[FIX] base_crypt: avoid table lock on res_users during simple auth check

Performing a full table lock is potentially very slow
due to the number of tables holding foreign keys towards
res_users, so we should avoid doing that for simple
auth check() calls. The point was only to avoid failing
the update of the last login timestamp, which we don't
actually care much about. So we can replace that with a
simple SELECT FOR UPDATE NOWAIT on that specific user
row and and skip the update in case the LOCK was
not granted

bzr revid: odo@openerp.com-20120813143552-3g3z0q9n1iox8a0b

addons/base_crypt/crypt.py

@@ -217,18 +217,25 @@ class users(osv.osv):
         encrypted_pw = encrypt_md5(password, salt)
     
         # Check if the encrypted password matches against the one in the db.
-        cr.execute("""UPDATE res_users
-                        SET date=now() AT TIME ZONE 'UTC'
-                        WHERE id=%s AND password=%s AND active
-                        RETURNING id""", 
-                   (int(id), encrypted_pw.encode('utf-8')))
-        res = cr.fetchone()
-        cr.commit()
+        login_ok = encrypted_pw == stored_pw
+        
+        # Attempt to update last login time, but don't fail if the row is
+        # currently locked.
+        if login_ok:
+            try:
+                cr.execute("SELECT 1 FROM res_users WHERE id=%s FOR UPDATE NOWAIT",
+                           params=(id,), log_exceptions=False)
+                cr.execute("""UPDATE res_users
+                              SET date=now() AT TIME ZONE 'UTC'
+                              WHERE id=%s""", (id,))
+                cr.commit()
+            except Exception:
+                # Failing to acquire the lock on the res_users row probably means
+                # another request is holding it. No big deal, we don't want to
+                # prevent/delay login in that case just for updating login timestamp.
+                cr.rollback()
     
-        if res:
-            return res[0]
-        else:
-            return False
+        return login_ok and id
 
     def check(self, db, uid, passwd):
         if not passwd:
@@ -245,8 +252,9 @@ class users(osv.osv):
         if (cached_pass is not None) and cached_pass == passwd:
             return True
 
+        # We should get here only if the registry was just reloaded
+        # (e.g. after server startup or module install/upgrade)
         with closing(pooler.get_db(db).cursor()) as cr:
-            cr.execute('LOCK res_users')
             if uid not in self._salt_cache.get(db, {}):
                 # If we don't have cache, we have to repeat the procedure
                 # through the login function.