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• Using thread inter-communication to increase my server app's IO throughput; not sure how

  - by Howard Guo

  My server application creates a new thread for each incoming connection. Incoming requests are serialized in a BlockingQueue. There is one worker thread taking items from the queue, produce a response and send the response through socket. I have noticed a throughput issue: Currently, worker thread is responsible of sending the response message through socket, thus severely wasting processing power and throughput. I am considering: rather than sending the response itself, why not telling network IO threads to send the response? However, when I think about thread inter-communication, I cannot yet figure out how to approach it: Worker thread will produce a response, but how will it inform the response message to IO thread? Is there a standard/best practice? Thank you.

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• Should XML be used server-side, and JSON client-side?

  - by Michel Carroll

  As a personal project, I'm making an AJAX chatroom application using XML as a server-side storage, and JSON for client-side processing. Here's how it works: AJAX Request gets sent to PHP using GET (chat messages/logins/logouts) PHP fetches/modifies the XML file on the server PHP encodes the XML into JSON, and sends back JSON response Javascript handles JSON information (chat messages/logins/logouts) I want to eventually make this a larger-scale chatroom application. Therefore, I want to make sure it's fast and efficient. Was this a bad design choice? In this case, is switching between XML and JSON ok, or is there a better way?

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• Add UIView Above All Other Views, Including StatusBar

  - by Mike Stead

  I'm wanting to create a view (UIControl) which blocks all input and shows a UIActivityIndicatorView while authenticating a user. The UIActionSheet and UIAlertView both manage to add a black semi-transparent view over the top of all other views to block input and I'd like to do similar. I've tried adding my view to the top UIWindow in the [[UIApplication sharedApplication] windows] array, and while this does place it above the UIKeyboard if it's visible, it doesn't place it over the StatusBar (which makes sense). My next attempt was to extend UIAlertView, remove all of its subviews and set its layer.contents = nil, then add the ActivityIndicator as a subview. This works well, but I can't seem to kill the default bouncy transition of the UIAlertView when you call it to "show". Does anyone have any pointers towards the best way tackle this problem that gives me full control? Oh and I know blocking input is not great but I do ensure it's for a short period of time and it has the benefit of making it clear to the user that their action, which must complete for them to progress, is processing.

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• Errors detected when loading a vim plugin from .vimrc

  - by Tejinder

  I have installed vim 7.3 on debian system along with some vimrc i have downloaded from internet. It used to work fine on my other debian machine but here i get these error messages while i load the vim editor. Here are the errors: Error detected while processing /home/tejinder/.vim/plugin/gundo.vim: line 196: E319: Sorry, the command is not available in this version: python << ENDPYTHON line 197: E492: Not an editor command: def asciiedges(seen, rev, parents): line 199: E121: Undefined variable: rev E15: Invalid expression: rev not in seen: line 221: E133: :return not inside a function line 231: E133: :return not inside a function line 233: E133: :return not inside a function line 235: E133: :return not inside a function line 238: E690: Missing "in" after :for line 347: E690: Missing "in" after :for line 356: E690: Missing "in" after :for line 453: E690: Missing "in" after :for line 464: E690: Missing "in" after :for line 469: E133: :return not inside a function line 795: E170: Missing :endfor Press ENTER or type command to continue If anyone could figure out thats going on, please guide me. Thanks a lot. Here is vimrc source: https://github.com/mitsuhiko/dotfiles/tree/master/vim

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• How do I get callgrind to dump source line information?

  - by Jeremybub

  I'm trying to profile a shared library on GNU/Linux which does real-time audio processing, so performance is important. I run another program which hooks it up to the audio input and output of my system, and profile that with callgrind. Looking at the results in KCacheGrind, I get great information about what functions are taking up most of my time. However, it won't let me look at the line by line information, and instead says I need to compile it with debugging symbols and run the profiling again. The program which I am profiling is not compiled with debug symbols, but the library is. And I know this, because interestingly, source code annotations for cachegrind work fine. When I run callgrind, it says the default is to dump source line information, but it just isn't doing that. Is there some way I could force it to, or figure out what's stopping it?

