Fix HTTPServer.serve_forever blocking whole process

Original report: https://github.com/eventlet/eventlet/issues/249

Explanation is in the comments in the code.

Originally reverted[1] because a commit preceding it[2] broke the build
but it wasn't clear what commit was responsible.

[1] 02b693a45d
[2] 4656eadfa5

eventlet/green/selectors.py

@@ -3,9 +3,29 @@ import sys
 from eventlet import patcher
 from eventlet.green import select
 
+__patched__ = [
+    'SelectSelector',
+    'PollSelector',
+    'EpollSelector',
+    'DevpollSelector',
+    'KqueueSelector',
+]
+
 patcher.inject('selectors', globals(), ('select', select))
 
 del patcher
 
 if sys.platform != 'win32':
     SelectSelector._select = staticmethod(select.select)
+
+
+# We only have green select so the options are:
+# * leave it be and have selectors that block
+# * try to pretend the "bad" selectors don't exist
+# * replace all with SelectSelector for the price of possibly different
+#   performance characteristic and missing fileno() method (if someone
+#   uses it it'll result in a crash, we may want to implement it in the future)
+PollSelector = SelectSelector
+EpollSelector = SelectSelector
+DevpollSelector = SelectSelector
+KqueueSelector = SelectSelector

eventlet/patcher.py

@@ -331,7 +331,13 @@ def _green_os_modules():
 
 def _green_select_modules():
     from eventlet.green import select
-    return [('select', select)]
+    modules = [('select', select)]
+
+    if sys.version_info >= (3, 4):
+        from eventlet.green import selectors
+        modules.append(('selectors', selectors))
+
+    return modules
 
 
 def _green_socket_modules():

tests/isolated/patcher_socketserver_selectors.py

@@ -0,0 +1,28 @@
+if __name__ == '__main__':
+    import eventlet
+    eventlet.monkey_patch()
+
+    from eventlet.support.six.moves.BaseHTTPServer import (
+        HTTPServer,
+        BaseHTTPRequestHandler,
+    )
+    import threading
+
+    server = HTTPServer(('localhost', 0), BaseHTTPRequestHandler)
+    thread = threading.Thread(target=server.serve_forever)
+
+    # Before fixing it the code would never go pass this line because:
+    # * socketserver.BaseServer that's used behind the scenes here uses
+    #   selectors.PollSelector if it's available and we don't have green poll
+    #   implementation so this just couldn't work
+    # * making socketserver use selectors.SelectSelector wasn't enough as
+    #   until now we just failed to monkey patch selectors module
+    #
+    # Due to the issues above this thread.start() call effectively behaved
+    # like calling server.serve_forever() directly in the current thread
+    #
+    # Original report: https://github.com/eventlet/eventlet/issues/249
+    thread.start()
+
+    server.shutdown()
+    print('pass')

tests/patcher_test.py

@@ -506,3 +506,7 @@ def test_threading_condition():
 
 def test_threading_join():
     tests.run_isolated('patcher_threading_join.py')
+
+
+def test_socketserver_selectors():
+    tests.run_isolated('patcher_socketserver_selectors.py')