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• Code Metrics: Number of IL Instructions

  - by DigiMortal

  In my previous posting about code metrics I introduced how to measure LoC (Lines of Code) in .NET applications. Now let’s take a step further and let’s take a look how to measure compiled code. This way we can somehow have a picture about what compiler produces. In this posting I will introduce you code metric called number of IL instructions. NB! Number of IL instructions is not something you can use to measure productivity of your team. If you want to get better idea about the context of this metric and LoC then please read my first posting about LoC. What are IL instructions? When code written in some .NET Framework language is compiled then compiler produces assemblies that contain byte code. These assemblies are executed later by Common Language Runtime (CLR) that is code execution engine of .NET Framework. The byte code is called Intermediate Language (IL) – this is more common language than C# and VB.NET by example. You can use ILDasm tool to convert assemblies to IL assembler so you can read them. As IL instructions are building blocks of all .NET Framework binary code these instructions are smaller and highly general – we don’t want very rich low level language because it executes slower than more general language. For every method or property call in some .NET Framework language corresponds set of IL instructions. There is no 1:1 relationship between line in high level language and line in IL assembler. There are more IL instructions than lines in C# code by example. How much instructions there are? I have no common answer because it really depends on your code. Here you can see some metrics from my current community project that is developed on SharePoint Server 2007. As average I have about 7 IL instructions per line of code. This is not metric you should use, it is just illustrative example so you can see the differences between numbers of lines and IL instructions. Why should I measure the number of IL instructions? Just take a look at chart above. Compiler does something that you cannot see – it compiles your code to IL. This is not intuitive process because you usually cannot say what is exactly the end result. You know it at greater plain but you don’t know it exactly. Therefore we can expect some surprises and that’s why we should measure the number of IL instructions. By example, you may find better solution for some method in your source code. It looks nice, it works nice and everything seems to be okay. But on server under load your fix may be way slower than previous code. Although you minimized the number of lines of code it ended up with increasing the number of IL instructions. How to measure the number of IL instructions? My choice is NDepend because Visual Studio is not able to measure this metric. Steps to make are easy. Open your NDepend project or create new and add all your application assemblies to project (you can also add Visual Studio solution to project). Run project analysis and wait until it is done. You can see over-all stats form global summary window. This is the same window I used to read the LoC and the number of IL instructions metrics for my chart. Meanwhile I made some changes to my code (enabled advanced caching for events and event registrations module) and then I ran code analysis again to get results for this section of this posting. NDepend is also able to tell you exactly what parts of code have problematically much IL instructions. The code quality section of CQL Query Explorer shows you how much problems there are with members in analyzed code. If you click on the line Methods too big (NbILInstructions) you can see all the problematic members of classes in CQL Explorer shown in image on right. In my case if have 10 methods that are too big and two of them have horrible number of IL instructions – just take a look at first two methods in this TOP10. Also note the query box. NDepend has easy and SQL-like query language to query code analysis results. You can modify these queries if you like and also you can define your own ones if default set is not enough for you. What is good result? As you can see from query window then the number of IL instructions per member should have maximally 200 IL instructions. Of course, like always, the less instructions you have, the better performing code you have. I don’t mean here little differences but big ones. By example, take a look at my first method in warnings list. The number of IL instructions it has is huge. And believe me – this method looks awful. Conclusion The number of IL instructions is useful metric when optimizing your code. For analyzing code at general level to find out too long methods you can use the number of LoC metric because it is more intuitive for you and you can therefore handle the situation more easily. Also you can use NDepend as code metrics tool because it has a lot of metrics to offer.

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• Subterranean IL: The ThreadLocal type

