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  • JavaOne Latin America 2012 is a wrap!

    - by arungupta
    Third JavaOne in Latin America (2010, 2011) is now a wrap! Like last year, the event started with a Geek Bike Ride. I could not attend the bike ride because of pre-planned activities but heard lots of good comments about it afterwards. This is a great way to engage with JavaOne attendees in an informal setting. I highly recommend you joining next time! JavaOne Blog provides a a great coverage for the opening keynotes. I talked about all the great set of functionality that is coming in the Java EE 7 Platform. Also shared the details on how Java EE 7 JSRs are willing to take help from the Adopt-a-JSR program. glassfish.org/adoptajsr bridges the gap between JUGs willing to participate and looking for areas on where to help. The different specification leads have identified areas on where they are looking for feedback. So if you are JUG is interested in picking a JSR, I recommend to take a look at glassfish.org/adoptajsr and jump on the bandwagon. The main attraction for the Tuesday evening was the GlassFish Party. The party was packed with Latin American JUG leaders, execs from Oracle, and local community members. Free flowing food and beer/caipirinhas acted as great lubricant for great conversations. Some of them were considering the migration from Spring -> Java EE 6 and replacing their primary app server with GlassFish. Locaweb, a local hosting provider sponsored a round of beer at the party as well. They are planning to come with Java EE hosting next year and GlassFish would be a logical choice for them ;) I heard lots of positive feedback about the party afterwards. Many thanks to Bruno Borges for organizing a great party! Check out some more fun pictures of the party! Next day, I gave a presentation on "The Java EE 7 Platform: Productivity and HTML 5" and the slides are now available: With so much new content coming in the plaform: Java Caching API (JSR 107) Concurrency Utilities for Java EE (JSR 236) Batch Applications for the Java Platform (JSR 352) Java API for JSON (JSR 353) Java API for WebSocket (JSR 356) And JAX-RS 2.0 (JSR 339) and JMS 2.0 (JSR 343) getting major updates, there is definitely lot of excitement that was evident amongst the attendees. The talk was delivered in the biggest hall and had about 200 attendees. Also spent a lot of time talking to folks at the OTN Lounge. The JUG leaders appreciation dinner in the evening had its usual share of fun. Day 3 started with a session on "Building HTML5 WebSocket Apps in Java". The slides are now available: The room was packed with about 150 attendees and there was good interaction in the room as well. A collaborative whiteboard built using WebSocket was very well received. The following tweets made it more worthwhile: A WebSocket speek, by @ArunGupta, was worth every hour lost in transit. #JavaOneBrasil2012, #JavaOneBr @arungupta awesome presentation about WebSockets :) The session was immediately followed by the hands-on lab "Developing JAX-RS Web Applications Utilizing Server-Sent Events and WebSocket". The lab covers JAX-RS 2.0, Jersey-specific features such as Server-Sent Events, and a WebSocket endpoint using JSR 356. The complete self-paced lab guide can be downloaded from here. The lab was planned for 2 hours but several folks finished the entire exercise in about 75 mins. The wonderfully written lab material and an added incentive of Java EE 6 Pocket Guide did the trick ;-) I also spoke at "The Java Community Process: How You Can Make a Positive Difference". It was really great to see several JUG leaders talking about Adopt-a-JSR program and other activities that attendees can do to participate in the JCP. I shared details about Adopt a Java EE 7 JSR as well. The community keynote in the evening was looking fun but I had to leave in between to go through the peak Sao Paulo traffic time :) Enjoy the complete set of pictures in the album:

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  • How To Clear An Alert - Part 2

    - by werner.de.gruyter
    There were some interesting comments and remarks on the original posting, so I decided to do a follow-up and address some of the issues that got raised... Handling Metric Errors First of all, there is a significant difference between an 'error' and an 'alert'. An 'alert' is the violation of a condition (a threshold) specified for a given metric. That means that the Agent is collecting and gathering the data for the metric, but there is a situation that requires the attention of an administrator. An 'error' on the other hand however, is a failure to collect metric data: The Agent is throwing the error because it cannot determine the value for the metric Whereas the 'alert' guarantees continuity of the metric data, an 'error' signals a big unknown. And the unknown aspect of all this is what makes an error a lot more serious than a regular alert: If you don't know what the current state of affairs is, there could be some serious issues brewing that nobody is aware of... The life-cycle of a Metric Error Clearing a metric error is pretty much the same workflow as a metric 'alert': The Agent signals the error after it failed to execute the metric The error is uploaded to the OMS/repository, where it becomes visible in the Console The error will remain active until the Agent is able to execute the metric successfully. Even though the metric is still getting scheduled and executed on a regular basis, the error will remain outstanding as long as the Agent is not capable of executing the metric correctly Knowing this, the way to fix the metric error should be obvious: Take the 'problem' away, and as soon as the metric is executed again (based on the frequency of the metric), the error will go away. The same tricks used to clear alerts can be used here too: Wait for the next scheduled execution. For those metrics that are executed regularly (like every 15 minutes or so), it's just a matter of waiting those minutes to see the updates. The 'Reevaluate Alert' button can be used to force a re-execution of the metric. In case a metric is executed once a day, this will be a better way to make sure that the underlying problem has been solved. And if it has been, the metric error will be removed, and the regular data points will be uploaded to the repository. And just in case you have to 'force' the issue a little: If you disable and re-enable a metric, it will get re-scheduled. And that means a new metric execution, and an update of the (hopefully) fixed problem. Database server-generated alerts and problem checkers There are various ways the Agent can collect metric data: Via a script or a SQL statement, reading a log file, getting a value from an SNMP OID or listening for SNMP traps or via the DBMS_SERVER_ALERTS mechanism of an Oracle database. For those alert which are generated by the database (like tablespace metrics for 10g and above databases), the Agent just 'waits' for the database to report any new findings. If the Agent has lost the current state of the server-side metrics (due to an incomplete recovery after a disaster, or after an improper use of the 'emctl clearstate' command), the Agent might be still aware of an alert that the database no longer has (or vice versa). The same goes for 'problem checker' alerts: Those metrics that only report data if there is a problem (like the 'invalid objects' metric) will also have a problem if the Agent state has been tampered with (again, the incomplete recovery, and after improper use of 'emctl clearstate' are the two main causes for this). The best way to deal with these kinds of mismatches, is to simple disable and re-enable the metric again: The disabling will clear the state of the metric, and the re-enabling will force a re-execution of the metric, so the new and updated results can get uploaded to the repository. Starting 10gR5, the Agent performs additional checks and verifications after each restart of the Agent and/or each state change of the database (shutdown/startup or failover in case of DataGuard) to catch these kinds of mismatches.

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  • Agile Database Techniques: Effective Strategies for the Agile Software Developer – book review

    - by DigiMortal
       Agile development expects mind shift and developers are not the only ones who must be agile. Every chain is as strong as it’s weakest link and same goes also for development teams. Agile Database Techniques: Effective Strategies for the Agile Software Developer by Scott W. Ambler is book that calls also data professionals to be part of agile development. Often are DBA-s in situation where they are not part of application development and later they have to survive large set of applications that all use databases different way. Of course, only some of these applications are not problematic when looking what database server has to do to serve them. I have seen many applications that rape database servers because developers have no clue what is going on in database (~3K queries to database per web application request – have you seen something like this? I have…) Agile Database Techniques covers some object and database design technologies and gives suggestions to development teams about topics they need help or assistance by DBA-s. The book is also good reading for DBA-s who usually are not very strong in object technologies. You can take this book as bridge between these two worlds. I think teams that build object applications that use databases should buy this book and try at least one or two projects out with Ambler’s suggestions. Table of contents Foreword by Jon Kern. Foreword by Douglas K. Barry. Acknowledgments. Introduction. About the Author. Part One: Setting the Foundation. Chapter 1: The Agile Data Method. Chapter 2: From Use Cases to Databases — Real-World UML. Chapter 3: Data Modeling 101. Chapter 4: Data Normalization. Chapter 5: Class Normalization. Chapter 6: Relational Database Technology, Like It or Not. Chapter 7: The Object-Relational Impedance Mismatch. Chapter 8: Legacy Databases — Everything You Need to Know But Are Afraid to Deal With. Part Two: Evolutionary Database Development. Chapter 9: Vive L’ Évolution. Chapter 10: Agile Model-Driven Development (AMDD). Chapter 11: Test-Driven Development (TDD). Chapter 12: Database Refactoring. Chapter 13: Database Encapsulation Strategies. Chapter 14: Mapping Objects to Relational Databases. Chapter 15: Performance Tuning. Chapter 16: Tools for Evolutionary Database Development. Part Three: Practical Data-Oriented Development Techniques. Chapter 17: Implementing Concurrency Control. Chapter 18: Finding Objects in Relational Databases. Chapter 19: Implementing Referential Integrity and Shared Business Logic. Chapter 20: Implementing Security Access Control. Chapter 21: Implementing Reports. Chapter 22: Realistic XML. Part Four: Adopting Agile Database Techniques. Chapter 23: How You Can Become Agile. Chapter 24: Bringing Agility into Your Organization. Appendix: Database Refactoring Catalog. References and Suggested Reading. Index.

