探索JVM运行状态的利器—JVMPI，HPROF

1．什么是JVMPI？Java Virtual Machine Profiler Interface。参考

http://java.sun.com/j2se/1.4.2/docs/guide/jvmpi/jvmpi.html#overview

JVMPI可以做什么？它可以监控VM发生的各种事件。例如当JVM创建，关闭，Java类被加载，创建对象，或GC回收，等37种事件。既然是接口自然就是有一个头文件，[JAVA_HOME]/include/jvmpi.h。您可以开发自己的Profiler监控Java VM的发生的各种事件。

 

下面是我编写的使用JVMPI的例子，输出结果说明了为了运行一个Java类，JVM需要做的各种操作。

 

#include <jvmpi.h>

//1.>cl -LDd -Zi -I. -IC:/j2sdk1.4.2_10/include -IC

//   :/j2sdk1.4.2_10/include/win32 -Tp./jvmtrace.c -o jvmtrace.dll

//2.>copy jvmtrace.dll C:/j2sdk1.4.2_10/bin/

//3.>java -Xrunjvmtrace org.colimas.jni.test.JniTest

//jvmpi interface 全局指针

static JVMPI_Interface *jvmpi_interface;

 

//时间通知处理函数

void notifyEvent(JVMPI_Event *event) {

  switch(event->event_type) {

       /*非常可怕的输出，好奇就试试。

case JVMPI_EVENT_CLASS_LOAD:

           fprintf(stderr, "trace> Class Load : %s/n", event->u.class_load.class_name);

           break;*/

       case JVMPI_EVENT_ARENA_DELETE :

           fprintf(stderr, "trace> The heap arena :%d is deleted./n", event->u.delete_arena.arena_id);

           break;    

       case JVMPI_EVENT_ARENA_NEW :

              fprintf(stderr, "trace> The heap arena %s:%d is created./n",

                     event->u.new_arena.arena_name,

                     event->u.new_arena.arena_id);

           break;    

       case JVMPI_EVENT_GC_FINISH :

              fprintf(stderr, "trace> GC is finished. Used object:%d, space:%d, total object space:%d./n",

                     event->u.gc_info.used_objects,

                     event->u.gc_info.used_object_space,

                     event->u.gc_info.total_object_space);

           break;

       case JVMPI_EVENT_GC_START :

              fprintf(stderr, "trace>GC is started./n");

           break;

       case JVMPI_EVENT_HEAP_DUMP :

              fprintf(stderr, "trace> The heap dump begin %s,end %s./n",

                     event->u.heap_dump.begin,

                     event->u.heap_dump.end);

           break;

       case JVMPI_EVENT_JVM_INIT_DONE :

              fprintf(stderr, "trace> JVM initialization is done./n");

           break;

       case JVMPI_EVENT_JVM_SHUT_DOWN :

              fprintf(stderr, "trace> JVM is shutting down./n");

           break;

       case JVMPI_EVENT_THREAD_END :

              fprintf(stderr, "trace> A thread ends./n");

           break;

       case JVMPI_EVENT_THREAD_START :

              fprintf(stderr, "trace> The thread %s begins whose group is %s, parent is %s./n",

              event->u.thread_start.thread_name ,

              event->u.thread_start.group_name,

              event->u.thread_start.parent_name);

           break;

  }                      

}

 

// profiler agent entry point

extern "C" {

  JNIEXPORT jint JNICALL JVM_OnLoad(JavaVM *jvm, char *options, void *reserved) {

    fprintf(stderr, "trace> initializing ..... /n");

   

    // get jvmpi interface pointer

    if ((jvm->GetEnv((void **)&jvmpi_interface, JVMPI_VERSION_1)) < 0) {

      fprintf(stderr, "trace> error in obtaining jvmpi interface pointer/n");

      return JNI_ERR;

    }

   

    // initialize jvmpi interface

    jvmpi_interface->NotifyEvent = notifyEvent;

   

    // enabling class load event notification

    //jvmpi_interface->EnableEvent(JVMPI_EVENT_CLASS_LOAD, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_ARENA_DELETE, NULL);

       jvmpi_interface->EnableEvent(JVMPI_EVENT_ARENA_NEW, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_GC_FINISH, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_GC_START, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_HEAP_DUMP, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_JVM_INIT_DONE, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_JVM_SHUT_DOWN, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_THREAD_END, NULL);

    jvmpi_interface->EnableEvent(JVMPI_EVENT_THREAD_START, NULL);

     

    fprintf(stderr, "trace> .... ok, dumping.../n");

    if (jvmpi_interface->RequestEvent(JVMPI_EVENT_HEAP_DUMP,NULL)<0)

    {

      fprintf(stderr, "trace> error in obtaining jvmpi interface pointer/n");

      return JNI_ERR;

    }

    fprintf(stderr, "trace> .... end/n/n");

    return JNI_OK;

  }

}

编译

>cl -LDd -Zi -I. -IC:/j2sdk1.4.2_10/include -IC

   :/j2sdk1.4.2_10/include/win32 -Tp./jvmtrace.c -o jvmtrace.dll

拷贝jvmtrace.dll到JAVA_HOME/bin

>copy jvmtrace.dll C:/j2sdk1.4.2_10/bin/

运行

>java -Xrunjvmtrace org.colimas.jni.test.JniTest

结果

trace> initializing .....

trace> .... ok, dumping...

trace> .... end

 

trace> The thread Finalizer begins whose group is system, parent is (null).

trace> The thread Reference Handler begins whose group is system, parent is (nul

l).

trace> The thread main begins whose group is main, parent is system.

trace> JVM initialization is done.

trace> The thread Signal Dispatcher begins whose group is system, parent is (nul

l).

hello JVM

trace> A thread ends.

trace> The thread DestroyJavaVM begins whose group is main, parent is system.

trace> A thread ends.

trace> JVM is shutting down.

 

2．HPROF又什么是？HPROF是J2SE自带的一个简单的profiler agent。 他是一个动态链接库文件，监控CPU的使用率，Heap分配情况等。将这些信息输出到文件或到socket。

java –Xrunhprof ToBeProfiledClass [:help]|[:=, ...]

例如：

>java -Xrunhprof:heap=all org.colimas.jni.test.JniTest

在当前目录会生成java.hprof.txt文件。文件内记载了JVM运行时Heap的运行情况。