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• Is ActiveMQ unreliable?

  - by user122991

  Hello, We have been using ActiveMQ 5.2 in our distributed enterprise application for about 3 months. During that time, we have experienced debilitating failures at least twice weekly. In particular, we see: 1) Topic publisher has its connection arbitrarily closed and experiences EOF on attempt to publish. Note well that this issue is not a function of some timeout. It does not correlate reliably with any inactivity. 2) Queue listeners never receive message. Message simply sits on Queue. 2) is much rarer (hardly ever) than 1). In both cases, the failures are highly intermittent-- they cannot be reliably reproduced through any testing usage pattern. Also, there are no errors or warning in the AMQ logs. Have others experienced similar problems? Is there an opinion that some other JMS provider is more reliable? thanks, Joe

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• memristor is a new paradigm (fourth element in integrated circuits)? [closed]

  - by lsalamon

  The memristor will bring a new paradigm of programming, opened enormous opportunities to enable the machines to gain knowledge, creating a new paradigm toward the intelligence altificial. Do you believe that we are paving the way for the era of intelligent machines? More info about : Brain-like systems? "As for the human brain-like characteristics, memristor technology could one day lead to computer systems that can remember and associate patterns in a way similar to how people do. This could be used to substantially improve facial recognition technology or to provide more complex biometric recognition systems that could more effectively restrict access to personal information. These same pattern-matching capabilities could enable appliances that learn from experience and computers that can make decisions." [EDITED] The way is open. News on the subject Brain-Like Computer Closer to Realization

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• Efficient storage/retrieval method for replayable comet style applications (Google Wave, Etherpad)

  - by Gareth Simpson

  I am considering a web application that would have the same kind of multi user, automatic saving, infinite undo / replay capabilities that you see in Google Wave and Etherpad (albeit on a drastically smaller scale and userbase). Before I go away and reinvent the wheel, is this something that has already been addressed as either a piece of technology or library, or even just a design pattern. I know this isn't necessarily the best Stack Overflow question as there is probably not a "right" answer, but my Google-fu has failed me and I'd just like a reading list! Ordinarily I would be developing under python/django but this is not a firm requirement just a preference :)

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• Recurrance Calendar Issue in Lotus Notes

  - by Preeti

  Hi all, I am creating a Daily Reccurrance pattern in calendar items. But there is a issue as before clicking "save and Send Invitations" button, but in the Document Properties field i am able to view the RepeatForUnit and based on its value i am identifying the Reccurrance type like (D: for daily, W: for Weekly, M: for montlhy etc). But, After clicking on the "save and Send Invitations" button, the Recurrance is getting saved but after that, i am unable to get the RepeatForUnit field in Document Properties. Kindly help me, how to identify the Reccurrance type and the related fields. Note: I am using Domino.dll using C#. Regards, Preeti

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• How to check connection leak using regular expression ?

  - by gauravkarnatak

  I have to check connection leak in my application i.e. open connections which have not been closed. After searching, after I found out that a thousands times connections have been opened but I can't manually go to each and every code fragment and check for connection close thing. I think, it could be possible using a regular expression but the fact is, I am not that well versed with regex that I could write one. Please suggest a regular expression for checking in a no of java files that a opened connection has been closed or not. My code pattern is something like this. try { /* Some code goes here */ con = EJBUtil.getConnection(JNDI_NAME); /* Some code goes here */ } finally { /* Some code goes here */ DBUtil.close(con); or closeConnection.close(con); /* Some code goes here */ }

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• Zend Framework - Database Table Singleton

  - by Sonny

  I have found myself doing this in my code to 'cache' the work done when instantiating my Zend_Db_Table models: if (Zend_Registry::isRegistered('x_table')) { $x_table = Zend_Registry::get('x_table'); } else { $x_table = new Default_Model_DbTable_X; Zend_Registry::set('x_table', $x_table); } It bothered me that this method isn't very DRY and it dawned on me today that a singleton pattern would probably be a better way to do this. Problem is, I've never written a singleton class. When I did some web searches, I found some offhand comments about Zend_Db_Table singletons, but no real examples. I already have meta-data caching configured. How do I make my Zend_Db_Table models singletons? Are there pitfalls or downsides?

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• MVVM View reference to ViewModel

  - by BrettRobi

  I'm using MVVM in a WPF app. I'm very new to both. Let me state that I am not a purest in the MVVM pattern, I am trying to use as many best practices as I can but am trying to make what I think are reasonable compromises to make it work in our environment. For example, I am not trying to achieve 0% code in my View codebehind. I have a couple of questions about best practices. 1) I understand I don't want my VM to know about the attached View, but is it reasonable for the View to have a reference to its VM? 2) If a control in a View opens another View (such as a dialog) should I handle this in the View? It seems wrong to handle it in the VM since then the VM has some knowledge of a specific View.