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  • SQL SERVER – List of All the Samples Database Available to Download for FREE

    - by Pinal Dave
    It is pretty much very common to have a sample database for any database product. Different companies keep on improving their product and keep on coming up with innovation in their product. To demonstrate the capability of their new enhancements they need the sample database. Microsoft have various sample database available for free download for their SQL Server Product. I have collected them here in a single blog post. Download an AdventureWorks Database The AdventureWorks OLTP database supports standard online transaction processing scenarios for a fictitious bicycle manufacturer (Adventure Works Cycles). Scenarios include Manufacturing, Sales, Purchasing, Product Management, Contact Management, and Human Resources. Coconut Dal Coconut Dal is a lightweight data access layer, for use in projects where the Entity Framework cannot be used or Microsoft’s Enterprise Library Data Block is unsuitable. Anyone who is handwriting ADO.NET should use a library instead and Coconut Dal might be the answer.  DataBooster – Extension to ADO.NET Data Provider The dbParallel DataBooster library is a high-performance extension to ADO.NET Data Provider, includes two aspects: 1) A slimmed down API encapsulation which simplified the most common data access operations (DbConnection -> DbCommand -> DbParameter -> DbDataReader) into a single class DbAccess, to help application with a clean DAL, avoid over-packing and redundant-copy of data transfer. 2) A booster for writing mass data onto database. Base on a rational utilization of database concurrency and a effective utilization of network bandwidth. Tabular AMO 2012 The sample is made of two project parts. The first part is a library of functions to manage tabular models -AMO2Tabular V2-. The second part is a sample to build a tabular model -AdventureWorks Tabular AMO 2012- using the AMO2Tabular library; the created model is similar to the ‘AdventureWorks Tabular Model 2012. SQL Server Analysis Services Product Samples SQL Server Analysis Services provides, a unified and integrated view of all your business data as the foundation for all of your traditional reporting, online analytical processing (OLAP) analysis, Key Performance Indicator (KPI) scorecards, and data mining. Analysis Services Samples for SQL Server 2008 R2 This release is dedicated to the samples that ship for Microsoft SQL Server 2008R2. For many of these samples you will also need to download the AdventureWorks family of databases. SQL Server Reporting Services Product Samples This project contains Reporting Services samples released with Microsoft SQL Server product. These samples are in the following five categories: Application Samples, Extension Samples, Model Samples, Report Samples, and Script Samples. If you are interested in contributing Reporting Services samples, please let us know by posting in the developers’ forum. Reporting Services Samples for SQL Server 2008 R2 This release is dedicated to the samples that ship for Microsoft SQL Server 2008 R2 PCU1. For many of these samples you will also need to download the AdventureWorks family of databases. SQL Server Integration Services Product Samples This project contains Integration Services samples released with Microsoft SQL Server product. These samples are in the following two categories: Package Samples and Programming Samples. If you are interested in contributing Integration Services samples, please let us know by posting in the developers’ forum. Integration Services Samples for SQL Server 2008 R2 This release is dedicated to the samples that ship for Microsoft SQL Server 2008R2. For many of these samples you will also need to download the AdventureWorks family of databases. Windows Azure SQL Reporting Admin Sample The SQLReportingAdmin sample for Windows Azure SQL Reporting demonstrates the usage of SQL Reporting APIs, and manages (add/update/delete) permissions of SQL Reporting users. Windows Azure SQL Reporting ReportViewer-SOAP API usage sample These sample projects demonstrate how to embed a Microsoft ReportViewer control that points to reports hosted on SQL Reporting report servers and how to use SQL Reporting SOAP APIs in your Windows Azure Web application. Enterprise Library 5.0 – Integration Pack for Windows Azure This NuGet package contains a zip file with the source code for the Enterprise Library Integration Pack for Windows Azure.  Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Sample Database

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  • The Evolution Of C#

    - by Paulo Morgado
    The first release of C# (C# 1.0) was all about building a new language for managed code that appealed, mostly, to C++ and Java programmers. The second release (C# 2.0) was mostly about adding what wasn’t time to built into the 1.0 release. The main feature for this release was Generics. The third release (C# 3.0) was all about reducing the impedance mismatch between general purpose programming languages and databases. To achieve this goal, several functional programming features were added to the language and LINQ was born. Going forward, new trends are showing up in the industry and modern programming languages need to be more: Declarative With imperative languages, although having the eye on the what, programs need to focus on the how. This leads to over specification of the solution to the problem in hand, making next to impossible to the execution engine to be smart about the execution of the program and optimize it to run it more efficiently (given the hardware available, for example). Declarative languages, on the other hand, focus only on the what and leave the how to the execution engine. LINQ made C# more declarative by using higher level constructs like orderby and group by that give the execution engine a much better chance of optimizing the execution (by parallelizing it, for example). Concurrent Concurrency is hard and needs to be thought about and it’s very hard to shoehorn it into a programming language. Parallel.For (from the parallel extensions) looks like a parallel for because enough expressiveness has been built into C# 3.0 to allow this without having to commit to specific language syntax. Dynamic There was been lots of debate on which ones are the better programming languages: static or dynamic. The fact is that both have good qualities and users of both types of languages want to have it all. All these trends require a paradigm switch. C# is, in many ways, already a multi-paradigm language. It’s still very object oriented (class oriented as some might say) but it can be argued that C# 3.0 has become a functional programming language because it has all the cornerstones of what a functional programming language needs. Moving forward, will have even more. Besides the influence of these trends, there was a decision of co-evolution of the C# and Visual Basic programming languages. Since its inception, there was been some effort to position C# and Visual Basic against each other and to try to explain what should be done with each language or what kind of programmers use one or the other. Each language should be chosen based on the past experience and familiarity of the developer/team/project/company and not by particular features. In the past, every time a feature was added to one language, the users of the other wanted that feature too. Going forward, when a feature is added to one language, the other will work hard to add the same feature. This doesn’t mean that XML literals will be added to C# (because almost the same can be achieved with LINQ To XML), but Visual Basic will have auto-implemented properties. Most of these features require or are built on top of features of the .NET Framework and, the focus for C# 4.0 was on dynamic programming. Not just dynamic types but being able to talk with anything that isn’t a .NET class. Also introduced in C# 4.0 is co-variance and contra-variance for generic interfaces and delegates. Stay tuned for more on the new C# 4.0 features.

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  • Silverlight Cream for March 31, 2010 -- #826

    - by Dave Campbell
    In this Issue: Andrea Boschin, Radenko Zec, Andrej Tozon, Bobby Diaz, Brad Abrams, Wolf Schmidt, Colin Eberhardt, Anand Iyer, Matthias Shapiro, Jaime Rodriguez, Bill Reiss, and Lee. Shoutouts: Cigdem has a post up about here MIX10 Interviewing experiences: MIX10 SilverlightShow Interviews Ian T. Lackey has his material up from his talk Silverlight SEO at the St. Louis .Net Users Group Not Silverlight but definitely WP7 cool, Michael Klucher reports that there are New Windows Phone Samples on Creators Club Online Tim Heuer posted a survey: What tools are the minimum to get started in Silverlight? From SilverlightCream.com: A RoleManager to apply roles declaratively to user interface Andrea Boschin also has a new post at SilverlightShow discussing the use of a RoleManager in WCF RIA Services to apply user roles to elements of the UI... good stuff, Andrea. Virtualization in Silverlight 4 RC Radenko Zec has a post out at SilverlightShow where he explains UI and Data Virtualization then gives some examples of their use in Silverlight 4RC, and some issues as well. MS Word Mail Merge with Silverlight 4 COM Automation Andrej Tozon has a post up at SilverlightShow that I missed in the rush of MIX10. He's doing MailMerge with COM automation and Silverlight 4... actually prett cool stuff and all the source! KISS and Tell - MVVM and the ViewModelLocator Bobby Diaz is blogging about a very popular subject right now: ViewModelLocator. He's not showing production code, but it's a thought... check it out. Silverlight 4 + RIA Services - Ready for Business: Validating Data I'm running behind, but Brad Abrams' next post in his series is about validating data in the business application. He also discusses setting up shared code validation. A One-stop Shopping XAML Namespace for Silverlight Client SDK Controls Wolf Schmidt at the Silverlight SDK has a post up highlighting the SL4 XAML namespace prefix. He starts with SL3 then demonstrates the feature's use in SL4. Binding a Silverlight 3 DataGrid to dynamic data via IDictionary (Updated) Colin Eberhardt has an update to his previous article of the same title. This one is a bug fix on an upgrade to SL3 and also an expansion of the previous post. Demo Apps from MIX10 on Windows Phone 7 Anand Iyer posted links to all the WP7 demos used at MIX10 and at least in the case of FourSquare, the source is on CodePlex. XAML Files for Location Visualizations in Silverlight and WPF Matthias Shapiro has graciously provided XAML for us for Silverlight and WPF for a bunch of different US maps... too cool, now we don't have to be asking 'where did you get that map?'... thanks Matthias! Theming in Windows Phone Jaime Rodriguez has a post up that deep-dives theming in general and demonstrates using it on WP7... end-user configurations and developer stuff. Space Rocks game step 7: Moving the ship It appears that in the heat of battle (blogging) I said Bill Reiss' Space Rocks game he's building is for WP7... obviously it's not, but it's a game folks... :) THis is Episode 7 and he's moving the ship now. SL4(RC) RichTextBox and Access Violation Lee has some code that looks like it should work for a RichTextBox in SL4RC, and it's throwing an error... see if you have a solution for him... or is it a bug? Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight    Silverlight 3    Silverlight 4    Windows Phone MIX10

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  • jtreg update, March 2012

