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  • Apache still running after uninstalling

    - by Ruslan Osipov
    I am trying to uninstall apache to install nginx, but it doesn't seem to work. $ ps aux | grep httpd root 22348 0.0 0.2 167252 8864 ? Ss 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22353 0.0 0.1 167624 6088 ? S 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22354 0.0 0.1 167252 5292 ? S 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22355 0.0 0.1 167252 5052 ? S 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22356 0.0 0.1 167252 5052 ? S 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22357 0.0 0.1 167252 5052 ? S 14:33 0:00 /usr/sbin/httpd -k start -DSSL apache 22797 0.0 0.1 167252 5052 ? S 14:38 0:00 /usr/sbin/httpd -k start -DSSL 1003 22883 0.0 0.0 9388 884 pts/1 S+ 14:46 0:00 grep httpd $ which apache2 $ dpkg -S apache bash-completion: /etc/bash_completion.d/apache2ctl apparmor: /etc/apparmor.d/abstractions/apache2-common $ dpkg -S `which httpd` dpkg-query: no path found matching pattern /usr/sbin/httpd. The package seem to be uninstalled, but the processes are still running. And /usr/bin/httpd is still there. Any hints?

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  • JavaOne + Develop Registration is Open!

    - by justin.kestelyn
    Welcome to "The Zone". Here's what the new JavaOne + Develop registration Website says: The world's most important developer conferences are creating the world's coolest neighborhood for the developer community. Having been intimately involved in the planning process, I can vouch for that statement. Remember, if either co-located conference - JavaOne or Oracle Develop - are the confines of your interest, you can experience either one in standalone mode, if you like (although there are some areas of common interest, of course). Or, considering that a single Full Conference Pass gives you access to both of them, you can partake in any measure that you like. It's up to you. Either way, you will get access not only to session content and keynotes, but also to the massive OTN Night party on Monday night, to open unconference sessions, and to the legendary Appreciate Night concert (acts TBD) on Wednesday. Furthermore, as is customary, the Oracle Technology Network team will offer a full slate of community-focused activities and goodies while the conferences are running - more details on those as we have them. A GOOD time is ensured for all; I look forward to seeing you there!

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  • DPKG errors after upgrade to 12.10

    - by James Wulfe
    So I was doing fine then i upgraded my system to 12.10 and now i cant get my system to update all of its packages properly. no matter what i do, cleaning apt cache, manual install using dpkg, etc, i just cant get them to install. what is happening here and how do i fix this. if i would have thought 12.10 would be this much of a hassle i would have never upgraded..... here is a sampling of the code that returns from "apt-get -f install" Preparing to replace usb-modeswitch-data 20120120-0ubuntu1 (using .../usb-modeswitch-data_20120815-1_all.deb) ... /var/lib/dpkg/info/usb-modeswitch-data.prerm: 4: /var/lib/dpkg/info/usb-modeswitch-data.prerm: dpkg-maintscript-helper: Input/output error dpkg: warning: subprocess old pre-removal script returned error exit status 2 dpkg: trying script from the new package instead ... /var/lib/dpkg/tmp.ci/prerm: 4: /var/lib/dpkg/tmp.ci/prerm: dpkg-maintscript-helper: Input/output error dpkg: error processing /var/cache/apt/archives/usb-modeswitch-data_20120815-1_all.deb (--unpack): subprocess new pre-removal script returned error exit status 2 /var/lib/dpkg/info/usb-modeswitch-data.postinst: 7: /var/lib/dpkg/info/usb-modeswitch-data.postinst: dpkg-maintscript-helper: Input/output error dpkg: error while cleaning up: subprocess installed post-installation script returned error exit status 2 Errors were encountered while processing: /var/cache/apt/archives/network-manager_0.9.6.0-0ubuntu7_i386.deb /var/cache/apt/archives/pcmciautils_018-8_i386.deb /var/cache/apt/archives/unity-common_6.10.0-0ubuntu2_all.deb /var/cache/apt/archives/whoopsie_0.2.7_i386.deb /var/cache/apt/archives/usb-modeswitch_1.2.3+repack0-1ubuntu3_i386.deb /var/cache/apt/archives/usb-modeswitch-data_20120815-1_all.deb E: Sub-process /usr/bin/dpkg returned an error code (1) It is also just these 6 packages only. no other packages have given me this kind of trouble. well i should say as of now. It was just 5, but them i got an update for unity, and now unity-common is added to the trouble makers. which prevents me from further upgrading the actual unity package as this package is a dependancy.....

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  • Models with more than one mesh in JMonkeyEngine

    - by Andrea Tucci
    I’m a new jmonkey engine developer and I’m beginning to import models. I tried to import simple models and no problems appeared, but when I export some obj models having more than one mesh in the OgreXML format, Blender saves multiple meshes with their own materials (e.g. one mesh for face, another for body etc). Can I export all the meshes in one? I’ve tried to join all the meshes to a major one with blender (face joins body), but when I export the model and then create the Spatial in jme(loading the path of the “merged” mesh), all the meshes that are joined to the major doesn’t have their materials! I give a more clear example: I have an .obj model with 3 meshes and I export it. I have : mesh1.mesh.xml , mesh2.mesh.xml , mesh3.mesh.xml and their materials mesh1.material, mesh2.material mesh3.material so I import the folder in Assets/Models/Test and now I have to create something like: Spatial head = assetManager.loadModel( [path] ); Spatial face = assetManager.loadModel( [path] ) one for each mesh and than attach them to a common node. I think there is a way to merge those mesh maintaining their materials! What do you think? Thanks

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  • Oracle Launches Mobile Applications User Experience Design Patterns

