Use libyaml if possible

PyYAML doesn't automatically use the much faster and more memory
efficient libyaml bindings, even if the extension is available. So we
provide our own module that exports the pieces needed to use the faster
one, or fall back to the pure python implementation.

Change-Id: I7ee99f5017cb83153ab8fa9bc23548ed639777c1
diff --git a/tests/make_playbooks.py b/tests/make_playbooks.py
index 17acba8..93c37bc 100755
--- a/tests/make_playbooks.py
+++ b/tests/make_playbooks.py
@@ -14,7 +14,7 @@
 
 import os
 
-import yaml
+from zuul.lib import yamlutil as yaml
 
 FIXTURE_DIR = os.path.join(os.path.dirname(__file__),
                            'fixtures')
diff --git a/tests/unit/test_model.py b/tests/unit/test_model.py
index f906095..2167a3b 100644
--- a/tests/unit/test_model.py
+++ b/tests/unit/test_model.py
@@ -18,11 +18,11 @@
 
 import fixtures
 import testtools
-import yaml
 
 from zuul import model
 from zuul import configloader
 from zuul.lib import encryption
+from zuul.lib import yamlutil as yaml
 
 from tests.base import BaseTestCase, FIXTURE_DIR
 
diff --git a/zuul/cmd/__init__.py b/zuul/cmd/__init__.py
index 9fa4c03..f2a2612 100644
--- a/zuul/cmd/__init__.py
+++ b/zuul/cmd/__init__.py
@@ -24,10 +24,10 @@
 import sys
 import traceback
 
-import yaml
 yappi = extras.try_import('yappi')
 
 import zuul.lib.connections
+from zuul.lib import yamlutil as yaml
 
 # Do not import modules that will pull in paramiko which must not be
 # imported until after the daemonization.
diff --git a/zuul/configloader.py b/zuul/configloader.py
index 64c8db4..c549461 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -15,13 +15,13 @@
 import os
 import logging
 import six
-import yaml
 import pprint
 import textwrap
 
 import voluptuous as vs
 
 from zuul import model
+from zuul.lib import yamlutil as yaml
 import zuul.manager.dependent
 import zuul.manager.independent
 from zuul import change_matcher
diff --git a/zuul/executor/ansiblelaunchserver.py b/zuul/executor/ansiblelaunchserver.py
index 875cf2b..0202bdd 100644
--- a/zuul/executor/ansiblelaunchserver.py
+++ b/zuul/executor/ansiblelaunchserver.py
@@ -35,13 +35,13 @@
 import Queue
 
 import gear
-import yaml
 import jenkins_jobs.builder
 import jenkins_jobs.formatter
 import zmq
 
 import zuul.ansible.library
 from zuul.lib import commandsocket
+from zuul.lib import yamlutil as yaml
 
 ANSIBLE_WATCHDOG_GRACE = 5 * 60
 ANSIBLE_DEFAULT_TIMEOUT = 2 * 60 * 60
diff --git a/zuul/executor/server.py b/zuul/executor/server.py
index d0741bb..c397dca 100644
--- a/zuul/executor/server.py
+++ b/zuul/executor/server.py
@@ -24,7 +24,7 @@
 import threading
 import time
 import traceback
-import yaml
+from zuul.lib.yamlutil import yaml
 
 import gear
 import git
diff --git a/zuul/lib/cloner.py b/zuul/lib/cloner.py
index 18dea91..bec8ebe 100644
--- a/zuul/lib/cloner.py
+++ b/zuul/lib/cloner.py
@@ -17,13 +17,13 @@
 import logging
 import os
 import re
-import yaml
 
 import six
 
 from git import GitCommandError
 from zuul import exceptions
 from zuul.lib.clonemapper import CloneMapper
+from zuul.lib import yamlutil as yaml
 from zuul.merger.merger import Repo
 
 
diff --git a/zuul/lib/yamlutil.py b/zuul/lib/yamlutil.py
new file mode 100644
index 0000000..2419906
--- /dev/null
+++ b/zuul/lib/yamlutil.py
@@ -0,0 +1,32 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+import yaml
+from yaml import YAMLObject, YAMLError  # noqa: F401
+
+try:
+    from yaml import cyaml
+    import _yaml
+    SafeLoader = cyaml.CSafeLoader
+    SafeDumper = cyaml.CSafeDumper
+    Mark = _yaml.Mark
+except ImportError:
+    SafeLoader = yaml.SafeLoader
+    SafeDumper = yaml.SafeDumper
+    Mark = yaml.Mark
+
+
+def safe_load(stream, *args, **kwargs):
+    return yaml.load(stream, *args, Loader=SafeLoader, **kwargs)
+
+
+def safe_dump(stream, *args, **kwargs):
+    return yaml.dump(stream, *args, Dumper=SafeDumper, **kwargs)