fncache: move fncache writing to be in a transaction

Previously the fncache was written at lock.release time. This meant it was not
tracked by a transaction, and if an error occurred during the fncache write it
would fail to update the fncache, but would not rollback the transaction,
resulting in an fncache that was not in sync with the files on disk (which
causes verify to fail, and causes streaming clones to not copy all the revlogs).

This uses the new transaction backup mechanism to make the fncache transacted.
It also moves the fncache from being written at lock.release time, to being
written at transaction.close time.

mercurial/localrepo.py

@@ -823,13 +823,17 b' class localrepository(object):'
             raise error.RepoError(
                 _("abandoned transaction found - run hg recover"))
 
+        def onclose():
+            self.store.write(tr)
+
         self._writejournal(desc)
         renames = [(vfs, x, undoname(x)) for vfs, x in self._journalfiles()]
         rp = report and report or self.ui.warn
         tr = transaction.transaction(rp, self.sopener,
                                      "journal",
                                      aftertrans(renames),
-                                     self.store.createmode)
+                                     self.store.createmode,
+                                     onclose)
         self._transref = weakref.ref(tr)
         return tr
 
@@ -1037,7 +1041,6 b' class localrepository(object):'
             return l
 
         def unlock():
-            self.store.write()
             if hasunfilteredcache(self, '_phasecache'):
                 self._phasecache.write()
             for k, ce in self._filecache.items():

mercurial/store.py

@@ -337,7 +337,7 b' class basicstore(object):'
     def copylist(self):
         return ['requires'] + _data.split()
 
-    def write(self):
+    def write(self, tr):
         pass
 
     def __contains__(self, path):
@@ -402,8 +402,9 b' class fncache(object):'
                     raise util.Abort(t)
         fp.close()
 
-    def write(self):
+    def write(self, tr):
         if self._dirty:
+            tr.addbackup('fncache')
             fp = self.vfs('fncache', mode='wb', atomictemp=True)
             if self.entries:
                 fp.write(encodedir('\n'.join(self.entries) + '\n'))
@@ -485,8 +486,8 b' class fncachestore(basicstore):'
         return (['requires', '00changelog.i'] +
                 ['store/' + f for f in d.split()])
 
-    def write(self):
-        self.fncache.write()
+    def write(self, tr):
+        self.fncache.write(tr)
 
     def _exists(self, f):
         ef = self.encode(f)

tests/test-fncache.t

@@ -177,4 +177,62 b' Encoding of reserved / long paths in the'
 
   $ cd ..
 
+Aborting lock does not prevent fncache writes
 
+  $ cat > exceptionext.py <<EOF
+  > import os
+  > from mercurial import commands, util
+  > from mercurial.extensions import wrapfunction
+  > 
+  > def lockexception(orig, vfs, lockname, wait, releasefn, acquirefn, desc):
+  >     def releasewrap():
+  >         raise util.Abort("forced lock failure")
+  >     return orig(vfs, lockname, wait, releasewrap, acquirefn, desc)
+  > 
+  > def reposetup(ui, repo):
+  >     wrapfunction(repo, '_lock', lockexception)
+  > 
+  > cmdtable = {}
+  > 
+  > EOF
+  $ extpath=`pwd`/exceptionext.py
+  $ hg init fncachetxn
+  $ cd fncachetxn
+  $ printf "[extensions]\nexceptionext=$extpath\n" >> .hg/hgrc
+  $ touch y
+  $ hg ci -qAm y
+  abort: forced lock failure
+  [255]
+  $ cat .hg/store/fncache
+  data/y.i
+
+Aborting transaction prevents fncache change
+
+  $ cat > ../exceptionext.py <<EOF
+  > import os
+  > from mercurial import commands, util, transaction
+  > from mercurial.extensions import wrapfunction
+  > 
+  > def wrapper(orig, self, *args, **kwargs):
+  >     origonclose = self.onclose
+  >     def onclose():
+  >         origonclose()
+  >         raise util.Abort("forced transaction failure")
+  >     self.onclose = onclose
+  >     return orig(self, *args, **kwargs)
+  > 
+  > def uisetup(ui):
+  >     wrapfunction(transaction.transaction, 'close', wrapper)
+  > 
+  > cmdtable = {}
+  > 
+  > EOF
+  $ rm "${extpath}c"
+  $ touch z
+  $ hg ci -qAm z
+  transaction abort!
+  rollback completed
+  abort: forced transaction failure
+  [255]
+  $ cat .hg/store/fncache
+  data/y.i