    - by ultan o'broin
    OK, you heard Joe Huang (@JoeHuang_Oracle) Product Manager for Oracle Application Development Framework (ADF) Mobile. If you're an ADF developer, or a Java (yeah, Java in iOS) developer, well now you're a mobile developer as well. And, using the newly launched Applications User Experience (UX) team's Mobile UX Design Patterns, you're a UX developer rockstar too, offering users so much more than just cool functionality. Mobile Design Pattern for Inline Actions Mobile design requires a different way of thinking. Use Oracle’s mobile design patterns to design iPhone, Android, or browser-based smartphone apps. Oracle's sharing these cutting edge mobile design patterns and their baked-in, scientifically proven usability to enable Oracle customers and partners to build mobile apps quickly. The design patterns are common solutions that developers can easily apply across all application suites. Crafted by the UX team's insight into Oracle Fusion Middleware, the patterns are designed to work with the mobile technology provided by the Oracle Application Development Framework. Other great UX-related information on using ADF Mobile to design task flows and the development experience on offer are on the ADF EMG podcast series. Check out FXAer Brian 'Bex' Huff (@bex of Bezzotech talking about ADF Mobile in podcast number 6 and also number 8 which has great tips about getting going with Android and iOS mobile app development too.

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  • Adaptive Case Management Modeling with CMMN by Jessica Ray

    - by JuergenKress
    A new version of Oracle BPM Suite 11.1.1.7 with Adaptive Case Management (ACM) is now available, so what will that mean for requirements gathering? BPM project requirements can be documented using Business Process Model and Notation (BPMN 2.0). For ACM, there is a new notation in the works. It is called Case Management Model and Notation (CMMN). For now, this notation isn’t included as a modeling tool in the new version of Oracle BPM Suite 11.1.1.7 with ACM, but it is possible that a modeling tool could be included in a future release. What is CMMN? CMMN is a standard intended to capture the common elements that Case Management Products use, the same way that BPMN is a standard for BPM products (such as Oracle BPM). CMMN is created by the Object Management Group (OMG) and is still in the beta version. In April 2014, OMG released the second beta version the CMMN 1.0, and the most recent version is available here. CMMN captures some of the elements that are commonly used when talking about ACM such as Cases, Milestones, and Tasks. It also introduces some elements that you may not automatically hear when talking about ACM such as Stages, Events, and Decorators. Here is a quick summary at a few (but not all) of the elements of CMMN taken from the CMMN spec. A Few CMMN Elements Read the complete article here SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Facebook Wiki Technorati Tags: Jessica Ray,Avio,Adaptive Case Management,ACM,CMMN,SOA Community,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

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  • Low-level game engine renderer design

    - by Mark Ingram
    I'm piecing together the beginnings of an extremely basic engine which will let me draw arbitrary objects (SceneObject). I've got to the point where I'm creating a few sensible sounding classes, but as this is my first outing into game engines, I've got the feeling I'm overlooking things. I'm familiar with compartmentalising larger portions of the code so that individual sub-systems don't overly interact with each other, but I'm thinking more of the low-level stuff, starting from vertices working up. So if I have a Vertex class, I can combine that with a list of indices to make a Mesh class. How does the engine determine identical meshes for objects? Or is that left to the level designer? Once we have a Mesh, that can be contained in the SceneObject class. And a list of SceneObject can be placed into the Scene to be drawn. Right now I'm only using OpenGL, but I'm aware that I don't want to be tying OpenGL calls right in to base classes (such as updating the vertices in the Mesh, I don't want to be calling glBufferData etc). Are there any good resources that discuss these issues? Are there any "common" heirachies which should be used?

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  • Mono is frequently used to say "Yes, .NET is cross-platform". How valid is that claim?

    - by Thorbjørn Ravn Andersen
    In What would you choose for your project between .NET and Java at this point in time? I say that I would consider the "Will you always deploy to Windows?" the single most important (EDIT: technical) decision to make up front in a new web project, and if the answer is "no", I would recommend Java instead of .NET. A very common counter-argument is that "If we ever want to run on Linux/OS X/Whatever, we'll just run Mono", which is a very compelling argument on the surface, but I don't agree for several reasons. OpenJDK and all the vendor supplied JVM's have passed the official Sun TCK ensuring things work correctly. I am not aware of Mono passing a Microsoft TCK. Mono trails the .NET releases. What .NET-level is currently fully supported? Does all GUI elements (WinForms?) work correctly in Mono? Businesses may not want to depend on Open Source frameworks as the official plan B. I am aware that with the new governance of Java by Oracle, the future is unsafe, but e.g. IBM provides JDK's for many platforms, including Linux. They are just not open sourced. So, under which circumstances is Mono a valid business strategy for .NET-applications? Edit: Mark H summarized it as: "If the claim is that "I have a windows application written in .NET, it should run on mono", then not, it's not a valid claim - but Mono has made efforts to make porting such applications simpler.".

