title: Spring Shedlock does not ensure synchronization
body: <p>I have following scheduled job which runs in multiple instances. </p>
  
  <pre><code>@Scheduled(fixedRate = 10000)
  @SchedulerLock(name = "AwesomeJob", lockAtLeastForString = "5S", lockAtMostForString = "5S")
  public void awesomeJob() throws InterruptedException {
  
      for (int i = 0; i &lt; 5; i++) {
          log.info("Processing {}", i);
          Thread.sleep(100000L);
      }
  }
  </code></pre>
  
  <p>I know that If the task takes longer than lockAtMostFor the resulting behavior may be unpredictable. Is there a way to avoid that behavior by using SimpleLock.extend method? I am using JdbcLockProvider. I got this idea from <a href="https://github.com/lukas-krecan/ShedLock/issues/151" rel="nofollow noreferrer">https://github.com/lukas-krecan/ShedLock/issues/151</a> . </p>