singleton_context_manager does not play well with RLock

[idanarye]

from easypy.decorations import singleton_contextmanager_method
from threading import RLock, Thread, Event
from time import sleep


def test_singleton_contextmanager_method_with_rlocks_bad_order():
    class Foo:
        lock = RLock()

        @singleton_contextmanager_method
        def cm(self):
            with self.lock:
                yield

    foo = Foo()
    event1 = Event()
    event2 = Event()

    def lock_and_wait(event):
        with foo.cm():
            event.wait()

    thread1 = Thread(target=lock_and_wait, args=(event1,))
    thread1.start()
    sleep(1)
    thread2 = Thread(target=lock_and_wait, args=(event2,))
    thread2.start()

    event1.set()
    thread1.join()

    event2.set()
    thread2.join()

Running this test prints:

$ py.test tests/ -s -k test_singleton_contextmanager_method_with_rlocks_bad_order
========================================== test session starts ===========================================
platform linux -- Python 3.6.2, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
rootdir: /files/code/easypy, inifile: pytest.ini
collected 118 items

tests/test_decorations.py Exception in thread Thread-3:
Traceback (most recent call last):
  File "/usr/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/files/code/easypy/tests/test_decorations.py", line 87, in lock_and_wait
    event.wait()
  File "/usr/lib/python3.6/contextlib.py", line 88, in __exit__
    next(self.gen)
  File "/files/code/easypy/easypy/decorations.py", line 114, in inner
    yield val
  File "/files/code/easypy/easypy/decorations.py", line 90, in __exit__
    self.ctm.__exit__(*sys.exc_info())
  File "/usr/lib/python3.6/contextlib.py", line 88, in __exit__
    next(self.gen)
  File "/files/code/easypy/tests/test_decorations.py", line 79, in cm
    yield
RuntimeError: cannot release un-acquired lock

.

========================================== 117 tests deselected ==========================================
================================ 1 passed, 117 deselected in 1.31 seconds ================================

(the test still passes, but there is an exception in a thread)

The problem here is that we lock in thread1 - the first thread to enter the singleton contextmanager - and release in thread2 - the last thread to exit the singleton contextmanager.

I'm... not really sure if we can fix this...