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Articles indexed in December 2010

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• What happens when we say "listen to a port" ?

  - by smwikipedia

  Hi, When we start a server application, we always need to speicify the port number it listens to. But how is this "listening mechanism" implemented under the hood? My current imagination is like this: The operating system associate the port number with some buffer. The server application's responsibiligy is to monitor this buffer. If there's no data in this buffer, the server application's listen operation will just block the application. When some data arrives from the wire, the operating system will know that check the data and see if it is targed at this port number. And then it will fill the buffer. And then OS will notify the blocked server application and the server application will get the data and continue to run. Question is: If the above scenario is correct, how could the opearting system know there's data arriving from wire? It cannot be a busy pooling. Is it some kind of interrupt-based mechanism? If there's too much data arriving and the buffer is not big enough, will there be data loss? Is the "listen to a port" operation really a blocking operation? Many thanks.

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• Collision Detection (Ground & Slopes) in 2D Platform Game using Pygame Rects

  - by RedCap

  Hi, First off, I am not after any instructions on logic for collision detection; I get it. What I am trying to work out is the least complicated way to do this with Pygame using Sprites & Rects. I want to be able to check collisions for the Player against ground, walls & slopes. In theory it is quite straight forward, but I'm having difficulty because it seems like you cannot do this with one Rect. One Rect is simple enough to get you collisions in the X plane against walls. The same Rect could be used also be used in the Y plane against solids, but not with slopes - since with the collision routines in Pygame it checks the whole Rect (or mask), rather than perhaps just the bottom middle of the Rect. It seems in addition you need to have a number of "sprites" to check collisions with, that are 1x1 pixel in various places around the Player. What's the easiest way to do this, without having a bunch of 3, 4, or more separate "collision pixels" to check against slopes? Geoff

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• WPF CollectionViewSource Grouping

  - by Miles

  I'm using a Collection View Source to group my data. In my data, I have Property1 and Property2 that I'm needing to group on. The only stipulation is that I don't want sub-groups of another group. So, when I group by these two properties, I don't want to have it so that Property2 because a subgroup of Property1's group. The reason why I'm wanting this is because I'm wanting to have a header that shows the following information: Header: <TextBlock.Text> <MultiBinding StringFormat="Property1: {0}, Property2: {1}"> <Binding Path="Property1"/> <Binding Path="Property2"/> </MultiBinding> </TextBlock.Text> I've tried this with my CollectionViewSource but was not able to "combine" the group and subgroup together: <CollectionViewSource x:Key="myKey" Source="{Binding myDataSource}"> <CollectionViewSource.GroupDescriptions> <PropertyGroupDescription PropertyName="Property1" /> <PropertyGroupDescription PropertyName="Property2" /> </CollectionViewSource.GroupDescriptions> </CollectionViewSource> Is it possible to group two properties together? Something like below? <CollectionViewSource x:Key="myKey" Source="{Binding myDataSource}"> <CollectionViewSource.GroupDescriptions> <PropertyGroupDescription PropertyName="Property1,Property2" /> </CollectionViewSource.GroupDescriptions> </CollectionViewSource>

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• Python Eggs on Google App Engine

  - by ott

  Usually I would use virtualenv and pip for deployment of web applications. With Google App Engine this doesn't work, because all import statement are relative to directory of the application. The most common approach I saw was to simply copy the packages from site-packages to the directory of the application. This involves manual work and is error-prone. Another approach was to changes install_lib and install_scripts in ~/.pydisutils.cfg, but this doesn't allow me to use pip in my home directory simultaneously. Do you have any suggestions for this?

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• Using code from this site

  - by user553798

  Hi, The legal section of this site mentions that all code by the contributors is licensed under the Creative Commons Attribution Share Alike License. Does this mean that I have to attribute the submitter even if the code in question is a few lines amongst hundreds or thousands of lines of code? What if I use code from a book or SDK? For eg; If I use the sample code from Google's Android SDK documentation, does that mean I need to attribute Google every time I write an app, after all it would be impossible to write an app without consulting the SDK docs, atleast initially... I am totally confused :S

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• a direct, simple api to run as system?

