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• Operating systems -- using minimum number of semaphores

  - by stackuser

  The three cooperating processes all read data from the same input device. Each process, when it gets the input device, must read two consecutive data. I want to use mutual exclusion to do this. The declaration and initialization that I think would work here are: semaphore s=1 sa1 = 0, sa2 = 0, sb1 = 0, sb2 = 0, sc1 = 0, sc2 = 0 I'd like to use semaphores to synchronize the following processes: P1: P2: P3: input(a1,a2) input (b1,b2) input(c1,c2) Y=a1+c1 W=b2+c2 Z=a2+b1 Print (X) X=Z-Y+W I'm wondering how to use the minimum number of semaphores to solve this. Diagram of cooperating Processes and one input device: It seems like P1 and P2 would start something like: wait(s) input (a1/b1, a2/b2) signal(s)

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• Infiniband: a highperformance network fabric - Part I

  - by Karoly Vegh

  Introduction:At the OpenWorld this year I managed to chat with interesting people again - one of them answering Infiniband deepdive questions with ease by coffee turned out to be one of Oracle's IB engineers, Ted Kim, who actually actively participates in the Infiniband Trade Association and integrates Oracle solutions with this highspeed network. This is why I love attending OOW. He granted me an hour of his time to talk about IB. This post is mostly based on that tech interview.Start of the actual post: Traditionally datatransfer between servers and storage elements happens in networks with up to 10 gigabit/seconds or in SANs with up to 8 gbps fiberchannel connections. Happens. Well, data rather trickles through.But nowadays data amounts grow well over the TeraByte order of magnitude, and multisocket/multicore/multithread Servers hunger data that these transfer technologies just can't deliver fast enough, causing all CPUs of this world do one thing at the same speed - waiting for data. And once again, I/O is the bottleneck in computing. FC and Ethernet can't keep up. We have half-TB SSDs, dozens of TB RAM to store data to be modified in, but can't transfer it. Can't backup fast enough, can't replicate fast enough, can't synchronize fast enough, can't load fast enough. The bad news is, everyone is used to this, like back in the '80s everyone was used to start compile jobs and go for a coffee. Or on vacation. The good news is, there's an alternative. Not so-called "bleeding-edge" 8gbps, but (as of now) 56. Not layers of overhead, but low latency. And it is available now. It has been for a while, actually. Welcome to the world of Infiniband. Short history:Infiniband was born as a result of joint efforts of HPAQ, IBM, Intel, Sun and Microsoft. They planned to implement a next-generation I/O fabric, in the 90s. In the 2000s Infiniband (from now on: IB) was quite popular in the high-performance computing field, powering most of the top500 supercomputers. Then in the middle of the decade, Oracle realized its potential and used it as an interconnect backbone for the first Database Machine, the first Exadata. Since then, IB has been booming, Oracle utilizes and supports it in a large set of its HW products, it is the backbone of the famous Engineered Systems: Exadata, SPARC SuperCluster, Exalogic, OVCA and even the new DB backup/recovery box. You can also use it to make servers talk highspeed IP to eachother, or to a ZFS Storage Appliance. Following Oracle's lead, even IBM has jumped the wagon, and leverages IB in its PureFlex systems, their first InfiniBand Machines.IB Structural Overview: If you want to use IB in your servers, the first thing you will need is PCI cards, in IB terms Host Channel Adapters, or HCAs. Just like NICs for Ethernet, or HBAs for FC. In these you plug an IB cable, going to an IB switch providing connection to other IB HCAs. Of course you're going to need drivers for those in your OS. Yes, these are long-available for Solaris and Linux. Now, what protocols can you talk over IB? There's a range of choices. See, IB isn't accepting package loss like Ethernet does, and hence doesn't need to rely on TCP/IP as a workaround for resends. That is, you still can run IP over IB (IPoIB), and that is used in various cases for control functionality, but the datatransfer can run over more efficient protocols - like native IB. About PCI connectivity: IB cards, as you see are fast. They bring low latency, which is just as important as their bandwidth. Current IB cards run at 56 gbit/s. That is slightly more than double of the capacity of a PCI Gen2 slot (of ~25 gbit/s). And IB cards are equipped usually with two ports - that is, altogether you'd need 112 gbit/s PCI slots, to be able to utilize FDR IB cards in an active-active fashion. PCI Gen3 slots provide you with around ~50gbps. This is why the most IB cards are configured in an active-standby way if both ports are used. Once again the PCI slot is the bottleneck. Anyway, the new Oracle servers are equipped with Gen3 PCI slots, an the new IB HCAs support those too. Oracle utilizes the QDR HCAs, running at 40gbp/s brutto, which translates to a 32gbp/s net traffic due to the 10:8 signal-to-data information ratio. Consolidation techniques: Technology never stops to evolve. Mellanox is working on the 100 gbps (EDR) version already, which will be optical, since signal technology doesn't allow EDR to be copper. Also, I hear you say "100gbps? I will never use/need that much". Are you sure? Have you considered consolidation scenarios, where (for example with Oracle Virtual Network) you could consolidate your platform to a high densitiy virtualized solution providing many virtual 10gbps interfaces through that 100gbps? Technology never stops to evolve. I still remember when a 10mbps network was impressively fast. Back in those days, 16MB of RAM was a lot. Now we usually run servers with around 100.000 times more RAM. If network infrastrucure speends could grow as fast as main memory capacities, we'd have a different landscape now :) You can utilize SRIOV as well for consolidation. That is, if you run LDoms (aka Oracle VM Server for SPARC) you do not have to add physical IB cards to all your guest LDoms, and you do not need to run VIO devices through the hypervisor either (avoiding overhead). You can enable SRIOV on those IB cards, which practically virtualizes the PCI bus, and you can dedicate Physical- and Virtual Functions of the virtualized HCAs as native, physical HW devices to your guests. See Raghuram's excellent post explaining SRIOV. SRIOV for IB is supported since LDoms 3.1.  This post is getting lengthier, so I will rename it to Part I, and continue it in a second post. 

