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• Why can final object be modified?

  - by Matt McCormick

  I came across the following code in a code base I am working on: public final class ConfigurationService { private static final ConfigurationService INSTANCE = new ConfigurationService(); private List providers; private ConfigurationService() { providers = new ArrayList(); } public static void addProvider(ConfigurationProvider provider) { INSTANCE.providers.add(provider); } ... INSTANCE is declared as final. Why can objects be added to INSTANCE? Shouldn't that invalidate the use of final. (It doesn't). I'm assuming the answer has to do something with pointers and memory but would like to know for sure.

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• Erlang: How to view output of io:format/2 calls in processes spawned on remote nodes.

  - by jkndrkn

  Hello, I am working on a decentralized Erlang application. I am currently working on a single PC and creating multiple nodes by initializing erl with the -sname flag. When I spawn a process using spawn/4 on its home node, I can see output generated by calls io:format/2 within that process in its home erl instance. When I spawn a process remotely by using spawn/4 in combination with register_name, output of io:format/2 is sometimes redirected back to the erl instance where the remote spawn/4 call was made, and sometimes remains completely invisible. Similarly, when I use rpc:call/4, output of io:format/2 calls is redirected back to the erl instance where the `rpc:call/4' call is made. How do you get a process to emit debugging output back to its parent erl instance?

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• The Return Of __FILE__ And __LINE__ In .NET 4.5

  - by Alois Kraus

  Good things are hard to kill. One of the most useful predefined compiler macros in C/C++ were __FILE__ and __LINE__ which do expand to the compilation units file name and line number where this value is encountered by the compiler. After 4.5 versions of .NET we are on par with C/C++ again. It is of course not a simple compiler expandable macro it is an attribute but it does serve exactly the same purpose. Now we do get CallerLineNumberAttribute  == __LINE__ CallerFilePathAttribute        == __FILE__ CallerMemberNameAttribute  == __FUNCTION__ (MSVC Extension)   The most important one is CallerMemberNameAttribute which is very useful to implement the INotifyPropertyChanged interface without the need to hard code the name of the property anymore. Now you can simply decorate your change method with the new CallerMemberName attribute and you get the property name as string directly inserted by the C# compiler at compile time.   public string UserName { get { return _userName; } set { _userName=value; RaisePropertyChanged(); // no more RaisePropertyChanged(“UserName”)! } } protected void RaisePropertyChanged([CallerMemberName] string member = "") { var copy = PropertyChanged; if(copy != null) { copy(new PropertyChangedEventArgs(this, member)); } } Nice and handy. This was obviously the prime reason to implement this feature in the C# 5.0 compiler. You can repurpose this feature for tracing to get your hands on the method name of your caller along other stuff very fast now. All infos are added during compile time which is much faster than other approaches like walking the stack. The example on MSDN shows the usage of this attribute with an example public static void TraceMessage(string message, [CallerMemberName] string memberName = "", [CallerFilePath] string sourceFilePath = "", [CallerLineNumber] int sourceLineNumber = 0) { Console.WriteLine("Hi {0} {1} {2}({3})", message, memberName, sourceFilePath, sourceLineNumber); }   When I do think of tracing I do usually want to have a API which allows me to Trace method enter and leave Trace messages with a severity like Info, Warning, Error When I do print a trace message it is very useful to print out method and type name as well. So your API must either be able to pass the method and type name as strings or extract it automatically via walking back one Stackframe and fetch the infos from there. The first glaring deficiency is that there is no CallerTypeAttribute yet because the C# compiler team was not satisfied with its performance.   A usable Trace Api might therefore look like   enum TraceTypes { None = 0, EnterLeave = 1 << 0, Info = 1 << 1, Warn = 1 << 2, Error = 1 << 3 } class Tracer : IDisposable { string Type; string Method; public Tracer(string type, string method) { Type = type; Method = method; if (IsEnabled(TraceTypes.EnterLeave,Type, Method)) { } } private bool IsEnabled(TraceTypes traceTypes, string Type, string Method) { // Do checking here if tracing is enabled return false; } public void Info(string fmt, params object[] args) { } public void Warn(string fmt, params object[] args) { } public void Error(string fmt, params object[] args) { } public static void Info(string type, string method, string fmt, params object[] args) { } public static void Warn(string type, string method, string fmt, params object[] args) { } public static void Error(string type, string method, string fmt, params object[] args) { } public void Dispose() { // trace method leave } } This minimal trace API is very fast but hard to maintain since you need to pass in the type and method name as hard coded strings which can change from time to time. But now we have at least CallerMemberName to rid of the explicit method parameter right? Not really. Since any acceptable usable trace Api should have a method signature like Tracexxx(… string fmt, params [] object args) we not able to add additional optional parameters after the args array. If we would put it before the format string we would need to make it optional as well which would mean the compiler would need to figure out what our trace message and arguments are (not likely) or we would need to specify everything explicitly just like before . There are ways around this by providing a myriad of overloads which in the end are routed to the very same method but that is ugly. I am not sure if nobody inside MS agrees that the above API is reasonable to have or (more likely) that the whole talk about you can use this feature for diagnostic purposes was not a core feature at all but a simple byproduct of making the life of INotifyPropertyChanged implementers easier. A way around this would be to allow for variable argument arrays after the params keyword another set of optional arguments which are always filled by the compiler but I do not know if this is an easy one. The thing I am missing much more is the not provided CallerType attribute. But not in the way you would think of. In the API above I did add some filtering based on method and type to stay as fast as possible for types where tracing is not enabled at all. It should be no more expensive than an additional method call and a bool variable check if tracing for this type is enabled at all. The data is tightly bound to the calling type and method and should therefore become part of the static type instance. Since extending the CLR type system for tracing is not something I do expect to happen I have come up with an alternative approach which allows me basically to attach run time data to any existing type object in super fast way. The key to success is the usage of generics.   class Tracer<T> : IDisposable { string Method; public Tracer(string method) { if (TraceData<T>.Instance.Enabled.HasFlag(TraceTypes.EnterLeave)) { } } public void Dispose() { if (TraceData<T>.Instance.Enabled.HasFlag(TraceTypes.EnterLeave)) { } } public static void Info(string fmt, params object[] args) { } /// <summary> /// Every type gets its own instance with a fresh set of variables to describe the /// current filter status. /// </summary> /// <typeparam name="T"></typeparam> internal class TraceData<UsingType> { internal static TraceData<UsingType> Instance = new TraceData<UsingType>(); public bool IsInitialized = false; // flag if we need to reinit the trace data in case of reconfigured trace settings at runtime public TraceTypes Enabled = TraceTypes.None; // Enabled trace levels for this type } } We do not need to pass the type as string or Type object to the trace Api. Instead we define a generic Api that accepts the using type as generic parameter. Then we can create a TraceData static instance which is due to the nature of generics a fresh instance for every new type parameter. My tests on my home machine have shown that this approach is as fast as a simple bool flag check. If you have an application with many types using tracing you do not want to bring the app down by simply enabling tracing for one special rarely used type. The trace filter performance for the types which are not enabled must be therefore the fasted code path. This approach has the nice side effect that if you store the TraceData instances in one global list you can reconfigure tracing at runtime safely by simply setting the IsInitialized flag to false. A similar effect can be achieved with a global static Dictionary<Type,TraceData> object but big hash tables have random memory access semantics which is bad for cache locality and you always need to pay for the lookup which involves hash code generation, equality check and an indexed array access. The generic version is wicked fast and allows you to add more features to your tracing Api with minimal perf overhead. But it is cumbersome to write the generic type argument always explicitly and worse if you do refactor code and move parts of it to other classes it might be that you cannot configure tracing correctly. I would like therefore to decorate my type with an attribute [CallerType] class Tracer<T> : IDisposable to tell the compiler to fill in the generic type argument automatically. class Program { static void Main(string[] args) { using (var t = new Tracer()) // equivalent to new Tracer<Program>() { That would be really useful and super fast since you do not need to pass any type object around but you do have full type infos at hand. This change would be breaking if another non generic type exists in the same namespace where now the generic counterpart would be preferred. But this is an acceptable risk in my opinion since you can today already get conflicts if two generic types of the same name are defined in different namespaces. This would be only a variation of this issue. When you do think about this further you can add more features like to trace the exception in your Dispose method if the method is left with an exception with that little trick I did write some time ago. You can think of tracing as a super fast and configurable switch to write data to an output destination or to execute alternative actions. With such an infrastructure you can e.g. Reconfigure tracing at run time. Take a memory dump when a specific method is left with a specific exception. Throw an exception when a specific trace statement is hit (useful for testing error conditions). Execute a passed delegate which e.g. dumps additional state when enabled. Write data to an in memory ring buffer and dump it when specific events do occur (e.g. method is left with an exception, triggered from outside). Write data to an output device. …. This stuff is really useful to have when your code is in production on a mission critical server and you need to find the root cause of sporadic crashes of your application. It could be a buggy graphics card driver which throws access violations into your application (ok with .NET 4 not anymore except if you enable a compatibility flag) where you would like to have a minidump or you have reached after two weeks of operation a state where you need a full memory dump at a specific point in time in the middle of an transaction. At my older machine I do get with this super fast approach 50 million traces/s when tracing is disabled. When I do know that tracing is enabled for this type I can walk the stack by using StackFrameHelper.GetStackFramesInternal to check further if a specific action or output device is configured for this method which is about 2-3 times faster than the regular StackTrace class. Even with one String.Format I am down to 3 million traces/s so performance is not so important anymore since I do want to do something now. The CallerMemberName feature of the C# 5 compiler is nice but I would have preferred to get direct access to the MethodHandle and not to the stringified version of it. But I really would like to see a CallerType attribute implemented to fill in the generic type argument of the call site to augment the static CLR type data with run time data.