  - by fejesjoco

  Suppose a program is running with elevated privileges already, and it needs to see the contents of the System Volume Information folder, and by default, only NT Authority\System can do that. A workaround would be to change ACL's on the folder, but I don't want to mess with that. I already found two ways to do it: the task scheduler and psexec. They are too indirect, I don't even need to describe the first one, and the second one works by installing a windows service, running it, telling it to run whatever I wanted to run, then uninstalling the service. Now the question is: is there a direct, simple WinAPI function to run something as system? I don't think that such an API would circumvent the security restrictions, as an administrator I have the right to schedule a task or install a service, so there must be a shortcut.

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• Signable, streamable, "readable" archive format?

  - by alexvoda

  Is there any archive format that offers the following: be digitally sign-able with a digital certificate from a trusted source like Verisign - for preventing changes to the file (I am not referring to read only, but in case the file was changed it should no longer be signed telling the user this is not the original file) be stream-able - be able to be opened even if not all of the content has been transfered (also not strictly linearly) be "readable" - be able to read the data without extracting to a temporary folder (AFAIK if you open a file in a zip archive it is extracted first, and this stays true even for zip based formats like OOXML. This is not what I want) be portable - support on at least Windows, Linux and Mac OS X is a must, or at least future support be free of patents - Be open source - also preferably a license that allows commercial use(as far as i know GPL a share-alike licence so it doesn't allow comercial use, BSD on the other hand alows it) Note: Though it may come in handy eventually I can not think right now of a scenario that would require both point 1 and point 2 simultaneously. Or lets leave it a be able to check the signature only when the whole file was downloaded. I am not interested in: being able to be compressed being supported on legacy systems Does any existing archive format fit this description (tar evolutions like DAR and pax come to mind) ? If there is, are there programing libraries available for the above mentioned OSs? If not, would it be hard to create such a thing? EDIT: clarrified piont 5 EDIT 2: added a note to clarify point 1 and 2 P.S.: This is my first question on StackOverflow

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• Self-signed ceritificates for many users/browsers/sites

  - by Demiurg

  Here is my problem - I have a lot of users using different browsers accessing many internal web sites using https. I can create my own Certificate Authority, than create a certificate for each server and after that have all the users import it. Obviously, it cannot work in reality - there are too many users and too many sites, and some sites will be added in the future. I'm looking for a way to automate this. Is there a way to create a certificate so that all major browsers (IE, FF, Opera, Chrome and Safari) would trust it for all servers ? If so, what is the best way to install it automatically in all major browsers ?

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• Changing overflow from div dynamically [closed]

  - by user552669

  Hello comunnity! I am filling a div using JQuery. This div has the CSS property 'overflow' set to 'auto' (to display scrollbars because the div has a lot of HTML inside). But the DIV doesn't display the scrollbars. I think that the problem is that I'm setting the CSS property using CSS and the DIV is filling dynamically. How can I do to display scrollbars if the HTML inside the DIV doesn't fit, but dynamically? I'm trying to set the property manually after fill the div, but didn't work: function createWB(tag){ // Fill the div // ... // Set the scrollbars $('.tab_content').css('overflow','auto'); } If a set the property to 'scroll', the scrollbars appear, but disabled. Thanks in advance! :)

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• display flex xml with dash

  - by user217582

  In Flex, how do I display "midi-channel" to s:Label? I tried songTitle.text = mainXML.child("movement-title").text(); it worked but unsure how to display for midi-channel part. <score-partwise> <movement-title>zsdf</movement-title> <part-list> <score-part id="P1"> <part-name>Piano</part-name> <score-instrument id="P1-I1"> <instrument-name>Acoustic Grand Piano</instrument-name> </score-instrument> <midi-instrument id="P1-I1"> <midi-channel>1</midi-channel> <midi-program>1</midi-program> </midi-instrument> </score-part> </part-list>

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• Is there any data missing?

  - by smwikipedia

  Hi experts, Here is some code quoted from Douglas.E.Comer's < Computer Networks and Internets 4th edition. This program will send back any data it received. ... while((len = recv(conn, buff, BUFFERSIZE,0)) >0) // receive data send(conn, buff, len, 0); // send it back ... I am wondering, what if some data arrived when the code is executing in send(..) function, will it miss that data? Because the recv() function is not being executed. If no data is missed, where is the data kept? And by whom? Thanks...

