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• RDA Health Checks for SOA

  - by ShawnBailey

  What is a health check in RDA? A health check evaluates something in your environment to determine whether a change needs to be considered in order to avoid a problem or optimize fuctionality. Examples of what this 'something' might be are: Configuration Parameters JVM Options Runtime Statistics What have we done for SOA? In the latest release of RDA, 4.30, we have added a Rule Set for SOA called 'Oracle SOA 11g (11.1.1) Post Installation (Generic)'. This Rule Set contains 14 SOA related health checks. These checks were all derived from common issues / solutions we see in support of the SOA product. Many of the recommendations come from the product documentation while others are covered in the SOA Knowledge Base. Our goal is that you will be able to easily identify the areas of concern and understand the guidance available from the output of the Rule Set. Running the health checks for SOA The rules that the checks use are installed with RDA and bundled by product or functional area into what are called 'Rule Sets'. To view the available Rule Sets simply run the command from the RDA home location: rda.cmd (or .sh) -dT hcve This will bring up a list of the available HCVE (Health Check / Verification Engine) Rule Sets. Each Rule Set contains a group of related rules that are used for evalutation and display of results. A rule can be considered synonymous with a single health check and they are assigned an ID, Name and Description that can be seen when they are executed. The Rule Set for SOA is option number 11 and you just enter this selection at the prompt. The Rule Set will then execute to completion. After running an HCVE Rule Set the tool will write the output to the RDA_HOME/output folder. The simplest way to view the output is to drag the .htm file to a browser but of course it can also be uploaded to a Service Request for evaluation by Oracle Support. Many of the Rule Sets will prompt you for information before they can execute their rules but the SOA Rule Set will identify the SOA domains configured in your RDA setup.cfg file. This means that you don't need to answer all of the questions again about where stuff is but it also means that you must have configured RDA for SOA. To run the Rule Set: Download the latest version of RDA from MOS Doc ID 314422.1 Configure RDA for your SOA domains. Detailed steps can be found here In it's simplest form the command is 'rda.cmd (.sh) -S SOA' Go to the RDA home location and enter the command 'rda.cmd (or .sh) -dT hcve' Select option '11' It should be noted that this our first release of a SOA Rule Set so there will probably be some things we need to clean up or fix. None of these rules will actually modify anything on your system as they are read only and do the evaluations internally. Please let us know if you have any issues with the rules or ideas for new ones so we can make them as useful as possible. The Checks Here is a list of the SOA health checks by ID, Name and Description. ID Name Description A00100 SOA Domain Homes Lists the SOA domains that were indentified from the RDA setup.cfg file A00200 Coherence Protocol Conflict Checks to see if you have both Unicast and Multicast configured in the same domain. Checks both the setDomainEnv and config.xml entries (if it exists). We recommend Unicast with fully qualified host names or IP addresses. A00210 Coherence Fully Qualified Host Checks that the host names are fully qualified or that IP addresses are used. Will fail if unqualified host names are detected. A00220 Unicast Local Host Checks that the Coherence localhost is specified for use with Unicast A00300 JTA Timeout Checks that the JTA timeout is configured for the domain and lists the value. The bundled rule will only list the current values of the JTA timeout for each SOA Domain. In the future the rule with fail with a warning if the value is 300 seconds or lower. It is recommended that timeouts follow the pattern 'syncMaxWaitTime' < EJB Timeouts < JTA Timeout. The 300 second value is important because the EJB Timeouts default to 300 seconds. Additional information can be found in MOS Doc ID 880313.1. A00310 XA Max Time Checks that the JTA Maximum XA call time is set for the domain. Fails if it is not explicitly set or if the value is less than or equal to the default of 12000 ms. A00320 XA Timeout Checks that the XA timeout is enabled and that the value is '0' for the SOA Data Source (SOADataSource-jdbc.xml) A00330 JDBC Statement Timeout Checks that the Statement Timeout is set for all SOA Data Sources. Fails if the value is not set or if it is set to the default of -1. A00400 XA Driver Checks that the SOA Data Source is configured to use an XA driver. Fails if it is not. A00410 JDBC Capacity Settings Checks that the minimum and maximum capacity are equal for all SOA Data Sources. Fails if they are not and lists specifically which data sources failed. A00500 SOA Roles Checks that the default SOA roles 'SOAAdmin' and 'SOAOperator' are configured for the soa-infra application in the file sytem-jazn-data.xml. Fails if they are not. A00700 SOA-INFRA Deployment Checks that the soa-infra application is deployed to either a cluster, all members of a cluster or a stand alone server. A00710 SOA Deployments Checks that the SOA related applications are deployed to the same domain members as soa-infra. A00720 SOA Library Deployments Checks that the SOA related libraries are deployed to the same domain members as soa-infra. A00730 Data Source Deployments Checks that the SOA Data Sources are all targeted to the same domain members as soa-infra

