upstream/mercurial-mirror Files · mercurial/cffi/bdiff.py

lock: fix race in lock-breaking code...

lock: fix race in lock-breaking code With low frequency, I see hg pulls fail with output like: abort: no such file or directory: .hg/store/lock I think what happens is, in lock.py, in: def _testlock(self, locker): if not self._lockshouldbebroken(locker): return locker # if locker dead, break lock. must do this with another lock # held, or can race and break valid lock. try: with lock(self.vfs, self.f + b'.break', timeout=0): self.vfs.unlink(self.f) except error.LockError: return locker if a lock is breakable on disk, and two hg processes concurrently get to the "if locker dead" comment, a possible interleaving is: process1 finishes executing the function and then process2 finishes executing the function. If that happens, process2 will either get ENOENT in self.vfs.unlink (resulting in the spurious failure above), or break a valid lock and potentially cause repository corruption. The fix is simple enough: make sure the lock is breakable _inside_ the critical section, because only then can we know that no other process can invalidate our knowledge on the lock on disk. I don't think there are tests for this. I've tested this manually with: diff --git a/mercurial/lock.py b/mercurial/lock.py --- a/mercurial/lock.py +++ b/mercurial/lock.py @@ -351,6 +351,8 @@ class lock(object): if not self._lockshouldbebroken(locker): return locker + import random + time.sleep(1. + random.random()) # if locker dead, break lock. must do this with another lock # held, or can race and break valid lock. try: @@ -358,6 +360,7 @@ class lock(object): self.vfs.unlink(self.f) except error.LockError: return locker + time.sleep(1) def testlock(self): """return id of locker if lock is valid, else None. and I see this change of behavior before/after this commit: $ $hg init repo $ cd repo $ ln -s $HOSTNAME/effffffc:987654321 .hg/wlock $ touch a $ $hg commit -Am_ & $hg commit -Am _; wait -abort: No such file or directory: '/tmp/repo/.hg/wlock' adding a +warning: ignoring unknown working parent 679a8959a8ca! +nothing changed Differential Revision: https://phab.mercurial-scm.org/D7199

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             bdiff.py
        
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        Yuya Nishihara
    
cffi: split modules from pure...

              r32512
            
      # bdiff.py - CFFI implementation of bdiff.c

      #

      # Copyright 2016 Maciej Fijalkowski <fijall@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 __future__ import absolute_import

      import struct

      from ..pure.bdiff import *

      from . import _bdiff

      ffi = _bdiff.ffi

      lib = _bdiff.lib

        Augie Fackler
    
formatting: blacken the codebase...

              r43346
            
        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
      def blocks(sa, sb):

        Augie Fackler
    
formatting: byteify all mercurial/ and hgext/ string literals...

              r43347
            
          a = ffi.new(b"struct bdiff_line**")

          b = ffi.new(b"struct bdiff_line**")

          ac = ffi.new(b"char[]", str(sa))

          bc = ffi.new(b"char[]", str(sb))

          l = ffi.new(b"struct bdiff_hunk*")

        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
          try:

              an = lib.bdiff_splitlines(ac, len(sa), a)

              bn = lib.bdiff_splitlines(bc, len(sb), b)

              if not a[0] or not b[0]:

                  raise MemoryError

              count = lib.bdiff_diff(a[0], an, b[0], bn, l)

              if count < 0:

                  raise MemoryError

              rl = [None] * count

              h = l.next

              i = 0

              while h:

                  rl[i] = (h.a1, h.a2, h.b1, h.b2)

                  h = h.next

                  i += 1

          finally:

              lib.free(a[0])

              lib.free(b[0])

              lib.bdiff_freehunks(l.next)

          return rl

        Yuya Nishihara
    
cffi: split modules from pure...

              r32512
            
        Augie Fackler
    
formatting: blacken the codebase...

              r43346
            
        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
      def bdiff(sa, sb):

        Augie Fackler
    
formatting: byteify all mercurial/ and hgext/ string literals...

              r43347
            
          a = ffi.new(b"struct bdiff_line**")

          b = ffi.new(b"struct bdiff_line**")

          ac = ffi.new(b"char[]", str(sa))

          bc = ffi.new(b"char[]", str(sb))

          l = ffi.new(b"struct bdiff_hunk*")

        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
          try:

              an = lib.bdiff_splitlines(ac, len(sa), a)

              bn = lib.bdiff_splitlines(bc, len(sb), b)

              if not a[0] or not b[0]:

                  raise MemoryError

              count = lib.bdiff_diff(a[0], an, b[0], bn, l)

              if count < 0:

                  raise MemoryError

              rl = []

              h = l.next

              la = lb = 0

              while h:

                  if h.a1 != la or h.b1 != lb:

                      lgt = (b[0] + h.b1).l - (b[0] + lb).l

        Augie Fackler
    
formatting: blacken the codebase...