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  • Cannot establish Wired connection on Acer Aspire 5930G

    - by drakos46
    I use an Acer Aspire 5930G, dual booted with Windows 7 and Ubuntu 13.10. My problem is that i cannot establish wired connection on my ubuntu. Wireless connection works in both of my OSs but the Wired connection does not, only on the Ubuntu. I have already tried the common fix: echo on | sudo tee /sys/class/net/eth0/device/power/control but without any results. Any ideas? eth0 Link encap:Ethernet HWaddr 00:1d:72:c2:21:a5 inet6 addr: fe80::21d:72ff:fec2:21a5/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:945 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:204318 (204.3 KB) Interrupt:16 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:7241 errors:0 dropped:0 overruns:0 frame:0 TX packets:7241 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:645874 (645.8 KB) TX bytes:645874 (645.8 KB) wlan0 Link encap:Ethernet HWaddr 00:16:ea:57:7b:cc inet addr:192.168.2.2 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::216:eaff:fe57:7bcc/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:19937 errors:0 dropped:0 overruns:0 frame:0 TX packets:16933 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:10877245 (10.8 MB) TX bytes:3131378 (3.1 MB) 02:00.0 Ethernet controller: Marvell Technology Group Ltd. 88E8071 PCI-E Gigabit Ethernet Controller (rev 16)

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  • How do you manage a complexity jump?

    - by glenatron
    It seems an infrequent but common experience that sometimes you're working on a project and suddenly something turns up unexpectedly, throws a massive spanner in the works and ramps up the complexity a whole lot. For example, I was working on an application that talked to SOAP services on various other machines. I whipped up a prototype that worked fine, then went on to develop a regular front end and generally get everything up and running in a nice, fairly simple and easy to follow fashion. It worked great until we started testing across a wider network and suddenly pages started timing out as the latency of the connections and the time required to perform calculations on remote machines resulted in timed out requests to the soap services. It turned out that we needed to change the architecture to spin requests out onto their own threads and cache the returned data so it could be updated progressively in the background rather than performing calculations on a request by request basis. The details of that scenario are not too important - indeed it's not a great example as it was quite forseeable and people who have written a lot of apps of this type for this type of environment might have anticipated it - except that it illustrates a way that one can start with a simple premise and model and suddenly have an escalation of complexity well into the development of the project. What strategies do you have for dealing with these types of functional changes whose need arises - often as a result of environmental factors rather than specification change - later on in the development process or as a result of testing? How do you balance between avoiding the premature optimisation/ YAGNI/ overengineering risks of designing a solution that mitigates against possible but not necessarily probable issues as opposed to developing a simpler and easier solution that is likely to be as effective but doesn't incorporate preparedness for every possible eventuality?

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  • Calling COM from Intel Fortran?

    - by user57460
    I'm trying to get COM working from my Fortran application. I do a "COMINITIALIZE" followed by a "COMCreateObjectByProgID". Both of these appear to be successful and return a status of zero. However, when I try to use the COM object, I get "Unhandled exception at 0x00000000 in FortranProg01.exe: 0xC0000005: Access violation." I realize that this error can mean almost anything, but has anyone got some suggestions of common problems with COM that produce this problem? Here are some more details. My program code: program FortranProg01 use myolepg implicit none integer*4 comInitStatus integer:: comCreateStatus INTEGER(INT_PTR_KIND()) $OBJECT INTEGER(4) funcResult REAL(8) pkgVersion call COMINITIALIZE(comInitStatus) print *, comInitStatus call COMCreateObjectByProgID('MyOlePg.MyOlePkg', $OBJECT, comCreateStatus) print *, comCreateStatus funcResult = IMyOlePkg_GetPackageVersion($OBJECT, pkgVersion) print *, funcResult call COMUNINITIALIZE() end program FortranProg01 The wizard-generated interface code: INTERFACE !property PackageVersion INTEGER(4) FUNCTION IMyOlePkg_GetPackageVersion($OBJECT, pVal) INTEGER(INT_PTR_KIND()), INTENT(IN) :: $OBJECT ! Object Pointer !DEC$ ATTRIBUTES VALUE :: $OBJECT REAL(8), INTENT(OUT) :: pVal !DEC$ ATTRIBUTES REFERENCE :: pVal !DEC$ ATTRIBUTES STDCALL :: IMyOlePkg_GetPackageVersion END FUNCTION IMyOlePkg_GetPackageVersion END INTERFACE Any help would be much appreciated! Thanks! Brad.

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  • Software Design Idea for multi tier architecture

    - by Preyash
    I am currently investigating multi tier architecture design for a web based application in MVC3. I already have an architecture but not sure if its the best I can do in terms of extendability and performance. The current architecure has following components DataTier (Contains EF POCO objects) DomainModel (Contains Domain related objects) Global (Among other common things it contains Repository objects for CRUD to DB) Business Layer (Business Logic and Interaction between Data and Client and CRUD using repository) Web(Client) (which talks to DomainModel and Business but also have its own ViewModels for Create and Edit Views for e.g.) Note: I am using ValueInjector for convering one type of entity to another. (which is proving an overhead in this desing. I really dont like over doing this.) My question is am I having too many tiers in the above architecure? Do I really need domain model? (I think I do when I exposes my Business Logic via WCF to external clients). What is happening is that for a simple database insert it (1) create ViewModel (2) Convert ViewModel to DomainModel for Business to understand (3) Business Convert it to DataModel for Repository and then data comes back in the same order. Few things to consider, I am not looking for a perfect architecure solution as it does not exits. I am looking for something that is scalable. It should resuable (for e.g. using design patterns ,interfaces, inheritance etc.) Each Layers should be easily testable. Any suggestions or comments is much appriciated. Thanks,

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  • Mono is frequently used to say "Yes, .NET is cross-platform". How valid is that claim?

