unsafe

问题 I use ASM library to generate bytecodes and load them using Unsafe.defineAnonymous as a Class. Both work in most of cases, but after for a short time, it fails. Then I add some debug instructions in the emitted bytecodes to print something, and the output confused me for two weeks. (GWT is short for GuardWithTestHandle). 1, Two classes are generated: DYNGWT70 and DYNGWT73, and both are loaded using Unsafe . For each class, there is only one instance is created. 2, The layout of DYNGWT70 is

问题 In this code I'm creating Transparent bitmap but coloring the pixels in the List testpoints in yellow. How can I keep make it Transparent but the pixels to be coloring or keep with the original colors of them instead yellow ? private void button2_Click(object sender, EventArgs e) { Graphics g; g = Graphics.FromImage(bmpBackClouds); g.Clear(Color.Transparent); g.Dispose(); BitmapData b1 = bmpBackClouds.LockBits(new System.Drawing.Rectangle(0, 0, bmpBackClouds.Width, bmpBackClouds.Height),

问题 I'm now using unsafe. When I run the following code: unsafe.allocateInstance(Class.class) There happen's Exception in thread "main" java.lang.IllegalAccessException: java.lang.Class Since Class is a non-abstract class, why it so special? And is there any way to construct an 'empty' Class like allocateInstance ? 回答1: Because there is an explicit check inside HotSpot JVM to ensure that java.lang.Class cannot be instantiated through JNI, Unsafe etc. See instanceKlass.cpp: void InstanceKlass:

问题 In C#, 64bit Windows + .NET 4.5 (or later) + enabling gcAllowVeryLargeObjects in the App.config file allows for objects larger than two gigabyte. That's cool, but unfortunately, the maximum number of elements that C# allows in a character array is still limited to about 2^31 = 2.15 billion chars. Testing confirmed this. To overcome this, Microsoft recommends in Option B creating the arrays natively (their 'Option C' doesn't even compile). That suits me, as speed is also a concern. Is there

问题 I found that almost all high level synchronization abstractions(like Semaphore, CountDownLatch, Exchanger from java.util.concurrent) and concurrent collections are using methods from Unsafe(like compareAndSwapInt method) to define critical section. In the same time I expected that synchronize block or method will be used for this purpose. Could you explain is the Unsafe methods(I mean only methods that could atomically set a value) more efficient than synchronize and why it is so? 回答1: Using

问题 In particular, I'm thinking of a scenario like this: unsafe struct Foo { public int Bar; public Foo* GetMyAddr() { fixed (Foo* addr = &this) return addr; } } Assuming a Foo stored in unmanaged memory, I'm trying to figure out what is involved in evaluating the fixed statement in GetMyAddr. I know as the programmer that this struct is never on the managed heap, I just need to get it's address in unmanaged memory in the most efficient manner. I'm especially concerned if there's any locking or

问题 I have written a struct and functions where I try to pass the struct by reference (i.e. struct value can be modified inside functions). enum RoomType { Economy, Buisness, Executive, Deluxe }; struct HotelRoom { public int Number; public bool Taken; public RoomType Category; public void Print() { String status = Taken ? "Occupied" : "available"; Console.WriteLine("Room {0} is of {1} class and is currently {2}", Number, Category, status); } } Now to pass this struct by reference I've found two

问题 Is there a way to get the "address" of an object? This is for demonstration purposes, I know this is a bad idea in general and if it works at all then as unsafe code. The project is tuned to allow unsafe code. However my tries were unsuccessful. The code I have so far is not compiling: unsafe static String AddressOf(Object o) { void* p = &o; return String.Format("{0}", new IntPtr(p)); } Error: Cannot take the address of, get the size of, or declare a pointer to a managed type ('object') Even

问题 I have C# code that interacts with C++ code, which performs operations with strings. I have this piece of code in a static helper class: internal static unsafe byte* GetConstNullTerminated(string text, Encoding encoding) { int charCount = text.Length; fixed (char* chars = text) { int byteCount = encoding.GetByteCount(chars, charCount); byte* bytes = stackalloc byte[byteCount + 1]; encoding.GetBytes(chars, charCount, bytes, byteCount); *(bytes + byteCount) = 0; return bytes; } } As you can see

问题 Is it possible to do Unsafe Image Processing in Python? As with C# I encountered a hard wall with my pixel processing in Python as getPixel method from Image is simply running too slow. Is it possible to get a direct access to the image in memory like LockBits in c# does? It will make my program run much faster. Thanks, Mark 回答1: There is nothing "unsafe" about this. Once you understand how Python works, it becomes patent that calling a method to retrieve information on each pixel is going to