  - by Simon Cooper

  I came across ThreadLocal<T> while I was researching ConcurrentBag. To look at it, it doesn't really make much sense. What's all those extra Cn classes doing in there? Why is there a GenericHolder<T,U,V,W> class? What's going on? However, digging deeper, it's a rather ingenious solution to a tricky problem. Thread statics Declaring that a variable is thread static, that is, values assigned and read from the field is specific to the thread doing the reading, is quite easy in .NET: [ThreadStatic] private static string s_ThreadStaticField; ThreadStaticAttribute is not a pseudo-custom attribute; it is compiled as a normal attribute, but the CLR has in-built magic, activated by that attribute, to redirect accesses to the field based on the executing thread's identity. TheadStaticAttribute provides a simple solution when you want to use a single field as thread-static. What if you want to create an arbitary number of thread static variables at runtime? Thread-static fields can only be declared, and are fixed, at compile time. Prior to .NET 4, you only had one solution - thread local data slots. This is a lesser-known function of Thread that has existed since .NET 1.1: LocalDataStoreSlot threadSlot = Thread.AllocateNamedDataSlot("slot1"); string value = "foo"; Thread.SetData(threadSlot, value); string gettedValue = (string)Thread.GetData(threadSlot); Each instance of LocalStoreDataSlot mediates access to a single slot, and each slot acts like a separate thread-static field. As you can see, using thread data slots is quite cumbersome. You need to keep track of LocalDataStoreSlot objects, it's not obvious how instances of LocalDataStoreSlot correspond to individual thread-static variables, and it's not type safe. It's also relatively slow and complicated; the internal implementation consists of a whole series of classes hanging off a single thread-static field in Thread itself, using various arrays, lists, and locks for synchronization. ThreadLocal<T> is far simpler and easier to use. ThreadLocal ThreadLocal provides an abstraction around thread-static fields that allows it to be used just like any other class; it can be used as a replacement for a thread-static field, it can be used in a List<ThreadLocal<T>>, you can create as many as you need at runtime. So what does it do? It can't just have an instance-specific thread-static field, because thread-static fields have to be declared as static, and so shared between all instances of the declaring type. There's something else going on here. The values stored in instances of ThreadLocal<T> are stored in instantiations of the GenericHolder<T,U,V,W> class, which contains a single ThreadStatic field (s_value) to store the actual value. This class is then instantiated with various combinations of the Cn types for generic arguments. In .NET, each separate instantiation of a generic type has its own static state. For example, GenericHolder<int,C0,C1,C2> has a completely separate s_value field to GenericHolder<int,C1,C14,C1>. This feature is (ab)used by ThreadLocal to emulate instance thread-static fields. Every time an instance of ThreadLocal is constructed, it is assigned a unique number from the static s_currentTypeId field using Interlocked.Increment, in the FindNextTypeIndex method. The hexadecimal representation of that number then defines the specific Cn types that instantiates the GenericHolder class. That instantiation is therefore 'owned' by that instance of ThreadLocal. This gives each instance of ThreadLocal its own ThreadStatic field through a specific unique instantiation of the GenericHolder class. Although GenericHolder has four type variables, the first one is always instantiated to the type stored in the ThreadLocal<T>. This gives three free type variables, each of which can be instantiated to one of 16 types (C0 to C15). This puts an upper limit of 4096 (163) on the number of ThreadLocal<T> instances that can be created for each value of T. That is, there can be a maximum of 4096 instances of ThreadLocal<string>, and separately a maximum of 4096 instances of ThreadLocal<object>, etc. However, there is an upper limit of 16384 enforced on the total number of ThreadLocal instances in the AppDomain. This is to stop too much memory being used by thousands of instantiations of GenericHolder<T,U,V,W>, as once a type is loaded into an AppDomain it cannot be unloaded, and will continue to sit there taking up memory until the AppDomain is unloaded. The total number of ThreadLocal instances created is tracked by the ThreadLocalGlobalCounter class. So what happens when either limit is reached? Firstly, to try and stop this limit being reached, it recycles GenericHolder type indexes of ThreadLocal instances that get disposed using the s_availableIndices concurrent stack. This allows GenericHolder instantiations of disposed ThreadLocal instances to be re-used. But if there aren't any available instantiations, then ThreadLocal falls back on a standard thread local slot using TLSHolder. This makes it very important to dispose of your ThreadLocal instances if you'll be using lots of them, so the type instantiations can be recycled. The previous way of creating arbitary thread-static variables, thread data slots, was slow, clunky, and hard to use. In comparison, ThreadLocal can be used just like any other type, and each instance appears from the outside to be a non-static thread-static variable. It does this by using the CLR type system to assign each instance of ThreadLocal its own instantiated type containing a thread-static field, and so delegating a lot of the bookkeeping that thread data slots had to do to the CLR type system itself! That's a very clever use of the CLR type system.

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• Subterranean IL: Pseudo custom attributes

