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• unbuffered I/O in Linux

  - by stuck

  I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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• Revision Control System Recommendations

  - by Jordan Arsenault

  I've reached a point in my independent development work where I would like to start using Subversion techniques. Up to now, I've been simply making backups by exporting my current database, and zipping them together with my PHP project files. I've read some articles online and watched a video with Linus Torvalds - the general verdict seems to be that Git is in and old CVS techniques are out. I'm not currently operating under Linux, I do all PHP work out of Windows - Eclipse. Due to the fact that Eclipse runs on JVM, jumping into Linux - Eclipse will be more or less transparent - file system aside. What I would like to accomplish is being able to keep a constant revision history - But I want this to be almost entirely transparent. Also, I work in an MVC framework, and I would like to be able to release my views to Designers, and have them work from within the revision control system too. Will Egit accomplish what I need? Or is it too much overhead for a one-man workforce? What do you recommend I use so that I can keep a revision history? I also require the service to be free! Thank you all - StackOverflow ftw!

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• Help me find article on Multi-threading and Event Handling in Java

  - by JDR

  I once read an article on how to properly write event handlers for multi-threading in Java, but I can't for the life of me find it anymore. It described the pitfalls and potentials for deadlocks that can occur when firing events (not Swing events mind you, but general events like model update notifications). To clarify, the situation would be as such: // let's say this is code from an MVC model somewhere public void setSomeProperty(String myProperty){ if(!this.myProperty.equals(myProperty)){ this.myProperty = myProperty; fireMyPropertyChangedEvent(...); } } The article described how passing control to arbitrary external listener code was a potential cause for deadlock. I now find myself in a situation where I need to fire such events in a multithreaded environment and I would very much like to read the article again to see what it has to say before I continue. Does anyone know the article I'm referring to? I believe it came as a (fairly short) PDF. It started off with an initial naive implementation and incrementally pointed out flaws and improved upon it. It ended with a sort of final proper-way-to-fire-multithreaded-events. I've searched endlessly in my browse history and on google, but all I could find were endless amounts topics on Swing event dispatch threads. Thank you.

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• Contacts & Autocomplete

  - by Vince

  First post. I'm new to android and programming in general. What I'm attempting to is to have an autocomplete text box pop up with auto complete names from the contact list. IE, if they type in "john" it will say "John Smith" or any john in their contacts. The code is basic, I pulled it from a few tutorials. private void autoCompleteBox() { ContentResolver cr = getContentResolver(); Uri contacts = Uri.parse("content://contacts/people"); Cursor managedCursor1 = cr.query(contacts, null, null, null, null); if (managedCursor1.moveToFirst()) { String contactname; String cphoneNumber; int nameColumn = managedCursor1.getColumnIndex("name"); int phoneColumn = managedCursor1.getColumnIndex("number"); Log.d("int Name", Integer.toString(nameColumn)); Log.d("int Number", Integer.toString(phoneColumn)); do { // Get the field values contactname = managedCursor1.getString(nameColumn); cphoneNumber = managedCursor1.getString(phoneColumn); if ((contactname != " " || contactname != null) && (cphoneNumber != " " || cphoneNumber != null)) { c_Name.add(contactname); c_Number.add(cphoneNumber); Toast.makeText(this, contactname, Toast.LENGTH_SHORT) .show(); } } while (managedCursor1.moveToNext()); } name_Val = (String[]) c_Name.toArray(new String[c_Name.size()]); phone_Val = (String[]) c_Number.toArray(new String[c_Name.size()]); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, name_Val); personName.setAdapter(adapter); } personName is my autocompletetextbox. So it actually works when I use it in the emulator (4.2) with manually entered contacts through the people app, but when I use it on my device, it will not pop up with any names. I'm sure it's something ridiculous but I've tried to find the answer and I'm getting nowhere. Can't learn if I don't ask.

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• New user register, script auto create problems!

  - by SKY

  Hi, im currently trying to create a php script that when a new user register, a script (eg:wordpress,blog etc..) will install for them. I'm currently got the code below for just single setup, but how can i setup a form for multi user? which only allowing them to input the username (subdomain) and password. <?php class scriptname_Config { public static $title = 'new_script_title'; // Domain name and path where new script will installed in public static $domain = 'username.domain.com'; public static $absolutePath = '/new_register_username/'; // Settings for general mysql database public static $db = array( 'host' => 'localhost', 'database' => 'scriptname', 'user' => 'root', 'password' => '', 'prefix' => 'scriptname_' ); } define( 'scriptname_BASE_URL', 'http://'.scriptname_Config::$domain.scriptname_Config::$absolutePath ); ?> Or any tutorial that will help is appreciate! Thanks!

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• Choropleth mapping issue in R

  - by chasec

  I am trying to follow the tutorial described here: http://www.thisisthegreenroom.com/2009/choropleths-in-r/ The below code executes, but it is either not matching my dataset with the maps_counties data properly, or it isn't plotting it in the order I would expect. For example, the resulting areas for the greater NYC area show no density while random counties in PA show the highest density. The general format of my data table is: county state count fairfield connecticut 17 hartford connecticut 6 litchfield connecticut 3 new haven connecticut 12 ... ... westchester new york 70 yates new york 1 luzerne pennsylvania 1 Note this data is in order by state and then county and includes data for CT, NJ, NY, & PA. First, I read in my data set: library(maps) library(RColorBrewer) d <- read.table("gissum.txt", sep="\t", header=TRUE) #Concatenate state and county info to match maps library d$stcon <- paste(d$state, d$county, sep=",") #Color bins colors = brewer.pal(5, "PuBu") d$colorBuckets <- as.factor(as.numeric(cut(d$count,c(0,10,20,30,40,50,300)))) Here is my matching mapnames <- map("county",plot=FALSE)[4]$names colorsmatched <- d$colorBuckets [na.omit(match(mapnames ,d$stcon))] Plotting: map("county" ,c("new york","new jersey", "connecticut", "pennsylvania") ,col = colors[d$colorBuckets[na.omit(match(mapnames ,d$stcon))]] ,fill = TRUE ,resolution = 0 ,lty = 0 ,lwd= 0.5 ) map("state" ,c("new york","new jersey", "connecticut", "pennsylvania") ,col = "black" ,fill=FALSE ,add=TRUE ,lty=1 ,lwd=2 ) map("county" ,c("new york","new jersey", "connecticut", "pennsylvania") ,col = "black" ,fill=FALSE ,add=TRUE , lty=1 , lwd=.5 ) title(main="Respondent Home ZIP Codes by County") I am sure I am missing something basic re: the order in which the maps function plots items - but I can't seem to figure it out. Thanks for the help. Please let me know if you need any more information.

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• Debug.Assert-s use the same error message. Should I promote it to a static variable?

  - by Hamish Grubijan

  I love Asserts and code readability but not code duplication, and in several places I use a Debug.Assert which checks for the same condition like so: Debug.Assert(kosherBaconList.SelectedIndex != -1, "An error message along the lines - you should not ever be able to click on edit button without selecting a kosher bacon first."); This is in response to an actual bug, although the actual list does not contain kosher bacon. Anyhow, I can think of two approaches: private static readonly mustSelectKosherBaconBeforeEditAssertMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; ... Debug.Assert( kosherBaconList.SelectedIndex != -1, mustSelectKosherBaconBeforeEditAssertMessage) or: if (kosherBaconList.SelectedIndex == -1) { AssertMustSelectKosherBaconBeforeEdit(); } ... [Conditional("DEBUG")] private void AssertMustSelectKosherBaconBeforeEdit() { // Compiler will optimize away this variable. string errorMessage = "An error message along the lines - you should not ever be able to " + "click on edit button without selecting a something first."; Debug.Assert(false, errorMessage); } or is there a third way which sucks less than either one above? Please share. General helpful relevant tips are also welcome.

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• Setting initial state of a JSF component to invalid

  - by user359391

  Hi there I have a small JSF application where the user is required to enter some data about themselves. For each component on the page that has required="true" I want to show an icon depending if there is data in the field or not. My problem is that when the page is initially shown all fields are valid, even if they do not have any data in them. So my question is how I can set a component to be invalid based on if there is data in the field or not? After a submit of the page (or after the component loses focus) the icon is shown properly, it is only on the initial page load I have a problem. (i.e there is no post data) Here is my xhtml for a component that needs to be validated: <s:decorate id="employeeIdDecoration" template="/general/util/errorStyle.xhtml"> <ui:define name="label">#{messages['userdetails.employeeId']}</ui:define> <h:inputText value="#{authenticator.user.employeeId}" required="true"> <a4j:support event="onblur" reRender="employeeIdDecoration" bypassUpdates="true"/> </h:inputText> the template: <s:label styleClass="#{invalid?'error':''}"> <ui:insert name="label"/> <s:span styleClass="required" rendered="#{required}">*</s:span> </s:label> <span class="#{invalid?'error':''}"> <s:validateAll> <ui:insert/> </s:validateAll> <h:graphicImage value="/resources/redx.png" rendered="#{invalid}" height="16" width="16" style="vertical-align:middle;"/> <h:graphicImage value="/resources/Checkmark.png" rendered="#{!invalid}" height="16" width="16" style="vertical-align:middle;"/> </span> Any help will be appreciated.

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• Heroku DJango app development on Windows

  - by Cliff

  I'm trying to start a Django app on Heroku using Windows and I'm getting stuck on the following error when I try to pip install psycopg2: Downloading/unpacking psycopg2 Downloading psycopg2-2.4.5.tar.gz (719Kb): 719Kb downloaded Running setup.py egg_info for package psycopg2 Error: pg_config executable not found. Please add the directory containing pg_config to the PATH or specify the full executable path with the option: python setup.py build_ext --pg-config /path/to/pg_config build ... or with the pg_config option in 'setup.cfg'. Complete output from command python setup.py egg_info: running egg_info creating pip-egg-info\psycopg2.egg-info writing pip-egg-info\psycopg2.egg-info\PKG-INFO writing top-level names to pip-egg-info\psycopg2.egg-info\top_level.txt writing dependency_links to pip-egg-info\psycopg2.egg-info\dependency_links.txt writing manifest file 'pip-egg-info\psycopg2.egg-info\SOURCES.txt' warning: manifest_maker: standard file '-c' not found I've googled the error and it seems you need libpq-dev python-dev as dependencies for postgres under Python. I also turned up a link that says you gt into trouble if you don't have the postgres bin folder in your Path so I installed Postgres manually and tried again. This time I get: error: Unable to find vcvarsall.bat I am still a python N00b so I am lost. Could someone point me in a general direction?

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• jQuery relative positioned hover

  - by danixd

  I want a link to the next or previous image to appear when hovering over the main image, only I want the next link to appear when hovered over the right hand side, and previous on the left. I have looked at jQuery's .position() and I don't think I am understanding it very well. At the moment all I have is general mouseenter/mouseleave events, which show both links when the image is hovered. jQuery(document).ready(function($) { $('.nav-controls a').hide(); $('#slideshow').mouseenter(function() { $('.nav-controls a').fadeIn(500); }); $('#slideshow').mouseleave(function() { $('.nav-controls a').fadeOut(500); }); }); I'd image it to be something like: jQuery(document).ready(function($) { $('.nav-controls a').hide(); var image = $('#slideshow'); var left = image.position().left(0); var right = image.position().left(50%); left.mouseenter(function() { $('.nav-controls a.previous').fadeIn(500); }); left.mouseleave(function() { $('.nav-controls a.previous').fadeOut(500); }); right.mouseenter(function() { $('.nav-controls a.next').fadeIn(500); }); right.mouseleave(function() { $('.nav-controls a.next').fadeOut(500); }); }); Not sure if I should be using position, if I am using it correctly. Any tips would be great. Edit: I do not want to add unnecessary markup in the form of divs, for the left/right selectors.

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• My iPhone app ran fine in simulator but crashed in device (iPod touch 3.1.2) test, I got the followi

  - by Mickey Shine

  I was running myapp on an iPod touch and I noticed it missed some libraries. Is that the reason? [Session started at 2010-03-19 15:57:04 +0800.] GNU gdb 6.3.50-20050815 (Apple version gdb-1128) (Fri Dec 18 10:08:53 UTC 2009) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "--host=i386-apple-darwin --target=arm-apple-darwin".tty /dev/ttys007 Loading program into debugger… Program loaded. target remote-mobile /tmp/.XcodeGDBRemote-237-78 Switching to remote-macosx protocol mem 0x1000 0x3fffffff cache mem 0x40000000 0xffffffff none mem 0x00000000 0x0fff none run Running… [Switching to thread 11779] [Switching to thread 11779] sharedlibrary apply-load-rules all (gdb) continue warning: Unable to read symbols for "/Library/MobileSubstrate/MobileSubstrate.dylib" (file not found). 2010-03-19 15:57:18.892 myapp[2338:207] MS:Notice: Installing: com.yourcompany.myapp [myapp] (478.52) 2010-03-19 15:57:19.145 myapp[2338:207] MS:Notice: Loading: /Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib warning: Unable to read symbols for "/Library/MobileSubstrate/DynamicLibraries/Backgrounder.dylib" (file not found). warning: Unable to read symbols for "/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.2.sdk/usr/lib/libsubstrate.dylib" (file not found). MS:Warning: message not found [myappAppDelegate applicationWillResignActive:] MS:Warning: message not found [myappAppDelegate applicationDidBecomeActive:] 2010-03-19 15:57:19.550 myapp[2338:207] in FirstViewController 2010-03-19 15:57:20.344 myapp[2338:207] in load table view 2010-03-19 15:57:20.478 myapp[2338:207] in loading splash view 2010-03-19 15:57:22.793 myapp[2338:207] in set interface Program received signal: “0”. warning: check_safe_call: could not restore current frame

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• Django: Storing ordered, arbitrary references

  - by Sarah

  I'm new to Django, and I'm not sure what I want is possible: I have a number of items that I want each AppUser (extended User model) to be able to reference. That is, given an AppUser, I want to be able to extract its list of items in the way that AppUser has chosen to order them. In general, these items would actually be references to something else in the database, and this led me to one possible solution: Store the keys for the given objects in a CommaSeparatedIntegerField in AppUser. This way, a user could have stored {7, 3, 232, 42, 1} in their items field and both the references and their preferred order would be stored. However, this feels hacky. Since most db backends store CommaSeparatedIntegerField as a VARCHAR internally, the user is not only limited by a number of objects, but also the number of digits in their chosen items. Eg. "you may store 10 items if you choose items with itemID < 10, but only 5 items if 10 < itemID < 100". Is there a better way to do this?

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• Is there any way to access codeigniter language and config properties from included javascript files

  - by ubermensch

  Good morning! I'm having great success so far with CodeIgniter. I'm new to PHP and web development in general, but I feel that CodeIgniter is giving me a leg up while I catch up on the basics. My question for today is this - I have been happily loading config and lang values from my views for a while now, and everything is working fine. But what about JavaScript files being linked into my views? Is there any way to make the $this-lang-line and $this-config-item function references available to me in my JavaScript files? I am implementing jQuery client-side validation, and would like to pull in my error messages from the server, both to support internationalisation and to make sure that validation gracefully degrades if JavaScript is not available, in that the error messages pushed back into the view from the server-side validation are identical to those displayed dynamically by the jQuery validation. I would not like to have to keep coming back to make sure that these strings are kept in sync. As for internationalisation, I'm fresh out of ideas on how to support that if it turns out that lang and config item strings are completely unavailable from my JS files. Any help you can provide would be greatly appreciated! :)

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• How to close and open access to SQL Server 2008 in Windows application?