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• How to print element values when iterating through XML document in PHP

  - by pharma_joe

  I am iterating through the results of a service call to yahoo news thus: //Send service request if (!$yahooResults = file_get_contents($yahooRequest)) { echo 'Error processing service request'; } //Read result into xml document $yahooResultXml = new DOMDocument('1.0', 'UTF-8'); $yahooResultXml-loadXML($yahooResults); //Build page include_once('components/pageHeader.php'); echo 'Search Results'; //echo $yahooResultXml-saveHTML(); //Iterate over each Result node $stories = $yahooResultXml-getElementsByTagName('Result'); foreach ($stories as $story) { //Title //Summary //Url //Source //Language //Publish Date //Modification Date } include_once('components/pageFooter.php'); Each Title is in a Title node within a Result Node. I cannot figure out how to simply echo the content of the Title node!

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• Quick Question: How can I make sure the current directory is not changed because of OpenFileDialog?

  - by pecker

  say my application is installed in C:\programfiles\xyz\ I've some setting & other data files (*.dat files) in this directory too. My application uses OpenFileDialog to open an image. Problem is that when ever user browses to some directory (say MyPictures) for an image. The current working directory of the application becomes that directory (MyPictures in this case). After user inputs the image. I do some processing over it and save some values to imagedata.dat which will be located in the path where original application is installed.(C:\programfiles\xyz here ) In my code I'm just using FileStream("imagedata.dat",...,...) without any path prefix before the filename. Problem here is that application is crashing because it is searching for imagedata.dat in 'MyPictures\imagedata.dat'. How can I avoid this?

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• How does Task Parallel Library scale on a terminal server or in a web application?

  - by Lasse V. Karlsen

  I understand that the TPL uses work-stealing queues for its tasks when I execute things like Parallel.For and similar constructs. If I understand this correctly, the construct will spin up a number of tasks, where each will start processing items. If one of the tasks complete their allotted items, it will start stealing items from the other tasks which hasn't yet completed theirs. This solves the problem where items 1-100 are cheap to process and items 101-200 are costly, and one of the two tasks would just sit idle until the other completed. (I know this is a simplified exaplanation.) However, how will this scale on a terminal server or in a web application (assuming we use TPL in code that would run in the web app)? Can we risk saturating the CPUs with tasks just because there are N instances of our application running side by side? Is there any information on this topic that I should read? I've yet to find anything in particular, but that doesn't mean there is none.

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• performance of parameterized queries for different db's

  - by tuinstoel

  A lot of people know that it is important to use parameterized queries to prevent sql injection attacks. Parameterized queries are also much faster in sqlite and oracle when doing online transaction processing because the query optimizer doesn't have to reparse every parameterized sql statement before executing. I've seen sqlite becoming 3 times faster when you use parameterized queries, oracle can become 10 times faster when you use parameterized queries in some extreme cases with a lot of concurrency. How about other db's like mysql, ms sql, db2 and postgresql? Is there an equal difference in performance between parameterized queries and literal queries?

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• Memory Warning but Small Live Bytes

  - by Kamchatka

  Hi everyone, In my application, I get a memory warning of level 1 and then 2 after repeating some action (choosing a picture + processing) several times and then a crash. The leak tool doesn't show any leak. I'm also following the Allocations tool in Instruments and my Live Bytes are roughly 4 MB, overall I allocate 113 MB. At maximum I have maybe 20 MB in memory when the picture is loaded. Since I have to repeat an action to get to the crash, it is very likely to be a memory leak. However, I don't know how to locate it since my live bytes are 4 MB and things supposed to be allocated (apart a small leak of ~100 KB in the UIImagePickerController). How much can I trust the memory leak/allocation tools? Would you have an advice to help me locate the reason of the problem?

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• help with matlab and Discrete Fourier transform

  - by user504363

  Hi all I have previous experience with Matlab, but the problem that I face some problems in apply a problem in (DSP : Digital signal processing) which is not my study field, but I must finish that problems in days to complete my project. all i want is help me with method and steps of solving this problem in matlab and then I can write the code with myself. the problem is about the signal x(t) = exp(-a*t); 1) what's the Discrete Fourier transform of the sampled signal with sample rate fs 2) if a=1 and fs =1 , plot the amplitude spectrum of sampled signal 3) fix the sampling frequency at fs = 1(hz) [what's it mean ?] and plot the magnitude of the Fourier Transform of the sampled signal at various values of a thanks

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• MYSQL and the LIMIT clause

  - by Lizard

  I was wondering if adding a LIMIT 1 to a query would speed up the processing? For example... I have a query that will most of the time return 1 result, but will occasionaly return 10's, 100's or even 1000's of records. But I will only ever want the first record. Would the limit 1 speed things up or make no difference? I know I could use GROUP BY to return 1 result but that would just add more computation. Any thoughts gladly accepted! Thanks

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• Java style FOR loop in a clojure interpeter ?

