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• SQL SERVER – Video – Beginning Performance Tuning with SQL Server Execution Plan

  - by pinaldave

  Traveling can be most interesting or most exhausting experience. However, traveling is always the most enlightening experience one can have. While going to long journey one has to prepare a lot of things. Pack necessary travel gears, clothes and medicines. However, the most essential part of travel is the journey to the destination. There are many variations one prefer but the ultimate goal is to have a delightful experience during the journey. Here is the video available which explains how to begin with SQL Server Execution plans. Performance Tuning is a Journey Performance tuning is just like a long journey. The goal of performance tuning is efficient and least resources consuming query execution with accurate results. Just as maps are the most essential aspect of performance tuning the same way, execution plans are essentially maps for SQL Server to reach to the resultset. The goal of the execution plan is to find the most efficient path which translates the least usage of the resources (CPU, memory, IO etc). Execution Plans are like Maps When online maps were invented (e.g. Bing, Google, Mapquests etc) initially it was not possible to customize them. They were given a single route to reach to the destination. As time evolved now it is possible to give various hints to the maps, for example ‘via public transport’, ‘walking’, ‘fastest route’, ‘shortest route’, ‘avoid highway’. There are places where we manually drag the route and make it appropriate to our needs. The same situation is with SQL Server Execution Plans, if we want to tune the queries, we need to understand the execution plans and execution plans internals. We need to understand the smallest details which relate to execution plan when we our destination is optimal queries. Understanding Execution Plans The biggest challenge with maps are figuring out the optimal path. The same way the  most common challenge with execution plans is where to start from and which precise route to take. Here is a quick list of the frequently asked questions related to execution plans: Should I read the execution plans from bottoms up or top down? Is execution plans are left to right or right to left? What is the relational between actual execution plan and estimated execution plan? When I mouse over operator I see CPU and IO but not memory, why? Sometime I ran the query multiple times and I get different execution plan, why? How to cache the query execution plan and data? I created an optimal index but the query is not using it. What should I change – query, index or provide hints? What are the tools available which helps quickly to debug performance problems? Etc… Honestly the list is quite a big and humanly impossible to write everything in the words. SQL Server Performance:  Introduction to Query Tuning My friend Vinod Kumar and I have created for the same a video learning course for beginning performance tuning. We have covered plethora of the subject in the course. Here is the quick list of the same: Execution Plan Basics Essential Indexing Techniques Query Design for Performance Performance Tuning Tools Tips and Tricks Checklist: Performance Tuning We believe we have covered a lot in this four hour course and we encourage you to go over the video course if you are interested in Beginning SQL Server Performance Tuning and Query Tuning. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Execution Plan

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• SQL SERVER – CXPACKET – Parallelism – Advanced Solution – Wait Type – Day 7 of 28

  - by pinaldave

  Earlier we discussed about the what is the common solution to solve the issue with CXPACKET wait time. Today I am going to talk about few of the other suggestions which can help to reduce the CXPACKET wait. If you are going to suggest that I should focus on MAXDOP and COST THRESHOLD – I totally agree. I have covered them in details in yesterday’s blog post. Today we are going to discuss few other way CXPACKET can be reduced. Potential Reasons: If data is heavily skewed, there are chances that query optimizer may estimate the correct amount of the data leading to assign fewer thread to query. This can easily lead to uneven workload on threads and may create CXPAKCET wait. While retrieving the data one of the thread face IO, Memory or CPU bottleneck and have to wait to get those resources to execute its tasks, may create CXPACKET wait as well. Data which is retrieved is on different speed IO Subsystem. (This is not common and hardly possible but there are chances). Higher fragmentations in some area of the table can lead less data per page. This may lead to CXPACKET wait. As I said the reasons here mentioned are not the major cause of the CXPACKET wait but any kind of scenario can create the probable wait time. Best Practices to Reduce CXPACKET wait: Refer earlier article regarding MAXDOP and Cost Threshold. De-fragmentation of Index can help as more data can be obtained per page. (Assuming close to 100 fill-factor) If data is on multiple files which are on multiple similar speed physical drive, the CXPACKET wait may reduce. Keep the statistics updated, as this will give better estimate to query optimizer when assigning threads and dividing the data among available threads. Updating statistics can significantly improve the strength of the query optimizer to render proper execution plan. This may overall affect the parallelism process in positive way. Bad Practice: In one of the recent consultancy project, when I was called in I noticed that one of the ‘experienced’ DBA noticed higher CXPACKET wait and to reduce them, he has increased the worker threads. The reality was increasing worker thread has lead to many other issues. With more number of the threads, more amount of memory was used leading memory pressure. As there were more threads CPU scheduler faced higher ‘Context Switching’ leading further degrading performance. When I explained all these to ‘experienced’ DBA he suggested that now we should reduce the number of threads. Not really! Lower number of the threads may create heavy stalling for parallel queries. I suggest NOT to touch the setting of number of the threads when dealing with CXPACKET wait. Read all the post in the Wait Types and Queue series. Note: The information presented here is from my experience and I no way claim it to be accurate. I suggest reading book on-line for further clarification. All the discussion of Wait Stats over here is generic and it varies by system to system. You are recommended to test this on development server before implementing to production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: DMV, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• RPi and Java Embedded GPIO: Writing Java code to blink LED

