[jira] [Created] (SLING-6945) avoid unnecessary error when OakViewChecker is deactivated

["Stefan Egli (JIRA)" <ji...@apache.org>]

Stefan Egli created SLING-6945:
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             Summary: avoid unnecessary error when OakViewChecker is deactivated
                 Key: SLING-6945
                 URL: https://issues.apache.org/jira/browse/SLING-6945
             Project: Sling
          Issue Type: Improvement
          Components: Extensions
    Affects Versions: Discovery Base 2.0.0
            Reporter: Stefan Egli
             Fix For: Discovery Base 2.0.2


The following series of log messages has been noticed:
{noformat}06.06.2017 11:47:41.774 *INFO* [Discovery-AsyncEventSender] org.apache.sling.discovery.oak.pinger.OakViewChecker triggerAsyncConnectorPing: firing job to trigger heartbeat
06.06.2017 11:47:41.811 *INFO* [OsgiInstallerImpl] org.apache.sling.discovery.oak.pinger.OakViewChecker deactivate: deactivated slingId: c2caefd0-7aab-4fbb-a120-985d6174d7ea, this: org.apache.sling.discovery.oak.pinger.OakViewChecker@7a9f2f75
06.06.2017 11:47:41.812 *ERROR* [sling-default-3-discovery.connectors.common.runner.c2caefd0-7aab-4fbb-a120-985d6174d7ea490b04a4-42f2-464a-ab15-15520e78e3a3] org.apache.sling.discovery.oak.pinger.OakViewChecker announcementRegistry is null
06.06.2017 11:47:45.339 *INFO* [OsgiInstallerImpl] org.apache.sling.discovery.oak Service [org.apache.sling.discovery.oak.pinger.OakViewChecker,10971, [org.apache.sling.discovery.oak.pinger.OakViewChecker]] ServiceEvent UNREGISTERING
06.06.2017 11:47:50.753 *INFO* [OsgiInstallerImpl] org.apache.sling.discovery.oak Service [org.apache.sling.discovery.oak.pinger.OakViewChecker,14874, [org.apache.sling.discovery.oak.pinger.OakViewChecker]] ServiceEvent REGISTERED
06.06.2017 11:47:50.757 *INFO* [OsgiInstallerImpl] org.apache.sling.discovery.oak.pinger.OakViewChecker doActivate: activated with runtimeId: 82b0e439-6040-44d0-abd7-6c0cbbb62339, slingId: c2caefd0-7aab-4fbb-a120-985d6174d7ea
{noformat}

Or in other words:
 * {{11:47:41.774}} a topology event triggering a heartbeat (a normal, low-level operation) happens
 * {{11:47:41.811}} OakViewChecker deactivate
 * {{11:47:41.812}} the heartbeat that was triggered before is now executed asynchronously (via scheduler) and fails because deactivate already {{null}}-ed the {{announcementRegistry}}

So this means {{OakViewChecker.deactivate}} didn't stop an already scheduled, asynchronous heartbeat - which then subsequently fails because deactivate has already happened.

Or, put slightly differently, {{deactivate}} and {{heartbeatAndCheckView}} are not synchronized (due to SLING-3365).

As a simple measure {{BaseViewChecker.doCheckView}} should be made thread-safe, ie it should be aware that deactivate can be called concurrently.

And the log.error should probably be lowered to log.info



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