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• We Are SQLFamily

  - by AllenMWhite

  On Monday, Tom LaRock ( b /@sqlrockstar) presented his #MemeMonday topic as What #SQLFamily Means To Me . The #sqlfamily hash tag is a relatively new one, but is amazingly appropriate. I've been working with relational databases for almost 20 years, and for most of that time I've been the lone DBA. The only one to set things up, explain how things work, fix the problems, make it go faster, etc., etc., yadda, yadda, yadda. I enjoy being 'the guy', but at the same time it gets hard. What if I'm wrong?...(read more)

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• Trying to setup first DirectX project (don't understand the error) [on hold]

  - by user1157885

  I've just started learning DirectX with the book "3D Game Programming with DirectX". I just finished setting up all the paths and adding the code to the project which I think I did correctly, but I get this massive error which I don't really understand and is hard to google. Could someone tell me what it means and how to fix it? Error 1 error TRK0002: Failed to execute command: ""C:\Program Files (x86)\Microsoft DirectX SDK (June 2010)\Utilities\bin\x64\fxc.exe" /nologo /Emain /Fo "C:\Desktop\DirectX 11 Projects\box\Win32Project2\Debug\color.cso" /Od /Zi "....\Book Files\3DGameProg\DVD\Code\Chapter 6 Drawing in Direct3D\Box\FX\color.fx"". The handle is invalid.

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• org.openide.awt.ColorComboBox

  - by Geertjan

  It's the time of year when a lot of NetBeans Platform tutorials are being reviewed, revised, and rewritten. Today I'm looking at the NetBeans Platform Paint Application Tutorial. Suddenly I remembered seeing something in a recent API Changes document about a new class, ColorComboBox. That means I can make the tutorial a lot simpler, since Tim Boudreau's external ColorChooser.jar is now superfluous. Here's what the ColorComboBox looks like: It works perfectly. Of course, the nice thing about using that JAR was that it showed the user how to incorporate external JARs, but I'll make sure to make a note of that in the tutorial, along the lines of "If you don't like the NetBeans Platform color combobox, and would like to replace it with your own, such as Tim's ColorChooser.jar or a JavaFX color chooser, take the following steps." In short, if you're using NetBeans APIs, write this on your ceiling above your bed: http://bits.netbeans.org/dev/javadoc/apichanges.html, check that page regularly (mark it in your calendar to do first thing every Monday morning) and you'll be aware of the latest changes as they happen.

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• Some non-generic collections