    - by jjg
    There is a new update for jtreg 4.1, b04, available. The primary changes have been to support faster and more reliable test runs, especially for tests in the jdk/ repository. [ For users inside Oracle, there is preliminary direct support for gathering code coverage data using jcov while running tests, and for generating a coverage report when all the tests have been run. ] -- jtreg can be downloaded from the OpenJDK jtreg page: http://openjdk.java.net/jtreg/. Scratch directories On platforms like Windows, if a test leaves a file open when the test is over, that can cause a problem for downstream tests, because the scratch directory cannot be emptied beforehand. This is addressed in agentvm mode by discarding any agents using that scratch directory and starting new agents using a new empty scratch directory. Successive directives use suffices _1, _2, etc. If you see such directories appearing in the work directory, that is an indication that files were left open in the preceding directory in the series. Locking support Some tests use shared system resources such as fixed port numbers. This causes a problem when running tests concurrently. So, you can now mark a directory such that all the tests within all such directories will be run sequentially, even if you use -concurrency:N on the command line to run the rest of the tests in parallel. This is seen as a short term solution: it is recommended that tests not use shared system resources whenever possible. If you are running multiple instances of jtreg on the same machine at the same time, you can use a new option -lock:file to specify a file to be used for file locking; otherwise, the locking will just be within the JVM used to run jtreg. "autovm mode" By default, if no options to the contrary are given on the command line, tests will be run in othervm mode. Now, a test suite can be marked so that the default execution mode is "agentvm" mode. In conjunction with this, you can now mark a directory such that all the tests within that directory will be run in "othervm" mode. Conceptually, this is equivalent to putting /othervm on every appropriate action on every test in that directory and any subdirectories. This is seen as a short term solution: it is recommended tests be adapted to use agentvm mode, or use "@run main/othervm" explicitly. Info in test result files The user name and jtreg version info are now stored in the properties near the beginning of the .jtr file. Build The makefiles used to build and test jtreg have been reorganized and simplified. jtreg is now using JT Harness version 4.4. Other jtreg provides access to GNOME_DESKTOP_SESSION_ID when set. jtreg ensures that shell tests are given an absolute path for the JDK under test. jtreg now honors the "first sentence rule" for the description given by @summary. jtreg saves the default locale before executing a test in samevm or agentvm mode, and restores it afterwards. Bug fixes jtreg tried to execute a test even if the compilation failed in agentvm mode because of a JVM crash. jtreg did not correctly handle the -compilejdk option. Acknowledgements Thanks to Alan, Amy, Andrey, Brad, Christine, Dima, Max, Mike, Sherman, Steve and others for their help, suggestions, bug reports and for testing this latest version.

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  • Give a session on C++ AMP – here is how

    - by Daniel Moth
    Ever since presenting on C++ AMP at the AMD Fusion conference in June, then the Gamefest conference in August, and the BUILD conference in September, I've had numerous requests about my material from folks that want to re-deliver the same session. The C++ AMP session I put together has evolved over the 3 presentations to its final form that I used at BUILD, so that is the one I recommend you base yours on. Please get the slides and the recording from channel9 (I'll refer to slide numbers below). This is how I've been presenting the C++ AMP session: Context (slide 3, 04:18-08:18) Start with a demo, on my dual-GPU machine. I've been using the N-Body sample (for VS 11 Developer Preview). (slide 4) Use an nvidia slide that has additional examples of performance improvements that customers enjoy with heterogeneous computing. (slide 5) Talk a bit about the differences today between CPU and GPU hardware, leading to the fact that these will continue to co-exist and that GPUs are great for data parallel algorithms, but not much else today. One is a jack of all trades and the other is a number cruncher. (slide 6) Use the APU example from amd, as one indication that the hardware space is still in motion, emphasizing that the C++ AMP solution is a data parallel API, not a GPU API. It has a future proof design for hardware we have yet to see. (slide 7) Provide more meta-data, as blogged about when I first introduced C++ AMP. Code (slide 9-11) Introduce C++ AMP coding with a simplistic array-addition algorithm – the slides speak for themselves. (slide 12-13) index<N>, extent<N>, and grid<N>. (Slide 14-16) array<T,N>, array_view<T,N> and comparison between them. (Slide 17) parallel_for_each. (slide 18, 21) restrict. (slide 19-20) actual restrictions of restrict(direct3d) – the slides speak for themselves. (slide 22) bring it altogether with a matrix multiplication example. (slide 23-24) accelerator, and accelerator_view. (slide 26-29) Introduce tiling incl. tiled matrix multiplication [tiling probably deserves a whole session instead of 6 minutes!]. IDE (slide 34,37) Briefly touch on the concurrency visualizer. It supports GPU profiling, but enhancements specific to C++ AMP we hope will come at the Beta timeframe, which is when I'll be spending more time talking about it. (slide 35-36, 51:54-59:16) Demonstrate the GPU debugging experience in VS 11. Summary (slide 39) Re-iterate some of the points of slide 7, and add the point that the C++ AMP spec will be open for other compiler vendors to implement, even on other platforms (in fact, Microsoft is actively working on that). (slide 40) Links to content – see slide – including where all your questions should go: http://social.msdn.microsoft.com/Forums/en/parallelcppnative/threads.   "But I don't have time for a full blown session, I only need 2 (or just 1, or 3) C++ AMP slides to use in my session on related topic X" If all you want is a small number of slides, you can take some from the session above and customize them. But because I am so nice, I have created some slides for you, including talking points in the notes section. Download them here. Comments about this post by Daniel Moth welcome at the original blog.

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  • Combining template method with strategy

    - by Mekswoll
    An assignment in my software engineering class is to design an application which can play different forms a particular game. The game in question is Mancala, some of these games are called Wari or Kalah. These games differ in some aspects but for my question it's only important to know that the games could differ in the following: The way in which the result of a move is handled The way in which the end of the game is determined The way in which the winner is determined The first thing that came to my mind to design this was to use the strategy pattern, I have a variation in algorithms (the actual rules of the game). The design could look like this: I then thought to myself that in the game of Mancala and Wari the way the winner is determined is exactly the same and the code would be duplicated. I don't think this is by definition a violation of the 'one rule, one place' or DRY principle seeing as a change in rules for Mancala wouldn't automatically mean that rule should be changed in Wari as well. Nevertheless from the feedback I got from my professor I got the impression to find a different design. I then came up with this: Each game (Mancala, Wari, Kalah, ...) would just have attribute of the type of each rule's interface, i.e. WinnerDeterminer and if there's a Mancala 2.0 version which is the same as Mancala 1.0 except for how the winner is determined it can just use the Mancala versions. I think the implementation of these rules as a strategy pattern is certainly valid. But the real problem comes when I want to design it further. In reading about the template method pattern I immediately thought it could be applied to this problem. The actions that are done when a user makes a move are always the same, and in the same order, namely: deposit stones in holes (this is the same for all games, so would be implemented in the template method itself) determine the result of the move determine if the game has finished because of the previous move if the game has finished, determine who has won Those three last steps are all in my strategy pattern described above. I'm having a lot of trouble combining these two. One possible solution I found would be to abandon the strategy pattern and do the following: I don't really see the design difference between the strategy pattern and this? But I am certain I need to use a template method (although I was just as sure about having to use a strategy pattern). I also can't determine who would be responsible for creating the TurnTemplate object, whereas with the strategy pattern I feel I have families of objects (the three rules) which I could easily create using an abstract factory pattern. I would then have a MancalaRuleFactory, WariRuleFactory, etc. and they would create the correct instances of the rules and hand me back a RuleSet object. Let's say that I use the strategy + abstract factory pattern and I have a RuleSet object which has algorithms for the three rules in it. The only way I feel I can still use the template method pattern with this is to pass this RuleSet object to my TurnTemplate. The 'problem' that then surfaces is that I would never need my concrete implementations of the TurnTemplate, these classes would become obsolete. In my protected methods in the TurnTemplate I could just call ruleSet.determineWinner(). As a consequence, the TurnTemplate class would no longer be abstract but would have to become concrete, is it then still a template method pattern? To summarize, am I thinking in the right way or am I missing something easy? If I'm on the right track, how do I combine a strategy pattern and a template method pattern? This is part of a homework assignment but I'm not looking to be gifted the answer, I have deliberately been very verbose in my question to show that I have thought about it before coming here to ask a question

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  • Bug in Delphi XE RegularExpressions Unit

    - by Jan Goyvaerts
    Using the new RegularExpressions unit in Delphi XE, you can iterate over all the matches that a regex finds in a string like this: procedure TForm1.Button1Click(Sender: TObject); var RegEx: TRegEx; Match: TMatch; begin RegEx := TRegex.Create('\w+'); Match := RegEx.Match('One two three four'); while Match.Success do begin Memo1.Lines.Add(Match.Value); Match := Match.NextMatch; end end; Or you could save yourself two lines of code by using the static TRegEx.Match call: procedure TForm1.Button2Click(Sender: TObject); var Match: TMatch; begin Match := TRegEx.Match('One two three four', '\w+'); while Match.Success do begin Memo1.Lines.Add(Match.Value); Match := Match.NextMatch; end end; Unfortunately, due to a bug in the RegularExpressions unit, the static call doesn’t work. Depending on your exact code, you may get fewer matches or blank matches than you should, or your application may crash with an access violation. The RegularExpressions unit defines TRegEx and TMatch as records. That way you don’t have to explicitly create and destroy them. Internally, TRegEx uses TPerlRegEx to do the heavy lifting. TPerlRegEx is a class that needs to be created and destroyed like any other class. If you look at the TRegEx source code, you’ll notice that it uses an interface to destroy the TPerlRegEx instance when TRegEx goes out of scope. Interfaces are reference counted in Delphi, making them usable for automatic memory management. The bug is that TMatch and TGroupCollection also need the TPerlRegEx instance to do their work. TRegEx passes its TPerlRegEx instance to TMatch and TGroupCollection, but it does not pass the instance of the interface that is responsible for destroying TPerlRegEx. This is not a problem in our first code sample. TRegEx stays in scope until we’re done with TMatch. The interface is destroyed when Button1Click exits. In the second code sample, the static TRegEx.Match call creates a local variable of type TRegEx. This local variable goes out of scope when TRegEx.Match returns. Thus the reference count on the interface reaches zero and TPerlRegEx is destroyed when TRegEx.Match returns. When we call MatchAgain the TMatch record tries to use a TPerlRegEx instance that has already been destroyed. To fix this bug, delete or rename the two RegularExpressions.dcu files and copy RegularExpressions.pas into your source code folder. Make these changes to both the TMatch and TGroupCollection records in this unit: Declare FNotifier: IInterface; in the private section. Add the parameter ANotifier: IInterface; to the Create constructor. Assign FNotifier := ANotifier; in the constructor’s implementation. You also need to add the ANotifier: IInterface; parameter to the TMatchCollection.Create constructor. Now try to compile some code that uses the RegularExpressions unit. The compiler will flag all calls to TMatch.Create, TGroupCollection.Create and TMatchCollection.Create. Fix them by adding the ANotifier or FNotifier parameter, depending on whether ARegEx or FRegEx is being passed. With these fixes, the TPerlRegEx instance won’t be destroyed until the last TRegEx, TMatch, or TGroupCollection that uses it goes out of scope or is used with a different regular expression.