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• How to implement VS 2010-like floating tabs?

  - by unclepaul84

  I'm building a tabbed WPF application. I'm planning to put MapPoint control (ActiveX) on one of the tabs. I want to have the option to float this tab just like in VS 2010. The resulting widow must contain the same instance of the MapPoint control (because each instance of the control starts up separate MapPoint instance). Any idea how to implement this?

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• Result Set Problem

  - by vipul

  Hello Friends, It is possible to Use two query with in single ResultSet

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• unable to add objects to saved collection in GAE using JDO

  - by Jeffrey Chee

  I have a ClassA containing an ArrayList of another ClassB I can save a new instance of ClassA with ClassB instances also saved using JDO. However, When I retrieve the instance of Class A, I try to do like the below: ClassA instance = PMF.get().getPersistenceManager().GetObjectByID( someid ); instance.GetClassBArrayList().add( new ClassB(...) ); I get an Exception like the below: Uncaught exception from servlet com.google.appengine.api.datastore.DatastoreNeedIndexException: no matching index found.. So I was wondering, Is it possible to add a new item to the previously saved collection? Or was it something I missed out. Best Regards

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• Problem using FluentNHibernate, SQLite and Enums

  - by weenet

  I have a Sharp Architecture based app using Fluent NHibernate with Automapping. I have the following Enum: public enum Topics { AdditionSubtraction = 1, MultiplicationDivision = 2, DecimalsFractions = 3 } and the following Class: public class Strategy : BaseEntity { public virtual string Name { get; set; } public virtual Topics Topic { get; set; } public virtual IList Items { get; set; } } If I create an instance of the class thusly: Strategy s = new Strategy { Name = "Test", Topic = Topics.AdditionSubtraction }; it Saves correctly (thanks to this mapping convention: public class EnumConvention : IPropertyConvention, IPropertyConventionAcceptance { public void Apply(FluentNHibernate.Conventions.Instances.IPropertyInstance instance) { instance.CustomType(instance.Property.PropertyType); } public void Accept(FluentNHibernate.Conventions.AcceptanceCriteria.IAcceptanceCriteria criteria) { criteria.Expect(x = x.Property.PropertyType.IsEnum); } } However, upon retrieval, I get an error regarding an attempt to convert Int64 to Topics. This works fine in SQL Server. Any ideas for a workaround? Thanks.

