如何衡量JVM启动时间？

Question

我有一个用java编写的应用程序,我想知道在达到它之前需要多长时间static void int main(String args)以及它在那个阶段做了什么我该如何实现呢？

我知道微软有一个名为MPGO的工具(管理器配置文件引导优化)是否有Java的等价物？

Answer 1

从Java应用程序内部测量启动时间的简单方法:

import java.lang.management.ManagementFactory;

public class Test {

    public static void main(String[] args) {
        long currentTime = System.currentTimeMillis();
        long vmStartTime = ManagementFactory.getRuntimeMXBean().getStartTime();
        System.out.println(currentTime - vmStartTime);
    }
}

您可以使用JVMTI代理来跟踪VM事件,如类加载,垃圾收集,方法编译等.这是一个我做过的简单代理--vmtrace(以及用于Windows 的编译后的dll).

运行java -agentpath:path\to\vmtrace.dll Main,事件跟踪将打印到stderr:

[0.00000] VMTrace started
[0.00182] Dynamic code generated: flush_icache_stub
[0.00187] Dynamic code generated: get_cpu_info_stub
[0.00519] Dynamic code generated: getCPUIDNameInfo_stub
[0.00524] Dynamic code generated: forward exception
[0.00526] Dynamic code generated: call_stub
...
[0.01182] Loading class: java/lang/Object
[0.01198] Loading class: java/lang/String
[0.01206] Loading class: java/io/Serializable
...
[0.05620] VM initialized
[0.05664] Class prepared: java/lang/invoke/MethodHandle
[0.05672] Loading class: java/lang/invoke/MethodHandleImpl
[0.05732] Class prepared: java/lang/invoke/MethodHandleImpl
[0.05738] Loading class: java/lang/invoke/MethodHandleImpl$1
[0.05743] Class prepared: java/lang/invoke/MethodHandleImpl$1
[0.05755] Loading class: java/lang/invoke/MethodHandleImpl$2
[0.05759] Loading class: java/util/function/Function
[0.05768] Class prepared: java/util/function/Function
...