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• Primary reasons why programming language runtimes use stacks?

  - by manuel aldana

  Many programming language runtime environments use stacks as their primary storage structure (e.g. see JVM bytecode to runtime example). Quickly recalling I see following advantages: Simple structure (pop/push), trivial to implement Most processors are anyway optimized for stack operations, so it is very fast Less problems with memory fragmentation, it is always about moving memory-pointer up and down for allocation and freeing complete blocks of memory by resetting the pointer to the last entry offset. Is the list complete or did I miss something? Are there programming language runtime environments which are not using stacks for storage at all?

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• A general question about compilation and interpretation.

  - by wucnuc

  Hi stackoverflow, I apologize in advance for the possible stupidity of this question. However, the following has been the source of some confusion for me and I know the people here will be able to handily clear up the confusion for me. Basically, I would like to finally understand the relationship between any and all of the following terms. Some of the terms I do actually understand pretty well, but some of them are similar in my mind and I would like to once and for all to see their relationships/distinctions laid out all at once. They are: compiler interpreter bytecode machine code assembler assembly language binary object code executable Ideally, an answer would use examples from Java and C++ and other well-known programming languages that a young-ish student like me would be familiar with. Also, if you want to throw in any other useful terms that would be fine too :)

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• Dynamically generating high performance functions in clojure

  - by mikera

  I'm trying to use Clojure to dynamically generate functions that can be applied to large volumes of data - i.e. a requirement is that the functions be compiled to bytecode in order to execute fast, but their specification is not known until run time. e.g. suppose I specify functions with a simple DSL like: (def my-spec [:add [:multiply 2 :param0] 3]) I would like to create a function compile-spec such that: (compile-spec my-spec) Would return a compiled function of one parameter x that returns 2x+3. What is the best way to do this in Clojure?

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• Ways to optimize Android App code based on function call stack?

  - by K-RAN

  I've been told that Android OS stores all function calls in a stack. This can lead to many problems and cause the 'hiccups' during runtime, even if a program is functionalized properly, correct? So the question is, how can we prevent this from happening? The obvious solution is to functionalize less, along with other sensible acts such as refraining from excessively/needlessly creating objects, performing static calls to functions that don't access fields, etc... Is there another way though? Or can this only be done through careful code writing on the programmers' part? Does the JVM/JIT automatically optimize the bytecode during compile time to account for this?? Thanks a lot for your responses!!

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• How can creating the SessionFactory become slow after updating Hibernate?

  - by DR

  In my Java SE application I used Hibernate 3.4 and creating the SessionFactory took about 5 seconds. Today I updated to Hibernate 3.5.1 and suddenly it takes over a minute. What can be the cause of such a dramatic effect? I tried different things the better part of the day and I have no clue... Some data I collected According to the profiler the most time is spent in PersisterFactory.createClassPersister and in that method ProxyFactory.createClass takes the most time. The log shows nothing unusual Changing hibernate.bytecode.use_reflection_optimizer makes no difference

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• Performance: float to int cast and clippling result to range

  - by durandai

  I'm doing some audio processing with float. The result needs to be converted back to PCM samples, and I noticed that the cast from float to int is surprisingly expensive. Whats furthermore frustrating that I need to clip the result to the range of a short (-32768 to 32767). While I would normally instictively assume that this could be assured by simply casting float to short, this fails miserably in Java, since on the bytecode level it results in F2I followed by I2S. So instead of a simple: int sample = (short) flotVal; I needed to resort to this ugly sequence: int sample = (int) floatVal; if (sample > 32767) { sample = 32767; } else if (sample < -32768) { sample = -32768; } Is there a faster way to do this? (about ~6% of the total runtime seems to be spent on casting, while 6% seem to be not that much at first glance, its astounding when I consider that the processing part involves a good chunk of matrix multiplications and IDCT)

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• Can I add and remove elements of enumeration at runtime in Java

  - by Brabster

  It is possible to add and remove elements from an enum in Java at runtime? For example, could I read in the labels and constructor arguments of an enum from a file? @saua, it's just a question of whether it can be done out of interest really. I was hoping there'd be some neat way of altering the running bytecode, maybe using BCEL or something. I've also followed up with this question because I realised I wasn't totally sure when an enum should be used. I'm pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.

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• Is Android IPC plumbing exposed in any official and/or supported way?

