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  • Why is my unsafe code block slower than my safe code?

    - by jomtois
    I am attempting to write some code that will expediently process video frames. I am receiving the frames as a System.Windows.Media.Imaging.WriteableBitmap. For testing purposes, I am just applying a simple threshold filter that will process a BGRA format image and assign each pixel to either be black or white based on the average of the BGR pixels. Here is my "Safe" version: public static void ApplyFilter(WriteableBitmap Bitmap, byte Threshold) { // Let's just make this work for this format if (Bitmap.Format != PixelFormats.Bgr24 && Bitmap.Format != PixelFormats.Bgr32) { return; } // Calculate the number of bytes per pixel (should be 4 for this format). var bytesPerPixel = (Bitmap.Format.BitsPerPixel + 7) / 8; // Stride is bytes per pixel times the number of pixels. // Stride is the byte width of a single rectangle row. var stride = Bitmap.PixelWidth * bytesPerPixel; // Create a byte array for a the entire size of bitmap. var arraySize = stride * Bitmap.PixelHeight; var pixelArray = new byte[arraySize]; // Copy all pixels into the array Bitmap.CopyPixels(pixelArray, stride, 0); // Loop through array and change pixels to black or white based on threshold for (int i = 0; i < pixelArray.Length; i += bytesPerPixel) { // i=B, i+1=G, i+2=R, i+3=A var brightness = (byte)((pixelArray[i] + pixelArray[i + 1] + pixelArray[i + 2]) / 3); var toColor = byte.MinValue; // Black if (brightness >= Threshold) { toColor = byte.MaxValue; // White } pixelArray[i] = toColor; pixelArray[i + 1] = toColor; pixelArray[i + 2] = toColor; } Bitmap.WritePixels(new Int32Rect(0, 0, Bitmap.PixelWidth, Bitmap.PixelHeight), pixelArray, stride, 0); } Here is what I think is a direct translation using an unsafe code block and the WriteableBitmap Back Buffer instead of the forebuffer: public static void ApplyFilterUnsafe(WriteableBitmap Bitmap, byte Threshold) { // Let's just make this work for this format if (Bitmap.Format != PixelFormats.Bgr24 && Bitmap.Format != PixelFormats.Bgr32) { return; } var bytesPerPixel = (Bitmap.Format.BitsPerPixel + 7) / 8; Bitmap.Lock(); unsafe { // Get a pointer to the back buffer. byte* pBackBuffer = (byte*)Bitmap.BackBuffer; for (int i = 0; i < Bitmap.BackBufferStride*Bitmap.PixelHeight; i+= bytesPerPixel) { var pCopy = pBackBuffer; var brightness = (byte)((*pBackBuffer + *pBackBuffer++ + *pBackBuffer++) / 3); pBackBuffer++; var toColor = brightness >= Threshold ? byte.MaxValue : byte.MinValue; *pCopy = toColor; *++pCopy = toColor; *++pCopy = toColor; } } // Bitmap.AddDirtyRect(new Int32Rect(0,0, Bitmap.PixelWidth, Bitmap.PixelHeight)); Bitmap.Unlock(); } This is my first foray into unsafe code blocks and pointers, so maybe the logic is not optimal. I have tested both blocks of code on the same WriteableBitmaps using: var threshold = Convert.ToByte(op.Result); var copy2 = copyFrame.Clone(); Stopwatch stopWatch = new Stopwatch(); stopWatch.Start(); BinaryFilter.ApplyFilterUnsafe(copyFrame, threshold); stopWatch.Stop(); var unsafesecs = stopWatch.ElapsedMilliseconds; stopWatch.Reset(); stopWatch.Start(); BinaryFilter.ApplyFilter(copy2, threshold); stopWatch.Stop(); Debug.WriteLine(string.Format("Unsafe: {1}, Safe: {0}", stopWatch.ElapsedMilliseconds, unsafesecs)); So I am analyzing the same image. A test run of an incoming stream of video frames: Unsafe: 110, Safe: 53 Unsafe: 136, Safe: 42 Unsafe: 106, Safe: 36 Unsafe: 95, Safe: 43 Unsafe: 98, Safe: 41 Unsafe: 88, Safe: 36 Unsafe: 129, Safe: 65 Unsafe: 100, Safe: 47 Unsafe: 112, Safe: 50 Unsafe: 91, Safe: 33 Unsafe: 118, Safe: 42 Unsafe: 103, Safe: 80 Unsafe: 104, Safe: 34 Unsafe: 101, Safe: 36 Unsafe: 154, Safe: 83 Unsafe: 134, Safe: 46 Unsafe: 113, Safe: 76 Unsafe: 117, Safe: 57 Unsafe: 90, Safe: 41 Unsafe: 156, Safe: 35 Why is my unsafe version always slower? Is it due to using the back buffer? Or am I doing something wrong? Thanks