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• What's the most common scenario for Cocoa app setup during first launch?

  - by Eimantas

  I am creating an app and I would like a user to set some obligatory preferences during first app launch. What is the most common scenario to achieve this? Should I set some user defaults to see if the app has been setup? Also - if I determine that the app is being launched for the first time - how should I display "Setup" window? If I load it from the separte xib file - how will I deffer the display of main app window?

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• Http Post Format for WCF Restful Service

  - by nextgenneo

  Hey, super newbie question. Consider the following WCF function: [ServiceContract] [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)] public class Service1 { private static NLog.Logger logger = NLog.LogManager.GetCurrentClassLogger(); [WebInvoke(UriTemplate = "", Method = "POST", ResponseFormat = WebMessageFormat.Json, RequestFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Bare) ] public SomeObject DoPost(string someText) { ... return someObject; In fiddler what would my request headers and body look like? Thanks for the help.

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• Python: How to get a value of datetime.today() that is "timezone aware"?

  - by mindthief

  Hi, I am trying to subtract one date value from the value of datetime.today() to calculate how long ago something was. But it complains: TypeError: can't subtract offset-naive and offset-aware datetimes The value datetime.today() doesn't seem to be "timezone aware", while my other date value is. How do I get a value of datetime.today() that is timezone aware? Right now it's giving me the time in local time, which happens to be PST, i.e. UTC-8hrs. Worst case, is there a way I can manually enter a timezone value into the datetime object returned by datetime.today() and set it to UTC-8? Of course, the ideal solution would be for it to automatically know the timezone. Thanks!

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• Yii problem in blog tutorial

  - by Kani

  When i login occurs following problem. PHP Error Description include(User.php) [<a href='function.include'>function.include</a>]: failed to open stream: No such file or directory Source File D:\Badrakh\xampp\htdocs\yii\framework\YiiBase.php(395) 00383: * @return boolean whether the class has been loaded successfully 00384: */ 00385: public static function autoload($className) 00386: { 00387: // use include so that the error PHP file may appear 00388: if(isset(self::$_coreClasses[$className])) 00389: include(YII_PATH.self::$_coreClasses[$className]); 00390: else if(isset(self::$classMap[$className])) 00391: include(self::$classMap[$className]); 00392: else 00393: { 00394: if(strpos($className,'\\')===false) 00395: include($className.'.php'); 00396: else // class name with namespace in PHP 5.3

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• low speed web application, Server problem or Application

  - by Ashian

  Hi, I have a web application written by asp.net (c#) sql server 2005. we host it on 2 dedicated server ( IIS and SQL server ) From some month ago , in some days of week we have many reports about speed issue. we have some other application on this server using same database. when we have speed problem all aplication on these server have this problem, but applications on other server in same data center work correctly. ram and cpu usage are ok. how can I check that the problem related to internet connection or my application design? which parameters must be checked. Some other information In applications users can upload several files to server , each file up to 3 MB. we use a sql web admin application, on same server that has same problem, this is a standard application which work perfectly on other servers. Thanks

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• Limited bandwidth and transfer rates per user.

  - by Cx03

  I searched for a while but couldn't find anything concrete, hopefully someone can help me. I'm going to be running a Debian server on a gigabit port, and want to give each user his/her fair share of internet access. The first objective is easy - transfer rates (speed) per user. From what I've looked at, IPTables/Shorewall could do the job easy. Is this easy to setup, or could one of you point me at a config? I was hoping to limit users at 300mbit or 650mbit each. The second objective gets complicated. Due to the usage of the boxes, most of the traffic will be internal network traffic that does NOT get counted to the quota. However, I still need to limit the external traffic, and if they go over, cut off access (or throttle traffic to a very low speed (10mbit?)). Let's say the user has a 3TB external traffic limit. The IF part is: If the hostname they are exchanging the traffic with DOES NOT MATCH .ovh. or .kimsufi. (company owns multiple TLDs), count to the quota. Once said quota exceeds 3TB, choke them. Where could I find a system to count that for me? It would also need to reset or be able to be manually reset on a monthly basis. Thanks ahead of time!