    - by Thorbjørn Ravn Andersen
    In What would you choose for your project between .NET and Java at this point in time ? I say that I would consider the "Will you always deploy to Windows?" the single most important decision to make up front in a new web project, and if the answer is "no", I would recommend Java instead of .NET. A very common counter-argument is that "If we ever want to run on Linux/OS X/Whatever, we'll just run Mono", which is a very compelling argument on the surface, but I don't agree for several reasons. OpenJDK and all the vendor supplied JVM's have passed the official Sun TCK ensuring things work correctly. I am not aware of Mono passing a Microsoft TCK. Mono trails the .NET releases. What .NET-level is currently fully supported? Does all GUI elements (WinForms?) work correctly in Mono? Businesses may not want to depend on Open Source frameworks as the official plan B. I am aware that with the new governance of Java by Oracle, the future is unsafe, but e.g. IBM provides JDK's for many platforms, including Linux. They are just not open sourced. So, under which circumstances is Mono a valid business strategy for .NET-applications?

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  • How to do dependency Injection and conditional object creation based on type?

    - by Pradeep
    I have a service endpoint initialized using DI. It is of the following style. This end point is used across the app. public class CustomerService : ICustomerService { private IValidationService ValidationService { get; set; } private ICustomerRepository Repository { get; set; } public CustomerService(IValidationService validationService,ICustomerRepository repository) { ValidationService = validationService; Repository = repository; } public void Save(CustomerDTO customer) { if (ValidationService.Valid(customer)) Repository.Save(customer); } Now, With the changing requirements, there are going to be different types of customers (Legacy/Regular). The requirement is based on the type of the customer I have to validate and persist the customer in a different way (e.g. if Legacy customer persist to LegacyRepository). The wrong way to do this will be to break DI and do somthing like public void Save(CustomerDTO customer) { if(customer.Type == CustomerTypes.Legacy) { if (LegacyValidationService.Valid(customer)) LegacyRepository.Save(customer); } else { if (ValidationService.Valid(customer)) Repository.Save(customer); } } My options to me seems like DI all possible IValidationService and ICustomerRepository and switch based on type, which seems wrong. The other is to change the service signature to Save(IValidationService validation, ICustomerRepository repository, CustomerDTO customer) which is an invasive change. Break DI. Use the Strategy pattern approach for each type and do something like: validation= CustomerValidationServiceFactory.GetStratedgy(customer.Type); validation.Valid(customer) but now I have a static method which needs to know how to initialize different services. I am sure this is a very common problem, What is the right way to solve this without changing service signatures or breaking DI?

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  • O'Reilly deals to April 5, 2012 14:00 PT on books on "where"

    - by TATWORTH
    At http://shop.oreilly.com/category/deals/where-conference.do, O'Reilly are offering a series of books on geo-location at 50% off until April 5, 2012 14:00 PT. HTML5 Geolocation Truly revolutionary: now you can write geolocation applications directly in the browser, rather than develop native apps for particular devices. This concise book demonstrates the W3C Geolocation API in action, with code and examples to help you build HTML5 apps using the "write once, deploy everywhere" model. Along the way, you get a crash course in geolocation, browser support, and ways to integrate the API with common geo tools like Google Maps. HTML5 Cookbook With scores of practical recipes you can use in your projects right away, this cookbook helps you gain hands-on experience with HTML5’s versatile collection of elements. You get clear solutions for handling issues with everything from markup semantics, web forms, and audio and video elements to related technologies such as geolocation and rich JavaScript APIs. Each informative recipe includes sample code and a detailed discussion on why and how the solution works. Perfect for intermediate to advanced web and mobile web developers, this handy book lets you choose the HTML5 features that work for you—and helps you experiment with the rest. HTML5 Applications HTML5 is not just a replacement for plugins. It also makes the Web a first-class development environment by giving JavaScript programmers a solid foundation for building industrial-strength applications. This practical guide takes you beyond simple site creation and shows you how to build self-contained HTML5 applications that can run on mobile devices and compete with desktop apps. You’ll learn powerful JavaScript tools for exploiting HTML5 elements, and discover new methods for working with data, such as offline storage and multi-threaded processing. Complete with code samples, this book is ideal for experienced JavaScript and mobile developers alike. There are also other books being offered at a discount at http://shop.oreilly.com/category/deals/where-conference.do

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  • Fn key sticks down

    - by Oli
    Just bought my significant other a shiny new Samsung Q330 13" netbook, stuck an OCZ Agility in it and installed Maverick. Just as a quick aside, this is a devastating combination. Graphics work perfectly and it cold-boots to desktop in about 7 seconds. Very quick. But (common to laptops) I've got a couple of problems. I'll start with the most problematic and start a new thread for the other. Like a lot of laptops, there is a Fn (function) modifier to allow some keys to have another purpose. When I tried to alter the brightness of the screen by tapping Fn+Down, it worked but kept on going until it was as dim as it could go. I tapped Fn+Up and it went to the other extreme. After that the entire keyboard ceases to work properly because the Fn modifier appears to be locked. Additionally, and as a direct side effect, I think, clicking on things doesn't result in a standard result. It's as if control is being held. A reboot is the only thing that seems to fix these problems. This isn't a problem if you don't touch the Fn key but as there are two of them on the keyboard, an accident is going to happen sooner than later, requiring a reboot (and probably some data loss). I don't have a lot of experience with laptops (I prefer my hulking great desktop) so this isn't my area of expertise. I'm open to all suggestions, even disabling the two Fn keys until we can find a better solution.

