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• No network upsets gnome

  - by Darren Cook

  An issue that has been bothering me for over a year now. My notebook, running ubuntu 10.04, is almost all the time using a wired connection, with static IP address. And a remote DNS server. Network is configured with entries in /etc/network/interfaces and /etc/resolv.conf, rather than whatever the gnome UI tool was (*) But if I'm out, or simply unplug the network cable, a few things get weird. Specifically the gnome-panel stops working - it is still there, but isn't updating. And opening a nautilus window (e.g. to look at files on the local disk) has huge time-outs. By that I mean it will not open the window for something like 30 or 60 seconds; but when it does finally open it I can see the files and it is perfectly usable. Everything else works fine, alt-tab between windows, etc. I use the commandline to find the pid of gnome-panel, kill it, wait a couple of seconds, and it opens up a fresh panel which is normally usable. (Something like 10 minutes later it will have locked/crashed again; the same for the nautilus windows.) I'm guessing this is a DNS issue? Would setting up a local DNS server help? Guess number 2 was related to having a file server mount (samba, though running on another linux box), and symbolic links to files and directories on that file server on my desktop. My question is a bit vague... Does anyone recognize these symptoms, and have a suggestion? Or do you have some troubleshooting suggestions for narrowing down the problem? My /etc/hosts: 127.0.0.1 localhost 127.0.1.1 myhost # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts 127.0.0.1 testsite.local #Other test website URLs here UPDATE: Some timings to open some desktop folder icons. This is after pulling out the network cable. A sub-directory of the desktop took 23 secs to open up. Content appears immediately (just 8 files, it has no further subdirectories). The home directory icon took 12 seconds to open up, but then took about 30 seconds for the files to appear. I closed it and tried again. This time it took 18 seconds to open up, but then 70 seconds before anything appeared. *: I couldn't work out how to use the gnome network tool for my needs, which include 3-4 static IPs for testing virtual hosts locally.

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• Detach current session and attach to another session, done with one script, can I?

  - by Jimm Chen

  After reading the vague official doc of GNU screen( http://www.gnu.org/software/screen/manual/screen.html ) and asking quite some questions at this site. I still cannot figure out how to accomplish such a task with a shell script. This task costs some words to describe. Assume I'm using PuTTY to telnet into my Linux server. ?STEP 1? Launch 2 telnet connections . From putty window 1 (PTWIN1),telnet into Linux Bash shell, execute screen -RR to launch a screen session, and get session name 21385.pts-4.linux-ic37 . From putty window 2 (PTWIN2), do that same as in PTWIN1, but this time, I get session name 22041.pts-9.linux-ic37 . Now, we have two screen sessions running simultaneously. We can check this: $ screen -ls There are screens on: 22041.pts-9.linux-ic37 (Attached) 21385.pts-4.linux-ic37 (Attached) 2 Sockets in /var/run/uscreens/S-chj2. ?STEP 2? Assume that for some reason, PTWIN1's TCP connection is lost abnormally(but server doesn't know that), and an urgent work is pending on session 21385 and I want to quickly regain control of it. Fortunately, we know the 21385 session is still there, so, I want to have PTWIN2 attach to session 21385. Because I hate to remember the esoteric screen option all the time, so I decide to write a script called sttach. I hope that sttach 21385.pts-4.linux-ic37 can let me attach to session 21385(for PTWIN2). Now, let's say sttach works well and I take control of 21385 on PTWIN2. ?STEP 3? Some minutes later. I want to go back to work on session 22041. Here, please allow me to have PTWIN2 remain associated with session 21385. What I would like to do is to launch another putty window (PTWIN3), telnet into server, and execute sttach 22041.pts-9.linux-ic37 in hope that I can resume session 22041 on PTWIN3 . You can see the benefit of sttach: as long as I know the target session name, I can call it to have my PuTTY window switch to that session, regardless whether the target session is "(Attached)" or "(Detached)", and regardless whether the running context is inside a screen session or not. Now the question: How to write the (Bash) script sttach? I mean, run screen with appropriate options in sttach to accomplish the goal. Waiting for your kind answer. Thank you. My previous questions regarding GNU screen: GNU screen, how to get current sessionname programmatically Is it possible to change GNU screen session name after created? How do I know I'm running inside a linux "screen" or not? My env: openSUSE Linux 11.3, GNU screen 4.00.03 (FAU) 23-Oct-06

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• DB2 Integrity Checks and Exception Tables

  - by imthefirestartr

  I am working on planning a migration of a DB2 8.1 database from a horrible IBM encoding to UTF-8 to support further languages etc. I am encountering an issue that I am stuck on. A few notes on this migration: We are using db2move to export and load the data and db2look to get the details fo the database (tablespaces, tables, keys etc). We found the loading process worked nicely with db2move import, however, the data takes 7 hours to load and this was unacceptable downtime when we actually complete the conversion on the main database. We are now using db2move load, which is much faster as it seems to simply throw the data in without integrity checks. Which leads to my current issue. After completing the db2move load process, several tables are in a check pending state and require integrity checks. Integrity checks are done via the following: set integrity for . immediate checked This works for most tables, however, some tables give an error: DB21034E The command was processed as an SQL statement because it was not a valid Command Line Processor command. During SQL processing it returned: SQL3603N Check data processing through the SET INTEGRITY statement has found integrity violation involving a constraint with name "blah.SQL120124110232400". SQLSTATE=23514 The internets tell me that the solution to this issue is to create an exception table based on the actual table and tell the SET INTEGRITY command to send any exceptions to that table (as below): db2 create table blah_EXCEPTION like blah db2 SET INTEGRITY FOR blah IMMEDIATE CHECKED FOR EXCEPTION IN blah USE blah_EXCEPTION NOW, here is the specific issue I am having! The above forces all the rows with issues to the specified exception table. Well that's just super, buuuuuut I can not lose data in this conversion, its simply unacceptable. The internets and IBM has a vague description of sending the violations to the exception tables and then "dealing with the data" that is in the exception table. Unfortunately, I am not clear what this means and I was hoping that some wise individual knows and could help me out and let me know how I can retrieve this data from these tables and place the data in the original/proper table rather than these exception tables. Let me know if you have any questions. Thanks!

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• Varnish + Plesk : vhost broken

  - by Raphaël

  I have an e-commerce site with 300,000 products and 20,000 categories. It is slow and currently in production. I decided to install Varnish to speed up. The trouble is that during installation, I got a Guru Meditation. Since the site is in production, I am not allowed to leave this error more than a second, thinking to have made an enormous stupidity. I followed the following tutorial: http://www.euperia.com/linux/setting-up-varnish-with-apache-tutorial I'm sure I followed all without error. I say that there may be a specific configuration with plesk. Has anyone already installed Varnish on a ubuntu 11.04 server with plesk 10? Does anyone have a better resource? I know it is "very vague" as an error, but maybe some of you have had this problem. edit 24/11/2011 I continued to work on Varnish + Plesk ... but it still does not work. 1) I changed the port for apache in plesk General # mysql -uadmin -p`cat /etc/psa/.psa.shadow` -D psa -e'replace into misc (param, val) values ("http_port", 8008)' 1.1) I rebuild the server conf # /usr/local/psa/admin/bin/httpdmng --reconfigure-all 2) I changed the apache conf files (if those were not taking full plesk top) vim /etc/apache2/ports.conf NameVirtualHost *:8008 Listen 8008 2.1) I do the same with /etc/apache2/sites-enables/000-default 3) I changed the port of my vhost (a single server) vim /var/www/vhosts/MYDOMAIN.COM/conf/XXXXXXXXX.http.include Replace the port 80 by this I want. Rebuild the vhost conf /usr/local/psa/admin/sbin/websrvmng --reconfigure-vhost --vhost-name=<domain_name> with without www (See my issue in serverfault: Edit vhost port in plesk 10.3 ) 4) I installed varnish by following this tutorial : http://www.euperia.com/linux/setting-up-varnish-with-apache-tutorial 5) I restart apache 2 + varnish service apache2 restart service varnish restart When I go to my site, I come across a page of apache It works! This is the default web page for this server. The web server software is running but no content has been added, yet. Can somebody help me ? This means that my vhost does not point to the right place. Why? What to do? How?

