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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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• c++ Sorting a vector based on values of other vector, or what's faster?

  - by pollux

  Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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• MS DOS function like ipconfig to get system performance specs?

  - by JustADude

  I am aware of MSINFO32, but I'm wondering if there is a MS DOS command similar to ipconfig in order to get system specifications? I would like for the system specifications to be displayed in the MS DOS prompt. I would like to see at least: CPU RAM BUS speed Thanks for any insights. Edit: I am unable to install any other software, so just have to use existing DOS programming commands to extract this information. Thank you again. 2nd Edit: Whoops. Using Windows XP and Windows Vista.

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• Is putting the javascript before the closing body tag okay on an asp.net website?

  - by Jason Weber

  I pretty much stated what I have to ask. But is taking all of your external .js files and putting them before the closing body tag on your master pages okay on an asp.net website? I'm just going off of what yslow and google speed have been showing. I can't combine these javascripts, so I'm trying to load them "after page load", but doing so makes them useless; some of my jquery things don't work. I moved my .js files above the opening body tag, and they work. What am I doing wrong? And what could I do to load my .js files after page load? Thanks for any advice anybody can offer!

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• How do I implement jQuery image cycle loops on rollover for multiple thumbnail sets on a page?

  - by Kendrick Ledet

  Here is the Javascript I currently have <script type="text/javascript"> $(function() { $('.slideshow').hover( function() { $('.slides').cycle('resume'); }, function() { $('.slides').cycle('pause'); } ); $('.slides').cycle({ fx: 'fade', speed: .3, timeout: 280, next: '#next', prev: '#prev' }).cycle("pause"); }); </script> It works; but the thing is it works for all thumbnail sets on the page, and whenever I mouseover on one set of images, every other set of images loops as well. I do see that this is because I'm targeting classes, but my jQuery experience is quite limited so I have no idea how to only target a single instance of each class without effecting the others, and I can't go in and hardcode id's because my thumbnails and amount of videos on each page are determined dynamically via this Django template. http://pastebin.com/nf42bSAx I would greatly appreciate any help, as this is essential for my project (open source media platform). Thank you.

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• SQL Server, fetching data from multiple joined tables. Why is slow?

  - by user562192

  I have problem with performance when retrieving data from SQL Server. My sql query looks something like this: SELECT table_1.id, table_1.value, table_2.id, table_2.value,..., table_20.id, table_20.value From table_1 INNER JOIN table_2 ON table_1.id = table_2.table_1_id INNER JOIN table_3 ON table_2.id = table_3.table_2_id... WHERE table_1.row_number BETWEEN 1 AND 20 So, I am fetching 20 results. This query takes about 5 seconds to execute. When I select only table_1.id, it returns results instantly. Because of that, I guess that problem is not in JOINs, it is in retrieving data from multiple tables. Any suggestions how I would speed up this query?

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• What's the most efficient way to manage large datasets with Javascript/jQuery in IE?

  - by RenderIn

  I have a search that returns JSON, which I then transform into a HTML table in Javascript. It repeatedly calls the jQuery.append() method, once for each row. I have a modern machine, and the Firefox response time is acceptable. But in IE 8 it is unbearably slow. I decided to move the transformation from data to HTML into the server-side PHP, changing the return type from JSON to HTML. Now, rather than calling the jQuery.append() time repeatedly, I call the jQuery.html() method once with the entire table. I noticed Firefox got faster, but IE got slower. These results are anecdotal and I have not done any benchmarking, but the IE performance is very disappointing. Is there something I can do to speed up the manipulation of large amounts of data in IE or is it simply a bad idea to process very much data at once with AJAX/Javascript?

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• Hold most of the object in cache/memory insted of database?

  - by feiroox

  Hi All, It just occurred to me why not to have most of the objects in a cache(memory) when an application start. if it's not that large web application. Or to have a settings for how much I want to put in the cache/memory. I just guess it could require to have something like below 1 GB RAM or a lot less. Everything in order to speed up the application even more by not querying database. Is it good idea?

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• Why is numpy c extension slow?

  - by Bitwise

  I am working on large numpy arrays, and some native numpy operations are too slow for my needs (for example simple operations such as "bitwise" A&B). I started looking into writing C extensions to try and improve performance. As a test case, I tried the example given here, implementing a simple trace calculation. I was able to get it to work, but was surprised by the performance: for a (1000,1000) numpy array, numpy.trace() was about 1000 times faster than the C extension! This happens whether I run it once or many times. Is this expected? Is the C extension overhead that bad? Any ideas how to speed things up?

