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Thread management advice - Is TPL a good idea?

- by Ian

I'm hoping to get some advice on the use of thread managment and hopefully the task parallel library, because I'm not sure I've been going down the correct route. Probably best is that I give an outline of what I'm trying to do. Given a Problem I need to generate a Solution using a heuristic based algorithm. I start of by calculating a base solution, this operation I don't think can be parallelised so we don't need to worry about. Once the inital solution has been generated, I want to trigger n threads, which attempt to find a better solution. These threads need to do a couple of things: They need to be initalized with a different 'optimization metric'. In other words they are attempting to optimize different things, with a precedence level set within code. This means they all run slightly different calculation engines. I'm not sure if I can do this with the TPL.. If one of the threads finds a better solution that the currently best known solution (which needs to be shared across all threads) then it needs to update the best solution, and force a number of other threads to restart (again this depends on precedence levels of the optimization metrics). I may also wish to combine certain calculations across threads (e.g. keep a union of probabilities for a certain approach to the problem). This is probably more optional though. The whole system needs to be thread safe obviously and I want it to be running as fast as possible. I tried quite an implementation that involved managing my own threads and shutting them down etc, but it started getting quite complicated, and I'm now wondering if the TPL might be better. I'm wondering if anyone can offer any general guidance? Thanks...

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detect shutdown in window service

- by deepu

hi, i have a windows service that get user details and save the result into log text file. and, my problem is when i shut down or log off my system, i also would like to save the time that i down my system into that log file. but, i don't know how to do that. I checked the winproc method to detect shutdown operation but i was not able to use it on window service, on googling found it can be used with forms only. how can we detect user have clicked shutdown or log off and do some action. so,please give me some idea or suggestion on that. i have used it for logoff but on log entry is made when i logoff the system protected override void OnSessionChange(SessionChangeDescription changeDescription) { this.RequestAdditionalTime(250000); //gives a 25 second delay on Logoff if (changeDescription.Reason == SessionChangeReason.SessionLogoff) { // Add your save code here StreamWriter str = new StreamWriter("D:\\Log.txt", true); str.WriteLine("Service stoped due to " + changeDescription.Reason.ToString() + "on" + DateTime.Now.ToString()); str.Close(); } base.OnSessionChange(changeDescription); }

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How to do drag-n-drop and resize on an image using jQuery?

- by Scott

How do I resize and image using jQuery but keep its aspect ratio the same? <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"> <head> <title>CrossSlide - A jQuery plugin to create pan and cross-fade animations</title> <link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css" rel="stylesheet" type="text/css"/> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js"></script> <script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js"></script> </head> <body> <style type="text/css"> #resizebleImage { background: silver; } </style> <script type="text/javascript"> $(document).ready(function(){ $("#resizebleImage").resizable().parent().draggable(); }); </script> <img id="resizebleImage" src="http://images.askmen.com/galleries/singer/gloria-estefan/pictures/gloria-estefan-picture-4.jpg"> </body> </html>

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C++ Implicit Conversion Operators

- by Imbue

I'm trying to find a nice inheritance solution in C++. I have a Rectangle class and a Square class. The Square class can't publicly inherit from Rectangle, because it cannot completely fulfill the rectangle's requirements. For example, a Rectangle can have it's width and height each set separately, and this of course is impossible with a Square. So, my dilemma. Square obviously will share a lot of code with Rectangle; they are quite similar. For examlpe, if I have a function like: bool IsPointInRectangle(const Rectangle& rect); it should work for a square too. In fact, I have a ton of such functions. So in making my Square class, I figured I would use private inheritance with a publicly accessible Rectangle conversion operator. So my square class looks like: class Square : private Rectangle { public: operator const Rectangle&() const; }; However, when I try to pass a Square to the IsPointInRectangle function, my compiler just complains that "Rectangle is an inaccessible base" in that context. I expect it to notice the Rectangle operator and use that instead. Is what I'm trying to do even possible? If this can't work I'm probably going to refactor part of Rectangle into MutableRectangle class. Thanks.