  - by hinkmond

  So, you've followed the previous steps to install Java Embedded on your Raspberry Pi ?, you went to Fry's and picked up some jumper wires, LEDs, and resistors ?, you hooked up the wires, LED, and resistor the the correct pins ?, and now you want to start programming in Java on your RPi? Yes? ???????! OK, then... Here we go. You can use the following source code to blink your first LED on your RPi using Java. In the code you can see that I'm not using any complicated gpio libraries like wiringpi or pi4j, and I'm not doing any low-level pin manipulation like you can in C. And, I'm not using python (hell no!). This is Java programming, so we keep it simple (and more readable) than those other programming languages. See: Write Java code to do this In the Java code, I'm opening up the RPi Debian Wheezy well-defined file handles to control the GPIO ports. First I'm resetting everything using the unexport/export file handles. (On the RPi, if you open the well-defined file handles and write certain ASCII text to them, you can drive your GPIO to perform certain operations. See this GPIO reference). Next, I write a "1" then "0" to the value file handle of the GPIO0 port (see the previous pinout diagram). That makes the LED blink. Then, I loop to infinity. Easy, huh? import java.io.* /* * Java Embedded Raspberry Pi GPIO app */ package jerpigpio; import java.io.FileWriter; /** * * @author hinkmond */ public class JerpiGPIO { static final String GPIO_OUT = "out"; static final String GPIO_ON = "1"; static final String GPIO_OFF = "0"; static final String GPIO_CH00="0"; /** * @param args the command line arguments */ public static void main(String[] args) { FileWriter commandFile; try { /*** Init GPIO port for output ***/ // Open file handles to GPIO port unexport and export controls FileWriter unexportFile = new FileWriter("/sys/class/gpio/unexport"); FileWriter exportFile = new FileWriter("/sys/class/gpio/export"); // Reset the port unexportFile.write(GPIO_CH00); unexportFile.flush(); // Set the port for use exportFile.write(GPIO_CH00); exportFile.flush(); // Open file handle to port input/output control FileWriter directionFile = new FileWriter("/sys/class/gpio/gpio"+GPIO_CH00+"/direction"); // Set port for output directionFile.write(GPIO_OUT); directionFile.flush(); /*--- Send commands to GPIO port ---*/ // Opne file handle to issue commands to GPIO port commandFile = new FileWriter("/sys/class/gpio/gpio"+GPIO_CH00+"/value"); // Loop forever while (true) { // Set GPIO port ON commandFile.write(GPIO_ON); commandFile.flush(); // Wait for a while java.lang.Thread.sleep(200); // Set GPIO port OFF commandFile.write(GPIO_OFF); commandFile.flush(); // Wait for a while java.lang.Thread.sleep(200); } } catch (Exception exception) { exception.printStackTrace(); } } } Hinkmond

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• Mission critical embedded language

  - by Moe

  Maybe the question sounds a bit strange, so i'll explain a the background a little bit. Currently i'm working on a project at y university, which will be a complete on-board software for an satellite. The system is programmed in c++ on top of a real-time operating system. However, some subsystems like the attitude control system and the fault detection and a space simulation are currently only implemented in Matlab/Simulink, to prototype the algorithms efficiently. After their verification, they will be translated into c++. The complete on-board software grew very complex, and only a handful people know the whole system. Furthermore, many of the students haven't program in c++ yet and the manual memory management of c++ makes it even more difficult to write mission critical software. Of course the main system has to be implemented in c++, but i asked myself if it's maybe possible to use an embedded language to implement the subsystem which are currently written in Matlab. This embedded language should feature: static/strong typing and compiler checks to minimize runtime errors small memory usage, and relative fast runtime attitude control algorithms are mainly numerical computations, so a good numeric support would be nice maybe some sort of functional programming feature, matlab/simulink encourage you to use it too I googled a bit, but only found Lua. It looks nice, but i would not use it in mission critical software. Have you ever encountered a situation like this, or do you know any language, which could satisfies the conditions? EDIT: To clarify some things: embedded means it should be able to embed the language into the existing c++ environment. So no compiled languages like Ada or Haskell ;)

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• Is there an alternative to Google Code Search?

