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  • How to get the newest (last modified) directory [C#]

    - by Shaitan00
    Currently my application uses string[] subdirs = Directory.GetDirectories(path) to get the list of subdirectories, and now I want to extract the path to the latest (last modified) subdirectory in the list. What is the easiest way to accomplish this? (efficiency is not a major concern - but robustness is)

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  • Which is the best sql schema comparison tool for Oracle?

    - by mike g
    It should be a tool to enable versioning of a database schema and efficiently updating databases with older versions of the schema: robustness, does it handle all edge cases support for data migration command line execution flexibility, can some data be compared as well In the answers a breakdown on support for these points (and anything I may have missed) would be appreciated.

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  • How could I portably split large backup files over multiple discs?

    - by sourcejedi
    Context: I make backups / archives, primarily of photos. I'm experimenting with Bup, which is designed for backup to hard disk. Basically it creates Git repos which include packfiles of up to 1GB. But I still need last-ditch backups to keep offline and move offsite (and keeping them on read-only media is good too!). What are the options for archiving and splitting large files over several discs like CDs (and reading them back!)? I'd prefer methods which will stay readable in future. are portable e.g. to Windows. have known simple implementations, so I could re-implement them myself if necessary. (Using Bup packs will stretch my robustness budget. So I want to be confident about how other parts of the system would behave). I heard split archives are possible with both ZIP and 7-Zip. Is that right?

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  • When to use MySQL replication or DRBD for HA on Xen VM?

    - by user62513
    I'm setting up a database which needs to be needs to provide High Availabilty. My primary concern is high performance and robustness (I don't want something that will fail fast and badly). The database is accessed by the application at an average of 300 qps. It's will run on Xen VMs and it has some InnoDB tables as well as MyISAM tables. The VMs are connected via ethernet 100Mbit/s ethernet cables. Which of the two - MySQL replication or DRBD - would you recommend in such a situation? Or should I use DRBD to make the master database Highly Available and use MySQL replication on the slaves? I'm a developer so these things are all not so easy for me to make a sound judgement.

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  • Tuxedo Runtime for CICS and Batch Webcast

    - by Jason Williamson
    There was a recent webcast about the new Tux ART solution that we released last month. Here is the link to hear Hassan talk about that Link to Listen to Webcast Below is the market speak about what the webcast is about and what you will hear. From my own experience, there is certainly an uptick in rehosting discussions and projects with customers all around the world. The notion that mainframes can be rehosted on open system is pretty well accepted. There are still some hold out CxO's who don't believe it, but those guys typically are not really looking to migrate anyway and don't take an honest look at the case studies, history and TPC reports. Maybe in my next blog I'll talk about "myth busters" -- to borrow some presentation details from Mark Rakhmilevich (Tuxedo PM for Rehosting). *********** Mainframe rehosting is a compelling approach for migrating and modernizing mainframe applications and data to lower data center cost and risk while increasing business agility. Oracle Tuxedo 11g with CICS application runtime (ART) capabilities is designed to facilitate the migration of IBM mainframe applications by allowing these to run on open systems in a distributed grid architecture. The brand new Oracle Tuxedo Application Runtime for CICS and Batch 11g can significantly reduce your costs and risks while preserving your investments in applications and data. In this on-demand Webcast, hear from Oracle Senior Vice President, Hasan Rizvi, on how Oracle Tuxedo 11g with CICS application runtime capabilities is changing the way customers think about mainframe migration. You'll learn: * What market forces drive mainframe migration and modernization * What technologies and capabilities are available for migrating mainframe transaction processing and batch applications * How Oracle brings rehosting technologies to a new level of scalability, robustness, and automation

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  • Dynamic real-time pathfinding with C# and unity

    - by Yakri
    A buddy and I are working on a simple 2D top down arena combat game similar to OpenGLAD (grew up on ye olde GLADIATOR). Thing is, we want to make some substantial deviation from our source of inspiration, including completely destructible/changeable terrain. Like rivers that can be frozen, walls which can be knocked down, etc. As well as letting players and NPC's build new terrain objects, some of which cannot be moved through or seen through. So I'm tasked with creating the AI, starting with pathfinding. Because of all the changeable terrain, we need something that can check to see if the player/other NPC's are in line of sight, and which can then check to find current paths around existing terrain, without getting completely confused by new terrain popping up, and old terrain vanishing, and even capable of breaking through terrain. A lot of that will just be filling in the framework of the feature, but I really just don't know where to start. What I'm really looking for are relevant websites, books, articles, or keywords to google. I just can't quite find a direction to start in, because most pathfinding types we've googled up just won't give us even the most basic level of robustness we need.