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• Any reason not to disable the Windows pagefile given enough physical RAM?

  - by Evgeny

  The question of disabling the Windows pagefile has already been discussed quite a bit, for example here and here and here. People continue to upvote answers that say "you should not disable your pagefile even if you have plenty of RAM", but I have yet to see any concrete, verifiable reasons being given for this advice. As far as I can see, if you never need to read from the pagefile (because you have enough RAM) then performance could only be worse with it enabled due to Windows pre-emptively writing to it. At best, performance would be the same. I can't see how it could possibly be improved by writing data you never need to read. So my question is: Assuming that I have enough physical RAM for everything I do, is there any reason I should not disable the pagefile? Let's say the version of Windows is Windows XP x64 SP2 or Windows Server 2003 x64 SP2 (same thing). If it's different for Windows Server 2008 x64 I'd be interested to hear an answer for that as well. I'm looking for specific, objective reasons from good sources, not just opinions. Something like "here are the benchmarks done with and without a pagefile and the results were better with a pagefile, even with enough RAM" or "according to this MS KB article problem X occurs if you disable the pagefile". So far the only reasons I've seen mentioned are: Even if you think you have enough RAM you might run out. OK, but for the purposes of this question, let's just take it as a given that I have enough. Maybe I only ever read my email and I have 16GB RAM. Or 128GB. Or 1TB. Or whatever - but it's enough for 100% of what I do, 100% of the time. Another way to think of it is: if I have x MB physical RAM and y MB pagefile and I never run out of RAM in that configuration, would I not be better off, performance-wise, with x+y MB physical RAM and no pagefile? Windows is "used to" having a paging file and it might not function as reliably (from Understanding the Impact of RAM on Overall System Performance That's rather vague and I find it hard to believe, given that MS has provided the option to disable the pagefile. Windows knows what it's doing better than you. No - it doesn't know that I won't run more programs or load more data, but I do.

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• System Requirements of a write-heavy applications serving hundreds of requests per second

  - by Rolando Cruz

  NOTE: I am a self-taught PHP developer who has little to none experience managing web and database servers. I am about to write a web-based attendance system for a very large userbase. I expect around 1000 to 1500 users logged-in at the same time making at least 1 request every 10 seconds or so for a span of 30 minutes a day, 3 times a week. So it's more or less 100 requests per second, or at the very worst 1000 requests in a second (average of 16 concurrent requests? But it could be higher given the short timeframe that users will make these requests. crosses fingers to avoid 100 concurrent requests). I expect two types of transactions, a local (not referring to a local network) and a foreign transaction. local transactions basically download userdata in their locality and cache it for 1 - 2 weeks. Attendance equests will probably be two numeric strings only: userid and eventid. foreign transactions are for attendance of those do not belong in the current locality. This will pass in the following data instead: (numeric) locality_id, (string) full_name. Both requests are done in Ajax so no HTML data included, only JSON. Both type of requests expect at the very least a single numeric response from the server. I think there will be a 50-50 split on the frequency of local and foreign transactions, but there's only a few bytes of difference anyways in the sizes of these transactions. As of this moment the userid may only reach 6 digits and eventid are 4 to 5-digit integers too. I expect my users table to have at least 400k rows, and the event table to have as many as 10k rows, a locality table with at least 1500 rows, and my main attendance table to increase by 400k rows (based on the number of users in the users table) a day for 3 days a week (1.2M rows a week). For me, this sounds big. But is this really that big? Or can this be handled by a single server (not sure about the server specs yet since I'll probably avail of a VPS from ServInt or others)? I tried to read on multiple server setups Heatbeat, DRBD, master-slave setups. But I wonder if they're really necessary. the users table will add around 500 1k rows a week. If this can't be handled by a single server, then if I am to choose a MySQL replication topology, what would be the best setup for this case? Sorry, if I sound vague or the question is too wide. I just don't know what to ask or what do you want to know at this point.

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• Generating/managing config files for hosted application

  - by mfinni

  I asked a question about config management, and haven't seen a reply. It's possible my question was too vague, so let's get down to brass tacks. Here's the process we follow when onboarding a new customer instance into our hosted application : how would you manage this? I'm leaning towards a Perl script to populate templates to generate shell scripts, config files, XML config files, etc. Looking briefly at CFengine and Chef, it seems like they're not going to reduce the amount of work, because I'd still have to manually specify all of the changes/edits within the tool. Doesn't seem to be much of a gain over touching the config files directly. We add a stanza to the main config file for the core (3rd-party) application. This stanza has values that defines the instance (customer) name the TCP listener port for this instance (not one currently used) the DB2 database name (serial numeric identifier, already exists, they get prestaged for us by the DBAs) three sub-config files, by name - they need to be created from 3 templates and be named after the instance The sub-config files define: The filepath for the DB2 volumes The filepath for the storage of objects The filepath for just one of the DB2 volumes (yes, redundant to the first item. We run some application commands, start the instance We do some LDAP thingies (make an OU for the instance, etc.) We add a stanza to the config file for our security listener that acts as a passthrough to LDAP instance name LDAP OU TCP port for instance DB2 database name We restart the security listener (off-hours), change the main config file from item 1, stop and restart the instance. It is now authenticating via LDAP. We add the stop and start commands for this instance to the HA failover scripts. We import an XML config file into the instance that defines things for the actual application for the customer - user names, groups, permissions, and business rules. The XML is supplied by the implementation team. Now, we configure the dataloading application We add a stanza to the existing top-level config file that points to a new customer-level config file. The new customer-level config file includes: the instance (customer) name the DB2 database name arbitrary number of sub-config files, by name Each of the sub-config files defines: filepaths to the directories for ingestion, feedback, backup, and failure those filepaths have a common path to a customer-specific folder, and then one folder for each sub-config file Each of those filepaths needs to be created We need to add this customer instance to our monitoring scripts that confirm the proper processes are running and can be logged into. Of course, those monitoring config files include the instance name, the TCP port, the DB2 database name, etc. There's also a reporting application that needs to be configured for the new instance. You get the idea. There's also XML that is loaded into WAS by the middleware team. We give them the values for them to plug into the XML - they could very easily hand us the template and we could give them back completed XML.