  - by blunders

  Per the Official Google Blog: Code Search, which was designed to help people search for open source code all over the web, will be shut down along with the Code Search API on January 15, 2012. Google Code Search is now gone, and since that makes it much harder to understand the features it presented, here's my attempt to render them via information I gathered from a cache of the page for the Search Options: The "In Search Box" just notes the syntax to type the command directly in the main search box instead of using the advance search interface. Package (In Search Box: "package:linux-2.6") Language (In Search Box: "lang:c++") (OPTIONS: any language, actionscript, ada, applescript, asp, assembly, autoconf, automake, awk, basic, bat, c, c#, c++, caja, cobol, coldfusion, configure, css, d, eiffel, erlang, fortran, go, haskell, inform, java, java, javascript, jsp, lex, limbo, lisp, lolcode, lua, m4, makefile, maple, mathematica, matlab, messagecatalog, modula2, modula3, objectivec, ocaml, pascal, perl, php, pod, prolog, proto, python, python, r, rebol, ruby, sas, scheme, scilab, sgml, shell, smalltalk, sml, sql, svg, tcl, tex, texinfo, troff, verilog, vhdl, vim, xslt, xul, yacc) File (In Search Box: "file:^.*.java$") Class (In Search Box: "class:HashMap") Function (In Search Box: "function:toString") License (In Search Box: "license:mozilla") (OPTIONS: null/any-license, aladdin/Aladdin-Public-License, artistic/Artistic-License, apache/Apache-License, apple/Apple-Public-Source-License, bsd/BSD-License, cpl/Common-Public-License, epl/Eclipse-Public-License, agpl/GNU-Affero-General-Public-License, gpl/GNU-General-Public-License, lgpl/GNU-Lesser-General-Public-License, disclaimer/Historical-Permission-Notice-and-Disclaimer, ibm/IBM-Public-License, lucent/Lucent-Public-License, mit/MIT-License, mozilla/Mozilla-Public-License, nasa/NASA-Open-Source-Agreement, python/Python-Software-Foundation-License, qpl/Q-Public-License, sleepycat/Sleepycat-License, zope/Zope-Public-License) Case Sensitive (In Search Box: "case:no") (OPTIONS: yes, no) Also of use in understanding the search tool would be the still live FAQs page for Google Code Search. Is there any code search engine that would fully replace Google Code Search's features?

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• SQLUG Events - London/Edinburgh/Cardiff/Reading - Masterclass, NoSQL, TSQL Gotcha's, Replication, BI

  - by tonyrogerson

  We have acquired two additional tickets to attend the SQL Server Master Class with Paul Randal and Kimberly Tripp next Thurs (17th June), for a chance to win these coveted tickets email us ([email protected]) before 9pm this Sunday with the subject "MasterClass" - people previously entered need not worry - your still in with a chance. The winners will be announced Monday morning.As ever plenty going on physically, we've got dates for a stack of events in Manchester and Leeds, I'm looking at Birmingham if anybody has ideas? We are growing our online community with the Cuppa Corner section, to participate online remember to use the #sqlfaq twitter tag; for those wanting to get more involved in presenting and fancy trying it out we are always after people to do 1 - 5 minute SQL nuggets or Cuppa Corners (short presentations) at any of these User Group events - just email us [email protected] removing from this email list? Then just reply with remove please on the subject line.Kimberly Tripp and Paul Randal Master Class - Thurs, 17th June - LondonREGISTER NOW AND GET A SECOND REGISTRATION FREE*The top things YOU need to know about managing SQL Server - in one place, on one day - presented by two of the best SQL Server industry trainers!This one-day MasterClass will focus on many of the top issues companies face when implementing and maintaining a SQL Server-based solution. In the case where a company has no dedicated DBA, IT managers sometimes struggle to keep the data tier performing well and the data available. This can be especially troublesome when the development team is unfamiliar with the affect application design choices have on database performance.The Microsoft SQL Server MasterClass 2010 is presented by Paul S. Randal and Kimberly L. Tripp, two of the most experienced and respected people in the SQL Server world. Together they have over 30 years combined experience working with SQL Server in the field, and on the SQL Server product team itself. This is a unique opportunity to hear them present at a UK event which will:>> Debunk many of the ingrained misconceptions around SQL Server's behaviour >> Show you disaster recovery techniques critical to preserving your company's life-blood - the data >> Explain how a common application design pattern can wreak havoc in the database >> Walk through the top-10 points to follow around operations and maintenance for a well-performing and available data tier! Where: Radisson Edwardian Heathrow Hotel, LondonWhen: Thursday 17th June 2010*REGISTER TODAY AT www.regonline.co.uk/kimtrippsql on the registration form simply quote discount code: BOGOF for both yourself and your colleague and you will save 50% off each registration – that’s a 249 GBP saving! This offer is limited, book early to avoid disappointment.Wed, 23 JunREADINGEvening Meeting, More info and registerIntroduction to NoSQL (Not Only SQL) - Gavin Payne; T-SQL Gotcha's and how to avoid them - Ashwani Roy; Introduction to Recency Frequency - Tony Rogerson; Reporting Services - Tim LeungThu, 24 JunCARDIFFEvening Meeting, More info and registerAlex Whittles of Purple Frog Systems talks about Data warehouse design case studies, Other BI related session TBC Mon, 28 JunEDINBURGHEvening Meeting, More info and registerReplication (Components, Adminstration, Performance and Troubleshooting) - Neil Hambly Server Upgrades (Notes and Best practice from the field) - Satya Jayanty Wed, 14 JulLONDONEvening Meeting, More info and registerMeeting is being sponsored by DBSophic (http://www.dbsophic.com/download), database optimisation software. Physical Join Operators in SQL Server - Ami LevinWorkload Tuning - Ami LevinSQL Server and Disk IO (File Groups/Files, SSD's, Fusion-IO, In-RAM DB's, Fragmentation) - Tony RogersonComplex Event Processing - Allan MitchellMany thanks,Tony Rogerson, SQL Server MVPUK SQL Server User Grouphttp://sqlserverfaq.com"

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• The enterprise vendor con - connecting SSD's using SATA 2 (3Gbits) thus limiting there performance

  - by tonyrogerson

  When comparing SSD against Hard drive performance it really makes me cross when folk think comparing an array of SSD running on 3GBits/sec to hard drives running on 6GBits/second is somehow valid. In a paper from DELL (http://www.dell.com/downloads/global/products/pvaul/en/PowerEdge-PowerVaultH800-CacheCade-final.pdf) on increasing database performance using the DELL PERC H800 with Solid State Drives they compare four SSD drives connected at 3Gbits/sec against ten 10Krpm drives connected at 6Gbits [Tony slaps forehead while shouting DOH!]. It is true in the case of hard drives it probably doesn’t make much difference 3Gbit or 6Gbit because SAS and SATA are both end to end protocols rather than shared bus architecture like SCSI, so the hard drive doesn’t share bandwidth and probably can’t get near the 600MiBytes/second throughput that 6Gbit gives unless you are doing contiguous reads, in my own tests on a single 15Krpm SAS disk using IOMeter (8 worker threads, queue depth of 16 with a stripe size of 64KiB, an 8KiB transfer size on a drive formatted with an allocation size of 8KiB for a 100% sequential read test) I only get 347MiBytes per second sustained throughput at an average latency of 2.87ms per IO equating to 44.5K IOps, ok, if that was 3GBits it would be less – around 280MiBytes per second, oh, but wait a minute [...fingers tap desk] You’ll struggle to find in the commodity space an SSD that doesn’t have the SATA 3 (6GBits) interface, SSD’s are fast not only low latency and high IOps but they also offer a very large sustained transfer rate, consider the OCZ Agility 3 it so happens that in my masters dissertation I did the same test but on a difference box, I got 374MiBytes per second at an average latency of 2.67ms per IO equating to 47.9K IOps – cost of an 240GB Agility 3 is £174.24 (http://www.scan.co.uk/products/240gb-ocz-agility-3-ssd-25-sata-6gb-s-sandforce-2281-read-525mb-s-write-500mb-s-85k-iops), but that same drive set in a box connected with SATA 2 (3Gbits) would only yield around 280MiBytes per second thus losing almost 100MiBytes per second throughput and a ton of IOps too. So why the hell are “enterprise” vendors still only connecting SSD’s at 3GBits? Well, my conspiracy states that they have no interest in you moving to SSD because they’ll lose so much money, the argument that they use SATA 2 doesn’t wash, SATA 3 has been out for some time now and all the commodity stuff you buy uses it now. Consider the cost, not in terms of price per GB but price per IOps, SSD absolutely thrash Hard Drives on that, it was true that the opposite was also true that Hard Drives thrashed SSD’s on price per GB, but is that true now, I’m not so sure – a 300GByte 2.5” 15Krpm SAS drive costs £329.76 ex VAT (http://www.scan.co.uk/products/300gb-seagate-st9300653ss-savvio-15k3-25-hdd-sas-6gb-s-15000rpm-64mb-cache-27ms) which equates to £1.09 per GB compared to a 480GB OCZ Agility 3 costing £422.10 ex VAT (http://www.scan.co.uk/products/480gb-ocz-agility-3-ssd-25-sata-6gb-s-sandforce-2281-read-525mb-s-write-410mb-s-30k-iops) which equates to £0.88 per GB. Ok, I compared an “enterprise” hard drive with a “commodity” SSD, ok, so things get a little more complicated here, most “enterprise” SSD’s are SLC and most commodity are MLC, SLC gives more performance and wear, I’ll talk about that another day. For now though, don’t get sucked in by vendor marketing, SATA 2 (3Gbit) just doesn’t cut it, SSD need 6Gbit to breath and even that SSD’s are pushing. Alas, SSD’s are connected using SATA so all the controllers I’ve seen thus far from HP and DELL only do SATA 2 – deliberate? Well, I’ll let you decide on that one.

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• ghc6 install trouble: hGetContents: invalid argument (invalid UTF-8 byte sequence)

  - by olimay

  Having trouble installing ghc6. Here's what seems to be the relevant error that comes up when I try to (apt-get|aptitude) install ghc6: A package failed to install. Trying to recover: Setting up ghc6 (6.12.1-13ubuntu1) ... ghc-pkg: /home/opm/.ghc/i386-linux-6.12.1/package.conf.d/unix-compat-0.2-edefa7bced91ebe610d455bab466e200.conf: hGetContents: invalid argument (invalid UTF-8 byte sequence) (Here's the full output, if you're interested: http://paste.ubuntu.com/566475/ ) This still happens after apt-get clean and apt-get update. My searching around has not really helped me understand what's going on, except that it might be caused by a mismatch in locale. So, here's the output of locale too: LANG=en_US.utf8 LANGUAGE=en_US:en LC_CTYPE="en_US.utf8" LC_NUMERIC="en_US.utf8" LC_TIME="en_US.utf8" LC_COLLATE="en_US.utf8" LC_MONETARY="en_US.utf8" LC_MESSAGES="en_US.utf8" LC_PAPER="en_US.utf8" LC_NAME="en_US.utf8" LC_ADDRESS="en_US.utf8" LC_TELEPHONE="en_US.utf8" LC_MEASUREMENT="en_US.utf8" LC_IDENTIFICATION="en_US.utf8" LC_ALL= Any ideas? Additional background: this all seems very strange to me, because I used to have ghc6 installed correctly--I use XMonad as my main window manager most of the time. I tried to install haskell-platform (through apt), which failed and told me that there was something wrong with ghc6, and so I reinstalled ghc6 and began to get the above error message. (Originally posted here to SuperUser, until I remembered today that this SE site existed.)

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• Functional Methods on Collections

  - by GlenPeterson

  I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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• How should I implement a command processing application?

  - by Nini Michaels

  I want to make a simple, proof-of-concept application (REPL) that takes a number and then processes commands on that number. Example: I start with 1. Then I write "add 2", it gives me 3. Then I write "multiply 7", it gives me 21. Then I want to know if it is prime, so I write "is prime" (on the current number - 21), it gives me false. "is odd" would give me true. And so on. Now, for a simple application with few commands, even a simple switch would do for processing the commands. But if I want extensibility, how would I need to implement the functionality? Do I use the command pattern? Do I build a simple parser/interpreter for the language? What if I want more complex commands, like "multiply 5 until >200" ? What would be an easy way to extend it (add new commands) without recompiling? Edit: to clarify a few things, my end goal would not be to make something similar to WolframAlpha, but rather a list (of numbers) processor. But I want to start slowly at first (on single numbers). I'm having in mind something similar to the way one would use Haskell to process lists, but a very simple version. I'm wondering if something like the command pattern (or equivalent) would suffice, or if I have to make a new mini-language and a parser for it to achieve my goals?

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• How can a large, Fortran-based number crunching codebase be modernized?

  - by Dave Mateer

  A friend in academia asked me for advice (I'm a C# business application developer). He has a legacy codebase which he wrote in Fortran in the medical imaging field. It does a huge amount of number crunching using vectors. He uses a cluster (30ish cores) and has now gone towards a single workstation with 500ish GPUS in it. However where to go next with the codebase so: Other people can maintain it over next 10 year cycle Get faster at tweaking the software Can run on different infrastructures without recompiles After some research from me (this is a super interesting area) some options are: Use Python and CUDA from Nvidia Rewrite in a functional language. For example, F# or Haskell Go cloud based and use something like Hadoop and Java Learn C What has been your experience with this? What should my friend be looking at to modernize his codebase? UPDATE: Thanks @Mark and everyone who has answered. The reasons my friend is asking this question is that it's a perfect time in the projects lifecycle to do a review. Bringing research assistants up to speed in Fortran takes time (I like C#, and especially the tooling and can't imagine going back to older languages!!) I liked the suggestion of keeping the pure number crunching in Fortran, but wrapping it in something newer. Perhaps Python as that seems to be getting a stronghold in academia as a general-purpose programming language that is fairly easy to pick up. See Medical Imaging and a guy who has written a Fortran wrapper for CUDA, Can I legally publish my Fortran 90 wrappers to Nvidias' CUFFT library (from the CUDA SDK)?.

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• Subterranean IL: Compiling C# exception handlers

  - by Simon Cooper

  An exception handler in C# combines the IL catch and finally exception handling clauses into a single try statement: try { Console.WriteLine("Try block") // ... } catch (IOException) { Console.WriteLine("IOException catch") // ... } catch (Exception e) { Console.WriteLine("Exception catch") // ... } finally { Console.WriteLine("Finally block") // ... } How does this get compiled into IL? Initial implementation If you remember from my earlier post, finally clauses must be specified with their own .try clause. So, for the initial implementation, we take the try/catch/finally, and simply split it up into two .try clauses (I have to use label syntax for this): StartTry: ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndTry: StartIOECatch: ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndIOECatch: StartECatch: ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndECatch: StartFinally: ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally EndFinally: End: // ... .try StartTry to EndTry catch [mscorlib]System.IO.IOException handler StartIOECatch to EndIOECatch catch [mscorlib]System.Exception handler StartECatch to EndECatch .try StartTry to EndTry finally handler StartFinally to EndFinally However, the resulting program isn't verifiable, and doesn't run: [IL]: Error: Shared try has finally or fault handler. Nested try blocks What's with the verification error? Well, it's a condition of IL verification that all exception handling regions (try, catch, filter, finally, fault) of a single .try clause have to be completely contained within any outer exception region, and they can't overlap with any other exception handling clause. In other words, IL exception handling clauses must to be representable in the scoped syntax, and in this example, we're overlapping catch and finally clauses. Not only is this example not verifiable, it isn't semantically correct. The finally handler is specified round the .try. What happens if you were able to run this code, and an exception was thrown? Program execution enters top of try block, and exception is thrown within it CLR searches for an exception handler, finds catch Because control flow is leaving .try, finally block is run The catch block is run leave.s End inside the catch handler branches to End label. We're actually running the finally before the catch! What we do about it What we actually need to do is put the catch clauses inside the finally clause, as this will ensure the finally gets executed at the correct time (this time using scoped syntax): .try { .try { ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.IO.IOException { ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.Exception { ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } } finally { ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally } End: ret Returning from methods There is a further semantic mismatch that the C# compiler has to deal with; in C#, you are allowed to return from within an exception handling block: public int HandleMethod() { try { // ... return 0; } catch (Exception) { // ... return -1; } } However, you can't ret inside an exception handling block in IL. So the C# compiler does a leave.s to a ret outside the exception handling area, loading/storing any return value to a local variable along the way (as leave.s clears the stack): .method public instance int32 HandleMethod() { .locals init ( int32 retVal ) .try { // ... ldc.i4.0 stloc.0 leave.s End } catch [mscorlib]System.Exception { // ... ldc.i4.m1 stloc.0 leave.s End } End: ldloc.0 ret } Conclusion As you can see, the C# compiler has quite a few hoops to jump through to translate C# code into semantically-correct IL, and hides the numerous conditions on IL exception handling blocks from the C# programmer. Next up: catch-all blocks, and how the runtime deals with non-Exception exceptions.

