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• Why would paperclip not assign an ID to my uploaded photos?

  - by Trip

  I just deployed to a cluster server, and my delayed_jobs recipe was overwritten in the process. I solved that, delayed_jobs is up and running but can't find the ID of images that are uploaded. The images are saved correctly : Processing PhotosController#create (for 173.161.167.41 at 2010-06-01 05:09:14) [POST] Parameters: {"Filename"="1.jpg", "gallery_id"="1298", "action"="create", "amp"=nil, "authenticity_token"="qmbnpwFY8a5E3YtS/4fMWF/Z8evCE4hMxqKVJw0I7Ek=", "Upload"="Submit Query", "controller"="photos", "organization_id"="470", "_hq_channel_session"="BAh7CSIYdXNlcl9jcmVkZW50aWFsc19pZGkHIhV1c2VyX2NyZWRlbnRpYWxzIgGAOGRlZDc0NGJlOWU3NTNlNDFlYmVlMDdjMzIzYjA1ZjQxNGE5ZDY4YjNmYjFmNjNkMDQ2OWY2ZDQyOTljZDhiMDFlNmRkMDljNThmMzBmOWJhMTIwNDhkMDI5MTMxYmU5MDczYjIxZmI4YmQxMDVlMTBmNjZmOWFhODE1ZTBjMGM6EF9jc3JmX3Rva2VuIjFxbWJucHdGWThhNUUzWXRTLzRmTVdGL1o4ZXZDRTRoTXhxS1ZKdzBJN0VrPToPc2Vzc2lvbl9pZCIlMjAwMDQ3ZDQ3ZWUyZTgzODIxYzdjOGI3OTdmZGJiMDM=--ac6aa580262938bf5a4d6b9a740722b680eb5d48", "Filedata"=#} [paperclip] Saving attachments. [paperclip] saving /data/HQ_Channel/releases/20100530153454/public/system/photos/9253/original/1.jpg [paperclip] Saving attachments. [paperclip] Saving attachments. Completed in 127ms (View: 2, DB: 91) | 200 OK [http://invent.hqchannel.com/organizations/470/media/galleries/1298/photos?_hq_channel_session=BAh7CSIYdXNlcl9jcmVkZW50aWFsc19pZGkHIhV1c2VyX2NyZWRlbnRpYWxzIgGAOGRlZDc0NGJlOWU3NTNlNDFlYmVlMDdjMzIzYjA1ZjQxNGE5ZDY4YjNmYjFmNjNkMDQ2OWY2ZDQyOTljZDhiMDFlNmRkMDljNThmMzBmOWJhMTIwNDhkMDI5MTMxYmU5MDczYjIxZmI4YmQxMDVlMTBmNjZmOWFhODE1ZTBjMGM6EF9jc3JmX3Rva2VuIjFxbWJucHdGWThhNUUzWXRTLzRmTVdGL1o4ZXZDRTRoTXhxS1ZKdzBJN0VrPToPc2Vzc2lvbl9pZCIlMjAwMDQ3ZDQ3ZWUyZTgzODIxYzdjOGI3OTdmZGJiMDM%3D--ac6aa580262938bf5a4d6b9a740722b680eb5d48&authenticity_token=qmbnpwFY8a5E3YtS%2F4fMWF%2FZ8evCE4hMxqKVJw0I7Ek%3D] And then delayed_jobs keeps spinning around in circles on this one : 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob 2010-06-01T05:09:02-0700: * [JOB] delayed_job host:ip-10-251-197-159 pid:19994 failed with ActiveRecord::RecordNotFound: Couldn't find Photo with ID=9247 - 0 failed attempts 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob 2010-06-01T05:09:02-0700: * [JOB] delayed_job host:ip-10-251-197-159 pid:19994 failed with ActiveRecord::RecordNotFound: Couldn't find Photo with ID=9245 - 0 failed attempts 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob So what I get is that the photos are not being assigned ID's by paperclip. Anyone know where I could poke and pry from here? UPDATE: I created a clone application on a single server. And there are no problems. The images on the cluster do show up (occassionally). If I keep clicking on the folders that lead to photos, it will 50% of the time return a 404 with it not being able to find the photo, and the other half it will present the photo. So the problem has got to be with the server interaction between the ActiveRecord through multiple servers.

