EdColeman commented on code in PR #2778:
URL: https://github.com/apache/accumulo/pull/2778#discussion_r930336843


##########
server/base/src/main/java/org/apache/accumulo/server/conf/ServerConfigurationFactory.java:
##########
@@ -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:
   Fixed in ac14691996
   
   Note - instead of creating a lock, I tried synchronizing on the 
AtomicBoolean - spotbugs didn't like it and flagged it as an error.



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