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  • Determine if method is unsafe via reflection

    - by hmemcpy
    I'm looking for a way to filter out methods which have the unsafe modifier via reflection. It doesn't seem to be a method attribute. Is there a way? EDIT: it seems that this info is not in the metadata, at least I can't see it in the IL. However reflector shows the unsafe modifier in C# view. Any ideas on how it's done? Thanks!

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  • C# memory management: unsafe keyword and pointers

    - by Alerty
    What are the consequences (positive/negative) of using the unsafe keyword in C# to use pointers? For example, what becomes of garbage collection, what are the performance gains/losses, what are the performance gains/losses compared to other languages manual memory management, what are the dangers, in which situation is it really justifiable to make use of this language feature... ?

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  • Create a subarray reference in C# (using unsafe ?)

    - by Wam
    Hello there, I'm refactoring a library we currently use, and I'm faced with the following problem. We used to have the following stuff : class Blah { float[][] data; public float[] GetDataReference(int index) { return data[index]; } } For various reasons, I have replaced this jagged array version with a 1 dimensionnal array version, concatenating inner arrays. My question is : how can I still return a reference to a sub array of data ? class Blah { float[] data; int rows; public float[] GetDataReference(int index) { // Return a reference data from offset i to offset j; } } I was thinking that unsafe and pointers stuff may be of use, is it doable ?

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  • Why is a fixed size buffers (arrays) must be unsafe?

    - by brickner
    Let's say I want to have a value type of 7 bytes (or 3 or 777). I can define it like that: public struct Buffer71 { public byte b0; public byte b1; public byte b2; public byte b3; public byte b4; public byte b5; public byte b6; } A simpler way to define it is using a fixed buffer public struct Buffer72 { public unsafe fixed byte bs[7]; } Of course the second definition is simpler. The problem lies with the unsafe keyword that must be provided for fixed buffers. I understand that this is implemented using pointers and hence unsafe. My question is why does it have to be unsafe? Why can't C# provide arbitrary constant length arrays and keep them as a value type instead of making it a C# reference type array or unsafe buffers?

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  • C#. How to pass message from unsafe callback to managed code?

    - by maxima120
    Is there a simple example of how to pass messages from unsafe callback to managed code? I have a proprietary dll which receives some messages packed in structs and all is coming to a callback function. The example of usage is as follows but it calls unsafe code too. I want to pass the messages into my application which is all managed code. *P.S. I have no experience in interop or unsafe code. I used to develop in C++ 8 yrs ago but remember very little from that nightmarish times :) P.P.S. The application is loaded as hell, the original devs claim it processes 2mil messages per sec.. I need a most efficient solution.* static unsafe int OnCoreCallback(IntPtr pSys, IntPtr pMsg) { // Alias structure pointers to the pointers passed in. CoreSystem* pCoreSys = (CoreSystem*)pSys; CoreMessage* pCoreMsg = (CoreMessage*)pMsg; // message handler function. if (pCoreMsg->MessageType == Core.MSG_STATUS) OnCoreStatus(pCoreSys, pCoreMsg); // Continue running return (int)Core.CALLBACKRETURN_CONTINUE; } Thank you.

