通常使用下面的JVM選項在GC日誌中列印”stop-the-world”（STW）暫停時間。

-XX:+PrintGCApplicationStoppedTime

       但是在GC日誌中看，會發現有許多這樣的暫停時間，時間很短，肯定不是垃圾回收引起的。

Total time for which application threads were stopped: 0.0013102 seconds, Stopping threads took: 0.0001792 seconds
Total time for which application threads were stopped: 0.0012521 seconds, Stopping threads took: 0.0001591 seconds
Total time for which application threads were stopped: 0.0008090 seconds, Stopping threads took: 0.0001030 seconds
Total time for which application threads were stopped: 0.0010226 seconds, Stopping threads took: 0.0001058 seconds
 

       實際上，觸發STW暫停的原因除了垃圾回收外，還有一些其他的操作會觸發STW，例如一些JIT活動、偏向鎖擦除、特定的JVMTI操作，以及許多場景也可能會導致應用程式暫停。
       上述例子中application threads stopped的時間表示應用暫停時間，Stopping threads took 的時間表示等待所有的應用執行緒都到達安全點花費的時間。只有應用程式執行緒到達安全點後，JVM才會做些特殊處理，比如垃圾收集、偏向鎖擦除等等。