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• Breaking out of .emacs script

  - by prosseek

  I use two emacs (Aquamcs and text based emacs) on my Mac. I normally use text based emacs for just editing something, so I don't want to load anything with it. What I came up with is to have the checking code in .emacs to exit/break if it's text based emacs (darwin system but not aquamacs). (when (and (equal system-type 'darwin) (not (boundp 'aquamacs-version))) (exit) ??? (break) ???? ) It seems to work, but I don't know how to break out of .emacs. How to do that? ADDED I just wanted to speed up in loading text based emacs on my mac, and I thought about breaking out as a solution. Based on the helpful answers, I came up with the following code that runs .emacs only when it's not a text based emacs. (setq inhibit-splash-screen t) (unless (null window-system)

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• Small questions on data structure

  - by John Graveston

  Hi, I'm trying to search the parent of a node with Kruskal's algorithm. My program works just fine, but I think I have heard of a method to improve the speed of the algorithm by reconstructing the tree while searching for the parent node and connecting it to the parent node. I'm pretty sure that I've heard of this somewhere, maybe in a lecture. Can anyone refresh my memory? And also, given a number of arrays, when searching for the minimum and the maximum value from a certain section of an array, what is the name of the tree that can calculate the minimum/maximum value from the array by making a binary tree that has the minimum/maximum value of each array in O(log N)?

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• Getting facts from documents

  - by dotnetdev

  Hi, I want to be able to get all the facts from webpages. But these have to be related to coding, and not, for example, about something irrelevant. For example: The Engine renders at a decent speed. May be a fact but is not what I am interested in. If the same article states: A class is a reference type. (This is C#) Then I am interested in that as it is coding related. Has an algorithm like this ever been done? How hard would this be? I'm thinking AI would come into play here. Any advice sought. Thanks

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• Can't get jQuery and IE to be friends

  - by Matthew

  Using jQuery and the Cycle plugin. Runs flawless in Safari, Chrome, Firefox, and the latest version of Opera. Won't run in older versions of Opera, and of course, IE. I know its running Java, because its picking up the rollovers. This is driving me batty. Hopefully its something simple. Here's the code... $(document).ready(function() { $("#slideshow").css("overflow", "hidden"); $("div#slides").cycle({ fx: 'scrollHorz', speed: 'slow', timeout: 0, prev: '#prev', next: '#next' }); Really appreciate the help guys.

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• how to create english language dictionary application with python (django)?

  - by sintaloo

  Hi All, I would like to create an online dictionary application by using python (or with django). It will be similar to http://dictionary.reference.com/. My question is (1) Are there any existing open source python package or modules or application which implements this functionality that I can use or study from? (2) If the answer to the first question is NO. which algorithm should I follow to create such web application? Can I simply use the python built-in dictionary object for this job? so that the dictionary object's key will be the english word and the value will be the explanation. is this OK in term of performance? OR Do I have to create my own Tree Object to speed up the search? or any existing package which handles this job properly? Thank you very much.

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• Is it possible to deploy a Ruby app on a plain clean Passenger setup?

  - by Folletto

  I'm thinking to something really similar on what you can do with mod_php: drop an application in some way inside Apache and making it run with Passenger, without adding anything inside httpd.conf (no vhost, nothing except the basic Passenger configuration). It's something very similar to Wordpress or many other frameworks: just unzip/svn checkout it inside a folder and run it. I know that it's possible with CGI and FCGI, but I'm wondering if it's also possible to tap in the speed of Passenger. I've tried fiddling with the Rack instructions on the official website trying to find a specific .htaccess and config.ru configuration, but nothing so far. I know it's not common, but... is it even possible?

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• If element has been 'mouseover'ed for 500ms, run function with jQuery

  - by PaulAdamDavis

  For the sanity of my users, I want a 'mouseover' event to run after the selector has been hovered for half a second rather than as soon as they hover it. I first tried a setTimeout function but that runs however long the element has been hovered, I didn't think it through too much I guess. I've also spent a day (on and off) searching (and playing Pacman) ti no result, unless I'm searching for the wrong things. I would like to keep this plugin-less if we can, purely for run speed & maintainability. $("#mySelector").mouseover(function(){ // Run after 500ms $(this).addClass("hasBeen500ms"); }); Let's see if we can crack this, I know it will have so many applications!

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• Distributing cpu-bound compression jobs to multiple computers?

  - by barnaby

  The other day I needed to archive a lot of data on our network and I was frustrated I had no immediate way to harness the power of multiple machines to speed-up the process. I understand that creating a distributed job management system is a leap from a command-line archiving tool. I'm now wondering what the simplest solution to this type of distributed performance scenario could be. Would a custom tool always be a requirement or are there ways to use standard utilities and somehow distribute their load transparently at a higher level? Thanks for any suggestions.

