Add hacking check for greenthread.spawn()

Because greenthread.spawn() and spawn_n() are missing a nova context
(see I3623e60c49e442e2431cf017540422aa59bc285a and
Ia5175c9729069df3d779237ba6039cf5bc920018), nova.utils.spawn() and
spawn_n() should be used when spawning threads. This change adds a
hacking check to assert this is being done during pep8.

Change-Id: Id52c30bb5ded2184d772e6026b0f04f9a0efeb55
Related-Bug: #1404268
Closes-Bug: #1468513

HACKING.rst

@@ -50,6 +50,7 @@ Nova Specific Commandments
   assertEqual(A in B, False) or assertEqual(False, A in B) to the more specific
   assertIn/NotIn(A, B)
 - [N339] Check common raise_feature_not_supported() is used for v2.1 HTTPNotImplemented response.
+- [N340] Check nova.utils.spawn() is used instead of greenthread.spawn()
 
 Creating Unit Tests
 -------------------

nova/hacking/checks.py

@@ -96,6 +96,8 @@ api_version_re = re.compile(r"@.*api_version")
 dict_constructor_with_list_copy_re = re.compile(r".*\bdict\((\[)?(\(|\[)")
 decorator_re = re.compile(r"@.*")
 http_not_implemented_re = re.compile(r"raise .*HTTPNotImplemented\(")
+greenthread_spawn_re = re.compile(r".*greenthread.spawn\(.*\)")
+greenthread_spawn_n_re = re.compile(r".*greenthread.spawn_n\(.*\)")
 
 
 class BaseASTChecker(ast.NodeVisitor):
@@ -519,6 +521,19 @@ def check_http_not_implemented(logical_line, physical_line, filename):
         yield(0, msg)
 
 
+def check_greenthread_spawns(logical_line, physical_line, filename):
+    """Check for use of greenthread.spawn() and greenthread.spawn_n()
+
+    N340
+    """
+    msg = ("N340: Use nova.utils.%(spawn)s() rather than "
+           "greenthread.%(spawn)s()")
+    if re.match(greenthread_spawn_re, logical_line):
+        yield (0, msg % {'spawn': 'spawn'})
+    if re.match(greenthread_spawn_n_re, logical_line):
+        yield (0, msg % {'spawn': 'spawn_n'})
+
+
 def factory(register):
     register(import_no_db_in_virt)
     register(no_db_session_in_public_api)
@@ -545,3 +560,4 @@ def factory(register):
     register(dict_constructor_with_list_copy)
     register(assert_equal_in)
     register(check_http_not_implemented)
+    register(check_greenthread_spawns)

nova/tests/unit/test_hacking.py

@@ -534,3 +534,24 @@ class HackingTestCase(test.NoDBTestCase):
         filename = "nova/api/openstack/compute/contrib/test.py"
         self._assert_has_no_errors(code, checks.check_http_not_implemented,
                                    filename=filename)
+
+    def test_check_greenthread_spawns(self):
+        errors = [(1, 0, "N340")]
+
+        code = "greenthread.spawn(func, arg1, kwarg1=kwarg1)"
+        self._assert_has_errors(code, checks.check_greenthread_spawns,
+                                expected_errors=errors)
+
+        code = "greenthread.spawn_n(func, arg1, kwarg1=kwarg1)"
+        self._assert_has_errors(code, checks.check_greenthread_spawns,
+                                expected_errors=errors)
+
+        code = "eventlet.greenthread.spawn(func, arg1, kwarg1=kwarg1)"
+        self._assert_has_errors(code, checks.check_greenthread_spawns,
+                                expected_errors=errors)
+
+        code = "nova.utils.spawn(func, arg1, kwarg1=kwarg1)"
+        self._assert_has_no_errors(code, checks.check_greenthread_spawns)
+
+        code = "nova.utils.spawn_n(func, arg1, kwarg1=kwarg1)"
+        self._assert_has_no_errors(code, checks.check_greenthread_spawns)