23 June 2012

原文地址: http://caoxudong818.iteye.com/blog/1565980

以下内容均已jdk1.7.0_04为准。

啥是 Serviceability ?

HotSpot Glossary of Terms写道

Serviceability Agent (SA) The Serviceablity Agent is collection of Sun internal code that aids in debugging HotSpot problems. It is also used by several JDK tools - jstack, jmap, jinfo, and jdb. See SA for more information.

简单说,这部分是用来调试查看hotspot的。

子曰,学而时习之 不亦说乎。这里就先习之,有个直观印象之后,再学之。 平时用来查看hotspot内部信息的常用的工具都在$JAVA_HOME/bin目录下,其中一些工具就是用Serviceability开发的。这里要介绍的是HSDB(其命令版本是CLHSDB),启动方式如下:

java -classpath $JAVA_HOME/lib/sa-jdi.jar sun.jvm.hotspot.HSDB

看到界面后,大家自己琢磨怎么玩吧,内容挺多。

类似的,启动CLHSDB的方式如下:

java -classpath $JAVA_HOME/lib/sa-jdi.jar sun.jvm.hotspot.CLHSDB

这里有一个简单的说明文档:http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/raw-file/tip/agent/doc/clhsdb.html

另外,还有一个DebugServer类,功能差不多。

java -classpath %JAVA_HOME%/lib/sa-jdi.jar sun.jvm.hotspot.DebugServer

在sun.jvm.hotspot包下,有个HelloWorld类。我觉着此类是在蛋疼的紧,各位请看代码:

/*
 * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

package sun.jvm.hotspot;

import java.lang.reflect.*;

public class HelloWorld {
    private static String helloWorldString = "Hello, world!";
    private static volatile int helloWorldTrigger = 0;
    private static final boolean useMethodInvoke = false;
    private static Object lock = new Object();

    public static void main(String[] args) {
        int foo = a();
        System.out.println("HelloWorld exiting. a() = " + foo);
    }

    private static int a() {
        return 1 + b();
    }

    private static int b() {
        return 1 + c();
    }

    private static int c() {
        return 1 + d("Hi");
    }

    private static int d(String x) {
        System.out.println("HelloWorld.d() received \"" + x + "\" as argument");
        synchronized(lock) {
            if (useMethodInvoke) {
                try {
                    Method method = HelloWorld.class.getMethod("e");
                    Integer result = (Integer) method.invoke(null, new Object[0]);
                    return result.intValue();
                }
                catch (Exception e) {
                    throw new RuntimeException(e.toString());
                }
            } else {
                int i = fib(10); // 89
                long l = i;
                float f = i;
                double d = i;
                char c = (char) i;
                short s = (short) i;
                byte b = (byte) i;
                int ret = e();
                System.out.println("Tenth Fibonacci number in all formats: " +
                       i + ", " +
                       l + ", " +
                       f + ", " +
                       d + ", " +
                       c + ", " +
                       s + ", " +
                       b);

                return ret;
            }
        }
    }

    public static int e() {
        System.out.println("Going to sleep...");
        int i = 0;

        while (helloWorldTrigger == 0) {
            if (++i == 1000000) {
                System.gc();
            }
        }

        System.out.println(helloWorldString);

        while (helloWorldTrigger != 0) {}

        return i;
    }

    // Tree-recursive implementation for test
    public static int fib(int n) {
        if (n < 2) {
            return 1;
        }
        return fib(n - 1) + fib(n - 2);
    }
}

  难道此类是用来硬件测性能的?

sa中的包主要分为以下几个部分: asm,ci,code,debugger,gc,interpreter,jdi,livevm,memory,oops,opto,prims,runtine,tools,types。 后续的文章会进行介绍,可能会跳过一些(我不懂的)。

回到CLHSDB,这个只是一个壳,主要的功能都是靠sun.jvm.hotspot.HotSpotAgent和sun.jvm.hotspot.CommandProcessor完成的。

CommandProcessor.DebuggerInterface di = new CommandProcessor.DebuggerInterface() {
            public HotSpotAgent getAgent() {
                return agent;
            }
            public boolean isAttached() {
                return attached;
            }
            public void attach(String pid) {
                attachDebugger(pid);
            }
            public void attach(String java, String core) {
                attachDebugger(java, core);
            }
            public void detach() {
                detachDebugger();
            }
            public void reattach() {
                if (attached) {
                    detachDebugger();
                }
                if (pidText != null) {
                    attach(pidText);
                } else {
                    attach(execPath, coreFilename);
                }
            }
        };
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
CommandProcessor cp = new CommandProcessor(di, in, System.out, System.err);</pre>

构造CommandProcessor类的实例前时,会对其中的一个成员变量commandList进行初始化,其中存储的就是预先注册的可执行命令:

private final Command[] commandList = {
    new Command("reattach", true) {
        public void doit(Tokens t) {
            int tokens = t.countTokens();
            if (tokens != 0) {
                usage();
                return;
            }
            preAttach();
            debugger.reattach();
            postAttach();
        }
    },
    new Command("attach", "attach pid | exec core", true) {
        public void doit(Tokens t) {
            int tokens = t.countTokens();
            if (tokens == 1) {
                preAttach();
                debugger.attach(t.nextToken());
                postAttach();
            } else if (tokens == 2) {
                preAttach();
                debugger.attach(t.nextToken(), t.nextToken());
                postAttach();
            } else {
                usage();
            }
        }
    },
......
    new Command("assert", "assert true | false", true) {
        public void doit(Tokens t) {
            if (t.countTokens() != 1) {
                usage();
            } else {
                Assert.ASSERTS_ENABLED = Boolean.valueOf(t.nextToken()).booleanValue();
            }
        }
    },
};

 

这样,程序就可以接收并处理用户输入的命令。

HotSpotAgent类的主要功能是根据主机环境设置调试器(debugger),并将debugger attach(这词儿该咋表述)到目标上(目标可以通过PID或dump文件)。流程如下(以Windows为例): attach($pid) -> setupDebugger() -> setupDebuggerWin32() -> attachDebugger() 在这期间会根据需要,判断是否建立一个远程调式服务器,以便于执行远程调试。

if (isServer) {
    RemoteDebuggerServer remote = null;
    try {
        remote = new RemoteDebuggerServer(debugger);
    }catch (RemoteException rem) {
        throw new DebuggerException(rem);
    }
    RMIHelper.rebind(serverID, remote);
} 

to be continued…