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  • Application development using google applications?

    - by Ali
    Hi guys I'm developing a collaboration system and our team has been at it for the past couple of years. However the boss suggested that we try and redevelop it using something robust. Basically our collaboration system incorporates a webmail client and a custom built contacts management system plus project management system. My boss likes the robustness of GMAIL and Google docs and really would like a solution that if possible could incorporate these two and other google applications - I'm not so sure how to get started on developing a custom application using google applications - especially consider the fact that in the long run we wish to host our collaboration system as a paid service - just like the services that 37signals basecamp and highrise have been.

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  • Learning Ruby on Rails

    - by Ethan Gunderson
    As it stands now I'm a Java and C# developer, but the more and more I look at Ruby on Rails, the more I really want to learn it. What have you found to be the best route to learn RoR? Would it be easier to develop on Windows, or should I just run a virtual machine with linux? Is there an ide that can match the robustness of Visual Studio? Any programs to develop that give a good overhead of what to do? Any good books? Seriously, any tips/tricks/rants would be awesome.

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  • Are Symphony and CakePHP too slow to be usable?

    - by Aziz Light
    Until now, I have always said that CakePHP is too bloated and slow. I don't really know that, I just saw "some" benchmarks. What I really want to know, is that if those two frameworks (Symfony and CakePHP) are too slow to be usable in a way that the user will get frustrated. I already know that those frameworks are slower than other alternatives, but that's not the question. I ask the question because I want to create a project management web application and I still hesitate between a couple frameworks. I've had some trouble learning Zend, but imho I haven't tried hard enough. So in conclusion, in addition to the first question above, I would like to ask another question: If I want to create a project management tool (which is a pretty big project), which of the following should you suggest, considering the developement time, the speed of the resulting application, and the robustness of the final product: Symphony CakePHP Zend Framework Also I should mention that I don't know any of those frameworks, and that I want to learn one of them (at least).

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  • "conveyor belt" cache architecture

    - by Andrew Matthews
    I'm producing an application with a few peculiar internal communication characteristics that make the usual suspects for data storage and transport (Qs and RDBMSs) ill-fitted. I'm wondering whether there is a product out there that matches the following characteristics: all data put into it is peristent all reads are delivered out of memory data is universally available data lives where it is most needed data is versioned (nice to have) updates are transactional (I'd like ACID characteristics) data is potentially replicated, but always in sync works on windows is based on or has bindings for .NET is really fast is really robust is redundant is scalable I'm looking at things like Microsoft codename "Velocity", but I am not sure whether it fits all of the above characteristics. Likewise, Memcached is not a perfect fit either. The current version of this app opts for an RDBMS with a signaling system for inter-system sync, but latency is too high and versioning of the DB is a pain. I need all the robustness, but with none of the trade-offs.

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  • P/Invoke or C++/CLI for wrapping a C library

    - by Ian G
    Have a moderate size (40-odd function) C API that needs to be called from a C# project. The functions logically break up to form a few classes that will be API presented to the rest of the project. Are there any objective reasons to prefer P/Invoke or C++/CLI for the interoperability underneath that API, in terms of robustness, maintainability, deployment, ...? The issues I could think of that might be, but aren't problematic are: C++/CLI will require an separate assembly, the P/Invoke classes can be in the main assembly. (We've already got multiple assemblies and there'll be the C dlls anyway so not a major issue). Performance doesn't seem differ noticeable between the two methods. Issues that I'm not sure about are: My feeling is C++/CLI will be easier to debug if there's inter-op problem, is this true? Language familiarity enough people know C# and C++ but knowledge of details of C++/CLI are rarer here. Anything else?

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  • Which "platform" should we use for a notifier-component?

    - by cwap
    Hi all We need to develop a notifier component. What it will do, is to scan a database at given intervals (say, every 15th minute), to see if any notifications needs to be sent out. We're running on Windows, and so we've been looking into either a Windows Service or the Windows Task Scheduler. Our biggest concern is the robustness of our implementation. If it, for some reason, crashes, can it be auto-restarted the next interval? Can we use custom logging logic, to take care of crashes? I'd like an educated guess on what to use here :) Feel free to say if you need additional info, to make such a guess.. Props will be given if someone could make a short listing of the pros n cons of a windows service vs. the windows task scheduler. Also, it should be noted, that we aren't set on either of these, so if you have any alternatives, please, do post away. Thanks in advance :)

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  • Running script constantly in background: daemon, lock file with crontab, or simply loop?