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Indices instead of pointers in STL containers?

- by zvrba

Due to specific requirements [*], I need a singly-linked list implementation that uses integer indices instead of pointers to link nodes. The indices are always interpreted with respect to a vector containing the list nodes. I thought I might achieve this by defining my own allocator, but looking into the gcc's implementation of , they explicitly use pointers for the link fields in the list nodes (i.e., they do not use the pointer type provided by the allocator): struct _List_node_base { _List_node_base* _M_next; ///< Self-explanatory _List_node_base* _M_prev; ///< Self-explanatory ... } (For this purpose, the allocator interface is also deficient in that it does not define a dereference function; "dereferencing" an integer index always needs a pointer to the underlying storage.) Do you know a library of STL-like data structures (i am mostly in need of singly- and doubly-linked list) that use indices (wrt. a base vector) instead of pointers to link nodes? [*] Saving space: the lists will contain many 32-bit integers. With two pointers per node (STL list is doubly-linked), the overhead is 200%, or 400% on 64-bit platform, not counting the overhead of the default allocator.

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Getting list of states/events from a model that AASM's

- by Jason Nerer

Hi, I successfully integrated the most recent AASM gem into an application, using it for the creation of a wizard. In my case I have a model order class Order < ActiveRecord::Base belongs_to :user has_one :billing_plan, :dependent => :destroy named_scope :with_user, ..... <snip> include AASM aasm_column :aasm_state aasm_initial_state :unauthenticated_user aasm_state :unauthenticated_user, :after_exit => [:set_state_completed] aasm_state : <snip> <and following the event definitions> end Now I would like to give an administrator the possibility to create his own graphs through the AASM states. Therefore I created two additional models called OrderFlow and Transition where there order_flow has many transitions and order belongs_to order_flow. No problem so far. Now I would like to give my admin the possibility to dynamically add existing transitions / events to an order_flow graph. The problem now is, that I do not find any possibility to get a list of all events / transitions out of my order model. aasm_states_for_select seems to be the correct candidate, but I cannot call it on my order model. Can anyone help? Thx in advance. J.

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Newbie: Render RGB to GTK widget -- howto?

- by Billy Pilgrim

Hi All, Big picture: I want to render an RGB image via GTK on a linux box. I'm a frustrated GTK newbie, so please forgive me. I assume that I should create a Drawable_area in which to render the image -- correct? Do I then have to create a graphics context attached to that area? How? my simple app (which doesn't even address the rgb issue yet is this: int main(int argc, char** argv) { GdkGC * gc = NULL; GtkWidget * window = NULL; GtkDrawingArea * dpage = NULL; GtkWidget * page = NULL; gtk_init( &argc, & argv ); window = gtk_window_new( GTK_WINDOW_TOPLEVEL ); page = gtk_drawing_area_new( ); dpage = GTK_DRAWING_AREA( page ); gtk_widget_set_size_request( page, PAGE_WIDTH, PAGE_HEIGHT ); gc = gdk_gc_new( GTK_DRAWABLE( dpage ) ); gtk_widget_show( window ); gtk_main(); return (EXIT_SUCCESS); } my dpage is apparently not a 'drawable' (though it is a drawing area). I am confused as to a) how do I get/create the graphics context which is required in subsequent function calls? b) am I close to a solution, or am I so completely *#&@& wrong that there is no hope c) a baby steps tutorial. (I started with hello world as my base, so I got that far). any and all help appreciated. bp

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How to deal with seniors' bad coding style/practices?

