Events

Coherence provides the ability to subscribe to notifications pertaining to a particular map/cache. In addition to listening for specific events, it is possible to listen to events for changes made to a specific key, or using a Filter, it’s possible to limit the events raised to be for a subset of the map entries.

The following example demonstrates using lifecycle and map events.

 1# Copyright (c) 2023, Oracle and/or its affiliates.
 2# Licensed under the Universal Permissive License v 1.0 as shown at
 3# https://oss.oracle.com/licenses/upl.
 4
 5import asyncio
 6
 7from coherence import Filters, NamedMap, Session
 8from coherence.event import MapLifecycleEvent, MapListener
 9from coherence.filter import MapEventFilter
10
11
12async def do_run() -> None:
13    """
14    Demonstrates listeners for entry events and cache lifecycle.
15
16    :return: None
17    """
18    session: Session = await Session.create()
19    try:
20        named_map: NamedMap[int, str] = await session.get_map("listeners-map")
21        await named_map.put(1, "1")
22
23        print("NamedMap lifecycle events")
24
25        named_map.on(MapLifecycleEvent.RELEASED, lambda x: print("RELEASED", x))
26        named_map.on(MapLifecycleEvent.TRUNCATED, lambda x: print("TRUNCATE", x))
27        named_map.on(MapLifecycleEvent.DESTROYED, lambda x: print("DESTROYED", x))
28
29        print("Truncating the NamedMap; this should generate an event ...")
30        await named_map.truncate()
31        await asyncio.sleep(1)
32
33        print("Releasing the NamedMap; this should generate an event ...")
34        named_map.release()
35        await asyncio.sleep(1)
36
37        print("Destroying the NamedMap; this should generate an event ...")
38        await named_map.destroy()
39        await asyncio.sleep(1)
40
41        print("\n\nNamedMap entry events")
42
43        named_map = await session.get_map("listeners-map")
44
45        listener1: MapListener[int, str] = MapListener()
46        listener1.on_any(lambda e: print(e))
47
48        print("Added listener for all events")
49        print("Events will be generated when an entry is inserted, updated, and removed")
50        await named_map.add_map_listener(listener1)
51
52        await named_map.put(1, "1")
53        await named_map.put(1, "2")
54        await named_map.remove(1)
55        await asyncio.sleep(1)
56
57        await named_map.remove_map_listener(listener1)
58
59        print("\nAdded listener for all entries, but only when they are inserted")
60        ins_filter = Filters.event(Filters.always(), MapEventFilter.INSERTED)
61        await named_map.add_map_listener(listener1, ins_filter)
62
63        await named_map.put(1, "1")
64        await named_map.put(1, "2")
65        await named_map.remove(1)
66        await asyncio.sleep(1)
67
68        await named_map.remove_map_listener(listener1, ins_filter)
69
70        print("\nAdded listener for entries with a length larger than one, but only when they are updated or removed")
71        upd_del_filter = Filters.event(Filters.greater("length()", 1), MapEventFilter.UPDATED | MapEventFilter.DELETED)
72        await named_map.add_map_listener(listener1, upd_del_filter)
73
74        for i in range(12):
75            await named_map.put(i, str(i))
76            await named_map.put(i, str(i + 1))
77            await named_map.remove(i)
78
79        await asyncio.sleep(1)
80
81        await named_map.remove_map_listener(listener1, upd_del_filter)
82        await named_map.clear()
83    finally:
84        await session.close()
85
86
87asyncio.run(do_run())

  • Lines 25-39 - Using NamedMap.on(), define listeners supported events and pass in a lambda to print the invocation. Then one by one, trigger each of the events and ensure enough time is given for the event to occur.

  • Lines 45-46 - Create a new MapListener and for any event, print the result.

  • Lines 50-54 - Add the MapListener that will be triggered on all events For this section, events will be printed for inserted, updated, and deleted.

  • Lines 60-66 - Add the MapListener that will be triggered when any entry is inserted. For this section, only the inserted event will be printed.

  • 71-77 - Add the MapListener that will be triggered when an entry’s value’s length is greater than 1 and only for updated and removed events. For this section, only updated and deleted events will be printed once the loop progresses enough to insert values larger than “9”