  - by Kevin

  I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; (def do-trace false) ;; ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error)))

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• Can Qt's QWebView display programatically generated XML?

  - by Dan Ellis

  Using Qt 4.6, I can dynamically add to an HTML page like this: ui->webView->page()->mainFrame()->documentElement().findFirst("body").appendInside("<i>some text</i>\n"); However, if I QWebView::load() an XML file, it displays it with the correct CSS styling (from an processing instruction), but doesn't show any changes when I do something like: ui->webView->page()->mainFrame()->documentElement().findFirst("lines").appendInside("<line>hello</line>\n"); Why is it treating them differently, and is there a way to modify an XML document in the same way I can an HTML one?

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• Best way to return a user-generated file, AJAX or Forms?

  - by Bill Zimmerman

  Hi, I'm new to web programming, so I need some help. I am writing a custom file-creation app for my site. A user visits the page, clicks on some various options and toggles some checkboxes, and the presses a 'download now' link. I have a PHP backend which will be processing the submission, and generating a PDF file. After the user presses the download link, I want the download to start like it would for any static link. My question is: What is the best way to do this? From my limited understanding, I have a choice between using AJAX or somehow using forms to submit the data. What are the advantages/disadvantages of each? Does anyone have any good links to examples? Thanks

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• XSD - problem with schema generation

  - by lm

  Hello I'm tring to generate schema for some type from assembly with xsd.exe here is command line : xsd.exe TestAssemby.dll /t:TestType Here is error I got Error: There was an error processing 'TestAssemby.dll'. - Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information I copied referenced dll into folder where is located according to http://social.msdn.microsoft.com/Forums/en/xmlandnetfx/thread/308e4f3a-e1c3-43f5-b7a6-a82f1395997d but still get the same error I have questions : 1) What can be possible reasons of such error ? 2) How should be used LoaderExceptions property ? ( example will be very helpful) Thanks in advance

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• Speeding up jQuery empty() or replaceWith() Functions When Dealing with Large DOM Elements

  - by Levi Hackwith

  Let me start off by apologizing for not giving a code snippet. The project I'm working on is proprietary and I'm afraid I can't show exactly what I'm working on. However, I'll do my best to be descriptive. Here's a breakdown of what goes on in my application: User clicks a button Server retrieves a list of images in the form of a data-table Each row in the table contains 8 data-cells that in turn each contain one hyperlink Each request by the user can contain up to 50 rows (I can change this number if need be) That means the table contains upwards of 800 individual DOM elements My analysis shows that jQuery("#dataTable").empty() and jQuery("#dataTable).replaceWith(tableCloneObject) take up 97% of my overall processing time and take on average 4 - 6 seconds to complete. I'm looking for a way to speed up either of the above mentioned jQuery functions when dealing with massive DOM elements that need to be removed / replaced. I hope my explanation helps.

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• How to block non-browser clients from submitting a request?

  - by Thomas Kohl

  I want to block non-browser clients from accessing certain pages / successfully making a request. The website content is served to authenticated users. What happens is that our user gives his credentials to our website to 3rd party - it can be another website or a mobile application - that performs requests on his behalf. Say there is a form that the user fills out and sends a message. Can I protect this form so that the server processing the submission can tell whether the user has submitted it directly from the browser or not? I don't want to use CAPTCHA for usability reasons. Can I do it with some javascript?