- by KaluSingh Gabbar

I am new to work but the company I work in hires a lot of non-comp-science people who are smart enough to get the work done (complex) but lack the style and practices that should help other people read their code. For example they adopt C++ but still use C-like 3 page functions which drives new folks nuts when they try to read that. Also we feel very risky changing it as it's never easy to be sure we are not breaking something. Now, I am involved in the project with these guys and I can't change the entire code base myself or design so that code looks good, what can I do in this situation? PS we actually have 3 page functions & because we do not have a concept of design, all we can do is assume what they might have thought as there is no way to know why is it designed the way it is. I am not complaining.I am asking for suggestion,already reading some books to solve the issues Pragmatic Programmer; Design portion from B.Stroustrup; Programming and principles by B.Stroustrup;

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Determine target architecture of binary file in Linux (library or executable)

- by Fernando Miguélez

We have an issue related to a Java application running under a (rather old) FC3 on a Advantech POS board with a Via C3 processor. The java application has several compiled shared libs that are accessed via JNI. Via C3 processor is suppossed to be i686 compatible. Some time ago after installing Ubuntu 6.10 on a MiniItx board with the same processor I found out that the previous statement is not 100% true. The Ubuntu kernel hanged on startup due to the lack of some specific and optional instructions of the i686 set in the C3 processor. These instructions missing in C3 implementation of i686 set are used by default by GCC compiler when using i686 optimizations. The solution in this case was to go with a i386 compiled version of Ubuntu distribution. The base problem with the Java application is that the FC3 distribution was installed on the HD by cloning from an image of the HD of another PC, this time an Intel P4. Afterwards the distribution needed some hacking to have it running such as replacing some packages (such as the kernel one) with the i383 compiled version. The problem is that after working for a while the system completely hangs without a trace. I am afraid that some i686 code is left somewhere in the system and could be executed randomly at any time (for example after recovering from suspend mode or something like that). My question is: Is there any tool or way to find out at what specific architecture is an binary file (executable or library) aimed provided that "file" does not give so much information?

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Duplicate C# web service proxy classes generated for Java types

- by Sergey

My question is about integration between a Java web service and a C# .NET client. Service: CXF 2.2.3 with Aegis databinding Client: C#, .NET 3.5 SP1 For some reason Visual Studio generates two C# proxy enums for each Java enum. The generated C# classes do not compile. For example, this Java enum: public enum SqlDialect { GENERIC, SYBASE, SQL_SERVER, ORACLE; } Produces this WSDL: <xsd:simpleType name="SqlDialect"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="GENERIC" /> <xsd:enumeration value="SYBASE" /> <xsd:enumeration value="SQL_SERVER" /> <xsd:enumeration value="ORACLE" /> </xsd:restriction> </xsd:simpleType> For this WSDL Visual Studio generates two partial C# classes (generated comments removed): [System.CodeDom.Compiler.GeneratedCodeAttribute("System.Runtime.Serialization", "3.0.0.0")] [System.Runtime.Serialization.DataContractAttribute(Name="SqlDialect", Namespace="http://somenamespace")] public enum SqlDialect : int { [System.Runtime.Serialization.EnumMemberAttribute()] GENERIC = 0, [System.Runtime.Serialization.EnumMemberAttribute()] SYBASE = 1, [System.Runtime.Serialization.EnumMemberAttribute()] SQL_SERVER = 2, [System.Runtime.Serialization.EnumMemberAttribute()] ORACLE = 3, } [System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "2.0.50727.3082")] [System.SerializableAttribute()] [System.Xml.Serialization.XmlTypeAttribute(Namespace="http://somenamespace")] public enum SqlDialect { GENERIC, SYBASE, SQL_SERVER, ORACLE, } The resulting C# code does not compile: The namespace 'somenamespace' already contains a definition for 'SqlDialect' I will appreciate any ideas...

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Is there a max recommended size on bundling js/css files due to chunking or packet loss?

- by George Mauer

So we all have heard that its good to bundle your javascript. Of course it is, but it seems to me that the story is too simple. See if my logic makes sense here. Obviously fewer HTTP requests is fewer round trips and hence better. However - and I don't know much about bare http - aren't http responses sent in chunks? And if a file is larger than one of those chunks doesn't it have to be downloaded as multiple (possibly synchronous?) round trips? As opposed to this, several requests for files just under the chunking size would arrive much quicker since modern web browsers download resources like javascripts in parallel. Even if chunking is not an issue, it seems like there would be some max recommended size just due to likelyhood of packet loss alone since a bundled file must wait till it is entirely downloaded to execute, versus the more lenient native rule that scripts must execute in order. Obviously there's also matters of browser caching and code volatility to consider but can someone confirm this or explain why I'm off base? Does anyone have any numbers to put to it?