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• JDBC programms running long time performance issue

  - by phyerbarte

  My program has an issue with Oracle query performance, I believe the SQL have good performance, because it returns quickly in SQLPlus. But when my program has been running for a long time, like 1 week, the SQL query (using JDBC) becomes slower (In my logs, the query time is much longer than when I originally started the program). When I restart my program, the query performance comes back to normal. I think it is could be something wrong with the way I use the preparedStatement, because the SQL I'm using does not use placeholders "?" at all. Just a complex select query. The query process is done by a util class. Here is the pertinent code building the query: public List<String[]> query(String sql, String[] args) { Connection conn = null; conn = openConnection(); conn.setAutocommit(true); .... PreparedStatement preStatm = null; ResultSet rs = null; ....//set preparedstatment arg code rs = preStatm.executeQuery(); .... finally{ //close rs //close prestatm //close connection } } In my case, the args is always null, so it just passes a query sql to this query method. Is that possible this way could slow down the DB query after program long time running? Or I should use statement instead, or just pass args with "?" in the SQL? How can I find out the root cause for my issue? Thanks.

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• Best practices for (over)using Azure queues

  - by John

  Hi, I'm in the early phases of designing an Azure-based application. One of the things that attracts me to Azure is the scalability, given the variability of the demand I'm likely to expect. As such I'm trying to keep things loosely coupled so I can add instances when I need to. The recommendations I've seen for architecting an application for Azure include keeping web role logic to a minimum, and having processing done in worker roles, using queues to communicate and some sort of back-end store like SQL Azure or Azure Tables. This seems like a good idea to me as I can scale up either or both parts of the application without any issue. However I'm curious if there are any best practices (or if anyone has any experiences) for when it's best to just have the web role talk directly to the data store vs. sending data by the queue? I'm thinking of the case where I have a simple insert to do from the web role - while I could set this up as a message, send it on the queue, and have a worker role pick it up and do the insert, it seems like a lot of double-handling. However I also appreciate that it may be the case that this is better in the long run, in case the web role gets overwhelmed or more complex logic ends up being required for the insert. I realise this might be a case where the answer is "it depends entirely on the situation, check your perf metrics" - but if anyone has any thoughts I'd be very appreciative! Thanks John

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• How to use observer_field in RoR?

  - by Sindri Guðmundsson

  Hi, I have a single select_tag with categories gathered from array in controller. When the user selects a category I want the application to redirect to the selected category. I have the following code in my view which. (I've tried both using :method = :get and :post, only change is in development.log) <%=select_tag "cat_selected", options_for_select(@cats_for_mt)%><br> <%=observe_field 'cat_selected', :url => {:action => :viewflokkur}, :with => 'cat', :method => :get %> When I select one of the options the following gets logged to development.log. Processing CategoriesController#viewflokkur (for 127.0.0.1 at 2010-06-12 12:33:26) [GET] Parameters: {"cat"=>"Taugasjúkraþjálfun", "authenticity_token"=> "B2u5ULNr7IJ/ta0+hiAMBjmjEtTtc/yMAQQvSxFn2d0="} Rendering template within layouts/main Rendering categories/viewflokkur Completed in 20ms (View: 18, DB: 0) | 200 OK [http://localhost/categories/viewflokkur?cat=Taugasj%C3%BAkra%C3%BEj%C3%A1lfun&authenticity_token=B2u5ULNr7IJ%2Fta0%2BhiAMBjmjEtTtc%2FyMAQQvSxFn2d0%3D] According to this I should now be in "viewflokkur", but nothing changes in the browser window. Is there anything else I need to do, maybe in the controller? BR, Sindri

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• Short snippet summarizing a webpage?

  - by Legend

  Is there a clean way of grabbing the first few lines of a given link that summarizes that link? I have seen this being done in some online bookmarking applications but have no clue on how they were implemented. For instance, if I give this link, I should be able to get a summary which is roughly like: I'll admit it, I was intimidated by MapReduce. I'd tried to read explanations of it, but even the wonderful Joel Spolsky left me scratching my head. So I plowed ahead trying to build decent pipelines to process massive amounts of data Nothing complex at first sight but grabbing these is the challenging part. Just the first few lines of the actual post should be fine. Should I just use a raw approach of grabbing the entire html and parsing the meta tags or something fancy like that (which obviously and unfortunately is not generalizable to every link out there) or is there a smarter way to achieve this? Any suggestions? Update: I just found InstaPaper do this but am not sure if it is getting the information from RSS feeds or some other way.

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• Show a PDF file to the user with perl or php, not creating it nor download it. Just show it.

  - by dimassony

  Hello guys. I want to show my users PDF files. The reason why I use cgi to show the pdf is I want to track the clicks for the pdf, and cloak the real location of the saved pdf. I've been searching on the Internet and only found how to show save dialog to the users and creating a pdf, not show the files to the users. What I wanted for is show the users my pdf files, not creating or download the pdf. Here is what I got form the official php documentation: <?php header('Content-type: application/pdf'); readfile('the.pdf'); ?> Also my google-search-result perl code: open(PDF, "the.pdf") or die "could not open PDF [$!]"; binmode PDF; my $output = do { local $/; <PDF> }; close (PDF); print "Content-Type: application/pdf\n"; print "Content-Length: " .length($output) . "\n\n"; print $output if you do it on ruby, please say it to me. But I'm not sure if my server support rails. Sorry if my code is too far away from the method to show the pdf, since I don't know anything about pdf processing and how to implement this problem. Lets assume that the users have the Adobe Reader plug-in. So, how to fix my problem?

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• Working with a list, performing arithmetic logic in Python

  - by haea ohoh

  Suppose I have made a large list of numbers, and I want to make another one which I will add, pairwise, with the first list. Here's the first list, A: [109, 77, 57, 34, 94, 68, 96, 72, 39, 67, 49, 71, 121, 89, 61, 84, 45, 40, 104, 68, 54, 60, 68, 62, 91, 45, 41, 118, 44, 35, 53, 86, 41, 63, 111, 112, 54, 34, 52, 72, 111, 113, 47, 91, 107, 114, 105, 91, 57, 86, 32, 109, 84, 85, 114, 48, 105, 109, 68, 57, 78, 111, 64, 55, 97, 85, 40, 100, 74, 34, 94, 78, 57, 77, 94, 46, 95, 60, 42, 44, 68, 89, 113, 66, 112, 60, 40, 110, 89, 105, 113, 90, 73, 44, 39, 55, 108, 110, 64, 108] And here's B: [35, 106, 55, 61, 81, 109, 82, 85, 71, 55, 59, 38, 112, 92, 59, 37, 46, 55, 89, 63, 73, 119, 70, 76, 100, 49, 117, 77, 37, 62, 65, 115, 93, 34, 107, 102, 91, 58, 82, 119, 75, 117, 34, 112, 121, 58, 79, 69, 68, 72, 110, 43, 111, 51, 102, 39, 52, 62, 75, 118, 62, 46, 74, 77, 82, 81, 36, 87, 80, 56, 47, 41, 92, 102, 101, 66, 109, 108, 97, 49, 72, 74, 93, 114, 55, 116, 66, 93, 56, 56, 93, 99, 96, 115, 93, 111, 57, 105, 35, 99] How might I generate the arithmatic addition logic, processing each pairwise value one by one (A[0] and B[0], through A[99], B[99]) and producing the list C (A[0] + B[0] through A[99]+ B[99])?

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• Instrumenting a string

  - by George Polevoy

  Somewhere in C++ era i have crafted a library, which enabled string representation of the computation history. Having a math expression like: TScalar Compute(TScalar a, TScalar b, TScalar c) { return ( a + b ) * c; } I could render it's string representation: r = Compute(VerbalScalar("a", 1), VerbalScalar("b", 2), VerbalScalar("c", 3)); Assert.AreEqual(9, r.Value); Assert.AreEqual("(a+b)*c==(1+2)*3", r.History ); C++ operator overloading allowed for substitution of a simple type with a complex self-tracking entity with an internal tree representation of everything happening with the objects. Now i would like to have the same possibility for NET strings, only instead of variable names i would like to see a stack traces of all the places in code which affected a string. And i want it to work with existing code, and existing compiled assemblies. Also i want all this to hook into visual studio debugger, so i could set a breakpoint, and see everything that happened with a string. Which technology would allow this kind of things? I know it sound like an utopia, but I think visual studio code coverage tools actually do the same kind of job while instrumenting the assemblies.

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• Is there a recommended way to communicate scientific/engineering programming to C developers?