  - by Simon Cooper

  Although the collections classes introduced in .NET 2, 3.5 and 4 cover most scenarios, there are still some .NET 1 collections that don't have generic counterparts. In this post, I'll be examining what they do, why you might use them, and some things you'll need to bear in mind when doing so. BitArray System.Collections.BitArray is conceptually the same as a List<bool>, but whereas List<bool> stores each boolean in a single byte (as that's what the backing bool[] does), BitArray uses a single bit to store each value, and uses various bitmasks to access each bit individually. This means that BitArray is eight times smaller than a List<bool>. Furthermore, BitArray has some useful functions for bitmasks, like And, Xor and Not, and it's not limited to 32 or 64 bits; a BitArray can hold as many bits as you need. However, it's not all roses and kittens. There are some fundamental limitations you have to bear in mind when using BitArray: It's a non-generic collection. The enumerator returns object (a boxed boolean), rather than an unboxed bool. This means that if you do this: foreach (bool b in bitArray) { ... } Every single boolean value will be boxed, then unboxed. And if you do this: foreach (var b in bitArray) { ... } you'll have to manually unbox b on every iteration, as it'll come out of the enumerator an object. Instead, you should manually iterate over the collection using a for loop: for (int i=0; i<bitArray.Length; i++) { bool b = bitArray[i]; ... } Following on from that, if you want to use BitArray in the context of an IEnumerable<bool>, ICollection<bool> or IList<bool>, you'll need to write a wrapper class, or use the Enumerable.Cast<bool> extension method (although Cast would box and unbox every value you get out of it). There is no Add or Remove method. You specify the number of bits you need in the constructor, and that's what you get. You can change the length yourself using the Length property setter though. It doesn't implement IList. Although not really important if you're writing a generic wrapper around it, it is something to bear in mind if you're using it with pre-generic code. However, if you use BitArray carefully, it can provide significant gains over a List<bool> for functionality and efficiency of space. OrderedDictionary System.Collections.Specialized.OrderedDictionary does exactly what you would expect - it's an IDictionary that maintains items in the order they are added. It does this by storing key/value pairs in a Hashtable (to get O(1) key lookup) and an ArrayList (to maintain the order). You can access values by key or index, and insert or remove items at a particular index. The enumerator returns items in index order. However, the Keys and Values properties return ICollection, not IList, as you might expect; CopyTo doesn't maintain the same ordering, as it copies from the backing Hashtable, not ArrayList; and any operations that insert or remove items from the middle of the collection are O(n), just like a normal list. In short; don't use this class. If you need some sort of ordered dictionary, it would be better to write your own generic dictionary combining a Dictionary<TKey, TValue> and List<KeyValuePair<TKey, TValue>> or List<TKey> for your specific situation. ListDictionary and HybridDictionary To look at why you might want to use ListDictionary or HybridDictionary, we need to examine the performance of these dictionaries compared to Hashtable and Dictionary<object, object>. For this test, I added n items to each collection, then randomly accessed n/2 items: So, what's going on here? Well, ListDictionary is implemented as a linked list of key/value pairs; all operations on the dictionary require an O(n) search through the list. However, for small n, the constant factor that big-o notation doesn't measure is much lower than the hashing overhead of Hashtable or Dictionary. HybridDictionary combines a Hashtable and ListDictionary; for small n, it uses a backing ListDictionary, but switches to a Hashtable when it gets to 9 items (you can see the point it switches from a ListDictionary to Hashtable in the graph). Apart from that, it's got very similar performance to Hashtable. So why would you want to use either of these? In short, you wouldn't. Any gain in performance by using ListDictionary over Dictionary<TKey, TValue> would be offset by the generic dictionary not having to cast or box the items you store, something the graphs above don't measure. Only if the performance of the dictionary is vital, the dictionary will hold less than 30 items, and you don't need type safety, would you use ListDictionary over the generic Dictionary. And even then, there's probably more useful performance gains you can make elsewhere.

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• Direct3d - Code structure

  - by marcg11

  I'm learning directx in a master's degree and they taught us to have a GraphicsLayer class which is the one connecting with the direct3d library. That way this class is completly independent from the other classes (my game classes), meaning changing the renderer to OpenGL wouldn't require much effort but only changing the graphicLayer. This classe has it's LoadAssets, Paint methods, but I have a question, they told us to load all the assets inside this class. This means all these methods will be in the loadAssets method: D3DXCreateTextureFromFileEx(g_pD3DDevice,"tiles.png",0,0,1,0,D3DFMT_UNKNOWN,D3DPOOL_DEFAULT,D3DX_FILTER_NONE,D3DX_FILTER_NONE,NULL,NULL,NULL,&texTiles); // And more resources to load //... texTiles as you see is a LPDIRECT3DTEXTURE9 instance which is declared in the graphicLayer.h. So my question is, how do you manage all the resources? Do I have to declare in the .h all my game textures even if I'm not using them? How would you load only those resources there are in a scene and draw them in a code-strucured way?

