[GitHub] [accumulo] ctubbsii commented on a diff in pull request #2778: Add version check to ZooPropStore

[GitBox <gi...@apache.org>]

ctubbsii commented on code in PR #2778:
URL: https://github.com/apache/accumulo/pull/2778#discussion_r972166515


##########
server/base/src/main/java/org/apache/accumulo/server/conf/ServerConfigurationFactory.java:
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@@ -140,4 +158,114 @@ public void connectionEvent() {
       // no-op. changes handled by prop store impl
     }
   }
+
+  private class ConfigRefreshRunner {
+    private static final long MIN_JITTER_DELAY = 1;
+
+    private static final long MAX_JITTER_DELAY = 23;
+    private final ScheduledFuture<?> refreshTaskFuture;
+
+    ConfigRefreshRunner() {
+
+      Runnable refreshTask = this::verifySnapshotVersions;
+      // staggering the initial delay prevents synchronization of Accumulo servers communicating
+      // with ZooKeeper for the sync process.
+      long randDelay = jitter(REFRESH_PERIOD_MINUTES / 4, REFRESH_PERIOD_MINUTES);
+
+      ScheduledThreadPoolExecutor executor = ThreadPools.getServerThreadPools()
+          .createScheduledExecutorService(4, "config-refresh", false);
+      refreshTaskFuture =
+          executor.scheduleWithFixedDelay(refreshTask, randDelay, REFRESH_PERIOD_MINUTES, MINUTES);
+    }
+
+    /**
+     * Check that the stored version in ZooKeeper matches the version held in the local snapshot.
+     * When a mismatch is detected, a change event is sent to the prop store which will cause a
+     * re-load. If the Zookeeper node has been deleted, the local cache entries are removed.
+     * <p>
+     * This method is designed to be called as a scheduled task, so it does not propagate exceptions
+     * other than interrupted Exceptions so the scheduled tasks will continue to run.
+     */
+
+    private synchronized void verifySnapshotVersions() {

Review Comment:
   You can still guard with an AtomicBoolean, but without synchronizing on it. It has its own internal synchronization. In any case, I don't think it's a problem if there's only a single instance of this object with only a single background thread running these checks.



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