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  • What is the underlying reason for not being able to put arrays of pointers in unsafe structs in C#?

    - by cons
    If one could put an array of pointers to child structs inside unsafe structs in C# like one could in C, constructing complex data structures without the overhead of having one object per node would be a lot easier and less of a time sink, as well as syntactically cleaner and much more readable. Is there a deep architectural reason why fixed arrays inside unsafe structs are only allowed to be composed of "value types" and not pointers? I assume only having explicitly named pointers inside structs must be a deliberate decision to weaken the language, but I can't find any documentation about why this is so, or the reasoning for not allowing pointer arrays inside structs, since I would assume the garbage collector shouldn't care what is going on in structs marked as unsafe. Digital Mars' D handles structs and pointers elegantly in comparison, and I'm missing not being able to rapidly develop succinct data structures; by making references abstract in C# a lot of power seems to have been removed from the language, even though pointers are still there at least in a marketing sense. Maybe I'm wrong to expect languages to become more powerful at representing complex data structures efficiently over time.

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  • Is there any difference between null and 0 when assigning to pointers in unsafe code?

    - by Eloff
    This may seem odd, but in C (size_t)(void*)0 == 0 is not guaranteed by the language spec. Compilers are allowed to use any value they want for null (although they almost always use 0.) In C#, you can assign null or (T*)0 to a pointer in unsafe code. Is there any difference? (long)(void*)0 == 0 (guaranteed or not? put another way: IntPtr.Zero.ToInt64() == 0) MSDN has this to say about IntPtr.Zero: "The value of this field is not equivalent to null." Well if you want to be compatible with C code, that makes a lot of sense - it'd be worthless for interop if it didn't convert to a C null pointer. But I want to know if IntPtr.Zero.ToInt64() == 0 which may be possible, even if internally IntPtr.Zero is some other value (the CLR may or may not convert null to 0 in the cast operation) Not a duplicate of this question

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  • Unsafe shutdown on power button press (Ubuntu Server 13.10)

    - by Sam Bloomberg
    I have Ubuntu Server 13.10 set up on a machine, and whenever I press (not press and hold) the power button the machine doesn't safely shutdown (it instantly powers off), though it does flash the message "acpid: exiting" before turning off. If I instead run shutdown -h now, it goes through the usual cycle of stopping processes, unmounting filesystems, etc... Any ideas why this might be? I want the power button to safely shut down the system (unless I hold it down, of course).

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  • How close can I get C# to the performance of C++ for small intensive tasks?

    - by SLC
    I was thinking about the speed difference of C++ to C# being mostly about C# compiling to byte-code that is taken in by the JIT compiler (is that correct?) and all the checks C# does. I notice that it is possible to turn a lot of these functions off, both in the compile options, and possibly through using the unsafe keyword as unsafe code is not verifiable by the common language runtime. Therefore if you were to write a simple console application in both languages, that flipped an imaginary coin an infinite number of times and displayed the results to the screen every 10,000 or so iterations, how much speed difference would there be? I chose this because it's a very simple program. I'd like to test this but I don't know C++ or have the tools to compile it. This is my C# version though: static void Main(string[] args) { unsafe { Random rnd = new Random(); int heads = 0, tails = 0; while (true) { if (rnd.NextDouble() > 0.5) heads++; else tails++; if ((heads + tails) % 1000000 == 0) Console.WriteLine("Heads: {0} Tails: {1}", heads, tails); } } } Is the difference enough to warrant deliberately compiling sections of code "unsafe" or into DLLs that do not have some of the compile options like overflow checking enabled? Or does it go the other way, where it would be beneficial to compile sections in C++? I'm sure interop speed comes into play too then. To avoid subjectivity, I reiterate the specific parts of this question as: Does C# have a performance boost from using unsafe code? Do the compile options such as disabling overflow checking boost performance, and do they affect unsafe code? Would the program above be faster in C++ or negligably different? Is it worth compiling long intensive number-crunching tasks in a language such as C++ or using /unsafe for a bonus? Less subjectively, could I complete an intensive operation faster by doing this?