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• Is there a realiable way to troubleshoot wake up from sleep in Windows?

  - by Borek

  Is there a reliable way to troubleshoot laptop wakes? I've seen "heuristics" posted here and there but isn't there really a simple and deterministic way to tell what's causing a problem? Specifically, my laptop wakes up about every hour for about 2 minutes. Exported event log entries are here: http://www.mediafire.com/?abcqb00v5wyo6pj. I've tried: powercfg -devicequery wake_armed Empty result set. Scheduled tasks - the main ones are not scheduled to run every hour. When go through a long list of all possible tasks, there are some that are set to be triggered every hour (e.g., MS "RacTask" whatever it is). But when I go to power options, Advanced settings, Sleep, Allow wake timers it is set to "Disable". Also, the specific task is not set to wake the computer if necessary. Power options for my Ethernet card don't enable it to wake the computer - the cable is disconnected anyway. There are no other HW devices attached - no USB disks, no keyboards / mice etc. I am really clueless and quite unhappy that it's so hard to troubleshoot this situation.

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• Can the OS X unlock panel trigger a login hook similar to loginwindow?

  - by Allen

  I'd like to automatically run a shell script every time I authenticate onto my computer. However, all the info I can find about loginhook and Global LoginItems applies only when authenticating to "loginwindow," and not to the "unlock panel." The unlock panel prompts for a password when waking up from sleep or from a locked screen. Is there any way to trigger script execution after successfully unlocking the screen?

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• Dynamic Disk: Revert back to basic or...?

  - by someguy

  When I was trying to create a new partition (via Disk Management) it warned me that the disk would be dynamic, but I thought it meant the partition and went ahead. Now, my hard disk, which has the main C partition, is dynamic. I haven't shut down the computer, and I'm not sure what the consequences are. Should I revert back to basic or...? What ever happens, I don't want to lose my data. Edit: I think I should mention that I don't know how to revert back to basic...

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• WebGL Not working in FF4b7 (with enabled_for_all_sites=true)

  - by tj111

  I was trying to load the cool Kataspace WebGL demo (more info) and I get the error message "Your browser doesn't support WebGL. Currently we recommend the latest Firefox 4 Beta for all platforms." I checked around and every piece of advice I can find on the internet says to set webgl.enabled_for_all_sites to true in the about:config page. Mine is set to true yet I still receive the same message. Does anyone know of any other items that may be conflicting with WebGL running properly?

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• Test script if host is back online

  - by brubelsabs

  E.g. system: Ubuntu/Debian. As many of you do this probably via ping and a terminal, I always forget this terminal when switching to other task... So a noftification popup would be useful. So can I do better as this?: while; do if ping -c 1 your.host.com; expr $? = 0; then notify-send "your.host.com back online"; sleep 30s; else sleep 30s; fi; done You will need zsh and libnotify to let the snippet work. As script: #!/usr/bin/env zsh while; do if ping -c 1 $1; expr $? = 0; then notify-send "$1 back online"; sleep 30s; else sleep 30s; fi; done

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• what is the best mid/high-end class audio/music creation audio sound card?