  - by Simon Cooper

  Custom attributes were designed to make the .NET framework extensible; if a .NET language needs to store additional metadata on an item that isn't expressible in IL, then an attribute could be applied to the IL item to represent this metadata. For instance, the C# compiler uses DecimalConstantAttribute and DateTimeConstantAttribute to represent compile-time decimal or datetime constants, which aren't allowed in pure IL, and FixedBufferAttribute to represent fixed struct fields. How attributes are compiled Within a .NET assembly are a series of tables containing all the metadata for items within the assembly; for instance, the TypeDef table stores metadata on all the types in the assembly, and MethodDef does the same for all the methods and constructors. Custom attribute information is stored in the CustomAttribute table, which has references to the IL item the attribute is applied to, the constructor used (which implies the type of attribute applied), and a binary blob representing the arguments and name/value pairs used in the attribute application. For example, the following C# class: [Obsolete("Please use MyClass2", true)] public class MyClass { // ... } corresponds to the following IL class definition: .class public MyClass { .custom instance void [mscorlib]System.ObsoleteAttribute::.ctor(string, bool) = { string('Please use MyClass2' bool(true) } // ... } and results in the following entry in the CustomAttribute table: TypeDef(MyClass) MemberRef(ObsoleteAttribute::.ctor(string, bool)) blob -> {string('Please use MyClass2' bool(true)} However, there are some attributes that don't compile in this way. Pseudo custom attributes Just like there are some concepts in a language that can't be represented in IL, there are some concepts in IL that can't be represented in a language. This is where pseudo custom attributes come into play. The most obvious of these is SerializableAttribute. Although it looks like an attribute, it doesn't compile to a CustomAttribute table entry; it instead sets the serializable bit directly within the TypeDef entry for the type. This flag is fully expressible within IL; this C#: [Serializable] public class MySerializableClass {} compiles to this IL: .class public serializable MySerializableClass {} For those interested, a full list of pseudo custom attributes is available here. For the rest of this post, I'll be concentrating on the ones that deal with P/Invoke. P/Invoke attributes P/Invoke is built right into the CLR at quite a deep level; there are 2 metadata tables within an assembly dedicated solely to p/invoke interop, and many more that affect it. Furthermore, all the attributes used to specify p/invoke methods in C# or VB have their own keywords and syntax within IL. For example, the following C# method declaration: [DllImport("mscorsn.dll", SetLastError = true)] [return: MarshalAs(UnmanagedType.U1)] private static extern bool StrongNameSignatureVerificationEx( [MarshalAs(UnmanagedType.LPWStr)] string wszFilePath, [MarshalAs(UnmanagedType.U1)] bool fForceVerification, [MarshalAs(UnmanagedType.U1)] ref bool pfWasVerified); compiles to the following IL definition: .method private static pinvokeimpl("mscorsn.dll" lasterr winapi) bool marshal(unsigned int8) StrongNameSignatureVerificationEx( string marshal(lpwstr) wszFilePath, bool marshal(unsigned int8) fForceVerification, bool& marshal(unsigned int8) pfWasVerified) cil managed preservesig {} As you can see, all the p/invoke and marshal properties are specified directly in IL, rather than using attributes. And, rather than creating entries in CustomAttribute, a whole bunch of metadata is emitted to represent this information. This single method declaration results in the following metadata being output to the assembly: A MethodDef entry containing basic information on the method Four ParamDef entries for the 3 method parameters and return type An entry in ModuleRef to mscorsn.dll An entry in ImplMap linking ModuleRef and MethodDef, along with the name of the function to import and the pinvoke options (lasterr winapi) Four FieldMarshal entries containing the marshal information for each parameter. Phew! Applying attributes Most of the time, when you apply an attribute to an element, an entry in the CustomAttribute table will be created to represent that application. However, some attributes represent concepts in IL that aren't expressible in the language you're coding in, and can instead result in a single bit change (SerializableAttribute and NonSerializedAttribute), or many extra metadata table entries (the p/invoke attributes) being emitted to the output assembly.

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• Problems with generation of dynamic code

  - by user308344

  This code gif an exception: Invocation exception, please help, I don't know what happen, I think is some thing with the Add because he work when I push onto the stack intergers, and when i push lvalue It's didn't work, thanks static void Main(string[] args) { AppDomain dominioAplicacion = System.Threading.Thread.GetDomain(); AssemblyName nombre_Del_Ensamblado = new AssemblyName("ASS"); AssemblyBuilder ensambladoBld = dominioAplicacion.DefineDynamicAssembly(nombre_Del_Ensamblado, AssemblyBuilderAccess.RunAndSave); ModuleBuilder moduloBld = ensambladoBld.DefineDynamicModule("<MOD"); TypeBuilder claseContenedoraBld = moduloBld.DefineType("claseContenedora"); MethodBuilder mainBld = claseContenedoraBld.DefineMethod("main", MethodAttributes.Public | MethodAttributes.Static, typeof(void), Type.EmptyTypes); ILGenerator il = mainBld.GetILGenerator(); FieldBuilder campoBld = claseContenedoraBld.DefineField("x", typeof(int), FieldAttributes.Public | FieldAttributes.Static); il.Emit(OpCodes.Ldc_I4, 2); il.Emit(OpCodes.Stsfld, campoBld); FieldBuilder campoBld1 = claseContenedoraBld.DefineField("x1", typeof(int), FieldAttributes.Public | FieldAttributes.Static); il.Emit(OpCodes.Ldc_I4, 2); il.Emit(OpCodes.Stsfld, campoBld1); il.Emit(OpCodes.Ldftn, campoBld); //il.Emit(OpCodes.Unbox, typeof(int)); //il.Emit(OpCodes.Stloc_0); il.Emit(OpCodes.Ldloc_0); il.Emit(OpCodes.Ldftn, campoBld1); //il.Emit(OpCodes.Unbox, typeof(int)); il.Emit(OpCodes.Stloc_1); il.Emit(OpCodes.Ldloc_1); //il.Emit(OpCodes.Box, typeof(int)); //il.Emit(OpCodes.Ldftn, campoBld1); //il.Emit(OpCodes.Unbox, typeof(int)); il.Emit(OpCodes.Add); il.Emit(OpCodes.Pop); //il.Emit(OpCodes.Stsfld, campoBld1); il.Emit(OpCodes.Ret); Type t = claseContenedoraBld.CreateType(); object ptInstance = Activator.CreateInstance(t, new Type[] { }); t.InvokeMember("main", BindingFlags.InvokeMethod | BindingFlags.Static | BindingFlags.Public, null, ptInstance, new object[0]); var x = t.GetField("x"); }

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• Il CRM è al passo con i tempi?