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• Tuning Default WorkManager - Advantages and Disadvantages

  - by Murali Veligeti

  Before discussing on Tuning Default WorkManager, lets have a brief introduction on What is Default WorkManger Before Weblogic Server 9.0 release, we had the concept of Execute Queues. WebLogic Server (before WLS 9.0), processing was performed in multiple execute queues. Different classes of work were executed in different queues, based on priority and ordering requirements, and to avoid deadlocks. In addition to the default execute queue, weblogic.kernel.default, there were pre-configured queues dedicated to internal administrative traffic, such as weblogic.admin.HTTP and weblogic.admin.RMI.Users could control thread usage by altering the number of threads in the default queue, or configure custom execute queues to ensure that particular applications had access to a fixed number of execute threads, regardless of overall system load. From WLS 9.0 release onwards WebLogic Server uses is a single thread pool (single thread pool which is called Default WorkManager), in which all types of work are executed. WebLogic Server prioritizes work based on rules you define, and run-time metrics, including the actual time it takes to execute a request and the rate at which requests are entering and leaving the pool.The common thread pool changes its size automatically to maximize throughput. The queue monitors throughput over time and based on history, determines whether to adjust the thread count. For example, if historical throughput statistics indicate that a higher thread count increased throughput, WebLogic increases the thread count. Similarly, if statistics indicate that fewer threads did not reduce throughput, WebLogic decreases the thread count. This new strategy makes it easier for administrators to allocate processing resources and manage performance, avoiding the effort and complexity involved in configuring, monitoring, and tuning custom executes queues. The Default WorkManager is used to handle thread management and perform self-tuning.This Work Manager is used by an application when no other Work Managers are specified in the application’s deployment descriptors. In many situations, the default Work Manager may be sufficient for most application requirements. WebLogic Server’s thread-handling algorithms assign each application its own fair share by default. Applications are given equal priority for threads and are prevented from monopolizing them. The default work-manager, as its name tells, is the work-manager defined by default.Thus, all applications deployed on WLS will use it. But sometimes, when your application is already in production, it's obvious you can't take your EAR / WAR, update the deployment descriptor(s) and redeploy it.The default work-manager belongs to a thread-pool, as initial thread-pool comes with only five threads, that's not much. If your application has to face a large number of hits, you may want to start with more than that.Well, that's quite easy. You have  two option to do so.1) Modify the config.xmlJust add the following line(s) in your server definition : <server> <name>AdminServer</name> <self-tuning-thread-pool-size-min>100</self-tuning-thread-pool-size-min> <self-tuning-thread-pool-size-max>200</self-tuning-thread-pool-size-max> [...] </server> 2) Adding some JVM parameters Add the following system property in setDomainEnv.sh/setDomainEnv.cmd or startWebLogic.sh/startWebLogic.cmd : -Dweblogic.threadpool.MinPoolSize=100 -Dweblogic.threadpool.MaxPoolSize=100 Reboot WLS and see the option has been taken into account . Disadvantage: So far its fine. But here there is an disadvantage in tuning Default WorkManager. Internally Weblogic Server has many work managers configured for different types of work.  if we run out of threads in the self-tuning pool(because of system property -Dweblogic.threadpool.MaxPoolSize) due to being undersized, then important work that WLS might need to do could be starved.  So, while limiting the self-tuning would limit the default WorkManager and internally it also limits all other internal WorkManagers which WLS uses.So the best alternative is to override the default WorkManager that means creating a WorkManager for the Application and assign the WorkManager for the application instead of tuning the Default WorkManager.