  - by ggkmath

  Hi, I have a lot of MATLAB code that needs to get ported to C (execution speed is critical for this work) as part of a back-end process for a web application. When I attempt to outsource this code to a C developer, I assume (correct me if I'm wrong) few C developers also understand MATLAB code (things like indexing and memory management are different, etc.). I wonder if there are any C developers out there that can recommend a procedure for me to follow to best communicate what the code does? For example, should I provide the MATLAB code and explain what it's doing line by line? Or, should I just provide the math/algorithm, explain it in plain English, and let the C developer implement it with this understanding in his/her own way (e.g. can I assume the developer understands how to work with complex math (i.e. imaginary numbers), how to generate histograms, perform an FFT, etc.)? Or, is there a better method? I expect I'm not the first to need to do this, so I wonder if any C developers out there ran into this situation and can share any conventional wisdom how they'd like this task to be transferred? Thanks in advance for any comments.

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• workaround for ORA-03113: end-of-file on communication channel

  - by Jefferstone

  The call to TEST_FUNCTION below fails with "ORA-03113: end-of-file on communication channel". A workaround is presented in TEST_FUNCTION2. I boiled down the code as my actual function is far more complex. Tested on Oracle 11G. Anyone have any idea why the first function fails? CREATE OR REPLACE TYPE "EMPLOYEE" AS OBJECT ( employee_id NUMBER(38), hire_date DATE ); CREATE OR REPLACE TYPE "EMPLOYEE_TABLE" AS TABLE OF EMPLOYEE; CREATE OR REPLACE FUNCTION TEST_FUNCTION RETURN EMPLOYEE_TABLE IS table1 EMPLOYEE_TABLE; table2 EMPLOYEE_TABLE; return_table EMPLOYEE_TABLE; BEGIN SELECT CAST(MULTISET ( SELECT user_id, created FROM all_users WHERE LOWER(username) < 'm' ) AS EMPLOYEE_TABLE) INTO table1 FROM dual; SELECT CAST(MULTISET ( SELECT user_id, created FROM all_users WHERE LOWER(username) >= 'm' ) AS EMPLOYEE_TABLE) INTO table2 FROM dual; SELECT CAST(MULTISET ( SELECT employee_id, hire_date FROM TABLE(table1) UNION SELECT employee_id, hire_date FROM TABLE(table2) ) AS EMPLOYEE_TABLE) INTO return_table FROM dual; RETURN return_table; END TEST_FUNCTION; CREATE OR REPLACE FUNCTION TEST_FUNCTION2 RETURN EMPLOYEE_TABLE IS table1 EMPLOYEE_TABLE; table2 EMPLOYEE_TABLE; return_table EMPLOYEE_TABLE; BEGIN SELECT CAST(MULTISET ( SELECT user_id, created FROM all_users WHERE LOWER(username) < 'm' ) AS EMPLOYEE_TABLE) INTO table1 FROM dual; SELECT CAST(MULTISET ( SELECT user_id, created FROM all_users WHERE LOWER(username) >= 'm' ) AS EMPLOYEE_TABLE) INTO table2 FROM dual; WITH combined AS ( SELECT employee_id, hire_date FROM TABLE(table1) UNION SELECT employee_id, hire_date FROM TABLE(table2) ) SELECT CAST(MULTISET ( SELECT * FROM combined ) AS EMPLOYEE_TABLE) INTO return_table FROM dual; RETURN return_table; END TEST_FUNCTION2; SELECT * FROM TABLE (TEST_FUNCTION()); -- Throws exception ORA-03113. SELECT * FROM TABLE (TEST_FUNCTION2()); -- Works

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• How to Bind a Command in WPF

  - by MegaMind

  Sometimes we used complex ways so many times, we forgot the simplest ways to do the task. I know how to do command binding, but i always use same approach. Create a class that implements ICommand interface and from the view model i create new instance of that class and binding works like a charm. This is the code that i used for command binding public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); DataContext = this; testCommand = new MeCommand(processor); } ICommand testCommand; public ICommand test { get { return testCommand; } } public void processor() { MessageBox.Show("hello world"); } } public class MeCommand : ICommand { public delegate void ExecuteMethod(); private ExecuteMethod meth; public MeCommand(ExecuteMethod exec) { meth = exec; } public bool CanExecute(object parameter) { return false; } public event EventHandler CanExecuteChanged; public void Execute(object parameter) { meth(); } } But i want to know the basic way to do this, no third party dll no new class creation. Do this simple command binding using a single class. Actual class implements from ICommand interface and do the work.