  - by mathrick

  I'm interested in knowing how much the IPC mechanisms are meant to be exposed to the outside world. That is, if I wanted to impersonate a dalvik VM instance without having my app actually written in Java, am I allowed to do so, or will the protocol change the next time I look away from the screen? If it's allowed, what are the stability guarantees or lack thereof? Is there anything like documentation, or am I supposed just to read the fine sources on android.git.kernel.org? The purpose of it all would be to write apps in !Java languages while retaining the ability to construct GUIs. I don't care or mind if the code is technically inside a dalvik process as a JNI callout, what I'm interested in is "if I'm really good at pretending I'm Java over the wire, can I do everything actual Java code can? Or is there something that's only available as Java bytecode and nothing else?"

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• Annotation retention policy: what real benefit is there in declaring `SOURCE` or `CLASS`?

  - by watery

  I know there are three retention policies for Java annotations: CLASS: Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time. RUNTIME: Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively. SOURCE: Annotations are to be discarded by the compiler. And although I understand their usage scenarios, I don't get why it is such an important thing to specify the retention policy that retention policies exist at all. I mean, why aren't all the annotations just kept at runtime? Do they generate so much bytecode / occupy so much memory that stripping those undeclared as RUNTIME does make that much difference?

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• How to compare Rails ''executables" before and after refactor?

  - by Kyle Heironimus

  In C, I could generate an executable, do an extensive rename only refactor, then compare executables again to confirm that the executable did not change. This was very handy to ensure that the refactor did not break anything. Has anyone done anything similar with Ruby, particularly a Rails app? Strategies and methods would be appreciated. Ideally, I could run a script that output a single file of some sort that was purely bytecode and was not changed by naming changes. I'm guessing JRuby or Rubinus would be helpful here.

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• A brief note for customers running SOA Suite on AIX platforms

  - by christian

  When running Oracle SOA Suite with IBM JVMs on the AIX platform, we have seen performance slowdowns and/or memory leaks. On occasion, we have even encountered some OutOfMemoryError conditions and the concomittant Java coredump. If you are experiencing this issue, the resolution may be to configure -Dsun.reflect.inflationThreshold=0 in your JVM startup parameters. https://www.ibm.com/developerworks/java/library/j-nativememory-aix/ contains a detailed discussion of the IBM AIX JVM memory model, but I will summarize my interpretation and understanding of it in the context of SOA Suite, below. Java ClassLoaders on IBM JVMs are allocated a native memory area into which they are anticipated to map such things as jars loaded from the filesystem. This is an excellent memory optimization, as the file can be loaded into memory once and then shared amongst many JVMs on the same host, allowing for excellent horizontal scalability on AIX hosts. However, Java ClassLoaders are not used exclusively for loading files from disk. A performance optimization by the Oracle Java language developers enables reflectively accessed data to optimize from a JNI call into Java bytecodes which are then amenable to hotspot optimizations, amongst other things. This performance optimization is called inflation, and it is executed by generating a sun.reflect.DelegatingClassLoader instance dynamically to inject the Java bytecode into the virtual machine. It is generally considered an excellent optimization. However, it interacts very negatively with the native memory area allocated by the IBM JVM, effectively locking out memory that could otherwise be used by the Java process. SOA Suite and WebLogic are both very large users of reflection code. They reflectively use many code paths in their operation, generating lots of DelegatingClassLoaders in normal operation. The IBM JVM slowdown and subsequent OutOfMemoryError are as a direct result of the Java memory consumed by the DelegatingClassLoader instances generated by SOA Suite and WebLogic. Java garbage collection runs more frequently to try and keep memory available, until it can no longer do so and throws OutOfMemoryError. The setting sun.reflect.inflationThreshold=0 disables this optimization entirely, never allowing the JVM to generate the optimized reflection code. IBM JVMs are susceptible to this issue primarily because all Java ClassLoaders have this native memory allocation, which is shared with the regular Java heap. Oracle JVMs don't automatically give all ClassLoaders a native memory area, and my understanding is that jar files are never mapped completely from shared memory in the same way as IBM does it. This results in different behaviour characteristics on IBM vs Oracle JVMs.

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• What's about Java?

