[hacking] N374 do not use time.sleep(0) to yield

We have a centralized nova.utils.cooperative_yield() instead of
time.sleep(0). It is better as it allows to turn off the sleep calls
when the service runs in threaded mode.

Change-Id: I625daec79ee5b7f8b92116f450e21f997cef0546
Signed-off-by: Balazs Gibizer <gibi@redhat.com>

HACKING.rst

@@ -79,6 +79,8 @@ Nova Specific Commandments
 - [N372] Don't use the setDaemon method. Use the daemon attribute instead.
 - [N373] Don't use eventlet specific concurrency primitives. Use the one
   from stdlib instead. E.g. eventlet.sleep => time.sleep
+- [N374] Don't use time.sleep(0) to trigger eventlet yielding.
+  Use nova.utils.cooperative_yield() instead.
 
 Creating Unit Tests
 -------------------

nova/hacking/checks.py

@@ -145,6 +145,7 @@ six_re = re.compile(r"^(import six(\..*)?|from six(\..*)? import .*)$")
 set_daemon_re = re.compile(r"\.setDaemon\(")
 eventlet_stdlib_primitives_re = re.compile(
     r".*(eventlet|greenthread)\.sleep\(.*")
+eventlet_yield_re = re.compile(r".*time\.sleep\(0\).*")
 
 
 class BaseASTChecker(ast.NodeVisitor):
@@ -1111,10 +1112,26 @@ def check_eventlet_primitives(logical_line, filename):
     N373
     """
     msg = (
-        "N373: Use the stdlib concurrency primitive instead of the Eventelt "
+        "N373: Use the stdlib concurrency primitive instead of the Eventlet "
         "specific one")
 
     match = re.match(eventlet_stdlib_primitives_re, logical_line)
 
     if match:
         yield (0, msg)
+
+
+@core.flake8ext
+def check_eventlet_yield(logical_line, filename):
+    """Check for use of time.sleep(0) triggering eventlet yield
+
+    N374
+    """
+    msg = (
+        "N374: Use the nova.utils.cooperative_yield instead of time.sleep(0) "
+        "to trigger an eventlet context switch")
+
+    match = re.match(eventlet_yield_re, logical_line)
+
+    if match:
+        yield (0, msg)

nova/tests/unit/test_hacking.py

@@ -1078,3 +1078,16 @@ class HackingTestCase(test.NoDBTestCase):
                     time.sleep(1)
                """
         self._assert_has_no_errors(code, checks.check_eventlet_primitives)
+
+    def test_check_eventlet_yield(self):
+        code = """
+                   time.sleep(0)
+               """
+        errors = [(x + 1, 0, 'N374') for x in range(1)]
+        self._assert_has_errors(
+            code, checks.check_eventlet_yield, expected_errors=errors)
+
+        code = """
+                    time.sleep(1)
+               """
+        self._assert_has_no_errors(code, checks.check_eventlet_yield)

nova/utils.py

@@ -85,7 +85,7 @@ def cooperative_yield():
     # TODO(ksambor) Remove all cooperative_yield calls after dropping Eventlet
     #  support.
     if not concurrency_mode_threading():
-        time.sleep(0)
+        time.sleep(0)  # noqa: N374
 
 
 def destroy_default_executor():

tox.ini

@@ -380,6 +380,7 @@ extension =
   N371 = checks:import_stock_mock
   N372 = checks:check_set_daemon
   N373 = checks:check_eventlet_primitives
+  N374 = checks:check_eventlet_yield
 paths =
   ./nova/hacking