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  • Give a session on C++ AMP – here is how

    - by Daniel Moth
    Ever since presenting on C++ AMP at the AMD Fusion conference in June, then the Gamefest conference in August, and the BUILD conference in September, I've had numerous requests about my material from folks that want to re-deliver the same session. The C++ AMP session I put together has evolved over the 3 presentations to its final form that I used at BUILD, so that is the one I recommend you base yours on. Please get the slides and the recording from channel9 (I'll refer to slide numbers below). This is how I've been presenting the C++ AMP session: Context (slide 3, 04:18-08:18) Start with a demo, on my dual-GPU machine. I've been using the N-Body sample (for VS 11 Developer Preview). (slide 4) Use an nvidia slide that has additional examples of performance improvements that customers enjoy with heterogeneous computing. (slide 5) Talk a bit about the differences today between CPU and GPU hardware, leading to the fact that these will continue to co-exist and that GPUs are great for data parallel algorithms, but not much else today. One is a jack of all trades and the other is a number cruncher. (slide 6) Use the APU example from amd, as one indication that the hardware space is still in motion, emphasizing that the C++ AMP solution is a data parallel API, not a GPU API. It has a future proof design for hardware we have yet to see. (slide 7) Provide more meta-data, as blogged about when I first introduced C++ AMP. Code (slide 9-11) Introduce C++ AMP coding with a simplistic array-addition algorithm – the slides speak for themselves. (slide 12-13) index<N>, extent<N>, and grid<N>. (Slide 14-16) array<T,N>, array_view<T,N> and comparison between them. (Slide 17) parallel_for_each. (slide 18, 21) restrict. (slide 19-20) actual restrictions of restrict(direct3d) – the slides speak for themselves. (slide 22) bring it altogether with a matrix multiplication example. (slide 23-24) accelerator, and accelerator_view. (slide 26-29) Introduce tiling incl. tiled matrix multiplication [tiling probably deserves a whole session instead of 6 minutes!]. IDE (slide 34,37) Briefly touch on the concurrency visualizer. It supports GPU profiling, but enhancements specific to C++ AMP we hope will come at the Beta timeframe, which is when I'll be spending more time talking about it. (slide 35-36, 51:54-59:16) Demonstrate the GPU debugging experience in VS 11. Summary (slide 39) Re-iterate some of the points of slide 7, and add the point that the C++ AMP spec will be open for other compiler vendors to implement, even on other platforms (in fact, Microsoft is actively working on that). (slide 40) Links to content – see slide – including where all your questions should go: http://social.msdn.microsoft.com/Forums/en/parallelcppnative/threads.   "But I don't have time for a full blown session, I only need 2 (or just 1, or 3) C++ AMP slides to use in my session on related topic X" If all you want is a small number of slides, you can take some from the session above and customize them. But because I am so nice, I have created some slides for you, including talking points in the notes section. Download them here. Comments about this post by Daniel Moth welcome at the original blog.

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  • Why Apple’s New SDK Limitation is So Offensive

    - by TStewartDev
    I am not an Apple fanboy, nor have I ever been. However, I have owned a Mac, an iPod, and an iPhone in my lifetime, and for more than a decade, I have defended Apple against the untruths that the haters so enjoy spewing. I encouraged my wife to buy a MacBook when she needed a new laptop two years ago, and I often recommend them to my friends and relatives. I have proudly and happily used my first generation iPhone for nearly three years. Now, for the first time in well over ten years, I find myself ready to swear off Apple and encourage everyone I know to do the same. I was disappointed when Apple wouldn't allow native apps, but I still bought the iPhone. I've stomached their ambiguous app approval process even though it's apparent that Steve may just reject your app because he doesn't like you or feels threatened by you (I'm still lamenting the rejection of the Google Voice app). But, as a developer, I can no longer tolerate Apple's terms and the kind of totalitarian control they indicate Apple wants. In case you are not already familiar, Apple has dictated in their OS 4.0 SDK license agreement (the now infamous Section 3.3.1) that all apps developed for the iPhone must be coded in C, C++, or Objective C, and moreover, that using any cross-compiling platforms is a violation of the agreement. For those of you who aren't developers, let me try to illustrate why this angers those of us who are. Imagine you're a professional writer. You've had articles published in some journals and magazines, and you've got a couple popular books out there, too. You've got an idea for a new book, and so you take it to your publisher. Your publisher agrees that it's a good idea. "But," says the publisher, "we want to hold our books to a tighter standard so that our readers get the experience we want them to have. Therefore, from now on, all our writers may only use words from this list of the 10,000 most common English words. Furthermore, if you cite any other works or quote anyone, they must comply with that same list, or you'll have to rewrite the entire work as well in case our readers want to look up your citation." What do you do? If your work is a children's book, this probably isn't a big deal to you. If it's an autobiography, textbook, or even a novel, though, you're going to have a lot of trouble describing your content with only common words. It's going to take you longer to complete your book, too, since you'll be looking up less common words frequently to see if you can use them. You could always go to another publisher, but this one has the best ability to distribute your book. The next largest distributor can only do a quarter as much. You could abandon the project altogether, but then everyone loses. Isn't this a silly scenario? Who would put such a limitation on writers? Yet this is very much what Apple is doing. They are using their dominant position in the market to coerce developers to write their apps exclusively for the iPhone OS by making it too expensive to write for multiple platforms. It is at least a threefold attack, striking at Adobe who is set to release a compiler that lets Flash source be compiled to iPhone binaries; striking at Google whose Android platform stands the best chance at the moment of providing serious competition to the iPhone; and reinforcing their own strong position by keeping popular apps exclusively to iPhone. And while developers are already very upset about this, the sad fact is that most of us will cave and give in to Apple because consumers don't know any better. They will continue to buy Apple's toy forcing developers to play Apple's maniacal game in order to make any money, at least until Steve Jobs decides he doesn't like them or he intends to release a competing application (bye-bye OpenFeint). Apple has been kept in check on the desktop front by a very dominant Microsoft, but I'm afraid that their success with iPods, iTunes, and iPhones has created a monster that we may have to bear until it is slain by an anti-trust suit or dies with the retirement of Steve Jobs.

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  • Asynchrony in C# 5 (Part II)

    - by javarg
    This article is a continuation of the series of asynchronous features included in the new Async CTP preview for next versions of C# and VB. Check out Part I for more information. So, let’s continue with TPL Dataflow: Asynchronous functions TPL Dataflow Task based asynchronous Pattern Part II: TPL Dataflow Definition (by quote of Async CTP doc): “TPL Dataflow (TDF) is a new .NET library for building concurrent applications. It promotes actor/agent-oriented designs through primitives for in-process message passing, dataflow, and pipelining. TDF builds upon the APIs and scheduling infrastructure provided by the Task Parallel Library (TPL) in .NET 4, and integrates with the language support for asynchrony provided by C#, Visual Basic, and F#.” This means: data manipulation processed asynchronously. “TPL Dataflow is focused on providing building blocks for message passing and parallelizing CPU- and I/O-intensive applications”. Data manipulation is another hot area when designing asynchronous and parallel applications: how do you sync data access in a parallel environment? how do you avoid concurrency issues? how do you notify when data is available? how do you control how much data is waiting to be consumed? etc.  Dataflow Blocks TDF provides data and action processing blocks. Imagine having preconfigured data processing pipelines to choose from, depending on the type of behavior you want. The most basic block is the BufferBlock<T>, which provides an storage for some kind of data (instances of <T>). So, let’s review data processing blocks available. Blocks a categorized into three groups: Buffering Blocks Executor Blocks Joining Blocks Think of them as electronic circuitry components :).. 1. BufferBlock<T>: it is a FIFO (First in First Out) queue. You can Post data to it and then Receive it synchronously or asynchronously. It synchronizes data consumption for only one receiver at a time (you can have many receivers but only one will actually process it). 2. BroadcastBlock<T>: same FIFO queue for messages (instances of <T>) but link the receiving event to all consumers (it makes the data available for consumption to N number of consumers). The developer can provide a function to make a copy of the data if necessary. 3. WriteOnceBlock<T>: it stores only one value and once it’s been set, it can never be replaced or overwritten again (immutable after being set). As with BroadcastBlock<T>, all consumers can obtain a copy of the value. 4. ActionBlock<TInput>: this executor block allows us to define an operation to be executed when posting data to the queue. Thus, we must pass in a delegate/lambda when creating the block. Posting data will result in an execution of the delegate for each data in the queue. You could also specify how many parallel executions to allow (degree of parallelism). 5. TransformBlock<TInput, TOutput>: this is an executor block designed to transform each input, that is way it defines an output parameter. It ensures messages are processed and delivered in order. 6. TransformManyBlock<TInput, TOutput>: similar to TransformBlock but produces one or more outputs from each input. 7. BatchBlock<T>: combines N single items into one batch item (it buffers and batches inputs). 8. JoinBlock<T1, T2, …>: it generates tuples from all inputs (it aggregates inputs). Inputs could be of any type you want (T1, T2, etc.). 9. BatchJoinBlock<T1, T2, …>: aggregates tuples of collections. It generates collections for each type of input and then creates a tuple to contain each collection (Tuple<IList<T1>, IList<T2>>). Next time I will show some examples of usage for each TDF block. * Images taken from Microsoft’s Async CTP documentation.