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• Jagran Prakashan Increases Staff Productivity by 40%

  - by Michael Snow

  Jagran Prakashan Increases Staff Productivity by 40%, Launches New IT Projects up to 4x Faster, Enables Mobile Service, and Improves Business Agility Oracle Customer: JPL Location:  Uttar Pradesh, India Industry: Media and Entertainment Employees:  10,000 Annual Revenue:  $100 to $500 Million Jagran Prakashan Ltd. (JPL) is one of India's premier media and communications groups with interests spanning print, advertising, event management, and mobile services for weather, cricket scores, and educational activities. It is a major media enterprise, with 300 locations across 15 states. Its impressive stable of print publications includes Dainik Jagran, the world’s most widely read daily newspaper––with a readership of over 55 million––the country’s leading afternoon dailies, and a range of popular local, bilingual, and English language newspapers. JPL was using multiple systems to manage its business processes. Users were resistant to using multiple passwords for various applications, preferring to continue their less efficient, legacy work practices. In addition, there was no single repository for sharing documents across the organization, such as company announcements or project documents. The company relied on e-mail to disseminate up-to-date company information, often missing employees. It was also time-consuming and difficult for managers to track the status of ongoing assignments or projects because collaboration and document sharing was inefficient and ineffective.With diverse businesses and many geographic locations, JPL needed to implement a centralized and user-friendly enterprise portal to improve document sharing and collaboration and increase business agility. The company implemented Oracle WebCenter Portal to create a dynamic, secure, and intuitive self-service enterprise portal to improve the user experience and increase operating efficiency. It improved staff productivity by 40%, accelerated new IT projects by up to 4x, boosted staff morale, and increased business agility.   Increases Staff Productivity by 40%, Launches New Products up to 2x Faster A word from JPL "With Oracle WebCenter Portal, we gained a dynamic, secure, and intuitive self-service enterprise portal that provided an exceptional user experience and enabled us to engage employees in a collaborative environment. It increased IT staff productivity by 40%, delivered new projects up to 4x faster, and enabled mobile service to improve our business agility.” Sarbani Bhatia, Vice President IT, Jagran Prakashahn Ltd Before implementing Oracle WebCenter Portal, JPL stored project-critical information, such as page planning of daily newspaper editions and the launch of new editions or supplements on individual laptops or in the e-mail system. Collaboration between colleagues was limited to physical meetings, telephone discussions, and e-mail. It was difficult to trace and recover important project documents when a staff member resigned, which represented a significant risk to business continuity. Employees were also averse to multiple passwords and resisted using the systems, affecting staff productivity. With Oracle WebCenter Portal, JPL created a dynamic, secure, and intuitive self-service enterprise portal with business activity streams. The portal allowed users to navigate, discover, and access information, such as advertising rates, requisition approvals, ad-hoc queries, and employee surveys from a single entry point with a single password. Managers can also upload important documents, such as new pricing for advertisers or newspaper distributors, and share them through the information and instruction section in the portal. In addition, managers can now easily track and review timelines for projects online rather than gathering information from meetings and e-mails. The company gained the ability to centrally manage information, ensured business continuity, and improved staff productivity by 40%.“In the media industry, news has a very short shelf life, so speed is crucial. Information delayed is like information lost,” said Sarbani Bhatia, vice president IT, Jagran Prakashahn Ltd. “Thanks to Oracle WebCenter Portal’s contextual collaboration tools, we can provide and share feedback for new project launches, such as career or education supplements, up to 2x faster through discussion forums or knowledge groups. Tasks that previously required four months, we now complete in one month.”In addition, the company can broadcast announcements, flash employee birthdays, and promote important events through the message section on the webpage, instead of using the e-mail system. The company can also conduct opinion polls to gauge employee response to organizational issues and improve management decision-making.“With over 10,000 employees across 300 locations, it is critical for management to hear the voice of employees and develop a cohesive organizational culture. Oracle WebCenter Portal enables employees to engage with business processes and systems in a collaborative environment, providing users with an exceptional experience,” Bhatia said. Enables Mobility Access and Increases Business Agility Newspaper advertisements generate the majority of JPL’s revenue. With most sales staff on the move, the company needed to ensure timely approval of print advertisement discounts for specific clients and meet tight publication deadlines.  By integrating Oracle WebCenter Portal seamlessly with its enterprise resource planning (ERP) system and other applications, such as the organizational mass mailing system, business intelligence, and management information system, JPL embedded its approval workflow processes into the enterprise portal and provided users with an integrated and intuitive interface. About 30% of JPL’s sales staff members now have tablets and receive advertising discount approval from managers while in the field and no longer need to return to the office, which has significantly improved efficiency and increased business agility.“Application mobility was critical for sales representatives in the field to meet stringent auditing requirements for online accountability, particularly for our newspaper advertising business. Staff member satisfaction has improved significantly now that the sales team can use tablets to access the portal––a capability we will extend to smart phones in the second stage of the implementation,” Bhatia said. Accelerates Application Development by up to 4x and Cuts Costs by up to 60% With Oracle WebCenter Portal, users can easily create, modify, and upload information to their personalized webpages without IT assistance. By seamlessly integrating Oracle WebCenter Portal with the payroll database, managers can decide which members of their team can access the page and with whom they will share information, a decision based on role or geographical location. A sales representative selling advertising space for a local language daily newspaper, for example, can upload an updated advertising rate relevant only to that particular publication. Users can also easily adapt to the new platform, thanks to its intuitive design and look, reducing the need for training and lowering resistance to using the system.Using Oracle WebCenter Portal’s out-of-the-box reusable components, such as portal pages and templates, provided JPL’s developers with a comprehensive and flexible user experience platform and increased the speed of application development. In less than five months, JPL developed more than 55 workflows. The IT team accelerated deployment of new applications by up to 4x, as they do not need to install them on individual machines now that they have a web-based environment.   “Previously, we would have spent a whole day deploying a new application for each department or location. With a browser-based environment, we have cut costs by up to 60% by reducing deployment time to zero, because our IT team can roll out a new application from a single point, thanks to Oracle WebCenter Portal,” Bhatia said. Challenges Provide a dynamic, secure, and intuitive self-service enterprise portal to improve staff productivity and ensure business continuity Enable seamless integration with multiple enterprise applications to improve workflow efficiency—including approval of print advertisement discounts—and increase business agility Improve engagement with employees and enable collaboration to enhance management decision-making Accelerate time-to-market for new services, such as new advertising programs Solutions Oracle Product and ServicesOracle WebCenter Portal 11g Increased staff productivity by 40% and enhanced user satisfaction by enabling employees to easily navigate, discover, and access information from a single, self-service enterprise portal without IT assistance Launched new products, such as career or education supplements, up to 2x faster by enabling peer collaboration and incorporating feedback generated through discussion forums, thanks to Oracle WebCenter Portal’s out-of-the-box collaboration tools Accelerated application development up to 4x by enabling developers to optimize reusable components for managing and deploying new applications in a browser-based environment rather than spending one day to install applications for each department, cutting costs by up to 60% Ensured business continuity by enabling managers to easily track and review project timelines online rather than storing important documents on individual laptops or relying on the e-mail system Increased business agility and operational efficiency by seamlessly integrating with the in-house, ERP system and embedding business processes into a single portal Boosted company revenue by enabling sales team members to submit print-advertising discount requests through mobile devices instead of waiting to return to office, ensuring timely approval from managers to meet tight publication deadlines Improved management decision-making by enabling employees to easily share and access feedback through opinion polls or forums, boosting staff morale Introduced the single sign-on capability and enhanced security by enabling managers to decide access level for staff members based on role or geographical location Reduced the need for staff training and minimized user resistance to systems by providing a dynamic and intuitive user experience Why Oracle JPL did not consider other products because the company was already using Oracle Database, Enterprise Edition with Real Application Clusters and had a positive experience with Oracle. JPL chose Oracle WebCenter Portal to ensure no compatibility issues for integration with its existing Oracle products and to take advantage of the experience and support of a reputable vendor to ensure business continuity. “We chose Oracle because we knew we could rely on its support and experience. In addition, Oracle WebCenter Portal’s speed, agility, and mobile access features were a perfect fit for our business requirements,” Bhatia said. Implementation Process JPL launched the enterprise portal to 500 users in the first phase of the project, and plans to extend this to 2,000 users when the portal is fully launched. Oracle partner PricewaterhouseCoopers used Oracle Application Development Framework for the intial set-up, user training and to develop and design sample workflows. JPL’s internal IT staff then took charge of the implementation, bringing it to completion on budget. Partner Oracle PartnerPricewaterhouseCoopers (India)