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• Top 4 Lame Tech Blogging Posts

  - by jkauffman

  From a consumption point of view, tech blogging is a great resource for one-off articles on niche subjects. If you spend any time reading tech blogs, you may find yourself running into several common, useless types of posts tech bloggers slip into. Some of these lame posts may just be natural due to common nerd psychology, and some others are probably due to lame, lemming-like laziness. I’m sure I’ll do my fair share of fitting the mold, but I quickly get bored when I happen upon posts that hit these patterns without any real purpose or personal touches. 1. The Content Regurgitation Posts This is a common pattern fueled by the starving pan-handlers in the web traffic economy. These are posts that are terse opinions or addendums to an existing post. I commonly see these involve huge block quotes from the linked article which almost always produces over 50% of the post itself. I’ve accidentally gone to these posts when I’m knowingly only interested in the source material. Web links can degrade as well, so if the source link is broken, then, well, I’m pretty steamed. I see this occur with simple opinions on technologies, Stack Overflow solutions, or various tech news like posts from Microsoft. It’s not uncommon to go to the linked article and see the author announce that he “added a blog post” as a response or summary of the topic. This is just rude, but those who do it are probably aware of this. It’s a matter of winning that sweet, juicy web traffic. I doubt this leeching is fooling anybody these days. I would like to rally human dignity and urge people to avoid these types of posts, and just leave a comment on the source material. 2. The “Sorry I Haven’t Posted In A While” Posts This one is far too common. You’ll most likely see this quote somewhere in the body of the offending post: I have been really busy. If the poster is especially guilt-ridden, you’ll see a few volleys of excuses. Here are some common reasons I’ve seen, which I’ll list from least to most painfully awkward. Out of town Vague allusions to personal health problems (these typically includes phrases like “sick”, “treatment'”, and “all better now!”) “Personal issues” (which I usually read as "divorce”) Graphic or specific personal health problems (maximum awkwardness potential is achieved if you see links to charity fund websites) I can’t help but to try over-analyzing why this occurs. Personally, I see this an an amalgamation of three plain factors: Life happens Us nerds are duty-driven, and driven to guilt at personal inefficiencies Tech blogs can become personal journals I don’t think we can do much about the first two, but on the third I think we could certainly contain our urges. I’m a pretty boring guy and, whether or I like it or not, I have an unspoken duty to protect the world from hearing about my unremarkable existence. Nobody cares what kind of sandwich I’m eating. Similarly, if I disappear for a while, it’s unlikely that anybody who happens upon my blog would care why. Rest assured, if I stop posting for a while due to a vasectomy, you will be the first to know. 3. The “At A Conference”, or “Conference Review” Posts I don’t know if I’m like everyone else on this one, but I have never been successfully interested in these posts. It even sounds like a good idea: if I can’t make it to a particular conference (like the KCDC this year), wouldn’t I be interested in a concentrated summary of events? Apparently, no! Within this realm, I’ve never read a post by a blogger that held my interest. What really baffles is is that, for whatever reason, I am genuinely engaged and interested when talking to someone in person regarding the same topic. I have noticed the same phenomenon when hearing about others’ vacations. If someone sends me an email about their vacation, I gloss over it and forget about it quickly. In contrast, if I’m speaking to that individual in person about their vacation, I’m actually interested. I’m unsure why the written medium eradicates the intrigue. I was raised by a roaming pack of friendly wild video games, so that may be a factor. 4. The “Top X Number of Y’s That Z” Posts I’ve seen this one crop up a lot more in the past few of years. Here are some fabricated examples: 5 Easy Ways to Improve Your Code Top 7 Good Habits Programmers Learn From Experience The 8 Things to Consider When Giving Estimates Top 4 Lame Tech Blogging Posts These are attention-grabbing headlines, and I’d assume they rack up hits. In fact, I enjoy a good number of these. But, I’ve been drawn to articles like this just to find an endless list of identically formatted posts on the blog’s archive sidebar. Often times these posts have overlapping topics, too. These types of posts give the impression that the author has given thought to prioritize and organize the points as a result of a comprehensive consideration of a particular topic. Did the author really weigh all the possibilities when identifying the “Top 4 Lame Tech Blogging Patterns”? Unfortunately, probably not. What a tool. To reiterate, I still enjoy the format, but I feel it is abused. Nowadays, I’m pretty skeptical when approaching posts in this format. If these trends continue, my brain will filter these blog posts out just as effectively as it ignores the encroaching “do xxx with this one trick” advertisements. Conclusion To active blog readers, I hope my guide has served you precious time in being able to identify lame blog posts at a glance. Save time and energy by skipping over the chaff of the internet! And if you author a blog, perhaps my insight will help you to avoid the occasional urge to produce these needless filler posts.

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• Best way to store a large amount of game objects and update the ones onscreen

  - by user3002473

  Good afternoon guys! I'm a young beginner game developer working on my first large scale game project and I've run into a situation where I'm not quite sure what the best solution may be (if there is a lone solution). The question may be vague (if anyone can think of a better title after having read the question, please edit it) or broad but I'm not quite sure what to do and I thought it would help just to discuss the problem with people more educated in the field. Before we get started, here are some of the questions I've looked at for help in the past: Best way to keep track of game objects Elegant way to simulate large amounts of entities within a game world What is the most efficient container to store dynamic game objects in? I've also read articles about different data structures commonly used in games to store game objects such as this one about slot maps, but none of them are really what I'm looking for. Also, if it helps at all I'm using Python 3 to design the game. It has to be Python 3, if I could I would use C++ or Unityscript or something else, but I'm restricted to having to use Python 3. My game will be a form of side scroller shooter game. In said game the player will traverse large rooms with large amounts of enemies and other game objects to update (think some of the larger areas in Cave Story or Iji). The player obviously can't see the entire room all at once, so there is a viewport that follows the player around and renders only a selection of the room and the game objects that it contains. This is not a foreign concept. The part that's getting me confused has to do with how certain game objects are updated. Some of them are to be updated constantly, regardless of whether or not they can be seen. Other objects however are only to be updated when they are onscreen (for example, an enemy would only be updated to react to the player when it is onscreen or when it is in a certain range of the screen). Another problem is that game objects have to be easily referable by other game objects; something that happens in the player's update() method may affect another object in the world. Collision detection in games is always a serious problem. I need a way of containing the game objects such that it minimizes the number of cases when testing for collisions against one another. The final problem is that of creating and destroying game objects. I think this problem is pretty self explanatory. To store the game objects then I've considered a number of different methods. The original method I had was to simply store all the objects in a hash table by an id. This method was simple, and decently fast as it allows all the objects to be looked up in O(1) complexity, and also allows them to be deleted fairly easily. Hash collisions would not be a major problem; I wasn't originally planning on using computer generated ids to store the game objects I was going to rely on them all using ids given to them by the game designer (such names would be strings like 'Player' or 'EnemyWeapon4'), and even if I did use computer generated ids, if I used a decent hashing algorithm then the chances of collisions would be around 1 in 4 billion. The problem with using a hash table however is that it is inefficient in checking to see what objects are in range of the viewport. Considering the fact that certain game objects move (as well as the viewport itself), the only solution I could think of in order to only update objects that are in the viewport would be to iterate through every object in the hash table and check if it is in the viewport or not, updating only the ones that are in the valid area. This would be incredibly slow in scenarios where the amount of game objects exceeds 500, or even 200. The second solution was to store everything in a 2-d list. The world is partitioned up into cells (a tilemap essentially), where each cell or tile is the same size and is square. Each cell would contain a list of the game objects that are currently occupying it (each game object would be inserted into a cell depending on the center of the object's collision mask). A 2-d list would allow me to take the top-left and bottom-right corners of the viewport and easily grab a rectangular area of the grid containing only the cells containing entities that are in valid range to be updated. This method also solves the problem of collision detection; when I take an entity I can find the cell that it is currently in, then check only against entities in it's cell and the 8 cells around it. One problem with this system however is that it prohibits easy lookup of game objects. One solution I had would be to simultaneously keep a hash table that would contain all the positions of the objects in the 2-d list indexed by the id of said object. The major problem with a 2-d list is that it would need to be rebuilt every single game frame (along with the hash table of object positions), which may be a serious detriment to game speed. Both systems have ups and downs and seem to solve some of each other's problems, however using them both together doesn't seem like the best solution either. If anyone has any thoughts, ideas, suggestions, comments, opinions or solutions on new data structures or better implementations of the existing data structures I have in mind, please post, any and all criticism and help is welcome. Thanks in advance! EDIT: Please don't close the question because it has a bad title, I'm just bad with names!