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• Why Are Dial-up Modems so Noisy?

  - by Jason Fitzpatrick

  Throughout the 1990s the majority of internet users began their session with the noisy handshake of a dial-up modem, but what exactly was all that electronic chatter about? Read on as we investigate one of the more iconic sounds of the burgeoning Internet age. Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-drive grouping of Q&A web sites. While dial-up modem use might be down from the nearly 100% market saturation in the 1990s to only 10% of current US internet users, the sound of a dial-up modem connecting lives on in the memories of geeks everywhere. This week we’re taking a look at the technology behind the noisy process and what exactly was going on when you dialed in for your internet session. Why Enabling “Do Not Track” Doesn’t Stop You From Being Tracked HTG Explains: What is the Windows Page File and Should You Disable It? How To Get a Better Wireless Signal and Reduce Wireless Network Interference

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• Massive Google Street View Update: 250,000 Miles of Roadways, New Special Collections, and More

  - by Jason Fitzpatrick

  If you like tooling around in Google Street View to check out attractions near and far, you just got a whole lot more to look at. Street View’s new update adds in 250,000 miles of roads, increased coverage in over a dozen countries, and a whole pile of new special collections. From Russia to Taiwan to Canada, there’s thousands of new places and tens of thousands of new roads to explore. Hit up the link below to read the full announcement at the Google Maps blog. Making Google Maps More Comprehensive with Ciggest Street View Update Ever [Google Maps] HTG Explains: What is the Windows Page File and Should You Disable It? How To Get a Better Wireless Signal and Reduce Wireless Network Interference How To Troubleshoot Internet Connection Problems

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• What are the relative merits for implementing an Erlang-style "Continuation" pattern in C#

  - by JoeGeeky

  What are the relative merits (or demerits) for implementing an Erlang-style "Continuation" pattern in C#. I'm working on a project that has a large number of Lowest priority threads and I'm wondering if my approach may be all wrong. It would seem there is a reasonable upper limit to the number of long-running threads that any one Process 'should' spawn. With that said, I'm not sure what would signal the tipping-point for too many thread or when alternate patterns such as "Continuation" would be more suitable. In this case, many of the threads do a small amount of work and then sleep until woken to go again (Ex. Heartbeat, purge caches, etc...). This continues for the life of the Process.

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• Opening a new Windows from ASP.NET code behind

