Fix to run an event loop in a thread different than the main thread in debug

mode: disable eventlet "debug_blocking", it is implemented with the SIGALRM
signal, but signal handlers can only be set in the main thread.

Add a test: run an event loop in a thread different than the main thread.

5 files changed, 76 insertions, 3 deletions

diff --git a/aiogreen.py b/aiogreen.py
index 79d005f..dead9a4 100644
--- a/aiogreen.py
+++ b/aiogreen.py
@@ -229,8 +229,15 @@ class EventLoop(asyncio.SelectorEventLoop):
         self._hub.debug_exceptions = debug
 
         # Detect blocking eventlet functions. The feature is implemented with
-        # signal.alarm() which is is not available on Windows.
-        self._hub.debug_blocking = debug and (sys.platform != 'win32')
+        # signal.alarm() which is is not available on Windows. Signal handlers
+        # can only be set from the main loop. So detecting blocking functions
+        # cannot be used on Windows nor from a thread different than the main
+        # thread.
+        self._hub.debug_blocking = (
+            debug
+            and (sys.platform != 'win32')
+            and isinstance(threading.current_thread(), threading._MainThread))
+
         if (self._hub.debug_blocking
         and hasattr(self, 'slow_callback_duration')):
             self._hub.debug_blocking_resolution = self.slow_callback_duration
diff --git a/doc/changelog.rst b/doc/changelog.rst
index 7c98919..f932f61 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -12,6 +12,9 @@ Version 0.3 (development version)
   greenthread of the aiogreen event loop.
 * Fix eventlet detection of blocking tasks: cancel the alarm when the aiogreen
   event loop stops.
+* Fix to run an event loop in a thread different than the main thread in debug
+  mode: disable eventlet "debug_blocking", it is implemented with the SIGALRM
+  signal, but signal handlers can only be set in the main thread.
 
 2014-10-21: version 0.2
 -----------------------
diff --git a/doc/status.rst b/doc/status.rst
index 545e974..c1fc995 100644
--- a/doc/status.rst
+++ b/doc/status.rst
@@ -12,7 +12,7 @@ To do
   - signals
   - subprocesses
 
-* run an event loop in a thread different than the main thread
+* experiment running an event loop in a thread different than the main thread
 * tox.ini: test Python 3.3 with monkey-patching, see eventlet bug:
   https://github.com/eventlet/eventlet/pull/168
 
diff --git a/doc/using.rst b/doc/using.rst
index 0956085..d36a34a 100644
--- a/doc/using.rst
+++ b/doc/using.rst
@@ -79,6 +79,22 @@ Hello World::
    <https://docs.python.org/dev/library/asyncio.html>`_.
 
 
+Threads
+-------
+
+Running an event loop in a thread different than the main thread is currently
+experimental.
+
+An eventlet Event object is not thread-safe, it must only be used in the
+same thread. Use threading.Event to signal events between threads,
+and threading.Queue to pass data between threads.
+
+Use ``threading = eventlet.patcher.original('threading')`` to get the original
+threading instead of ``import threading``.
+
+It is not possible to run two aiogreen event loops in the same thread.
+
+
 Debug mode
 ----------
 
diff --git a/tests/test_thread.py b/tests/test_thread.py
index 2c9caae..c41eeaa 100644
--- a/tests/test_thread.py
+++ b/tests/test_thread.py
@@ -55,6 +55,53 @@ class ThreadTests(tests.TestCase):
         self.loop.run_until_complete(fut)
         self.assertIsInstance(result['loop'], AssertionError)
 
+    def test_run_in_thread(self):
+        class LoopThread(threading.Thread):
+            def __init__(self, event):
+                super(LoopThread, self).__init__()
+                self.loop = None
+                self.event = event
+
+            def run(self):
+                self.loop = asyncio.new_event_loop()
+                try:
+                    self.loop.set_debug(True)
+                    asyncio.set_event_loop(self.loop)
+
+                    self.event.set()
+                    self.loop.run_forever()
+                finally:
+                    self.loop.close()
+                    asyncio.set_event_loop(None)
+
+        result = []
+
+        # start an event loop in a thread
+        event = threading.Event()
+        thread = LoopThread(event)
+        thread.start()
+        event.wait()
+        loop = thread.loop
+
+        def func(loop):
+            result.append(threading.current_thread().ident)
+            loop.stop()
+
+        # FIXME: call_soon() must raise an exception if if the main thread
+        # has no event loop, bugs.python.org/issue22926
+        #self.loop.close()
+        #asyncio.set_event_loop(None)
+        # call_soon() must fail when called from the wrong thread
+        self.assertRaises(RuntimeError, loop.call_soon, func, loop)
+
+        # call func() in a different thread using the event loop
+        tid = thread.ident
+        loop.call_soon_threadsafe(func, loop)
+
+        # stop the event loop
+        thread.join()
+        self.assertEqual(result, [tid])
+
 
 if __name__ == '__main__':
     import unittest