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Static Variables somehow maintaining state?

- by gfoley

I am working on an existing project, setup by another coder. I'm having some trouble understanding how state is being maintained between pages. There is a Class library which has some helper objects. Mostly these objects are just used for there static methods and rarely instantiated or inherited. This is an example class I'm testing with. public sealed class Application { public static string Test; } Now when i run something like the following in the base class of my page, I would expect the result to be "1: 2:Test" all the time (note that "1" is empty), but strangly its only this way the first time it is run. Then every time afterwards its "1:Test 2:Test". Somehow its maintaining the state of the static variable between pages and being refreshed?? Response.Write("1:" + SharedLibrary.Application.Test); SharedLibrary.Application.Test = "Test"; Response.Write(" 2:" + SharedLibrary.Application.Test); I need to create more classes like this, but want to understand why this is occurring in the first place. Many Thanks

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How do I build a filtered_streambuf based on basic_streambuf?

- by swestrup

I have a project that requires me to insert a filter into a stream so that outgoing data will be modified according to the filter. After some research, it seems that what I want to do is create a filtered_streambuf like this: template <class StreamBuf class filtered_streambuf: public StreamBuf { ... } And then insert a filtered_streambuf<> into whichever stream I need to be filtered. My problem is that I don't know what invariants I need to maintain while filtering a stream, in order to ensure that Derived classes can work as expected. In particular, I may find I have filtered_streambufs built over other filtered_streambufs. All the various stream inserters, extractors and manipulators work as expected. The trouble is that I just can't seem to work out what the minimal interface is that I need to supply in order to guarantee that an iostream will have what it needs to work correctly. In particular, do I need to fake the movement of the protected pointer variables, or not? Do I need a fake data buffer, or not? Can I just override the public functions, rewriting them in terms of the base streambuf, or is that too simplistic?

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subquery in join with doctrine dql

- by Martijn de Munnik

I want to use DQL to create a query which looks like this in SQL: select e.* from e inner join ( select uuid, max(locale) as locale from e where locale = 'nl_NL' or locale = 'nl' group by uuid ) as e_ on e.uuid = e_.uuid and e.locale = e_.locale I tried to use QueryBuilder to generate the query and subquery. I think they do the right thing by them selves but I can't combine them in the join statement. Does anybody now if this is possible with DQL? I can't use native SQL because I want to return real objects and I don't know for which object this query is run (I only know the base class which have the uuid and locale property). $subQueryBuilder = $this->_em->createQueryBuilder(); $subQueryBuilder ->addSelect('e.uuid, max(e.locale) as locale') ->from($this->_entityName, 'e') ->where($subQueryBuilder->expr()->in('e.locale', $localeCriteria)) ->groupBy('e.uuid'); $queryBuilder = $this->_em->createQueryBuilder(); $queryBuilder ->addSelect('e') ->from($this->_entityName, 'e') ->join('('.$subQueryBuilder.') as', 'e_')->join ->where('e.uuid = e_.uuid') ->andWhere('e.locale = e_.locale');

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Spawning a thread in python

- by morpheous

I have a series of 'tasks' that I would like to run in separate threads. The tasks are to be performed by separate modules. Each containing the business logic for processing their tasks. Given a tuple of tasks, I would like to be able to spawn a new thread for each module as follows. from foobar import alice, bob charles data = getWorkData() # these are enums (which I just found Python doesn't support natively) :( tasks = (alice, bob, charles) for task in tasks # Ok, just found out Python doesn't have a switch - @#$%! # yet another thing I'll need help with then ... switch case alice: #spawn thread here - how ? alice.spawnWorker(data) No prizes for guessing I am still thinking in C++. How can I write this in a Pythonic way using Pythonic 'enums' and 'switch'es, and be able to run a module in a new thread. Obviously, the modules will all have a class that is derived from a ABC (abstract base class) called Plugin. The spawnWorker() method will be declared on the Plugin interface and defined in the classes implemented in the various modules. Maybe, there is a better (i.e. Pythonic) way of doing all this?. I'd be interested in knowing

