@Override
          public Thread newThread(Runnable runnable) {
            Thread t = Executors.defaultThreadFactory().newThread(runnable);
            if (t != null) {
              t.setName(String.format("%s active cleanup timer", InMemoryCredentialStore.class.getSimpleName()));
              t.setDaemon(true);
            }
            return t;
          }
Constructs a new InMemoryCredentialStore with a specified credential timeout

@param retentionDuration the time in some units to keep stored credentials, from the time they are added
@param units             the units for the retention duration (minutes, seconds, etc...)
@param activelyPurge     true to actively purge credentials after the retention time has expired;
                         otherwise false, to passively purge credentials after the retention time has expired
ambari-server/src/main/java/org/apache/ambari/server/security/encryption/InMemoryCredentialStore.java