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From "Gerd Behrmann (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CURATOR-328) PathChildrenCache fails silently if server is unavailable for sufficient time when client starts
Date Fri, 20 May 2016 21:23:13 GMT
Gerd Behrmann created CURATOR-328:
-------------------------------------

             Summary: PathChildrenCache fails silently if server is unavailable for sufficient
time when client starts
                 Key: CURATOR-328
                 URL: https://issues.apache.org/jira/browse/CURATOR-328
             Project: Apache Curator
          Issue Type: Bug
          Components: Recipes
    Affects Versions: 2.10.0
            Reporter: Gerd Behrmann


When initializing the PathChildrenCache, if the curator client is not yet connected to the
ZooKeeper server (e.g. the server is down or the network connection is unavailable), then
the internal initialization of the cache will eventually fail silently and the cache stays
empty even after the client finally connects to the server and the path is populated with
znodes.

The following unit test demonstrates the problem (the unit test is ugly as the problem depends
on timing, but it suffices to demonstrate the issue):

{code:java}
    @Test
    public void pathChildrenCacheTest() throws Exception
    {
        TestingServer server = new TestingServer(false);

        Timing timing = new Timing();
        CuratorFramework client = CuratorFrameworkFactory.newClient(
                server.getConnectString(), timing.session(), timing.connection(), new ExponentialBackoffRetry(1000,
3));
        try {
            new Thread() {
                @Override
                public void run()
                {
                    try {
                        Thread.sleep(60000);
                        server.start();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }.start();

            client.start();

            PathChildrenCache cache = new PathChildrenCache(client, "/", true);
            cache.start();

            client.blockUntilConnected();

            client.create().creatingParentContainersIfNeeded().forPath("/baz", new byte[]
{1,2,3});

            assertNotNull("/baz does not exist", client.checkExists().forPath("/baz"));

            /* Ugly hack for this test to ensure the cache got time to update itself. */
            Thread.sleep(1000);

            assertNotNull("cache doesn't see /baz", cache.getCurrentData("/baz"));
        } finally {
            client.close();
            server.stop();
        }
    }
{code}

Here the server startup is delayed until some point after the curator client was started and
after the recipe has been created. Eventually the server starts and the path is populated
with data - some time is given for the cache to update itself, yet no data is visible: The
second assertion fails.

If the startup time is reduced to - say - 20 seconds, the test passes.

If the client is allowed to first connect to the server before creating the recipe and then
disconnect and reconnect after creating the recipe, then the test passes too.

I tracked down the problem to the state change listener of the recipe: If the connection to
the server is down for long enough, the refresh call during the background initialization
will eventually fail (ensurePath throws an exception). This isn't a problem as the recipe
has a state change listener, so it gets notified when the client eventually connects to the
server. The handleStateChange method however doesn't react to a CONNECTED event - only to
a RECONNECTED event. Thus if the client has been connected to the server in the past, everything
works, however if this is the first time it connects, the recipe will not react to the event
and thus not refresh itself.



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