  - by TATWORTH

  At http://weblogs.asp.net/infinitiesloop/archive/2007/09/25/response-redirect-into-a-new-window-with-extension-methods.aspx there is an excellent post on how to open a new windows from code behind. The purists may not like it but it helped solve a problem for a client's client. Here is an update for VS2010 users: using System; using System.Web; using System.Web.UI; /// <summary> /// Response Helper for opening popup windo from code behind. /// </summary> public static class ResponseHelper {   /// <summary>   /// Redirect to popup window   /// </summary>   /// <param name="response">The response.</param>   /// <param name="url">URL to open to</param>   /// <param name="target">Target of window _self or _blank</param>   /// <param name="windowFeatures">Features such as window bar</param>   /// <remarks>   ///     <list type="bullet">   ///         <item>   /// From http://weblogs.asp.net/infinitiesloop/archive/2007/09/25/response-redirect-into-a-new-window-with-extension-methods.aspx   /// </item>   /// <item>   /// Note: If you use it outside the context of a Page request, you can't redirect to a new window. The reason is the need to call the ResolveClientUrl method on Page, which I can't do if there is no Page. I could have just built my own version of that method, but it's more involved than you might think to do it right. So if you need to use this from an HttpHandler other than a Page, you are on your own.   /// </item>   ///         <item>   /// Beware of popup blockers.   /// </item>   /// <item>   /// Note: Obviously when you are redirecting to a new window, the current window will still be hanging around. Normally redirects abort the current request -- no further processing occurs. But for these redirects, processing continues, since we still have to serve the response for the current window (which also happens to contain the script to open the new window, so it is important that it completes).   /// </item>   /// <item>   /// Sample call Response.Redirect("popup.aspx", "_blank", "menubar=0,width=100,height=100");   /// </item>   ///     </list>   /// </remarks>   public static void Redirect(this HttpResponse response, string url, string target, string windowFeatures)   {     if ((String.IsNullOrEmpty(target) || target.Equals("_self", StringComparison.OrdinalIgnoreCase)) && String.IsNullOrEmpty(windowFeatures))     {       response.Redirect(url);     }     else     {       Page page = (Page)HttpContext.Current.Handler;       if (page == null)       {         throw new InvalidOperationException("Cannot redirect to new window outside Page context.");       }       url = page.ResolveClientUrl(url);       string script;       if (!String.IsNullOrEmpty(windowFeatures))       {         script = @"window.open(""{0}"", ""{1}"", ""{2}"");";       }       else       {         script = @"window.open(""{0}"", ""{1}"");";       }       script = String.Format(script, url, target, windowFeatures);       ScriptManager.RegisterStartupScript(page, typeof(Page), "Redirect", script, true);     }   } }

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• Algorithm for tracking progress of controller method running in background

  - by SilentAssassin

  I am using Codeigniter framework for PHP on Windows platform. My problem is I am trying to track progress of a controller method running in background. The controller extracts data from the database(MySQL) then does some processing and then stores the results again in the database. The complete aforesaid process can be considered as a single task. A new task can be assigned while another task is running. The newly assigned task will be added in a queue. So if I can track progress of the controller, I can show status for each of these tasks. Like I can show "Pending" status for tasks in the queue, "In Progress" for tasks running and "Done" for tasks that are completed. Main Issue: Now first thing I need to find is an algorithm to track the progress of how much amount of execution the controller method has completed and that means tracking how much amount of method has completed execution. For instance, this PHP script tracks progress of array being counted. Here the current state and state after total execution are known so it is possible to track its progress. But I am not able to devise anything analogous to it in my case. Maybe what I am trying to achieve is programmtically not possible. If its not possible then suggest me a workaround or a completely new approach. If some details are pending you can mention them. Sorry for my ignorance this is my first post here. I welcome you to point out my mistakes. EDIT: Database outline: The URL(s) and keyword(s) are first entered by user which are stored in a database table called link_master and keyword_master respectively. Then keywords are extracted from all the links present in this table and compared with keywords entered by user and their frequency is calculated which is the final result. And the results are stored in another table called link_result. Now sub-links are extracted from the domain links and stored in a table called sub_link_master. Now again the keywords are extracted from these sub-links and the corresponding results are stored in a table called sub_link_result. The number of records cannot be defined beforehand as the number of links on any web page can be different. Only the cardinality of *link_result* table can be known which will be equal to multiplication of number of keyword(s) and URL(s) . I insert multiple records at a time using this resource. Controller outline: The controller extracts keywords from a web page and also extracts keywords from all the links present on that page. There is a method called crawlLink. I used Rolling Curl to extract keywords and web page content. It has callback function which I used for extracting keywords alongwith generating results and extracting valid sub-links. There is a insertResult method which stores results for links and sub-links in the respective tables. Yes, the processing depends on the number of records. The more the number of records, the more time it takes to execute: Consider this scenario: Number of Domain Links = 1 Number of Keywords = 3 Number of Domain Links Result generated = 3 (3 x 1 as described in the question) Number of Sub Links generated = 41 Number of Sub Links Result = 117 (41 x 3 = 123 but some links are not valid or searchable) Approximate time taken for above process to complete = 55 seconds. The above result is for a single link. I want to track the progress of the above results getting stored in database. When all results are stored, the task is complete. If results are getting stored, the task is In Progress. I am not clear how can I track this progress.

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• Ubuntu 12.10 64bit fresh install, wireless issue!