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• convert SQL Server StoredPorcedure to MySql

  - by karthik

  I need to covert the following SP of SQL Server To MySql. I am new to MySql.. Help needed. CREATE PROC InsertGenerator (@tableName varchar(100)) as --Declare a cursor to retrieve column specific information --for the specified table DECLARE cursCol CURSOR FAST_FORWARD FOR SELECT column_name,data_type FROM information_schema.columns WHERE table_name = @tableName OPEN cursCol DECLARE @string nvarchar(3000) --for storing the first half --of INSERT statement DECLARE @stringData nvarchar(3000) --for storing the data --(VALUES) related statement DECLARE @dataType nvarchar(1000) --data types returned --for respective columns SET @string='INSERT '+@tableName+'(' SET @stringData='' DECLARE @colName nvarchar(50) FETCH NEXT FROM cursCol INTO @colName,@dataType IF @@fetch_status<>0 begin print 'Table '+@tableName+' not found, processing skipped.' close curscol deallocate curscol return END WHILE @@FETCH_STATUS=0 BEGIN IF @dataType in ('varchar','char','nchar','nvarchar') BEGIN SET @stringData=@stringData+'''''''''+ isnull('+@colName+','''')+'''''',''+' END ELSE if @dataType in ('text','ntext') --if the datatype --is text or something else BEGIN SET @stringData=@stringData+'''''''''+ isnull(cast('+@colName+' as varchar(2000)),'''')+'''''',''+' END ELSE IF @dataType = 'money' --because money doesn't get converted --from varchar implicitly BEGIN SET @stringData=@stringData+'''convert(money,''''''+ isnull(cast('+@colName+' as varchar(200)),''0.0000'')+''''''),''+' END ELSE IF @dataType='datetime' BEGIN SET @stringData=@stringData+'''convert(datetime,''''''+ isnull(cast('+@colName+' as varchar(200)),''0'')+''''''),''+' END ELSE IF @dataType='image' BEGIN SET @stringData=@stringData+'''''''''+ isnull(cast(convert(varbinary,'+@colName+') as varchar(6)),''0'')+'''''',''+' END ELSE --presuming the data type is int,bit,numeric,decimal BEGIN SET @stringData=@stringData+'''''''''+ isnull(cast('+@colName+' as varchar(200)),''0'')+'''''',''+' END SET @string=@string+@colName+',' FETCH NEXT FROM cursCol INTO @colName,@dataType END

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• How to write a simple Lexer/Parser with antlr 2.7?

  - by Burkhard

  Hello, I have a complex grammar (in antlr 2.7) which I need to extend. Having never used antlr before, I wanted to write a very simple Lexer and Parser first. I found a very good explanation for antlr3 and tried to adapt it: header{ #include <iostream> using namespace std; } options { language="Cpp"; } class P2 extends Parser; /* This will be the entry point of our parser. */ eval : additionExp ; /* Addition and subtraction have the lowest precedence. */ additionExp : multiplyExp ( "+" multiplyExp | "-" multiplyExp )* ; /* Multiplication and addition have a higher precedence. */ multiplyExp : atomExp ( "*" atomExp | "/" atomExp )* ; /* An expression atom is the smallest part of an expression: a number. Or when we encounter parenthesis, we're making a recursive call back to the rule 'additionExp'. As you can see, an 'atomExp' has the highest precedence. */ atomExp : Number | "(" additionExp ")" ; /* A number: can be an integer value, or a decimal value */ number : ("0".."9")+ ("." ("0".."9")+)? ; /* We're going to ignore all white space characters */ protected ws : (" " | "\t" | "\r" | "\n") { newline(); } ; It does generate four files without errors: P2.cpp, P2.hpp, P2TokenTypes.hpp and P2TokenTypes.txt. But now what? How do I create a working programm with that? I tried to add these files to a VS2005-WinConsole-Project but it does not compile: p2.cpp(277) : fatal error C1010: unexpected end of file while looking for precompiled header. Did you forget to add '#include "stdafx.h"' to your source?

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• open current page in new window including query string

  - by Hatch

  First of all, I am a total dud at all things related to web developement, so please bear with me here. I suspect this question is laughable for the web guys, but unfortunately I can't figure this out. Here goes: I have an application, that does some processing, writes some result files and then displays the results in an embedded IE browser control. This is done by navigating the browser control to a local html file together with a query string containing the generated result files to display it all. The link target would look something like: c:\SomeFolder\results.htm?results=file%201.xml;file%202.xml;file%203.xml So far, everything's fine. However, in the html page is a href that is suppossed to open up the exact same just in a normal browser window. What I thought would work is: <a href="#" target="_blank">Show in browser</a> Since it is a link in an html page displayed in an IE control, the link will open up in IE no matter what the default browser might be. This works for IE7 and 8, but not for IE6. With IE6 the query string gets cut off and the browser opens file://c:/results/results.htm# without the query string. I am sure there must be a much better way to do this without the # and which would work in all IEs. How would the pros solve this?