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  • Algorithm to infer tag hierarchy

    - by Tom
    I'm looking for an algorithm to infer a hierarchy from a set of tagged items. E.g. if the following items have the tags: 1 a 2 a,b 3 a,c 4 a,c,e 5 a,b 6 a,c 7 d 8 d,f Then I can construct an undirected graph (or graphs) by tallying the node weights and edge weights: node weights edge weights a 6 a-b 2 b 2 a-c 3 c 3 c-e 1 d 2 a-e 1 <-- this edge is parallel to a-c and c-e and not wanted e 1 d-f 1 f 1 The first problem is how to drop any redundant edges to get to the simplified graph? Note that it's only appropriate to remove that redundant a-e edge in this case because something is tagged as a-c-e, if that wasn't the case and the tag was a-e, that edge would have to remain. I suspect that means the removal of edges can only happen during the construction of the graph, not after everything has been tallied up. What I'd then like to do is identify the direction of the edges to create a directed graph (or graphs) and pick out root nodes to hopefully create a tree (or trees): trees a d // \\ | b c f \ e It seems like it could be a string algorithm - longest common subsequences/prefixes - or a tree/graph algorithm, but I am a little stuck since I don't know the correct terminology to search for it.

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  • Use jQuery and ASP.NET to Build a News Ticker

    Many websites display a news ticker of one sort or another. A news ticker is a user interface element that displays a subset of a list of items, cycling through them one at a time after a set interval. For example, on Cisco's website there is a news ticker that shows the company's latest news items. Each news item is a one sentence link, such as "Desktop Virtualization Gathers Steam," or "Cisco Reports First Quarter Earnings." Clicking a headline whisks you to a page that shows the full story. Cisco's news ticker shows one headline at a time; every few seconds the currently displayed headline fades out and the next one appears. In total, Cisco has five different headlines - the ticker displays each of the five and then starts back from the beginning. This article is the first in a series that explores how to create your own news ticker widget using jQuery and ASP.NET. jQuery is a free, popular, open-source JavaScript library that simplifies many common client-side tasks, like event handling, DOM manipulation, and Ajax. This article kicks off the series and shows how to build a fairly simple news ticker whose contents can be specified statically in HTML markup or created dynamically from server-side code. Future installments will explore adding bells and whistles, such as: stopping the news ticker rotation when the mouse is hovered over it; adding controls to start, stop and pause the headlines; loading new headlines dynamically using Ajax; and packaging the JavaScript used by the ticker into a jQuery plugin. Read on to learn more! Read More >

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  • Recommened design pattern to handle multiple compression algorithms for a class hierarchy

    - by sgorozco
    For all you OOD experts. What would be the recommended way to model the following scenario? I have a certain class hierarchy similar to the following one: class Base { ... } class Derived1 : Base { ... } class Derived2 : Base { ... } ... Next, I would like to implement different compression/decompression engines for this hierarchy. (I already have code for several strategies that best handle different cases, like file compression, network stream compression, legacy system compression, etc.) I would like the compression strategy to be pluggable and chosen at runtime, however I'm not sure how to handle the class hierarchy. Currently I have a tighly-coupled design that looks like this: interface ICompressor { byte[] Compress(Base instance); } class Strategy1Compressor : ICompressor { byte[] Compress(Base instance) { // Common compression guts for Base class ... // if( instance is Derived1 ) { // Compression guts for Derived1 class } if( instance is Derived2 ) { // Compression guts for Derived2 class } // Additional compression logic to handle other class derivations ... } } As it is, whenever I add a new derived class inheriting from Base, I would have to modify all compression strategies to take into account this new class. Is there a design pattern that allows me to decouple this, and allow me to easily introduce more classes to the Base hierarchy and/or additional compression strategies?

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  • Oracle Linux Tips and Tricks: Using SSH