  - by Dave

  Just installed a fresh Ubuntu 12.10 64bit on my laptop, run the update manager, restarted and suddenly I can't use my wifi anymore. Ubuntu software center installed automatically the wifi additional driver as you can see in my screenshot. If I mark the option "Do not use the device" and apply changes, restarting Ubuntu my wifi is back and I can use it. If I run iwconfig my terminal is showing this Now if I use Ubuntu for more than 20 minutes surfing the web my wifi it keeps to be connected but I don't receive any signal from it. Any page I try to open it simply don't open (just waiting icon). If I disconnect my wifi and connect it again, same issue, it doesn't work. The only way to make it work again is to restart Ubuntu. And the same story it happens again after aprox. 20, 30 minutes. WIFI device details: 03:00.0 Network controller [0280]: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller [14e4:4727] (rev 01) Thanks, Dave

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• Cannot connect to a Wifi network chipset AR9287

  - by Fritz

  After updating my newly installed ubuntu 10.10. I can't connect to the wifi network anymore although it is showing it. Tried to install manufacturer driver INF file via ndiswrapper only makes things worst - lost my wifi. Downloaded and installed the compat-wireless driver for the Atheros AR9287. After installing, i got my wifi connection again but after rebooting I can't reconnect again. The Wifi access point is showing 2/5 to 3/5 signal strength. Laptop: Acer Aspire 4741G Wifi Adapter: Atheros AR9287 OS: Ubuntu 10.10 64bit

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• HTG Explains: What is the Windows Page File and Should You Disable It?

  - by Chris Hoffman

  Windows uses a page file to store data that can’t be held by your computer’s random-access memory when it fills up. While you can tweak the page file settings, Windows can manage the page file fine on its own. The Windows page file is somewhat misunderstood. People see it as the cause of slowdowns because it’s slower to use the page file than your computer’s RAM, but having a page file is better than not having one. Image Credit: Blake Patterson on Flickr HTG Explains: What is the Windows Page File and Should You Disable It? How To Get a Better Wireless Signal and Reduce Wireless Network Interference How To Troubleshoot Internet Connection Problems

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• How do I recover from upgrading while using bad version of gcc/binutils?

  - by Shawn J. Goff

  I upgraded from 9.04 to 10.10 a couple of days ago, and things are really messed up - X is crashing constantly. Since then, I had an application segfault for no reason, when I was debugging, I found that it was strlen() that was causing the segfault (pointing to libc being the problem)! Upon investigation, I found that it was because I had a bad version of gcc and binutils installed in /usr/bin/local; I removed it, recompiled the application, and it no longer crashes. Now, looking at my logs, I see that X is also crashing due to libc. Backtrace: 0: /usr/bin/X11/X (xorg_backtrace+0x3b) [0x80ef31b] 1: /usr/bin/X11/X (0x8048000+0x5d00d) [0x80a500d] 2: (vdso) (__kernel_rt_sigreturn+0x0) [0xb77e240c] 3: /usr/bin/X11/X (0x8048000+0xbb0b6) [0x81030b6] 4: /usr/bin/X11/X (0x8048000+0xbc3ef) [0x81043ef] 5: /usr/bin/X11/X (0x8048000+0x26ee7) [0x806eee7] 6: /usr/bin/X11/X (0x8048000+0x1a5da) [0x80625da] 7: /lib/libc.so.6 (__libc_start_main+0xe7) [0xb750ace7] 8: /usr/bin/X11/X (0x8048000+0x1a1b1) [0x80621b1] Segmentation fault at address 0x32156654 Caught signal 11 (Segmentation fault). Server aborting So, how can I recover from this?

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• After suspend, my monitor wont turn back on

  - by David

  I set my pc to suspend after 5 minutes of inactivity, when I return to my computer I mash a couple of keys and the pc turns back on and the drives start spinning etc etc, but I get no signal to either of my monitors. My peripherals are powered as the num/caps lock lights turn on and off. I should add I have two monitors, I have the same problem on both. As I am writing the last line from my previous paragraph keeps disappearing. I press control z and it comes back but kinda weird. Thanks in advance for any help :)

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• How To Log Into Multiple Accounts On the Same Website At Once

  - by Chris Hoffman

  If you ever want to sign into two different accounts on the same website at once – say, to have multiple Gmail inboxes open next to each other – you can’t just open a new tab or browser window. Websites store your login state in browser-specific cookies. There are a number of ways you can get another browser window with its own cookies and stay logged into multiple accounts at once. HTG Explains: What is the Windows Page File and Should You Disable It? How To Get a Better Wireless Signal and Reduce Wireless Network Interference How To Troubleshoot Internet Connection Problems

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• Hybrid wireless network repeating

  - by Oli

  Summary: I'd like to use two Ubuntu computers to extend/compliment an existing wireless access point. I have a network which currently looks a bit like this: What the diagram doesn't show is the interference caused by our house. It's a wifi-blocking robot sent here from the past. The two wired computers are in areas where the signal is most blocked (not by design, just a happy co-incidence). Both wired computers have fairly good network cards. They're both Ubuntu machines and I would like to turn them into additional base stations. I know I could throw more networking hardware at this (network extenders or cable in additional, pure wireless access points) but I've got two Linux machines sitting in ideal places and I feel like they should be able to help me out. I've tried ad-hoc networks but I need something that is a lot more transparent (eg you can migrate from base to base without a connection dropping); it should look like one network to clients.

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• Question on the implementation of my Entity System

  - by miguel.martin

  I am currently creating an Entity System, in C++, it is almost completed (I have all the code there, I just have to add a few things and test it). The only thing is, I can't figure out how to implement some features. This Entity System is based off a bit from the Artemis framework, however it is different. I'm not sure if I'll be able to type this out the way my head processing it. I'm going to basically ask whether I should do something over something else. Okay, now I'll give a little detail on my Entity System itself. Here are the basic classes that my Entity System uses to actually work: Entity - An Id (and some methods to add/remove/get/etc Components) Component - An empty abstract class ComponentManager - Manages ALL components for ALL entities within a Scene EntitySystem - Processes entities with specific components Aspect - The class that is used to help determine what Components an Entity must contain so a specific EntitySystem can process it EntitySystemManager - Manages all EntitySystems within a Scene EntityManager - Manages entities (i.e. holds all Entities, used to determine whether an Entity has been changed, enables/disables them, etc.) EntityFactory - Creates (and destroys) entities and assigns an ID to them Scene - Contains an EntityManager, EntityFactory, EntitySystemManager and ComponentManager. Has functions to update and initialise the scene. Now in order for an EntitySystem to efficiently know when to check if an Entity is valid for processing (so I can add it to a specific EntitySystem), it must recieve a message from the EntityManager (after a call of activate(Entity& e)). Similarly the EntityManager must know when an Entity is destroyed from the EntityFactory in the Scene, and also the ComponentManager must know when an Entity is created AND destroyed. I do have a Listener/Observer pattern implemented at the moment, but with this pattern I may remove a Listener (which is this case is dependent on the method being called). I mainly have this implemented for specific things related to a game, i.e. Teams, Tagging of entities, etc. So... I was thinking maybe I should call a private method (using friend classes) to send out when an Entity has been activated, deleted, etc. i.e. taken from my EntityFactory void EntityFactory::killEntity(Entity& e) { // if the entity doesn't exsist in the entity manager within the scene if(!getScene()->getEntityManager().doesExsist(e)) { return; // go back to the caller! (should throw an exception or something..) } // tell the ComponentManager and the EntityManager that we killed an Entity getScene()->getComponentManager().doOnEntityWillDie(e); getScene()->getEntityManager().doOnEntityWillDie(e); // notify the listners for(Mouth::iterator i = getMouth().begin(); i != getMouth().end(); ++i) { (*i)->onEntityWillDie(*this, e); } _idPool.addId(e.getId()); // add the ID to the pool delete &e; // delete the entity } As you can see on the lines where I am telling the ComponentManager and the EntityManager that an Entity will die, I am calling a method to make sure it handles it appropriately. Now I realise I could do this without calling it explicitly, with the help of that for loop notifying all listener objects connected to the EntityFactory's Mouth (an object used to tell listeners that there's an event), however is this a good idea (good design, or what)? I've gone over the PROS and CONS, I just can't decide what I want to do. Calling Explicitly: PROS Faster? Since these functions are explicitly called, they can't be "removed" CONS Not flexible Bad design? (friend functions) Calling through Listener objects (i.e. ComponentManager/EntityManager inherits from a EntityFactoryListener) PROS More Flexible? Better Design? CONS Slower? (virtual functions) Listeners can be removed, i.e. may be removed and not get called again during the program, which could cause in a crash. P.S. If you wish to view my current source code, I am hosting it on BitBucket.

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• How do engines avoid "Phase Lock" (multiple objects in same location) in a Physics Engine?

  - by C0M37

  Let me explain Phase Lock first: When two objects of non zero mass occupy the same space but have zero energy (no velocity). Do they bump forever with zero velocity resolution vectors or do they just stay locked together until an outside force interacts? In my home brewed engine, I realized that if I loaded a character into a tree and moved them, they would signal a collision and hop back to their original spot. I suppose I could fix this by implementing impulses in the event of a collision instead of just jumping back to the last spot I was in (my implementation kind of sucks). But while I make my engine more robust, I'm just curious on how most other physics engines handle this case. Do objects that start in the same spot with no movement speed just shoot out from each other in a random direction? Or do they sit there until something happens? Which option is generally the best approach?

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• Which programming language do you think is the most beautiful and which the ugliest? [closed]

  - by user1598390

  I would like to hear opinions about what programming language do you consider to produce the most legible, self-documenting, intention-transparent, beautiful-looking code ? And which produces the most messy-looking, unintentionally obfuscated, ugly code, regardless of it being good code ? Let me clarify: I'm talking about the syntax, "noise vs signal", structure of the language. Assignment operators. De-referencing. Whether it's dot syntax or "-" syntax. What languages do you think are inherently harder to read than others, given all other things being equal like, say, code quality, absence of code smells, etc. ?

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• Slow wifi with D-link DWA-160 A2

  - by Tommy Brunn

  I recently bought a USB wifi adapter for my new desktop computer. It's a D-link DWA-160 A2. From the start it didn't want to work at all, but after unplugging and then plugging it back in, it seems to work. However, my browsing is painfully slow. NetworkManager reports the connection to be at around 78-85% signal strength, which seems perfectly acceptable. Is there anything I can do to make it faster? I'm dual booting with Windows 7, where it seems to work fine, so I'm guessing that the problem occurs because of crappy drivers.

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• Keyword does not work in dash

  - by sev

  Since the last update of my OS ubuntu 11.10, I am not able to type in the dash. In any other application (like Firefox for this message), the keyboard is working fine, but in the dash "window" of unity (I am not sure what it is called officially), the keyboard is buggy. Sometimes I manage to enter one or two characters, but most of the time nothing appears as if the key-press signal was not received. Before the update, I actually was working with gnome-classic (I had removed unity from oneiric). The update seemed to have reinstalled unity, but something apparently is missing or damaged. Does anybody have a clue about what could be done to repair the dash?

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• Do I need a wifi card to have internet access?

  - by Sarah

  I am attempting to set up a wireless network on 11.04, freshly download today. The router is on and working. However, I do not have a wifi "card" (which I am assuming is a little USB-type thing that allows internet access, but correct me if I am wrong) and every time I try to type in the MAC address and everything, nothing works. I also get the "firmware missing" error when I scroll over the signal strength, which I have tried looking up but have been unsuccessful with completely understanding it. I guess my main question is do I need another little device to be able to use wifi on my ubuntu? I do have an ethernet cable but another person is using it and I do not want to be tied down to that cable. the problem is that none of the wireless networks show up, however they show up when I go into Windows mode on my laptop. I get an error message at the top saying "firmware missing" which I have tried looking up but still have no straight answer for.

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• How to completely remove a package that didn't install properly?