    - by Mauritz Hansen
    I have a Perl script that queries a database for a list of files to process processes the files and then exits Upon startup this script creates a file (let's say script.lock), and upon exit it removes this file. I have a crontab entry that runs this script every minute. If the lockfile exists then the script exits, assuming that another instance of itself is running. The above process works fine but I am not very happy with the robustness of this approach. Specifically, if for some reason the script exits prematurely and the lockfile is not removed then a new instance will not execute properly. I would appreciate some advice on the following: Is using the lock file a good approach or is there a better/more robust way to do this? Is using crontab for this a good idea or could I better write an endless loop with sleep()? Should I use the GNU 'daemon' program or the Perl Proc::Daemon module (or some other equivalent) for this?

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  • Is the science of Computer Science dead?

    - by Veaviticus
    Question : Is the science and art of CS dead? By that I mean, the real requirements to think, plan and efficiently solve problems seems to be falling away from CS these days. The field seems to be lowering the entry-barrier so more people can 'program' without having to learn how to truly program. Background : I'm a recent graduate with a BS in Computer Science. I'm working a starting position at a decent sized company in the IT department. I mostly do .NET and other Microsoft technologies at my job, but before this I've done Java stuff through internships and the like. I personally am a C++ programmer for my own for-fun projects. In Depth : Through the work I've been doing, it seems to me that the intense disciplines of a real science don't exist in CS anymore. In the past, programmers had to solve problems efficiently in order for systems to be robust and quick. But now, with the prevailing technologies like .NET, Java and scripting languages, it seems like efficiency and robustness have been traded for ease of development. Most of the colleagues that I work with don't even have degrees in Computer Science. Most graduated with Electrical Engineering degrees, a few with Software Engineering, even some who came from tech schools without a 4 year program. Yet they get by just fine without having the technical background of CS, without having studied theories and algorithms, without having any regard for making an elegant solution (they just go for the easiest, cheapest solution). The company pushes us to use Microsoft technologies, which take all the real thought out of the matter and replace it with libraries and tools that can auto-build your project for you half the time. I'm not trying to hate on the languages, I understand that they serve a purpose and do it well, but when your employees don't know how a hash-table works, and use the wrong sorting methods, or run SQL commands that are horribly inefficient (but get the job done in an acceptable time), it feels like more effort is being put into developing technologies that coddle new 'programmers' rather than actually teaching people how to do things right. I am interested in making efficient and, in my opinion, beautiful programs. If there is a better way to do it, I'd rather go back and refactor it than let it slide. But in the corporate world, they push me to complete tasks quickly rather than elegantly. And that really bugs me. Is this what I'm going to be looking forward to the rest of my life? Are there still positions out there for people who love the science and art of CS rather than just the paycheck? And on the same note, here's a good read if you haven't seen it before The Perils Of Java Schools

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  • Bay Area Coherence Special Interest Group Next Meeting July 21, 2011

    - by csoto
    Date: Thursday, July 21, 2011 Time: 4:30pm - 8:15pm ET (note that Parking at 475 Sansome Closes at 8:30pm) Where: Oracle Office, 475 Sansome Street, San Francisco, CA Google Map We will be providing snacks and beverages. Register! - Registration is required for building security. Presentation Line Up:? 5:10pm - Batch Processing Using Coherence in Oracle Group Policy Administration - Paul Cleary, Oracle Oracle Insurance Policy Administration (OIPA) is a flexible, rules-based policy administration solution that provides full record keeping for all policy lifecycle transactions. One component of OIPA is Cycle processing, which is the batch processing of pending insurance transactions. This presentation introduces OIPA and Cycle processing, describing the unique challenges of processing a high volume of transactions within strict time windows. It then reviews how OIPA uses Oracle Coherence and the Processing Pattern to meet these challenges, describing implementation specifics that highlight the simplicity and robustness of the Processing Pattern. 6:10pm - Secure, Optimize, and Load Balance Coherence with F5 - Chris Akker, F5 F5 Networks, Inc., the global leader in Application Delivery Networking, helps the world’s largest enterprises and service providers realize the full value of virtualization, cloud computing, and on-demand IT. Recently, F5 and Oracle partnered to deliver a novel solution that integrates Oracle Coherence 3.7 with F5 BIG-IP Local Traffic Manager (LTM). This session will introduce F5 and how you can leverage BIG-IP LTM to secure, optimize, and load balance application traffic generated from Coherence*Extend clients across any number of servers in a cluster and to hardware-accelerate CPU-intensive SSL encryption. 7:10pm - Using Oracle Coherence to Enable Database Partitioning and DC Level Fault Tolerance - Alexei Ragozin, Independent Consultant and Brian Oliver, Oracle Partitioning is a very powerful technique for scaling database centric applications. One tricky part of partitioned architecture is routing of requests to the right database. The routing layer (routing table) should know the right database instance for each attribute which may be used for routing (e.g. account id, login, email, etc): it should be fast, it should fault tolerant and it should scale. All the above makes Oracle Coherence a natural choice for implementing such routing tables in partitioned architectures. This presentation will cover synchronization of the grid with multiple databases, conflict resolution, cross cluster replication and other aspects related to implementing robust partitioned architecture. Additional Info:?? - Download Past Presentations: The presentations from the previous meetings of the BACSIG are available for download here. Click on the presentation titles to download the PDF files. - Join the Coherence online community on our Oracle Coherence Users Group on LinkedIn. - Contact BACSIG with any comments, questions, presentation proposals and content suggestions.