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  • What's new in Servlet 3.1 ? - Java EE 7 moving forward

    - by arungupta
    Servlet 3.0 was released as part of Java EE 6 and made huge changes focused at ease-of-use. The idea was to leverage the latest language features such as annotations and generics and modernize how Servlets can be written. The web.xml was made as optional as possible. Servet 3.1 (JSR 340), scheduled to be part of Java EE 7, is an incremental release focusing on couple of key features and some clarifications in the specification. The main features of Servlet 3.1 are explained below: Non-blocking I/O - Servlet 3.0 allowed asynchronous request processing but only traditional I/O was permitted. This can restrict scalability of your applications. Non-blocking I/O allow to build scalable applications. TOTD #188 provide more details about how non-blocking I/O can be done using Servlet 3.1. HTTP protocol upgrade mechanism - Section 14.42 in the HTTP 1.1 specification (RFC 2616) defines an upgrade mechanism that allows to transition from HTTP 1.1 to some other, incompatible protocol. The capabilities and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen. After an upgrade is negotiated between the client and the server, the subsequent requests use the new chosen protocol for message exchanges. A typical example is how WebSocket protocol is upgraded from HTTP as described in Opening Handshake section of RFC 6455. The decision to upgrade is made in Servlet.service method. This is achieved by adding a new method: HttpServletRequest.upgrade and two new interfaces: javax.servlet.http.HttpUpgradeHandler and javax.servlet.http.WebConnection. TyrusHttpUpgradeHandler shows how WebSocket protocol upgrade is done in Tyrus (Reference Implementation for Java API for WebSocket). Security enhancements Applying run-as security roles to #init and #destroy methods Session fixation attack by adding HttpServletRequest.changeSessionId and a new interface HttpSessionIdListener. You can listen for any session id changes using these methods. Default security semantic for non-specified HTTP method in <security-constraint> Clarifying the semantics if a parameter is specified in the URI and payload Miscellaneous ServletResponse.reset clears any data that exists in the buffer as well as the status code, headers. In addition, Servlet 3.1 will also clears the state of calling getServletOutputStream or getWriter. ServletResponse.setCharacterEncoding: Sets the character encoding (MIME charset) of the response being sent to the client, for example, to UTF-8. Relative protocol URL can be specified in HttpServletResponse.sendRedirect. This will allow a URL to be specified without a scheme. That means instead of specifying "http://anotherhost.com/foo/bar.jsp" as a redirect address, "//anotherhost.com/foo/bar.jsp" can be specified. In this case the scheme of the corresponding request will be used. Clarification in HttpServletRequest.getPart and .getParts without multipart configuration. Clarification that ServletContainerInitializer is independent of metadata-complete and is instantiated per web application. A complete replay of What's New in Servlet 3.1: An Overview from JavaOne 2012 can be seen here (click on CON6793_mp4_6793_001 in Media). Each feature will be added to the JSR subject to EG approval. You can share your feedback to [email protected]. Here are some more references for you: Servlet 3.1 Public Review Candidate Downloads Servlet 3.1 PR Candidate Spec Servlet 3.1 PR Candidate Javadocs Servlet Specification Project JSR Expert Group Discussion Archive Java EE 7 Specification Status Several features have already been integrated in GlassFish 4 Promoted Builds. Have you tried any of them ? Here are some other Java EE 7 primers published so far: Concurrency Utilities for Java EE (JSR 236) Collaborative Whiteboard using WebSocket in GlassFish 4 (TOTD #189) Non-blocking I/O using Servlet 3.1 (TOTD #188) What's New in EJB 3.2 ? JPA 2.1 Schema Generation (TOTD #187) WebSocket Applications using Java (JSR 356) Jersey 2 in GlassFish 4 (TOTD #182) WebSocket and Java EE 7 (TOTD #181) Java API for JSON Processing (JSR 353) JMS 2.0 Early Draft (JSR 343) And of course, more on their way! Do you want to see any particular one first ?

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  • Webcast On-Demand: Building Java EE Apps That Scale

    - by jeckels
    With some awesome work by one of our architects, Randy Stafford, we recently completed a webcast on scaling Java EE apps efficiently. Did you miss it? No problem. We have a replay available on-demand for you. Just hit the '+' sign drop-down for access.Topics include: Domain object caching Service response caching Session state caching JSR-107 HotCache and more! Further, we had several interesting questions asked by our audience, and we thought we'd share a sampling of those here for you - just in case you had the same queries yourself. Enjoy! What is the largest Coherence deployment out there? We have seen deployments with over 500 JVMs in the Coherence cluster, and deployments with over 1000 JVMs using the Coherence jar file, in one system. On the management side there is an ecosystem of monitoring tools from Oracle and third parties with dashboards graphing values from Coherence's JMX instrumentation. For lifecycle management we have seen a lot of custom scripting over the years, but we've also integrated closely with WebLogic to leverage its management ecosystem for deploying Coherence-based applications and managing process life cycles. That integration introduces a new Java EE archive type, the Grid Archive or GAR, which embeds in an EAR and can be seen by a WAR in WebLogic. That integration also doesn't require any extra WebLogic licensing if Coherence is licensed. How is Coherence different from a NoSQL Database like MongoDB? Coherence can be considered a NoSQL technology. It pre-dates the NoSQL movement, having been first released in 2001 whereas the term "NoSQL" was coined in 2009. Coherence has a key-value data model primarily but can also be used for document data models. Coherence manages data in memory currently, though disk persistence is in a future release currently in beta testing. Where the data is managed yields a few differences from the most well-known NoSQL products: access latency is faster with Coherence, though well-known NoSQL databases can manage more data. Coherence also has features that well-known NoSQL database lack, such as grid computing, eventing, and data source integration. Finally Coherence has had 15 years of maturation and hardening from usage in mission-critical systems across a variety of industries, particularly financial services. Can I use Coherence for local caching? Yes, you get additional features beyond just a java.util.Map: you get expiration capabilities, size-limitation capabilities, eventing capabilites, etc. Are there APIs available for GoldenGate HotCache? It's mostly a black box. You configure it, and it just puts objects into your caches. However you can treat it as a glass box, and use Coherence event interceptors to enhance its behavior - and there are use cases for that. Are Coherence caches updated transactionally? Coherence provides several mechanisms for concurrency control. If a project insists on full-blown JTA / XA distributed transactions, Coherence caches can participate as resources. But nobody does that because it's a performance and scalability anti-pattern. At finer granularity, Coherence guarantees strict ordering of all operations (reads and writes) against a single cache key if the operations are done using Coherence's "EntryProcessor" feature. And Coherence has a unique feature called "partition-level transactions" which guarantees atomic writes of multiple cache entries (even in different caches) without requiring JTA / XA distributed transaction semantics.

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  • Random servers in Citrix servers suddenly bluescreens (mostly 0x0000008e and 0x0000007e)

    - by Rasmus Rask
    I'm responsible for a Citrix Presentation Server 4.5 farm. Starting Friday 30. November, my servers started to crash randomly. So far we've experienced 80 crashes, so it's obviously becoming an increasingly big problem for us. I have 12+ years experience with IT, so I know the difference between 0 and 1, but I have a hard time cracking this. We've rolled back any recent changes I can think of for different groups of servers, but all groups still seem to crash. I don't have the skills to interpret the memory dumps to find the culprit. Has anyone encountered the same or a similar problem? - might be a generic Windows issue Other than executing "analyze -v" in WinDbg, how do I work my way through the memory dumps to see what actually triggered the BSOD? Any suggested steps in getting to the bottom of this? Any help is greatly appreciated. I can also provide links to kernel memory dumps or WinDbg output if necessary. Thanks! Problem description The majority of the STOP errors we encounter are: 0x0000008e KERNEL_MODE_EXCEPTION_NOT_HANDLED (50%) 0x0000007e SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (26%) 0x00000050 PAGE_FAULT_IN_NONPAGED_AREA (21%) We also see a few 0x0000000a IRQL_NOT_LESS_OR_EQUAL (3%). For both 0x0000008e and 0x0000007e bug checks, the exception code is 0xc0000005 (Access Violation). When opening dump files in WinDbg, most details are exactly the same, for all the 0x0000008e and 0x0000007e bug checks respectively: 0x0000008e Exception address: 0x808bc9e3 Trap frame: [varies] FAILURE_BUCKET_ID: 0x8E_nt!HvpGetCellMapped+97 Probably Caused by (IMAGE_NAME): ntkrpamp.exe 0x0000007e Exception address: 0x808369b6 Exception record address: 0xf70d3be0 Context record address: 0xf70d38dc FAILURE_BUCKET_ID: 0x7E_nt!MmPurgeSection+14 Probably Caused by: memory_corruption About 30% of the crashes happens between 17:00 and 19:00, which leads me to believe this tend to happen more often during logoffs. But then again, only ~15% occurs between 15:00 and 17:00. Summary of farm Citrix Presentation Server 4.5 R06 on Windows Server 2003 R2 SP2 All high priority patches, at least as of October installed Virtualized using VMWare ESX/vSphere 4.1 on HP Proliant BL460c G6 blade servers About 53 Presentation Servers in production, divided into three silos - only one of which, the largest, is affected 2 vCPU's (5 GHz reserved), 8 GB RAM (all reserved) for each Presentation Server Plenty of free disk space Very few printer drivers - automated deletion of non-approved drivers every night ~1.000 peak concurrent users, which is reached at around 10:30 (on weekdays) Number of sessions steadily decline between 15:00 and 19:00 to ~230

