synchronized void awaitConfigChecked(long millis) throws InterruptedException {
         long remaining, doom = System.currentTimeMillis() + millis;
         while ( ! doubleChecked && (remaining = doom - System.currentTimeMillis()) > 0) wait(remaining);
        assertTrue(doubleChecked, "some config should be checked more than once during " + millis + " millis; checked ones: " + checked);
    }
@author Tony Vaagenes
@author gjoranv
@author ollivir
container-core/src/test/java/com/yahoo/container/di/DirConfigSource.java