問(wèn)題描述

我的印象是 lock() 會(huì)阻止多個(gè)線程同時(shí)訪問(wèn)一個(gè)對(duì)象.

I was under the impression that lock() would prevent multiple threads from accessing an object simultaneously.

但是，以下代碼仍然經(jīng)常拋出 InvalidOperationException(對(duì)象當(dāng)前正在其他地方使用):

But, an InvalidOperationException (Object is currently in use elsewhere) is still frequently thrown by the following code:

lock (this)
{
    localCopy = (Bitmap)this.bm.Clone();
    int x, y;
    float pX = this.p.x;
    int width = localCopy.Width;
    x = (int)Math.Round((double)(pX * (float)width));
    if (x >= localCopy.Width) x = localCopy.Width - 1;
    y = (int)Math.Round((double)(this.p.y * (float)localCopy.Height));
    if (y >= localCopy.Height) y = localCopy.Height - 1;
    colourPixel = localCopy.GetPixel(x, y);
}

注意事項(xiàng):

• 我拆分了x的計(jì)算來(lái)隔離異常的原因.它似乎來(lái)自訪問(wèn)位圖.
• 我嘗試創(chuàng)建位圖的本地副本，但這只會(huì)導(dǎo)致相同的異常.我試過(guò) Clone()ing 并創(chuàng)建一個(gè)新的位圖.兩者都不起作用.
• 我嘗試鎖定 this(如所見(jiàn))和位圖對(duì)象.兩者都不起作用.

• I split up the calculation of x to isolate the cause of the exception. It appears to come from accessing the bitmap.
• I tried creating a local copy of the bitmap, but this just causes the same exception. I've tried Clone()ing and creating a new Bitmap. Neither works.
• I've tried locking on this (as seen) and on the bitmap object. Neither works.

我是否試圖以一種不應(yīng)該的方式使用 lock()?我誤解了它的目的嗎?如何防止 InvalidOperationExceptions?

Am I trying to use lock() in a way I'm not supposed to? Have I misunderstood it's purpose? How can I prevent InvalidOperationExceptions?

推薦答案

我最終找到了這個(gè)問(wèn)題的根源.我把鎖移到了位圖屬性的getter/setter方法中，并實(shí)現(xiàn)了一個(gè)深拷貝"的方法來(lái)盡快釋放這個(gè)屬性.

I eventually got to the bottom of this. I moved the locks into the getter / setter methods of the bitmap property and implemented a "deep copy" method to free up the property as soon as possible.

private static object syncRoot = new Object();
private Bitmap _bm;
private Bitmap bm
{
    get
    {
        lock (syncRoot)
            return this._bm.DeepClone();
    }
    set
    {
        lock (syncRoot)
        {
            this._bm = value.DeepClone();
        }
    }
}

DeepClone() 擴(kuò)展方法來(lái)自另一個(gè)問(wèn)題的答案:

The DeepClone() extension method was cribbed from an answer to another question:

public static T DeepClone<T>(this T a)
{
    using (MemoryStream stream = new MemoryStream())
    {
        BinaryFormatter formatter = new BinaryFormatter();
        formatter.Serialize(stream, a);
        stream.Position = 0;
        return (T)formatter.Deserialize(stream);
    }
}

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