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  • Oracle Database In-Memory

    - by Mike.Hallett(at)Oracle-BI&EPM
    Normal 0 false false false EN-GB X-NONE X-NONE Larry Ellison unveiled the next major milestone in database technology, Oracle Database In-Memory, on June 10, 2014. Oracle Database In-Memory will be generally available in July 2014 and can be used with all hardware platforms on which Oracle Database 12c is supported. This option will accelerate database performance by orders of magnitude for analytics, data warehousing, and reporting while also speeding up online transaction processing (OLTP). It allows any existing Oracle Database-compatible application to automatically and transparently take advantage of columnar in-memory processing, without additional programming or application changes. Benefits Fast ad-hoc analytics without the need to pre-create indexes Completely transparent to existing applications Faster mixed workload OLTP No database size limit Industrial strength availability and security Robustness and maturity of Oracle Database 12c To find out more see Oracle Database In-Memory Comment from Rittman Mead on Oracle In-Memory Option Launch  ... and I will let you know how this unfolds in regards to advantages for OBI11g and Exalytics and Big Data over the coming months. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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  • What are the advantages and disadvantages of the various virtual machine image formats?

    - by Matt
    Xen and Virtualbox etc both support a range of different virtual machine image formats. These are: vmdk, vdi, qcow & qcow2, hdd & vhd. Without any bias toward a particular product, I'm wanting to know what are the advantages and disadvantages of the various formats both from a features perspective, robustness and speed? One piece of info I discovered in a forum post was this: "The major difference is that VDI uses relatively large blocks (1MB) when growing an image, and thus has less overhead for block pointers etc. but isn't ultimately space efficient in the sense that if a single byte is non-zero in such a 1MB block the entire space is used. VMDK in contrast uses 64K blocks, and thus has more management overhead and generally a bit less disk space consumption What offsets this is that VDI is more efficient when it comes to snapshots." You might be thinking, I want to know this because I want to know which format to choose? Not exactly, I'm developing some software which utilises these formats and want to support one or more of them. Simplicity, large disks and ease of development are my main drivers.

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  • New keyboard for linux: Adesso Tru-Form or MS Natural Keyboard 4000?

    - by Andrea
    Hi folks! I'm going to buy a new ergonomic keyboard for my laptop. In the following, keep in mind I live in Italy. I considered the following models: Adesso PCK-308UB - Adesso Tru-Form™ Pro - Contoured Ergonomic Keyboard with TouchPad-PS2 Pro: has a built-in touchpad in the same position of my laptop somewhat cheaper than the alternative below Cons: the surface doesn't seem to be bowl-shaped. keys seem to lay on a straight slightly-inclined surface. It seems an idea used extensively in other ergonomic keyboards according to a few comments on the net, new Adesso keyboards seem to lack robustness, they're likely to loose small parts after a few weeks or months. Other users, instead, seem to never had any problem in years and swear by their quality and comfortability. Those who had problems, however, lamented a lack of responsiveness from the manufacturer. I'm not sure whether the keyboard, at least the standard keys, and the touchpad will both be recognized correctly under linux distros (I mostly use FC btw) last time I checked, Adesso didn't have local resellers in my country Microsoft Natural Ergonomic Keyboard Pro: recognized as one of the most comfortable keyboards reliable customer service operating in my country AFAIK there are several documented ways to get extra buttons work with linux Cons: it doesn't have a builtin touchpad and has a numeric keypad wasting space to reach mouse But there could be other keyboards I haven't considered yet, so here follows my ideal keyboard wishlist, ordered by priority linux compatible basic ergonomic design, which entails split tilted keyboard and pads advanced ergonomic design, like true-ergonomic's or kinesis , where special keys (like enter, caps-lock...) are placed symmetrically in the middle to be used by thumbs a builtin touchpad/trackball placed under the keyboard. I just love this on my notebook. I think it's pretty effective, since it allows my hand to rest naturally everytime I use it. Any opinion on this? high-quality switches, like cherry's (unsure about this one) additional programmable keys placed near usual ones, to simplify typing shortcuts TIA Andrea