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• Most efficient way to implement delta time

  - by Starkers

  Here's one way to implement delta time: /// init /// var duration = 5000, currentTime = Date.now(); // and create cube, scene, camera ect ////// function animate() { /// determine delta /// var now = Date.now(), deltat = now - currentTime, currentTime = now, scalar = deltat / duration, angle = (Math.PI * 2) * scalar; ////// /// animate /// cube.rotation.y += angle; ////// /// update /// requestAnimationFrame(render); ////// } Could someone confirm I know how it works? Here what I think is going on: Firstly, we set duration at 5000, which how long the loop will take to complete in an ideal world. With a computer that is slow/busy, let's say the animation loop takes twice as long as it should, so 10000: When this happens, the scalar is set to 2.0: scalar = deltat / duration scalar = 10000 / 5000 scalar = 2.0 We now times all animation by twice as much: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 2.0; angle = (Math.PI * 4) // which is 2 rotations When we do this, the cube rotation will appear to 'jump', but this is good because the animation remains real-time. With a computer that is going too quickly, let's say the animation loop takes half as long as it should, so 2500: When this happens, the scalar is set to 0.5: scalar = deltat / duration scalar = 2500 / 5000 scalar = 0.5 We now times all animation by a half: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 0.5; angle = (Math.PI * 1) // which is half a rotation When we do this, the cube won't jump at all, and the animation remains real time, and doesn't speed up. However, would I be right in thinking this doesn't alter how hard the computer is working? I mean it still goes through the loop as fast as it can, and it still has render the whole scene, just with different smaller angles! So this a bad way to implement delta time, right? Now let's pretend the computer is taking exactly as long as it should, so 5000: When this happens, the scalar is set to 1.0: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 1; angle = (Math.PI * 2) // which is 1 rotation When we do this, everything is timsed by 1, so nothing is changed. We'd get the same result if we weren't using delta time at all! My questions are as follows Mostly importantly, have I got the right end of the stick here? How do we know to set the duration to 5000 ? Or can it be any number? I'm a bit vague about the "computer going too quickly". Is there a way loop less often rather than reduce the animation steps? Seems like a better idea. Using this method, do all of our animations need to be timesed by the scalar? Do we have to hunt down every last one and times it? Is this the best way to implement delta time? I think not, due to the fact the computer can go nuts and all we do is divide each animation step and because we need to hunt down every step and times it by the scalar. Not a very nice DSL, as it were. So what is the best way to implement delta time? Below is one way that I do not really get but may be a better way to implement delta time. Could someone explain please? // Globals INV_MAX_FPS = 1 / 60; frameDelta = 0; clock = new THREE.Clock(); // In the animation loop (the requestAnimationFrame callback)… frameDelta += clock.getDelta(); // API: "Get the seconds passed since the last call to this method." while (frameDelta >= INV_MAX_FPS) { update(INV_MAX_FPS); // calculate physics frameDelta -= INV_MAX_FPS; } How I think this works: Firstly we set INV_MAX_FPS to 0.01666666666 How we will use this number number does not jump out at me. We then intialize a frameDelta which stores how long the last loop took to run. Come the first loop frameDelta is not greater than INV_MAX_FPS so the loop is not run (0 = 0.01666666666). So nothing happens. Now I really don't know what would cause this to happen, but let's pretend that the loop we just went through took 2 seconds to complete: We set frameDelta to 2: frameDelta += clock.getDelta(); frameDelta += 2.00 Now we run an animation thanks to update(0.01666666666). Again what is relevance of 0.01666666666?? And then we take away 0.01666666666 from the frameDelta: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 2 - 0.01666666666 frameDelta = 1.98333333334 So let's go into the second loop. Let's say it took 2(? Why not 2? Or 12? I am a bit confused): frameDelta += clock.getDelta(); frameDelta = frameDelta + clock.getDelta(); frameDelta = 1.98333333334 + 2 frameDelta = 3.98333333334 This time we enter the while loop because 3.98333333334 = 0.01666666666 We run update We take away 0.01666666666 from frameDelta again: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 3.98333333334 - 0.01666666666 frameDelta = 3.96666666668 Now let's pretend the loop is super quick and runs in just 0.1 seconds and continues to do this. (Because the computer isn't busy any more). Basically, the update function will be run, and every loop we take away 0.01666666666 from the frameDelta untill the frameDelta is less than 0.01666666666. And then nothing happens until the computer runs slowly again? Could someone shed some light please? Does the update() update the scalar or something like that and we still have to times everything by the scalar like in the first example?

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• Lessons learnt in implementing Scrum in a Large Organization that has traditional values

  - by MarkPearl

  I recently had the experience of being involved in a “test” scrum implementation in a large organization that was used to a traditional project management approach. Here are some lessons that I learnt from it. Don’t let the Project Manager be the Product Owner First lesson learnt is to identify the correct product owner – in this instance the product manager assumed the role of the product owner which was a mistake. The product owner is the one who has the most to loose if the project fails. With a methodology that advocates removing the role of the project manager from the process then it is not in the interests of the person who is employed as a project manager to be the product owner – in fact they have the most to gain should the project fail. Know the time commitments of team members to the Project Second lesson learnt is to get a firm time commitment of the members on a team for the sprint and to hold them to it. In this project instance many of the issues we faced were with team members having to double up on supporting existing projects/systems and the scrum project. In many situations they just didn’t get round to doing any work on the scrum project for several days while they tried to meet other commitments. Initially this was not made transparent to the team – in stand up team members would say that had done some work but would be very vague on how much time they had actually spent using the blackhole of their other legacy projects as an excuse – putting up a time burn down chart made time allocations transparent and easy to hold the team to. In addition, how can you plan for a sprint without knowing the actual time available of the members – when I mean actual time, the exercise of getting them to go through all their appointments and lunch times and breaks and removing them from their time commitment helps get you to a realistic time that they can dedicate. Make sure you meet your minimum team sizes In a recent post I wrote about the difference between a partnership and a team. If you are going to do scrum in a large organization make sure you have a minimum team size of at least 3 developers. My experience with larger organizations is that people have a tendency to be sick more, take more leave and generally not be around – if you have a team size of two it is so easy to loose momentum on the project – the more people you have in the team (up to about 9) the more the momentum the project will have when people are not around. Swapping from one methodology to another can seem as waste to the customer It sounds bad, but most customers don’t care what methodology you use. Often they have bought into the “big plan upfront”. If you can, avoid taking a project on midstream from a traditional approach unless the customer has not bought into the process – with this particular project they had a detailed upfront planning breakaway with the customer using the traditional approach and then before the project started we moved onto a scrum implementation – this seemed as waste to the customer. We should have managed the customers expectation properly. Don’t play the role of the scrum master if you can’t be the scrum master With this particular implementation I was the “scrum master”. But all I did was go through the process of the formal meetings of scrum – I attended stand up, retrospectives and planning – but I was not hands on the ground. I was not performing the most important role of removing blockages – and by the end of the project there were a number of blockages “cropping up”. What could have been a better approach was to take someone on the team and train them to be the scrum master and be present to coach them. Alternatively actually be on the team on a fulltime basis and be the scrum master. By just going through the meetings of scrum didn’t mean we were doing scrum. So we failed with this one, if you fail look at it from an agile perspective As this particular project drew to a close and it became more and more apparent that it was not going to succeed the failure of it became depressing. Emotions were expressed by various people on the team that we not encouraging and enforced the failure. Embracing the failure and looking at it for what it is instead of taking it as the end of the world can change how you grow from the experience. Acknowledging that it failed and then focussing on learning from why and how to avoid the failure in the future can change how you feel emotionally about the team, the project and the organization.