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  • How do I use unsafe values in an enum?

    - by Jon Tackabury
    I need to use this enum in my C# application, but it won't let me use these values. When I specify the type as uint I can use the -1 value, and when I specify int I can't use the last 2 values. Is there a way to use the unchecked keyword here to allow me to define all of these values? These values are coming from an external source, so I can't change them. internal enum MyValues : int { value1 = -1, value2 = 0, value3 = 0x80000000, value4 = 0xFFFFFFFF }

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  • AccessViolationException, attempted to read or write protected memory

    - by Malfist
    I'm using a dll that contains unsafe code for interacting with specific hardware, and I'm trying to use it from C#, but I keep getting an AccessViolationException. What's causing it, and how can I fix it? namespace FingerPrint { public unsafe partial class Form1 : Form { [DllImport("MyDll.dll")] public static extern int DoesExist(); public unsafe Form1() { InitializeComponent(); MessageBox.Show(DoesExist() + ""); } } }

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  • C# huge size 2-dim arrays

    - by 4eburek
    I need to declare square matrices in C# WinForms with more than 20000 items in a row. I read about 2GB .Net object size limit in 32bit and also the same case in 64bit OS. So as I understood the single answer - is using unsafe code or separate library built withing C++ compiler. The problem for me is worth because ushort[20000,20000] is smaller then 2GB but actually I cannot allocate even 700MB of memory. My limit is 650MB and I don't understand why - I have 32bit WinXP with 3GB of memory. I tried to use Marshal.AllocHGlobal(700<<20) but it throws OutOfMemoryException, GC.GetTotalMemory returns 4.5MB before trying to allocate memory. I found only that many people say use unsafe code but I cannot find example of how to declare 2-dim array in heap (any stack can't keep so huge amount of data) and how to work with it using pointers. Is it pure C++ code inside of unsafe{} brackets? Could you please provide a small example of working with matrices using pointers in unsafe code.

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  • Selectively allow unsafe html tags in Plone

    - by dhill
    I'm searching for a way to put widgets from several services (PicasaWeb, Yahoo Pipes, Delicious bookmarks, etc.) on the community site I host on Plone (currently 3.2.1). I'm looking for a way to allow a group of users to use dangerous html tags. There are some ways I see, but I don't know how to implement those. One would be changing safe_html for the pages editors own (1). Another would be to allow those tags on some subtree (2). And yet another finding an equivalent of "static text portlet" that would display in the middle panel (3). We could then use some of the composite products (I stumbled upon Collage and CMFContentPanels), to include the unsafe content on other sites. My site has been ridden by advert bots, so I don't want to remove the filtering all together. I don't have an easy (no false positives) way of checking which users are bots, so deploying captcha now wouldn't help either. The question is: How to implement any of those solutions? (I already asked that on plone mailing list without an answer, so I thought I would give it another try here.)

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  • Is it valid to use unsafe struct * as an opaque type instead of IntPtr in .NET Platform Invoke?