  - by antonella.buonagurio(at)oracle.com

  Il Social Customer Relationship Management è nato grazie alla rivoluzione portata dal Web 2.0, un cambiamento epocale nelle modalità di comunicazione che ha aggiunto una incredibile ricchezza alle conversazioni tra aziende e consumatori. Le aziende dispongono adesso di strumenti per comprendere il proprio mercato senza precedenti, i consumatori, a loro volta, hanno il potere di utilizzare nuovi canali per esprimere le proprie esigenze e per comunicare e condividere commenti ed esperienze. Ma il Web 2.0 non è il solo fattore che impatta sulle scelte strategiche in ambito CRM  che ogni azienda deve considerare per sostenere  questo nuovo rapporto con i propri consumatori.    Vuoi scoprire quali sono le forze (o fattori) che le aziende devono considerare affinchè i processi di gestione della relazione con i clienti stiano al passo con le mutate condizioni sociali ed economiche?   Per saperne di più:   Il whitepaper realizzato da Oracle, Paul Gillin ed  IT Business Edge  ne delinea alcuni: 1.      Il Business. Come è cambiato in funzione dell'esperienza multicanale ora possible, della centralità del cliente e dei social networking che dominano le relazioni on line? 2.      La tecnologiaLe aziende oggi per guadagnare vantaggio competitivo devono dotarsi delle più innovative tecnologie per dare maggior valore al proprio business e per ridurre al minimo i costi di infrastruttura. Quali sono e quali sono gli effettivi vantaggi?   e altri ancora ...... leggendo il white paper "Is your CRM solution keeping up with the times?"

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• Visual Studio support for coding directly in *IL?

  - by jdk

  For the longest time I've been curious to code in Intermediate Language just as an academic endeavour and to gain a better understanding of what's "happening under the hood". Does anybody provide Visual Studio support for *IL in the form of: project templates, IntelliSense integration, and those kind of RAD features? Edits: I don't mean restricted to out of the box support. For example, I can download Visual Studio extensions to support Python, COBOL, etc. Want the same for *IL. There is a stand-alone Intermediate Assembler tool.

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• Le métier d'ingénieur logiciel passionne-t-il encore ? Un développeur raconte comment il a perdu la flamme

  Le métier d'ingénieur logiciel passionne-t-il encore ? Un développeur raconte comment il a perdu la flamme Sur un billet blog, un développeur se remémore les circonstances dans lesquelles est née sa passion pour la programmation. Avec quelquefois une pointe d'humour, il se rappelle comment il griffonnait des lignes de code sur des bouts de papier pendant les cours d'histoire. « Elle (le professeur) pensait probablement que je prenais des notes. Ou alors elle savait que je n'y prêtais aucune...

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• Android est-il un OS de Geeks ? Il serait fait par des ingénieurs qui travaillent dans leur coin et n'écoutent jamais personne

  Android est-il un OS de Geeks ? Il serait fait par des ingénieurs qui travaillent dans leur coin et qui n'écoutent jamais personne Faîtes un test simple. Prenez une tablette ou un smartphone sous Android. Mettez-le dans les mains du premier venu (vos enfant, votre conjoint, vos grand-parents, peu importe). Et observez. Sauf à ce qu'il travaille dans l'IT ou ait été familiarisé avec l'OS, il y a fort à parier que votre « cobaye » soit vite déboussolé. Recommencez avec un iPad ou un iPhone, et l'avis sera neuf fois sur dix radicalement différent. Je calme tout de suite les fan-boys. Il ne s'agit pas de dire qu'Android est moins bon qu'iOS. ...

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• 'if' block in IL

  - by Luke Schafer

  I think I might be missing something important, but I can't seem to figure out how to construct a conditional statement in IL with dynamic method. I've only dabbled lightly in it before, but I need to extend some code now. Is there some documentation somewhere that I haven't found (apart from the CLI documentation), or does someone have some sample code? That would be fantastic. Cheers,

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• Subterranean IL: Compiling C# exception handlers

