FakeSubSocket and FakePubSocket for IPC synchronization (#439)

* Implementation of FakeSubSocket and FakePubSocket using eventfd with support for one-in/one-out synchronization

* Expose FakeEvent to Python

* Add demo showcasing synchronization between processes

* Fix linter errors

* Expose more FakeEvent APIs in Python bindings

* Add FakePoller implementation

* Remove suffix from poll env vars

* Set poller timeout to zero when events are enabled

* Replace poll with ppoll. Add invalidation methods

* Fix lint issues

* Fix comment indent

* Remove fake_demo

* Remove FakePubSocket. Simpler FakePoller implementation. Ability to wait for multiple events

* Rename FakeEvent to Event and move it to event.cc

* Rename event purpose constants in py

* Add support for timeout in wait methods

* Add tests for events and fake sockets

* Fix lint errors

* Add zmq sleeps

* Temporarly disable TestFakeSockets on ZMQ

* Add exception type specifiers to test_fake

* Event Manager implementation

* Fix fake sockets tests

* Update EventManager API

* Add test for enable/disable

* Add tests for cereal prefix

* Remove EventPurpose from python bindings

* Fix lint issues

* event_state_shm_mmap implementation shared by EventManager and FakeSubSocket

* Rename EventManager to SocketEventHandle

* More renames

SConscript

@@ -26,8 +26,10 @@ services_h = env.Command(['services.h'], ['services.py'], 'python3 ' + cereal_di
 
 messaging_objects = env.SharedObject([
   'messaging/messaging.cc',
+  'messaging/event.cc',
   'messaging/impl_zmq.cc',
   'messaging/impl_msgq.cc',
+  'messaging/impl_fake.cc',
   'messaging/msgq.cc',
   'messaging/socketmaster.cc',
 ])