java - Android 上的 I/O 基准测试

Question

我为 I/O 创建了自己的基准，但我无法理解它是否真实。

你有示例代码可以向我展示有关 i/o 的性能吗？

有什么优化建议吗？

提前谢谢你:)

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Random;

import android.content.Context;
import android.os.Environment;


public class MainHandler {

    protected Context mContext;
    public String Data = new String("");
    /** Called when the activity is first created. 
     * @throws Exception */



    public MainHandler(Context c) throws Exception{
        this.mContext = c;
        generateString();
        writeOnHd();
        readOnHd();
        writeOnSd();
        readOnSd();
    }




    public void writeOnHd() throws Exception {
        System.out.println("-------------------------------------------------------");
        long startTime = System.currentTimeMillis();


        FileOutputStream fOut = mContext.openFileOutput("samplefile.txt", 777);
        OutputStreamWriter osw = new OutputStreamWriter(fOut);  

        int c = 2000;
        for (int i = 0; i < c; i++) {
            osw.write(this.Data);
            osw.flush();
        }
        osw.close();
        System.out.println("Total time to write: " 
                + ((System.currentTimeMillis() - startTime)) 
                + " miliseconds ");

        System.gc();
    }





    public void readOnHd() throws Exception {

        long startTime = System.currentTimeMillis();

        FileInputStream fIn = mContext.openFileInput("samplefile.txt");
        InputStreamReader isr = new InputStreamReader(fIn);

        char[] inputBuffer = new char[1024];
        int len = 0;
        int length= 1024;

        while((len = isr.read(inputBuffer)) != -1){
            //System.out.println("Total bytes read: " + len);


        }

        fIn.close();


        System.out.println("Total time to read: " 
                + ((System.currentTimeMillis() - startTime)) 
                + " miliseconds number block ");
        mContext.deleteFile("samplefile.txt");

        System.gc();
    }







    public void writeOnSd (){

        long startTime = System.currentTimeMillis();

        File sd = Environment.getExternalStorageDirectory();
        File f = new File(sd, "provafile.txt");


        FileWriter fw = null;
        BufferedWriter bw = null;
        try{
            fw = new FileWriter(f, true);
            bw = new BufferedWriter(fw);
            int c = 2000;
            for (int i = 0; i < c; i++) {
                bw.write(this.Data);
                bw.flush();
            }
            bw.close();
            fw.close();


            } 
            catch (IOException e) {       
                e.printStackTrace();
            }
            System.gc();
            System.out.println("Total time to write on sd: " 
                    + ((System.currentTimeMillis() - startTime)) 
                    + " miliseconds ");
        }





    public void readOnSd(){

        long startTime = System.currentTimeMillis();
        try{

            File f = new File(Environment.getExternalStorageDirectory()+"/provafile.txt");
            FileInputStream fIn = new FileInputStream(f);
            InputStreamReader isr = new InputStreamReader(fIn);

            char[] inputBuffer = new char[1024];
            int len = 0;
            int length= 1024;

            while((len = isr.read(inputBuffer)) != -1){
                //System.out.println("Total bytes read on sd: " + len);

            }


            fIn.close();
            f.delete();



        }catch(Exception e){
            e.printStackTrace();
        }

        System.gc();
        System.out.println("Total time to read on sd: " +
                ((System.currentTimeMillis() - startTime)) +
                " miliseconds ");

    }

    public void generateString(){
        int c = 2000;
        for(int i =0; i<=c; i++) {
            Random randomGenerator = new Random();
            String container[]= {"a", "D","£","&","e","f","ç","h","§","j","*","]","{","n","o","|",")","4","s","t","u","=","z"};
            int n = randomGenerator.nextInt(22);
            this.Data += container[n];
        }
        System.gc();
    }



}

Answer 1

众所周知，这些类型的微基准测试很难以您可以分析结果的方式编写。

SO 上有很多关于这个的问题，结论通常是很难得出任何结论:-)

例如考虑以下事实:您有 JIT 编译、非确定性垃圾收集以及运行时和 VM 的各种实现...

例如，我什至不确定在 2000 次迭代的紧密循环中执行某些操作是否会触发 JIT。

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