  - by hgulyan

  Hi, I have a MS Access 97 application (but the question is general) working directly with SQL Server 2008 (without application server or anything). Numbers of users can be up to 1000. Windows Authentication is used. The question is: How to handle modes, so some users will be allowed to work in read-only mode some users won't have access to db for some time My versions: Using a table with a mode id for every group of users, that will work the same way. On Form Load application will query that table for mode id. Using trigger on the tables, that must work according to that mode. The trigger will query mode value and doesn't work if access is closed or it's in read-only mode I know these are not the best solutions, that's why I'm asking for your advice. There's one more point. If the mode is changed to "access-is-closed" for a group of users, that group must not be able to query to DB starting that moment. With first solution I wrote it won't work, because user can be in application at that moment and no form load event will work. How can I do this? Is there any optimal solution? Thank you. Any help would be appreciated.

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• Finding patterns of failure in a Unit Test

  - by Pekka

  I'm new to Unit Testing, and I'm only getting into the routine of building test suites. I have what is going to be a rather large project that I want to build tests for from the start. I'm trying to figure out general strategies and patterns for building test suites. When you look at a class, many tests come to you obviously due to the nature of the class. Say for a "user account" class with basic CRUD operations, being related to a database table, we will want to test - well, the CRUD. creating an object and seeing whether it exists query its properties change some properties change some properties to incorrect values and delete it again. As for how to break things, there are "fail" tests common to most CRUD classes like: Invalid input data types A number as the ID key that exceeds the range of the chosen data type Input in an incorrect character encoding Input that is too long And so on and so on. For a unit test concerned with file operations, the list of "breaking things" could be Invalid characters in file name File name too long File name uses incorrect protocol or path I'm pretty sure similar patterns - applicable beyond the unit test one is currently working on - can be found for most units that are being tested. Now my question is: Am I correct in seeing such "breaking patterns"? Or am I getting something completely wrong about Unit testing, and if I did it right, this wouldn't be an issue at all? Is Unit Testing as a process of finding as many ways to break the unit as possible the right way to go? If I am correct: Are there existing definitions, lists, cheat sheets for such patterns? Are there any provisions (mainly in PHPUnit, as that's the framework I'm working in) to automate such patterns? Is there any assistance - in the form of check lists, or software - to aid in writing complete tests?

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• sql queries slower than expected

  - by neubert

  Before I show the query here are the relevant table definitions: CREATE TABLE phpbb_posts ( topic_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, poster_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, KEY topic_id (topic_id), KEY poster_id (poster_id), ); CREATE TABLE phpbb_topics ( topic_id mediumint(8) UNSIGNED NOT NULL auto_increment ); Here's the query I'm trying to do: SELECT p.topic_id, p.poster_id FROM phpbb_topics AS t LEFT JOIN phpbb_posts AS p ON p.topic_id = t.topic_id AND p.poster_id <> ... WHERE p.poster_id IS NULL; Basically, the query is an attempt to find all topics where the number of times someone other than the target user has posted in is zero. In other words, the topics where the only person who has posted is the target user. Problem is that query is taking a super long time. My general assumption when it comes to SQL is that JOINs of any are super fast and can be done in no time at all assuming all relevant columns are primary or foreign keys (which in this case they are). I tried out a few other queries: SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id; That returns 353340 pretty quickly. I then do these: SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id AND p.poster_id <> 77198; SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id WHERE p.poster_id <> 77198; And both of those take quite a while (between 15-30 seconds). If I change the < to a = it takes no time at all. Am I making some incorrect assumptions? Maybe my DB is just foobar'd?

