Question

您好我使用以下代码使用sun.misc.Unsafe存储字符串：

package com.util.OffHeapStorage;

import java.lang.reflect.Field;

import sun.misc.Unsafe;

public class OffHeapStorage {
    static Unsafe unsafe = getUnsafe();

    static Unsafe getUnsafe() {
        try {
            Field f = Unsafe.class.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            return (Unsafe) f.get(null);
        } catch (Exception x) {
            x.printStackTrace();
        }

        return null;
    }

    static long storeString(String str){
        long bytes = 2;
        long startAddress = unsafe.allocateMemory(bytes);
        int strlength = str.length();

        for(long i=0;i<strlength;i++){
            char ch = str.charAt((int)i);
            unsafe.putChar(startAddress + i*2, ch);
            System.out.println("Stored "+ch+" to address "+(startAddress+i*2));
        }

        return startAddress;
    }

    static String fetchString(long startAddress, int strlength){
        StringBuilder strOut = new StringBuilder();

        for(long i = startAddress; i < startAddress + strlength * 2; i += 2 ){
            strOut.append(unsafe.getChar(i));
        }

        return strOut.toString();
    }

    static void freeStringMemory(long startAddress, int strlength ){
        for(long i = startAddress; i < startAddress + strlength * 2; i += 2 ){
            unsafe.freeMemory(i);
        }
    }


    public static void main(String [] args){
        String message = "Hello World";

        long stringAddress = storeString(message);
        System.out.println(fetchString(stringAddress, message.length()));
        //freeStringMemory(stringAddress, message.length());
    }


}

正如你所看到的，我没有释放记忆。

此代码的输出将告诉我存储的字符串的起始地址，我想检查是否可以在另一个类中使用以获取字符串值。

所以我的另一堂课看起来像：

public static void main(String [] args){
        String message = "Hello World";

        long stringAddress = 413100824;
        System.out.println(fetchString(stringAddress, message.length()));
        freeStringMemory(stringAddress, message.length());
    }

然而，在执行此类时，我收到此错误：

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x6ce8d1b3, pid=11624, tid=0x000025c0
#
# JRE version: Java(TM) SE Runtime Environment (8.0_131-b11) (build 1.8.0_131-b11)
# Java VM: Java HotSpot(TM) Client VM (25.131-b11 mixed mode windows-x86 )
# Problematic frame:
# V  [jvm.dll+0x13d1b3]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# An error report file with more information is saved as:
# C:\localeclipseworkspace\OffHeapStorage\hs_err_pid11624.log
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#

我刚试过Java Unsafe，也许我的整个概念都错了。本质上，我试图检查是否可以将数据存储在操作系统内存中，而不是增加我的JVM负担。

非常感谢任何帮助。

是否可以使用类中的sun.misc.Unsafe存储字符串并从另一个类中检索它？

0 个答案: