[PATCH STABLE] localrepo: discard objects in _filecache at transaction failure (issue4876)

FUJIWARA Katsunori foozy at lares.dti.ne.jp
Wed Oct 21 20:20:17 UTC 2015


# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1445458662 -32400
#      Thu Oct 22 05:17:42 2015 +0900
# Branch stable
# Node ID 865862bdaa59319b0304864ca20066a81529830d
# Parent  b57e5bfaad7ccc9d45884717115ba9a36d6b7b41
localrepo: discard objects in _filecache at transaction failure (issue4876)

'repo.invalidate()' deletes 'filecache'-ed properties by
'filecache.__delete__()' below via 'delattr(unfiltered, k)'. But
cached objects are still kept in 'repo._filecache'.

    def __delete__(self, obj):
        try:
            del obj.__dict__[self.name]
        except KeyError:
            raise AttributeError(self.name)

If 'repo' object is reused even after failure of command execution,
referring 'filecache'-ed property may reuse one kept in
'repo._filecache', even if reloading from a file is expected.

Executing command sequence on command server is a typical case of this
situation (a710936c3037 also tried to fix this issue). For example:

  1. start a command execution

  2. 'changelog.delayupdate()' is invoked in a transaction scope

     This replaces own 'opener' by '_divertopener()' for additional
     accessing to '00changelog.i.a'

  3. transaction is aborted, and command (1) execution is ended

     After 'repo.invalidate()' at releasing store lock, changelog
     object above (= 'opener' of it is still replaced) is deleted from
     'repo.__dict__', but still kept in 'repo._filecache'

  4. start next command execution with same 'repo'

  5. referring 'repo.changelog' may reuse changelog object kept in
     'repo._filecache' according to timestamp

     Then, "No such file or directory" error occurs for
     '00changelog.i.a', which is already removed at (3)

This patch discards objects in '_filecache' at transaction failure.

'repo.invalidate()' at failure of "hg qpush" is removed, because now
it is redundant.

This patch doesn't make 'repo.invalidate()' always discard objects in
'_filecache', because 'repo.invalidate()' is invoked also at unlocking
store lock.

  - "always discard objects in filecache at unlocking" may cause
    serious performance problem for subsequent procedures at normal
    execution

  - but it is impossible to "discard objects in filecache at unlocking
    only at failure", because 'releasefn' of lock can't know whether a
    lock scope is terminated normally or not

    BTW, using "with" statement described in PEP343 for lock may
    resolve this ?

IMHO, fundamental cause of this issue seems that truncation of
'00changelog.i' occurs at failure of transaction, even though newly
added revisions exist only in '00changelog.i.a' (aka "pending
file"). This truncation implies useless updating 'st_mtime' of
'00changelog.i', even though size of '00changelog.i' isn't changed by
truncation itself.

In order to avoid this redundant truncation in the future,
'revlog._writeentry()' and so on may have to be changed around
'transaction.add()' invocations.

diff --git a/hgext/mq.py b/hgext/mq.py
--- a/hgext/mq.py
+++ b/hgext/mq.py
@@ -847,7 +847,6 @@
                 try:
                     tr.abort()
                 finally:
-                    repo.invalidate()
                     self.invalidate()
                 raise
         finally:
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1014,6 +1014,8 @@
                 # out) in this transaction
                 repo.vfs.rename('journal.dirstate', 'dirstate')
 
+                repo.invalidate(clearfilecache=True)
+
         tr = transaction.transaction(rp, self.svfs, vfsmap,
                                      "journal",
                                      "undo",
@@ -1205,13 +1207,15 @@
                     pass
             delattr(self.unfiltered(), 'dirstate')
 
-    def invalidate(self):
+    def invalidate(self, clearfilecache=False):
         unfiltered = self.unfiltered() # all file caches are stored unfiltered
-        for k in self._filecache:
+        for k in self._filecache.keys():
             # dirstate is invalidated separately in invalidatedirstate()
             if k == 'dirstate':
                 continue
 
+            if clearfilecache:
+                del self._filecache[k]
             try:
                 delattr(unfiltered, k)
             except AttributeError:


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