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• Pass a captured named regular expression to URL dictionary in generic view

  - by Trent Jurewicz

  I am working with a generic view in Django. I want to capture a named group parameter in the URL and pass the value to the URL pattern dictionary. For example, in the URLConf below, I want to capture the parent_slug value in the URL and pass it to the queryset dictionary value like so: urlpatterns = patterns('django.views.generic.list_detail', (r'^(?P<parent_slugs>[-\w])$', 'object_list', {'queryset':Promotion.objects.filter(category=parent_slug)}, 'promo_promotion_list'), ) Is this possible to do in one URLConf entry, or would it be wiser if I create a custom view to capture the value and pass the queryset directly to the generic view from my overridden view?

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• VB.net: Custom ' TODO: List on an Interface

  - by Shiftbit

  How do I add my own todo and comments list to appear on Interfaces? I want it to pop up like IDisposable does: Public Class Foo : Implements IDisposable Private disposedValue As Boolean = False ' To detect redundant calls ' IDisposable Protected Overridable Sub Dispose(ByVal disposing As Boolean) If Not Me.disposedValue Then If disposing Then ' TODO: free other state (managed objects). End If ' TODO: free your own state (unmanaged objects). ' TODO: set large fields to null. End If Me.disposedValue = True End Sub #Region " IDisposable Support " ' This code added by Visual Basic to correctly implement the disposable pattern. Public Sub Dispose() Implements IDisposable.Dispose ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above. Dispose(True) GC.SuppressFinalize(Me) End Sub #End Region End Class Whenever I enter my own comments and todo list they are never autogenerated like IDisposable Interface does. I would like my own Interfaces to preserve the comments so that I can share my Interfaces with in source documentation.

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• Sqlalchemy layout with WSGI application

  - by TheDude

  I'm working on writing a small WSGI application using Bottle and SqlAlchemy and am confused on how the "layout" of my application should be in terms of SqlAlchemy. My confusion is with creating engines and sessions. My understanding is that I should only create one engine with the 'create_engine' method. Should I be creating an engine instance in the global namespace in some sort of singleton pattern and creating sessions based off of it? How have you done this in your projects? Any insight would be appreciated. The examples in the documentation dont seem to make this entirely clear (unless I'm missing something obvious). Any thoughts?

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• GridView items are displaying the wrong drawables sometimes.

  - by originalbryan

  I've implemented a GridView based on this tutorial. It works great unless open up the search dialog or rotate the screen then scroll around. When the search dialog and virtual keyboard appear, the drawables for each of my grid items shift. I can click on them and they do what I expect, except the drawable is wrong. The same problem happens when I go into landscape mode and scroll around. If I scroll down, up, the down again, the drawables are shuffled. For better illustration, let's say I have three objects, each with an image. Obj A shows an Apple Obj B shows a Banana Obj C shows a Cantaloupe When the shift occurs I end up with: Obj A shows an Cantaloupe Obj B shows a Banana Obj C shows a Apple The problem isn't consistent between the two causes (search dialog and screen rotate n' scroll), but each cause itself is consistent. Scrolling around repeatedly reveals a pattern as does the search dialog appearing. How can I stop this from happening?

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• Session is Closed! NHibernate shouldn't be trying to grab data

  - by Jeremy Holovacs

  I have a UnitOfWork/Service pattern where I populate my model using NHibernate before sending it to the view. For some reason I still get the YSOD, and I don't understand why the object collection is not already populated. My controller method looks like this: public ActionResult PendingRegistrations() { var model = new PendingRegistrationsModel(); using (var u = GetUnitOfWork()) { model.Registrations = u.UserRegistrations.GetRegistrationsPendingAdminApproval(); } return View(model); } The service/unit of work looks like this: public partial class NHUserRegistrationRepository : IUserRegistrationRepository { public IEnumerable<UserRegistration> GetRegistrationsPendingAdminApproval() { var r = from UserRegistration ur in _Session.Query<UserRegistration>() where ur.Status == AccountRegistrationStatus.PendingAdminReview select ur; NHibernateUtil.Initialize(r); return r; } } What am I doing wrong?

