changegroup: store old heads as a set Previously, the "oldheads" variable was a list. On a repository at Mozilla with 46,492 heads, profiling revealed that list membership testing was dominating execution time of applying small changegroups. This patch converts the list of old heads to a set. This makes membership testing significantly faster. On the aforementioned repository with 46,492 heads: $ hg unbundle <file with 1 changeset> before: 18.535s wall after: 1.303s Consumers of this variable only check for truthiness (`if oldheads`), length (`len(oldheads)`), and (most importantly) item membership (`h not in oldheads` - which occurs twice). So, the change to a set should be safe and suitable for stable. The practical effect of this change is that changegroup application and related operations (like `hg push`) no longer exhibit an O(n^2) CPU explosion as the number of heads grows.

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from __future__ import absolute_import

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from mercurial.i18n import _

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from mercurial import (

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        changegroup,

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        error,

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        extensions

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    )

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def abort(orig, *args, **kwargs):

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    raise error.Abort(_('this is an exercise'))

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def uisetup(ui):

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    extensions.wrapfunction(changegroup, 'getbundler', abort)