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• The architecture and technologies to use for a secure, fast, reliable and easily scalable web application

  - by DSoul

  ^ For actual questions, skip to the lists down below I understand, that his is a vague topic, but please, before you turn the other way and disregard me, hear me out. I am currently doing research for a web application(I don't know if application is the correct word for it, but I will proceed w/ that for now), that one day might need to be everything mentioned in the title. I am bound by nothing. That means that every language, OS and framework is acceptable, but only if it proves it's usefulness. And if you are going to say, that scalability and speed depend on the code I write for this application, then I agree, but I am just trying to find something, that wouldn't stand in my way later on. I have done quite a bit reading on this subject, but I still don't have a clear picture, to what suits my needs, so I come to you, StackOverflow, to give me directions. I know you all must be wondering what I'm building, but I assure you, that it doesn't matter. I have heard of 12 factor app though, if you have any similar guidelines or what is, to suggest the please, go ahead. For the sake of keeping your answers as open as possible, I'm not gonna provide you my experience regarding anything written in this question. ^ Skippers, start here First off - the weights of the requirements are probably something like that (on a scale of 10): Security - 10 Speed - 5 Reliability (concurrency) - 7.5 Scalability - 10 Speed and concurrency are not a top priority, in the sense, that the program can be CPU intensive, and therefore slow, and only accept a not-that-high number of concurrent users, but both of these factors must be improvable by scaling the system Anyway, here are my questions: How many layers should the application have, so it would be future-proof and could best fulfill the aforementioned requirements? For now, what I have in mind is the most common version: Completely separated front end, that might be a web page or an MMI application or even both. Some middle-ware handling communication between the front and the back end. This is probably a server that communicates w/ the front end via HTTP. How the communication w/ the back end should be handled is probably dependent on the back end. The back end. Something that handles data through resources like DB and etc. and does various computations w/ the data. This, as the highest priority part of the software, must be easily spread to multiple computers later on and have no known security holes. I think ideally the middle-ware should send a request to a queue from where one of the back end processes takes this request, chops it up to smaller parts and buts these parts of the request back onto the same queue as the initial request, after what these parts will be then handled by other back end processes. Something *map-reduce*y, so to say. What frameworks, languages and etc. should these layers use? The technologies used here are not that important at this moment, you can ignore this part for now I've been pointed to node.js for this part. Do you guys know any better alternatives, or have any reasons why I should (not) use node.js for this particular job. I actually have no good idea, what to use for this job, there are too many options out there, so please direct me. This part (and the 2. one also, I think) depend a lot on the OS, so suggest any OSs alongside w/ the technologies/frameworks. Initially, all computers (or 1 for starters) hosting the back end are going to be virtual machines. Please do give suggestions to any part of the question, that you feel you have comprehensive knowledge and/or experience of. And also, point out if you feel that any part of the current set-up means an instant (or even distant) failure or if I missed a very important aspect to consider. I'm not looking for a definitive answer for how to achieve my goals, because there certainly isn't one, for I haven't provided you w/ all the required information. I'm just looking for recommendations and directions on what to look into. Also, bare in mind, that this isn't something that I have to get done quickly, to sell and let it be re-written by the new owner (which, I've been told for multiple times, is what I should aim for). I have all the time in the world and I really just want to learn doing something really high-end. Also, excuse me if my language isn't the best, I'm not a native. Anyway. Thanks in advance to anyone, who takes the time to help me out here. PS. When I do seem to come up w/ a good architecture/design for this project, I will certainly make it an open project and keep you guys up to date w/ it's development. As in what you could have told me earlier and etc. For obvious reasons the very same question got closed on SO, but could you guys still help me?.

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• Using GraphicsServices.h/GSEvent as well as compiling CLI iPhone tools with XCode

  - by Peter Hajas

  I sent this to KennyTM (has all the private framework headers on GitHub) but I figured I'd ask here too just in case someone has some good ideas or any way to help me out. I'm trying to write a command line utility that sends GSEvents to operate the keyboard, touch/drag elements onscreen, and operate hardware buttons (volume, home, sleep, etc.) I grabbed the MouseSupport code and tried to look through it, but I couldn't find the easiest way to send GSEvents. I'm hoping someone here can help me. First, what's the simplest way to declare a GSEvent and send it? I looked at the iPhone development wiki, but the documentation was very vague. I understand that there's a purple event port (?) that I have to send these events to, but I don't understand how to do that. Could someone offer examples for, say, touching at a coordinate, typing a certain key, or pressing a hardware button? Also, do I have to write or do anything special if I want this utility to operate all applications as well as Springboard? I don't know if this is a special case because I want it at the OS level. Ideally, I would SSH into the phone, start the program, and it would send GSEvents that would be handled by whatever application was open. As far as compiling this code, is there any way to do so under XCode? I don't know what sort of project template I should use (if any) and this is throwing me off. I don't need "build and go" support, I'm more than happy to scp the program over to the phone. I understand that compiling the code is also feasible on the phone. I have all of the headers from the SDK on my phone along with iphone-gcc, but when compiling some test programs I still get errors about not finding mach headers and CoreFoundation. Is there an easier way to do this? Lastly, are there other guides or pieces of literature that anyone can point me towards for learning more about this? I'm excited to get into open iPhone development (I have experience with the official SDK, but I want to go deeper). Thanks for any and all help people can offer!

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• Asyncronus javascript rendering widgets

  - by Joe J

  Hey all, I'm creating a javascript widget so third partys (web designers) can post a link on their website and it will render the widget on their site. Currently, I'm doing this with just a script link tag: <div class="some_random_div_in_html_body"> <script type='text/javascript' src='http://remotehost.com/link/to/widget.js'></script> </div> However, this has the side-effect of slowing down a thrid party's website render times of the page if my site is under a load. Therefore, I'd like the third party website to request the widget link from my site asyncronously and then render it on their site when the widget link loads completely. The Google Analytics javascript snippet seems to have a nice bit of asyncronous code that does a nice async request to model off of, but I'm wondering if I can modify it so that it will render content on the third party's site. Using the example below, I want the content of http://mysite.com/link/to/widget.js to render something in the "message" id field. <HTML> <HEAD><TITLE>Third Party Site</TITLE><STYLE>#message { background-color: #eee; } </STYLE></HEAD> <BODY> <div id="message">asdf</div> <script type="text/javascript"> (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = 'http://mysite.com/link/to/widget.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script> </BODY> </HTML> I don't know if what I'm trying to do constitutes Cross Site Scripting (still a bit vague on that concept) but am wondering if what I'm trying to do is possible. Or if anyone has any other approaches to creating javascript widgets effectively, I'd appreciate any advice. Thanks for reading this. Joe

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• Java Webservice java.lang.ClassCastException: org.apache.cxf.jaxws.ServiceImpl

