[2856] Extend SegmentInfo and add some basic tests

This is according to the description in #2856, but it needs further
testing and also documentation. These will be added in future commits
after handling "load" command in the MemorySegmentBuilder.

src/lib/python/isc/memmgr/datasrc_info.py

@@ -43,6 +43,97 @@ class SegmentInfo:
     READER = 0
     WRITER = 1
 
+    # Enumerated values for state
+    UPDATING = 0
+    SYNCHRONIZING = 1
+    COPYING = 2
+    READY = 3
+
+    def __init__(self):
+        self.__state = self.READY
+        self.__readers = set()
+        self.__old_readers = set()
+        self.__events = []
+
+    def get_state(self):
+        return self.__state
+
+    def get_readers(self):
+        return self.__readers
+
+    def get_old_readers(self):
+        return self.__old_readers
+
+    def get_events(self):
+        return self.__events
+
+    def complete_update(self):
+        if self.__state == self.UPDATING:
+            self.__state = self.SYNCHRONIZING
+        elif self.__state == self.COPYING:
+            self.__state = self.READY
+        else:
+            raise SegmentInfoError('complete_update() called in ' +
+                                   'incorrect state: ' + str(self.__state))
+
+    def __sync_reader_helper(self):
+        if len(self.__old_readers) == 0:
+            self.__state = self.COPYING
+            if len(self.__events) > 0:
+                e = self.__events[0]
+                del self.__events[0]
+                return e
+
+        return None
+
+    def sync_reader(self, reader_session_id):
+        if self.__state != self.SYNCHRONIZING:
+            raise SegmentInfoError('sync_reader() called in ' +
+                                   'incorrect state: ' + str(self.__state))
+        if reader_session_id not in self.__old_readers:
+            raise SegmentInfoError('Reader session ID is not in old readers set: ' +
+                                   reader_session_id)
+        if reader_session_id in self.__readers:
+            raise SegmentInfoError('Reader session ID is already in readers set: ' +
+                                   reader_session_id)
+
+        self.__old_readers.remove(reader_session_id)
+        self.__readers.add(reader_session_id)
+
+        return self.__sync_reader_helper()
+
+    def remove_reader(self, reader_session_id):
+        if self.__state != self.SYNCHRONIZING:
+            raise SegmentInfoError('remove_reader() called in ' +
+                                   'incorrect state: ' + str(self.__state))
+        if reader_session_id in self.__old_readers:
+            self.__old_readers.remove(reader_session_id)
+            return self.__sync_reader_helper()
+        elif reader_session_id in self.__readers:
+            self.__readers.remove(reader_session_id)
+            return None
+        else:
+            raise SegmentInfoError('Reader session ID is not in current ' +
+                                   'readers or old readers set: ' +
+                                   reader_session_id)
+
+    def add_event(self, event_data):
+        self.__events.append(event_data)
+
+    def start_update(self):
+        if self.__state == self.READY and len(self.__events) > 0:
+            self.__state = self.UPDATING
+            return self.__events[0]
+
+        return None
+
+    def add_reader(self, reader_session_id):
+        if reader_session_id in self.__readers:
+            raise SegmentInfoError('Reader session ID is already in readers set: ' +
+                                   reader_session_id)
+
+        self.__readers.add(reader_session_id)
+
     def create(type, genid, rrclass, datasrc_name, mgr_config):
         """Factory of specific SegmentInfo subclass instance based on the
         segment type.

src/lib/python/isc/memmgr/tests/datasrc_info_tests.py

@@ -60,6 +60,25 @@ class TestSegmentInfo(unittest.TestCase):
         self.__check_sgmt_reset_param(SegmentInfo.WRITER, 0)
         self.__check_sgmt_reset_param(SegmentInfo.READER, None)
 
+        self.assertEqual(self.__sgmt_info.get_state(), SegmentInfo.READY)
+        self.assertEqual(len(self.__sgmt_info.get_readers()), 0)
+        self.assertEqual(len(self.__sgmt_info.get_old_readers()), 0)
+        self.assertEqual(len(self.__sgmt_info.get_events()), 0)
+
+    def test_complete_update_when_ready(self):
+        self.assertRaises(SegmentInfoError, self.__sgmt_info.complete_update)
+
+    def test_sync_reader_when_ready(self):
+        self.assertRaises(SegmentInfoError, self.__sgmt_info.sync_reader, (None))
+
+    def test_remove_reader_when_ready(self):
+        self.assertRaises(SegmentInfoError, self.__sgmt_info.remove_reader, (None))
+
+    def test_add_event(self):
+        self.assertEqual(len(self.__sgmt_info.get_events()), 0)
+        self.__sgmt_info.add_event(None)
+        self.assertNotEqual(len(self.__sgmt_info.get_events()), 0)
+
     def test_swtich_versions(self):
         self.__sgmt_info.switch_versions()
         self.__check_sgmt_reset_param(SegmentInfo.WRITER, 1)