    - by David Jeske
    .NET Platform Invoke advocates declaring pointer types as IntPtr. For example, the following [DllImport("user32.dll")] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam); However, I find when interfacing with interesting native interfaces, that have many pointer types, flattening everything into IntPtr makes the code very hard to read and removes the typical typechecking that a compiler can do. I've been using a pattern where I declare an unsafe struct to be an opaque pointer type. I can store this pointer type in a managed object, and the compiler can typecheck it form me. For example: class Foo { unsafe struct FOO {}; // opaque type unsafe FOO *my_foo; class if { [DllImport("mydll")] extern static unsafe FOO* get_foo(); [DllImport("mydll")] extern static unsafe void do_something_foo(FOO *foo); } public unsafe Foo() { this.my_foo = if.get_foo(); } public unsafe do_something_foo() { if.do_something_foo(this.my_foo); } While this example may not seem different than using IntPtr, when there are several pointer types moving between managed and native code, using these opaque pointer types for typechecking is a godsend. I have not run into any trouble using this technique in practice. However, I also have not seen an examples of anyone using this technique, and I wonder why. Is there any reason that the above code is invalid in the eyes of the .NET runtime? My main question is about how the .NET GC system treats "unsafe FOO *my_foo". Is this pointer something the GC system is going to try to trace, or is it simply going to ignore it? My hope is that because the underlying type is a struct, and it's declared unsafe, that the GC would ignore it. However, I don't know for sure. Thoughts?

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  • comprehensive list of unsafe functions in C

    - by Dervin Thunk
    Hello. I've been looking online unsuccessfully for a comprehensive list of unsafe (dangerous) functions in C (see here for a few). When I say "dangerous" I mean functions like gets or strcopy, but I was wondering if someone has actually compiled a comprehensive list. Thank you. PD: Neil Butterworth, you should abstain from answering my posts. You're seldom helpful.

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  • Safe vs Unsafe code

    - by Lumpy
    Read this question today about safe and unsafe code I then read about it in MSDN but I still don't understand it. Why would you want to use pointers in C#? Is this purely for speed?

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  • Exception in thread "main" java.lang.NoSuchMethodError: sun/misc/Unsafe.allocateDBBMemory