    - by Robert Chase
    Out of all of the utilities available to systems administrators ssh is probably the most useful of them all. Not only does it allow you to log into systems securely, but it can also be used to copy files, tunnel IP traffic and run remote commands on distant servers. It’s truly the Swiss army knife of systems administration. Secure Shell, also known as ssh, was developed in 1995 by Tau Ylonen after the University of Technology in Finland suffered a password sniffing attack. Back then it was common to use tools like rcp, rsh, ftp and telnet to connect to systems and move files across the network. The main problem with these tools is they provide no security and transmitted data in plain text including sensitive login credentials. SSH provides this security by encrypting all traffic transmitted over the wire to protect from password sniffing attacks. One of the more common use cases involving SSH is found when using scp. Secure Copy (scp) transmits data between hosts using SSH and allows you to easily copy all types of files. The syntax for the scp command is: scp /pathlocal/filenamelocal remoteuser@remotehost:/pathremote/filenameremote In the following simple example, I move a file named myfile from the system test1 to the system test2. I am prompted to provide valid user credentials for the remote host before the transfer will proceed.  If I were only using ftp, this information would be unencrypted as it went across the wire.  However, because scp uses SSH, my user credentials and the file and its contents are confidential and remain secure throughout the transfer.  [user1@test1 ~]# scp /home/user1/myfile user1@test2:/home/user1user1@test2's password: myfile                                    100%    0     0.0KB/s   00:00 You can also use ssh to send network traffic and utilize the encryption built into ssh to protect traffic over the wire. This is known as an ssh tunnel. In order to utilize this feature, the server that you intend to connect to (the remote system) must have TCP forwarding enabled within the sshd configuraton. To enable TCP forwarding on the remote system, make sure AllowTCPForwarding is set to yes and enabled in the /etc/ssh/sshd_conf file: AllowTcpForwarding yes Once you have this configured, you can connect to the server and setup a local port which you can direct traffic to that will go over the secure tunnel. The following command will setup a tunnel on port 8989 on your local system. You can then redirect a web browser to use this local port, allowing the traffic to go through the encrypted tunnel to the remote system. It is important to select a local port that is not being used by a service and is not restricted by firewall rules.  In the following example the -D specifies a local dynamic application level port forwarding and the -N specifies not to execute a remote command.   ssh –D 8989 [email protected] -N You can also forward specific ports on both the local and remote host. The following example will setup a port forward on port 8080 and forward it to port 80 on the remote machine. ssh -L 8080:farwebserver.com:80 [email protected] You can even run remote commands via ssh which is quite useful for scripting or remote system administration tasks. The following example shows how to  log in remotely and execute the command ls –la in the home directory of the machine. Because ssh encrypts the traffic, the login credentials and output of the command are completely protected while they travel over the wire. [rchase@test1 ~]$ ssh rchase@test2 'ls -la'rchase@test2's password: total 24drwx------  2 rchase rchase 4096 Sep  6 15:17 .drwxr-xr-x. 3 root   root   4096 Sep  6 15:16 ..-rw-------  1 rchase rchase   12 Sep  6 15:17 .bash_history-rw-r--r--  1 rchase rchase   18 Dec 20  2012 .bash_logout-rw-r--r--  1 rchase rchase  176 Dec 20  2012 .bash_profile-rw-r--r--  1 rchase rchase  124 Dec 20  2012 .bashrc You can execute any command contained in the quotations marks as long as you have permission with the user account that you are using to log in. This can be very powerful and useful for collecting information for reports, remote controlling systems and performing systems administration tasks using shell scripts. To make your shell scripts even more useful and to automate logins you can use ssh keys for running commands remotely and securely without the need to enter a password. You can accomplish this with key based authentication. The first step in setting up key based authentication is to generate a public key for the system that you wish to log in from. In the following example you are generating a ssh key on a test system. In case you are wondering, this key was generated on a test VM that was destroyed after this article. [rchase@test1 .ssh]$ ssh-keygen -t rsaGenerating public/private rsa key pair.Enter file in which to save the key (/home/rchase/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/rchase/.ssh/id_rsa.Your public key has been saved in /home/rchase/.ssh/id_rsa.pub.The key fingerprint is:7a:8e:86:ef:59:70:ef:43:b7:ee:33:03:6e:6f:69:e8 rchase@test1The key's randomart image is:+--[ RSA 2048]----+|                 ||  . .            ||   o .           ||    . o o        ||   o o oS+       ||  +   o.= =      ||   o ..o.+ =     ||    . .+. =      ||     ...Eo       |+-----------------+ Now that you have the key generated on the local system you should to copy it to the target server into a temporary location. The user’s home directory is fine for this. [rchase@test1 .ssh]$ scp id_rsa.pub rchase@test2:/home/rchaserchase@test2's password: id_rsa.pub                  Now that the file has been copied to the server, you need to append it to the authorized_keys file. This should be appended to the end of the file in the event that there are other authorized keys on the system. [rchase@test2 ~]$ cat id_rsa.pub >> .ssh/authorized_keys Once the process is complete you are ready to login. Since you are using key based authentication you are not prompted for a password when logging into the system.   [rchase@test1 ~]$ ssh test2Last login: Fri Sep  6 17:42:02 2013 from test1 This makes it much easier to run remote commands. Here’s an example of the remote command from earlier. With no password it’s almost as if the command ran locally. [rchase@test1 ~]$ ssh test2 'ls -la'total 32drwx------  3 rchase rchase 4096 Sep  6 17:40 .drwxr-xr-x. 3 root   root   4096 Sep  6 15:16 ..-rw-------  1 rchase rchase   12 Sep  6 15:17 .bash_history-rw-r--r--  1 rchase rchase   18 Dec 20  2012 .bash_logout-rw-r--r--  1 rchase rchase  176 Dec 20  2012 .bash_profile-rw-r--r--  1 rchase rchase  124 Dec 20  2012 .bashrc As a security consideration it's important to note the permissions of .ssh and the authorized_keys file.  .ssh should be 700 and authorized_keys should be set to 600.  This prevents unauthorized access to ssh keys from other users on the system.   An even easier way to move keys back and forth is to use ssh-copy-id. Instead of copying the file and appending it manually to the authorized_keys file, ssh-copy-id does both steps at once for you.  Here’s an example of moving the same key using ssh-copy-id.The –i in the example is so that we can specify the path to the id file, which in this case is /home/rchase/.ssh/id_rsa.pub [rchase@test1]$ ssh-copy-id -i /home/rchase/.ssh/id_rsa.pub rchase@test2 One of the last tips that I will cover is the ssh config file. By using the ssh config file you can setup host aliases to make logins to hosts with odd ports or long hostnames much easier and simpler to remember. Here’s an example entry in our .ssh/config file. Host dev1 Hostname somereallylonghostname.somereallylongdomain.com Port 28372 User somereallylongusername12345678 Let’s compare the login process between the two. Which would you want to type and remember? ssh somereallylongusername12345678@ somereallylonghostname.somereallylongdomain.com –p 28372 ssh dev1 I hope you find these tips useful.  There are a number of tools used by system administrators to streamline processes and simplify workflows and whether you are new to Linux or a longtime user, I'm sure you will agree that SSH offers useful features that can be used every day.  Send me your comments and let us know the ways you  use SSH with Linux.  If you have other tools you would like to see covered in a similar post, send in your suggestions.

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  • My first time in the gambling industry

    - by sfrj
    I am a Java enterprise developer with almost 3 years of professional experience. Soon i am going to have a face to face interview with a company in the gambling industry. I already did successfully a phone screening and now for the personal interview i suppose they will ask me about some kind of white board problem or system design task. I think i am in the right place to ask about this, and would appreciate a lot if someone would give me some tips or share something related to his own experience. The things i am more interested in regarding my interview are: What are the most common challenges for programmers, in this industry? Any idea or suggestion on a white board problem they may ask me? Could you point me to some links where i can find information on the topic or sample problems in this industry?. I personally find this question very interesting not just for me. Also i think, the given answers can help also others in a similar situation. Just what i want to say whit this last comment is: Please avoid, answers like: www.google.com and so on...