  - by Silviu Turuga

  What is Java? In very short words, Java is a programming language that let you make an application that can be run on different operating systems, no matter we are talking about Windows, Mac OS, Linux or even embedded devices, such as RaspberryPi. When you compile a Java program, instead of getting a binary output as you get on other programming languages, you'll get a Java intermediate code, called Java bytecode. This is interpreted at run time, by a virtual machine that is specifically for the hardware and operating system you are using. What Java do i need? There are 5 major versions of Java: Java SE(Standard Edition) - this is what I'll use on most of my tutorials. Most of the examples will run on Java 6, but for others you'll need Java 7. Java EE (Enterprise Edition) - used for enterprise development Java ME (Micro Edition) - for running Java on mobile and different embedded devices such as PDAs, TV set-top boxes, printers, etc. Java Embedded - for some embedded devices such as Raspberry Pi, where the resources are limited JavaFX - to develop rich content User Interfaces. This is also something that will use a lot. More detailed information can be found on Oracle's website If you just want to run java applications you'll need the JRE (Java Runtime Environment) installed. If you want to program and create new applications, then you'll need the JDK (Java Development Kit).  How to check if Java is already installed? From command line, if you are on Windows, or from Terminal on Mac enter the following: java -version You should get something like this, if you have java installed on your system: java version "1.6.0_37" Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909) Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode) Note: your current Java version might be different from mine. More information https://www.java.com/en/download/faq/whatis_java.xml http://en.wikipedia.org/wiki/Java_(programming_language) Next steps Install Java SDK Chose an IDE. I recommend NetBeans as it is very easy to use and also let you quickly create the GUI of your application Alternatives are Eclipse, Komodo Edit (for Mac), etc. There are plenty of solutions both free or paid. Resources on web Oracle Tutorials - lot of tutorials and useful resources JavaRanch - forum about java

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• calculate AUC (GAM) in R [migrated]

  - by ahmad

  I used the following script to calculate AUC in R: library(mgcv) library(ROCR) library(AUC) data1=read.table("d:\\2005.txt", header=T) GAM<-gam(tuna ~ s(chla)+s(sst)+s(ssha),family=binomial, data=data1) gampred<- predict(GAM, type="response") rp <- prediction(gampred, data1$tuna) auc <- performance( rp, "auc")@y.values[[1]] auc roc <- performance( rp, "tpr", "fpr") plot( roc ) But when I was running the script, the result is: **rp <- prediction(gampred, data1$tuna) Error in prediction(gampred, data1$tuna) : Format of predictions is invalid. > > auc <- performance( rp, "auc")@y.values[[1]] Error in performance(rp, "auc") : object 'rp' not found > auc function (x, min = 0, max = 1) { if (any(class(x) == "roc")) { if (min != 0 || max != 1) { x$fpr <- x$fpr[x$cutoffs >= min & x$cutoffs <= max] x$tpr <- x$tpr[x$cutoffs >= min & x$cutoffs <= max] } ans <- 0 for (i in 2:length(x$fpr)) { ans <- ans + 0.5 * abs(x$fpr[i] - x$fpr[i - 1]) * (x$tpr[i] + x$tpr[i - 1]) } } else if (any(class(x) %in% c("accuracy", "sensitivity", "specificity"))) { if (min != 0 || max != 1) { x$cutoffs <- x$cutoffs[x$cutoffs >= min & x$cutoffs <= max] x$measure <- x$measure[x$cutoffs >= min & x$cutoffs <= max] } ans <- 0 for (i in 2:(length(x$cutoffs))) { ans <- ans + 0.5 * abs(x$cutoffs[i - 1] - x$cutoffs[i]) * (x$measure[i] + x$measure[i - 1]) } } return(as.numeric(ans)) } <bytecode: 0x03012f10> <environment: namespace:AUC> > > roc <- performance( rp, "tpr", "fpr") Error in performance(rp, "tpr", "fpr") : object 'rp' not found > plot( roc ) Error in levels(labels) : argument "labels" is missing, with no default** Can anybody help me to solve this problem? Thank you in advance.

