Make nested transaction thread aware

Previously, if create_transaction() was called from different threads or
greenthreads, always a single transaction was returned even when the
thread was different.

This patch makes a map between thread ID and a transaction therefore
nested transaction is returned only for the same threads.

Change-Id: I884e7973d05434d798e0aeaa0f1f826905a8113e
Closes-bug: 1793499
Closes-bug: 1735154

ovsdbapp/api.py

@@ -16,6 +16,11 @@
 import contextlib
 
 import six
+try:
+    # Python 3 no longer has thread module
+    import thread  # noqa
+except ImportError:
+    import threading as thread
 
 
 @six.add_metaclass(abc.ABCMeta)
@@ -67,7 +72,8 @@ def __exit__(self, exc_type, exc_val, tb):
 @six.add_metaclass(abc.ABCMeta)
 class API(object):
     def __init__(self):
-        self._nested_txn = None
+        # Mapping between a (green)thread and its transaction.
+        self._nested_txns_map = {}
 
     @abc.abstractmethod
     def create_transaction(self, check_error=False, log_errors=True, **kwargs):
@@ -92,16 +98,18 @@ def transaction(self, check_error=False, log_errors=True, **kwargs):
         :returns: Either a new transaction or an existing one.
         :rtype: :class:`Transaction`
         """
-        if self._nested_txn:
-            yield self._nested_txn
-        else:
+        cur_thread_id = thread.get_ident()
+
+        try:
+            yield self._nested_txns_map[cur_thread_id]
+        except KeyError:
             with self.create_transaction(
                     check_error, log_errors, **kwargs) as txn:
-                self._nested_txn = txn
+                self._nested_txns_map[cur_thread_id] = txn
                 try:
                     yield txn
                 finally:
-                    self._nested_txn = None
+                    del self._nested_txns_map[cur_thread_id]
 
     @abc.abstractmethod
     def db_create(self, table, **col_values):

ovsdbapp/tests/unit/test_api.py

@@ -14,10 +14,24 @@
 
 import mock
 import testtools
+import time
 
 from ovsdbapp import api
 from ovsdbapp.tests import base
 
+try:
+    import eventlet
+
+    def create_thread(executable):
+        eventlet.spawn_n(executable)
+
+except ImportError:
+    import threading
+
+    def create_thread(executable):
+        thread = threading.Thread(target=executable)
+        thread.start()
+
 
 class FakeTransaction(object):
     def __enter__(self):
@@ -60,3 +74,30 @@ class TestException(Exception):
 
         with self.api.transaction() as txn2:
             self.assertIsNot(txn1, txn2)
+
+    def test_transaction_nested_multiple_threads(self):
+        shared_resource = []
+
+        def thread1():
+            with self.api.transaction() as txn:
+                shared_resource.append(txn)
+                while len(shared_resource) == 1:
+                    time.sleep(0.1)
+            shared_resource.append(0)
+
+        def thread2():
+            while len(shared_resource) != 1:
+                time.sleep(0.1)
+            with self.api.transaction() as txn:
+                shared_resource.append(txn)
+            shared_resource.append(0)
+
+        create_thread(thread1)
+        create_thread(thread2)
+
+        while len(shared_resource) != 4:
+            time.sleep(0.1)
+
+        txn1, txn2 = shared_resource[:2]
+
+        self.assertNotEqual(txn1, txn2)