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  • Storing large data in HTTP Session (Java Application)

    - by Umesh Awasthi
    I am asking this question in continuation with http-session-or-database-approach. I am planning to follow this approach. When user add product to cart, create a Cart Model, add items to cart and save to DB. Convert Cart model to cart data and save it to HTTP session. Any update/ edit update underlying cart in DB and update data snap shot in Session. When user click on view cart page, just pick cart data from Session and display to customer. I have following queries regarding HTTP Session How good is it to store large data (Shopping Cart) in Session? How scalable this approach can be ? (With respect to Session) Won't my application going to eat and demand a lot of memory? Is my approach is fine or do i need to consider other points while designing this? Though, we can control what all cart data should be stored in the Session, but still we need to have certain information in cart data being stored in session?

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  • International Radio Operators Alphabet in F# &amp; Silverlight &ndash; Part 1

    - by MarkPearl
    So I have been delving into F# more and more and thought the best way to learn the language is to write something useful. I have been meaning to get some more Silverlight knowledge (up to now I have mainly been doing WPF) so I came up with a really simple project that I can actually use at work. Simply put – I often get support calls from clients wanting new activation codes. One of our main app’s was written in VB6 and had its own “security” where it would require about a 45 character sequence for it to be activated. The catch being that each time you reopen the program it would require a different character sequence, which meant that when we activate clients systems we have to do it live! This involves us either referring them to a website, or reading the characters to them over the phone and since nobody in the office knows the IROA off by heart we would come up with some interesting words to represent characters… 9 times out of 10 the client would type in the wrong character and we would have to start all over again… with this app I am hoping to reduce the errors of reading characters over the phone by treating it like a ham radio. My “Silverlight” application will allow for the user to input a series of characters and the system will then generate the equivalent IROA words… very basic stuff e.g. Character Input – abc Words Generated – Alpha Bravo Charlie After listening to Anders Hejlsberg on Dot Net Rocks Show 541 he mentioned that he felt many applications could make use of F# but in an almost silo basis – meaning that you would write modules that leant themselves to Functional Programming in F# and then incorporate it into a solution where the front end may be in C# or where you would have some other sort of glue. I buy into this kind of approach, so in this project I will use F# to do my very intensive “Business Logic” and will use Silverlight/C# to do the front end. F# Business Layer I am no expert at this, so I am sure to get some feedback on way I could improve my algorithm. My approach was really simple. I would need a function that would convert a single character to a string – i.e. ‘A’ –> “Alpha” and then I would need a function that would take a string of characters, convert them into a sequence of characters, and then apply my converter to return a sequence of words… make sense? Lets start with the CharToString function let CharToString (element:char) = match element.ToString().ToLower() with | "1" -> "1" | "5" -> "5" | "9" -> "9" | "2" -> "2" | "6" -> "6" | "0" -> "0" | "3" -> "3" | "7" -> "7" | "4" -> "4" | "8" -> "8" | "a" -> "Alpha" | "b" -> "Bravo" | "c" -> "Charlie" | "d" -> "Delta" | "e" -> "Echo" | "f" -> "Foxtrot" | "g" -> "Golf" | "h" -> "Hotel" | "i" -> "India" | "j" -> "Juliet" | "k" -> "Kilo" | "l" -> "Lima" | "m" -> "Mike" | "n" -> "November" | "o" -> "Oscar" | "p" -> "Papa" | "q" -> "Quebec" | "r" -> "Romeo" | "s" -> "Sierra" | "t" -> "Tango" | "u" -> "Uniform" | "v" -> "Victor" | "w" -> "Whiskey" | "x" -> "XRay" | "y" -> "Yankee" | "z" -> "Zulu" | element -> "Unknown" Quite simple, an element is passed in, this element is them converted to a lowercase single character string and then matched up with the equivalent word. If by some chance a character is not recognized, “Unknown” will be returned… I know need a function that can take a string and can parse each character of the string and generate a new sequence with the converted words… let ConvertCharsToStrings (s:string) = s |> Seq.toArray |> Seq.map(fun elem -> CharToString(elem)) Here… the Seq.toArray converts the string to a sequence of characters. I then searched for some way to parse through every element in the sequence. Originally I tried Seq.iter, but I think my understanding of what iter does was incorrect. Eventually I found Seq.map, which applies a function to every element in a sequence and then creates a new collection with the adjusted processed element. It turned out to be exactly what I needed… To test that everything worked I created one more function that parsed through every element in a sequence and printed it. AT this point I realized the the Seq.iter would be ideal for this… So my testing code is below… let PrintStrings items = items |> Seq.iter(fun x -> Console.Write(x.ToString() + " ")) let newSeq = ConvertCharsToStrings("acdefg123") PrintStrings newSeq Console.ReadLine()   Pretty basic stuff I guess… I hope my approach was right? In Part 2 I will look into doing a simple Silverlight Frontend, referencing the projects together and deploying….