  - by Simon Cooper

  An exception handler in C# combines the IL catch and finally exception handling clauses into a single try statement: try { Console.WriteLine("Try block") // ... } catch (IOException) { Console.WriteLine("IOException catch") // ... } catch (Exception e) { Console.WriteLine("Exception catch") // ... } finally { Console.WriteLine("Finally block") // ... } How does this get compiled into IL? Initial implementation If you remember from my earlier post, finally clauses must be specified with their own .try clause. So, for the initial implementation, we take the try/catch/finally, and simply split it up into two .try clauses (I have to use label syntax for this): StartTry: ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndTry: StartIOECatch: ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndIOECatch: StartECatch: ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndECatch: StartFinally: ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally EndFinally: End: // ... .try StartTry to EndTry catch [mscorlib]System.IO.IOException handler StartIOECatch to EndIOECatch catch [mscorlib]System.Exception handler StartECatch to EndECatch .try StartTry to EndTry finally handler StartFinally to EndFinally However, the resulting program isn't verifiable, and doesn't run: [IL]: Error: Shared try has finally or fault handler. Nested try blocks What's with the verification error? Well, it's a condition of IL verification that all exception handling regions (try, catch, filter, finally, fault) of a single .try clause have to be completely contained within any outer exception region, and they can't overlap with any other exception handling clause. In other words, IL exception handling clauses must to be representable in the scoped syntax, and in this example, we're overlapping catch and finally clauses. Not only is this example not verifiable, it isn't semantically correct. The finally handler is specified round the .try. What happens if you were able to run this code, and an exception was thrown? Program execution enters top of try block, and exception is thrown within it CLR searches for an exception handler, finds catch Because control flow is leaving .try, finally block is run The catch block is run leave.s End inside the catch handler branches to End label. We're actually running the finally before the catch! What we do about it What we actually need to do is put the catch clauses inside the finally clause, as this will ensure the finally gets executed at the correct time (this time using scoped syntax): .try { .try { ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.IO.IOException { ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.Exception { ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } } finally { ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally } End: ret Returning from methods There is a further semantic mismatch that the C# compiler has to deal with; in C#, you are allowed to return from within an exception handling block: public int HandleMethod() { try { // ... return 0; } catch (Exception) { // ... return -1; } } However, you can't ret inside an exception handling block in IL. So the C# compiler does a leave.s to a ret outside the exception handling area, loading/storing any return value to a local variable along the way (as leave.s clears the stack): .method public instance int32 HandleMethod() { .locals init ( int32 retVal ) .try { // ... ldc.i4.0 stloc.0 leave.s End } catch [mscorlib]System.Exception { // ... ldc.i4.m1 stloc.0 leave.s End } End: ldloc.0 ret } Conclusion As you can see, the C# compiler has quite a few hoops to jump through to translate C# code into semantically-correct IL, and hides the numerous conditions on IL exception handling blocks from the C# programmer. Next up: catch-all blocks, and how the runtime deals with non-Exception exceptions.

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• IL short-form instructions aren't short?

  - by Alix

  Hi. I was looking at the IL code of a valid method with Reflector and I've run into this: L_00a5: leave.s L_0103 Instructions with the suffix .s are supposed to take an int8 operand, and sure enough this is should be the case with Leave_S as well. However, 0x0103 is 259, which exceeds the capacity of an int8. The method somehow works, but when I read the instructions with method Mono.Reflection.Disassembler.GetInstructions it retrieves L_00a5: leave.s L_0003 that is, 3 instead of 259, because it's supposed to be an int8. So, my question: how is the original instruction (leave.s L_0103) possible? I have looked at the ECMA documentation for that (Partition III: CIL Instruction Set) and I can't find anything that explains it. Any ideas? Thanks.

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• Il suffit de critiquer l'AppStore pour voir ses applications censurées, suivant l'expérience d'un dé

  Mise à jour du 22.03.2010 par Katleen Il suffit de critiquer l'AppStore pour voir ses applications censurées, suivant l'expérience d'un développeur américain Il y a quelques jours, le développeur de jeux vidéo Tommy Refenes a publiquement décrit la plateforme de vente d'applications d'Apple comme ?atroce? et ?horrible?. L'homme vit cependant du commerce d'une de ses créations, Zits&Giggles (jeu qui consiste à faire éclater des boutons d'acné), qu'il distribue sur l'Appstore à des prix variant suivant ses humeurs (de 15 à 299 dollars). Allant plus loin, il déclare avoir une "pu**** d'aversion pour l'App Store" qui serait "affreux". Apple n'...

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• Subterranean IL: Custom modifiers

  - by Simon Cooper

  In IL, volatile is an instruction prefix used to set a memory barrier at that instruction. However, in C#, volatile is applied to a field to indicate that all accesses on that field should be prefixed with volatile. As I mentioned in my previous post, this means that the field definition needs to store this information somehow, as such a field could be accessed from another assembly. However, IL does not have a concept of a 'volatile field'. How is this information stored? Attributes The standard way of solving this is to apply a VolatileAttribute or similar to the field; this extra metadata notifies the C# compiler that all loads and stores to that field should use the volatile prefix. However, there is a problem with this approach, namely, the .NET C++ compiler. C++ allows methods to be overloaded using properties, like volatile or const, on the parameters; this is perfectly legal C++: public ref class VolatileMethods { void Method(int *i) {} void Method(volatile int *i) {} } If volatile was specified using a custom attribute, then the VolatileMethods class wouldn't be compilable to IL, as there is nothing to differentiate the two methods from each other. This is where custom modifiers come in. Custom modifiers Custom modifiers are similar to custom attributes, but instead of being applied to an IL element separately to its declaration, they are embedded within the field or parameter's type signature itself. The VolatileMethods class would be compiled to the following IL: .class public VolatileMethods { .method public instance void Method(int32* i) {} .method public instance void Method( int32 modreq( [mscorlib]System.Runtime.CompilerServices.IsVolatile)* i) {} } The modreq([mscorlib]System.Runtime.CompilerServices.IsVolatile) is the custom modifier. This adds a TypeDef or TypeRef token to the signature of the field or parameter, and even though they are mostly ignored by the CLR when it's executing the program, this allows methods and fields to be overloaded in ways that wouldn't be allowed using attributes. Because the modifiers are part of the signature, they need to be fully specified when calling such a method in IL: call instance void Method( int32 modreq([mscorlib]System.Runtime.CompilerServices.IsVolatile)*) There are two ways of applying modifiers; modreq specifies required modifiers (like IsVolatile), and modopt specifies optional modifiers that can be ignored by compilers (like IsLong or IsConst). The type specified as the modifier argument are simple placeholders; if you have a look at the definitions of IsVolatile and IsLong they are completely empty. They exist solely to be referenced by a modifier. Custom modifiers are used extensively by the C++ compiler to specify concepts that aren't expressible in IL, but still need to be taken into account when calling method overloads. C++ and C# That's all very well and good, but how does this affect C#? Well, the C++ compiler uses modreq(IsVolatile) to specify volatility on both method parameters and fields, as it would be slightly odd to have the same concept represented using a modifier or attribute depending on what it was applied to. Once you've compiled your C++ project, it can then be referenced and used from C#, so the C# compiler has to recognise the modreq(IsVolatile) custom modifier applied to fields, and vice versa. So, even though you can't overload fields or parameters with volatile using C#, volatile needs to be expressed using a custom modifier rather than an attribute to guarentee correct interoperability and behaviour with any C++ dlls that happen to come along. Next up: a closer look at attributes, and how certain attributes compile in unexpected ways.

