ReadHandler and WriteHandler decorators

modules with a couple of parameters with similar read_* or
write_* methods may handle them by generic methods wrapped
with decorators ReadHandler / WriteHandler

The trinamic driver is included in this change for demonstrating
how it works.

In a further step, the special handling for the iohandler stuff can
be moved away from secop.server and secop.params, using this feature.

+ fix problem on startup of trinamic driver (needs MultiEvent.queue)
+ some other small fixes
+ apply recommended functools.wraps for wrapping

Change-Id: Ibfeff9209f53c47194628463466cee28366e17ac
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27460
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/lib/multievent.py

@@ -59,6 +59,7 @@ class MultiEvent(threading.Event):
         self._lock = threading.Lock()
         self.default_timeout = default_timeout or None  # treat 0 as None
         self.name = None  # default event name
+        self._actions = []  # actions to be executed on trigger
         super().__init__()
 
     def new(self, timeout=None, name=None):
@@ -81,6 +82,12 @@ class MultiEvent(threading.Event):
             self.events.discard(event)
             if self.events:
                 return
+            try:
+                for action in self._actions:
+                    action()
+            except Exception:
+                pass  # we silently ignore errors here
+            self._actions = []
             super().set()
 
     def clear_(self, event):
@@ -116,3 +123,19 @@ class MultiEvent(threading.Event):
         as a convenience method
         """
         return self.new(timeout, name).set
+
+    def queue(self, action):
+        """add an action to the queue of actions to be executed at end
+
+        :param action: a function, to be executed after the last event is triggered,
+            and before the multievent is set
+
+        - if no events are waiting, the actions are executed immediately
+        - if an action raises an exception, it is silently ignore and further
+          actions in the queue are skipped
+        - if this is not desired, the action should handle errors by itself
+        """
+        with self._lock:
+            self._actions.append(action)
+            if self.is_set():
+                self.set_(None)