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Creating a Linq->HQL provider

- by Mike Q

Hi all, I have a client application that connects to a server. The server uses hibernate for persistence and querying so it has a set of annotated hibernate objects for persistence. The client sends HQL queries to the server and gets responses back. The client has an auto-generated set of objects that match the server hibernate objects for query results and basic persistence. I would like to support using Linq to query as well as Hql as it makes the queries typesafe and quicker to build (no more typos in HQL string queries). I've looked around at the following but I can't see how to get them to fit with what I have. NHibernate's Linq provider - requires using NHibernate ISession and ISessionFactory, which I don't have LinqExtender - requires a lot of annotations on the objects and extending a base type, too invasive What I really want is something that will generate give me a nice easy to process structure to build the HQL queries from. I've read most of a 15 page article written by one of the C# developers on how to create custom providers and it's pretty fraught, mainly because of the complexity of the expression tree. Can anyone suggest an approach for implementing Linq - HQL translation? Perhaps a library that will the cleanup of the expression tree into something more SQL/HQLish. I would like to support select/from/where/group by/order by/joins. Not too worried about subqueries.

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.save puts NULL in id field in Rails

- by mathee

Here's the model file: class ProfileTag < ActiveRecord::Base def self.create_or_update(options = {}) id = options.delete(:id) record = find_by_id(id) || new record.id = id record.attributes = options puts "record.profile_id is" puts record.profile_id record.save! record end end This gives me the correct print out in my log. But it also says that there's a call to UPDATE that sets profile_id to NULL. Here's some of the output in the log file: Processing ProfilesController#update (for 127.0.0.1 at 2010-05-28 18:20:54) [PUT] Parameter: {"commit"=>"Save", ...} ?[4;36;1mProfileTag Create (0.0ms)?[0m ?[0;1mINSERT INTO `profile_tags` (`reputation_value`, `updated_at`, `tag_id`, `id`, `profile_id`, `created_at`) VALUES(0, '2010-05-29 01:20:54', 1, NULL, 4, '2010-05-29 01:20:54')?[0m ?[4;35;1mSQL (2.0ms)?[0m ?[0mCOMMIT?[0m ?[4;36;1mSQL (0.0ms)?[0m ?[0;1mBEGIN?[0m ?[4;35;1mSQL (0.0ms)?[0m ?[0mCOMMIT?[0m ?[4;36;1mProfileTag Load (0.0ms)?[0m ?[0;1mSELECT * FROM `profile_tags` WHERE (`profile_tags`.profile_id = 4) ?[0m ?[4;35;1mSQL (1.0ms)?[0m ?[0mBEGIN?[0m ?[4;36;1mProfileTag Update (0.0ms)?[0m ?[0;1mUPDATE `profile_tags` SET profile_id = NULL WHERE (profile_id = 4 AND id IN (35)) ?[0m I'm not sure I understand why the INSERT puts the value into profile_id properly, but then it sets it to NULL on an UPDATE. If you need more specifics, please let me know. I'm thinking that the save functionality does many things other than INSERTs into the database, but I don't know what I need to specify so that it will properly set profile_id.