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• Subterranean IL: Volatile

  - by Simon Cooper

  This time, we'll be having a look at the volatile. prefix instruction, and one of the differences between volatile in IL and C#. The volatile. prefix volatile is a tricky one, as there's varying levels of documentation on it. From what I can see, it has two effects: It prevents caching of the load or store value; rather than reading or writing to a cached version of the memory location (say, the processor register or cache), it forces the value to be loaded or stored at the 'actual' memory location, so it is then immediately visible to other threads. It forces a memory barrier at the prefixed instruction. This ensures instructions don't get re-ordered around the volatile instruction. This is slightly more complicated than it first seems, and only seems to matter on certain architectures. For more details, Joe Duffy has a blog post going into the details. For this post, I'll be concentrating on the first aspect of volatile. Caching field accesses To demonstrate this, I created a simple multithreaded IL program. It boils down to the following code: .class public Holder { .field public static class Holder holder .field public bool stop .method public static specialname void .cctor() { newobj instance void Holder::.ctor() stsfld class Holder Holder::holder ret }}.method private static void Main() { .entrypoint // Thread t = new Thread(new ThreadStart(DoWork)) // t.Start() // Thread.Sleep(2000) // Console.WriteLine("Stopping thread...") ldsfld class Holder Holder::holder ldc.i4.1 stfld bool Holder::stop call instance void [mscorlib]System.Threading.Thread::Join() ret}.method private static void DoWork() { ldsfld class Holder Holder::holder // while (!Holder.holder.stop) {} DoWork: dup ldfld bool Holder::stop brfalse DoWork pop ret} If you compile and run this code, you'll find that the call to Thread.Join() never returns - the DoWork spinlock is reading a cached version of Holder.stop, which is never being updated with the new value set by the Main method. Adding volatile to the ldfld fixes this: dupvolatile.ldfld bool Holder::stopbrfalse DoWork The volatile ldfld forces the field access to read direct from heap memory, which is then updated by the main thread, rather than using a cached copy. volatile in C# This highlights one of the differences between IL and C#. In IL, volatile only applies to the prefixed instruction, whereas in C#, volatile is specified on a field to indicate that all accesses to that field should be volatile (interestingly, there's no mention of the 'no caching' aspect of volatile in the C# spec; it only focuses on the memory barrier aspect). Furthermore, this information needs to be stored within the assembly somehow, as such a field might be accessed directly from outside the assembly, but there's no concept of a 'volatile field' in IL! How this information is stored with the field will be the subject of my next post.

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• "Il faut repenser les OS pour les processeurs multi-coeurs", d'après Microsoft

  "Il faut repenser les OS pour les processeurs multi-coeurs", d'après Microsoft Dave Probert est expert du noyau chez Microsoft. Selon lui, l'approche actuelle du multi-coeur n'est pas encore à même d'en exploiter toute la puissance, et est trop "compliquée". Aussi, propose-t-il une autre organisation. Car, d'après lui, "la solution" ne se situerait pas dans l'amélioration de techniques "comme le parallel programming, mais plutôt dans le refonte des abstractions de base qui constituent le modèle du système d'exploitation". Il explique qu'on ne tire pas assez parti des performances offertes par les processeurs multicoeurs et qu'aujourd'hui, on ne devrait plus avoir à patienter de...

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• L'empire Google est-il « Evil » ? le géant se développe-t-il trop ?

  L'empire Google est-il "Evil" ? le géant se développe-t-il trop ? Une vidéo (pas très objective) publiée récemment sur le Net tend à raviver la psychose qui tourne autour de Google et du contrôle quasi-mondial que la firme pourrait opèrer sur les êtres humains. En reprenant certains chiffres liés aux activités de l'entreprise, la dimension tentaculaire de l'énorme empire Google est montrée avec force. Même si le groupe de Moutain View n'a pas encore dépassé les bornes, pourrait-il le faire ?

