为什么启用带有异常的调试要慢得多?

考虑以下代码:

public class JMain {
    private final static int forLength = 6;

    private static void returnFromFor(int breakAt) {
        try {
            for (int j = 0; j < forLength; j++) {
                if (j == breakAt) {
                    throw new Throwable("break");
                }
            }
        } catch (Throwable ignored) {
        }
    }

    public static void main(String args[]) {
        long start = System.currentTimeMillis();
        int iterations = 100000;
        for (int i = 0; i < iterations; i++) {
            returnFromFor(i % forLength);
        }

        long end = System.currentTimeMillis();
        System.out.println(((Long) (end - start)).toString() + " ms");
    }
}

当我在启用了异常断点的Intellij IDEA调试器中运行此代码时, java.lang.IllegalArgumentException ,运行非常慢,在我的电脑上大约1800毫秒。当我运行它时没有异常断点,或者启用了断点 java.lang.UnsupportedOperationException ,大约快10倍。

我的问题是:

• 为什么用调试 IllegalArgumentException 比…慢得多 UnsupportedOperationException ?

• 是因为jvm调试器或intellij导致的速度减慢?

运行此操作的系统是:

• Windows X64
• Intellij Idea Ultimate 2018.2版
• JRE:1.8.0_-release-1248-B8 AMD64

注意:上面的代码演示了我在复杂scala中遇到的问题。如果有人对更自然的scala代码演示感兴趣,请看:

object Main extends App {

  val forLength = 6
  def returnFromFor(breakAt: Int): Unit = {
    for (j <- 0 until forLength) {
      if (j == breakAt) return
    }
  }

  val start = System.currentTimeMillis()
  val iterations = 100000
  for (i <- 0 until iterations) {
    returnFromFor(i%forLength)
  }
  val end = System.currentTimeMillis()
  println(s"Duration ${end-start} ms")

}