  - by JohnC

  I am using Maven, CXF 2.2.7, JBoss 4.2.3 and JRE 1.5 I have a Webservice that I can see on the server by using the URL myURL/myService?wsdl I am trying to develop a web app to ping that webservice by calling this in my bean: MyWebService webservice = new MyWebService(); However, it dies and throws the following error, which is very vague: java.lang.ClassCastException: org.apache.cxf.jaxws.ServiceImpl 09:25:59,450 ERROR [STDERR] at javax.xml.ws.Service.<init>(Service.java:81) 09:25:59,450 ERROR [STDERR] at org.otherservice.webservice.MyWebServiceService.<init>(MyWebService.java:44) 09:25:59,450 ERROR [STDERR] at net.myservice.beans.MyBean.getMyServiceSoap(MyBean.java:109) 09:25:59,450 ERROR [STDERR] at net.myservice.beans.MyBean.ack(MyBean.java:240) 09:25:59,450 ERROR [STDERR] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 09:25:59,450 ERROR [STDERR] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 09:25:59,450 ERROR [STDERR] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 09:25:59,450 ERROR [STDERR] at java.lang.reflect.Method.invoke(Method.java:585) 09:25:59,450 ERROR [STDERR] at org.apache.el.parser.AstValue.invoke(AstValue.java:131) 09:25:59,450 ERROR [STDERR] at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276) 09:25:59,450 ERROR [STDERR] at org.apache.jasper.el.JspMethodExpression.invoke(JspMethodExpression.java:68) 09:25:59,450 ERROR [STDERR] at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:77) 09:25:59,450 ERROR [STDERR] at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:95) 09:25:59,450 ERROR [STDERR] at javax.faces.component.UICommand.broadcast(UICommand.java:383) 09:25:59,450 ERROR [STDERR] at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:450) 09:25:59,450 ERROR [STDERR] at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:759) 09:25:59,450 ERROR [STDERR] at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:97) 09:25:59,450 ERROR [STDERR] at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:266) 09:25:59,450 ERROR [STDERR] at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:132) 09:25:59,450 ERROR [STDERR] at javax.faces.webapp.FacesServlet.service(FacesServlet.java:244) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 09:25:59,450 ERROR [STDERR] at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:301) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 09:25:59,450 ERROR [STDERR] at net.faces.filters.AuthorizationFilter.doFilter(AuthorizationFilter.java:84) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 09:25:59,450 ERROR [STDERR] at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) 09:25:59,450 ERROR [STDERR] at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182) 09:25:59,450 ERROR [STDERR] at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) 09:25:59,450 ERROR [STDERR] at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) 09:25:59,450 ERROR [STDERR] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262) 09:25:59,450 ERROR [STDERR] at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844) 09:25:59,450 ERROR [STDERR] at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583) 09:25:59,450 ERROR [STDERR] at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446) 09:25:59,450 ERROR [STDERR] at java.lang.Thread.run(Thread.java:595) I am hoping someone has seen this exception before and can help me.

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• Arranging models, views, controllers in a Kohana 3 project

  - by Pekka

  I'm looking at how to set up a mid-sized web application with Kohana 3. I have implemented MVC patterns in the past but never worked against a "formalized" MVC framework so I'm still getting my head around the terminology - toying around with basic examples, building views and templates, and so on. I'm progressing fairly well but I want to set up a real-world web project (one of my own that I've been planning for quite some time now) as a learning object. I learn best by example, but example-based documentation is a bit sparse for Kohana 3 right now - they say so themselves on the site. While I'm not worried about getting into the framework soon enough, I'm a bit concerned about arranging a healthily structured code base from the start - i.e. how to split up controllers, how to name them, and how to separate the functionality into the appropriate models. My application could, in its core, be described as a business directory with a main businesses table. Businesses can be listed by category and by street name. Each business has a detail page. Business owners can log in and edit their business's entry. Businesses can post offers into an offers table. I know this is pretty vague, but I don't want to cram too much information into this question. I'll be more than happy to go into more detail if needed. Supposing I have all the basic functionality worked out and in place already - list all businesses, edit business, list businesses by street name, create offer, and so on, and I'm just looking for how to fit the functionality into a MVC pattern and into a Kohana application structure that can be easily extended: Do you know real-life, publicly accessible examples of "database-heavy" applications like directories, online communities... with a log-in area built on Kohana 3 where I could take a peek how they do it? Are there conventions or best practices on how to structure an extendable login area for end users in a Kohana project that is not only able to handle a business directory page, but further products on separate pages as well? Do you know application structuring HOWTOs or best practices for Kohana 3 not mentioned in the user guide and the inofficial Wiki? Have you built something similar and could give me some recommendations?

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• When is it worth using a BindingSource?

  - by Justin

  I think I understand well enough what the BindingSource class does - i.e. provide a layer of indirection between a data source and a UI control. It implements the IBindingList interface and therefore also provides support for sorting. And I've used it frequently enough, without too many problems. But I'm wondering if I use it more often than I should. Perhaps an example would help. Let's say I have just a simple textbox on a form (using WinForms), and I'd like to bind that textbox to a simple property inside a class that returns a string. Is it worth using a BindingSource in this situation? Now let's say I have a grid on my form, and I'd like to bind it to a DataTable. Should I use a BindingSource now? In the latter case, I probably would not use a BindingSource, as a DataTable, from what I can gather, provides the same functionality that the BindingSource itself would. The DataTable will fire the the right events when a row is added, deleted, etc so that the grid will automatically update. But in the first case with the textbox being bound to a string, I would probably have the class that contains the string property implement INotifyPropertyChanged, so that it could fire the PropertyChanged event when the string changes. I would use a BindingSource so that it could listen to these PropertyChanged events so that it could update the textbox automatically when the string changes. How does this sound so far? I still feel like there's a gap in my understanding that's preventing me from seeing the whole picture. This has been a pretty vague question so far, so I'll try to ask some more specific questions - ideally the answers will reference the above examples or something similar... (1) Is it worth using a BindingSource in either of the above examples? (2) It seems that developers just "assume" that the DataTable class will do the right thing, in firing PropertyChanged events at the right time. How does one know if a data source is capable of doing this? Is there a particular interface that a data source should implement in order for developers to be able to assume this behaviour? (3) Does it matter what Control is being bound to, when considering whether or not to use a BindingSource? Or is it only the data source that should affect the decision? Perhaps the answer is (and this would seem logical enough): the Control needs to be intelligent enough to listen to the PropertyChanged events, otherwise a BindingSource is required. So how does one tell if the Control is capable of doing this? Again, is there a particular interface that developers can look for that the Control must implement? It is this confusion that has, in the past, led to me always using a BindingSource. But I'd like to understand better exactly when to use one, so that I do so only when necessary.