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• First languages with generic programming support

  - by oluies

  Which was the first language with generic programming support, and what was the first major staticly typed language (widely used) with generics support. Generics implement the concept of parameterized types to allow for multiple types. The term generic means "pertaining to or appropriate to large groups of classes." I have seen the following mentions of "first": First-order parametric polymorphism is now a standard element of statically typed programming languages. Starting with System F [20,42] and functional programming lan- guages, the constructs have found their way into mainstream languages such as Java and C#. In these languages, first-order parametric polymorphism is usually called generics. From "Generics of a Higher Kind", Adriaan Moors, Frank Piessens, and Martin Odersky Generic programming is a style of computer programming in which algorithms are written in terms of to-be-specified-later types that are then instantiated when needed for specific types provided as parameters. This approach, pioneered by Ada in 1983 From Wikipedia Generic Programming

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• How to setup NX server and client?

  - by javanoob

  I installed NX server on my desktop and able to run it successfully following this tutorial: http://michigantelephone.wordpress.com/2007/10/15/how-to-install-nx-server-and-client-under-ubuntukubuntu-linux/ When i run the command sudo /usr/NX/bin/nxserver –status I am seeing the following output : NX 900 Connecting to server .. NX 110 NX Server is running. NX 999 Bye. It means i have setup NX server correctly.. But on other machine when i open NX client it is asking for hostname..what name should i give there? Every tutorial is explaining about how to install and start NX server but not about how to connect to the server from client.. Could you guys please help me? Thanks in Advance Deter

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• Acceptable GC frequency for a SlimDX/Windows/.NET game?

  - by Rei Miyasaka

  I understand that the Windows GC is much better than the Xbox/WP7 GC, being that it's generational and multithreaded -- so I don't need to worry quite as much about avoiding memory allocation. SlimDX even has some unavoidable functions that generate some amount of garbage (specifically, MapSubresource creates DataBoxes), yet people don't seem to be too upset about it. I'd like to use some functional paradigms to write my code too, which also means creating objects like closures and monads. I know premature optimization isn't a good thing, but are there rules of thumb or metrics that I can follow to know whether I need to cut down on allocations? Is, say, one gen 0 GC per frame too much? One thing that has me stumped is object promotions. Gen 0 GCs will supposedly finish within a millisecond or two, but if I'm understanding correctly, it's the gen 1 and 2 promotions that start to hurt. I'm not too sure how I can predict/prevent these.

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• Understanding binary numbers in terms of real world objects

  - by Kaushik

  When I represent a number in the decimal system, I have an intuitive knowledge of what it amounts to. For example take the number '10': I understand that it means 10 apples or 10 people... i.e I can count in the real world. But as soon as the number is converted to any other system, this understanding no longer applies. For example 10 when converted to binary will be 1010...now what does this represent? Is there a way to understand this number 1010 in terms of counting objects in the real world?

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• Unity 3d (Using Blender) - anime/manga/cel-shaded style characters

  - by David Archer

  Making a game using Blender for 3D models and Unity for the game engine. Just wondering if anyone knows any links to pages that give a tutorial on Japanese anime style 3D modelling, texturing and shading through blender. I'm actually looking to create a cel-shaded look eventually (read: Okami/Jet Set Radio style) and I'm kind of stuck with the design stuff. I'm not a Blender expert by any means, and still kind of new to the design side of things (I'm a programmer by trade), so please don't vote me down too hard. I've tried googling, but there doesn't seem to be much in the way of what I'm after. The only thing I've found really is a plugin for blender called freestyle, or using the ToonShader shading tool. If there are any good tutorials or anything, I'm really happy to sit through them - just want to learn :) Thanks for any help :)

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• SQL SERVER – Detect Virtual Log Files (VLF) in LDF