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• Problem Rewriting URL's from HTTPS to HTTP using IIS7 URL Rewriter, when using Webforms ReturnURL=

  - by theminesgreg

  I took Jeff's Re-write rules from this post and the HTTP to HTTPS conversion works great. However, going back to HTTP is giving me problems because of the ReturnUrl= in the URL (I'm using webforms). Here's an example of the url: https://localhost/Login.aspx?ReturnUrl=%2f Here's the rewrite rule I'm using: <rule name="HTTPS to HTTP redirect for all other pages" stopProcessing="true"> <match url="^login\.aspx$" ignoreCase="true" negate="true" /> <conditions> <add input="{SERVER_PORT}" pattern="^443$" /> </conditions> <action type="Redirect" redirectType="Found" url="http://{HTTP_HOST}{REQUEST_URI}" /> </rule> Here's the resulting re-written URL: http://localhost/,/ Has anyone found a work around for this?

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• Type patterns in Haskell

  - by finnsson

  I'm trying to compile a simple example of generic classes / type patterns (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html) in Haskell but it won't compile. Any ideas about what's wrong with the code would be helpful. According to the documentation there should be a module Generics with the data types Unit, :*:, and :+: but ghc (6.12.1) complaints about Not in scope: data constructor 'Unit' etc. It seems like there's a package instant-generics with the data types :*:, :+: and U but when I import that module (instead of Generics) I get the error Illegal type pattern in the generic bindings {myPrint _ = ""} The complete source code is import Generics.Instant class MyPrint a where myPrint :: a -> String myPrint {| U |} _ = "" myPrint {| a :*: b |} (x :*: y) = "" (show x) ++ ":*:" ++ (show y) myPrint {| a :+: b |} _ = "" data Foo = Foo String instance MyPrint a => MyPrint a main = myPrint $ Foo "hi" and I compile it using ghc --make Foo.hs -fglasgow-exts -XGenerics -XUndecidableInstances P.S. The module Generics export no data types, only the functions: canDoGenerics mkGenericRhs mkTyConGenericBinds validGenericInstanceType validGenericMethodType

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• How can I create a qr// in Perl 5.12 from C?

  - by kristina

  This has been working for me in 5.8 and 5.10, but in 5.12 my code creates this weird non-qr object: # running "print Dumper($regex)" $VAR1 = bless( do{\(my $o = '')}, 'Regexp' ); Whereas printing a qr// not created by my code looks like this: # running "print Dumper(qr/foo/i)" $VAR1 = qr/(?i-xsm:foo)/; My code is basically: REGEXP *rx = re_compile(pattern, flags); SV *regex = sv_2mortal(newSVpv("",0)); sv_magic(regex, (SV*)rx, PERL_MAGIC_qr, 0, 0); stash = gv_stashpv("Regexp", 0); sv_bless(newRV((SV*)regex), stash); Anyone know how to correctly create a regex from a string in 5.12?

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• How should I implement items that are normalized in the Database, in Object Oriented Design?

  - by Jonas

  How should I implement items that are normalized in the Database, in Object Oriented classes? In the database I have a big table of items and a smaller of groups. Each item belong to one group. This is how my database design look like: +----------------------------------------+ | Inventory | +----+------+-------+----------+---------+ | Id | Name | Price | Quantity | GroupId | +----+------+-------+----------+---------+ | 43 | Box | 34.00 | 456 | 4 | | 56 | Ball | 56.50 | 3 | 6 | | 66 | Tin | 23.00 | 14 | 4 | +----+------+-------+----------+---------+ Totally 3000 lines +----------------------+ | Groups | +---------+------+-----+ | GroupId | Name | VAT | +---------+------+-----+ | 4 | Mini | 0.2 | | 6 | Big | 0.3 | +---------+------+-----+ Totally 10 lines I will use the OOP classes in a GUI, where the user can edit Items and Groups in the inventory. It should also be easy to do calculations with a bunch of items. The group information like VAT are needed for the calculations. I will write an Item class, but do I need a Group class? and if I need it, should I keep them in a global location or how do I access it when I need it for Item-calculations? Is there any design pattern for this case?

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• Is there a better way to serially submit multiple AJAX requests?

  - by friedo

  I have a page with multiple forms that I submit via Ajax POSTs serially. At first, I tried using synchronous XHR requests, but this causes the browser to lock up for the duration of the request, and breaks my DOM-manipulation effects, which is unacceptable. So the pattern I ended up using is basically this: var fcount = 0; // incremented for each form to be submitted function submit_form( num ) { var fdata = { ... }; // data from form # num $.ajax( { async: true, url: '/index.cgi', data: fdata, type: 'POST', success: function() { if ( num < fcount ) { submit_form( ++num ); } } } ); } $( '#submit_form_btn' ).click( function() { submit_form( 1 ) } ); The recursion strikes me as a bit of an ugly solution to what is essentially an iterative problem. Is there a cleaner or more elegant way that this could be handled?

