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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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• Java: IDE working well with Maven War overlays

  - by Thorbjørn Ravn Andersen

  We have a Java EE 6 web application which is fully mavenized, and we use the Maven "war overlay" facility to add customer specific files, and which currently runs in Glassfish 3.1. We have traditionally used Eclipse for development, but I have found that the combination of Maven processing and War deployments may not be optimal in terms of deployment times, and that the mavenization allows us to use any IDE with good Maven support. Therefore is Eclipse the best bet for our particular scenario (maven war overlays - glassfish, and debugging it) or is e.g. Netbeans or IntelliJ better? Please, back opinions with actual experiences, thanks.

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• How do I set default values on new properties for existing entities after light weight core data migration?

  - by Moritz

  I've successfully completed light weight migration on my core data model. My custom entity Vehicle received a new property 'tirePressure' which is an optional property of type double with the default value 0.00. When 'old' Vehicles are fetched from the store (Vehicles that were created before the migration took place) the value for their 'tirePressure' property is nil. (Is that expected behavior?) So I thought: "No problem, I'll just do this in the Vehicle class:" - (void)awakeFromFetch { [super awakeFromFetch]; if (nil == self.tirePressure) { [self willChangeValueForKey:@"tirePressure"]; self.tirePressure = [NSNumber numberWithDouble:0.0]; [self didChangeValueForKey:@"tirePressure"]; } } Since "change processing is explicitly disabled around" awakeFromFetch I thought the calls to willChangeValueForKey and didChangeValueForKey would mark 'tirePresure' as dirty. But they don't. Every time these Vehicles are fetched from the store 'tirePressure' continues to be nil despite having saved the context.

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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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• 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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• 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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• 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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• 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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• Android on Eclipse - Adding jar files to an Eclipse Android Project

  - by Shalini

  I am developing an Android App that uses the Google APIs Client Library for Java version 1.12.0. I have added the jar files to the /libs folder (and not to a new /lib folder). I get the following error: Dx trouble processing "javax/xml/namespace/QName.class": Ill-advised or mistaken usage of a core class (java.* or javax.*) when not building a core library. I am NOT using Maven though, and all the answers by others seem to make use of Maven. Android version - 4.1.2 API level 16 Eclipse - Java EE Juno Any suggestions on how I can solve this?

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• How can I detect whether an image is a PNG or APNG format?

  - by perlit

  APNG is backwards compatible with PNG. I opened up an apng and png file in a hex editor and the first few bytes look identical. So if a user uploads either of these formats, how do I detect what the format really is? I've seen this done on some sites that block apng. I'm guessing the ImageMagick library makes this easy, but what if I were to do the detect without the use of an image processing library (for learning purposes)? Can I look for specific bytes that tell me if the file is apng? Solutions in any language is welcome.

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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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• 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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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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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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• Does QThread::sleep() require the event loop to be running?

  - by suszterpatt

  I have a simple client-server program written in Qt, where processes communicate using MPI. The basic design I'm trying to implement is the following: The first process (the "server") launches a GUI (derived from QMainWindow), which listens for messages from the clients (using repeat fire QTimers and asynchronous MPI receive calls), updates the GUI depending on what messages it receives, and sends a reply to every message. Every other process (the "clients") runs in an infinite loop, and all they are intended to do is send a message to the server process, receive the reply, go to sleep for a while, then wake up and repeat. Every process instantiates a single object derived from QThread, and calls its start() method. The run() method of these classes all look like this: from foo.cpp: void Foo::run() { while (true) { // Send message to the first process // Wait for a reply // Do uninteresting stuff with the reply sleep(3); // also tried QThread::sleep(3) } } In the client's code, there is no call to exec() anywhere, so no event loop should start. The problem is that the clients never wake up from sleeping (if I surround the sleep() call with two writes to a log file, only the first one is executed, control never reaches the second). Is this because I didn't start the event loop? And if so, what is the simplest way to achieve the desired functionality?

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• Rails messing up with HTTP POST Params

  - by Julien Genestoux

  Our app provides an API that people can use to submit URLs like this: curl -X POST http://app.local/resource -d'url=http://news.google.com/newshl=en&q=obama&um=1&ie=UTF-8&output=rss' Unfortunately, it seems that Rails messes up with this param. Any idea on how to fix this? See the log below : Processing ApplicationController#index (for 127.0.0.1 at 2010-06-08 19:03:09) [POST] Parameters: {"um"=>"1", "url"=>"http://news.google.com/newshl=en", "output"=>"rss", "q"=>"obama", "ie"=>"UTF-8"} I would expect the following : Parameters: {"url"=>"hhttp://news.google.com/newshl=en&q=obama&um=1&ie=UTF-8&output=rss"}

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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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• 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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• Two questions on ensuring EndInvoke() gets called on a list of IAsyncResult objects

  - by RobV

  So this question is regarding the .Net IAsyncResult design pattern and the necessity of calling EndInvoke as covered in this question Background I have some code where I'm firing off potentially many asynchronous calls to a particular function and then waiting for all these calls to finish before using EndInvoke() to get back all the results. Question 1 I don't know whether any of the calls has encountered an exception until I call EndInvoke() and in the event that an exception occurs in one of the calls the entire method should fail and the exception gets wrapped into an API specific exception and thrown upwards. So my first question is what's the best way then to ensure that the remainder of the async calls get properly terminated? Is a finally block which calls EndInvoke() on the remainder of the unterminated calls (and ignores any further exceptions) the best way to do this? Question 2 Secondly when I first fire off all my asyc calls I then call WaitHandle.WaitAll() on the array of WaitHandle instances that I've got from my IAsyncResult instances. The method which is firing all these async calls has a timeout to adhere to so I provide this to the WaitAll() method. Then I test whether all the calls have completed, if not then the timeout must have been reached so the method should also fail and throw another API specific exception. So my second question is what should I do in this case? I need to call EndInvoke() to terminate all these async calls before I throw the error but at the same time I don't want the code to get stuck since EndInvoke() is blocking. In theory at least if the WaitAll() call times out then all the async calls should themselves have timed out and thrown exceptions (thus completing the call) since they are also governed by a timeout but this timeout is potentially different from the main timeout

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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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• 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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• 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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• 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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• 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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• 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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