Serviceability 简介 —— 概述

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);

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...

评论

1 楼 qiuboboy 2013-04-09