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mmap only needed pages of kernel buffer to user space

- by axeoth

See also this answer: http://stackoverflow.com/a/10770582/1284631 I need something similar, but without having to allocate a buffer: the buffer is large, in theory, but the user space program only needs to access some parts of it (it mocks some registers of a hardware). As I cannot allocate with vmalloc_user() such a large buffer (kernel 32 bit, in embedded environment, no swap...), I followed the same approach as in the quoted answer, trying to allocate only those pages that are really requested by the user space. So: I use a my_mmap() function for the device file (actually, is the .mmap field of a struct uio_info) to set up the fields of the vma, then, in the vm_area_struct's .fault field (also named my_fault()), I should return a page. except that: In the my_fault() method of vm_area_struct, I cannot obtain a page through: vmf->page=vmalloc_to_page(my_buf + (vmf->pgoff << PAGE_SHIFT)); since there is no allocated buffer: my_buf = vmalloc_user(MY_BUF_SIZE); fails with "allocation failed: out of vmalloc space - use vmalloc= to increase size." (and there is no room or swap to increase that vmalloc= parameter). So, I would need to get a page from the kernel and fill the vmf->page field. How to allocate a page (I assume that the offset of the page is known, as it is vm->pgoff). What base memory should I use instead of my_buf? PS: I also did set up the vma->flags |= VM_NORESERVE; (in the my_mmap()), but not sure if it helps. Is there any vmalloc_user_unreserved()-like function? (let's say, lazy allocation) Also, writing 1 to /proc/sys/vm/overcommit_memory and large values (eg 500) to /proc/sys/vm/overcommit_ratio before trying to my_buf=vmalloc_user(<large_size>) didn't work.

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Why doesn't the Java Collections API include a Graph implementation?

- by dvanaria

I’m currently learning the Java Collections API and feel I have a good understanding of the basics, but I’ve never understood why this standard API doesn’t include a Graph implementation. The three base classes are easily understandable (List, Set, and Map) and all their implementations in the API are mostly straightforward and consistent. Considering how often graphs come up as a potential way to model a given problem, this just doesn’t make sense to me (it’s possible it does exist in the API and I’m not looking in the right place of course). Steve Yegge suggests in one of his blog posts that a programmer should consider graphs first when attacking a problem, and if the problem domain doesn’t fit naturally into this data structure, only then consider the alternative structures. My first guess is that there is no universal way to represent graphs, or that their interfaces may not be generic enough for an API implementation to be useful? But if you strip down a graph to its basic components (vertices and a set of edges that connect some or all of the vertices) and consider the ways that graphs are commonly constructed (methods like addVertex(v) and insertEdge(v1, v2)) it seems that a generic Graph implementation would be possible and useful. Thanks for helping me understand this better.

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Trying to make a plugin system in C++

- by Pirate for Profit

I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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NHibernate + Fluent long startup time

- by PaRa

Hi all, am new to NHibernate. When performing below test took 11.2 seconds (debug mode) i am seeing this large startup time in all my tests (basically creating the first session takes a tone of time) setup = Windows 2003 SP2 / Oracle10gR2 latest CPU / ODP.net 2.111.7.20 / FNH 1.0.0.636 / NHibernate 2.1.2.4000 / NUnit 2.5.2.9222 / VS2008 SP1 using System; using System.Collections; using System.Data; using System.Globalization; using System.IO; using System.Text; using System.Data; using NUnit.Framework; using System.Collections.Generic; using System.Data.Common; using NHibernate; using log4net.Config; using System.Configuration; using FluentNHibernate; [Test()] public void GetEmailById() { Email result; using (EmailRepository repository = new EmailRepository()) { results = repository.GetById(1111); } Assert.IsTrue(results != null); } public class EmailRepository : RepositoryBase { public EmailRepository():base() { } } In my RepositoryBase public T GetById(object id) { using (var session = sessionFactory.OpenSession()) using (var transaction = session.BeginTransaction()) { try { T returnVal = session.Get(id); transaction.Commit(); return returnVal; } catch (HibernateException ex) { // Logging here transaction.Rollback(); return null; } } } The query time is very small. The resulting entity is really small. Subsequent queries are fine. Its seems to be getting the first session started. Has anyone else seen something similar?