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  • Stop squid caching 302 and 307 with deny_info

    - by 0xception
    TLDR: 302, 307 and Error pages are being cached. Need to force a refresh of the content. Long version: I've setup a very minimal squid instance running on a gateway which shouldn't not cache ANYTHING but needs to be solely used as a domain based web filter. I'm using another application which redirects un-authenticated users to the proxy which then uses the deny_info option redirects any non-whitelisted request to the login page. After the user has authenticated the firewall rule gets placed so they no longer get sent to the proxy. The problem is that when a user hits a website (xkcd.com) they are unauthenticated so they get redirected via the firewall: iptables -A unknown-user -t nat -p tcp --dport 80 -j REDIRECT --to-port 39135 to the proxy at this point squid redirects the user to the login page using a 302 (i've also tried 307, and i've also make sure the headers are set to no-cache and/or no-store for Cache-Control and Pragma). Then when the user logs into the system they get firewall rule which no longer directs them to the squid proxy. But if they go to xkcd.com again they will have the original redirection page cached and will once again get the login page. Any idea how to force these redirects to NOT be cached by the browser? Perhaps this is a problem w/ the browsers and not squid, but not sure how to get around it. Full squid config below. # # Recommended minimum configuration: # acl manager proto cache_object acl localhost src 127.0.0.1/32 ::1 acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1 acl localnet src 192.168.182.0/23 # RFC1918 possible internal network acl localnet src fc00::/7 # RFC 4193 local private network range acl localnet src fe80::/10 # RFC 4291 link-local (directly plugged) machines acl https port 443 acl http port 80 acl CONNECT method CONNECT # # Disable Cache # cache deny all via off negative_ttl 0 seconds refresh_all_ims on #error_default_language en # Allow manager access only from localhost http_access allow manager localhost http_access deny manager # Deny access to anything other then http http_access deny !http # Deny CONNECT to other than secure SSL ports http_access deny CONNECT !https visible_hostname gate.ovatn.net # Disable memory pooling memory_pools off # Never use neigh cache objects for cgi-bin scripts hierarchy_stoplist cgi-bin ? # # URL rewrite Test Settings # #acl whitelist dstdomain "/etc/squid/domains-pre.lst" #url_rewrite_program /usr/lib/squid/redirector #url_rewrite_access allow !whitelist #url_rewrite_children 5 startup=0 idle=1 concurrency=0 #http_access allow all # # Deny Info Error Test # acl whitelist dstdomain "/etc/squid/domains-pre.lst" deny_info http://login.domain.com/ whitelist #deny_info ERR_ACCESS_DENIED whitelist http_access deny !whitelist http_access allow whitelist http_port 39135 transparent ## Debug Values access_log /var/log/squid/access-pre.log cache_log /var/log/squid/cache-pre.log # Production Values #access_log /dev/null #cache_log /dev/null # Set PID file pid_filename /var/run/gatekeeper-pre.pid SOLUTION: I believe I might have found a solution to this. After days and days trying to figure it out, only through a random stumble I found client_persistent_connections off server_persistent_connections off This did the trick. So it wasn't so much cache as it was a single persistent connection messing things up. W000T!

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  • DB2 Integrity Checks and Exception Tables

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

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  • SQL SERVER – Simple Example of Snapshot Isolation – Reduce the Blocking Transactions

    - by pinaldave
    To learn any technology and move to a more advanced level, it is very important to understand the fundamentals of the subject first. Today, we will be talking about something which has been quite introduced a long time ago but not properly explored when it comes to the isolation level. Snapshot Isolation was introduced in SQL Server in 2005. However, the reality is that there are still many software shops which are using the SQL Server 2000, and therefore cannot be able to maintain the Snapshot Isolation. Many software shops have upgraded to the later version of the SQL Server, but their respective developers have not spend enough time to upgrade themselves with the latest technology. “It works!” is a very common answer of many when they are asked about utilizing the new technology, instead of backward compatibility commands. In one of the recent consultation project, I had same experience when developers have “heard about it” but have no idea about snapshot isolation. They were thinking it is the same as Snapshot Replication – which is plain wrong. This is the same demo I am including here which I have created for them. In Snapshot Isolation, the updated row versions for each transaction are maintained in TempDB. Once a transaction has begun, it ignores all the newer rows inserted or updated in the table. Let us examine this example which shows the simple demonstration. This transaction works on optimistic concurrency model. Since reading a certain transaction does not block writing transaction, it also does not block the reading transaction, which reduced the blocking. First, enable database to work with Snapshot Isolation. Additionally, check the existing values in the table from HumanResources.Shift. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO Now, we will need two different sessions to prove this example. First Session: Set Transaction level isolation to snapshot and begin the transaction. Update the column “ModifiedDate” to today’s date. -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO Please note that we have not yet been committed to the transaction. Now, open the second session and run the following “SELECT” statement. Then, check the values of the table. Please pay attention on setting the Isolation level for the second one as “Snapshot” at the same time when we already start the transaction using BEGIN TRAN. -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values in the table are still original values. They have not been modified yet. Once again, go back to session 1 and begin the transaction. -- Session 1 COMMIT After that, go back to Session 2 and see the values of the table. -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values are yet not changed and they are still the same old values which were there right in the beginning of the session. Now, let us commit the transaction in the session 2. Once committed, run the same SELECT statement once more and see what the result is. -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that it now reflects the new updated value. I hope that this example is clear enough as it would give you good idea how the Snapshot Isolation level works. There is much more to write about an extra level, READ_COMMITTED_SNAPSHOT, which we will be discussing in another post soon. If you wish to use this transaction’s Isolation level in your production database, I would appreciate your comments about their performance on your servers. I have included here the complete script used in this example for your quick reference. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 COMMIT -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Transaction Isolation

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  • SQL SERVER – Simple Example of Snapshot Isolation – Reduce the Blocking Transactions

    - by pinaldave
    To learn any technology and move to a more advanced level, it is very important to understand the fundamentals of the subject first. Today, we will be talking about something which has been quite introduced a long time ago but not properly explored when it comes to the isolation level. Snapshot Isolation was introduced in SQL Server in 2005. However, the reality is that there are still many software shops which are using the SQL Server 2000, and therefore cannot be able to maintain the Snapshot Isolation. Many software shops have upgraded to the later version of the SQL Server, but their respective developers have not spend enough time to upgrade themselves with the latest technology. “It works!” is a very common answer of many when they are asked about utilizing the new technology, instead of backward compatibility commands. In one of the recent consultation project, I had same experience when developers have “heard about it” but have no idea about snapshot isolation. They were thinking it is the same as Snapshot Replication – which is plain wrong. This is the same demo I am including here which I have created for them. In Snapshot Isolation, the updated row versions for each transaction are maintained in TempDB. Once a transaction has begun, it ignores all the newer rows inserted or updated in the table. Let us examine this example which shows the simple demonstration. This transaction works on optimistic concurrency model. Since reading a certain transaction does not block writing transaction, it also does not block the reading transaction, which reduced the blocking. First, enable database to work with Snapshot Isolation. Additionally, check the existing values in the table from HumanResources.Shift. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO Now, we will need two different sessions to prove this example. First Session: Set Transaction level isolation to snapshot and begin the transaction. Update the column “ModifiedDate” to today’s date. -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO Please note that we have not yet been committed to the transaction. Now, open the second session and run the following “SELECT” statement. Then, check the values of the table. Please pay attention on setting the Isolation level for the second one as “Snapshot” at the same time when we already start the transaction using BEGIN TRAN. -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values in the table are still original values. They have not been modified yet. Once again, go back to session 1 and begin the transaction. -- Session 1 COMMIT After that, go back to Session 2 and see the values of the table. -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that the values are yet not changed and they are still the same old values which were there right in the beginning of the session. Now, let us commit the transaction in the session 2. Once committed, run the same SELECT statement once more and see what the result is. -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO You will notice that it now reflects the new updated value. I hope that this example is clear enough as it would give you good idea how the Snapshot Isolation level works. There is much more to write about an extra level, READ_COMMITTED_SNAPSHOT, which we will be discussing in another post soon. If you wish to use this transaction’s Isolation level in your production database, I would appreciate your comments about their performance on your servers. I have included here the complete script used in this example for your quick reference. ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON GO SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN UPDATE HumanResources.Shift SET ModifiedDate = GETDATE() GO -- Session 2 SET TRANSACTION ISOLATION LEVEL SNAPSHOT BEGIN TRAN SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 1 COMMIT -- Session 2 SELECT ModifiedDate FROM HumanResources.Shift GO -- Session 2 COMMIT SELECT ModifiedDate FROM HumanResources.Shift GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Transaction Isolation

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  • An Alphabet of Eponymous Aphorisms, Programming Paradigms, Software Sayings, Annoying Alliteration