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• Problem with jQuery.ajax with 'delete' method in ie

  - by Max Williams

  I have a page where the user can edit various content using buttons and selects that trigger ajax calls. In particular, one action causes a url to be called remotely, with some data and a 'put' request, which (as i'm using a restful rails backend) triggers my update action. I also have a delete button which calls the same url but with a 'delete' request. The 'update' ajax call works in all browsers but the 'delete' one doesn't work in IE. I've got a vague memory of encountering something like this before...can anyone shed any light? here's my ajax calls: //update action - works in all browsers jQuery.ajax({ async:true, data:data, dataType:'script', type:'put', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ initializeQuizQuestions(); setPublishButtonStatus(); } }); //delete action - fails in ie function deleteQuizQuestion(quizQuestionId, quizId){ //send ajax call to back end to change the difficulty of the quiz question //back end will then refresh the relevant parts of the page (progress bars, flashes, quiz status) jQuery.ajax({ async:true, dataType:'script', type:'delete', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ alert("success"); initializeQuizQuestions(); setSelectStatus(quizQuestionId, true); jQuery("tr[id*='quiz_question_"+quizQuestionId+"']").removeClass('selected'); }, error: function(msg){ alert("error:" + msg); } }); } I put the alerts in success and error in the delete ajax just to see what happens, and the 'error' part of the ajax call is triggered, but WITH NO CALL BEING MADE TO THE BACK END (i know this by watching my back end server logs). So, it fails before it even makes the call. I can't work out why - the 'msg' i get back from the error block is blank. Any ideas anyone? Is this a known problem? I've tested it in ie6 and ie8 and it doesn't work in either. thanks - max EDIT - the solution - thanks to Nick Craver for pointing me in the right direction. Rails (and maybe other frameworks?) has a subterfuge for the unsupported put and delete requests: a post request with the parameter "_method" (note the underscore) set to 'put' or 'delete' will be treated as if the actual request type was that string. So, in my case, i made this change - note the 'data' option': jQuery.ajax({ async:true, data: {"_method":"delete"}, dataType:'script', type:'post', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ alert("success"); initializeQuizQuestions(); setSelectStatus(quizQuestionId, true); jQuery("tr[id*='quiz_question_"+quizQuestionId+"']").removeClass('selected'); }, error: function(msg){ alert("error:" + msg); } }); } Rails will now treat this as if it were a delete request, preserving the REST system. The reason my PUT example worked was just because in this particular case IE was happy to send a PUT request, but it officially does not support them so it's best to do this for PUT requests as well as DELETE requests.

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• Problem with return 2 libc method

  - by jth

  Hi, I'am trying to understand the return2libc method. I'am using an ubuntu linux 9.10, 32 bit with ASLR disabled. In theory, it sounds quite easy, overwrite the saved eip with the address of system() (or whatever function you want), then put the address to which system() should return and after that, the parameter for system, the "/bin/bash"-string. But what happens is that my exploit keeps segfaulting the vulnerable program. I assume something with the system()-address went wrong. This is what I did so far: Determined the address of system(): (gdb) print system $1 = {<text variable, no debug info>} 0x167020 <system> (gdb) x/x system 0x167020 <system>: 0x890cec83 I used the subsequent x/x system because those 3 bytes returned by print system looks like an index in some sort of jumptable (PLT?), so I assume 0x890cec83 is the right address which is used to overwrite the saved eip. After that I determined the address of the /bin/bash string in memory, using a small C program which basically consists of this line: printf("Address of string /bin/bash: %p\n", getenv("SHELL")); Then I looked a little bit around in the memory and fount /bin/bash: (gdb) x/s 0xbffff6ca 0xbffff6ca: "/bin/bash" After I gathered this information, I filled the buffer: (gdb) b 9 Breakpoint 1 at 0x8048407: file victim.c, line 9. (gdb) r `perl -e 'print "A"x9 . "\x83\xec\x0c\x89FAKE\xca\f6\ff\bf";'` Breakpoint 1, main (argc=1111638594, argv=0xc360cca) at victim.c:10 10 return 0; (gdb) x/s 0xbffff6ca 0xbffff6ca: "/bin/bash" Stack frame looks like this: (gdb) i f Stack level 0, frame at 0xbffff440: eip = 0x8048407 in main (victim.c:10); saved eip 0x890cec83 source language c. Arglist at 0xbffff438, args: argc=1111638594, argv=0xc360cca Locals at 0xbffff438, Previous frame's sp is 0xbffff440 Saved registers: ebp at 0xbffff438, eip at 0xbffff43c This seems all right to me, saved eip was overwritten with the (hopefully) correct system()-address, return address for system was set to "FAKE" (shouldn't matter) and the address of /bin/bash also seems to be correct. When I'am continuing the execution, victim segfaults on some strange address and certainly not in 0x890cec83: (gdb) cont Continuing. Program received signal SIGSEGV, Segmentation fault. 0x0804840d in main (argc=Cannot access memory at address 0x41414149 ) at victim.c:11 11 } Has anyone an explanation or a hint what happens here and why the execution isn't redirected to 0x890cec83? Thanks in advance, any hint, and be it only vague, would be appreciated. I have no idea why this doesn't work.

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• Design pattern question: encapsulation or inheritance

  - by Matt

  Hey all, I have a question I have been toiling over for quite a while. I am building a templating engine with two main classes Template.php and Tag.php, with a bunch of extension classes like Img.php and String.php. The program works like this: A Template object creates a Tag objects. Each tag object determines which extension class (img, string, etc.) to implement. The point of the Tag class is to provide helper functions for each extension class such as wrap('div'), addClass('slideshow'), etc. Each Img or String class is used to render code specific to what is required, so $Img->render() would give something like <img src='blah.jpg' /> My Question is: Should I encapsulate all extension functionality within the Tag object like so: Tag.php function __construct($namespace, $args) { // Sort out namespace to determine which extension to call $this->extension = new $namespace($this); // Pass in Tag object so it can be used within extension return $this; // Tag object } function render() { return $this->extension->render(); } Img.php function __construct(Tag $T) { $args = $T->getArgs(); $T->addClass('img'); } function render() { return '<img src="blah.jpg" />'; } Usage: $T = new Tag("img", array(...); $T->render(); .... or should I create more of an inheritance structure because "Img is a Tag" Tag.php public static create($namespace, $args) { // Sort out namespace to determine which extension to call return new $namespace($args); } Img.php class Img extends Tag { function __construct($args) { // Determine namespace then call create tag $T = parent::__construct($namespace, $args); } function render() { return '<img src="blah.jpg" />'; } } Usage: $Img = Tag::create('img', array(...)); $Img->render(); One thing I do need is a common interface for creating custom tags, ie I can instantiate Img(...) then instantiate String(...), I do need to instantiate each extension using Tag. I know this is somewhat vague of a question, I'm hoping some of you have dealt with this in the past and can foresee certain issues with choosing each design pattern. If you have any other suggestions I would love to hear them. Thanks! Matt Mueller

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• How can I model the data in a multi-language data editor in WPF with MVVM?

  - by Patrick Szalapski

  Are there any good practices to follow when designing a model/ViewModel to represent data in an app that will view/edit that data in multiple languages? Our top-level class--let's call it Course--contains several collection properties, say Books and TopicsCovered, which each might have a collection property among its data. For example, the data needs to represent course1.Books.First().Title in different languages, and course1.TopicsCovered.First().Name in different languages. We want a app that can edit any of the data for one given course in any of the available languages--as well as edit non-language-specific data, perhaps the Author of a Book (i.e. course1.Books.First().Author). We are having trouble figuring out how best to set up the model to enable binding in the XAML view. For example, do we replace (in the single-language model) each String with a collection of LanguageSpecificString instances? So to get the author in the current language: course1.Books.First().Author.Where(Function(a) a.Language = CurrentLanguage).SingleOrDefault If we do that, we cannot easily bind to any value in one given language, only to the collection of language values such as in an ItemsControl. <TextBox Text={Binding Author.???} /> <!-- no way to bind to the current language author --> Do we replace the top-level Course class with a collection of language-specific Courses? So to get the author in the current language: course1.GetLanguage(CurrentLanguage).Books.First.Author If we do that, we can only easily work with one language at a time; we might want a view to show one language and let the user edit the other. <TextBox Text={Binding Author} /> <!-- good --> <TextBlock Text={Binding ??? } /> <!-- no way to bind to the other language author --> Also, that has the disadvantage of not representing language-neutral data as such; every property (such as Author) would seem to be in multiple languages. Even non-string properties would be in multiple languages. Is there an option in between those two? Is there another way that we aren't thinking of? I realize this is somewhat vague, but it would seem to be a somewhat common problem to design for. Note: This is not a question about providing a multilingual UI, but rather about actually editing multi-language data in a flexible way.