  - by pinaldave

  In one of the recent training engagements, I was asked if it true that there are multiple small log files in the large log file (LDF). I found this question very interesting as the answer is yes. Multiple small Virtual Log Files commonly known as VLFs together make an LDF file. The writing of the VLF is sequential and resulting in the writing of the LDF file is sequential as well. This leads to another talk that one does not need more than one log file in most cases. However, in short, you can use following DBCC command to know how many Virtual Log Files or VLFs are present in your log file. DBCC LOGINFO You can find the result of above query to something as displayed in following image. You can see the column which is marked as 2 which means it is active VLF and the one with 0 which is inactive VLF. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• TTS on App Engine

  - by yati sagade

  I have written a small front-end to the Festival TTS system using Python/Django. I wish to deploy it on the Google App Engine cloud. A few questions: My application uses the Festival app 'text2wave'. Will is work on the cloud? I have used Python primitives like subprocess.call() to invoke the aforementioned program. Will that work? If your answer to any or both of (1) and (2) is no, is there a free api on the web that I can use (from the appengine)? I read somewhere about placing calls from Phono to a Voxeo backend, but I'm not sure what that means. I am aware of the Google Translate extension that allows translation using an HTTP GET (REST) request, but here the text is limited to 100 chars. Bad. Plus, they may take it down any point of time.

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• Timing Calculations for Opengl ES 2.0 draw calls

  - by Arun AC

  I am drawing a cube in OpenGL ES 2.0 in Linux. I am calculating the time taken for each frame using below function #define NANO 1000000000 #define NANO_TO_MICRO(x) ((x)/1000) uint64_t getTick() { struct timespec stCT; clock_gettime(CLOCK_MONOTONIC, &stCT); uint64_t iCurrTimeNano = (1000000000 * stCT.tv_sec + stCT.tv_nsec); // in Nano Secs uint64_t iCurrTimeMicro = NANO_TO_MICRO(iCurrTimeNano); // in Micro Secs return iCurrTimeMicro; } I am running my code for 100 frames with simple x-axis rotation. I am getting around 200 to 220 microsecs per frame. that means am i getting around (1/220microsec = 4545) FPS Is my GPU is that fast? I strongly doubt this result. what went wrong in the code? Regards, Arun AC

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• How can I reduce lagging with GUI/GPU stuff -- make Unity run smaller, quicker, faster?

  - by chris

  Finally installed Ubuntu 12.04 on my HP Pavilion 2000. Have all of my apps on and loaded and am happy thus far. ONE ISSUE -- I'm experiencing a small amount of GUI/GPU style lagging when I go to open menus, move windows, etc. What settings can I disable to allow it to run sharply and quickly, even if i t means sacrificing some of the graphics? Have already installed pre-load. Just want the OS to run sharply and quickly with menu refreshes, window moves, etc. I do not mind sacrificing graphics. Somone mentionted to me I have to install video drivers but the two that come up in system settings under drivers it won't let me install. ALSO : I am driving a second 19" monitor -- would that make a difference performance wise as well? Thanks in advance. Chris

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• WIF, ADFS 2 and WCF&ndash;Part 5: Service Client (more Flexibility with WSTrustChannelFactory)

  - by Your DisplayName here!

