TestLoadXml.cs

using UnityEngine;
using System.Collections;
using System.IO;
using System.Diagnostics;

public class TestLoadXml:MonoBehaviour {
    
    private Stopwatch _stopwatch;
    // Use this for initialization
    void Start() {
        handler();
    }

    private void handler(){
        var gameObject=new GameObject("XmlLoader");
        var xmlLoader=gameObject.AddComponent<FileLoader>();
        _stopwatch=new Stopwatch();
        _stopwatch.Start();

        xmlLoader.onProgress+=onProgress;
        xmlLoader.onComplete+=onComplete;

        Stopwatch sw=new Stopwatch();
        sw.Start();

        xmlLoader.load(@"G:\Downloads\vs2013.5_ult_chs.iso");
        sw.Stop();
        Debug2.Log("ElapsedMilliseconds:",sw.ElapsedMilliseconds);


        
    }

    // Update is called once per frame
    void Update() {
        if(Input.GetMouseButtonDown(0)){
            handler();
        }
    }

    private void onProgress(float progress,byte[] bytes,int position){
        Debug2.Log(progress);
    }

    private void onComplete(byte[] bytes){
        _stopwatch.Stop();

        Debug2.Log("onComplete",bytes.Length,_stopwatch.Elapsed.TotalMilliseconds);

        
    }
}

FileLoader.cs

using System;
using System.Collections;
using System.IO;
using System.Threading;
using UnityEngine;

public class FileLoader:BaseMonoBehaviour{
    
    /// <summary>
    /// void(float progress,byte[] bytes,int position)
    /// <br>progress：表示加载进度，范围[0,1]</br>
    /// <br>bytes：表示已加载的字节</br>
    /// <br>position：文件流读取到的位置，Array.Copy(bytes,loadedBytes,position)表示已加载的字节</br>
    /// </summary>
    public event Action<float,byte[],int> onProgress;
    /// <summary>
    /// void(byte[] bytes)
    /// <br>bytes：表示文件的总字节</br>
    /// </summary>
    public event Action<byte[]> onComplete;

    private FileStream _fileStream;
    private CancellationTokenSource _tokenSource;

    public void load(string filePath){
        
        //StartCoroutine(loadHandler(filePath));
        //loadHandler2(filePath);
        //loadHandler3(filePath);
        loadAsync(filePath);
    }

    IEnumerator loadHandler(string filePath){
        FileStream fileStream=File.OpenRead(filePath);

        int fileLength=(int)fileStream.Length;
        byte[] buffer=new byte[fileLength];
        yield return fileStream.ReadAsync(buffer,0,fileLength);
        onComplete?.Invoke(buffer);
    }

    void loadHandler2(string filePath){
        FileStream fileStream=File.OpenRead(filePath);

        int fileLength=(int)fileStream.Length;
        byte[] buffer=new byte[fileLength];
        fileStream.Read(buffer,0,fileLength);
        onComplete?.Invoke(buffer);
    }

    async void loadHandler3(string filePath){
        FileStream fileStream=File.OpenRead(filePath);

        int fileLength=(int)fileStream.Length;
        byte[] buffer=new byte[fileLength];
        int count=await fileStream.ReadAsync(buffer,0,fileLength);
        onComplete?.Invoke(buffer);
    }

    async void loadAsync(string filePath){
        FileStream fileStream=File.OpenRead(filePath);
        _fileStream=fileStream;

        int fileLength=(int)fileStream.Length;
        int bufferSize=Mathf.Max((int)(fileLength/5.0f),2048);
        byte[] buffer=new byte[bufferSize];
        
        byte[] bytes=new byte[fileLength];
        int position=0;
        int i=0;

        _tokenSource=new CancellationTokenSource();

        while(true){
            if(_tokenSource.IsCancellationRequested)break;

            Array.Clear(buffer,0,bufferSize);
            int readCount=await fileStream.ReadAsync(buffer,0,bufferSize,_tokenSource.Token);
            //on await complete
            if(position<fileLength){
                for(i=0;i<readCount;i++){
                    bytes[position]=buffer[i];
                    position++;
                }
                float progress=(float)position/fileLength;
                onProgress?.Invoke(progress,bytes,position);
            }else{
                onComplete?.Invoke(bytes);
                _tokenSource.Dispose();
                _tokenSource=null;
                _fileStream.Dispose();
                _fileStream.Close();
                _fileStream=null;
                break;
            }
        }
    }

    protected override void OnDestroy(){
        if(_tokenSource!=null){
            _tokenSource.Cancel();
        }
        if(_fileStream!=null){
            _fileStream.Dispose();
            _fileStream.Close();
        }
        base.OnDestroy();
    }

}