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• ARM cortex: mutex using bit banding

  - by Jeff V

  Given that, on the ARM Cortex M3, I can: atomically read a single bit atomically set a single bit atomically clear a single bit How can I combine these for a mutex style set of operations: try lock take lock release lock It seems that try_lock or take_lock would require two operations that would not be atomic. Do I need more control to accomplish this? Disable global interrupts would do it but it seems there should be a more surgical approach.

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• Merging two templates in iText

  - by Shaggy Frog

  Let's say I have two PDF templates created with Adobe Acrobat, which are both single-page, 8.5x11 documents. The first template (A.pdf) has content for the top half of the page. The second template (B.pdf) has content for the bottom half of the page. (It just so happens the content in both templates does not "overlap" each other.) I would like to use iText to take these two templates and create a single, "merged" template from it (C.pdf) that is only a single page (with A.pdf's content on the top half and B.pdf's content on the bottom half). (I do not want to "merge" these two files into a 2-page document. I need the final product to be a single page.) I will be running iText in a servlet environment (Tomcat 6) but I don't think that makes a difference to the answer. Is this possible?

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• How to delay static initialization within a property

  - by Mystagogue

  I've made a class that is a cross between a singleton (fifth version) and a (dependency injectable) factory. Call this a "Mono-Factory?" It works, and looks like this: public static class Context { public static BaseLogger LogObject = null; public static BaseLogger Log { get { return LogFactory.instance; } } class LogFactory { static LogFactory() { } internal static readonly BaseLogger instance = LogObject ?? new BaseLogger(null, null, null); } } //USAGE EXAMPLE: //Optional initialization, done once when the application launches... Context.LogObject = new ConLogger(); //Example invocation used throughout the rest of code... Context.Log.Write("hello", LogSeverity.Information); The idea is for the mono-factory could be expanded to handle more than one item (e.g. more than a logger). But I would have liked to have made the mono-factory look like this: public static class Context { private static BaseLogger LogObject = null; public static BaseLogger Log { get { return LogFactory.instance; } set { LogObject = value; } } class LogFactory { static LogFactory() { } internal static readonly BaseLogger instance = LogObject ?? new BaseLogger(null, null, null); } } The above does not work, because the moment the Log property is touched (by a setter invocation) it causes the code path related to the getter to be executed...which means the internal LogFactory "instance" data is always set to the BaseLogger (setting the "LogObject" is always too late!). So is there a decoration or other trick I can use that would cause the "get" path of the Log property to be lazy while the set path is being invoked?

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• NHibernate mapping one table on two classes with where selection

  - by Rene Schulte

  We would like to map a single table on two classes with NHibernate. The mapping has to be dynamically depending on the value of a column. Here's a simple example to make it a bit clearer: We have a table called Person with the columns id, Name and Sex. The data from this table should be mapped either on the class Male or on the class Female depending on the value of the column Sex. In Pseudocode: create instance of Male with data from table Person where Person.Sex = 'm'; create instance of Female with data from table Person where Person.Sex = 'f'; The benefit is we have strongly typed domain models and can later avoid switch statements. Is this possible with NHibernate or do we have to map the Person table into a flat Person class first? Then afterwards we would have to use a custom factory method that takes a flat Person instance and returns a Female or Male instance. Would be good if NHibernate (or another library) can handle this.

