Add faulthandler.

.travis.yml

@@ -174,7 +174,7 @@ jobs:
         # First, the build dependencies (see setup.cfg)
         # so that we don't have to use build isolation and can better use the cache;
         # Note that we can't use -U for cffi and greenlet on PyPy.
-        - &build-gevent-deps pip install -U setuptools wheel twine && pip install -U 'cffi;platform_python_implementation=="CPython"' cython 'greenlet;platform_python_implementation=="CPython"'
+        - &build-gevent-deps pip install -U setuptools wheel twine && pip install -U 'faulthandler; python_version == "2.7" and platform_python_implementation == "CPython"' 'cffi;platform_python_implementation=="CPython"' cython 'greenlet;platform_python_implementation=="CPython"'
         # Next, build the wheel *in place*. This helps ccache, and also lets us cache the configure
         # output (pip install uses a random temporary directory, making this difficult)
         - python setup.py bdist_wheel

dev-requirements.txt

@@ -9,6 +9,9 @@ pylint>=1.8.0 ; python_version < "3.4"
 pylint >= 2.5.0 ; python_version >= "3.4"  and platform_python_implementation == "CPython"
 astroid >= 2.4.0 ; python_version >= "3.4" and platform_python_implementation == "CPython"
 
+# backport of faulthandler
+faulthandler ; python_version == "2.7"  and platform_python_implementation == "CPython"
+
 # For generating CHANGES.rst
 towncrier
 # For making releases

src/gevent/testing/__init__.py

@@ -28,10 +28,22 @@ import unittest
 # It's important to do this ASAP, because if we're monkey patched,
 # then importing things like the standard library test.support can
 # need to construct the hub (to check for IPv6 support using a socket).
+# We can't do it in the testrunner, as the testrunner spaws new, unrelated
+# processes.
 from .hub import QuietHub
 import gevent.hub
 gevent.hub.set_default_hub_class(QuietHub)
 
+try:
+    import faulthandler
+except ImportError:
+    # The backport isn't installed.
+    pass
+else:
+    # Enable faulthandler for stack traces. We have to do this here
+    # for the same reasons as above.
+    faulthandler.enable()
+
 from .sysinfo import VERBOSE
 from .sysinfo import WIN
 from .sysinfo import LINUX