diff -r 1817f8946c22 -r faf279e33298 cubicweb/pyramid/tools.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cubicweb/pyramid/tools.py	Mon Sep 26 14:52:12 2016 +0200
@@ -0,0 +1,79 @@
+"""Various tools.
+
+.. warning::
+
+    This module should be considered as internal implementation details. Use
+    with caution, as the API may change without notice.
+"""
+
+#: A short-term cache for user clones.
+#: used by cached_build_user to speed-up repetitive calls to build_user
+#: The expiration is handled in a dumb and brutal way: the whole cache is
+#: cleared every 5 minutes.
+_user_cache = {}
+
+
+def clone_user(repo, user):
+    """Clone a CWUser instance.
+
+    .. warning::
+
+        The returned clone is detached from any cnx.
+        Before using it in any way, it should be attached to a cnx that has not
+        this user already loaded.
+    """
+    CWUser = repo.vreg['etypes'].etype_class('CWUser')
+    clone = CWUser(
+        None,
+        rset=user.cw_rset.copy(),
+        row=user.cw_row,
+        col=user.cw_col,
+        groups=set(user._groups) if hasattr(user, '_groups') else None,
+        properties=dict(user._properties)
+        if hasattr(user, '_properties') else None)
+    clone.cw_attr_cache = dict(user.cw_attr_cache)
+    return clone
+
+
+def cnx_attach_entity(cnx, entity):
+    """Attach an entity to a cnx."""
+    entity._cw = cnx
+    if entity.cw_rset:
+        entity.cw_rset.req = cnx
+
+
+def cached_build_user(repo, eid):
+    """Cached version of
+    :meth:`cubicweb.server.repository.Repository._build_user`
+    """
+    with repo.internal_cnx() as cnx:
+        if eid in _user_cache:
+            entity = clone_user(repo, _user_cache[eid])
+            # XXX the cnx is needed here so that the CWUser instance has an
+            # access to the vreg, which it needs when its 'prefered_language'
+            # property is accessed.
+            # If this property did not need a cnx to access a vreg, we could
+            # avoid the internal_cnx() and save more time.
+            cnx_attach_entity(cnx, entity)
+            return entity
+
+        user = repo._build_user(cnx, eid)
+        user.cw_clear_relation_cache()
+        _user_cache[eid] = clone_user(repo, user)
+        return user
+
+
+def clear_cache():
+    """Clear the user cache"""
+    _user_cache.clear()
+
+
+def includeme(config):
+    """Start the cache maintenance loop task.
+
+    Automatically included by :func:`cubicweb.pyramid.make_cubicweb_application`.
+    """
+    repo = config.registry['cubicweb.repository']
+    interval = int(config.registry.settings.get(
+        'cubicweb.usercache.expiration_time', 60*5))
+    repo.looping_task(interval, clear_cache)