GC overhead limit exceeded

今天本想验证一下字符串常量池移动到堆内存中去了，验证的思路很简单，使用String::intern()不停的往字符串常量池中添加字符串，验证是否会出现java.lang.OutOfMemoryError:java heap space错误。代码清单如下：

public class RuntimeConstantPoolOOM {
    public static void main(String[] args) {
        List list = new ArrayList<>();
        int i = 1;
        while(true){
            list.add(String.valueOf(i++).intern());
        }
    }
}

VM options: -Xms20M -Xmx20M.

结果以外的报错：java.lang.OutOfMemoryError: GC overhead limit exceeded.

查阅官方文档发现这是jdk 6以后引入的一种类似于内存溢出的预警策略：当虚拟式运行时超过98%的时间用来做GC却只回收了不到2%的堆内存。

Exception in thread thread_name: java.lang.OutOfMemoryError: GC Overhead limit exceeded Cause: The detail message "GC overhead limit exceeded" indicates that the garbage collector is running all the time and Java program is making very slow progress. After a garbage collection, if the Java process is spending more than approximately 98% of its time doing garbage collection and if it is recovering less than 2% of the heap and has been doing so far the last 5 (compile time constant) consecutive garbage collections, then a java.lang.OutOfMemoryError is thrown. This exception is typically thrown because the amount of live data barely fits into the Java heap having little free space for new allocations.
Action: Increase the heap size. The java.lang.OutOfMemoryError exception for GC Overhead limit exceeded can be turned off with the command line flag -XX:-UseGCOverheadLimit.

此时JVM认为马上就要发生OOM了，让程序提前结束。此时如果想演示heap OOM的话可以使用参数：-XX:-UseGCOverheadLimit关闭这一策略，否则JVM启动时是默认开启的。