問題描述

我最近經常使用鎖定位圖，并且不斷收到試圖訪問無效內存"錯誤.這主要是因為位圖已在內存中移動.有些人使用 GCHandle.Alloc() 在 CLR 中分配內存并固定它.Bitmap.LockBits() 做同樣的事情嗎?我不明白鎖定"內存和固定"內存之間的區別.您能否解釋一下術語和差異(如果有)?

I'm using locked bitmaps a lot recently, and I keep getting "attempted to access invalid memory" errors. This is mostly because the bitmap has been moved in memory. Some people using GCHandle.Alloc() to allocate memory in the CLR and pin it. Does Bitmap.LockBits() do the same? I don't understand the difference between "locking" memory and "pinning" memory. Can you also explain the terminology and the differences if any?

推薦答案

GCHandle.Alloc 是一種更通用的方法，它允許您為任何托管對象分配一個句柄并將其固定在內存中(或不).固定內存可防止 GC 移動它，這在您必須將某些數據(例如數組)傳遞給非托管代碼時特別有用.

GCHandle.Alloc is a more generic method, that allows you to allocate a handle to any managed object and pin it in memory (or not). Pinning memory prevents GC from moving it around, which is especially useful when you have to pass some data, for example an array, to a unmanaged code.

GCHandle.Alloc 不會以任何方式幫助您訪問位圖的數據，因為固定此對象只會阻止托管對象四處移動(位圖對象)(并被垃圾收集).

GCHandle.Alloc will not help you access bitmap's data in any way, because pinning this object will just prevent the managed object from moving around (the Bitmap object) (and being garbage collected).

然而，位圖是對原生 GDI+ 的 BITMAP 結構的包裝.它不會將數據保存在您必須固定的任何托管數組中，它只是管理 GDI+ 位圖對象的本機句柄.因為 Bitmap.LockBits 是一種告訴這個位圖你有興趣訪問它的內存的方式，它只是一個關于 GdipBitmapLockBits 函數的包裝器.因此，您需要調用它更多地與您使用 GDI+ 位圖的事實有關，而不是與您在使用 GC 的托管環境中工作的事實有關.

Bitmap however is a wrapper around native GDI+'s BITMAP structure. It doesn't keep data in any managed array that you would have to pin, it just managed a native handle to GDI+ bitmap object. Because of that Bitmap.LockBits is a way of telling this bitmap that you are interested in accessing it's memory, and it's just a wrapper around GdipBitmapLockBits function. So your need of calling it has more to do with the fact that you are working with GDI+ bitmaps than with the fact, that you're working in managed environment with GC.

一旦您使用了LockBits，您應該能夠通過BitmapData.Scan0 使用指針訪問它的內存——它是數據第一個字節的地址.只要您不訪問 BitmapData.Scan0 + Height * Stride 后面的內存，您就不應該有問題.

Once you have used LockBits you should be able to access it's memory using pointers through BitmapData.Scan0 - it's an address of first byte of data. You should not have problems as long, as you do not access memory behind BitmapData.Scan0 + Height * Stride.

完成后記得UnlockBits.

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