[HDFS-6786] Fix potential issue of cache refresh interval

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 2.4.0
• Component/s: caching
• Target Version/s: 2.6.0
• Assignee: Yi Liu
• Reporter: Yi Liu
• Created: 30/Jul/14 10:50
• Updated: 01/Aug/14 07:48
• Resolved: 31/Jul/14 21:34

Description

In CacheReplicationMonitor, following code is try to check whether needs to rescan every interval ms, if rescan takes n ms, then subtract n ms for the interval. But if the delta <=0, it breaks and start rescan, there will be potential issue: if user set the interval to a small value or rescan finished after a while exceeding the interval, then rescan will happen in loop. Furthermore, delta <= 0 trigger the rescan should not be the intention, since if needs rescan, needsRescan will be set.

         while (true) {
            if (shutdown) {
              LOG.info("Shutting down CacheReplicationMonitor");
              return;
            }
            if (needsRescan) {
              LOG.info("Rescanning because of pending operations");
              break;
            }
            long delta = (startTimeMs + intervalMs) - curTimeMs;
            if (delta <= 0) {
              LOG.info("Rescanning after " + (curTimeMs - startTimeMs) +
                  " milliseconds");
              break;
            }
            doRescan.await(delta, TimeUnit.MILLISECONDS);
            curTimeMs = Time.monotonicNow();
          }