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• RPi and Java Embedded GPIO: Sensor Reading using Java Code

  - by hinkmond

  And, now to program the Java code for reading the fancy-schmancy static electricity sensor connected to your Raspberry Pi, here is the source code we'll use: First, we need to initialize ourselves... /* * Java Embedded Raspberry Pi GPIO Input app */ package jerpigpioinput; import java.io.FileWriter; import java.io.RandomAccessFile; import java.text.DateFormat; import java.text.SimpleDateFormat; import java.util.Calendar; /** * * @author hinkmond */ public class JerpiGPIOInput { static final String GPIO_IN = "in"; // Add which GPIO ports to read here static String[] GpioChannels = { "7" }; /** * @param args the command line arguments */ public static void main(String[] args) { try { /*** Init GPIO port(s) for input ***/ // Open file handles to GPIO port unexport and export controls FileWriter unexportFile = new FileWriter("/sys/class/gpio/unexport"); FileWriter exportFile = new FileWriter("/sys/class/gpio/export"); for (String gpioChannel : GpioChannels) { System.out.println(gpioChannel); // Reset the port unexportFile.write(gpioChannel); unexportFile.flush(); // Set the port for use exportFile.write(gpioChannel); exportFile.flush(); // Open file handle to input/output direction control of port FileWriter directionFile = new FileWriter("/sys/class/gpio/gpio" + gpioChannel + "/direction"); // Set port for input directionFile.write(GPIO_IN); directionFile.flush(); } And, next we will open up a RandomAccessFile pointer to the GPIO port. /*** Read data from each GPIO port ***/ RandomAccessFile[] raf = new RandomAccessFile[GpioChannels.length]; int sleepPeriod = 10; final int MAXBUF = 256; byte[] inBytes = new byte[MAXBUF]; String inLine; int zeroCounter = 0; // Get current timestamp with Calendar() Calendar cal; DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS"); String dateStr; // Open RandomAccessFile handle to each GPIO port for (int channum=0; channum Then, loop forever to read in the values to the console. // Loop forever while (true) { // Get current timestamp for latest event cal = Calendar.getInstance(); dateStr = dateFormat.format(cal.getTime()); // Use RandomAccessFile handle to read in GPIO port value for (int channum=0; channum Rinse, lather, and repeat... Compile this Java code on your host PC or Mac with javac from the JDK. Copy over the JAR or class file to your Raspberry Pi, "sudo -i" to become root, then start up this Java app in a shell on your RPi. That's it! You should see a "1" value get logged each time you bring a statically charged item (like a balloon you rub on the cat) near the antenna of the sensor. There you go. You've just seen how Java Embedded technology on the Raspberry Pi is an easy way to access sensors. Hinkmond

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• What kinds of demos are good to make for a software engineer job

  - by user23012

  I have created my cv site and sent out my demos for a while now, but most of my demos are either from my course or games related since my course was a games programming course, I was wondering what kind of demos are good to show off my skills in programming in general. These are what i already have Pennies:just a simple game first coursework i did. Compiler:coursework for compiler writing module Pongout: basic a pong game in 68k using colour detection Snake: snake in 68k same thing as the pong Game Cube Maze: gamecube work BeatmyBot: basic Ai Basic plat-former game: 2d game with different types of collision Turing Lambda Simulation: my dissertation Turing machine simulated in Miranda. alpha and Beta reduction,and SKI calculus simulated in the Turing machine. What I am asking here is what kind of demos are good to add or have, i have been looking and have hit a tough spot I cant think of anything to make more than games. so for a general graduate software engineer what types would be good examples? EDIT: since responding to the comments bellow well for what languages well my main one would be C++, followed by Java, Erlang and abit of Haskell

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• JPedal Action for Converting PDF to JavaFX