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• iPhone reachability checking

  - by Sneakyness

  I've found several examples of code to do what I want (check for reachability), but none of it seems to be exact enough to be of use to me. I can't figure out why this doesn't want to play nice. I have the reachability.h/m in my project, I'm doing #import <SystemConfiguration/SystemConfiguration.h> And I have the framework added. I also have: #import "Reachability.h" at the top of the .m in which I'm trying to use the reachability. Reachability* reachability = [Reachability sharedReachability]; [reachability setHostName:@"http://www.google.com"]; // set your host name here NetworkStatus remoteHostStatus = [reachability remoteHostStatus]; if(remoteHostStatus == NotReachable) {NSLog(@"no");} else if (remoteHostStatus == ReachableViaWiFiNetwork) {NSLog(@"wifi"); } else if (remoteHostStatus == ReachableViaCarrierDataNetwork) {NSLog(@"cell"); } This is giving me all sorts of problems. What am I doing wrong? I'm an alright coder, I just have a hard time when it comes time to figure out what needs to be put where to enable what I want to do, regardless if I want to know what I want to do or not. (So frustrating) Update: This is what's going on. This is in my viewcontroller, which I have the #import <SystemConfiguration/SystemConfiguration.h> and #import "Reachability.h" set up with. This is my least favorite part of programming by far. FWIW, we never ended up implementing this in our code. The two features that required internet access (entering the sweepstakes, and buying the dvd), were not main features. Nothing else required internet access. Instead of adding more code, we just set the background of both internet views to a notice telling the users they must be connected to the internet to use this feature. It was in theme with the rest of the application's interface, and was done well/tastefully. They said nothing about it during the approval process, however we did get a personal phone call to verify that we were giving away items that actually pertained to the movie. According to their usually vague agreement, you aren't allowed to have sweepstakes otherwise. I would also think this adheres more strictly to their "only use things if you absolutely need them" ideaology as well. Here's the iTunes link to the application, EvoScanner.

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• What is the best way to read and write cXML documents in C# ?

  - by tetranz

  I know this is a vague open ended question. I'm hoping to get some general direction. I need to add cXML punchout to an ASP.NET C# site / application. This is replacing something that I wrote years ago in ColdFusion. I'm a reasonably experienced C# developer but I haven't done much with XML. There seems to be lots of different options for processing XML in .NET. Here's the open ended question: Assuming that I have an XML document in some form, eg a file or a string, what is the best way to read it into my code? I want to get the data and then query databases etc. The cXML document size and our traffic volumes are easily small enough so that loading the a cXML document into memory is not a problem. Should I: 1) Manually build classes based on the dtd and use the XML Serializer? 2) Use a tool to generate classes. There are sample cXML files downloadable from Ariba.com. I tried xsd.exe to generate an xsd and then xsd.exe /c to generate classes. When I try to deserialize I get errors because there seems to be "confusion" around whether some elements should be single values or arrays. I tried the CodeXS online tool but that gives errors in it's log and errors if I try to deserialize a sample document. 2) Create a dataset and ReadXml()? 3) Create a typed dataset and ReadXml()? 4) Use Linq to XML. I often use Linq to Objects so I'm familiar with Linq in general but I'm struggling to see what it gives me in this situation. 5) Some other means. I guess I need to improve my understanding of XML in general but even so ... am I missing some obvious way of doing this? In the old ColdFusion site I found a free component ("tag") which basically ignored any schema and read the XML into a "structure" which is essentially a series of nested hash tables which was then easy to read in code. That was probably quite sloppy but it worked. I also need to generate XML files from my C# objects. Maybe Linq to XML will be good for that. I could start with a default "template" document and manipulate it before saving. Thanks for any pointers ...

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• Sorting a list of colors in one dimension?

  - by Ptah- Opener of the Mouth

  I would like to sort a one-dimensional list of colors so that colors that a typical human would perceive as "like" each other are near each other. Obviously this is a difficult or perhaps impossible problem to get "perfectly", since colors are typically described with three dimensions, but that doesn't mean that there aren't some sorting methods that look obviously more natural than others. For example, sorting by RGB doesn't work very well, as it will sort in the following order, for example: (1) R=254 G=0 B=0 (2) R=254 G=255 B=0 (3) R=255 G=0 B=0 (4) R=255 G=255 B=0 That is, it will alternate those colors red, yellow, red, yellow, with the two "reds" being essentially imperceivably different than each other, and the two yellows also being imperceivably different from each other. But sorting by HLS works much better, generally speaking, and I think HSL even better than that; with either, the reds will be next to each other, and the yellows will be next to each other. But HLS/HSL has some problems, too; things that people would perceive as "black" could be split far apart from each other, as could things that people would perceive as "white". Again, I understand that I pretty much have to accept that there will be some splits like this; I'm just wondering if anyone has found a better way than HLS/HSL. And I'm aware that "better" is somewhat arbitrary; I mean "more natural to a typical human". For example, a vague thought I've had, but have not yet tried, is perhaps "L is the most important thing if it is very high or very low", but otherwise it is the least important. Has anyone tried this? Has it worked well? What specifically did you decide "very low" and "very high" meant? And so on. Or has anyone found anything else that would improve upon HSL? I should also note that I am aware that I can define a space-filling curve through the cube of colors, and order them one-dimensionally as they would be encountered while travelling along that curve. That would eliminate perceived discontinuities. However, it's not really what I want; I want decent overall large-scale groupings more than I want perfect small-scale groupings. Thanks in advance for any help.

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• How to get started with testing(jMock)

  - by London

  Hello, I'm trying to learn how to write tests. I'm also learning Java, I was told I should learn/use/practice jMock, I've found some articles online that help to certain extend like : http://www.theserverside.com/news/1365050/Using-JMock-in-Test-Driven-Development http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock And most articles I found was about test driven development, write tests first then write code to make the test pass. I'm not looking for that at the moment, I'm trying to write tests for already existing code with jMock. The official documentation is vague to say the least and just too hard for me. Does anybody have better way to learn this. Good books/links/tutorials would help me a lot. thank you EDIT - more concrete question : http://jeantessier.com/SoftwareEngineering/Mocking.html#jMock - from this article Tried this to mock this simple class : import java.util.Map; public class Cache { private Map<Integer, String> underlyingStorage; public Cache(Map<Integer, String> underlyingStorage) { this.underlyingStorage = underlyingStorage; } public String get(int key) { return underlyingStorage.get(key); } public void add(int key, String value) { underlyingStorage.put(key, value); } public void remove(int key) { underlyingStorage.remove(key); } public int size() { return underlyingStorage.size(); } public void clear() { underlyingStorage.clear(); } } Here is how I tried to create a test/mock : public class CacheTest extends TestCase { private Mockery context; private Map mockMap; private Cache cache; @Override @Before public void setUp() { context = new Mockery() { { setImposteriser(ClassImposteriser.INSTANCE); } }; mockMap = context.mock(Map.class); cache = new Cache(mockMap); } public void testCache() { context.checking(new Expectations() {{ atLeast(1).of(mockMap).size(); will(returnValue(int.class)); }}); } } It passes the test and basically does nothing, what I wanted is to create a map and check its size, and you know work some variations try to get a grip on this. Understand better trough examples, what else could I test here or any other exercises would help me a lot. tnx

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