    - by user2524935
    Has anyone been able to compile JRuby on a s390x Linux system? I am trying to use LogStash, which apparently requires JRuby, however SLES 11 has no JRuby repo included. jar ant produces the following. compile-annotation-binder: [javac] Compiling 18 source files to /home/user7/jruby-1.7.4/build/classes/jruby [javac] warning: [options] bootstrap class path not set in conjunction with -source 1.6 [javac] Note: /home/user7/jruby-1.7.4/src/org/jruby/util/CodegenUtils.java uses unchecked or unsafe operations. [javac] Note: Recompile with -Xlint:unchecked for details. [javac] 1 warning compile-jruby: [javac] Compiling 1395 source files to /home/user7/jruby-1.7.4/build/classes/jruby [javac] Exception in thread "main" java.lang.NoSuchMethodError: sun/misc/Unsafe.allocateDBBMemory(J)J [javac] at java.nio.DirectByteBuffer.(DirectByteBuffer.java:127) [javac] at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:306) [javac] at sun.misc.Perf.createLong(Native Method) [javac] at sun.misc.PerfCounter.(PerfCounter.java:77) [javac] at sun.misc.PerfCounter.newPerfCounter(PerfCounter.java:83) [javac] at sun.misc.PerfCounter$CoreCounters.(PerfCounter.java:140) [javac] at java.lang.J9VMInternals.initializeImpl(Native Method) [javac] at java.lang.J9VMInternals.initialize(J9VMInternals.java:236) [javac] at sun.misc.PerfCounter.getZipFileOpenTime(PerfCounter.java:194) [javac] at java.util.zip.ZipFile.(ZipFile.java:230) [javac] at java.util.zip.ZipFile.(ZipFile.java:159) [javac] at java.util.jar.JarFile.(JarFile.java:167) [javac] at java.util.jar.JarFile.(JarFile.java:104) [javac] at sun.misc.URLClassPath$JarLoader.getJarFile(URLClassPath.java:958) [javac] at sun.misc.URLClassPath$JarLoader.access$700(URLClassPath.java:826) [javac] at sun.misc.URLClassPath$JarLoader$1.run(URLClassPath.java:909) [javac] at sun.misc.URLClassPath$JarLoader$1.run(URLClassPath.java:899) [javac] at java.security.AccessController.doPrivileged(AccessController.java:280) [javac] at sun.misc.URLClassPath$JarLoader.ensureOpen(URLClassPath.java:898) [javac] at sun.misc.URLClassPath$JarLoader.(URLClassPath.java:871) [javac] at sun.misc.URLClassPath$3.rtJarLoader(URLClassPath.java:596) [javac] at sun.misc.URLClassPath$3.run(URLClassPath.java:546) [javac] at sun.misc.URLClassPath$3.run(URLClassPath.java:536) [javac] at java.security.AccessController.doPrivileged(AccessController.java:280) [javac] at sun.misc.URLClassPath.getLoader(URLClassPath.java:535) [javac] at sun.misc.URLClassPath.getLoader(URLClassPath.java:498) [javac] at sun.misc.URLClassPath.getResource(URLClassPath.java:324) [javac] at java.net.URLClassLoader$ClassFinder.run(URLClassLoader.java:1157) [javac] at java.security.AccessController.doPrivileged(AccessController.java:314) [javac] at java.net.URLClassLoader.findClass(URLClassLoader.java:594) [javac] at java.lang.ClassLoader.loadClassHelper(ClassLoader.java:743) [javac] at java.lang.ClassLoader.loadClass(ClassLoader.java:711) [javac] at java.lang.ClassLoader.loadClassHelper(ClassLoader.java:735) [javac] at java.lang.ClassLoader.loadClass(ClassLoader.java:711) [javac] at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325) [javac] at java.lang.ClassLoader.loadClass(ClassLoader.java:690) [javac] at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:494) BUILD FAILED /home/user7/jruby-1.7.4/build.xml:636: The following error occurred while executing this line: /home/user7/jruby-1.7.4/build.xml:289: Compile failed; see the compiler error output for details. Total time: 1 minute 37 seconds Line 636 of build.xml <target name="jar" depends="init" description="Create the jruby.jar file. Used during dev."> -> <antcall target="jar-jruby" inheritall="true"/> </target> Line 289 of build.xml <javac destdir="${jruby.classes.dir}" fork="true" debug="true" source="${javac.version}" target="${javac.version}" -> deprecation="true" encoding="UTF-8" includeantruntime="true" memorymaximumsize="${jruby.compile.memory}"> <classpath refid="jruby.execute.classpath"/> <src path="${src.dir}"/> <exclude name="org/jruby/runtime/Constants.java"/> java -version java version "1.7.0" Java(TM) SE Runtime Environment (build pxz6470sr4fp1-20130325_01(SR4 FP1)) IBM J9 VM (build 2.6, JRE 1.7.0 Linux s390x-64 Compressed References 20130306_140761 (JIT enabled, AOT enabled) J9VM - R26_Java726_SR4_FP1_20130306_1011_B140761 JIT - r11.b03_20130131_32403ifx1 GC - R26_Java726_SR4_FP1_20130306_1011_B140761_CMPRSS J9CL - 20130306_140761) JCL - 20130315_01 based on Oracle 7u13-b08 ant -version Apache Ant version 1.7.1

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  • Selectively allow unsafe html tags in Plone

    - by dhill
    I'm searching for a way to put widgets from several services (PicasaWeb, Yahoo Pipes, Delicious bookmarks, etc.) on the community site I host on Plone (currently 3.2.1). I'm looking for a way to allow a group of users to use dangerous html tags. There are some ways I see, but I don't know how to implement those. One would be changing safe_html for the pages editors own (1). Another would be to allow those tags on some subtree (2). And yet another finding an equivalent of "static text portlet" that would display in the middle panel (3). We could then use some of the composite products (I stumbled upon Collage and CMFContentPanels), to include the unsafe content on other sites. My site has been ridden by advert bots, so I don't want to remove the filtering all together. I don't have an easy (no false positives) way of checking which users are bots, so deploying captcha now wouldn't help either. The question is: How to implement any of those solutions? (I already asked that on plone mailing list without an answer, so I thought I would give it another try here.)