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• why sitecolumn title is blank after feature activation....

  - by Rosh Malai

  After installing using stsadmin, and activating using site UI "Site Collection Feature" these columns shows up but no title is showing for them. So no link is attached. It looks like this. Site Column Type Source Car Custom Columns Single line of text SiteCol1 Single line of text SiteCol1 Single line of text SiteCol1 Date and Time SiteCol1 here is feature.xml here is elements.xml StaticName="Car_VinNumber" xmlns="http://schemas.microsoft.com/sharepoint/"

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• Referring to the type of an inner class in Scala

  - by saucisson

  The following code tries to mimic Polymorphic Embedding of DSLs: rather than giving the behavior in Inner, it is encoded in the useInner method of its enclosing class. I added the enclosing method so that user has only to keep a reference to Inner instances, but can always get their enclosing instance. By doing this, all Inner instances from a specific Outer instance are bound to only one behavior (but it is wanted here). abstract class Outer { sealed class Inner { def enclosing = Outer.this } def useInner(x:Inner) : Boolean } def toBoolean(x:Outer#Inner) : Boolean = x.enclosing.useInner(x) It does not compile and scala 2.8 complains about: type mismatch; found: sandbox.Outer#Inner required: _81.Inner where val _81:sandbox.Outer From Programming Scala: Nested classes and A Tour of Scala: Inner Classes, it seems to me that the problem is that useInnerexpects as argument an Inner instance from a specific Outer instance. What is the true explanation and how to solve this problem ?

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• What is the basic pattern for using (N)Hibernate?

  - by Vilx-

  I'm creating a simple Windows Forms application with NHibernate and I'm a bit confused about how I'm supposed to use it. To quote the manual: ISession (NHibernate.ISession) A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps an ADO.NET connection. Factory for ITransaction. Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier. Now, suppose I have the following scenario: I have a simple classifier which is a MSSQL table with two columns - ID (auto_increment) and Name (nvarchar). To edit this classifier I create a form which contains a single gridview and two buttons - OK and Cancel. The user can nearly directly edit the table in the gridview, and when he hits OK the changes he made are persisted to the DB (or if he hits cancel, nothing happens). Now, I have several questions about how to organize this: What should the lifetime of my ISession be? Should I create a single ISession for my whole application; an ISession for each of my forms (the application is single-threaded MDI); or an ISession for every DB operation/transaction? Does NHibernate offer some kind of built-in dirty tracking or must I do this myself? The manual mentions something like it here and there but does not go into details. How is this done? Is there not a huge overhead? Is it somehow tied with the cache(s) that NHibernate has? What are these caches for? Are they not specific to a single ISession? That is, if I use a seperate ISession for every transaction, won't it break the dirty tracking? How does the built-in dirty tracking detect deleted objects?

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• how to reflect the changes of a inastance of a class on other page.

  - by Aarsh Thakur

  hi evary one I have one class.I need the same instance of the same class at two differnt pages with previous values assigend to that instance.? so how to maintain the value of a instance b/w two pages.... Its very urgent ..pls suggest something..?]

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• How to implement Xml Serialization with inherited classes in C#

  - by liorafar

  I have two classes : base class name Component and inheritd class named DBComponent [Serializable] public class Component { private string name = string.Empty; private string description = string.Empty; } [Serializable] public class DBComponent : Component { private List<string> spFiles = new List<string>(); // Storage Procedure Files [XmlArrayItem("SPFile", typeof(string))] [XmlArray("SPFiles")] public List<string> SPFiles { get { return spFiles; } set { spFiles = value; } } public DBComponent(string name, string description) : base(name, description) { } } [Serializable] public class ComponentsCollection { private static ComponentsCollection instance = null; private List<Component> components = new List<Component>(); public List<Component> Components { get { return components; } set { components = value; } } public static ComponentsCollection GetInstance() { if (ccuInstance == null) { lock (lockObject) { if (instance == null) PopulateComponents(); } } return instance; } private static void PopulateComponents() { instance = new CCUniverse(); XmlSerializer xs = new XmlSerializer(instance.GetType()); instance = xs.Deserialize(XmlReader.Create("Components.xml")) as ComponentsCollection; } } } I want read\write from a Xml file. I know that I need to implement the Serialization for DBComponent class otherwise it will not read it.But i cannot find any simple article for that. all the articles that I found were too complex for this simple scenario. The Xml file looks like this: <?xml version="1.0" encoding="utf-8" ?> <ComponentsCollection> <Components> <DBComponent Name="Tenant Historical Database" Description="Tenant Historical Database"> <SPFiles> <SPFile>Setup\TenantHistoricalSP.sql</SPFile> </SPFiles> </DBComponent> <Component Name="Agent" Description="Desktop Agent" /> </Components> </ComponentsCollection> Can someone please give me a simple example of how to read this kind of xml file and what should be implemented ? Thanks Lior