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• Problem w/ Paperclip, MacPorts, ImageMagick & Snow Leopard

  - by Kyle Decot

  I'm attempting to use ImageMagick along w/ Paperclip to handle the images on my rails app. The problem is whenever I try to upload an image I get the following in the terminal: [paperclip] An error was received while processing: #<Paperclip::NotIdentifiedByImageMagickError: /var/folders/go/goZ833AaFaqyvv5RnLqQmE+++TM/-Tmp-/stream20110107-6356-1xfs9j1-0.jpg is not recognized by the 'identify' command.> I have added the following to my environments/development.rb file: Paperclip.options[:command_path] = "/usr/local/bin" If I try to interact w/ ImageMagick in the terminal by using "convert" or something similar I get: dyld: Library not loaded: /opt/local/lib/libltdl.7.dylib Referenced from: /usr/local/bin/convert Reason: Incompatible library version: convert requires version 10.0.0 or later, but libltdl.7.dylib provides version 9.0.0 Trace/BPT trap I've already tried updating everything w/ port but the problem still persists. Does anyone have any ideas or suggestions?

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• Rails ActiveRecord: Find All Users Except Current User

  - by SingleShot

  I feel this should be very simple but my brain is short-circuiting on it. If I have an object representing the current user, and want to query for all users except the current user, how can I do this, taking into account that the current user can sometimes be nil? This is what I am doing right now: def index @users = User.all @users.delete current_user end What I don't like is that I am doing post-processing on the query result. Besides feeling a little wrong, I don't think this will work nicely if I convert the query over to be run with will_paginate. Any suggestions for how to do this with a query? Thanks.

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• Struts/JSP/J2EE performance and memory profiling and issues

  - by Berlin Brown

  We are using Struts and having performance issues. And making heavy use of jsp includes, tiles, EL expressions. I am sure this is eating up a lot of memory and processing time. What are some approaches to profile the JSP page? What tools could I use? What should I look for when profiling? I have seen the code generated JSP Java Servlet Code and I see the bottlenecks but would rather measure it more accurately. This is under JDK1.5 and IBM Websphere 6.1 (RAD7)

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• Will there be IQueryable-like additions to IObservable? (.NET Rx)

  - by Jason

  The new IObservable/IObserver frameworks in the System.Reactive library coming in .NET 4.0 are very exciting (see this and this link). It may be too early to speculate, but will there also be a (for lack of a better term) IQueryable-like framework built for these new interfaces as well? One particular use case would be to assist in pre-processing events at the source, rather than in the chain of the receiving calls. For example, if you have a very 'chatty' event interface, using the Subscribe().Where(...) will receive all events through the pipeline and the client does the filtering. What I am wondering is if there will be something akin to IQueryableObservable, whereby these LINQ methods will be 'compiled' into some 'smart' Subscribe implementation in a source. I can imagine certain network server architectures that could use such a framework. Or how about an add-on to SQL Server (or any RDBMS for that matter) that would allow .NET code to receive new data notifications (triggers in code) and would need those notifications filtered server-side.

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• Wait for tasks to get completed in threadpool.

  - by Alien01

  Hello I have created a thread pool in C++ which stores all tasks in a queue. Thread pool start n number of threads which takes tasks from queue , process each task and then delete tasks from queue. Now , I want to wait till all tasks get completed. Checking for empty queue for completion of tasks may not work as , task can be given to each thread and queue can be emptied but still the tasks can in processing mode. I am not getting idea how to wait for all the tasks completion.This is a design problem. Any suggestions?

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• How do I hide data/field in a List in J2ME

  - by pi

  Hi, I am working on a J2ME app which has dynamically generated Lists. Items on this list may be consequently selected, and the selection processed within the commandAction block. Is there a way to have the IDs of variables populating the List (from a remote database) included in the List item definition as in: this.append("A", null); this.append("B", null); or: String[] arrayOfValues = {"A", "B"}; new List("Menu", List.IMPLICIT, arrayOfValues, null); such that when an item is selected, perhaps A, I can also have its database ID for perhaps further processing. Is it possible to hide a field/data? Thanks.

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• Python - question regarding the concurrent use of `multiprocess`.

  - by orokusaki

  I want to use Python's multiprocessing to do concurrent processing without using locks (locks to me are the opposite of multiprocessing) because I want to build up multiple reports from different resources at the exact same time during a web request (normally takes about 3 seconds but with multiprocessing I can do it in .5 seconds). My problem is that, if I expose such a feature to the web and get 10 users pulling the same report at the same time, I suddenly have 60 interpreters open at the same time (which would crash the system). Is this just the common sense result of using multiprocessing, or is there a trick to get around this potential nightmare? Thanks

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