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  • Ubuntu server or Debian server (to run C++ apps developed on Ubuntu)

    - by skyeagle
    I have written a number of C++ server side daemons for my website, using my Ubuntu 9.10 dev machine. The C++ apps I mentioned above are "GUI-less" daemons (and libraries used by the daemons). I am now about to host my website and need to decide whether to go with Debian server or Ubuntu server. In a nutshell, here is the situation: I developed on Ubuntu desktop because I preferred the more friendly GUI I would like to deploy on Debian Server because of the (perceived?) robustness of the Debian server over Ubuntu server (I may be totally wrong here - and in fact, this is really what this question is all about) If Debian server is indeed more robust than Ubuntu server, then I have no choice but to go with Debian server - BUT, will my Ubuntu developed C++ apps run on the server? (or do I need to recompile them on the server? (I'd HATE to have to do this, because I want to keep the server machine clean and light - no GUI, no dev tools etc). This last question is really about binary compatability between Ubuntu and Debian. I want the server to be robust, secure and stable, and simply act as a server (i.e. LAMP and very little else - no GUI etc). Given that requirement, and the fact that I need to run my C++ apps (developed on Ubuntu 9.10), I need advice on which OS to choose for the server. Ideally, any advice will be backed with a reason. I am particularly interested in hearing from people who have been in an identical situation, or done something similar.

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  • Serious 64-bit laptop

    - by Daniel Gehriger
    For the past couple of years, I have been using an IBM Thinkpad T60p for daily work (software development, desktop & embedded). I am extremely satisfied with this machine, due to its robustness. It also has a few features I depend on: a high resolution display: 15.0" TFT FlexView display with 1600x1200 (UXGA); excellent keyboard; decent graphics and CPU performance. Some of the software I develop benefits from larger amounts of RAM, and 3GB (Windows 7 32-bit) or 4GB (Windows 7 64-bit on T60p) are no longer sufficient. My customers run desktop computers with 20GB and more, and I need to have at least 8GB to at least be able to run reasonable test cases. So I'm shopping around for a new laptop, but I'm struggling to find anything that matches my requirements: must run Windows 7 64-bit Pro or higher; must support at least 8GB of RAM (more is better) high screen resolution! While I prefer 4:3 I can live with wide screen. But I really hope to find something with a vertical screen resolution similar to what I have now... portable, so < 16" but = 14" I realize that FlexView isn't available anymore, but I'd like to avoid a glossy screen if possible. decent (not more) graphics performance, ideally hybrid (I'm doing a lot of CAD, never games). good keyboard reasonable CPU -- but I'm still fine with my current Core 2 Duo, so that shouldn't be too complicated. The T60p fits all those requirements, except the 8GB of RAM. Can you help me find a current notebook that would match most of them? I don't mind changing brand. Thanks!

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  • Review: ComponentOne Studio for Entity Framework

