upstream/mercurial-mirror Files · mercurial/peer.py

parsers: a C implementation of the new ancestors algorithm...

parsers: a C implementation of the new ancestors algorithm The performance of both the old and new Python ancestor algorithms depends on the number of revs they need to traverse. Although the new algorithm performs far better than the old when revs are numerically and topologically close, both algorithms become slow under other circumstances, taking up to 1.8 seconds to give answers in a Linux kernel repo. This C implementation of the new algorithm is a fairly straightforward transliteration. The only corner case of interest is that it raises an OverflowError if the number of GCA candidates found during the first pass is greater than 24, to avoid the dual perils of fixnum overflow and trying to allocate too much memory. (If this exception is raised, the Python implementation is used instead.) Performance numbers are good: in a Linux kernel repo, time for "hg debugancestors" on two distant revs (24bf01de7537 and c2a8808f5943) is as follows: Old Python: 0.36 sec New Python: 0.42 sec New C: 0.02 sec For a case where the new algorithm should perform well: Old Python: 1.84 sec New Python: 0.07 sec New C: measures as zero when using --time (This commit includes a paranoid cross-check to ensure that the Python and C implementations give identical answers. The above performance numbers were measured with that check disabled.)

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      # peer.py - repository base classes for mercurial

      #

      # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>

      # Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>

      #

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

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

      from i18n import _

      import error

      class peerrepository(object):

          def capable(self, name):

              '''tell whether repo supports named capability.

              return False if not supported.

              if boolean capability, return True.

              if string capability, return string.'''

              caps = self._capabilities()

              if name in caps:

                  return True

              name_eq = name + '='

              for cap in caps:

                  if cap.startswith(name_eq):

                      return cap[len(name_eq):]

              return False

          def requirecap(self, name, purpose):

              '''raise an exception if the given capability is not present'''

              if not self.capable(name):

                  raise error.CapabilityError(

                      _('cannot %s; remote repository does not '

                        'support the %r capability') % (purpose, name))

          def local(self):

              '''return peer as a localrepo, or None'''

              return None

          def peer(self):

              return self

          def canpush(self):

              return True

          def close(self):

              pass

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				# peer.py - repository base classes for mercurial
				#
				# Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
				# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
				#
				# This software may be used and distributed according to the terms of the
				# GNU General Public License version 2 or any later version.

				from i18n import _
				import error

				class peerrepository(object):

				def capable(self, name):
				'''tell whether repo supports named capability.
				return False if not supported.
				if boolean capability, return True.
				if string capability, return string.'''
				caps = self._capabilities()
				if name in caps:
				return True
				name_eq = name + '='
				for cap in caps:
				if cap.startswith(name_eq):
				return cap[len(name_eq):]
				return False

				def requirecap(self, name, purpose):
				'''raise an exception if the given capability is not present'''
				if not self.capable(name):
				raise error.CapabilityError(
				_('cannot %s; remote repository does not '
				'support the %r capability') % (purpose, name))

				def local(self):
				'''return peer as a localrepo, or None'''
				return None

				def peer(self):
				return self

				def canpush(self):
				return True

				def close(self):
				pass