    - by Brian Schroer
    Malcolm Anderson blogged about “Einstein’s Razor” yesterday, which reminded me of my favorite software development “law”, the name of which I can never remember. It took much Wikipedia-ing to find it (Hofstadter’s Law – see below), but along the way I compiled the following list: Amara’s Law: We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run. Brook’s Law: Adding manpower to a late software project makes it later. Clarke’s Third Law: Any sufficiently advanced technology is indistinguishable from magic. Law of Demeter: Each unit should only talk to its friends; don't talk to strangers. Einstein’s Razor: “Make things as simple as possible, but not simpler” is the popular paraphrase, but what he actually said was “It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience”, an overly complicated quote which is an obvious violation of Einstein’s Razor. (You can tell by looking at a picture of Einstein that the dude was hardly an expert on razors or other grooming apparati.) Finagle's Law of Dynamic Negatives: Anything that can go wrong, will—at the worst possible moment. - O'Toole's Corollary: The perversity of the Universe tends towards a maximum. Greenspun's Tenth Rule: Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp. (Morris’s Corollary: “…including Common Lisp”) Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law. Issawi’s Omelet Analogy: One cannot make an omelet without breaking eggs - but it is amazing how many eggs one can break without making a decent omelet. Jackson’s Rules of Optimization: Rule 1: Don't do it. Rule 2 (for experts only): Don't do it yet. Kaner’s Caveat: A program which perfectly meets a lousy specification is a lousy program. Liskov Substitution Principle (paraphrased): Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it Mason’s Maxim: Since human beings themselves are not fully debugged yet, there will be bugs in your code no matter what you do. Nils-Peter Nelson’s Nil I/O Rule: The fastest I/O is no I/O.    Occam's Razor: The simplest explanation is usually the correct one. Parkinson’s Law: Work expands so as to fill the time available for its completion. Quentin Tarantino’s Pie Principle: “…you want to go home have a drink and go and eat pie and talk about it.” (OK, he was talking about movies, not software, but I couldn’t find a “Q” quote about software. And wouldn’t it be cool to write a program so great that the users want to eat pie and talk about it?) Raymond’s Rule: Computer science education cannot make anybody an expert programmer any more than studying brushes and pigment can make somebody an expert painter.  Sowa's Law of Standards: Whenever a major organization develops a new system as an official standard for X, the primary result is the widespread adoption of some simpler system as a de facto standard for X. Turing’s Tenet: We shall do a much better programming job, provided we approach the task with a full appreciation of its tremendous difficulty, provided that we respect the intrinsic limitations of the human mind and approach the task as very humble programmers.  Udi Dahan’s Race Condition Rule: If you think you have a race condition, you don’t understand the domain well enough. These rules didn’t exist in the age of paper, there is no reason for them to exist in the age of computers. When you have race conditions, go back to the business and find out actual rules. Van Vleck’s Kvetching: We know about as much about software quality problems as they knew about the Black Plague in the 1600s. We've seen the victims' agonies and helped burn the corpses. We don't know what causes it; we don't really know if there is only one disease. We just suffer -- and keep pouring our sewage into our water supply. Wheeler’s Law: All problems in computer science can be solved by another level of indirection... Except for the problem of too many layers of indirection. Wheeler also said “Compatibility means deliberately repeating other people's mistakes.”. The Wrong Road Rule of Mr. X (anonymous): No matter how far down the wrong road you've gone, turn back. Yourdon’s Rule of Two Feet: If you think your management doesn't know what it's doing or that your organisation turns out low-quality software crap that embarrasses you, then leave. Zawinski's Law of Software Envelopment: Every program attempts to expand until it can read mail. Zawinski is also responsible for “Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems.” He once commented about X Windows widget toolkits: “Using these toolkits is like trying to make a bookshelf out of mashed potatoes.”

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  • Verizon Wireless Supports its Mission-Critical Employee Portal with MySQL

    - by Bertrand Matthelié
    Normal 0 false false false EN-US X-NONE X-NONE /* 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:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Cambria","serif"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;} Verizon Wireless, the #1 mobile carrier in the United States, operates the nation’s largest 3G and 4G LTE network, with the most subscribers (109 millions) and the highest revenue ($70.2 Billion in 2011). Verizon Wireless built the first wide-area wireless broadband network and delivered the first wireless consumer 3G multimedia service in the US, and offers global voice and data services in more than 200 destinations around the world. To support 4.2 million daily wireless transactions and 493,000 calls and emails transactions produced by 94.2 million retail customers, Verizon Wireless employs over 78,000 employees with area headquarters across the United States. The Business Challenge Seeing the stupendous rise in social media, video streaming, live broadcasting…etc which redefined the scope of technology, Verizon Wireless, as a technology savvy company, wanted to provide a platform to its employees where they could network socially, view and host microsites, stream live videos, blog and provide the latest news. The IT team at Verizon Wireless had abundant experience with various technology platforms to support the huge number of applications in the company. However, open-source products weren’t yet widely used in the organization and the team had the ambition to adopt such technologies and see if the architecture could meet Verizon Wireless’ rigid requirements. After evaluating a few solutions, the IT team decided to use the LAMP stack for Vzweb, its mission-critical, 24x7 employee portal, with Drupal as the front end and MySQL on Linux as the backend, and for a few other internal websites also on MySQL. The MySQL Solution Verizon Wireless started to support its employee portal, Vzweb, its online streaming website, Vztube, and internal wiki pages, Vzwiki, with MySQL 5.1 in 2010. Vzweb is the main internal communication channel for Verizon Wireless, while Vztube hosts important company-wide webcasts regularly for executive-level announcements, so both channels have to be live and accessible all the time for its 78,000 employees across the United States. However during the initial deployment of the MySQL based Intranet, the application experienced performance issues. High connection spikes occurred causing slow user response time, and the IT team applied workarounds to continue the service. A number of key performance indexes (KPI) for the infrastructure were identified and the operational framework redesigned to support a more robust website and conform to the 99.985% uptime SLA (Service-Level Agreement). The MySQL DBA team made a series of upgrades in MySQL: Step 1: Moved from MyISAM to InnoDB storage engine in 2010 Step 2: Upgraded to the latest MySQL 5.1.54 release in 2010 Step 3: Upgraded from MySQL 5.1 to the latest GA release MySQL 5.5 in 2011, and leveraging MySQL Thread Pool as part of MySQL Enterprise Edition to scale better After making those changes, the team saw a much better response time during high concurrency use cases, and achieved an amazing performance improvement of 1400%! In January 2011, Verizon CEO, Ivan Seidenberg, announced the iPhone launch during the opening keynote at Consumer Electronic Show (CES) in Las Vegas, and that presentation was streamed live to its 78,000 employees. The event was broadcasted flawlessly with MySQL as the database. Later in 2011, Hurricane Irene attacked the East Coast of United States and caused major life and financial damages. During the hurricane, the team directed more traffic to its west coast data center to avoid potential infrastructure damage in the East Coast. Such transition was executed smoothly and even though the geographical distance became longer for the East Coast users, there was no impact in the performance of Vzweb and Vztube, and the SLA goal was achieved. “MySQL is the key component of Verizon Wireless’ mission-critical employee portal application,” said Shivinder Singh, senior DBA at Verizon Wireless. “We achieved 1400% performance improvement by moving from the MyISAM storage engine to InnoDB, upgrading to the latest GA release MySQL 5.5, and using the MySQL Thread Pool to support high concurrent user connections. MySQL has become part of our IT infrastructure, on which potentially more future applications will be built.” To learn more about MySQL Enterprise Edition, Get our Product Guide.

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  • Why lock-free data structures just aren't lock-free enough