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  • Alien deletes .deb when converting from .rpm

    - by Stann
    I'm trying to convert .rpm to .deb using alien. sudo alien -k libtetra-1.0.0-2.i386.rpm Alien says that: libtetra-1.0.0-2.i386.deb generated But when I check the folder - there is just original .rpm and no .deb. Also - I can see that for a split second there is a .deb file in a folder. so it looks like alien create .deb and deletes it right away. I suspect that it's maybe because I run 64 bit os and package is 32? Can somebody explain why alien deletes .deb automatically? Verbose output: LANG=C rpm -qp --queryformat %{NAME} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{VERSION} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{RELEASE} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{ARCH} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{CHANGELOGTEXT} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{SUMMARY} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{DESCRIPTION} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{PREFIXES} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{POSTIN} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{POSTUN} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{PREUN} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{LICENSE} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qp --queryformat %{PREIN} libtetra-1.0.0-2.i386.rpm LANG=C rpm -qcp libtetra-1.0.0-2.i386.rpm rpm -qpi libtetra-1.0.0-2.i386.rpm LANG=C rpm -qpl libtetra-1.0.0-2.i386.rpm mkdir libtetra-1.0.0 chmod 755 libtetra-1.0.0 rpm2cpio libtetra-1.0.0-2.i386.rpm | lzma -t -q > /dev/null 2>&1 rpm2cpio libtetra-1.0.0-2.i386.rpm | (cd libtetra-1.0.0; cpio --extract --make-directories --no-absolute-filenames --preserve-modification-time) 2>&1 chmod 755 libtetra-1.0.0/./ chmod 755 libtetra-1.0.0/./usr chmod 755 libtetra-1.0.0/./usr/lib chown 0:0 libtetra-1.0.0//usr/lib/libtetra.so.1.0.0 chmod 755 libtetra-1.0.0//usr/lib/libtetra.so.1.0.0 mkdir libtetra-1.0.0/debian date -R date -R chmod 755 libtetra-1.0.0/debian/rules debian/rules binary 2>&1 libtetra_1.0.0-3_i386.deb generated find libtetra-1.0.0 -type d -exec chmod 755 {} ; rm -rf libtetra-1.0.0 Very Verbose output LANG=C rpm -qp --queryformat %{NAME} libtetra-1.0.0-2.i386.rpm libtetra LANG=C rpm -qp --queryformat %{VERSION} libtetra-1.0.0-2.i386.rpm 1.0.0 LANG=C rpm -qp --queryformat %{RELEASE} libtetra-1.0.0-2.i386.rpm 2 LANG=C rpm -qp --queryformat %{ARCH} libtetra-1.0.0-2.i386.rpm i386 LANG=C rpm -qp --queryformat %{CHANGELOGTEXT} libtetra-1.0.0-2.i386.rpm - First RPM Package LANG=C rpm -qp --queryformat %{SUMMARY} libtetra-1.0.0-2.i386.rpm Panasonic KX-MC6000 series Printer Driver for Linux. LANG=C rpm -qp --queryformat %{DESCRIPTION} libtetra-1.0.0-2.i386.rpm This software is Panasonic KX-MC6000 series Printer Driver for Linux. You can print from applications by using CUPS(Common Unix Printing System) which is the printing system for Linux. Other functions for KX-MC6000 series are not supported by this software. LANG=C rpm -qp --queryformat %{PREFIXES} libtetra-1.0.0-2.i386.rpm (none) LANG=C rpm -qp --queryformat %{POSTIN} libtetra-1.0.0-2.i386.rpm (none) LANG=C rpm -qp --queryformat %{POSTUN} libtetra-1.0.0-2.i386.rpm (none) LANG=C rpm -qp --queryformat %{PREUN} libtetra-1.0.0-2.i386.rpm (none) LANG=C rpm -qp --queryformat %{LICENSE} libtetra-1.0.0-2.i386.rpm GPL and LGPL (Version2) LANG=C rpm -qp --queryformat %{PREIN} libtetra-1.0.0-2.i386.rpm (none) LANG=C rpm -qcp libtetra-1.0.0-2.i386.rpm rpm -qpi libtetra-1.0.0-2.i386.rpm Name : libtetra Relocations: (not relocatable) Version : 1.0.0 Vendor: Panasonic Communications Co., Ltd. Release : 2 Build Date: Tue 27 Apr 2010 05:16:40 AM EDT Install Date: (not installed) Build Host: localhost.localdomain Group : System Environment/Daemons Source RPM: libtetra-1.0.0-2.src.rpm Size : 31808 License: GPL and LGPL (Version2) Signature : (none) URL : http://panasonic.net/pcc/support/fax/world.htm Summary : Panasonic KX-MC6000 series Printer Driver for Linux. Description : This software is Panasonic KX-MC6000 series Printer Driver for Linux. You can print from applications by using CUPS(Common Unix Printing System) which is the printing system for Linux. Other functions for KX-MC6000 series are not supported by this software. LANG=C rpm -qpl libtetra-1.0.0-2.i386.rpm /usr/lib/libtetra.so /usr/lib/libtetra.so.1.0.0 mkdir libtetra-1.0.0 chmod 755 libtetra-1.0.0 rpm2cpio libtetra-1.0.0-2.i386.rpm | lzma -t -q > /dev/null 2>&1 rpm2cpio libtetra-1.0.0-2.i386.rpm | (cd libtetra-1.0.0; cpio --extract --make-directories --no-absolute-filenames --preserve-modification-time) 2>&1 63 blocks chmod 755 libtetra-1.0.0/./ chmod 755 libtetra-1.0.0/./usr chmod 755 libtetra-1.0.0/./usr/lib chown 0:0 libtetra-1.0.0//usr/lib/libtetra.so.1.0.0 chmod 755 libtetra-1.0.0//usr/lib/libtetra.so.1.0.0 mkdir libtetra-1.0.0/debian date -R Mon, 07 Feb 2011 11:03:58 -0500 date -R Mon, 07 Feb 2011 11:03:58 -0500 chmod 755 libtetra-1.0.0/debian/rules debian/rules binary 2>&1 dh_testdir dh_testdir dh_testroot dh_clean -k -d dh_clean: No packages to build. dh_installdirs dh_installdocs dh_installchangelogs find . -maxdepth 1 -mindepth 1 -not -name debian -print0 | \ xargs -0 -r -i cp -a {} debian/ dh_compress dh_makeshlibs dh_installdeb dh_shlibdeps dh_gencontrol dh_md5sums dh_builddeb libtetra_1.0.0-2_i386.deb generated find libtetra-1.0.0 -type d -exec chmod 755 {} ; rm -rf libtetra-1.0.0 Resolution Oh well. It looks like it's perhaps a bug? or I don't know. I simply installed 32-bit version of Ubuntu in VirtualBox and converted package there. For some reason I couldn't convert 32-bit package in 64 OS. and that is that. If someone ever finds the reason ffor this behavior - plz. post somewhere in comments. Thanks

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  • How can I run sudo gedit as gksu gedit

    - by SimplySimon
    I'm looking into ways of automatically loading Gedit as gksu gedit when I enter sudo gedit by mistake? I have found that I have made a number of files unreachable by using gedit and I have only just found out why! ACHIEVED SO FAR I have written a script which will make an alias so that if I type in sudo <application> it can automatically convert that to gksu <application> but I want to make this alias stick, so that I don't have to run the script every time I boot the computer. Is there a config file I can edit or should I run this script as a start up script (which would be inconvenient!)?

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  • Can GMod/SFM models be converted to Unity GameObjects?

    - by Supuhstar
    Someone made a suite of GMod/SFM models available for free for people making games and videos in GMod and SFM. These are of type .dmx, .dx80.vtx, .dx90.vtx, .mdl, .phy, .sw.vtx, .vvd, .vmt, and .vtf. I fon't use GMod or SFM, so I don't know what these are, thus making it hard for me to manually convert them. Is there any way to change these into files Unity can recognize and use? I'd like to have an easy step from converting them, but I would also accept instructions on how to export them to generic mesh/skeleton/texture files, and then how to import and combine these in Unity.

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  • Java default Integer value is int

    - by Chris Okyen
    My code looks like this import java.util.Scanner; public class StudentGrades { public static void main(String[] argv) { Scanner keyboard = new Scanner(System.in); byte q1 = keyboard.nextByte() * 10; } } It gives me an error "Type mismatch: cannot convert from int to byte." Why the heck would Java store a literal operand that is small enough to fit in a byte,. into a int type? Do literals get stored in variables/registers before the ALU performs arithmatic operations.

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  • Reformating xml document

    - by Joseph Reeves
    I have an xml document in the format below: <key>value</key> <key>value</key> <key>value</key> But need to convert it to the following: <tag k='key' v='value' /> <tag k='key' v='value' /> <tag k='key' v='value' /> The original xml file is roughly 20,000 lines long, so I'm keen to automate as much as possible! I've looked at xmlstarlet, but drew a blank with it. Presumably it would be a good place to start though? Help gratefully received, thanks.

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  • Which Free Online Antivirus Scanner is the Best? [Comparison Test and Results]

    - by Asian Angel
    There are times when an online or supplementary scanner can be very useful when cleaning up an infected computer or just to get a second opinion on the security of your system. With this purpose in mind, the good folks over at the 7 Tutorials blog decided to do a test using the ten most popular online security scanners to see what worked the best and what did not. The following scanners were used for the test: Bitdefender QuickScan, BullGuard Online Scanner, Comodo Cloud Scanner, ESET Free Online Scanner, F-Secure Online Scanner, Kaspersky Security Scan, McAfee Security Scan Plus, Norton Security Scan, Panda ActiveScan and Trend Micro HouseCall. Are there any online or supplementary scanners that you use and depend on? Do you agree or disagree with the results? Let us know in the comments! Test Comparison – What is the Best Free Online Antivirus Scanner? [7 Tutorials] HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More

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  • Error 255 samba share simple file share Ubuntu 14.04

    - by Rose Offthorns
    I have been using simple file share on Ubuntu 12.04 for several years not a problem now I have up graded to 14.04 all the problems error 255, tried all sights to fix the problem nothing works even went back to 12.04 still the same problem error 255 'net usershare' returned error 255: net usershare add: cannot convert name "Everyone" to a SID. The connection was refused. Maybe smbd is not running. There appears to be a bug with the new upgrade or has there been a new upgrade. Thanks for any help would be appreciated.

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  • Monitoring Database disk space

    - by Michael Freidgeim
    An article Data files: To Autogrow Or Not To Autogrow? recommends NOT to rely on auto-grow, because it causing delays in unplanned times.We should mtonitor database files(both data and log), and if they close to max capacity, manually increase the size. However it doesn't give references, how to monitor the free space inside databases. I've tried to look how to do it. It can be done manually using   execute sp_spaceused for the database in question or  sp_SOS (can be downloaded from http://searchsqlserver.techtarget.com/tip/Find-size-of-SQL-Server-tables-and-other-objects-with-stored-procedure)Alternatively you can run SQL commands as suggested in Http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=82359 by Michael Valentine Jonesselect [FREE_SPACE_MB] = convert(decimal(12,2),round((a.size-fileproperty(a.name,'SpaceUsed'))/128.000,2)) from dbo.sysfiles aMore useful article Monitor database file sizes with SQL Server Jobs describes how to setup monitoring Finally I found the excellent articleManaging Database Data Usage With Custom Space Alerts, that can be followed even support personnel without much DBA experience.

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  • Understanding Photography and Color Temperature

    - by Jason Fitzpatrick
    Most digital cameras have the ability to set the “color temperature” based on the condition, but what exactly does that mean? This simple cheat sheet highlights the differences between various lighting situations and what settings you should use. Courtesy of Digital Camera World, the above chart shows where on the scale various color temperatures fall, how the automatic white balance works, and which presets you should use if available. What Is Color Temperature? [via Unpluggd] HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More

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  • Should my URLs be lowercase?

    - by Rowan Freeman
    According to this blog ("Understanding SEO Friendly URL Syntax Practices") I should change http://example.com/Hello-Dolly To http://example.com/hello-dolly The reasons given are: URLs, in general, are case-sensitive it will simplify any case sensitive SEO and analytics reports According to this GIF that I found on Wikipedia's article on URL Normalization I should convert my URLs from any uppercase to all lowercase. However I use ASP.NET MVC4 and by default my URLs are structured like this (CamelCase): http://www.domain.com/Controller/Action/Parameter http://www.greatsite.com/Categories/List/Bicycles I've skimmed through the RFC1738 but I didn't see any definitive answers to this. Should I go out of my way to force the framework to change everything to lower case? Why did Microsoft choose to design their framework like this if everybody is telling me to use lowercase?

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  • Douglas Adams Describes the Invention of the Ebook [Video]

    - by Jason Fitzpatrick
    In 1993, Douglas Adams–of The Hitch Hikers Guide to the Galaxy fame–lent his creative talent and voice to explaining the invention of the Ebook. The audio segment was produced almost 20 years ago by Adams to both promote his own work in digital format and the work of early ebook publisher Voyager Expanded Books. You may notice Adams refers to their product as a PowerBook, a name they kept until they heard Apple would be releasing a laptop with the same name (from then on the product was simply referred to as Expanded Books). The thoroughly modern video accompanying Adams concise and entertaining description of book history is an animation courtesy of U.K. designer Gavin Edwards, which he submitted to a contest hosted by The Literary Platform intended to match a clever animation with Adam’s monologue. [via Neatorama] HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More

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  • assigning values to shader parameters in the XNA content pipeline

    - by Nick
    I have tried creating a simple content processor that assigns the custom effect I created to models instead of the default BasicEffect. [ContentProcessor(DisplayName = "Shadow Mapping Model")] public class ShadowMappingModelProcessor : ModelProcessor { protected override MaterialContent ConvertMaterial(MaterialContent material, ContentProcessorContext context) { EffectMaterialContent shadowMappingMaterial = new EffectMaterialContent(); shadowMappingMaterial.Effect = new ExternalReference<EffectContent>("Effects/MultipassShadowMapping.fx"); return context.Convert<MaterialContent, MaterialContent>(shadowMappingMaterial, typeof(MaterialProcessor).Name); } } This works, but when I go to draw a model in a game, the effect has no material properties assigned. How would I go about assigning, say, my DiffuseColor or SpecularColor shader parameter to white or (better) can I assign it to some value specified by the artist in the model? (I think this may have something to do with the OpaqueDataDictionary but I am confused on how to use it--the content pipeline has always been a black box to me.)

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  • Week in Geek: New Malware Steals Bitcoin Currency

    - by Asian Angel
    This week we learned how to easily change a dual-booting PC’s default OS, “extract audio from any video using VLC, sneak around paywalls, & delay Windows Live Mesh during boot”, shrink videos to fit an Android phone with VLC, fix damaged or broken audio cables, “decide between an ISO or TS folder, help Windows 7 remember folder locations, & convert books for the Kindle”, and more. Photo by Profound Whatever.How to Make and Install an Electric Outlet in a Cabinet or DeskHow To Recover After Your Email Password Is CompromisedHow to Clean Your Filthy Keyboard in the Dishwasher (Without Ruining it)

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  • Why is Python slower than Java but faster than PHP

    - by good_computer
    I have many times seen various benchmarks that show how a bunch of languages perform on a given task. Always these benchmarks reveal that Python is slower then Java and faster than PHP. And I wonder why is that the case. Java, Python, and PHP run inside a virtual machine All three languages convert their programs into their custom byte codes that run on top of OS -- so none is running natively Both Java and Python can be "complied" (.pyc for Python) but the __main__ module for Python is not compiled Python and PHP are dynamically typed and Java statically -- is this the reason Java is faster, and if so, please explain how that affects speed. And, even if the dynamic-vs-static argument is correct, this does not explain why PHP is slower than Python -- because both are dynamic languages. You can see some benchmarks here and here, and here

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  • Is it worth learning either GWT or Vaadin?

    - by NimChimpsky
    I consider myself a decent java/web developer. In my career I have always used servlets and ejb's with a web front end, most recently incoporating jquery and ajax. I can see the theoretical benefit of using GWT or Vaadin: it is my understanding they convert Java code to the required JavaScript/HTML. So the developer gets the benefit of cross browser compatibility and compile time error checking (of web GUI elements). My question is threefold: Are there any other benefits I am missing that would be gained using Vaadin or GWT? I am actually quite confident and productive using HTML and JavaScript - so will I actually see any benefit? Or will it just make my knowledge of these areas redundant (as they are handled by GWT/Vaadin)? Will the end result be that I can create enterprise scale data driven websites in a reasonably short time? I can however already do this, and I have not wasted any time learning GWT/Vaadin.

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  • How can I get my dynamic site search results content indexed by Google?

