[tornado] auto-patch futures is python 2.7 compatible when futures are not available

Author: Emanuele Palazzetti

ddtrace/contrib/tornado/__init__.py

@@ -3,7 +3,7 @@
 Auto instrumentation is available using the ``patch`` function that **must be called before**
 importing the tornado library. The following is an example::
 
-    # patch before importing tornado
+    # patch before importing tornado and concurrent.futures
     from ddtrace import tracer, patch
     patch(tornado=True)
 

ddtrace/contrib/tornado/compat.py

@@ -0,0 +1,9 @@
+from ..util import require_modules
+
+
+optional_modules = ['concurrent.futures']
+
+with require_modules(optional_modules) as missing_modules:
+    # detect if concurrent.futures is available as a Python
+    # stdlib or Python 2.7 backport
+    futures_available = len(missing_modules) == 0

ddtrace/contrib/tornado/patch.py

@@ -1,10 +1,9 @@
 import ddtrace
 import tornado
-import concurrent
 
 from wrapt import wrap_function_wrapper as _w
 
-from . import handlers, application, decorators, template, futures, TracerStackContext
+from . import handlers, application, decorators, template, futures, compat, TracerStackContext
 from ...util import unwrap as _u
 
 
@@ -26,7 +25,7 @@ def patch():
     _w('tornado.web', 'RequestHandler.on_finish', handlers.on_finish)
     _w('tornado.web', 'RequestHandler.log_exception', handlers.log_exception)
 
-    # patch Tornado decorators
+    # patch Tornado concurrent modules
     _w('tornado.concurrent', 'run_on_executor', decorators._run_on_executor)
 
     # patch Template system
@@ -36,7 +35,8 @@ def patch():
     # TODO: this may be a generic module and should be moved
     # in a separate contributions when we want to support multi-threading
     # context propagation
-    _w('concurrent.futures', 'ThreadPoolExecutor.submit', futures._wrap_submit)
+    if compat.futures_available:
+        _w('concurrent.futures', 'ThreadPoolExecutor.submit', futures._wrap_submit)
 
     # configure the global tracer
     ddtrace.tracer.configure(
@@ -60,4 +60,6 @@ def unpatch():
     _u(tornado.web.Application, '__init__')
     _u(tornado.concurrent, 'run_on_executor')
     _u(tornado.template.Template, 'generate')
-    _u(concurrent.futures.ThreadPoolExecutor, 'submit')
+
+    if compat.futures_available:
+        _u('concurrent.futures.ThreadPoolExecutor', 'submit')

tests/contrib/tornado/test_executor_decorator.py

@@ -2,6 +2,7 @@
 import unittest
 
 from nose.tools import eq_, ok_
+from ddtrace.contrib.tornado.compat import futures_available
 
 from tornado import version_info
 
@@ -43,6 +44,7 @@ def test_on_executor_handler(self):
         eq_(0, executor_span.error)
         ok_(executor_span.duration >= 0.05)
 
+    @unittest.skipUnless(futures_available, 'Futures must be available to test direct submit')
     def test_on_executor_submit(self):
         # it should propagate the context when a handler uses directly the `executor.submit()`
         response = self.fetch('/executor_submit_handler/')