  - by Geertjan

  The question of the day comes from Mark Stephens, from JPedal (JPedal is the leading 100% Java PDF library, providing a Java PDF viewer, PDF to image conversion, PDF printing or adding PDF search and PDF extraction features), in the form of a screenshot: The question is clear. By looking at the annotations above, you can see that Mark has an ActionListener that has been bound to the right-click popup menu on PDF files. Now he needs to get hold of the file to which the Action has been bound. How, oh  how, can one get hold of that file? Well, it's simple. Leave everything you see above exactly as it is but change the Java code section to this: public final class PDF2JavaFXContext implements ActionListener {     private final DataObject context;     public PDF2JavaFXContext(DataObject context) {         this.context = context;     }     public void actionPerformed(ActionEvent ev) {         FileObject fo = context.getPrimaryFile();         File theFile = FileUtil.toFile(fo);         //do something with your file...     } } The point is that the annotations at the top of the class bind the Action to either Actions.alwaysEnabled, which is a factory method for creating always-enabled Actions, or Actions.context, which is a factory method for creating context-sensitive Actions. How does the Action get bound to the factory method? The annotations are converted, when the module is compiled, into XML registration entries in the "generated-layer.xml", which you can find in your "build" folder, in the Files window, after building the module. In Mark's case, since the Action should be context-sensitive to PDF files, he needs to bind his PDF2JavaFXContext ActionListener (which should probably be named "PDF2JavaFXActionListener", since the class is an ActionListener) to Actions.context. All he needs to do that is pass in the object he wants to work with into the constructor of the ActionListener. Now, when the module is built, the annotation processor is going to take the annotations and convert them to XML registration entries, but the constructor will also be checked to see whether it is empty or not. In this case, the constructor isn't empty, hence the Action should be context-sensitive and so the ActionListener is bound to Actions.context. The Actions.context will do all the enablement work for Mark, so that he will not need to provide any code for enabling/disabling the Action. The Action will be enabled whenever a DataObject is selected. Since his Action is bound to Nodes in the Projects window that represent PDF files, the Action will always be enabled whenever Mark right-clicks on a PDF Node, since the Node exposes its own DataObject. Once Mark has access to the DataObject, he can get the underlying FileObject via getPrimaryFile and he can then convert the FileObject to a java.io.File via FileUtil.getConfigFile. Once he's got the java.io.File, he can do with it whatever he needs. Further reading: http://bits.netbeans.org/dev/javadoc/

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• How can I make sense of the word "Functor" from a semantic standpoint?

  - by guillaume31

  When facing new programming jargon words, I first try to reason about them from an semantic and etymological standpoint when possible (that is, when they aren't obscure acronyms). For instance, you can get the beginning of a hint of what things like Polymorphism or even Monad are about with the help of a little Greek/Latin. At the very least, once you've learned the concept, the word itself appears to go along with it well. I guess that's part of why we name things names, to make mental representations and associations more fluent. I found Functor to be a tougher nut to crack. Not so much the C++ meaning -- an object that acts (-or) as a function (funct-), but the various functional meanings (in ML, Haskell) definitely left me puzzled. From the (mathematics) Functor Wikipedia article, it seems the word was borrowed from linguistics. I think I get what a "function word" or "functor" means in that context - a word that "makes function" as opposed to a word that "makes sense". But I can't really relate that to the notion of Functor in category theory, let alone functional programming. I imagined a Functor to be something that creates functions, or behaves like a function, or short for "functional constructor", but none of those seems to fit... How do experienced functional programmers reason about this ? Do they just need any label to put in front of a concept and be fine with it ? Generally speaking, isn't it partly why advanced functional programming is hard to grasp for mere mortals compared to, say, OO -- very abstract in that you can't relate it to anything familiar ? Note that I don't need a definition of Functor, only an explanation that would allow me to relate it to something more tangible, if there is any.

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• Discuss: PLs are characterised by which (iso)morphisms are implemented

  - by Yttrill

  I am interested to hear discussion of the proposition summarised in the title. As we know programming language constructions admit a vast number of isomorphisms. In some languages in some places in the translation process some of these isomorphisms are implemented, whilst others require code to be written to implement them. For example, in my language Felix, the isomorphism between a type T and a tuple of one element of type T is implemented, meaning the two types are indistinguishable (identical). Similarly, a tuple of N values of the same type is not merely isomorphic to an array, it is an array: the isomorphism is implemented by the compiler. Many other isomorphisms are not implemented for example there is an isomorphism expressed by the following client code: match v with | ((?x,?y),?z = x,(y,z) // Felix match v with | (x,y), - x,(y,z) (* Ocaml *) As another example, a type constructor C of int in Felix may be used directly as a function, whilst in Ocaml you must write a wrapper: let c x = C x Another isomorphism Felix implements is the elimination of unit values, including those in tuples: Felix can do this because (most) polymorphic values are monomorphised which can be done because it is a whole program analyser, Ocaml, for example, cannot do this easily because it supports separate compilation. For the same reason Felix performs type-class dispatch at compile time whilst Haskell passes around dictionaries. There are some quite surprising issues here. For example an array is just a tuple, and tuples can be indexed at run time using a match and returning a value of a corresponding sum type. Indeed, to be correct the index used is in fact a case of unit sum with N summands, rather than an integer. Yet, in a real implementation, if the tuple is an array the index is replaced by an integer with a range check, and the result type is replaced by the common argument type of all the constructors: two isomorphisms are involved here, but they're implemented partly in the compiler translation and partly at run time.