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• Creating a OS X Cocoa App Web View in Xcode 5.0.1

  - by user1822824

  I created a HTML5 web app that I’m trying to wrap in a web view and submit to the Mac App Store. I’ve done the following: 1) Opened Xcode 5.0.1 and selected “Create a new Xcode project” 2) Under “OS X” I selected “Application” then I selected “Cocoa Application” then “Next” 3) I entered a “Product Name” and a “Company Identifier” then selected “Next” (I left all the other settings untouched) then “Create” 4) Under “General” “Deployment Info” “Deployment Target” I selected 10.6 — because I want the app to be compatible with all versions of OS X that support the Mac App Store 5) I clicked “MainMenu.xib” and selected “Window - My App” 6) From the “Object library” I drug the “Web View” object into my window and made it fill the window size 7) I saved my project and click the Play button in the upper left corner of Xcode The app tries to open but freezes. I don’t get an error in Xcode but it does open “main.m” and highlight “return NSApplicationMain(argc, argv);” in green and says “Thread 1: signal SIGABRT” I was hoping that someone could clarify why this isn’t working? And provide me with the last step to link the web view object? I searched Google and found tutorials for iOS and a few for OS X but for different versions of Xcode.

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• Determining Best Table Structure for MySQL Performance

  - by Joe Majewski

  I'm working on a browser-based RPG for one of my websites, and right now I'm trying to determine the best way to organize my SQL tables for performance and maintenance. Here's my question: Does the number of columns in an SQL table affect the speed in which it can be queried? I am not a newbie when it comes to PHP or MySQL. I used to develop things with the common goal of getting them to work, but I've recently advanced to the stage where a functional program is not good enough unless it's fast and reliable. Anyways, right now I have a members table that has around 15 columns. It contains information such as the player's username, password, email, logins, page views, etcetera. It doesn't contain any information on the player's progress in the game, however. If I added columns for things such as army size, gold, turns, and whatnot, then it could easily rise to around 40 or 50 total columns. Oh, and my database structure IS normalized. Will a table with 50 columns that gets constantly queried be a bad idea? Should I split it into two tables; one for the user's general information and one for the user's game statistics? I know I could check the query time myself, but I haven't actually created the tables yet and I think I'd be better off with some professional advice on this important decision for my game. Thank you for your time! :)

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• How can I compare the performance of log() and fp division in C++?

  - by Ventzi Zhechev

  Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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• Storing large numbers of varying size objects on disk

  - by Foredecker

  I need to develop a system for storing large numbers (10's to 100's of thousands) of objects. Each object is email-like - there is a main text body, and several ancillary text fields of limited size. A body will be from a few bytes, to several KB in size. Each item will have a single unique ID (probably a GUID) that identifies it. The store will only be written to when an object is added to it. It will be read often. Deletions will be rare. The data is almost all human readable text so it will be readily compressible. A system that lets me issue the I/Os and mange the memory and caching would be ideal. I'm going to keep the indexes in memory, using it to map indexes to the single (and primary) key for the objects. Once I have the key, then I'll load it from disk, or the cache. The data management system needs to be part of my application - I do not want to depend on OS services. Or separately installed packages. Native (C++) would be best, but a manged (C#) thing would be ok. I believe that a database is an obvious choice, but this needs to be super-fast for look up and loading into memory of an object. I am not experienced with data base tech and I'm concerned that general relational systems will not handle all this variable sized data efficiently. (Note, this has nothing to do with my job - its a personal project.) In your experience, what are the viable alternatives to a traditional relational DB? Or would a DB work well for this?

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• Isotope.js help: Changing item image after sorting

  - by user3643081

  This is a general question on how to go about building a project I have in mind, and the best way to set off on the right foot. I am fairly new to JS, please be gentle. I want to use isotope.js (or a similar script) to display a page with multiple items (about 30 different plants found in a garden) and the ability to sort them by seasons of the year + "what is most beautiful now" + and "view all" (a total of 6 categories) . On load, or when sorted by either "what is beautiful now" or "view all", I need each item to reflect the image of the current season we are in. When sorted by season, I need those "current" images to switch over to a designated seasonal image of that plant. Therefore, each sortable item will ultimately have 4 different versions with 4 different images in the background ready to surface when plants are sorted. (perhaps 5 if it makes more sense to have a "current" version besides the 4 seasonal versions.) My question: what approach can I take to achieve this effect in a manageable way? Can isotope apply a class to items sorted? Assuming it can: Should each item have 4 inline images, each with a css class, that I then control by using display:inline; and display:none; properties from my stylesheets? (I worry that this approach would significantly increase load times) Would it make more sense to create a blank dummy div who's background I control similarly to the example above -relying mostly on CSS. Or is there some other way involving JS I am overlooking? Any help would be appreciated. Examples of what you suggest would be immensely helpful.