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  • Data structure for bubble shooter game

    - by SundayMonday
    I'm starting to make a bubble shooter game for a mobile OS. Assume this is just the basic "three or more same-color bubbles that touch pop" and all bubbles that are separated from their group fall/pop. What data structures are common for storing the bubbles? I've considered using an undirected, connected graph where each node is a bubble. This seems like it could help answer the question "which bubbles (if any) should fall now?" after some arbitrary bubbles are popped and corresponding nodes are removed from the graph. I think the answer is all bubbles that were just disconnected from the graph should fall. However the graph approach might be overkill so I'm not sure. Another consideration for the data structure is collision detection. Perhaps being able to grab a list of neighboring bubbles in constant time for a particular "bubble slot" is useful. So the collision detection would be something like "moving bubble is closest to slot ij, neighbors of slot ij are bubbles a,b,c, moving bubble is sufficiently close to bubble b hence moving bubble should come to rest in slot ij". A game like this could be probably be made with a relatively crude grid structure as the primary data structure. However it seems like answering "which bubbles (if any) should fall now?" would be trickier with this data structure.

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  • install libreoffice in Ubuntu 12.04 is impossible

    - by user1587239
    What is wrong with Ubuntu repositories? sudo apt-get install libreoffice Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: libreoffice : Depends: libreoffice-core (= 1:3.5.4-0ubuntu1.1) but it is not going to be installed Depends: libreoffice-writer but it is not going to be installed Depends: libreoffice-calc but it is not going to be installed Depends: libreoffice-impress but it is not going to be installed Depends: libreoffice-draw but it is not going to be installed Depends: libreoffice-math but it is not going to be installed Depends: libreoffice-base but it is not going to be installed Depends: libreoffice-filter-mobiledev but it is not going to be installed Depends: libreoffice-java-common (>= 1:3.5.4~) but it is not going to be installed Recommends: libreoffice-gnome but it is not going to be installed or libreoffice-kde but it is not going to be installed E: Unable to correct problems, you have held broken packages.

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  • Why isn't there a typeclass for functions?

    - by Steve314
    I already tried this on Reddit, but there's no sign of a response - maybe it's the wrong place, maybe I'm too impatient. Anyway... In a learning problem I've been messing around with, I realised I needed a typeclass for functions with operations for applying, composing etc. Reasons... It can be convenient to treat a representation of a function as if it were the function itself, so that applying the function implicitly uses an interpreter, and composing functions derives a new description. Once you have a typeclass for functions, you can have derived typeclasses for special kinds of functions - in my case, I want invertible functions. For example, functions that apply integer offsets could be represented by an ADT containing an integer. Applying those functions just means adding the integer. Composition is implemented by adding the wrapped integers. The inverse function has the integer negated. The identity function wraps zero. The constant function cannot be provided because there's no suitable representation for it. Of course it doesn't need to spell things as if it the values were genuine Haskell functions, but once I had the idea, I thought a library like that must already exist and maybe even using the standard spellings. But I can't find such a typeclass in the Haskell library. I found the Data.Function module, but there's no typeclass - just some common functions that are also available from the Prelude. So - why isn't there a typeclass for functions? Is it "just because there isn't" or "because it's not so useful as you think"? Or maybe there's a fundamental problem with the idea? The biggest possible problem I've thought of so far is that function application on actual functions would probably have to be special-cased by the compiler to avoid a looping problem - in order to apply this function I need to apply the function application function, and to do that I need to call the function application function, and to do that...

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  • Of transactions and Mongo