    - by Alex.Davies
    Today's post will explore why the current ways to communicate between threads don't scale, and show you a possible way to build scalable parallel programming on top of shared memory. The problem with shared memory Soon, we will have dozens, hundreds and then millions of cores in our computers. It's inevitable, because individual cores just can't get much faster. At some point, that's going to mean that we have to rethink our architecture entirely, as millions of cores can't all access a shared memory space efficiently. But millions of cores are still a long way off, and in the meantime we'll see machines with dozens of cores, struggling with shared memory. Alex's tip: The best way for an application to make use of that increasing parallel power is to use a concurrency model like actors, that deals with synchronisation issues for you. Then, the maintainer of the actors framework can find the most efficient way to coordinate access to shared memory to allow your actors to pass messages to each other efficiently. At the moment, NAct uses the .NET thread pool and a few locks to marshal messages. It works well on dual and quad core machines, but it won't scale to more cores. Every time we use a lock, our core performs an atomic memory operation (eg. CAS) on a cell of memory representing the lock, so it's sure that no other core can possibly have that lock. This is very fast when the lock isn't contended, but we need to notify all the other cores, in case they held the cell of memory in a cache. As the number of cores increases, the total cost of a lock increases linearly. A lot of work has been done on "lock-free" data structures, which avoid locks by using atomic memory operations directly. These give fairly dramatic performance improvements, particularly on systems with a few (2 to 4) cores. The .NET 4 concurrent collections in System.Collections.Concurrent are mostly lock-free. However, lock-free data structures still don't scale indefinitely, because any use of an atomic memory operation still involves every core in the system. A sync-free data structure Some concurrent data structures are possible to write in a completely synchronization-free way, without using any atomic memory operations. One useful example is a single producer, single consumer (SPSC) queue. It's easy to write a sync-free fixed size SPSC queue using a circular buffer*. Slightly trickier is a queue that grows as needed. You can use a linked list to represent the queue, but if you leave the nodes to be garbage collected once you're done with them, the GC will need to involve all the cores in collecting the finished nodes. Instead, I've implemented a proof of concept inspired by this intel article which reuses the nodes by putting them in a second queue to send back to the producer. * In all these cases, you need to use memory barriers correctly, but these are local to a core, so don't have the same scalability problems as atomic memory operations. Performance tests I tried benchmarking my SPSC queue against the .NET ConcurrentQueue, and against a standard Queue protected by locks. In some ways, this isn't a fair comparison, because both of these support multiple producers and multiple consumers, but I'll come to that later. I started on my dual-core laptop, running a simple test that had one thread producing 64 bit integers, and another consuming them, to measure the pure overhead of the queue. So, nothing very interesting here. Both concurrent collections perform better than the lock-based one as expected, but there's not a lot to choose between the ConcurrentQueue and my SPSC queue. I was a little disappointed, but then, the .NET Framework team spent a lot longer optimising it than I did. So I dug out a more powerful machine that Red Gate's DBA tools team had been using for testing. It is a 6 core Intel i7 machine with hyperthreading, adding up to 12 logical cores. Now the results get more interesting. As I increased the number of producer-consumer pairs to 6 (to saturate all 12 logical cores), the locking approach was slow, and got even slower, as you'd expect. What I didn't expect to be so clear was the drop-off in performance of the lock-free ConcurrentQueue. I could see the machine only using about 20% of available CPU cycles when it should have been saturated. My interpretation is that as all the cores used atomic memory operations to safely access the queue, they ended up spending most of the time notifying each other about cache lines that need invalidating. The sync-free approach scaled perfectly, despite still working via shared memory, which after all, should still be a bottleneck. I can't quite believe that the results are so clear, so if you can think of any other effects that might cause them, please comment! Obviously, this benchmark isn't realistic because we're only measuring the overhead of the queue. Any real workload, even on a machine with 12 cores, would dwarf the overhead, and there'd be no point worrying about this effect. But would that be true on a machine with 100 cores? Still to be solved. The trouble is, you can't build many concurrent algorithms using only an SPSC queue to communicate. In particular, I can't see a way to build something as general purpose as actors on top of just SPSC queues. Fundamentally, an actor needs to be able to receive messages from multiple other actors, which seems to need an MPSC queue. I've been thinking about ways to build a sync-free MPSC queue out of multiple SPSC queues and some kind of sign-up mechanism. Hopefully I'll have something to tell you about soon, but leave a comment if you have any ideas.

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  • How do I prove or disprove "god" objects are wrong?

    - by honestduane
    Problem Summary: Long story short, I inherited a code base and an development team I am not allowed to replace and the use of God Objects is a big issue. Going forward, I want to have us re-factor things but I am getting push-back from the teams who want to do everything with God Objects "because its easier" and this means I would not be allowed to re-factor. I pushed back citing my years of dev experience, that I'm the new boss who was hired to know these things, etc, and so did the third party offshore companies account sales rep, and this is now at the executive level and my meeting is tomorrow and I want to go in with a lot of technical ammo to advocate best practices because I feel it will be cheaper in the long run (And I personally feel that is what the third party is worried about) for the company. My issue is from a technical level, I know its good long term but I'm having trouble with the ultra short term and 6 months term, and while its something I "know" I cant prove it with references and cited resources outside of one person (Robert C. Martin, aka Uncle Bob), as that is what I am being asked to do as I have been told having data from one person and only one person (Robert C Martin) is not good enough of an argument. Question: What are some resources I can cite directly (Title, year published, page number, quote) by well known experts in the field that explicitly say this use of "God" Objects/Classes/Systems is bad (or good, since we are looking for the most technically valid solution)? Research I have already done: I have a number of books here and I have searched their indexes for the use of the words "god object" and "god class". I found that oddly its almost never used and the copy of the GoF book I have for example, never uses it (At least according to the index in front of me) but I have found it in 2 books per the below, but I want more I can use. I checked the Wikipedia page for "God Object" and its currently a stub with little reference links so although I personally agree with that it says, It doesn't have much I can use in an environment where personal experience is not considered valid. The book cited is also considered too old to be valid by the people I am debating these technical points with as the argument they are making is that "it was once thought to be bad but nobody could prove it, and now modern software says "god" objects are good to use". I personally believe that this statement is incorrect, but I want to prove the truth, whatever it is. In Robert C Martin's "Agile Principles, Patterns, and Practices in C#" (ISBN: 0-13-185725-8, hardcover) where on page 266 it states "Everybody knows that god classes are a bad idea. We don't want to concentrate all the intelligence of a system into a single object or a single function. One of the goals of OOD is the partitioning and distribution of behavior into many classes and many function." -- And then goes on to say sometimes its better to use God Classes anyway sometimes (Citing micro-controllers as an example). In Robert C Martin's "Clean Code: A Handbook of Agile Software Craftsmanship" page 136 (And only this page) talks about the "God class" and calls it out as a prime example of a violation of the "classes should be small" rule he uses to promote the Single Responsibility Principle" starting on on page 138. The problem I have is all my references and citations come from the same person (Robert C. Martin), and am from the same single person/source. I am being told that because he is just one guy, my desire to not use "God Classes" is invalid and not accepted as a standard best practice in the software industry. Is this true? Am I doing things wrong from a technical perspective by trying to keep to the teaching of Uncle Bob? God Objects and Object Oriented Programming and Design: The more I think of this the more I think this is more something you learn when you study OOP and its never explicitly called out; Its implicit to good design is my thinking (Feel free to correct me, please, as I want to learn), The problem is I "know" this, but but not everybody does, so in this case its not considered a valid argument because I am effectively calling it out as universal truth when in fact most people are statistically ignorant of it since statistically most people are not programmers. Conclusion: I am at a loss on what to search for to get the best additional results to cite, since they are making a technical claim and I want to know the truth and be able to prove it with citations like a real engineer/scientist, even if I am biased against god objects due to my personal experience with code that used them. Any assistance or citations would be deeply appreciated.

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  • C# async and actors

    - by Alex.Davies
    If you read my last post about async, you might be wondering what drove me to write such odd code in the first place. The short answer is that .NET Demon is written using NAct Actors. Actors are an old idea, which I believe deserve a renaissance under C# 5. The idea is to isolate each stateful object so that only one thread has access to its state at any point in time. That much should be familiar, it's equivalent to traditional lock-based synchronization. The different part is that actors pass "messages" to each other rather than calling a method and waiting for it to return. By doing that, each thread can only ever be holding one lock. This completely eliminates deadlocks, my least favourite concurrency problem. Most people who use actors take this quite literally, and there are plenty of frameworks which help you to create message classes and loops which can receive the messages, inspect what type of message they are, and process them accordingly. But I write C# for a reason. Do I really have to choose between using actors and everything I love about object orientation in C#? Type safety Interfaces Inheritance Generics As it turns out, no. You don't need to choose between messages and method calls. A method call makes a perfectly good message, as long as you don't wait for it to return. This is where asynchonous methods come in. I have used NAct for a while to wrap my objects in a proxy layer. As long as I followed the rule that methods must always return void, NAct queued up the call for later, and immediately released my thread. When I needed to get information out of other actors, I could use EventHandlers and callbacks (continuation passing style, for any CS geeks reading), and NAct would call me back in my isolated thread without blocking the actor that raised the event. Using callbacks looks horrible though. To remind you: m_BuildControl.FilterEnabledForBuilding(    projects,    enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(        enabledProjects,             newDirtyProjects =             {                 ....... Which is why I'm really happy that NAct now supports async methods. Now, methods are allowed to return Task rather than just void. I can await those methods, and C# 5 will turn the rest of my method into a continuation for me. NAct will run the other method in the other actor's context, but will make sure that when my method resumes, we're back in my context. Neither actor was ever blocked waiting for the other one. Apart from when they were actually busy doing something, they were responsive to concurrent messages from other sources. To be fair, you could use async methods with lock statements to achieve exactly the same thing, but it's ugly. Here's a realistic example of an object that has a queue of data that gets passed to another object to be processed: class QueueProcessor {    private readonly ItemProcessor m_ItemProcessor = ...     private readonly object m_Sync = new object();    private Queue<object> m_DataQueue = ...    private List<object> m_Results = ...     public async Task ProcessOne() {         object data = null;         lock (m_Sync)         {             data = m_DataQueue.Dequeue();         }         var processedData = await m_ItemProcessor.ProcessData(data); lock (m_Sync)         {             m_Results.Add(processedData);         }     } } We needed to write two lock blocks, one to get the data to process, one to store the result. The worrying part is how easily we could have forgotten one of the locks. Compare that to the version using NAct: class QueueProcessorActor : IActor { private readonly ItemProcessor m_ItemProcessor = ... private Queue<object> m_DataQueue = ... private List<object> m_Results = ... public async Task ProcessOne()     {         // We are an actor, it's always thread-safe to access our private fields         var data = m_DataQueue.Dequeue();         var processedData = await m_ItemProcessor.ProcessData(data);         m_Results.Add(processedData);     } } You don't have to explicitly lock anywhere, NAct ensures that your code will only ever run on one thread, because it's an actor. Either way, async is definitely better than traditional synchronous code. Here's a diagram of what a typical synchronous implementation might do: The left side shows what is running on the thread that has the lock required to access the QueueProcessor's data. The red section is where that lock is held, but doesn't need to be. Contrast that with the async version we wrote above: Here, the lock is released in the middle. The QueueProcessor is free to do something else. Most importantly, even if the ItemProcessor sometimes calls the QueueProcessor, they can never deadlock waiting for each other. So I thoroughly recommend you use async for all code that has to wait a while for things. And if you find yourself writing lots of lock statements, think about using actors as well. Using actors and async together really takes the misery out of concurrent programming.

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