  See the previous posts first. WIF includes an API to manually request tokens from a token service. This gives you more control over the request and more flexibility since you can use your own token caching scheme instead of being bound to the channel object lifetime. The API is straightforward. You first request a token from the STS and then use that token to create a channel to the relying party service. I’d recommend using the WS-Trust bindings that ship with WIF to talk to ADFS 2 – they are pre-configured to match the binding configuration of the ADFS 2 endpoints. The following code requests a token for a WCF service from ADFS 2: private static SecurityToken GetToken() {     // Windows authentication over transport security     var factory = new WSTrustChannelFactory(         new WindowsWSTrustBinding(SecurityMode.Transport),         stsEndpoint);     factory.TrustVersion = TrustVersion.WSTrust13;       var rst = new RequestSecurityToken     {         RequestType = RequestTypes.Issue,         AppliesTo = new EndpointAddress(svcEndpoint),         KeyType = KeyTypes.Symmetric     };       var channel = factory.CreateChannel();     return channel.Issue(rst); } Afterwards, the returned token can be used to create a channel to the service. Again WIF has some helper methods here that make this very easy: private static void CallService(SecurityToken token) {     // create binding and turn off sessions     var binding = new WS2007FederationHttpBinding(         WSFederationHttpSecurityMode.TransportWithMessageCredential);     binding.Security.Message.EstablishSecurityContext = false;       // create factory and enable WIF plumbing     var factory = new ChannelFactory<IService>(binding, new EndpointAddress(svcEndpoint));     factory.ConfigureChannelFactory<IService>();       // turn off CardSpace - we already have the token     factory.Credentials.SupportInteractive = false;       var channel = factory.CreateChannelWithIssuedToken<IService>(token);       channel.GetClaims().ForEach(c =>         Console.WriteLine("{0}\n {1}\n  {2} ({3})\n",             c.ClaimType,             c.Value,             c.Issuer,             c.OriginalIssuer)); } Why is this approach more flexible? Well – some don’t like the configuration voodoo. That’s a valid reason for using the manual approach. You also get more control over the token request itself since you have full control over the RST message that gets send to the STS. One common parameter that you may want to set yourself is the appliesTo value. When you use the automatic token support in the WCF federation binding, the appliesTo is always the physical service address. This means in turn that this address will be used as the audience URI value in the SAML token. Well – this in turn means that when you have an application that consists of multiple services, you always have to configure all physical endpoint URLs in ADFS 2 and in the WIF configuration of the service(s). Having control over the appliesTo allows you to use more symbolic realm names, e.g. the base address or a completely logical name. Since the URL is never de-referenced you have some degree of freedom here. In the next post we will look at the necessary code to request multiple tokens in a call chain. This is a common scenario when you first have to acquire a token from an identity provider and have to send that on to a federation gateway or Resource STS. Stay tuned.

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• Subterranean IL: Generics and array covariance

  - by Simon Cooper

  Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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• Balancing game difficulty against player progression

  - by Raven Dreamer

  It seems that the current climate of games seems to cater to an obvious progression of player power, whether that means getting a bigger, more explosive gun in Halo, leveling up in an RPG, or unlocking new options in Command and Conquer 4. Yet this concept is not exclusive to video or computer games -- even in Dungeons and Dragons players can strive to acquire a +2 sword to replace the +1 weapon they've been using. Yet as a systems designer, the concept of player progression is giving me headache after headache. Should I balance around the players exact capabilities and give up on a simple linear progression? (I think ESIV:Oblivion is a good example of this) Is it better to throw the players into an "arms race" with their opponents, where if the players don't progress in an orderly manner, it is only a matter of time until gameplay is unbearably difficult? (4th Edition DnD strikes me as a good example of this) Perhaps it would make most sense to untether the core gameplay mechanics from progression at all -- give them flashier, more interesting (but not more powerful!) ways to grow?

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• Is true multithreading really necessary?

  - by Jonathan Graef

  So yeah, I'm creating a programming language. And the language allows multiple threads. But, all threads are synchronized with a global interpreter lock, which means only one thread is allowed to execute at a time. The only way to get the threads to switch off is to explicitly tell the current thread to wait, which allows another thread to execute. Parallel processing is of course possible by spawning multiple processes, but the variables and objects in one process cannot be accessed from another. However the language does have a fairly efficient IPC interface for communicating between processes. My question is: Would there ever be a reason to have multiple, unsynchronized threads within a single process (thus circumventing the GIL)? Why not just put thread.wait() statements in key positions in the program logic (presuming thread.wait() isn't a CPU hog, of course)? I understand that certain other languages that use a GIL have processor scheduling issues (cough Python), but they have all been resolved.

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• Why does PHP create these log entries on every page access?