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• ASMLib

  - by wcoekaer

  Oracle ASMlib on Linux has been a topic of discussion a number of times since it was released way back when in 2004. There is a lot of confusion around it and certainly a lot of misinformation out there for no good reason. Let me try to give a bit of history around Oracle ASMLib. Oracle ASMLib was introduced at the time Oracle released Oracle Database 10g R1. 10gR1 introduced a very cool important new features called Oracle ASM (Automatic Storage Management). A very simplistic description would be that this is a very sophisticated volume manager for Oracle data. Give your devices directly to the ASM instance and we manage the storage for you, clustered, highly available, redundant, performance, etc, etc... We recommend using Oracle ASM for all database deployments, single instance or clustered (RAC). The ASM instance manages the storage and every Oracle server process opens and operates on the storage devices like it would open and operate on regular datafiles or raw devices. So by default since 10gR1 up to today, we do not interact differently with ASM managed block devices than we did before with a datafile being mapped to a raw device. All of this is without ASMLib, so ignore that one for now. Standard Oracle on any platform that we support (Linux, Windows, Solaris, AIX, ...) does it the exact same way. You start an ASM instance, it handles storage management, all the database instances use and open that storage and read/write from/to it. There are no extra pieces of software needed, including on Linux. ASM is fully functional and selfcontained without any other components. In order for the admin to provide a raw device to ASM or to the database, it has to have persistent device naming. If you booted up a server where a raw disk was named /dev/sdf and you give it to ASM (or even just creating a tablespace without asm on that device with datafile '/dev/sdf') and next time you boot up and that device is now /dev/sdg, you end up with an error. Just like you can't just change datafile names, you can't change device filenames without telling the database, or ASM. persistent device naming on Linux, especially back in those days ways to say it bluntly, a nightmare. In fact there were a number of issues (dating back to 2004) : Linux async IO wasn't pretty persistent device naming including permissions (had to be owned by oracle and the dba group) was very, very difficult to manage system resource usage in terms of open file descriptors So given the above, we tried to find a way to make this easier on the admins, in many ways, similar to why we started working on OCFS a few years earlier - how can we make life easier for the admins on Linux. A feature of Oracle ASM is the ability for third parties to write an extension using what's called ASMLib. It is possible for any third party OS or storage vendor to write a library using a specific Oracle defined interface that gets used by the ASM instance and by the database instance when available. This interface offered 2 components : Define an IO interface - allow any IO to the devices to go through ASMLib Define device discovery - implement an external way of discovering, labeling devices to provide to ASM and the Oracle database instance This is similar to a library that a number of companies have implemented over many years called libODM (Oracle Disk Manager). ODM was specified many years before we introduced ASM and allowed third party vendors to implement their own IO routines so that the database would use this library if installed and make use of the library open/read/write/close,.. routines instead of the standard OS interfaces. PolyServe back in the day used this to optimize their storage solution, Veritas used (and I believe still uses) this for their filesystem. It basically allowed, in particular, filesystem vendors to write libraries that could optimize access to their storage or filesystem.. so ASMLib was not something new, it was basically based on the same model. You have libodm for just database access, you have libasm for asm/database access. Since this library interface existed, we decided to do a reference implementation on Linux. We wrote an ASMLib for Linux that could be used on any Linux platform and other vendors could see how this worked and potentially implement their own solution. As I mentioned earlier, ASMLib and ODMLib are libraries for third party extensions. ASMLib for Linux, since it was a reference implementation implemented both interfaces, the storage discovery part and the IO part. There are 2 components : Oracle ASMLib - the userspace library with config tools (a shared object and some scripts) oracleasm.ko - a kernel module that implements the asm device for /dev/oracleasm/* The userspace library is a binary-only module since it links with and contains Oracle header files but is generic, we only have one asm library for the various Linux platforms. This library is opened by Oracle ASM and by Oracle database processes and this library interacts with the OS through the asm device (/dev/asm). It can install on Oracle Linux, on SuSE SLES, on Red Hat RHEL,.. The library itself doesn't actually care much about the OS version, the kernel module and device cares. The support tools are simple scripts that allow the admin to label devices and scan for disks and devices. This way you can say create an ASM disk label foo on, currently /dev/sdf... So if /dev/sdf disappears and next time is /dev/sdg, we just scan for the label foo and we discover it as /dev/sdg and life goes on without any worry. Also, when the database needs access to the device, we don't have to worry about file permissions or anything it will be taken care of. So it's a convenience thing. The kernel module oracleasm.ko is a Linux kernel module/device driver. It implements a device /dev/oracleasm/* and any and all IO goes through ASMLib - /dev/oracleasm. This kernel module is obviously a very specific Oracle related device driver but it was released under the GPL v2 so anyone could easily build it for their Linux distribution kernels. Advantages for using ASMLib : A good async IO interface for the database, the entire IO interface is based on an optimal ASYNC model for performance A single file descriptor per Oracle process, not one per device or datafile per process reducing # of open filehandles overhead Device scanning and labeling built-in so you do not have to worry about messing with udev or devlabel, permissions or the likes which can be very complex and error prone. Just like with OCFS and OCFS2, each kernel version (major or minor) has to get a new version of the device drivers. We started out building the oracleasm kernel module rpms for many distributions, SLES (in fact in the early days still even for this thing called United Linux) and RHEL. The driver didn't make sense to get pushed into upstream Linux because it's unique and specific to the Oracle database. As it takes a huge effort in terms of build infrastructure and QA and release management to build kernel modules for every architecture, every linux distribution and every major and minor version we worked with the vendors to get them to add this tiny kernel module to their infrastructure. (60k source code file). The folks at SuSE understood this was good for them and their customers and us and added it to SLES. So every build coming from SuSE for SLES contains the oracleasm.ko module. We weren't as successful with other vendors so for quite some time we continued to build it for RHEL and of course as we introduced Oracle Linux end of 2006 also for Oracle Linux. With Oracle Linux it became easy for us because we just added the code to our build system and as we churned out Oracle Linux kernels whether it was for a public release or for customers that needed a one off fix where they also used asmlib, we didn't have to do any extra work it was just all nicely integrated. With the introduction of Oracle Linux's Unbreakable Enterprise Kernel and our interest in being able to exploit ASMLib more, we started working on a very exciting project called Data Integrity. Oracle (Martin Petersen in particular) worked for many years with the T10 standards committee and storage vendors and implemented Linux kernel support for DIF/DIX, data protection in the Linux kernel, note to those that wonder, yes it's all in mainline Linux and under the GPL. This basically gave us all the features in the Linux kernel to checksum a data block, send it to the storage adapter, which can then validate that block and checksum in firmware before it sends it over the wire to the storage array, which can then do another checksum and to the actual DISK which does a final validation before writing the block to the physical media. So what was missing was the ability for a userspace application (read: Oracle RDBMS) to write a block which then has a checksum and validation all the way down to the disk. application to disk. Because we have ASMLib we had an entry into the Linux kernel and Martin added support in ASMLib (kernel driver + userspace) for this functionality. Now, this is all based on relatively current Linux kernels, the oracleasm kernel module depends on the main kernel to have support for it so we can make use of it. Thanks to UEK and us having the ability to ship a more modern, current version of the Linux kernel we were able to introduce this feature into ASMLib for Linux from Oracle. This combined with the fact that we build the asm kernel module when we build every single UEK kernel allowed us to continue improving ASMLib and provide it to our customers. So today, we (Oracle) provide Oracle ASMLib for Oracle Linux and in particular on the Unbreakable Enterprise Kernel. We did the build/testing/delivery of ASMLib for RHEL until RHEL5 but since RHEL6 decided that it was too much effort for us to also maintain all the build and test environments for RHEL and we did not have the ability to use the latest kernel features to introduce the Data Integrity features and we didn't want to end up with multiple versions of asmlib as maintained by us. SuSE SLES still builds and comes with the oracleasm module and they do all the work and RHAT it certainly welcome to do the same. They don't have to rebuild the userspace library, it's really about the kernel module. And finally to re-iterate a few important things : Oracle ASM does not in any way require ASMLib to function completely. ASMlib is a small set of extensions, in particular to make device management easier but there are no extra features exposed through Oracle ASM with ASMLib enabled or disabled. Often customers confuse ASMLib with ASM. again, ASM exists on every Oracle supported OS and on every supported Linux OS, SLES, RHEL, OL withoutASMLib Oracle ASMLib userspace is available for OTN and the kernel module is shipped along with OL/UEK for every build and by SuSE for SLES for every of their builds ASMLib kernel module was built by us for RHEL4 and RHEL5 but we do not build it for RHEL6, nor for the OL6 RHCK kernel. Only for UEK ASMLib for Linux is/was a reference implementation for any third party vendor to be able to offer, if they want to, their own version for their own OS or storage ASMLib as provided by Oracle for Linux continues to be enhanced and evolve and for the kernel module we use UEK as the base OS kernel hope this helps.

