add multiplexer/router

in case a remote is disconnected and can be reconnected quickly,
a seamless routing is possible. However, when after reconnection
the description has changed, the server is restarted.

+ more information in error messages from dispatcher

Change-Id: I0837e0254aee3d12a26481f6fd697081a53aabba
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22506
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>

secop/lib/multievent.py

@@ -0,0 +1,83 @@
+#  -*- coding: utf-8 -*-
+# *****************************************************************************
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Module authors:
+#   Markus Zolliker <markus.zolliker@psi.ch>
+#
+# *****************************************************************************
+
+import threading
+
+
+class MultiEvent(threading.Event):
+    """Class implementing multi event objects.
+
+    meth:`new` creates Event like objects
+    meth:'wait` waits for all of them being set
+    """
+
+    class SingleEvent:
+        """Single Event
+
+        remark: :meth:`wait` is not implemented on purpose
+        """
+        def __init__(self, multievent):
+            self.multievent = multievent
+            self.multievent._clear(self)
+
+        def clear(self):
+            self.multievent._clear(self)
+
+        def set(self):
+            self.multievent._set(self)
+
+        def is_set(self):
+            return self in self.multievent.events
+
+    def __init__(self):
+        self.events = set()
+        self._lock = threading.Lock()
+        super().__init__()
+
+    def new(self):
+        """create a new SingleEvent"""
+        return self.SingleEvent(self)
+
+    def set(self):
+        raise ValueError('a multievent must not be set directly')
+
+    def clear(self):
+        raise ValueError('a multievent must not be cleared directly')
+
+    def _set(self, event):
+        """internal: remove event from the event list"""
+        with self._lock:
+            self.events.discard(event)
+            if self.events:
+                return
+            super().set()
+
+    def _clear(self, event):
+        """internal: add event to the event list"""
+        with self._lock:
+            self.events.add(event)
+            super().clear()
+
+    def wait(self, timeout=None):
+        if not self.events:  # do not wait if events are empty
+            return
+        super().wait(timeout)