  - by Chris

  Hello, I have a computershop myself, and I repair computers. But one of the things I really don't know (yet) is the performace od audio cards for music creation with midi. I have searched and searched and came up with some good reviews, but after browsing for a couple of hours I could't see the trees trough the forrest :-D (it's a dutch expression) At one moment I thought the M-Audio - Delta 1010LT would be a good PCIe card, later on I read that this card was released years ago. (but that could be false information) Also any personal expierence would be great, but not necessairy. I have searched a few cards, and I hope someone can help me make a choice for a friend of mine. He's buget is between $100 and $350 I know there are audio cards from $ 500 - $1850,- this is just too expensive. The following specs are crucial: ASIO Midi Mic in minimal 5.1, 7.1 recommended it's not for airplay, but just to compose music at home. using Ableton and midi keyboard. 1. M-Audio - Delta 1010LT: 8 x 8 analog I/O 2 mic preamps or line inputs S/PDIF digital I/O (coaxial) with 2-channel PCM SCMS copy protection control digital I/O supports surround-encoded AC-3 and DTS pass-through 1 x 1 MIDI I/O directly drive up to 7.1 surround (bass management software included) software controlled 36-bit internal DSP digital mixing/routing +4dbu/-10dBV operation individually switched in software word clock I/O for sample accurate device synchronization 2. RME HDSP 9632: * Stereo Analog Ein- und Ausgang, symmetrisch*, 24-Bit/192kHz, > 110 dB SNR * Optionale Erweiterungsboards mit je 4 symmetrischen Ein- und Ausgängen * Alle analogen I/Os voll 192 kHz-fähig, also keine Reduzierung der Kanalzahl * 1 x ADAT Digital In/Out, 96 kHz-fähig (S/MUX) * 1 x SPDIF Digital In/Out, 192 kHz-fähig * 1 x Breakout Kabel für koaxialen SPDIF-Betrieb* * Also bis zu 16 Ein-und Ausgänge gleichzeitig nutzbar! * 1 x Stereo Kopfhörerausgang, parallel zum analogen Ausgang, aber eigene Pegelanpassung * 1 x MIDI I/O für 16 Kanäle Hi-Speed MIDI über Breakout Kabel * DIGICheck, RMEs einzigartiges Meter- und Analysetool mit Spectral Analyser, Professionelle Level Meter 2/8/16-Kanalig, Vector Audio Scope und diversen weiteren Analysefunktionen * HDSP Meter Bridge: Frei skalierbare Levelmeter mit Peak- und RMS Berechnung in Hardware * TotalMix: 512-Kanal Mischer mit 40 Bit interner Auflösung 3. EMU 1212M (1212 M) PCIe: * Top kwaliteit convertors 24-bit/192kHz convertors. * Hardware gestuurde effecten. * DSP zero-latency hardware mixen en monitoring. * Analoge en digitale I/O plus MIDI. * EMU Production Tools Software Bundle - Cakewalk SONAR , Steinberg Cubase LE, Ableton Live E-MU Edition **EMU 1212M PCI-e inputs/outputs:** * 2 balanced jack inputs. * 2 balanced jack outputs. * 24-bit/192kHz ADAT I/O. * 24-bit/192kHz Coaxiale S/PDif I/O switchable to AES/EBU. * MIDI I/O. 4. M-Audio Audiophile 192: - Up to 24-bit/192kHz audio - 2 balanced analog inputs (1/4” TRS) - 2 balanced analog outputs (1/4” TRS) - S/PDIF digital I/O (coaxial RCA connectors) with 2-channel PCM - SCMS copy protection control - Digital I/O supports surround-encoded AC-3 and DTS pass-through - Direct hardware input monitoring via separate balanced 1/4” TRS monitor outputs - Software routing of inputs and outputs - Digital I/O can be routed to/from external effects - 16-channel MIDI I/O - ASIO, WDM, GSIF 2 and Core Audio driver support for compatibility with most applications - 64-bit driver support for Windows - PCI 2.2 compatibility - Apple G5 compatible - Incompatible exceptions - Includes Ableton Live Lite music production software, so you can make music right away - Works with other Delta cards Technical Specifcations: - Compatibility - ASIO - WDM - GSIF 2 - Core Audio

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• Downgrade 'local' packages in Debian/Ubuntu

  - by Matt Joiner

  I recently unticked the "pre-released updates" option in Software Sources on my Ubuntu Lucid 10.04.1 installation. The Ubuntu wiki states the following regarding this source: The proposed updates are updates which are waiting to be moved into the recommended updates queue after some testing. They may never reach recommended or they may be replaced with a more recent update. Roughly 20 installed packages have indeed not made it into recommended updates, and occasionally cause conflicts when I install new software, as related packages of the newer version are unavailable now that I've disabled the source. How can I force a downgrade of all packages for which an earlier version exists in a enabled repository?

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• To Switch To The Design View Of A Windows Form

  - by June

  Hi Friends I create new project in Windows Form Application using Visual Studio in VB.Net. I place some controls on my form. I don't write any code at this time. I close this project. When i open this project again , i found Form1.vb. I double-click that file , but the design view doesn't appear. I also find Form1.Designer.vb. What in this file is code. How can i switch to Design View of Form1 ? I need to write some codes for that form's objects like Button Click Event. June

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