    - by Tim Murphy
    While I have always been a fan of libraries that improve coding efficiency and reduce code redundancy I have mostly been using ones that were in the public domain.  As part of the Geeks With Blogs Influencers program a got my hands on ComponentOne’s Studio for Entity Framework.  Below are my thought after working with the product for several weeks. My coding preference has always been maintainable code that is reusable across an enterprises protfolio.  Because of this my focus in reviewing this product is less on the RAD components and more on its benefits for layered applications using code first Entity Framework. Before we get into the pros and cons here is a summary of the main feature listed for SEF. Unified Data Context Virtual Data Access More Powerful Data Binding Pros The first thing that I found to my liking is the C1DataSource. It basically manages a cache for your Entity Model context.  Under RAD conditions this is setup automatically when you drop the object on a your design surface.  If you are like me and want to abstract you data management into a library it takes a little more work, but it is still acceptable and gains the same benefits. The second feature that I found beneficial is the definition of views with improved sorting and filtering.  Again the ease of use of these features is greater on the RAD side but no capabilities are missing when manipulating object in code. Linq has become my friend over the last couple of years and it was great to see that ComponentOne had ensured that it remained a first class citizen in their design.  When you look into this product yourself I would suggest taking a dive into LiveLinq which allow the joining of different data source types. As I went through discovering the features of this framework I appreciated the number of examples that they supplied for different uses.  Besides showing how to use SEF with WinForms, WPF and Silverlight they also showed how to accomplish tasks both RAD, code only and MVVM approaches. Cons The only area that I would really like to see improvement is in there level of detail in their documentation.  Specifically I would like to have seen some of the supporting code explained, such as what some supporting object did, in the examples instead of having to go to the programmer’s reference. I did find some times where currently existing projects had some trouble determining scope that the RAD controls were allowed, but I expect this is something that is in part end user related. Summary Overall I found the Studio for Entity Framework capable and well thought out.  If you are already using the Entity Framework this product will fit into your environment with little effort in return for greater flexibility and greater robustness in your solutions. Whether the $895 list price for a standard version works for you will depend on your return on investment. Smaller companies with only a small number of projects may not be able to stomach it, you get a full featured product that is supported by a well established company.  The more projects and the more code you have the greater your return on investment will be. Personally I intend to apply this product to some production systems and will probably have some tips and tricks in the future. del.icio.us Tags: ComponentOne,Studio for Entity Framework,Geeks With Blogs,Influencers,Product Reviews

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  • What are the disadvantages of self-encapsulation?

    - by Dave Jarvis
    Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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  • Is there a theory for "transactional" sequences of failing and no-fail actions?

    - by Ross Bencina
    My question is about writing transaction-like functions that execute sequences of actions, some of which may fail. It is related to the general C++ principle "destructors can't throw," no-fail property, and maybe also with multi-phase transactions or exception safety. However, I'm thinking about it in language-neutral terms. My concern is with correctly designing error handling in C++ functions that must be reliable. I would like to know what the concepts below are called so that I can learn more about them. I'm sorry that I can't ask the question more directly. Since I don't know this area I have provided an example to explain my question. The question is at the end. Here goes: Consider a sequence of steps or actions executed sequentially, where actions belong to one of two classes: those that always succeed, and those that may fail. In the examples below: S stands for an action that always succeeds (called "no-fail" in some settings). F stands for an action that may fail (for example, it might fail to allocate memory or do I/O that could fail). Consider a sequences of actions (executed sequentially from left to right): S->S->S->S Since each action in the sequence above succeeds, the whole sequence succeeds. On the other hand, the following sequence may fail because the last action may fail: S->S->S->F So, claim: a sequence has the no-fail (S) property if and only if all of its actions are no-fail. Now, I'm interested in action sequences that form "atomic transactions", with "failure atomicity," i.e. where either the whole sequence completes successfully, or there is no effect. I.e. if some action fails, the earlier ones must be rolled back. This requires that any successfully executed actions prior to a failing action must always be able to be rolled back. Consider the sequence: S->S->S->F S<-S<-S In the example above, the first row is the forward path of the transaction, and the second row are inverse actions (executed from right to left) that can be used to roll back if the final top row actions fails. It seems to me that for a transaction to support failure atomicity, the following invariant must hold: Claim: To support failure atomicity (either completion or complete roll-back on failure) all actions preceding the latest failable (F) action on the forward path (marked * in the example below) must have no-fail (S) inverses. The following is an example of a sequence that supports failure atomicity: * S->F->F->F S<-S<-S Further, if we want the transaction to be able to attempt cancellation mid-way through, but still guarantee either full completion or full rollback then we need the following property: Claim: To support failure atomicity and cancellation mid-way through execution, in the face of errors in the inverse (cancellation) path, all actions following the earliest failable (F) inverse on the reverse path (marked *) must be no-fail (S). F->F->F->S->S S<-S<-F<-F * I believe that these two conditions guarantee that an abortable/cancelable transaction will never get "stuck". My questions are: What is the study and theory of these properties called? are my claims correct? and what else is there to know? UPDATE 1: Updated terminology: what I previously called "robustness" is called atomicity in the database literature. UPDATE 2: Added explicit reference to failure atomicity, which seems to be a thing.

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