file: update .metadata atomically

This change the method writing the .metadata file for each group to do
it in an atomic fashion. This avoids the need to lock the whole driver
to read/write the group information.

Change-Id: Id615145b936463f13eb4d45717cd88f2ab34b105

1 files changed, 9 insertions, 7 deletions

diff --git a/tooz/drivers/file.py b/tooz/drivers/file.py
index fa68e28..c1fc12d 100644
--- a/tooz/drivers/file.py
+++ b/tooz/drivers/file.py
@@ -23,6 +23,7 @@ import os
 import re
 import shutil
 import sys
+import tempfile
 import threading
 import weakref
 
@@ -210,10 +211,11 @@ class FileDriver(coordination._RunWatchersMixin,
         self._dir = self._normalize_path(parsed_url.path)
         self._executor = utils.ProxyExecutor.build("File", options)
         self._group_dir = os.path.join(self._dir, 'groups')
+        self._tmpdir = os.path.join(self._dir, 'tmp')
         self._driver_lock_path = os.path.join(self._dir, '.driver_lock')
         self._driver_lock = self._get_raw_lock(self._driver_lock_path,
                                                self._member_id)
-        self._reserved_dirs = [self._dir, self._group_dir]
+        self._reserved_dirs = [self._dir, self._group_dir, self._tmpdir]
         self._reserved_paths = list(self._reserved_dirs)
         self._reserved_paths.append(self._driver_lock_path)
         self._joined_groups = set()
@@ -269,17 +271,18 @@ class FileDriver(coordination._RunWatchersMixin,
         }
         details[u'encoded'] = details[u"group_id"] != group_id
         details_blob = utils.dumps(details)
-        with open(path, "wb") as fh:
+        fd, name = tempfile.mkstemp("tooz", dir=self._tmpdir)
+        with os.fdopen(fd, "wb") as fh:
             fh.write(details_blob)
+        os.rename(name, path)
 
     def create_group(self, group_id):
         safe_group_id = self._make_filesystem_safe(group_id)
         group_dir = os.path.join(self._group_dir, safe_group_id)
         group_meta_path = os.path.join(group_dir, '.metadata')
 
-        @_lock_me(self._driver_lock)
         def _do_create_group():
-            if os.path.isdir(group_dir):
+            if os.path.exists(os.path.join(group_dir, ".metadata")):
                 # NOTE(sileht): We update the group metadata even
                 # they are already good, so ensure dict key are convert
                 # to unicode in case of the file have been written with
@@ -299,7 +302,7 @@ class FileDriver(coordination._RunWatchersMixin,
 
         @_lock_me(self._driver_lock)
         def _do_join_group():
-            if not os.path.isdir(group_dir):
+            if not os.path.exists(os.path.join(group_dir, ".metadata")):
                 raise coordination.GroupNotCreated(group_id)
             if os.path.isfile(me_path):
                 raise coordination.MemberAlreadyExist(group_id,
@@ -326,7 +329,7 @@ class FileDriver(coordination._RunWatchersMixin,
 
         @_lock_me(self._driver_lock)
         def _do_leave_group():
-            if not os.path.isdir(group_dir):
+            if not os.path.exists(os.path.join(group_dir, ".metadata")):
                 raise coordination.GroupNotCreated(group_id)
             try:
                 os.unlink(me_path)
@@ -465,7 +468,6 @@ class FileDriver(coordination._RunWatchersMixin,
 
     def get_groups(self):
 
-        @_lock_me(self._driver_lock)
         def _do_get_groups():
             groups = []
             for entry in os.listdir(self._group_dir):