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• C# reflection instantiation

  - by NickLarsen

  I am currently trying to create a generic instance factory for which takes an interface as the generic parameter (enforced in the constructor) and then lets you get instantiated objects which implement that interface from all types in all loaded assemblies. The current implementation is as follows:     public class InstantiationFactory     {         protected Type Type { get; set; }         public InstantiationFactory()         {             this.Type = typeof(T);             if (!this.Type.IsInterface)             {                 // is there a more descriptive exception to throw?                 throw new ArgumentException(/* Crafty message */);             }         }         public IEnumerable GetLoadedTypes()         {             // this line of code found in other stack overflow questions             var types = AppDomain.CurrentDomain.GetAssemblies()                 .SelectMany(a = a.GetTypes())                 .Where(/* lambda to identify instantiable types which implement this interface */);             return types;         }         public IEnumerable GetImplementations(IEnumerable types)         {             var implementations = types.Where(/* lambda to identify instantiable types which implement this interface */                 .Select(x = CreateInstance(x));             return implementations;         }         public IEnumerable GetLoadedImplementations()         {             var loadedTypes = GetLoadedTypes();             var implementations = GetImplementations(loadedTypes);             return implementations;         }         private T CreateInstance(Type type)         {             T instance = default(T);             var constructor = type.GetConstructor(Type.EmptyTypes);             if (/* valid to instantiate test */)             {                 object constructed = constructor.Invoke(null);                 instance = (T)constructed;             }             return instance;         }     } It seems useful to me to have my CreateInstance(Type) function implemented as an extension method so I can reuse it later and simplify the code of my factory, but I can't figure out how to return a strongly typed value from that extension method. I realize I could just return an object:     public static class TypeExtensions     {         public object CreateInstance(this Type type)         {             var constructor = type.GetConstructor(Type.EmptyTypes);             return /* valid to instantiate test */ ? constructor.Invoke(null) : null;         }     } Is it possible to have an extension method create a signature per instance of the type it extends? My perfect code would be this, which avoids having to cast the result of the call to CreateInstance():     Type type = typeof(MyParameterlessConstructorImplementingType);     MyParameterlessConstructorImplementingType usable = type.CreateInstance();

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• How do I improve the efficiency of the queries executed by this generic Linq-to-SQL data access clas

  - by Lee D

  Hi all, I have a class which provides generic access to LINQ to SQL entities, for example: class LinqProvider<T> //where T is a L2S entity class { DataContext context; public virtual IEnumerable<T> GetAll() { return context.GetTable<T>(); } public virtual T Single(Func<T, bool> condition) { return context.GetTable<T>().SingleOrDefault(condition); } } From the front end, both of these methods appear to work as you would expect. However, when I run a trace in SQL profiler, the Single method is executing what amounts to a SELECT * FROM [Table], and then returning the single entity that meets the given condition. Obviously this is inefficient, and is being caused by GetTable() returning all rows. My question is, how do I get the query executed by the Single() method to take the form SELECT * FROM [Table] WHERE [condition], rather than selecting all rows then filtering out all but one? Is it possible in this context? Any help appreciated, Lee

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• Django: Save data from form in DB