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• Help in optimizing a for loop in matlab

  - by HH

  I have a 1 by N double array consisting of 1 and 0. I would like to map all the 1 to symbol '-3' and '3' and all the 0 to symbol '-1' and '1' equally. Below is my code. As my array is approx 1 by 8 million, it is taking a very long time. How to speed things up? [row,ll] = size(Data); sym_zero = -1; sym_one = -3; for loop = 1 : row if Data(loop,1) == 0 Data2(loop,1) = sym_zero; if sym_zero == -1 sym_zero = 1; else sym_zero = -1; end else Data2(loop,1) = sym_one; if sym_one == -3 sym_zero = 3; else sym_zero = -3; end end end

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• question on revrse array

  - by davit-datuashvili

  we know algorithm how reverse array of n integers for (int i=0;i<n/2;i++){ swap(a[i],a[n-1-i]): } is this method better according the speed of algorithm or not because swap using xor is more fast then in other method here is code public class swap{ public static void main(String[]args){ int a[]=new int[]{2,4,5,7,8,11,13,12,14,24}; System.out.println(" array at the begining:"); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } for (int j=0;j<a.length/2;j++){ a[j]^=a[a.length-1-j]; a[a.length-1-j]^=a[j]; a[j]^=a[a.length-1-j]; } System.out.println("reversed array:"); for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } //result array at the begining: 2 4 5 7 8 11 13 12 14 24 reversed array: 24 14 12 13 11 8 7 5 4 2

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• Java SWT - dissolve (fade) from one image to the next.

  - by carillonator

  I'm pretty new to Java and SWT, hoping to have one image dissolve into the next. I have one image now in a Label (relevant code): Device dev = shell.getDisplay(); try { Image photo = new Image(dev, "photo.jpg"); } catch(Exception e) { } Label label = new Label(shell, SWT.IMAGE_JPEG); label.setImage(photo); Now I'd like photo to fade into a different image at a speed that I specify. Is this possible as set up here, or do I need to delve more into the org.eclipse.swt.graphics api? Also, this will be a slide show that may contain hundreds of photos, only ever moving forward (never back to a previous image)---considering this, is there something I explicitly need to do in order to remove the old images from memory? Thanks!!

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• strategy to allocate/free lots of small objects

  - by aaa

  hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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• Measure data transfer rate over tcp using c#

  - by publicENEMY

  i want to measure current download speed. im sending huge file over tcp. how can i capture the transfer rate every second? if i use IPv4InterfaceStatistics or similar method, instead of capturing the file transfer rate, i capture the device transfer rate. the problem with capturing device transfer rate is that it captures all ongoing data through the network device instead of the single file that i transfer. how can i capture the file transfer rate? im using c#.

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• SMS connecting to phone from C# and getting response

  - by I__

  here's my VBA code: Public Sub SendSMS() Dim n As Integer n = FreeFile ' Change the string below if using a different COM port or the port speed Open "COM3:9600,N,8,1" For Output As #n Print #n, "AT" Close #n End Sub i'm trying to connect to my phone that is attached to this computer. i need the solution either in VBA or c# and i need to be able to send a receive SMS with my code and get responses from the phone. how do i catch responses to my AT COMMANDS? in hyperterminal you see responses right away, i want to be able to see them here as well, how do i do it? any takers?

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• ValidateRect vs BeginPaint

  - by Armentage

  From the MSDN documentation: The BeginPaint function validates the entire client area. The ValidateRect function should not be called if a portion of the update region must be validated before the next WM_PAINT message is generated.1 I've been programming with Win32 API for years, and I've never thought to call the ValidateRect function. A co-worker of mine today pointed that we were missing a call to ValidateRect, which fixed a bug we were having doing some high-speed animation using GDI (I know, an oxymoron) Can someone tell me whether or not a call to ValidateRect is neccessary after a BeginPaint/EndPaint pair? I have seen no documentation at MSDN that sheds light on this, and what documentation and examples I do see that you do not need to.

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• How to reduce latency of data sent through a REST api

  - by Sid

  I have an application which obtains data in JSON format from one of our other servers. The problem I am facing is, there is is significant delay when when requesting for this information. Since a lot of data is passed (approx 1000 records per request where each record is pretty huge) is there a way that compression would help reducing the speed. If so which compression scheme would you recommend. I read on another thread that they pattern of data also matters a lot on they type of compression that needs to be used. The pattern of data is consistent and resembles the following :desc=>some_description :url=>some_url :content=>some_content :score=>some_score :more_attributes=>more_data Can someone recommend a solution to how I could reduce this delay. They delay is approx 6-8 seconds. I'm using Ruby on Rails to develop this application and the server providing the data uses Python for the most part.

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