[PATCH 1 of 5] transaction: introduce scope

Gregory Szorc gregory.szorc at gmail.com
Mon Feb 27 13:05:52 EST 2017



> On Feb 27, 2017, at 09:35, Jun Wu <quark at fb.com> wrote:
> 
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1488185788 28800
> #      Mon Feb 27 00:56:28 2017 -0800
> # Node ID 5dac612ec9a87553fcd329100846bcb01bae9d80
> # Parent  b4cb86ab4c719eb615a4308eafd8b1386a511eeb
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r 5dac612ec9a8
> transaction: introduce scope
> 
> Previously, transaction tries to cover everything: bookmarks, dirstate,
> phaseroots, and branch. It backs them up unconditionally.
> 
> That could be inefficient if we still back up the dirstate in a giant repo,
> where the transaction is only intended to change bookmarks.
> 
> This patch introduces "scope" to transactions, which is a set of things that
> the transaction should cover. For bookmark-only update, it could avoid
> specifying the "dirstate" scope to be more efficient.
> 
> diff --git a/mercurial/transaction.py b/mercurial/transaction.py
> --- a/mercurial/transaction.py
> +++ b/mercurial/transaction.py
> @@ -102,5 +102,6 @@ def _playback(journal, report, opener, v
> class transaction(object):
>     def __init__(self, report, opener, vfsmap, journalname, undoname=None,
> -                 after=None, createmode=None, validator=None, releasefn=None):
> +                 after=None, createmode=None, validator=None, releasefn=None,
> +                 scope=None):
>         """Begin a new transaction
> 
> @@ -111,4 +112,5 @@ class transaction(object):
>         * `createmode`: the mode of the journal file that will be created
>         * `releasefn`: called after releasing (with transaction and result)
> +        * `scope`: a set-like, nested transaction's scope must be a subset
>         """
>         self.count = 1
> @@ -171,4 +173,7 @@ class transaction(object):
>         self._abortcallback = {}
> 
> +        # a set indicating what's covered
> +        self._scope = scope or frozenset()
> +
>     def __del__(self):
>         if self.journal:
> @@ -342,5 +347,10 @@ class transaction(object):
> 
>     @active
> -    def nest(self):
> +    def nest(self, scope=None):
> +        scope = scope or frozenset()
> +        if not scope.issubset(self._scope):
> +            raise error.ProgrammingError(
> +                'nested transaction has a superset scope (%s > %s)'
> +                % (scope, self._scope))

Sets are unordered, so this message isn't deterministic. If you think this could interfere with testing, you should throw some sorted() in here.

>         self.count += 1
>         self.usages += 1
> @@ -555,4 +565,7 @@ class transaction(object):
>             self.releasefn(self, False) # notify failure of transaction
> 
> +    def scope(self):
> +        return self._scope
> +

This seems like an anti-pattern. Can the attribute not be exposed directly?

> def rollback(opener, vfsmap, file, report):
>     """Rolls back the transaction contained in the given file
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