1 files changed, 84 insertions, 7 deletions
diff --git a/nova/utils.py b/nova/utils.py
index fabc01532..d3375abc3 100644
--- a/nova/utils.py
+++ b/nova/utils.py
@@ -41,6 +41,7 @@ from xml.sax import saxutils
 
 from eventlet import event
 from eventlet import greenthread
+from eventlet import semaphore
 from eventlet.green import subprocess
 None
 from nova import exception
@@ -338,6 +339,14 @@ def utcnow():
 utcnow.override_time = None
 
 
+def is_older_than(before, seconds):
+    """Return True if before is older than 'seconds'"""
+    if utcnow() - before > datetime.timedelta(seconds=seconds):
+        return True
+    else:
+        return False
+
+
 def utcnow_ts():
     """Timestamp version of our utcnow function."""
     return time.mktime(utcnow().timetuple())
@@ -535,17 +544,76 @@ def loads(s):
     return json.loads(s)
 
 
-def synchronized(name):
+_semaphores = {}
+
+
+class _NoopContextManager(object):
+    def __enter__(self):
+        pass
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        pass
+
+
+def synchronized(name, external=False):
+    """Synchronization decorator
+
+    Decorating a method like so:
+    @synchronized('mylock')
+    def foo(self, *args):
+       ...
+
+    ensures that only one thread will execute the bar method at a time.
+
+    Different methods can share the same lock:
+    @synchronized('mylock')
+    def foo(self, *args):
+       ...
+
+    @synchronized('mylock')
+    def bar(self, *args):
+       ...
+
+    This way only one of either foo or bar can be executing at a time.
+
+    The external keyword argument denotes whether this lock should work across
+    multiple processes. This means that if two different workers both run a
+    a method decorated with @synchronized('mylock', external=True), only one
+    of them will execute at a time.
+    """
+
     def wrap(f):
         @functools.wraps(f)
         def inner(*args, **kwargs):
-            LOG.debug(_("Attempting to grab %(lock)s for method "
-                        "%(method)s..." % {"lock": name,
+            # NOTE(soren): If we ever go natively threaded, this will be racy.
+            #              See http://stackoverflow.com/questions/5390569/dyn\
+            #              amically-allocating-and-destroying-mutexes
+            if name not in _semaphores:
+                _semaphores[name] = semaphore.Semaphore()
+            sem = _semaphores[name]
+            LOG.debug(_('Attempting to grab semaphore "%(lock)s" for method '
+                      '"%(method)s"...' % {"lock": name,
                                            "method": f.__name__}))
-            lock = lockfile.FileLock(os.path.join(FLAGS.lock_path,
-                                                  'nova-%s.lock' % name))
-            with lock:
-                return f(*args, **kwargs)
+            with sem:
+                if external:
+                    LOG.debug(_('Attempting to grab file lock "%(lock)s" for '
+                                'method "%(method)s"...' %
+                                {"lock": name, "method": f.__name__}))
+                    lock_file_path = os.path.join(FLAGS.lock_path,
+                                                  'nova-%s.lock' % name)
+                    lock = lockfile.FileLock(lock_file_path)
+                else:
+                    lock = _NoopContextManager()
+
+                with lock:
+                    retval = f(*args, **kwargs)
+
+            # If no-one else is waiting for it, delete it.
+            # See note about possible raciness above.
+            if not sem.balance < 1:
+                del _semaphores[name]
+
+            return retval
         return inner
     return wrap
 
@@ -597,3 +665,12 @@ def get_from_path(items, path):
         return results
     else:
         return get_from_path(results, remainder)
+
+
+def check_isinstance(obj, cls):
+    """Checks that obj is of type cls, and lets PyLint infer types"""
+    if isinstance(obj, cls):
+        return obj
+    raise Exception(_("Expected object of type: %s") % (str(cls)))
+    # TODO(justinsb): Can we make this better??
+    return cls()  # Ugly PyLint hack