              r43346
            
                      rl.append(

                          struct.pack(

        Augie Fackler
    
formatting: byteify all mercurial/ and hgext/ string literals...

              r43347
            
                              b">lll",

        Augie Fackler
    
formatting: blacken the codebase...

              r43346
            
                              (a[0] + la).l - a[0].l,

                              (a[0] + h.a1).l - a[0].l,

                              lgt,

                          )

                      )

        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
                      rl.append(str(ffi.buffer((b[0] + lb).l, lgt)))

                  la = h.a2

                  lb = h.b2

                  h = h.next

        Yuya Nishihara
    
cffi: split modules from pure...

              r32512
            
        Yuya Nishihara
    
cffi: remove superfluous "if True" blocks

              r32513
            
          finally:

              lib.free(a[0])

              lib.free(b[0])

              lib.bdiff_freehunks(l.next)

        Augie Fackler
    
formatting: byteify all mercurial/ and hgext/ string literals...

              r43347
            
          return b"".join(rl)

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Yuya Nishihara cffi: split modules from pure...	r32512	# bdiff.py - CFFI implementation of bdiff.c
		#
		# Copyright 2016 Maciej Fijalkowski <fijall@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 __future__ import absolute_import

		import struct

		from ..pure.bdiff import *
		from . import _bdiff

		ffi = _bdiff.ffi
		lib = _bdiff.lib

Augie Fackler formatting: blacken the codebase...	r43346
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	def blocks(sa, sb):
Augie Fackler formatting: byteify all mercurial/ and hgext/ string literals...	r43347	a = ffi.new(b"struct bdiff_line**")
		b = ffi.new(b"struct bdiff_line**")
		ac = ffi.new(b"char[]", str(sa))
		bc = ffi.new(b"char[]", str(sb))
		l = ffi.new(b"struct bdiff_hunk*")
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	try:
		an = lib.bdiff_splitlines(ac, len(sa), a)
		bn = lib.bdiff_splitlines(bc, len(sb), b)
		if not a[0] or not b[0]:
		raise MemoryError
		count = lib.bdiff_diff(a[0], an, b[0], bn, l)
		if count < 0:
		raise MemoryError
		rl = [None] * count
		h = l.next
		i = 0
		while h:
		rl[i] = (h.a1, h.a2, h.b1, h.b2)
		h = h.next
		i += 1
		finally:
		lib.free(a[0])
		lib.free(b[0])
		lib.bdiff_freehunks(l.next)
		return rl
Yuya Nishihara cffi: split modules from pure...	r32512
Augie Fackler formatting: blacken the codebase...	r43346
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	def bdiff(sa, sb):
Augie Fackler formatting: byteify all mercurial/ and hgext/ string literals...	r43347	a = ffi.new(b"struct bdiff_line**")
		b = ffi.new(b"struct bdiff_line**")
		ac = ffi.new(b"char[]", str(sa))
		bc = ffi.new(b"char[]", str(sb))
		l = ffi.new(b"struct bdiff_hunk*")
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	try:
		an = lib.bdiff_splitlines(ac, len(sa), a)
		bn = lib.bdiff_splitlines(bc, len(sb), b)
		if not a[0] or not b[0]:
		raise MemoryError
		count = lib.bdiff_diff(a[0], an, b[0], bn, l)
		if count < 0:
		raise MemoryError
		rl = []
		h = l.next
		la = lb = 0
		while h:
		if h.a1 != la or h.b1 != lb:
		lgt = (b[0] + h.b1).l - (b[0] + lb).l
Augie Fackler formatting: blacken the codebase...	r43346	rl.append(
		struct.pack(
Augie Fackler formatting: byteify all mercurial/ and hgext/ string literals...	r43347	b">lll",
Augie Fackler formatting: blacken the codebase...	r43346	(a[0] + la).l - a[0].l,
		(a[0] + h.a1).l - a[0].l,
		lgt,
		)
		)
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	rl.append(str(ffi.buffer((b[0] + lb).l, lgt)))
		la = h.a2
		lb = h.b2
		h = h.next
Yuya Nishihara cffi: split modules from pure...	r32512
Yuya Nishihara cffi: remove superfluous "if True" blocks	r32513	finally:
		lib.free(a[0])
		lib.free(b[0])
		lib.bdiff_freehunks(l.next)
Augie Fackler formatting: byteify all mercurial/ and hgext/ string literals...	r43347	return b"".join(rl)