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• Le codec VP8 de Google déjà critiqué, il serait instable et lent

  Mise à jour du 21.05.2010 par Katleen Le codec VP8 de Google déjà critiqué, il serait instable et lent Nous vous parlions avant hier du VP8, le nouveau codec vidéo de Google. Mais, selon certains experts en la matière, il ne serait pas aussi incontournable que le dit son créateur... Jason Garett-Glaser, spécialiste en vidéo digitale, en livre une analyse bien peu flatteuse : "Ses spécifications consistent majoritairement en du code C copié-collé du code source de son noyau." Se faisant plus critique, il continue : "La spécification VP8 est imprécise et non claire. Trop courte, elle laisse de larges portions du format trop vaguement expliquées. Certaines parties refusent même explicitem...

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• Android pourra-t-il surpasser Windows ? En 2016, il y aurait plus de dispositifs sous Android que sous Windows selon Gartner

  Android pourra-t-il surpasser Windows ? En 2016, il y aurait plus de dispositifs sous Android que sous Windows. Le cabinet d'études Gartner prédit des changements massifs dans le secteur de la technologie et plus précisément des systèmes d'exploitation. Selon son rapport publié mercredi dernier, Android, le Système d'exploitation de Google équipera d'ici quatre ans plus d'appareils que Windows. [IMG]http://rdonfack.developpez.com/images/AndroidStand.png[/IMG] Selon les statistiques de Gartner, à la fin de 2016, il y aurait environ 2,3 milliards d'ordinateurs, tablettes et smartphones dotés d'Android, contre 2,28 milliards d'appareils Windows. Les analyste...

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• Le premier homme bionique voit le jour : il marche, parle et respire

  Rich Walker et Matthew Godden de la Shadow Robot Co., ont dévoilé le premier homme bionique : il marche, parle et respire. C'est un Frankenstein des temps moderne qui coûte la bagatelle de 1 million de dollars ! Il est en effet composé des prothèses humaines les plus avancées :Des membres robotisés (dont celui-ci) Une tête, avec la réplique du visage d'un de ses concepteurs. Des yeux (fabriqués par Second Sight à Sylmar en Californie). Un coeur artificiel (créé par SynCardia Systems à Tucson en...

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• Subterranean IL: Constructor constraints

  - by Simon Cooper

  The constructor generic constraint is a slightly wierd one. The ECMA specification simply states that it: constrains [the type] to being a concrete reference type (i.e., not abstract) that has a public constructor taking no arguments (the default constructor), or to being a value type. There seems to be no reference within the spec to how you actually create an instance of a generic type with such a constraint. In non-generic methods, the normal way of creating an instance of a class is quite different to initializing an instance of a value type. For a reference type, you use newobj: newobj instance void IncrementableClass::.ctor() and for value types, you need to use initobj: .locals init ( valuetype IncrementableStruct s1 ) ldloca 0 initobj IncrementableStruct But, for a generic method, we need a consistent method that would work equally well for reference or value types. Activator.CreateInstance<T> To solve this problem the CLR designers could have chosen to create something similar to the constrained. prefix; if T is a value type, call initobj, and if it is a reference type, call newobj instance void !!0::.ctor(). However, this solution is much more heavyweight than constrained callvirt. The newobj call is encoded in the assembly using a simple reference to a row in a metadata table. This encoding is no longer valid for a call to !!0::.ctor(), as different constructor methods occupy different rows in the metadata tables. Furthermore, constructors aren't virtual, so we would have to somehow do a dynamic lookup to the correct method at runtime without using a MethodTable, something which is completely new to the CLR. Trying to do this in IL results in the following verification error: newobj instance void !!0::.ctor() [IL]: Error: Unable to resolve token. This is where Activator.CreateInstance<T> comes in. We can call this method to return us a new T, and make the whole issue Somebody Else's Problem. CreateInstance does all the dynamic method lookup for us, and returns us a new instance of the correct reference or value type (strangely enough, Activator.CreateInstance<T> does not itself have a .ctor constraint on its generic parameter): .method private static !!0 CreateInstance<.ctor T>() { call !!0 [mscorlib]System.Activator::CreateInstance<!!0>() ret } Going further: compiler enhancements Although this method works perfectly well for solving the problem, the C# compiler goes one step further. If you decompile the C# version of the CreateInstance method above: private static T CreateInstance() where T : new() { return new T(); } what you actually get is this (edited slightly for space & clarity): .method private static !!T CreateInstance<.ctor T>() { .locals init ( [0] !!T CS$0$0000, [1] !!T CS$0$0001 ) DetectValueType: ldloca.s 0 initobj !!T ldloc.0 box !!T brfalse.s CreateInstance CreateValueType: ldloca.s 1 initobj !!T ldloc.1 ret CreateInstance: call !!0 [mscorlib]System.Activator::CreateInstance<T>() ret } What on earth is going on here? Looking closer, it's actually quite a clever performance optimization around value types. So, lets dissect this code to see what it does. The CreateValueType and CreateInstance sections should be fairly self-explanatory; using initobj for value types, and Activator.CreateInstance for reference types. How does the DetectValueType section work? First, the stack transition for value types: ldloca.s 0 // &[!!T(uninitialized)] initobj !!T // ldloc.0 // !!T box !!T // O[!!T] brfalse.s // branch not taken When the brfalse.s is hit, the top stack entry is a non-null reference to a boxed !!T, so execution continues to to the CreateValueType section. What about when !!T is a reference type? Remember, the 'default' value of an object reference (type O) is zero, or null. ldloca.s 0 // &[!!T(null)] initobj !!T // ldloc.0 // null box !!T // null brfalse.s // branch taken Because box on a reference type is a no-op, the top of the stack at the brfalse.s is null, and so the branch to CreateInstance is taken. For reference types, Activator.CreateInstance is called which does the full dynamic lookup using reflection. For value types, a simple initobj is called, which is far faster, and also eliminates the unboxing that Activator.CreateInstance has to perform for value types. However, this is strictly a performance optimization; Activator.CreateInstance<T> works for value types as well as reference types. Next... That concludes the initial premise of the Subterranean IL series; to cover the details of generic methods and generic code in IL. I've got a few other ideas about where to go next; however, if anyone has any itching questions, suggestions, or things you've always wondered about IL, do let me know.