  - by chtfn

  I recently installed a package from a ppa on Ubuntu 12.04 beta, but apparently it didn't work out, and now it is giving me errors at every update or install I make, even after deactivating the ppa from my sources. This is what I get when I try uninstalling from USC: installArchives() failed: (Reading database ... (Reading database ... 5% (Reading database ... 10% (Reading database ... 15% (Reading database ... 20% (Reading database ... 25% (Reading database ... 30% (Reading database ... 35% (Reading database ... 40% (Reading database ... 45% (Reading database ... 50% (Reading database ... 55% (Reading database ... 60% (Reading database ... 65% (Reading database ... 70% (Reading database ... 75% (Reading database ... 80% (Reading database ... 85% (Reading database ... 90% (Reading database ... 95% (Reading database ... 100% (Reading database ... 295120 files and directories currently installed.) Removing oracle-java7-installer ... update-alternatives: error: unknown argument `cdrom' dpkg: error processing oracle-java7-installer (--remove): subprocess installed pre-removal script returned error exit status 2 No apport report written because MaxReports is reached already Downloading... --2012-04-12 13:13:21-- http://download.oracle.com/otn-pub/java/jdk/7u3-b04/jdk-7u3-linux-i586.tar.gz Rsolution de download.oracle.com (download.oracle.com)... 203.13.161.233, 203.13.161.234 Connexion vers download.oracle.com (download.oracle.com)|203.13.161.233|:80... connect. requte HTTP transmise, en attente de la rponse... 302 Moved Temporarily Emplacement: https://edelivery.oracle.com/otn-pub/java/jdk/7u3-b04/jdk-7u3-linux-i586.tar.gz [suivant] --2012-04-12 13:13:21-- https://edelivery.oracle.com/otn-pub/java/jdk/7u3-b04/jdk-7u3-linux-i586.tar.gz Rsolution de edelivery.oracle.com (edelivery.oracle.com)... 173.223.150.174 Connexion vers edelivery.oracle.com (edelivery.oracle.com)|173.223.150.174|:443... connect. requte HTTP transmise, en attente de la rponse... 302 Moved Temporarily Emplacement: http://download.oracle.com/errors/download-fail-1505220.html [suivant] --2012-04-12 13:13:22-- http://download.oracle.com/errors/download-fail-1505220.html Connexion vers download.oracle.com (download.oracle.com)|203.13.161.233|:80... connect. requte HTTP transmise, en attente de la rponse... 200 OK Longueur: 5307 (5,2K) [text/html] Sauvegarde en : ./jdk-7u3-linux-i586.tar.gz 0K ..... 100% 4,94M=0,001s 2012-04-12 13:13:22 (4,94 MB/s) - ./jdk-7u3-linux-i586.tar.gz sauvegard [5307/5307] Download done. sha256sum mismatch jdk-7u3-linux-i586.tar.gz Oracle JDK 7 is NOT installed. dpkg: error while cleaning up: subprocess installed post-installation script returned error exit status 1 Errors were encountered while processing: oracle-java7-installer Error in function: I also tried "remove completely" from synaptic but it doesn't work either. Thank you for your help in advance!

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• Design Patterns for these scenarios

  - by user1899749

  Please help me to find design patterns for following situations. Situation 1: how can a smart robot use Wi-Fi? Situation 2: How can a Smart robot automatically go to rechargeable unit while there is no remote signal? Situation 3: Voice recognition component (If homeowner itself at home and motion detection is off then how can Smart Robot voice recognition component will recognize those very sensitive sentences) Situation 4: Motion detection component (How can Smart Robot send video stream on cell phone while homeowner/resident driving) I am looking for the design patterns for above Situations to answer following question. if not using design patterns, then what’re the difficulties?

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• How to Make a 9 Layer Density Column [Video]

  - by Jason Fitzpatrick

  Density columns, layers of varying density liquid in a glass cylinder, are nothing new in the world of science demonstrations, but this nine layer one with seven floating objects is something to see. Courtesy of Steve Spangler Science, the experiment goes above and beyond the traditional five layer column by adding another four layers and sinking objects of varying density into the column. The end result is a colorful demonstration of the varying densities of liquids and solids. [via Boing Boing] How To Get a Better Wireless Signal and Reduce Wireless Network Interference How To Troubleshoot Internet Connection Problems 7 Ways To Free Up Hard Disk Space On Windows

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• slow speed transfering files to a local network device

  - by F. Ariel Jung

  I'm having troubles copying files from my pc(ubuntu 13.04 64 bits) to a Media Center(WDTV Live: with an SATA2 HDD attached) through the local network. the speed is to slow, it's up to 2.0 MB/s image: http://s11.postimg.org/g1nuai92b/Captura_de_pantalla_de_2013_06_24_07_46_55.png (I don't use image tag because it is a big image) my PC has a wifi network card Tp Link TL-WN951N and it is connected to a TP Link TL-WDR3500 router via wifi, and the WDTV Live is connected via LAN here is a iwconfig: eth0 no wireless extensions. lo no wireless extensions. wlan0 IEEE 802.11bgn ESSID:"TL-WDR3500" Mode:Managed Frequency:2.462 GHz Access Point: A0:F3:C1:6C:3B:F1 Bit Rate=39 Mb/s Tx-Power=20 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:off Link Quality=62/70 Signal level=-48 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:33521 Invalid misc:2245290 Missed beacon:0 if more data is required I'll post it as needed. I can't figure this out, needed help. please

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