  - by HXCaine

  My server's error log (in cPanel) has an entry for every single time a PHP page is loaded that looks like this (where 'username' has been substituted for my actual username): [2012-06-09 09:02:07]: info: [usr/grp]: username/username cmd: /home/username/public_html/error.php php: /usr/local/php53/bin/php I know it's only an 'info' message but it's filling up my error log. It can't be related to the content of my PHP files because it even happens when I load a page with this as its content: <?php phpinfo(); ?> Any ideas on what it means or if I can get rid of it?

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• Problem with installing programs

  - by Brian Buck

  I am unable to install programs for the Ubuntu 10.10 system. These download ok, but when attempting to install them, the following message is displayed: AN ERROR OCCURRED WHILE OPENING THE ARCHIVE END-OF-CENTRAL-DIRECTORY SIGNATURE NOT FOUND etc....... ZIPINFO: CANNOT FIND ZIPFILE DIRECTORY IN etc...... As I am new to Ubuntu and also fairly "green" as far as computer terminology is concerned, I have no idea what this means and don't have a clue on how to fix it. Can you help please? Many thanks, Brian Buck

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• How to clone a VirtualBox Disk

  - by [email protected]

   How to clone a VirtualBox DiskCopying the image of Virtual Disk (.vdi file) is a convenient way to duplicate the disk, in cases you want to avoid re-installing an operating system from scratch. However, simply copying the .vdi file into another location will make a verbatim copy of the virtual disk, including the UUID of the disk. If you try to add the copy in the Virtual Media Manager, you will get an error like this:In this case, you have to do is to clone the vdi disk: cd C:\Program Files\Sun\VirtualBox\C:\Program Files\Sun\VirtualBox>vboxmanage clonevdi G:\VMWARES\Database\11GR2onOEL5forVbox\11GR2_OEL5_32GB.vdi G:\VMWARES\Database\11GR2onOEL5forVbox\OEL5_32GB.vdi$ VBoxManage clonevdi Master.vdi Clone.vdiIn case you receive a error like this. It means that the disk is already a copy of other VirtualBox Disk.In that case you chould change the UUID before to clone the Disk.Follow the steps given here in order to do that.

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• How vibrations might effect Kinect depth measurements

  - by dreza

  I'm currently doing some research into development with the Microsoft Kinect product. My project manager has come up with a potential design for mounting the camera to do the capturing. However the solution means that the camera might be subject to vibrations as the platform it is on is directly connected to where the subjects will be moving. It was my thought that vibrations would effect the quality of the results, however I could not come up with a viable explanation as to why, other than it's the same as if you held a camera in your hand and your hand was shaking vs using a tripod. Do vibrations effect the depth measurements on a Kinect and if so how can I explain this in simple terms to my PM to help come up with a better design to attach the sensor to?

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• A deadlock was detected while trying to lock variables in SSIS

