 +569,18 @@ class markerindex(radixlink.radixlink):
>              return default
>
> +    def flush(self):
> +        """write index state to disk"""

Nit: this method should be called save() or write(), not flush() - the
latter makes it sound like the file was already staged and we're just
committing the write, and we're doing a fair amount more than that.

> +        svfs = self._obsstore.svfs
> +        # fast path: no need to write if file size matches
> +        try:
> +            if svfs.stat(self._path).st_size == len(self):
> +                return
> +        except OSError as inst:
> +            if inst.errno != errno.ENOENT:
> +                raise
> +        svfs.makedirs('cache')
> +        with svfs(self._path, 'w', atomictemp=True) as f:
> +            f.write(self.data)
> +
>  class markerreader(object):
>      """read a range of markers with proper caching"""
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