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• Sprinkle Some Magik on that Java Virtual Machine

  - by Jim Connors

  GE Energy, through its Smallworld subsidiary, has been providing geospatial software solutions to the utility and telco markets for over 20 years.  One of the fundamental building blocks of their technology is a dynamically-typed object oriented programming language called Magik.  Like Java, Magik source code is compiled down to bytecodes that run on a virtual machine -- in this case the Magik Virtual Machine. Throughout the years, GE has invested considerable engineering talent in the support and maintenance of this virtual machine.  At the same time vast energy and resources have been invested in the Java Virtual Machine. The question for GE has been whether to continue to make that investment on its own or to leverage massive effort provided by the Java community? Utilizing the Java Virtual Machine instead of maintaining its own virtual machine would give GE more opportunity to focus on application solutions.   At last count, there are dozens, perhaps hundreds of examples of programming languages that have been hosted atop the Java Virtual Machine.  Prior to the release of Java 7, that effort, although certainly possible, was generally less than optimal for languages like Magik because of its dynamic nature.  Java, as a statically typed language had little use for this capability.  In the quest to be a more universal virtual machine, Java 7, via JSR-292, introduced a new bytecode called invokedynamic.  In short, invokedynamic affords a more flexible method call mechanism needed by dynamic languages like Magik. With this new capability GE Energy has succeeded in hosting their Magik environment on top of the Java Virtual Machine.  So you may ask, why would GE wish to do such a thing?  The benefits are many: Competitors to GE Energy claimed that the Magik environment was proprietary.  By utilizing the Java Virtual Machine, that argument gets put to bed.  JVM development is done in open source, where contributions are made world-wide by all types of organizations and individuals. The unprecedented wealth of class libraries and applications written for the Java platform are now opened up to Magik/JVM platform as first class citizens. In addition, the Magik/JVM solution vastly increases the developer pool to include the 9 million Java developers -- the largest developer community on the planet. Applications running on the JVM showed substantial performance gains, in some cases as much as a 5x speed up over the original Magik platform. Legacy Magik applications can still run on the original platform.  They can be seamlessly migrated to run on the JVM by simply recompiling the source code. GE can now leverage the huge Java community.  Undeniably the best virtual machine ever created, hundreds if not thousands of world class developers continually improve, poke, prod and scrutinize all aspects of the Java platform.  As enhancements are made, GE automatically gains access to these. As Magik has little in the way of support for multi-threading, GE will benefit from current and future Java offerings (e.g. lambda expressions) that aim to further facilitate multi-core/multi-threaded application development. As the JVM is available for many more platforms, it broadens the reach of Magik, including the potential to run on a class devices never envisioned just a few short years ago.  For example, Java SE compatible runtime environments are available for popular embedded ARM/Intel/PowerPC configurations that could theoretically host this software too. As compared to other JVM language projects, the Magik integration differs in that it represents a serious commercial entity betting a sizable part of its business on the success of this effort.  Expect to see announcements not only from General Electric, but other organizations as they realize the benefits of utilizing the Java Virtual Machine.

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• Crazy idea: Connect .NET and SAP with SAP JCo using IKVM.NET

  - by Kottan

  Because the SAP Connector for .NET is no longer maintained by SAP, I am now looking for an alternative to connect the Microsoft world with the SAP world. I know there a third party products like ERPConnect, but I want to do this with tools from SAP. Therefore there arised the crazy idea to use the SAP Java Connector in combination with the tool IKVM.NET (www.ikvm.net/devguide/net2java.html). IKVM.NET provides The IKVMC tool, which converts Java bytecode to .NET dll's and exe's. "No sooner said than done!" I converted the SAP JCo to .NET dlls and created a new Visual Studio solution. I put all the JCO files into a subdirectory of my solution. I set 2 references to the generated IKVM.OpenJDK.Core.dll and sapjco.dll. Great, all JCO classes where now available as .NET classes. Full of optimism I wrote some little code to connect to a SAP system. JCO.Client client = null; client = JCO.createClient(...) The compiliation of my testcode had no errors. "Wonderful !" I thought. Then I started my tetstapplication. Unfortunately I got an exception calling JCO.createClient: Could not load middleware layer 'com.sap.mw.jco.rfc.MiddlewareRFC'\r\nno sapjcorfc in java.library.path I have 2 questions on this topic. 1) Do you think my idea using SAP Java Connector to connect .NET with SAP is a good idea or is it nonsens ? Perhaps someone had already the same idea ;-) 2) How can the above exception be solved ?

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• Why 'timeout expired' exception thrown with StructureMap?

