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setdiscovery: precompute children revisions to avoid quadratic lookup...

setdiscovery: precompute children revisions to avoid quadratic lookup Moving away from dagutil a few commits ago introduced quadratic behavior when resolving children revisions during discovery. This commit introduces a precompute step of the children revisions to avoid the bad behavior. I believe the new code should have near identical performance to what dagutil was doing before. Behavior is still slightly different because we take into account filtered revisions. But this change was made when we moved off dagutil. I added a comment about multiple invocations of this function redundantly calculating the children revisions. I believe this potentially undesirable behavior was present when we used dagutil, as the call to inverse() previously in this function created a new object and required computing children on every invocation. I thought we should document the potential for a performance issue rather than let it go undocumented. Differential Revision: https://phab.mercurial-scm.org/D4326

FUJIWARA Katsunori - - Load All Authors

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      # txnutil.py - transaction related utilities

      #

      #  Copyright FUJIWARA Katsunori <foozy@lares.dti.ne.jp> and others

      #

      # This software may be used and distributed according to the terms of the

      # GNU General Public License version 2 or any later version.

      from __future__ import absolute_import

      import errno

      from . import (

          encoding,

      )

      def mayhavepending(root):

          '''return whether 'root' may have pending changes, which are

          visible to this process.

          '''

          return root == encoding.environ.get('HG_PENDING')

      def trypending(root, vfs, filename, **kwargs):

          '''Open  file to be read according to HG_PENDING environment variable

          This opens '.pending' of specified 'filename' only when HG_PENDING

          is equal to 'root'.

          This returns '(fp, is_pending_opened)' tuple.

          '''

          if mayhavepending(root):

              try:

                  return (vfs('%s.pending' % filename, **kwargs), True)

              except IOError as inst:

                  if inst.errno != errno.ENOENT:

                      raise

          return (vfs(filename, **kwargs), False)

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				# txnutil.py - transaction related utilities
				#
				# Copyright FUJIWARA Katsunori <foozy@lares.dti.ne.jp> and others
				#
				# This software may be used and distributed according to the terms of the
				# GNU General Public License version 2 or any later version.

				from __future__ import absolute_import

				import errno

				from . import (
				encoding,
				)

				def mayhavepending(root):
				'''return whether 'root' may have pending changes, which are
				visible to this process.
				'''
				return root == encoding.environ.get('HG_PENDING')

				def trypending(root, vfs, filename, **kwargs):
				'''Open file to be read according to HG_PENDING environment variable

				This opens '.pending' of specified 'filename' only when HG_PENDING
				is equal to 'root'.

				This returns '(fp, is_pending_opened)' tuple.
				'''
				if mayhavepending(root):
				try:
				return (vfs('%s.pending' % filename, **kwargs), True)
				except IOError as inst:
				if inst.errno != errno.ENOENT:
				raise
				return (vfs(filename, **kwargs), False)