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• What are CAD apps written in, and how are they organized ?

  - by ldigas

  What are CAD applications (Rhino, Autocad) of today written in and how are they organized internally ? I gave as an example, Autocad and Rhino, although I would love to hear of other examples as well. I'm particularly interested in knowing what is their backend written in (multilanguage ?) and how is it organized, and how do they handle their frontend (GUI) in real time ? Do they use native windows API's or some libraries of their own, since I imagine, as good as may be, the open source solutions on today's market won't cut it. I may be wrong ... As most of you who have used them know, they handle amongs other things relatively complex rotational operations in realtime (shading is not interesting me). I've been doing some experiments with several packages recently, and for some larger models found that there is considerable difference in speed in, for example, programed rotation (big full ship models) amongst some of them (which I won't name). So I'm wondering about their internals ... Also, if someone knows of some book on the subject, I'd be interested to hear of it.

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• IIS doesn't send two responses to the same client at the same time (only for ASP)

  - by dr. evil

  I've got 2 ASP pages. I do a request to the first page from Firefox (which takes 30 seconds to process on server-side), and during the execution of 30 seconds I do another request from Firefox to the second page (takes less than 1 second in server-side), but it does come after 31 second. Because it waits first requests to finish. When I request to the first page from Firefox and then request the second page from IE it's just instant. So basically ASP - IIS 6 somehow limiting every client to one request (long processing request) at a time. I need to get around this problem in my .NET client application. This is tested in 3 different systems. If you want to test you can try the ASP scripts at the end. This behaviour is same in a long SQL execution or just in a time consuming ASP operation. Note: It's not about HTTP Keep Alive It's not about persistent connection limit (we tried to increase this in firefox and in .NET with Net.ServicePointManager.DefaultConnectionLimit) It's not about User Agent This doesn't happen in ASP.NET so I assume it's something to the with ASP.dll I'm trying to solve this on the client not the server. I don't have direct control over the server it's a 3rd party solution. Is there any way to get around this? Sample ASP Code: First ASP: <% Set cnn = Server.CreateObject("Adodb.Connection") cnn.Open "Provider=sqloledb;Data Source=.;Initial Catalog=master;User Id=sa;Password=;" cnn.Execute("WAITFOR DELAY '0:0:30'") cnn.Close %> Second ASP: <% Response.Write "bla bla" %>

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• How not to lose binding source updates?

  - by Fyodor Soikin

  Suppose I have a modal dialog with a textbox and OK/Cancel buttons. And it is built on MVVM - i.e. it has a ViewModel object with a string property that the textbox is bound to. Say, I enter some text in the textbox and then grab my mouse and click "OK". Everything works fine: at the moment of click, the textbox loses focus, which causes the binding engine to update the ViewModel's property. I get my data, everybody's happy. Now suppose I don't use my mouse. Instead, I just hit Enter on the keyboard. This also causes the "OK" button to "click", since it is marked as IsDefault="True". But guess what? The textbox doesn not lose focus in this case, and therefore, the binding engine remains innocently ignorant, and I don't get my data. Dang! Another variation of the same scenario: suppose I have a data entry form right in the main window, enter some data into it, and then hit Ctrl+S for "Save". Guess what? My latest entry doesn't get saved! This may be somewhat remedied by using UpdateSourceTrigger=PropertyChanged, but that is not always possible. One obvious case would be the use of StringFormat with binding - the text keeps jumping back into "formatted" state as I'm trying to enter it. And another case, which I have encountered myself, is when I have some time-consuming processing in the viewmodel's property setter, and I only want to perform it when the user is "done" entering text. This seems like an eternal problem: I remember trying to solve it systematically from ages ago, ever since I've started working with interactive interfaces, but I've never quite succeeded. In the past, I always ended up using some sort of hacks - like, say, adding an "EnsureDataSaved" method to every "presenter" (as in "MVP") and calling it at "critical" points, or something like that... But with all the cool technologies, as well as empty hype, of WPF, I expected they'd come up with some good solution.