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  • WebKit "Refused to set unsafe header "content-length"

    - by Paul
    I am trying to implement simple xhr abstraction, and am getting this warning when trying to set the headers for a POST. I think it might have something to do with setting the headers in a separate js file, because when i set them in the <script> tag in the .html file, it worked fine. The POST request is working fine, but I get this warning, and am curious why. I get this warning for both content-length and connection headers, but only in WebKit browsers (Chrome 5 beta and Safari 4). In Firefox, I don't get any warnings, the Content-Length header is set to the correct value, but the Connection is set to keep-alive instead of close, which makes me think that it is also ignoring my setRequestHeader calls and generating it's own. I have not tried this code in IE. Here is the markup & code: test.html: <!DOCTYPE html> <html> <head> <script src="jsfile.js"></script> <script> var request = new Xhr('POST', 'script.php', true, 'data=somedata', function(data) { console.log(data.text); }); </script> </head> <body> </body> </html> jsfile.js: function Xhr(method, url, async, data, callback) { var x; if(window.XMLHttpRequest) { x = new XMLHttpRequest(); x.open(method, url, async); x.onreadystatechange = function() { if(x.readyState === 4) { if(x.status === 200) { var data = { text: x.responseText, xml: x.responseXML }; callback.call(this, data); } } } if(method.toLowerCase() === "post") { x.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); x.setRequestHeader("Content-Length", data.length); x.setRequestHeader("Connection", "close"); } x.send(data); } else { // ... implement IE code here ... } return x; }

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  • Avoiding unsafe cast for generic situation involving runtime passing of class

    - by Bart van Heukelom
    public class AutoKeyMap<K,V> { public interface KeyGenerator<K> { public K generate(); } private KeyGenerator<K> generator; public AutoKeyMap(Class<K> keyType) { // WARNING: Unchecked cast from AutoKeyMap.IntKeyGen to AutoKeyMap.KeyGenerator<K> if (keyType == Integer.class) generator = (KeyGenerator<K>) new IntKeyGen(); else throw new RuntimeException("Cannot generate keys for " + keyType); } public void put(V value) { K key = generator.generate(); ... } private static class IntKeyGen implements KeyGenerator<Integer> { private final AtomicInteger ai = new AtomicInteger(1); @Override public Integer generate() { return ai.getAndIncrement(); } } } In the code sample above, what is the correct way to prevent the given warning, without adding a @SuppressWarnings, if any?

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  • Is this overly clever or unsafe?

    - by Liberalkid
    I was working on some code recently and decided to work on my operator overloading in c++, because I've never really implemented it before. So I overloaded the comparison operators for my matrix class using a compare function that returned 0 if LHS was less than RHS, 1 if LHS was greater than RHS and 2 if they were equal. Then I exploited the properties of logical not in c++ on integers, to get all of my compares in one line: inline bool Matrix::operator<(Matrix &RHS){ return ! (compare(*this,RHS)); } inline bool Matrix::operator>(Matrix &RHS){ return ! (compare((*this),RHS)-1); } inline bool Matrix::operator>=(Matrix &RHS){ return compare((*this),RHS); } inline bool Matrix::operator<=(Matrix &RHS){ return compare((*this),RHS)-1; } inline bool Matrix::operator!=(Matrix &RHS){ return compare((*this),RHS)-2; } inline bool Matrix::operator==(Matrix &RHS){ return !(compare((*this),RHS)-2); } Obviously I should be passing RHS as a const, I'm just probably not going to use this matrix class again and I didn't feel like writing another function that wasn't a reference to get the array index values solely for the comparator operation.

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  • Unsafe, super-fast cross-process memory buffer?

    - by John
    Cross-process memory buffers always have some overhead, and my understanding is this is quite high. But what if you're implementing a cross-process render-buffer, this isn't critically important in the same way as other data so are there techniques we can use to get 'raw' access to a chunk of memory from multiple processes, with no safety nets apart from it not crashing? Or do modern operating systems simply not work with unabstracted memory in a way to make this possible? I'm working in C++ but the question applies to Win XP/Vista/7, MacOSX 10.5+ (& Linux less importantly).