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• If I cast an IQueryable as an IEnumerable then call a Linq extension method, which implementation gets called?

  - by James Morcom

  Considering the following code: IQueryable<T> queryable; // something to instantiate queryable var enumerable = (IEnumerable<T>) queryable; var filtered = enumerable.Where(i => i > 3); In the final line, which extension method gets called? Is it IEnumerable<T>.Where(...)? Or will IQueryable<T>.Where(...) be called because the actual implementation is still obviously a queryable? Presumably the ideal would be for the IQueryable version to be called, in the same way that normal polymorphism will always use the more specific override. In Visual Studio though when I right-click on the Where method and "Go to Definition" I'm taken to the IEnumerable version, which kind of makes sense from a visual point-of-view. My main concern is that if somewhere in my app I use Linq to NHibernate to get a Queryable, but I pass it around using an interface that uses the more general IEnumerable signature, I'll lose the wonders of deferred database execution!

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• What is a good "Error Checking" Pattern (Java)?

  - by Jack

  I'll explain what I mean by input error checking. Say you have a function doSomething(x). If the function completes successfully doSomething does something and returns nothing. However, if there are errors I'd like to be notified. That is what I mean by error checking. I'm looking for, in general, the best way to check for errors. I've thought of the following solutions, each with a potential problem. Flag error checking. If doSomething(x) completes successfully return null. Otherwise, it returns a boolean or an error string. Problem: Side effects. Throwing an exception. Throw an exception if doSomething(x) encounters an error. Problem: If you are performing error checking for parameters only, throwing an IllegalArgumentExceptionseems inappropriate. Validating input prior to function call. If the error checking is only meant for the parameters of the function, then you can call a validator function before calling the doSomething(x) function. Problem: What if a client of the class forgets to call the validator function before calling doSomething(x)? I often encounter this problem and any help or a point in the right direction would be much appreciated.

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• Java Equivalent of C++ .dll?

  - by Matt D

  So, I've been programming for a while now, but since I haven't worked on many larger, modular projects, I haven't come across this issue before. I know what a .dll is in C++, and how they are used. But every time I've seen similar things in Java, they've always been packaged with source code. For instance, what would I do if I wanted to give a Java library to someone else, but not expose the source code? Instead of the source, I would just give a library as well as a Javadoc, or something along those lines, with the public methods/functions, to another programmer who could then implement them in their own Java code. For instance, if I wanted to create a SAX parser that could be "borrowed" by another programmer, but (for some reason--can't think of one in this specific example lol) I don't want to expose my source. Maybe there's a login involved that I don't want exploited--I don't know. But what would be the Java way of doing this? With C++, .dll files make it much easier, but I have never run into a Java equivalent so far. (I'm pretty new to Java, and a pretty new "real-world" programmer, in general as well)

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• Ruby, Python, or PHP?

  - by Gabe

  And so we return to the age old question - but with a few twists. This morning, I searched and read up on which web development language to learn first. I'm thinking Ruby, Python, or perhaps PHP. But I have a few questions before deciding. Background: I'm a year into C++ (through school), but want to get into web development. I have all summer to commit to one language, learn it, do some projects, get up some websites, and so on. Now my questions (and these are assuming that I should choose between Ruby, Python, and PHP - if I should choose a different language, let me know.): I hope to use whichever language I learn for websites/web apps. Some of the threads on stackoverflow suggested Python was the best overall language, but others were unanimous that Ruby was best specifically for web development. For a first language suited towards web development, which language do you recommend, and why? This might tie into the first question, but which language looks most promising for future work, future personal projects, and basically the future in general? I'm just a freshman in college. Ideally, the language I choose would be on the rise, community-wise and opportunity-wise. (One reason I'm leaning towards Ruby is that it seems a lot of the newer tech startups/successes are using it.)

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