转: mmap文件映射内存分析

来源：互联网发布：淘宝详情页怎么做编辑：程序博客网时间：2024/04/28 07:11

http://edisonlz.iteye.com/blog/1197453

http://blog.yufeng.info/archives/2456

主要是了解mac下vmmap命令配合使用情况，mmap内存映射对应java nio的RandomAccessFile的FileChannel进行map()操作。

public class RandomMapFileReadTest {    static int length = 0x8000000; // 128 Mb    public static void main(String[] args) throws FileNotFoundException {        try{            // 为了以可读可写的方式打开文件，这里使用RandomAccessFile来创建文件。            FileChannel fc = new RandomAccessFile("test.dat", "rw").getChannel();            //注意，文件通道的可读可写要建立在文件流本身可读写的基础之上            MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE, 0, length);            //写128M的内容            byte[] readArray = new byte[1024];            for (int i = 0; i < length; i++) {                byte byteChar = out.get();                readArray[i%1024] = byteChar;                if(i == length/2) {                    Thread.sleep(20);                    System.out.println("read half...");                }            }//            System.out.println("Finished writing");            //读取文件中间6个字节内容            System.out.println("Finished getting " + readArray.length);            fc.close();        }catch (Exception e) {            e.printStackTrace();        }    }}

一个已经存在的128M文件，在map后，通过for循环不断读入内存，可以通过

vmmap -resident <pid>

命令看出，map的resident内存是一步一步读入的：

yangyamin:~ yangyamin$ vmmap -resident 1486 | grep testmapped file            0000000115a8d000-000000011da8d000 [128.0M  56.9M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.datyangyamin:~ yangyamin$ vmmap -resident 1486 | grep testmapped file            0000000115a8d000-000000011da8d000 [128.0M  89.7M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.datyangyamin:~ yangyamin$ vmmap -resident 1486 | grep test\mapped file            0000000115a8d000-000000011da8d000 [128.0M 107.5M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.datyangyamin:~ yangyamin$ vmmap -resident 1486 | grep testmapped file            0000000115a8d000-000000011da8d000 [128.0M 125.9M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.datyangyamin:~ yangyamin$ vmmap -resident 1486 | grep testmapped file            0000000115a8d000-000000011da8d000 [128.0M 128.0M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.datyangyamin:~ yangyamin$ vmmap -resident 1486 | grep testmapped file            0000000115a8d000-000000011da8d000 [128.0M 128.0M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat

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