  - by Martin

  I'm getting a "timeout expired" exception thrown from a relatively heavily trafficked ASP.NET MVC 2 site I developed using StructureMap and Fluent NHibernate. I think that perhaps the connections aren't being disposed properly. What do you think may be causing this? Could it be my use of InstanceScope.Hybrid? Here's my NHibernateRegistry class; thanks in advance for your help: using MyProject.Core.Persistence.Impl; using FluentNHibernate.Cfg; using FluentNHibernate.Cfg.Db; using NHibernate; using NHibernate.ByteCode.LinFu; using NHibernate.Cfg; using MyProject.Core.FluentMapping; using StructureMap.Attributes; using StructureMap.Configuration.DSL; namespace MyProject.Core.Persistence { public class NHibernateRegistry : Registry { public NHibernateRegistry() { FluentConfiguration cfg = Fluently.Configure() .Database(MsSqlConfiguration.MsSql2005.ConnectionString( x => x.FromConnectionStringWithKey( "MyConnectionString")) .ProxyFactoryFactory(typeof (ProxyFactoryFactory).AssemblyQualifiedName)) .Mappings(m => m.FluentMappings.AddFromAssemblyOf<EntryMap>()); Configuration configuration = cfg.BuildConfiguration(); ISessionFactory sessionFactory = cfg.BuildSessionFactory(); ForRequestedType<Configuration>().AsSingletons() .TheDefault.IsThis(configuration); ForRequestedType<ISessionFactory>().AsSingletons() .TheDefault.IsThis(sessionFactory); ForRequestedType<ISession>().CacheBy(InstanceScope.Hybrid) .TheDefault.Is.ConstructedBy(ctx => ctx.GetInstance<ISessionFactory>().OpenSession()); ForRequestedType<IUnitOfWork>().CacheBy(InstanceScope.Hybrid) .TheDefaultIsConcreteType<UnitOfWork>(); ForRequestedType<IDatabaseBuilder>().TheDefaultIsConcreteType<DatabaseBuilder>(); } } }

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• What's all this fuss about?

  - by atch

  Hi guys, At the beginning I want to state that it is not my intention to upset anyone who uses/like language other than C++. I'm saying that due to the fact that on one forum everytime when I've tried to ask questions of similiar nature I was almost always accused of trying to create a raw. Ok that's having done this is my question: I don't understand why java/c# creators thought/think that having something like vm and having source code compiled to bytecode instead of native code is in a long run any advantage. And why having function compiled for a first time when they are invoked is any advantege? And what's the story about write once run everywhere? When I think about the business of having something written once and it can run everywhere - well in theory this is all well. But I know for a fact that in practice it doesn't look that well at all. It is rather like write once test everywhere. And why would I preffer something to be compiled on runtime instead of compiletime. If I would have to wait even one hour longer for program to be installed once and for all and all the compilation would be done and nothing would be compiled after that I would preffer that. And I don't really know how it works in the real world (I'm a student never worked in IT business) but for example if I have working program written in C++ for Windows and I have wish to move it to another platform wouldn't I have to take my source code and compile it on desired machine? So in other words isn't that rather problem of having compiler which will compile source code on different machines (as far as I'm concerned there is just one C++ and source code will look identical in every machine). And last but not least if you think about it how many programs they are which are really word porting? I personnally can think of 3 maybe four.

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• Why does Java's invokevirtual need to resolve the called method's compile-time class?

  - by Chris

  Consider this simple Java class: class MyClass { public void bar(MyClass c) { c.foo(); } } I want to discuss what happens on the line c.foo(). At the bytecode level, the meat of c.foo() will be the invokevirtual opcode, and, according to the documentation for invokevirtual, more or less the following will happen: Look up the foo method defined in compile-time class MyClass. (This involves first resolving MyClass.) Do some checks, including: Verify that c is not an initialization method, and verify that calling MyClass.foo wouldn't violate any protected modifiers. Figure out which method to actually call. In particular, look up c's runtime type. If that type has foo(), call that method and return. If not, look up c's runtime type's superclass; if that type has foo, call that method and return. If not, look up c's runtime type's superclass's superclass; if that type has foo, call that method and return. Etc.. If no suitable method can be found, then error. Step #3 alone seems adequate for figuring out which method to call and verifying that said method has the correct argument/return types. So my question is why step #1 gets performed in the first place. Possible answers seem to be: You don't have enough information to perform step #3 until step #1 is complete. (This seems implausible at first glance, so please explain.) The linking or access modifier checks done in #1 and #2 are essential to prevent certain bad things from happening, and those checks must be performed based on the compile-time type, rather than the run-time type hierarchy. (Please explain.)