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  • C# Implementing a custom stream writer-esque class

    - by Luke
    How would I go about writing my own stream manipulator class? Basically what I'm trying to wrap my head around is storing the reference to the underlying stream in the writer. For example, when writing to a memory stream using a StreamWriter, when a Write() is made, the underlying memory stream is written to. Can I store the reference to an underlying stream without using pointers or unsafe code? Even if it was just a string I wanted to "write" to. Really this has little to do with stream writers, and I'm just wondering how I could store references in a class. The StreamWriter was the best example I could come up with for this.

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  • C# Generic Arrays and math operations on it

    - by msedi
    Hello, I'm currently involved in a project where I have very large image volumes. This volumes have to processed very fast (adding, subtracting, thresholding, and so on). Additionally most of the volume are so large that they event don't fit into the memory of the system. For that reason I have created an abstract volume class (VoxelVolume) that host the volume and image data and overloads the operators so that it's possible to perform the regular mathematical operations on volumes. Thereby two more questions opened up which I will put into stackoverflow into two additional threads. Here is my first question. My volume is implemented in a way that it only can contain float array data, but most of the containing data is from an UInt16 image source. Only operations on the volume can create float array images. When I started implementing such a volume the class looked like following: public abstract class VoxelVolume<T> { ... } but then I realized that overloading the operators or return values would get more complicated. An example would be: public abstract class VoxelVolume<T> { ... public static VoxelVolume<T> Import<T>(param string[] files) { } } also adding two overloading operators would be more complicated: ... public static VoxelVolume<T> operator+(VoxelVolume<T> A, VoxelVolume<T> B) { ... } Let's assume I can overcome the problems described above, nevertheless I have different types of arrays that contain the image data. Since I have fixed my type in the volumes to float the is no problem and I can do an unsafe operation when adding the contents of two image volume arrays. I have read a few threads here and had a look around the web, but found no real good explanation of what to do when I want to add two arrays of different types in a fast way. Unfortunately every math operation on generics is not possible, since C# is not able to calculate the size of the underlying data type. Of course there might by a way around this problem by using C++/CLR, but currently everything I have done so far, runs in 32bit and 64bit without having to do a thing. Switching to C++/CLR seemed to me (pleased correct me if I'm wrong) that I'm bound to a certain platform (32bit) and I have to compile two assemblies when I let the application run on another platform (64bit). Is this true? So asked shortly: How is it possible to add two arrays of two different types in a fast way. Is it true that the developers of C# haven't thought about this. Switching to a different language (C# - C++) seems not to be an option. I realize that simply performing this operation float []A = new float[]{1,2,3}; byte []B = new byte[]{1,2,3}; float []C = A+B; is not possible and unnecessary although it would be nice if it would work. My solution I was trying was following: public static class ArrayExt { public static unsafe TResult[] Add<T1, T2, TResult>(T1 []A, T2 []B) { // Assume the length of both arrays is equal TResult[] result = new TResult[A.Length]; GCHandle h1 = GCHandle.Alloc (A, Pinned); GCHandle h2 = GCHandle.Alloc (B, Pinned); GCHandle hR = GCHandle.Alloc (C, Pinned); void *ptrA = h1.ToPointer(); void *ptrB = h2.ToPointer(); void *ptrR = hR.ToPointer(); for (int i=0; i<A.Length; i++) { *((TResult *)ptrR) = (TResult *)((T1)*ptrA + (T2)*ptrB)); } h1.Free(); h2.Free(); hR.Free(); return result; } } Please excuse if the code above is not quite correct, I wrote it without using an C# editor. Is such a solution a shown above thinkable? Please feel free to ask if I made a mistake or described some things incompletely. Thanks for your help Martin

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