问题描述

我的印象是 lock() 会阻止多个线程同时访问一个对象.

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

但是，以下代码仍然经常抛出 InvalidOperationException(对象当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);
}

注意事项:

• 我拆分了x的计算来隔离异常的原因.它似乎来自访问位图.
• 我尝试创建位图的本地副本，但这只会导致相同的异常.我试过 Clone()ing 并创建一个新的位图.两者都不起作用.
• 我尝试锁定 this(如所见)和位图对象.两者都不起作用.

• 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.

我是否试图以一种不应该的方式使用 lock()?我误解了它的目的吗?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?

推荐答案

我最终找到了这个问题的根源.我把锁移到了位图属性的getter/setter方法中，并实现了一个深拷贝"的方法来尽快释放这个属性.

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() 扩展方法来自另一个问题的答案:

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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