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• NHibernate with Framework .NET Framework 2

  - by Daniel Dolz

  Hi. I can not make NHibernate 2.1 work in machines without framework 3.X (basically, windows 2000 SP4, although it happens with XP too). NHibernate doc do no mention this. Maybe you can help? I NEED to make NHibernate 2.1 work in Windows 2000 PCs, so you think this can be done? Thanks! PD: DataBase is SQL 2000/2005. Error is: NHibernate.MappingException: Could not compile the mapping document: Datos.NH_VEN_ComprobanteBF.hbm.xml ---> NHibernate.HibernateException: Could not instantiate dialect class NHibernate.Dialect.MsSql2000Dialect ---> System.Reflection.TargetInvocationException: Se produjo una excepción en el destino de la invocación. ---> System.TypeInitializationException: Se produjo una excepción en el inicializador de tipo de 'NHibernate.NHibernateUtil'. ---> System.TypeLoadException: No se puede cargar el tipo 'System.DateTimeOffset' del ensamblado'mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. en NHibernate.Type.DateTimeOffsetType.get_ReturnedClass() en NHibernate.NHibernateUtil..cctor() --- Fin del seguimiento de la pila de la excepción interna --- en NHibernate.Dialect.Dialect..ctor() en NHibernate.Dialect.MsSql2000Dialect..ctor() --- Fin del seguimiento de la pila de la excepción interna --- en System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) en System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) en System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) en System.Activator.CreateInstance(Type type, Boolean nonPublic) en NHibernate.Bytecode.ActivatorObjectsFactory.CreateInstance(Type type) en NHibernate.Dialect.Dialect.InstantiateDialect(String dialectName) --- Fin del seguimiento de la pila de la excepción interna --- en NHibernate.Dialect.Dialect.InstantiateDialect(String dialectName) en NHibernate.Dialect.Dialect.GetDialect(IDictionary`2 props) en NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) --- Fin del seguimiento de la pila de la excepción interna --- en NHibernate.Cfg.Configuration.LogAndThrow(Exception exception) en NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) en NHibernate.Cfg.Configuration.ProcessMappingsQueue() and continues...

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• Why use SQL database?

  - by martinthenext

  I'm not quite sure stackoverflow is a place for such a general question, but let's give it a try. Being exposed to the need of storing application data somewhere, I've always used MySQL or sqlite, just because it's always done like that. As it seems like the whole world is using these databases, most of all software products, frameworks, etc. It is rather hard for a beginning developer like me to ask a question - why? Ok, say we have some object-oriented logic in our application, and objects are related to each other somehow. We need to map this logic to the storage logic, so we need relations between database objects too. This leads us to using relational database and I'm ok with that - to put it simple, our database rows sometimes will need to have references to other tables' rows. But why do use SQL language for interaction with such a database? SQL query is a text message. I can understand this is cool for actually understanding what it does, but isn't it silly to use text table and column names for a part of application that no one ever seen after deploynment? If you had to write a data storage from scratch, you would have never used this kind of solution. Personally, I would have used some 'compiled db query' bytecode, that would be assembled once inside a client application and passed to the database. And it surely would name tables and colons by id numbers, not ascii-strings. In the case of changes in table structure those byte queries could be recompiled according to new db schema, stored in XML or something like that. What are the problems of my idea? Is there any reason for me not to write it myself and to use SQL database instead?

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• searching for a programming platform with hot code swap

  - by Andreas

  I'm currently brainstorming over the idea how to upgrade a program while it is running. (Not while debugging, a "production" system.) But one thing that is required for it, is to actually submit the changed source code or compiled byte code into the running process. Pseudo Code var method = typeof(MyClass).GetMethod("Method1"); var content = //get it from a database (bytecode or source code) SELECT content FROM methods WHERE id=? AND version=? method.SetContent(content); At first, I want to achieve the system to work without the complexity of object-orientation. That leads to the following requirements: change source code or byte code of function drop functions add new functions change the signature of a function With .NET (and others) I could inject a class via an IoC and could thus change the source code. But the loading would be cumbersome, because everything has to be in an Assembly or created via Emit. Maybe with Java this would be easier? The whole ClassLoader is replacable, I think. With JavaScript I could achieve many of the goals. Simply eval a new function (MyMethod_V25) and assign it to MyClass.prototype.MyMethod. I think one can also drop functions somehow with "del" Which general-purpose platform can handle such things?

