Fixes a race condition where multiple greenthreads were attempting to resize a file at the same time. Adds tests to verify that the image caching call will run concurrently for different files, but will block other greenthreads trying to cache the same file.

2 files changed, 81 insertions, 5 deletions

diff --git a/nova/tests/test_virt.py b/nova/tests/test_virt.py
index dfa607f14..0625296a4 100644
--- a/nova/tests/test_virt.py
+++ b/nova/tests/test_virt.py
@@ -14,6 +14,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import os
+
+import eventlet
 from xml.etree.ElementTree import fromstring as xml_to_tree
 from xml.dom.minidom import parseString as xml_to_dom
 
@@ -30,6 +33,70 @@ FLAGS = flags.FLAGS
 flags.DECLARE('instances_path', 'nova.compute.manager')
 
 
+def _concurrency(wait, done, target):
+    wait.wait()
+    done.send()
+
+
+class CacheConcurrencyTestCase(test.TestCase):
+    def setUp(self):
+        super(CacheConcurrencyTestCase, self).setUp()
+
+        def fake_exists(fname):
+            basedir = os.path.join(FLAGS.instances_path, '_base')
+            if fname == basedir:
+                return True
+            return False
+
+        def fake_execute(*args, **kwargs):
+            pass
+
+        self.stubs.Set(os.path, 'exists', fake_exists)
+        self.stubs.Set(utils, 'execute', fake_execute)
+
+    def test_same_fname_concurrency(self):
+        """Ensures that the same fname cache runs at a sequentially"""
+        conn = libvirt_conn.LibvirtConnection
+        wait1 = eventlet.event.Event()
+        done1 = eventlet.event.Event()
+        eventlet.spawn(conn._cache_image, _concurrency,
+                       'target', 'fname', False, wait1, done1)
+        wait2 = eventlet.event.Event()
+        done2 = eventlet.event.Event()
+        eventlet.spawn(conn._cache_image, _concurrency,
+                       'target', 'fname', False, wait2, done2)
+        wait2.send()
+        eventlet.sleep(0)
+        try:
+            self.assertFalse(done2.ready())
+            self.assertTrue('fname' in conn._image_sems)
+        finally:
+            wait1.send()
+        done1.wait()
+        eventlet.sleep(0)
+        self.assertTrue(done2.ready())
+        self.assertFalse('fname' in conn._image_sems)
+
+    def test_different_fname_concurrency(self):
+        """Ensures that two different fname caches are concurrent"""
+        conn = libvirt_conn.LibvirtConnection
+        wait1 = eventlet.event.Event()
+        done1 = eventlet.event.Event()
+        eventlet.spawn(conn._cache_image, _concurrency,
+                       'target', 'fname2', False, wait1, done1)
+        wait2 = eventlet.event.Event()
+        done2 = eventlet.event.Event()
+        eventlet.spawn(conn._cache_image, _concurrency,
+                       'target', 'fname1', False, wait2, done2)
+        wait2.send()
+        eventlet.sleep(0)
+        try:
+            self.assertTrue(done2.ready())
+        finally:
+            wait1.send()
+            eventlet.sleep(0)
+
+
 class LibvirtConnTestCase(test.TestCase):
     def setUp(self):
         super(LibvirtConnTestCase, self).setUp()
diff --git a/nova/virt/libvirt_conn.py b/nova/virt/libvirt_conn.py
index 6b555ecbb..f7ed164fd 100644
--- a/nova/virt/libvirt_conn.py
+++ b/nova/virt/libvirt_conn.py
@@ -44,9 +44,8 @@ import uuid
 from xml.dom import minidom
 
 
-from eventlet import greenthread
-from eventlet import event
 from eventlet import tpool
+from eventlet import semaphore
 
 import IPy
 
@@ -515,7 +514,10 @@ class LibvirtConnection(object):
         subprocess.Popen(cmd, shell=True)
         return {'token': token, 'host': host, 'port': port}
 
-    def _cache_image(self, fn, target, fname, cow=False, *args, **kwargs):
+    _image_sems = {}
+
+    @staticmethod
+    def _cache_image(fn, target, fname, cow=False, *args, **kwargs):
         """Wrapper for a method that creates an image that caches the image.
 
         This wrapper will save the image into a common store and create a
@@ -534,8 +536,15 @@ class LibvirtConnection(object):
             if not os.path.exists(base_dir):
                 os.mkdir(base_dir)
             base = os.path.join(base_dir, fname)
-            if not os.path.exists(base):
-                fn(target=base, *args, **kwargs)
+
+            if fname not in LibvirtConnection._image_sems:
+                LibvirtConnection._image_sems[fname] = semaphore.Semaphore()
+            with LibvirtConnection._image_sems[fname]:
+                if not os.path.exists(base):
+                    fn(target=base, *args, **kwargs)
+            if not LibvirtConnection._image_sems[fname].locked():
+                del LibvirtConnection._image_sems[fname]
+
             if cow:
                 utils.execute('qemu-img', 'create', '-f', 'qcow2', '-o',
                               'cluster_size=2M,backing_file=%s' % base,