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• Le SEO est-il mort ? Pas vraiment, répond l'agence de content-marketing Lobi : il est « mort-vivant »

  Le SEO est-il mort ? Pas vraiment, répond l'agence de content-marketing Lobi : il est « mort-vivant » Fondée en 2005, Lobi est une des premières agences françaises de content marketing on-line, . Pour elle, « le SEO (NDR Search Engine Optimization) est un mort-vivant ». « Ce n'est pas un scoop, écrit Thierry GILLMAN sur le blog de l'agence. Chaque nouvelle avancée dans l'algorithme de Google va dans le même sens : privilégier les contenus utiles et pénaliser les contenus bidons», c'est à dire ceux sensément reconnaissables parce que « sur-optimisés ». Conséquence du travail continu de Google sur son algorithme ? et du fait que 99% ...

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• IL and case-sensitivity

  - by Ali .NET

  Quoted from A Brief Introduction To IL code, CLR, CTS, CLS and JIT In .NET CLS stands for Common Language Specifications. It is a subset of CTS. CLS is a set of rules or guidelines which if followed ensures that code written in one .NET language can be used by another .NET language. For example one rule is that we cannot have member functions with same name with case difference only i.e we should not have add() and Add(). This may work in C# because it is case-sensitive but if try to use that C# code in VB.NET, it is not possible because VB.NET is not case-sensitive. Based on above text I want to confirm two points here: Does the case-sensitivity of IL is a condition for member functions only, and not for member properties? Is it true that C# wouldn't be inter-operable with VB.NET if it didn't take care of the case sensitivity?

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• Le CEO d'AMD renvoyé sans ménagement, il aurait sous-estimé le marché des appareils mobiles

  Le CEO d'AMD renvoyé sans ménagement, il aurait sous-estimé le marché des appareils mobiles Dirk Meyer, patron d'AMD, a été éjecté de la direction de l'entreprise de façon brutale. Les raisons de ce départ subite étaient floues, mais les langues commencent à se délier. Ainsi, des cadres de la compagnie déclarent que le gros problème venait de l'apathie du CEO en termes de stratégie mobile. Il aurait ainsi raté le coche du boom de ce marché, en refusant notamment de construire des puces pour d'autres appareils nomades que les netbooks. Les parts d'AMD se seraient récemment effondrées de 9%, ce qui aurait précipité ce renvoi. L'homme affirmait que la priorité du groupe, c'était d'être en compétition avec le gros poisso...

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• "Le problème que le XML résout n'est pas difficile, et il ne le résout pas bien": que manque-t-il le plus au langage ?

  L'essence du XML : le problème qu'il résout n'est pas difficile et il ne le résout pas correctement qu'est-ce qui manque le plus au langage Normalisé par le W3C, le langage XML (Extensible Markup Language) a été largement adopté comme format d'échange de données entre différents systèmes, plateformes et organisations. Mais, le langage a quelques faiblesses qui font souvent l'objet de plusieurs discussions et de rejet par certains. « The Essence Of Xml », l'un des documents fondamentaux sur le langage écrit par Philip Wadler et Jérôme Siméon procède à une analyse de celui-ci. Selon le document, les deux propriétés clés nécessaires pour n'importe quel format sont les suivant...

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• IX eCommerce Forum: Oracle ed Euronics presentano il loro caso di successo

  - by Claudia Caramelli-Oracle

  Promosso da Netcomm, l'evento ha raggiunto la nona edizione. La tematica principale permette di indagare le dinamiche di tutta la filiera del commercio elettronico, offrendo spunti utili grazie al coinvolgimento di ospiti illustri e relatori. L'e-Commerce Forum è il luogo ideale per scoprire le opportunità del mercato italiano.Oracle, insieme a Reply, ha organizzato un workshop lunch rivolto a tutti coloro che sono interessati a sentire storie di successo circa come la piattaforma eCommerce di Oracle è stata implementata con successo. Il testimonial in questa occasione è stato Euronics. Abbiamo avuto in sala quasi 40 persone che hanno trascorso la loro pausa pranzo con noi! La tematica del resto è attuale e in continua evoluzione/espansione: l'interesse è alto e Oracle offre i mezzi più all'avanguardia per costruire la propria storia di successo proiettando le altre realtà sempre più avanti nel commercio elettronico.Per maggiori informazioni scrivi a Silvia Valgoi

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