    - by Nuri Halperin
    Originally posted on: http://geekswithblogs.net/nuri/archive/2014/05/20/of-transactions-and-mongo-again.aspxWhat's the first thing you hear about NoSQL databases? That they lose your data? That there's no transactions? No joins? No hope for "real" applications? Well, you *should* be wondering whether a certain of database is the right one for your job. But if you do so, you should be wondering that about "traditional" databases as well! In the spirit of exploration let's take a look at a common challenge: You are a bank. You have customers with accounts. Customer A wants to pay B. You want to allow that only if A can cover the amount being transferred. Let's looks at the problem without any context of any database engine in mind. What would you do? How would you ensure that the amount transfer is done "properly"? Would you prevent a "transaction" from taking place unless A can cover the amount? There are several options: Prevent any change to A's account while the transfer is taking place. That boils down to locking. Apply the change, and allow A's balance to go below zero. Charge person A some interest on the negative balance. Not friendly, but certainly a choice. Don't do either. Options 1 and 2 are difficult to attain in the NoSQL world. Mongo won't save you headaches here either. Option 3 looks a bit harsh. But here's where this can go: ledger. See, and account doesn't need to be represented by a single row in a table of all accounts with only the current balance on it. More often than not, accounting systems use ledgers. And entries in ledgers - as it turns out – don't actually get updated. Once a ledger entry is written, it is not removed or altered. A transaction is represented by an entry in the ledger stating and amount withdrawn from A's account and an entry in the ledger stating an addition of said amount to B's account. For sake of space-saving, that entry in the ledger can happen using one entry. Think {Timestamp, FromAccountId, ToAccountId, Amount}. The implication of the original question – "how do you enforce non-negative balance rule" then boils down to: Insert entry in ledger Run validation of recent entries Insert reverse entry to roll back transaction if validation failed. What is validation? Sum up the transactions that A's account has (all deposits and debits), and ensure the balance is positive. For sake of efficiency, one can roll up transactions and "close the book" on transactions with a pseudo entry stating balance as of midnight or something. This lets you avoid doing math on the fly on too many transactions. You simply run from the latest "approved balance" marker to date. But that's an optimization, and premature optimizations are the root of (some? most?) evil.. Back to some nagging questions though: "But mongo is only eventually consistent!" Well, yes, kind of. It's not actually true that Mongo has not transactions. It would be more descriptive to say that Mongo's transaction scope is a single document in a single collection. A write to a Mongo document happens completely or not at all. So although it is true that you can't update more than one documents "at the same time" under a "transaction" umbrella as an atomic update, it is NOT true that there' is no isolation. So a competition between two concurrent updates is completely coherent and the writes will be serialized. They will not scribble on the same document at the same time. In our case - in choosing a ledger approach - we're not even trying to "update" a document, we're simply adding a document to a collection. So there goes the "no transaction" issue. Now let's turn our attention to consistency. What you should know about mongo is that at any given moment, only on member of a replica set is writable. This means that the writable instance in a set of replicated instances always has "the truth". There could be a replication lag such that a reader going to one of the replicas still sees "old" state of a collection or document. But in our ledger case, things fall nicely into place: Run your validation against the writable instance. It is guaranteed to have a ledger either with (after) or without (before) the ledger entry got written. No funky states. Again, the ledger writing *adds* a document, so there's no inconsistent document state to be had either way. Next, we might worry about data loss. Here, mongo offers several write-concerns. Write-concern in Mongo is a mode that marshals how uptight you want the db engine to be about actually persisting a document write to disk before it reports to the application that it is "done". The most volatile, is to say you don't care. In that case, mongo would just accept your write command and say back "thanks" with no guarantee of persistence. If the server loses power at the wrong moment, it may have said "ok" but actually no written the data to disk. That's kind of bad. Don't do that with data you care about. It may be good for votes on a pole regarding how cute a furry animal is, but not so good for business. There are several other write-concerns varying from flushing the write to the disk of the writable instance, flushing to disk on several members of the replica set, a majority of the replica set or all of the members of a replica set. The former choice is the quickest, as no network coordination is required besides the main writable instance. The others impose extra network and time cost. Depending on your tolerance for latency and read-lag, you will face a choice of what works for you. It's really important to understand that no data loss occurs once a document is flushed to an instance. The record is on disk at that point. From that point on, backup strategies and disaster recovery are your worry, not loss of power to the writable machine. This scenario is not different from a relational database at that point. Where does this leave us? Oh, yes. Eventual consistency. By now, we ensured that the "source of truth" instance has the correct data, persisted and coherent. But because of lag, the app may have gone to the writable instance, performed the update and then gone to a replica and looked at the ledger there before the transaction replicated. Here are 2 options to deal with this. Similar to write concerns, mongo support read preferences. An app may choose to read only from the writable instance. This is not an awesome choice to make for every ready, because it just burdens the one instance, and doesn't make use of the other read-only servers. But this choice can be made on a query by query basis. So for the app that our person A is using, we can have person A issue the transfer command to B, and then if that same app is going to immediately as "are we there yet?" we'll query that same writable instance. But B and anyone else in the world can just chill and read from the read-only instance. They have no basis to expect that the ledger has just been written to. So as far as they know, the transaction hasn't happened until they see it appear later. We can further relax the demand by creating application UI that reacts to a write command with "thank you, we will post it shortly" instead of "thank you, we just did everything and here's the new balance". This is a very powerful thing. UI design for highly scalable systems can't insist that the all databases be locked just to paint an "all done" on screen. People understand. They were trained by many online businesses already that your placing of an order does not mean that your product is already outside your door waiting (yes, I know, large retailers are working on it... but were' not there yet). The second thing we can do, is add some artificial delay to a transaction's visibility on the ledger. The way that works is simply adding some logic such that the query against the ledger never nets a transaction for customers newer than say 15 minutes and who's validation flag is not set. This buys us time 2 ways: Replication can catch up to all instances by then, and validation rules can run and determine if this transaction should be "negated" with a compensating transaction. In case we do need to "roll back" the transaction, the backend system can place the timestamp of the compensating transaction at the exact same time or 1ms after the original one. Effectively, once A or B visits their ledger, both transactions would be visible and the overall balance "as of now" would reflect no change.  The 2 transactions (attempted/ reverted) would be visible , since we do actually account for the attempt. Hold on a second. There's a hole in the story: what if several transfers from A to some accounts are registered, and 2 independent validators attempt to compute the balance concurrently? Is there a chance that both would conclude non-sufficient-funds even though rolling back transaction 100 would free up enough for transaction 117 (some random later transaction)? Yes. there is that chance. But the integrity of the business rule is not compromised, since the prime rule is don't dispense money you don't have. To minimize or eliminate this scenario, we can also assign a single validation process per origin account. This may seem non-scalable, but it can easily be done as a "sharded" distribution. Say we have 11 validation threads (or processing nodes etc.). We divide the account number space such that each validator is exclusively responsible for a certain range of account numbers. Sounds cunningly similar to Mongo's sharding strategy, doesn't it? Each validator then works in isolation. More capacity needed? Chop the account space into more chunks. So where  are we now with the nagging questions? "No joins": Huh? What are those for? "No transactions": You mean no cross-collection and no cross-document transactions? Granted - but don't always need them either. "No hope for real applications": well... There are more issues and edge cases to slog through, I'm sure. But hopefully this gives you some ideas of how to solve common problems without distributed locking and relational databases. But then again, you can choose relational databases if they suit your problem.

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