Avoid concurrent sync attempts from the same replica in the client (#4451).

2 files changed, 20 insertions, 5 deletions

diff --git a/client/changes/feature_4451_avoid_concurrent_syncs b/client/changes/feature_4451_avoid_concurrent_syncs
new file mode 100644
index 00000000..04a2c4df
--- /dev/null
+++ b/client/changes/feature_4451_avoid_concurrent_syncs
@@ -0,0 +1,2 @@
+  o Avoid concurrent syncs for the same account, but allow for distinct
+    accounts (4451).
diff --git a/client/src/leap/soledad/client/__init__.py b/client/src/leap/soledad/client/__init__.py
index a0b3f45a..d35d3a2a 100644
--- a/client/src/leap/soledad/client/__init__.py
+++ b/client/src/leap/soledad/client/__init__.py
@@ -34,6 +34,8 @@ import urlparse
 import hmac
 
 from hashlib import sha256
+from threading import Lock
+from collections import defaultdict
 
 try:
     import cchardet as chardet
@@ -245,6 +247,12 @@ class Soledad(object):
     Prefix for default values for path.
     """
 
+    syncing_lock = defaultdict(Lock)
+    """
+    A dictionary that hold locks which avoid multiple sync attempts from the
+    same database replica.
+    """
+
     def __init__(self, uuid, passphrase, secrets_path, local_db_path,
                  server_url, cert_file, auth_token=None, secret_id=None):
         """
@@ -1063,6 +1071,9 @@ class Soledad(object):
         """
         Synchronize the local encrypted replica with a remote replica.
 
+        This method blocks until a syncing lock is acquired, so there are no
+        attempts of concurrent syncs from the same client replica.
+
         :param url: the url of the target replica to sync with
         :type url: str
 
@@ -1071,11 +1082,13 @@ class Soledad(object):
         :rtype: str
         """
         if self._db:
-            local_gen = self._db.sync(
-                urlparse.urljoin(self.server_url, 'user-%s' % self._uuid),
-                creds=self._creds, autocreate=True)
-            signal(SOLEDAD_DONE_DATA_SYNC, self._uuid)
-            return local_gen
+            # acquire lock before attempt to sync
+            with Soledad.syncing_lock[self._db._get_replica_uid()]:
+                local_gen = self._db.sync(
+                    urlparse.urljoin(self.server_url, 'user-%s' % self._uuid),
+                    creds=self._creds, autocreate=True)
+                signal(SOLEDAD_DONE_DATA_SYNC, self._uuid)
+                return local_gen
 
     def need_sync(self, url):
         """