From bdc66633b3255c8a33553124eeb60ae33c6f8380 Mon Sep 17 00:00:00 2001
From: Markus Unterwaditzer <markus@unterwaditzer.net>
Date: Thu, 29 Jan 2015 12:49:00 +0100
Subject: [PATCH] Implement Storage.at_once()

---
 CHANGELOG.rst                    |  1 +
 vdirsyncer/storage/base.py       | 21 +++++++++++++++++++++
 vdirsyncer/storage/singlefile.py | 30 +++++++++++++++++++++++++++---
 vdirsyncer/sync.py               |  6 ++++--
 4 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 68ac08d..9370257 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -22,6 +22,7 @@ Version 0.4.2
 - Catch harmless threading exceptions that occur when shutting down vdirsyncer.
   See :gh:`167`.
 - Vdirsyncer now depends on ``atomicwrites``.
+- Massive performance improvements to ``singlefile``-storage.
 
 Version 0.4.1
 =============
diff --git a/vdirsyncer/storage/base.py b/vdirsyncer/storage/base.py
index 52a9c1f..2f6d4c8 100644
--- a/vdirsyncer/storage/base.py
+++ b/vdirsyncer/storage/base.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import contextlib
 import functools
 
 from .. import exceptions
@@ -186,3 +187,23 @@ class Storage(with_metaclass(StorageMeta)):
             a different etag or doesn't exist.
         '''
         raise NotImplementedError()
+
+    @contextlib.contextmanager
+    def at_once(self):
+        '''A contextmanager that buffers all writes.
+
+        Essentially, this::
+
+            s.upload(...)
+            s.update(...)
+
+        becomes this::
+
+            with s.at_once():
+                s.upload(...)
+                s.update(...)
+
+        Note that this removes guarantees about which exceptions are returned
+        when.
+        '''
+        yield
diff --git a/vdirsyncer/storage/singlefile.py b/vdirsyncer/storage/singlefile.py
index c8fc95b..0db8465 100644
--- a/vdirsyncer/storage/singlefile.py
+++ b/vdirsyncer/storage/singlefile.py
@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 
 import collections
+import contextlib
+import functools
 import os
 
 from atomicwrites import atomic_write
@@ -14,6 +16,15 @@ from ..utils.vobject import join_collection, split_collection
 logger = log.get(__name__)
 
 
+def _write_after(f):
+    @functools.wraps(f)
+    def inner(self, *args, **kwargs):
+        rv = f(self, *args, **kwargs)
+        if not self._at_once:
+            self._write()
+        return rv
+    return inner
+
 class SingleFileStorage(Storage):
     '''Save data in single local ``.vcf`` or ``.ics`` file.
 
@@ -75,6 +86,7 @@ class SingleFileStorage(Storage):
 
         self.path = path
         self.encoding = encoding
+        self._at_once = False
 
     @classmethod
     def create_collection(cls, collection, **kwargs):
@@ -117,6 +129,7 @@ class SingleFileStorage(Storage):
         except KeyError:
             raise exceptions.NotFoundError(href)
 
+    @_write_after
     def upload(self, item):
         href = item.ident
         self.list()
@@ -124,9 +137,9 @@ class SingleFileStorage(Storage):
             raise exceptions.AlreadyExistingError(href)
 
         self._items[href] = item, item.hash
-        self._write()
         return href, item.hash
 
+    @_write_after
     def update(self, href, item, etag):
         self.list()
         if href not in self._items:
@@ -137,9 +150,9 @@ class SingleFileStorage(Storage):
             raise exceptions.WrongEtagError(etag, actual_etag)
 
         self._items[href] = item, item.hash
-        self._write()
         return item.hash
 
+    @_write_after
     def delete(self, href, etag):
         self.list()
         if href not in self._items:
@@ -150,7 +163,6 @@ class SingleFileStorage(Storage):
             raise exceptions.WrongEtagError(etag, actual_etag)
 
         del self._items[href]
-        self._write()
 
     def _write(self):
         if self._last_mtime is not None and \
@@ -166,3 +178,15 @@ class SingleFileStorage(Storage):
         finally:
             self._items = None
             self._last_mtime = None
+
+    @contextlib.contextmanager
+    def at_once(self):
+        self._at_once = True
+        try:
+            yield self
+        except:
+            raise
+        else:
+            self._write()
+        finally:
+            self._at_once = False
diff --git a/vdirsyncer/sync.py b/vdirsyncer/sync.py
index 825bea7..d91f6ca 100644
--- a/vdirsyncer/sync.py
+++ b/vdirsyncer/sync.py
@@ -170,8 +170,10 @@ def sync(storage_a, storage_b, status, conflict_resolution=None,
 
     actions = list(_get_actions(storages, status))
 
-    for action in actions:
-        action(storages, status, conflict_resolution)
+    with storage_a.at_once():
+        with storage_b.at_once():
+            for action in actions:
+                action(storages, status, conflict_resolution)
 
 
 def _action_upload(ident, dest):