  Error: 0xC001405C at SQL Log Status: A deadlock was detected while trying to lock variables "User::RowCount" for read/write access. A lock cannot be acquired after 16 attempts. The locks timed out. Have you ever considered variable locking when building your SSIS packages? I expect many people haven’t just because most of the time you never see an error like the one above. I’ll try and explain a few key concepts about variable locking and hopefully you never will see that error. First of all, what is all this variable locking all about? Put simply SSIS variables have to be locked before they can be accessed, and then of course unlocked once you have finished with them. This is baked into SSIS, presumably to reduce the risk of race conditions, but with that comes some additional overhead in that you need to be careful to avoid lock conflicts in some scenarios. The most obvious place you will come across any hint of locking (no pun intended) is the Script Task or Script Component with their ReadOnlyVariables and ReadWriteVariables properties. These two properties allow you to enter lists of variables to be used within the task, or to put it another way, these lists of variables to be locked, so that they are available within the task. During the task pre-execute phase the variables and locked, you then use them during the execute phase when you code is run, and then unlocked for you during the post-execute phase. So by entering the variable names in one of the two list, the locking is taken care of for you, and you just read and write to the Dts.Variables collection that is exposed in the task for the purpose. As you can see in the image above, the variable PackageInt is specified, which means when I write the code inside that task I don’t have to worry about locking at all, as shown below. public void Main() { // Set the variable value to something new Dts.Variables["PackageInt"].Value = 199; // Raise an event so we can play in the event handler bool fireAgain = true; Dts.Events.FireInformation(0, "Script Task Code", "This is the script task raising an event.", null, 0, ref fireAgain); Dts.TaskResult = (int)ScriptResults.Success; } As you can see as well as accessing the variable, hassle free, I also raise an event. Now consider a scenario where I have an event hander as well as shown below. Now what if my event handler uses tries to use the same variable as well? Well obviously for the point of this post, it fails with the error quoted previously. The reason why is clearly illustrated if you consider the following sequence of events. Package execution starts Script Task in Control Flow starts Script Task in Control Flow locks the PackageInt variable as specified in the ReadWriteVariables property Script Task in Control Flow executes script, and the On Information event is raised The On Information event handler starts Script Task in On Information event handler starts Script Task in On Information event handler attempts to lock the PackageInt variable (for either read or write it doesn’t matter), but will fail because the variable is already locked. The problem is caused by the event handler task trying to use a variable that is already locked by the task in Control Flow. Events are always raised synchronously, therefore the task in Control Flow that is raising the event will not regain control until the event handler has completed, so we really do have un-resolvable locking conflict, better known as a deadlock. In this scenario we can easily resolve the problem by managing the variable locking explicitly in code, so no need to specify anything for the ReadOnlyVariables and ReadWriteVariables properties. public void Main() { // Set the variable value to something new, with explicit lock control Variables lockedVariables = null; Dts.VariableDispenser.LockOneForWrite("PackageInt", ref lockedVariables); lockedVariables["PackageInt"].Value = 199; lockedVariables.Unlock(); // Raise an event so we can play in the event handler bool fireAgain = true; Dts.Events.FireInformation(0, "Script Task Code", "This is the script task raising an event.", null, 0, ref fireAgain); Dts.TaskResult = (int)ScriptResults.Success; } Now the package will execute successfully because the variable lock has already been released by the time the event is raised, so no conflict occurs. For those of you with a SQL Engine background this should all sound strangely familiar, and boils down to getting in and out as fast as you can to reduce the risk of lock contention, be that SQL pages or SSIS variables. Unfortunately we cannot always manage the locking ourselves. The Execute SQL Task is very often used in conjunction with variables, either to pass in parameter values or get results out. Either way the task will manage the locking for you, and will fail when it cannot lock the variables it requires. The scenario outlined above is clear cut deadlock scenario, both parties are waiting on each other, so it is un-resolvable. The mechanism used within SSIS isn’t actually that clever, and whilst the message says it is a deadlock, it really just means it tried a few times, and then gave up. The last part of the error message is actually the most accurate in terms of the failure, A lock cannot be acquired after 16 attempts. The locks timed out.  Now this may come across as a recommendation to always manage locking manually in the Script Task or Script Component yourself, but I think that would be an overreaction. It is more of a reminder to be aware that in high concurrency scenarios, especially when sharing variables across multiple objects, locking is important design consideration. Update – Make sure you don’t try and use explicit locking as well as leaving the variable names in the ReadOnlyVariables and ReadWriteVariables lock lists otherwise you’ll get the deadlock error, you cannot lock a variable twice!

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• How are Java ByteBuffer's limit and position variable's updated?

  - by Dummy Derp

  There are two scenarios: writing and reading Writing: Whenever I write something to the ByteBuffer by calling its put(byte[]) method the position variable is incremented as: current position + size of byte[] and limit stays at the max. If, however, I put the data in a view buffer then I will have to, manually, calculate and update the position Before I call the write(ByteBuffer) method of the channel to write something, I will have to flip() the Bytebuffer so that position points to zero and limit points to the last byte that was written to the ByteBuffer. Reading: Whenever I call the read(ByteBuffer) method of a channel to read something, the position variable stays at 0 and the limit variable of the ByteBuffer points to the last byte that was read. So, if the ByteBuffer is smaller than the file being read, the limit variable is pushed to max This means that the ByteBuffer is already flipped and I can proceed to extracting the values from the ByteBuffer. Please, correct me where I am wrong :)

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