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• Is there really such a thing as "being good at math"?

  - by thezhaba

  Aside from gifted individuals able to perform complex calculations in their head, I'm wondering if proficiency in mathematics, namely calculus and algebra, has really got to do with one's natural inclination towards sciences, if you can put it that way. A number of students in my calculus course pick up material in seemingly no time whereas I, personally, have to spend time thinking about and understanding most concepts. Even then, if a question that requires a bit more 'imagination' comes up I don't always recognize the concepts behind it, as is the case with calculus proofs, for instance. Nevertheless, I refuse to believe that I'm simply not made for it. I do very well in programming and software engineering courses where a lot of students struggle. At first I could not grasp what they found to be so difficult, but eventually I realized that having previous programming experience is a great asset -- once I've seen and made practical use of the programming concepts learning about them in depth in an academic setting became much easier as I have then already seen their use "in the wild". I suppose I'm hoping that something similar happens with mathematics -- perhaps once the practical idea behind a concept (which authors of textbooks sure do a great job of concealing..) is evident, understanding the seemingly dry and symbolic ideas and proofs would be more obvious? I'm really not sure. All I'm sure of is I'd like to get better at calculus, but I don't yet understand why some of us pick it up easily while others have to spend considerable amounts of time on it and still not have complete understanding if an unusual problem is given.

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• Array passing between classes, gone?

  - by Kenneth

  Hey guys . i have two classes, SelectionScreenTable & GraphView. In the SelectionScreenTable class .h, i declared a NSMutableArray called usagedatas NSMutableArray *usagedatas; } @property (nonatomic, retain) NSMutableArray *usagedatas; In the SelectionScreenTable class.m i remembered to @synthesize. Later on, while processing my methods, i did a NSLog(@"usagedatas count:%i",usagedatas.count); to check whether it has value and it returned 1. so yeah its good up to this point. And in the -(void) dealloc , i remembered to released it . [usagedatas release]; So now comes ME trying to use it in another class. In GraphView.m i imported the "SelectionScreenTable.h". in the -(void)viewDidLoad i did SelectionScreenTable *UD = [SelectionScreenTable alloc]; NSLog(@"GraphView UD.usagedataas.count = :%i",UD.usagedatas.count); it returned 0. Any idea guys?

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• Four-color theorem in Prolog (using a dynamic predicate)

  - by outa

  Hi, I'm working on coloring a map according to the four-color theorem (http://en.wikipedia.org/wiki/Four_color_theorem) with SWI-Prolog. So far my program looks like this: colour(red). colour(blue). map_color(A,B,C) :- colour(A), colour(B), colour(C), C \= B, C \= A. (the actual progam would be more complex, with 4 colors and more fields, but I thought I'd start out with a simple case) Now, I want to avoid double solutions that have the same structure. E.g. for a map with three fields, the solution "red, red, blue" would have the same structure as "blue, blue, red", just with different color names, and I don't want both of them displayed. So I thought I would have a dynamic predicate solution/3, and call assert(solution(A,B,C)) at the end of my map_color predicate. And then, for each solution, check if they already exist as a solution/3 fact. The problem is that I would have to assert something like solution(Color1,Color1,Color2), i.e. with variables in order to make a unification check. And I can't think of a way to achieve this. So, the question is, what is the best way to assert a found solution and then make a unification test so that "red, red, blue" would unify with "blue, blue, red"?

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• OOP/MVC advice on where to place a global helper function

  - by franko75

  Hi, I have a couple of controllers on my site which are handling form data. The forms use AJAX and I have quite a few methods across different controllers which are having to do some specific processing to return errors in a JSON encoded format - see code below. Obviously this isn't DRY and I need to move this code into a single helper function which I can use globally, but I'm wondering where this should actually go! Should I create a static helper class which contains this function (e.g Validation::build_ajax_errors()), or as this code is producing a format which is application specific and tied into the jQuery validation plugin I'm using, should it be a static method stored in, for example, my main Website controller which the form handling controllers extend from? //if ajax request, output errors if (request::is_ajax()) { //need to build errors into array form for javascript validation - move this into a helper method accessible globally $errors = $post->errors('form_data/form_error_messages'); $i = 0; $new_errors = array(); foreach ($errors as $key => $value) { $new_errors[$i][0] = '#' . $key; $new_errors[$i][1] = $value; $new_errors[$i][2] = "error"; $i++; } echo '{"jsonValidateReturn":' . json_encode($new_errors) . '}'; return; }

