Question "Exception:Sharing violation on path" When antivirus software is running in the background

I am trying to implement the pause/resume download function.
It work find if turn off the antivirus software.
But i cannot demand that all users turn off their antivirus software.
It only happen after called StopDownload then call StartDownload again.
So is there any other solution？

using System;

using System.IO;

using UnityEngine;

using UnityEngine.Networking;



public class SelfDownloadHandler : DownloadHandlerScript

{

    public long downloadedLength;

    FileStream fileStream ;

    public SelfDownloadHandler(string savePath) : base(new byte[1024 * 200])

    {

        try

        {

            fileStream = new FileStream(savePath, FileMode.Append, FIleAccess.Write);

            downloadedLength = fileStream.Length;

        }

        catch(Exception e)

        {

            //"Sharing violation on path" Exception catched here

            Debug.LogError("open file exception:" + e);

        }

    }



    //call every frame

    protected override bool ReceiveData(byte[] data, int dataLength)

    {

        if (data == null || data.Length == 0)

        {

            Debug.Log("download failed");

            return false;

        }

        fileStream?.Write(data, 0, dataLength);

        downloadedLength += dataLength;

        return true;

    }



    public void Close()

    {

        if (fileStream != null)

        {

            fileStream.Close();

            fileStream.Dispose();

            fileStream = null;

            Debug.Log("close filestream");

        }



        Dispose();

    }

}



public class TestDownload : MonoBehaviour

{   

    public string downloadUrl;

    public string savePath;

    UnityWebRequest unityWebRequest;



    void Start()

    {

        

    }



    IEnumerator StartDownload()

    {

        SelfDownloadHandler downloadHandler = new SelfDownloadHandler(savePath);



        unityWebRequest = UnityWebRequest.Get(downloadUrl)

        unityWebRequest.SetRequestHeader("Range", "bytes=" + downloadHandler.downloadedLength + "-");

        unityWebRequest.downloadHandler = downloadHandler;

        yield return unityWebRequest.SendWebRequest();

        CloseWebRequest();

    }



    void StopDownload()

    {

        if (unityWebRequest  != null)

        {

            unityWebRequest .Abort();

            CloseWebRequest();

        }

    }



   void CloseWebRequest()

   {

        if (unityWebRequest  != null)

        {

            ((SelfDownloadHandler)unityWebRequest .downloadHandler).Close();

            unityWebRequest .Dispose();

            unityWebRequest  = null;

        }

    }



    void Update()

    {

        if (Input.GetKeyDown(KeyCode.Space))

        {

            StartCoroutine(StartDownload());

        }

        else if(Input.GetKeyDown(KeyCode.Tag))

        {

            StopDownload();

        }

    }

}

 

Testing with other downloaded software does not have this issue