--- a/mercurial/hg.py	Sat Aug 22 18:15:42 2015 -0700
+++ b/mercurial/hg.py	Sat Aug 22 18:54:34 2015 -0700
@@ -823,3 +823,72 @@
         dst.setconfig('web', 'cacerts', util.expandpath(v), 'copied')
 
     return dst
+
+# Files of interest
+# Used to check if the repository has changed looking at mtime and size of
+# theses files.
+foi = [('spath', '00changelog.i'),
+       ('spath', 'phaseroots'), # ! phase can change content at the same size
+       ('spath', 'obsstore'),
+       ('path', 'bookmarks'), # ! bookmark can change content at the same size
+      ]
+
+class cachedlocalrepo(object):
+    """Holds a localrepository that can be cached and reused."""
+
+    def __init__(self, repo):
+        """Create a new cached repo from an existing repo.
+
+        We assume the passed in repo was recently created. If the
+        repo has changed between when it was created and when it was
+        turned into a cache, it may not refresh properly.
+        """
+        assert isinstance(repo, localrepo.localrepository)
+        self._repo = repo
+        self._state, self.mtime = self._repostate()
+
+    def fetch(self):
+        """Refresh (if necessary) and return a repository.
+
+        If the cached instance is out of date, it will be recreated
+        automatically and returned.
+
+        Returns a tuple of the repo and a boolean indicating whether a new
+        repo instance was created.
+        """
+        # We compare the mtimes and sizes of some well-known files to
+        # determine if the repo changed. This is not precise, as mtimes
+        # are susceptible to clock skew and imprecise filesystems and
+        # file content can change while maintaining the same size.
+
+        state, mtime = self._repostate()
+        if state == self._state:
+            return self._repo, False
+
+        self._repo = repository(self._repo.baseui, self._repo.url())
+        self._state = state
+        self.mtime = mtime
+
+        return self._repo, True
+
+    def _repostate(self):
+        state = []
+        maxmtime = -1
+        for attr, fname in foi:
+            prefix = getattr(self._repo, attr)
+            p = os.path.join(prefix, fname)
+            try:
+                st = os.stat(p)
+            except OSError:
+                st = os.stat(prefix)
+            state.append((st.st_mtime, st.st_size))
+            maxmtime = max(maxmtime, st.st_mtime)
+
+        return tuple(state), maxmtime
+
+    def copy(self):
+        """Obtain a copy of this class instance."""
+        c = cachedlocalrepo(self._repo)
+        c._state = self._state
+        c.mtime = self.mtime
+        return c

--- a/mercurial/hgweb/hgweb_mod.py	Sat Aug 22 18:15:42 2015 -0700
+++ b/mercurial/hgweb/hgweb_mod.py	Sat Aug 22 18:54:34 2015 -0700
@@ -25,15 +25,6 @@
     'pushkey': 'push',
 }
 
-## Files of interest
-# Used to check if the repository has changed looking at mtime and size of
-# theses files. This should probably be relocated a bit higher in core.
-foi = [('spath', '00changelog.i'),
-       ('spath', 'phaseroots'), # ! phase can change content at the same size
-       ('spath', 'obsstore'),
-       ('path', 'bookmarks'), # ! bookmark can change content at the same size
-      ]
-
 def makebreadcrumb(url, prefix=''):
     '''Return a 'URL breadcrumb' list
 
@@ -66,8 +57,8 @@
     is prone to race conditions. Instances of this class exist to hold
     mutable and race-free state for requests.
     """
-    def __init__(self, app):
-        self.repo = app.repo
+    def __init__(self, app, repo):
+        self.repo = repo
         self.reponame = app.reponame
 
         self.archives = ('zip', 'gz', 'bz2')
@@ -217,10 +208,8 @@
         # break some wsgi implementation.
         r.ui.setconfig('progress', 'disable', 'true', 'hgweb')
         r.baseui.setconfig('progress', 'disable', 'true', 'hgweb')
-        self.repo = self._webifyrepo(r)
+        self._repo = hg.cachedlocalrepo(self._webifyrepo(r))
         hook.redirect(True)
-        self.repostate = None
-        self.mtime = -1
         self.reponame = name
 
     def _webifyrepo(self, repo):
@@ -228,25 +217,13 @@
         self.websubtable = webutil.getwebsubs(repo)
         return repo
 
-    def refresh(self):
-        repostate = []
-        mtime = 0
-        # file of interrests mtime and size
-        for meth, fname in foi:
-            prefix = getattr(self.repo, meth)
-            st = get_stat(prefix, fname)
-            repostate.append((st.st_mtime, st.st_size))
-            mtime = max(mtime, st.st_mtime)
-        repostate = tuple(repostate)
-        # we need to compare file size in addition to mtime to catch
-        # changes made less than a second ago
-        if repostate != self.repostate:
-            r = hg.repository(self.repo.baseui, self.repo.url())
-            self.repo = self._webifyrepo(r)
-            # update these last to avoid threads seeing empty settings
-            self.repostate = repostate
-            # mtime is needed for ETag
-            self.mtime = mtime
+    def _getrepo(self):
+        r, created = self._repo.fetch()
+        if created:
+            r = self._webifyrepo(r)
+
+        self.mtime = self._repo.mtime
+        return r
 
     def run(self):
         """Start a server from CGI environment.
@@ -274,8 +251,8 @@
         This is typically only called by Mercurial. External consumers
         should be using instances of this class as the WSGI application.
         """
-        self.refresh()
-        rctx = requestcontext(self)
+        repo = self._getrepo()
+        rctx = requestcontext(self, repo)
 
         # This state is global across all threads.
         encoding.encoding = rctx.config('web', 'encoding', encoding.encoding)

--- a/tests/test-extension.t	Sat Aug 22 18:15:42 2015 -0700
+++ b/tests/test-extension.t	Sat Aug 22 18:54:34 2015 -0700
@@ -115,8 +115,6 @@
   3) bar extsetup
   4) foo reposetup
   4) bar reposetup
-  4) foo reposetup
-  4) bar reposetup
 
   $ echo 'foo = !' >> $HGRCPATH
   $ echo 'bar = !' >> $HGRCPATH

--- a/tests/test-hgweb-non-interactive.t	Sat Aug 22 18:15:42 2015 -0700
+++ b/tests/test-hgweb-non-interactive.t	Sat Aug 22 18:54:34 2015 -0700
@@ -64,7 +64,7 @@
   > print '---- OS.ENVIRON wsgi variables'
   > print sorted([x for x in os.environ if x.startswith('wsgi')])
   > print '---- request.ENVIRON wsgi variables'
-  > print sorted([x for x in i.repo.ui.environ if x.startswith('wsgi')])
+  > print sorted([x for x in i._getrepo().ui.environ if x.startswith('wsgi')])
   > EOF
   $ python request.py
   ---- STATUS