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• Regular expressions and matching URLs with metacharacters

  - by James P.

  I'm having trouble finding a regular expression that matches the following String. Korben;http://feeds.feedburner.com/KorbensBlog-UpgradeYourMind?format=xml;1 One problem is escaping the question mark. Java's pattern matcher doesn't seem to accept \? as a valid escape sequence but it also fails to work with the tester at myregexp.com. Here's what I have so far: ([a-zA-Z0-9])+;http://([a-zA-Z0-9./-]+);[0-9]+ Any suggestions? Edit: The original intent was to match all URLs that could be found after the first semi colon.

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• Why use hashing to create pathnames for large collections of files?

  - by Stephen

  Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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• How to code for Alternate Course AKA Rainy Day Scenary?

  - by janetsmith

  Alternate course is something when user doesn't do what you expected, e.g. key in wrong password, pressing back button, or database error. For any programming project, alternate course accounts for more than 50% of a project timeline. It is important. However, most computer books only focus on Basic Course (when everything goes fine). Basic course is rather simple, compared to Alternate course, because this is normally given by client. Alternate course is what we, as a programmer or Business Analyst needs to take care of. Java has some built-in mechanism (try-catch) to force us to handle those unexpected behavior. The question is, how to handle them? Any pattern to follow? Any guideline or industry practice for handling alternate course?

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• How to tell when my batch of EAP calls are completed?

  - by codemonkie

  This is following my question: http://stackoverflow.com/questions/2607038/c-how-to-consume-web-service-adheres-to-the-event-based-asynchronous-pattern My program is calling the DoStuffAsync() x many times in a batch, hence the callback will get invoked the same number of times upon OnComplete(). Is there a way to find out when my batch is finished such that I can generate a report on the success/failed results? All I can think of is to have a static count variable for x and deduct 1 every time OnComplete() is called, but its kind of silly and error prone I'm afraid. TIA.

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• Accessing database problem

  - by anarche

  Ok, so I've got an SQLiteOpenHelper that prepares and returns a SQLiteDatabase object; this is written singleton-pattern, so the database is opened once and only closed when the Activity closes. From there I have three database wrappers encapsulating the queries (some returning cursors to datasets, some inserting data) used by the Activity. I want to insert data from one View, then have that automatically update in another View on the same Dialogue. I'm writing this on a notepad and testing on the phone (since the emulator crashes the notepad...), so I can't pull up stacktraces atm. So questions: 1) are there limitations to writing to a database, when there are cursors open on the database? 2) Does a Cursor.requery()? call update the ListView with the cursor as a data connector?

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• Efficient persistent storage for simple id to table of values map for java

  - by wds

  I need to store some data that follows the simple pattern of mapping an "id" to a full table (with multiple rows) of several columns (i.e. some integer values [u, v, w]). The size of one of these tables would be a couple of KB. Basically what I need is to store a persistent cache of some intermediary results. This could quite easily be implemented as simple sql, but there's a couple of problems, namely I need to compress the size of this structure on disk as much as possible. (because of amount of values I'm storing) Also, it's not transactional, I just need to write once and simply read the contents of the entire table, so a relational DB isn't actually a very good fit. I was wondering if anyone had any good suggestions? For some reason I can't seem to come up with something decent atm. Especially something with an API in java would be nice.

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• How to disable UI control based on domain object's state?

  - by Subb

  Here's my problem. I have a somewhat complex domain object, which, depending on its state, responds to certain actions. I think the state pattern is pretty much the solution for that. However, I need to display which actions are possible at any moment in the UI. Ex: The domain object is an audio player. Some songs can't be skipped (like ads), so I need to disable the "next" and "previous" buttons in the GUI so the user have some kind of feedback of which action he can execute. I've looked at Swing's Action class (note: this is not a Java project), but I think I would need to keep every Actions in my domain object class (audio player), so it can enable or disable them depending on its own state (thus, affecting the UI). Is it the way to do it?

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• Partitioning requests in code among several servers

  - by Jacques René Mesrine

  I have several forum servers (what they are is irrelevant) which stores posts from users and I want to be able to partition requests among these servers. I'm currently leaning towards partitioning them by geographic location. To improve the locality of data, users will be separated into regions e.g. North America, South America and so on. Is there any design pattern on how to implement the function that maps the partioning property to the server, so that this piece of code has high availability and would not become a single point of failure ? f( Region ) -> Server IP

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