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

tracked-key: remove the dual write and rename to tracked-hint...

tracked-key: remove the dual write and rename to tracked-hint The dual-write approach was mostly useless. As explained in the previous version of the help, the key had to be read twice before we could cache a value. However this "read twice" limitation actually also apply to any usage of the key. If some operation wants to rely of the "same value == same tracked set" property it would need to read the value before, and after running that operation (or at least, after, in all cases). So it cannot be sure the operation it did is "valid" until checking the key after the operation. As a resultat such operation can only be read-only or rollbackable. This reduce the utility of the "same value == same tracked set" a lot. So it seems simpler to drop the double write and to update the documentation to highlight that this file does not garantee race-free operation. As a result the "key" is demoted to a "hint". Documentation is updated accordingly. Differential Revision: https://phab.mercurial-scm.org/D12201

Augie Fackler - - 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(b'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(b'%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(b'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(b'%s.pending' % filename, **kwargs), True)
				except IOError as inst:
				if inst.errno != errno.ENOENT:
				raise
				return (vfs(filename, **kwargs), False)