    - by Kris
    I have a site that is simply a search box to search a cloud-hosted database of .tiff images, and then all of my content can only be accessed by entering a search term. So for example, you're on the home page www.example.com and you type in "search" to the box and hit submit. Then it takes you to www.example.com/?q=search, which is a page of all my .tiff images with "search" in the description. How can I get a page like www.example.com/?q=search indexed, WITHOUT making a humungous list of search terms that people might type in?? I know about mod_rewrite, but it seems like for that you need to know ahead of time which URLs you'll need to convert, which I don't. All of these pages will be dynamically user-generated by typing into the search field. Please help!

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  • alien deletes .deb automatically while converting from .rpm

    - by Andre
    I'm trying to convert .rpm to .deb using alien. alien -k libtetra-1.0.0-2.i386.rpm Alien says that: libtetra-1.0.0-2.i386.deb generated But when I check the folder - there is just original .rpm and no .deb. Also - I can see that for a split second there is a .deb file in a folder. so it looks like alien create .deb and deletes it right away. I suspect that it's maybe because I run 64 bit os and package is 32? Can somebody explain why alien deletes .deb automatically?

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  • Disable Add-Ons to Speed Up Browsing in Internet Explorer 9

    - by Lori Kaufman
    We’ve shown you how to enhance Internet Explorer with add-ons, similar to Firefox and Chrome. However, too many add-ons can slow down Internet Explorer and even cause it to crash. However, you can easily disable some or all add-ons. To begin, activate the Command bar, if it’s not already available. Right-click on an empty area of the tab bar and select Command bar from the popup menu. Click the Tools button on the Command bar and select Toolbars | Disable add-ons from the popup menu. Here’s How to Download Windows 8 Release Preview Right Now HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre

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  • Creating Wizard in ASP.NET MVC (Part 2)

    - by bipinjoshi
    In Part 1 of this article series you developed a wizard in an ASP.NET MVC application. Although the wizard developed in Part 1 works as expected it has one shortcoming. It causes full page postback whenever you click on Previous or Next button. This behavior may not pose much problem if a wizard has only a few steps. However, if a wizard has many steps and each step accepts many entries then full page postback can deteriorate the user experience. To overcome this shortcoming you can add Ajax to the wizard so that only the form is posted to the server. In this part of the series you will convert the application developed in Part 1 to use Ajax.http://www.binaryintellect.net/articles/8e278bfa-7244-4e3e-b5aa-2954a91331da.aspx 

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  • Flash intro or embedded video?

    - by Ray
    So a client of mine wants his homepage to start off something like this: http://www.roche-bobois.com/#/en-CA/home (It's basically a Flash intro that starts with a vector drawing of a furniture showroom that eventually transitions into the image of the actual showroom). Given that some of his users will be using an iPad to view his site, what are some of the alternatives that other developers here use? I'm thinking: Option 1: With PHP, detect if the user is using an iPad/iPhone by checking their user agent string. If they are using a mobile device, then forward to m.abccompany.com (mobile version of the site). Option 2: Convert the Flash video to MP4 or AVI and then embed that, which would allow all users to view his site. Any suggestions if either of these approaches are a good idea?

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  • PTLQueue : a scalable bounded-capacity MPMC queue

    - by Dave
    Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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  • Ubuntu One using 500 MB memory also when idle

    - by cdysthe
    I'm a Dropbox convert (I hope!), but after having used Ubuntu One for a couple of weeks I notice a few differences from Dropbox. The most glaring difference is that the sync daemon constantly takes 500MB ram on my system (Ubuntu 12.04 x64). It hogs this amount of memory as soon as I log in, does it's initial sync/check but keeps the memory. All in all it seems to me that Ubuntu One uses more system resources than Dropbox. I am syncing the same folders and files with Ubuntu One as I was with Dropbox. Also, afte I log in Ubuntu One grids at 100% CPU for at least five minutes which can be annoying on a laptop, but is not a showstopper. I'm wondering if this is a problem on my system, or if Ubuntu One is expected to use that amount of memory even when idle?

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  • How does key-based caching work?

    - by Dominic Santos
    I recently read an article on the 37Signals blog and I'm left wondering how it is that they get the cache key. It's all well and good having a cache key that includes the object's timestamp (this means that when you update the object the cache will be invalidated); but how do you then use the cache key in a template without causing a DB hit for the very object that you are trying to fetch from the cache. Specifically, how does this affect One to Many relations where you are rendering a Post's Comments for example. Example in Django: {% for comment in post.comments.all %} {% cache comment.pk comment.modified %} <p>{{ post.body }}</p> {% endcache %} {% endfor %} Is caching in Rails different to just requests to memcached for example (I know that they convert your cache key to something different). Do they also cache the cache key?

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