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• Debian packaging of a Python package.

  - by chrisdew

  I need to write (or find) a script to create a Debian package (using python-support) from a Python package. The Python package will be pure Python (no C extensions). The Python package (for testing purposes) will just be a directory with an empty __init__.py file and a single Python module, package_test.py. The packaging script must use python-support to provide the correct bytecode for possible multiple installations of Python on a target platform. (i.e. v2.5 and v2.6 on Ubuntu Jaunty.) Most advice I find while googling are just examples nasty hacks that don't even use python-support or python-central. I have so far spent hours researching this, and the best I can come up with is to hack around the script from an existing open source project - but I don't know which bits are required for what I'm doing. Has anyone here made a Debian package out of a Python package in a reasonably non-hacky way? I'm starting to think that it will take me more than a week to go from no knowledge of Debian packaging and python-support to getting a working script. How long has it taken others? Any advice? Chris.

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• Running an existing LINQ query against a dynamic object (DataTable like)

  - by TomTom

  Hello, I am working on a generic OData provider to go against a custom data provider that we have here. Thsi is fully dynamic in that I query the data provider for the table it knows. I have a basic storage structure in place so far based on the OData sample code. My problem is: OData supports queries and expects me to hand in an IQueryable implementation. On the lowe rside, I dont have any query support. Not a joke - the provider returns tables and the WHERE clause is not supported. Performance is not an issue here - the tables are small. It is ok to sort them in the OData provider. My main problem is this. I submit a SQL statement to get out the data of a table. The result is some sort of ADO.NET data reader here. I need to expose an IQueryable implementation for this data to potentially allow later filtering. Any ide ahow to best touch that? .NET 3.5 only (no 4.0 planned for some time). I was seriously thinking of creating dynamic DTO classes for every table (emitting bytecode) so I can use standard LINQ. Right now I am using a dictionary per entry (not too efficient) but I see no real way to filter / sort based on them.

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• Hibernate - Problem in parsing mapping file (.hbm.xml)

  - by Yatendra Goel

  I am new to Hibernate. I have an exception while running an Hibernate-based application. The exception is as follows: 16 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.3.2.GA 16 [main] INFO org.hibernate.cfg.Environment - hibernate.properties not found 16 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : javassist 31 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4 java.sql.Timestamp handling 94 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: /hibernate.cfg.xml 94 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml 219 [main] INFO org.hibernate.cfg.Configuration - Reading mappings from resource : app/data/City.hbm.xml 266 [main] ERROR org.hibernate.util.XMLHelper - Error parsing XML: XML InputStream(12) Attribute "coloumn" must be declared for element type "property". 266 [main] ERROR org.hibernate.util.XMLHelper - Error parsing XML: XML InputStream(13) Attribute "coloumn" must be declared for element type "property". 266 [main] ERROR org.hibernate.util.XMLHelper - Error parsing XML: XML InputStream(14) Attribute "coloumn" must be declared for element type "property". It seems that it is not finding coloumn attribute of the property element in the mappings file but my mappings file do have the coloumn attribute. Below is the mappings file (City.hbm.xml) <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="app.data"> <class name="City" table="CITY"> <id column="CITY_ID" name="cityId"> <generator class="native"/> </id> <property name="cityDisplyaName" coloumn="CITY_DISPLAY_NAME" /> <property coloumn="CITY_MEANINGFUL_NAME" name="cityMeaningFulName" /> <property coloumn="CITY_URL" name="cityURL" /> </class> </hibernate-mapping>

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• Why do case class companion objects extend FunctionN?

  - by retronym

  When you create a case class, the compiler creates a corresponding companion object with a few of the case class goodies: an apply factory method matching the primary constructor, equals, hashCode, and copy. Somewhat oddly, this generated object extends FunctionN. scala> case class A(a: Int) defined class A scala> A: (Int => A) res0: (Int) => A = <function1> This is only the case if: There is no manually defined companion object There is exactly one parameter list There are no type arguments The case class isn't abstract. Seems like this was added about two years ago. The latest incarnation is here. Does anyone use this, or know why it was added? It increases the size of the generated bytecode a little with static forwarder methods, and shows up in the #toString() method of the companion objects: scala> case class A() defined class A scala> A.toString res12: java.lang.String = <function0>

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