  - by Anry

  I have a model: class Cost(models.Model): project = models.ForeignKey(Project) cost = models.FloatField() date = models.DateField() For the model I created a class form: class CostForm(ModelForm): class Meta: model = Cost fields = ['date', 'cost'] view.py: def cost(request, offset): if request.method == 'POST': #HOW save data in DB? return HttpResponseRedirect('/') else: form = CostForm() In the template file determined: <form action="/cost/{{ project }}/" method="post" accept-charset="utf-8"> <label for="date">Date:</label><input type="text" name="date" value={{ current_date }} id="date" /> <label for="cost">Cost:</label><input type="text" name="cost" value="0" id="cost" /> <p><input type="submit" value="Add"></p> </form> How save data from form in DB? P.S. offset = project name Model: class Project(models.Model): title = models.CharField(max_length=150) url = models.URLField() manager = models.ForeignKey(User) timestamp = models.DateTimeField() I tried to write: def cost(request, offset): if request.method == 'POST': form = CostForm(request.POST) if form.is_valid(): instance = form.save(commit=False) instance.project = Project.objects.filter(title=offset) instance.date = request.date instance.cost = request.cost instance.save() return HttpResponseRedirect('/') else: form = CostForm() But it does not work :(

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• Using clases in PHP to store function

  - by Artur

  Hello! I need some advise on my PHP code organisation. I need classes where I can store different functions, and I need access to those classes in different parts of my project. Making an object of this classes each time is too sadly, so I've found a two ways have to solve it. First is to use static methods, like class car { public static $wheels_count = 4; public static function change_wheels_count($new_count) { car::$wheels_count = $new_count; } } Second is to use singleton pattern: class Example { // Hold an instance of the class private static $instance; // The singleton method public static function singleton() { if (!isset(self::$instance)) { $c = __CLASS__; self::$instance = new $c; } return self::$instance; } } But author of the article about singletons said, that if I have too much singletons in my code I should reconstruct it. But I need a lot of such classes. Can anybody explain prons and cons of each way? Which is mostly used? Are there more beautiful ways?

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• Java dynamic proxy questions.

  - by Tony

  1.Does dynamic proxy instance subclass the target class? The java doc says the proxy instance implements "a list of interfaces", says nothing about subclassing, but through debugging, I saw that the proxy instance did inherit the target class properites.What does the "a list of interfaces " mean? Can I exclude those interfaces implemented by target class ? 2.Can I invoke target class specific methods on a proxy instance? 3. I think dynamic proxy is an interface methods invocation proxy but rather than a target class proxy, is that right (I am deeply infected by hibernate proxy object concept)?

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• Calling 32 bit unmanaged dlls from C# randomly failing

  - by Bert

  Hi, I'm having an issue when calling 32 bit delphi dll's from c# web site. The code generally runs fine, but occasionally I get an error Unable to load DLL '': The specified module could not be found. (Exception from HRESULT: 0x8007007E). This issue persists until I recycle the app pool for the site, and then it works fine again. On the same server, there is also a web service that is calling the same set of dlls. This web service doesn't seem to have the same issue that the web site has. Both applications are using .net framework 3.5, separate app pools on IIS. Here is the code I'm using to wrap the dlls: public sealed class Mapper { static Mapper instance = null; [DllImport("kernel32.dll")] private static extern bool SetDllDirectory(string lpPathName); private Mapper() { SetDllDirectory(ConfigManager.Path); } public static Mapper Instance { get { if (instance == null) { instance = new Mapper(); } return instance; } } public int Foo(string bar, ref double val) { return Loader.Foo(bar, ref val); } } public static class Loader { [DllImport("some.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Unicode, EntryPoint = "foo")] public static extern int Foo(string bar, ref double val); } Then I call it like this: double val = 0.0; Mapper.Instance.Foo("bar", ref val); Any ideas as to why it would "randomly" Unable to load DLL '': The specified module could not be found. (Exception from HRESULT: 0x8007007E). The other problem is that I haven't been able to replicate the issue in the development environment. I thought that due to 2 applications calling the same dlls, that there could be some locks occurring. To replicate this, I created an app that spawned multiple threads and repeatedly called the 32bit dlls, and then used the web site to call these same dlls. I still couldn't replicate the issue. Some possible fixes that I can think of: Wrap the 32 bit dlls in web service (because the webservice doesn't seem to suffer from the same problem). But this may be worthless if it turns out that the web service also fails. Set up state server for the session state and periodically recycle the app pool for the site.This isn't fixing the problem, only avoiding it. Wrap the dll's in exe, and call that exe. Then I shouldn't get the same issue. But this also seems like a hacky solution. Implement the mapper class differently ? But how else should I be doing the call? The other draw back is that other applications are using this mapper, so I'd need to change there code too. Thanks

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• Why this Either-monad code does not type check?

  - by pf_miles

  instance Monad (Either a) where return = Left fail = Right Left x >>= f = f x Right x >>= _ = Right x this code frag in 'baby.hs' caused the horrible compilation error: Prelude> :l baby [1 of 1] Compiling Main ( baby.hs, interpreted ) baby.hs:2:18: Couldn't match expected type `a1' against inferred type `a' `a1' is a rigid type variable bound by the type signature for `return' at <no location info> `a' is a rigid type variable bound by the instance declaration at baby.hs:1:23 In the expression: Left In the definition of `return': return = Left In the instance declaration for `Monad (Either a)' baby.hs:3:16: Couldn't match expected type `[Char]' against inferred type `a1' `a1' is a rigid type variable bound by the type signature for `fail' at <no location info> Expected type: String Inferred type: a1 In the expression: Right In the definition of `fail': fail = Right baby.hs:4:26: Couldn't match expected type `a1' against inferred type `a' `a1' is a rigid type variable bound by the type signature for `>>=' at <no location info> `a' is a rigid type variable bound by the instance declaration at baby.hs:1:23 In the first argument of `f', namely `x' In the expression: f x In the definition of `>>=': Left x >>= f = f x baby.hs:5:31: Couldn't match expected type `b' against inferred type `a' `b' is a rigid type variable bound by the type signature for `>>=' at <no location info> `a' is a rigid type variable bound by the instance declaration at baby.hs:1:23 In the first argument of `Right', namely `x' In the expression: Right x In the definition of `>>=': Right x >>= _ = Right x Failed, modules loaded: none. why this happen? and how could I make this code compile ? thanks for any help~

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