<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def call_sync(func):
 """Decorates a function to be called sync on the loop thread"""


    @wraps(func)
    def wrapper(self, *args, **kw):
        """Wraps instance method to be called on loop thread"""

        # Just return when already on the event thread
        if self.thread.ident == get_ident():
            return func(self, *args, **kw)

        barrier = Barrier(2)
        result = None
        ex = None

        def call():
            """Calls function on loop thread"""
            nonlocal result, ex
            try:
                result = func(self, *args, **kw)
            except Exception as exc:
                ex = exc
            finally:
                barrier.wait()

        self.loop.call_soon_threadsafe(call)
        barrier.wait()
        if ex:
            raise ex or Exception("Unknown error")
        return result

    return wrapper