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• How to write an R function that evaluates an expression within a data-frame

  - by Prasad Chalasani

  Puzzle for the R cognoscenti: Say we have a data-frame: df <- data.frame( a = 1:5, b = 1:5 ) I know we can do things like with(df, a) to get a vector of results. But how do I write a function that takes an expression (such as a or a > 3) and does the same thing inside. I.e. I want to write a function fn that takes a data-frame and an expression as arguments and returns the result of evaluating the expression "within" the data-frame as an environment. Never mind that this sounds contrived (I could just use with as above), but this is just a simplified version of a more complex function I am writing. I tried several variants ( using eval, with, envir, substitute, local, etc) but none of them work. For example if I define fn like so: fn <- function(dat, expr) { eval(expr, envir = dat) } I get this error: > fn( df, a ) Error in eval(expr, envir = dat) : object 'a' not found Clearly I am missing something subtle about environments and evaluation. Is there a way to define such a function?

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• Object Design catalog and resources

  - by Tauren

  I'm looking for web sites, books, or other resources that provide a catalog of object designs used in common scenarios. I'm not looking for generic design patterns, but for samples of actual object designs that were used to solve real problems. For instance, I'm about to build an internal messaging system for a web application, similar to Facebook's messaging system. This system will allow administrators to send messages to all members, to selected groups of members, or to individuals. Members can send messages to other members or groups of members. Fairly common stuff and a feature that I'm sure thousands of web applications require. I know each situation is different and there are a million ways to design this solution. Although this scenario isn't really all that complex, I'm sure the basic design of the necessary objects and relationships for a system like this has already been done many times. It would be nice to review other similar designs before building my own. Is there a place where people can share their designs and others can browse/search through the catalog to review and provide feedback on them? StackOverflow could be used to a degree for this, but doesn't really provide a catalog of designs. Any other resources that would relate?

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• How to filter and intercept Linux packets by using net_dev_add() API?

  - by Khajavi

  I'm writing ethernet network driver for linux. I want to receive packets, edit and resend them. I know how to edit the packet in packet_interceptor function, but how can I drop incoming packets in this function?? #include <linux/netdevice.h> #include <linux/skbuff.h> #include <linux/ip.h> #include <net/sock.h> struct packet_type my_proto; int packet_interceptor(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev) { // I dont want certain packets go to upper in net_devices for further processing. // How can I drop sk_buff here?! return 0; } static int hello_init( void ) { printk(KERN_INFO "Hello, world!\n"); my_proto.type = htons(ETH_P_ALL); my_proto.dev = NULL; my_proto.func = packet_interceptor; dev_add_pack(&my_proto); return 0; } static void hello_exit(void) { dev_remove_pack(&my_proto); printk(KERN_INFO "Bye, world\n"); } module_init(hello_init); module_exit(hello_exit);

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• When to use @Singleton in a Jersey resource

  - by dexter

  I have a Jersey resource that access the database. Basically it opens a database connection in the initialization of the resource. Performs queries on the resource's methods. I have observed that when I do not use @Singleton, the database is being open at each request. And we know opening a connection is really expensive right? So my question is, should I specify that the resource be singleton or is it really better to keep it at per request especially when the resource is connecting to the database? My resource code looks like this: //Use @Singleton here or not? @Path(/myservice/) public class MyResource { private ResponseGenerator responser; private Log logger = LogFactory.getLog(MyResource.class); public MyResource() { responser = new ResponseGenerator(); } @GET @Path("/clients") public String getClients() { logger.info("GETTING LIST OF CLIENTS"); return responser.returnClients(); } ... // some more methods ... } And I connect to the database using a code similar to this: public class ResponseGenerator { private Connection conn; private PreparedStatement prepStmt; private ResultSet rs; public ResponseGenerator(){ Class.forName("org.h2.Driver"); conn = DriverManager.getConnection("jdbc:h2:testdb"); } public String returnClients(){ String result; try{ prepStmt = conn.prepareStatement("SELECT * FROM hosts"); rs = prepStmt.executeQuery(); ... //do some processing here ... } catch (SQLException se){ logger.warn("Some message"); } finally { rs.close(); prepStmt.close(); // should I also close the connection here (in every method) if I stick to per request // and add getting of connection at the start of every method // conn.close(); } return result } ... // some more methods ... } Some comments on best practices for the code will also be helpful.

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