Java中的逃逸分析 [英] Escape analysis in Java

问题描述

据我所知，JVM使用转义分析来获得某些性能 optimisations 像锁定粗化和锁定省略。
我很感兴趣，如果JVM有可能决定使用转义分析在堆栈上分配任何特定对象。

As far as I know the JVM uses escape analysis for some performance optimisations like lock coarsening and lock elision. I'm interested if there is a possibility for the JVM to decide that any particular object can be allocated on stack using escape analysis.

一些资源让我觉得我是对的。是否有JVM实际执行此操作？

Some resources make me think that I am right. Is there JVMs that actually do it?

推荐答案

我认为它不会逃避堆栈分配的分析。示例：

I don't think it does escape analysis for stack allocation. example:

public class EscapeAnalysis {

    private static class Foo {
        private int x;
        private static int counter;

        public Foo() {
            x = (++counter);
        }
    }
    public static void main(String[] args) {
        System.out.println("start");
        for (int i = 0; i < 10000000; ++i) {
            Foo foo = new Foo();
        }

        System.out.println(Foo.counter);
    }
}

-server -verbose ：gc -XX + DoEscapeAnalysis ：

start
[GC 3072K->285K(32640K), 0.0065187 secs]
[GC 3357K->285K(35712K), 0.0053043 secs]
[GC 6429K->301K(35712K), 0.0030797 secs]
[GC 6445K->285K(41856K), 0.0033648 secs]
[GC 12573K->285K(41856K), 0.0050432 secs]
[GC 12573K->301K(53952K), 0.0043682 secs]
[GC 24877K->277K(53952K), 0.0031890 secs]
[GC 24853K->277K(78528K), 0.0005293 secs]
[GC 49365K->277K(78592K), 0.0006699 secs]
10000000

据说 JDK 7支持堆栈分配。

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