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Django: DatabaseError column does not exist

- by Rosarch

I'm having a problem with Django 1.2.4. Here is a model: class Foo(models.Model): # ... ftw = models.CharField(blank=True) bar = models.ForeignKey(Bar) Right after flushing the database, I use the shell: Python 2.6.6 (r266:84292, Sep 15 2010, 15:52:39) [GCC 4.4.5] on linux2 Type "help", "copyright", "credits" or "license" for more information. (InteractiveConsole) >>> from apps.foo.models import Foo >>> Foo.objects.all() Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 67, in __repr__ data = list(self[:REPR_OUTPUT_SIZE + 1]) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 82, in __len__ self._result_cache.extend(list(self._iter)) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 271, in iterator for row in compiler.results_iter(): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 677, in results_iter for rows in self.execute_sql(MULTI): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 732, in execute_sql cursor.execute(sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/util.py", line 15, in execute return self.cursor.execute(sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute return self.cursor.execute(query, args) DatabaseError: column foo_foo.bar_id does not exist LINE 1: ...t_omg", "foo_foo"."ftw", "foo_foo... What am I doing wrong here?

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Nullability (Regular Expressions)

- by danportin

In Brzozowski's "Derivatives of Regular Expressions" and elsewhere, the function d(R) returning ? if a R is nullable, and Ø otherwise, includes clauses such as the following: d(R1 + R2) = d(R1) + d(R2) d(R1 · R2) = d(R1) ? d(R2) Clearly, if both R1 and R2 are nullable then (R1 · R2) is nullable, and if either R1 or R2 is nullable then (R1 + R2) is nullable. It is unclear to me what the above clauses are supposed to mean, however. My first thought, mapping (+), (·), or the Boolean operations to regular sets is nonsensical, since in the base case, d(a) = Ø (for all a ? S) d(?) = ? d(Ø) = Ø and ? is not a set (nor is the return type of d, which is a regular expression). Furthermore, this mapping isn't indicated, and there is a separate notation for it. I understand nullability, but I'm lost on the definition of the sum, product, and Boolean operations in the definition of d: how are ? or Ø returned from d(R1) ? d(R2), for instance, in the definition off d(R1 · R2)?

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Program to find the result of primitive recursive functions

- by alphomega

I'm writing a program to solve the result of primitive recursive functions: 1 --Basic functions------------------------------ 2 3 --Zero function 4 z :: Int -> Int 5 z = \_ -> 0 6 7 --Successor function 8 s :: Int -> Int 9 s = \x -> (x + 1) 10 11 --Identity/Projection function generator 12 idnm :: Int -> Int -> ([Int] -> Int) 13 idnm n m = \(x:xs) -> ((x:xs) !! (m-1)) 14 15 --Constructors-------------------------------- 16 17 --Composition constructor 18 cn :: ([Int] -> Int) -> [([Int] -> Int)] -> ([Int] -> Int) 19 cn f [] = \(x:xs) -> f 20 cn f (g:gs) = \(x:xs) -> (cn (f (g (x:xs))) gs) these functions and constructors are defined here: http://en.wikipedia.org/wiki/Primitive_recursive_function The issue is with my attempt to create the compositon constructor, cn. When it gets to the base case, f is no longer a partial application, but a result of the function. Yet the function expects a function as the first argument. How can I deal with this problem? Thanks.

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How To Deal With Exceptions In Large Code Bases

- by peter

Hi All, I have a large C# code base. It seems quite buggy at times, and I was wondering if there is a quick way to improve finding and diagnosing issues that are occuring on client PCs. The most pressing issue is that exceptions occur in the software, are caught, and even reported through to me. The problem is that by the time they are caught the original cause of the exception is lost. I.e. If an exception was caught in a specific method, but that method calls 20 other methods, and those methods each call 20 other methods. You get the picture, a null reference exception is impossible to figure out, especially if it occured on a client machine. I have currently found some places where I think errors are more likely to occur and wrapped these directly in their own try catch blocks. Is that the only solution? I could be here a long time. I don't care that the exception will bring down the current process (it is just a thread anyway - not the main application), but I care that the exceptions come back and don't help with troubleshooting. Any ideas? I am well aware that I am probably asking a question which sounds silly, and may not have a straightforward answer. All the same some discussion would be good.

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