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• Expanding existing DVCS Wiki

  - by A Lion

  A portion of my job is to maintain technical documentation for a rapidly expanding manufacturing company. Because it is only a portion of my job and the company's product line is expanding so quickly, I can't stay on top of the documentation. As a result, I've been yearning for an information management system with a handful of specific features. I've found many products that have a subset, but none that have all the features I'm looking for. I'm at the point of picking an existing product and expanding it to cover my desired feature set, however, this will be a pet project and I will be learning the underlying language as I go. So, the main question is which existing product will be the easiest to expand to cover the full feature set and has a relatively easy to learn language? Alternatively, have I missed another existing program that will cover the feature set or should be in my list of "close, but not quite there"? Feature Set web interface based on a distributed version control system (e.g., git) easy to edit by logged in novices (e.g. wiki, multimarkdown) outputs in more traditional formats (e.g., doc, odt, pdf) edits held in queue until editor/engineer/manager approves them (e.g., MS Word editing) [this is the really big elephant in list - suggestions on where to start appreciated] edits held in queue specifically for engineer approval [extra limb of the elephant in the list] well-supported in the open source community Closest, but not quite there ikiwiki - http://ikiwiki.info (php) lots of awesome functionality and extensions, including easy to edit and based on DVCS lacks a review/forward for review queue appears to be well-supported within the OSS community gitit - http://gitit.net/ (haskell) easy to edit and based on DVCS lots of outputs in traditional formats a great web-based gui diff interface lacks a review/forward for review queue appears to be primarily maintained by one individual

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• What's cool about Lisp nowadays? [closed]

  - by Kos

  Possible Duplicates: Why is Lisp useful? Is LISP still useful in today's world? Which version is most used? First of all, let me clarify: I'm aware of Lisp's place in history, as well as in education. I'm asking about its place in practical application, as of 2011. The question is: What features of Lisp make it the preferred choice for projects today? It's widely used in various AI areas as far as I know, and probably also elsewhere. I can imagine projects choosing, for instance... Python because of its concise, readable syntax and it being dynamic, Haskell for being pure functional with a powerful type system, Matlab/Octave for the focus on numerics and big standard libraries, Etc. When should I consider Lisp the proper language for a given problem? What language features make it the preferred choice then? Is its "purity and generality" an advantage which makes it a better choice for some subset of projects than the modern languages? edit- On your demand, a little rephrase (or simply a tl;dr) to make this more specific: a) What problems are solvable with Lisp much more easily than with more common, modern languages like Python or C# (or even F# or Scala)? b) What language features specific for Lisp make it the best choice for those problems?

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• How often is your "Go-To" language the same as your favorite??

  - by K-RAN

  I know that there's already a question asking for your favorite programming language here. I'm curious though, what's your go-to language? The two can be very different. For example, I love Haskell. I learned it this past semester and I fell in love with it's very concise solutions and awesome syntax (I love theoretical math so something like fib = 1 : 1 : [ f | f <- zipWith (+) fibSeq (tail fibSeq)] makes my inner mathematician and computer scientist jump with joy!). However, the majority of my projects for classes and jobs have been in C/C++ & Java. As a result, most of the time when I'm testing something like an algorithm or Data Structure I go straight to C++. What about you guys? What languages do you love and why? What about your go-to language? What language do you use most often to get things done for work or personal projects and why? How often does a language fall into both categories??

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• Functional programming compared to OOP with classes

  - by luckysmack

  I have been interested in some of the concepts of functional programming lately. I have used OOP for some time now. I can see how I would build a fairly complex app in OOP. Each object would know how to do things that object does. Or anything it's parents class does as well. So I can simply tell Person().speak() to make the person talk. But how do I do similar things in functional programming? I see how functions are first class items. But that function only does one specific thing. Would I simply have a say() method floating around and call it with an equivalent of Person() argument so I know what kind of thing is saying something? So I can see the simple things, just how would I do the comparable of OOP and objects in functional programming, so I can modularize and organize my code base? For reference, my primary experience with OOP is Python, PHP, and some C#. The languages that I am looking at that have functional features are Scala and Haskell. Though I am leaning towards Scala. Basic Example (Python): Animal(object): def say(self, what): print(what) Dog(Animal): def say(self, what): super().say('dog barks: {0}'.format(what)) Cat(Animal): def say(self, what): super().say('cat meows: {0}'.format(what)) dog = Dog() cat = Cat() dog.say('ruff') cat.say('purr')

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• Can higher-order functions in FP be interpreted as some kind of dependency injection?

  - by Giorgio

  According to this article, in object-oriented programming / design dependency injection involves a dependent consumer, a declaration of a component's dependencies, defined as interface contracts, an injector that creates instances of classes that implement a given dependency interface on request. Let us now consider a higher-order function in a functional programming language, e.g. the Haskell function filter :: (a -> Bool) -> [a] -> [a] from Data.List. This function transforms a list into another list and, in order to perform its job, it uses (consumes) an external predicate function that must be provided by its caller, e.g. the expression filter (\x -> (mod x 2) == 0) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] selects all even numbers from the input list. But isn't this construction very similar to the pattern illustrated above, where the filter function is the dependent consumer, the signature (a -> Bool) of the function argument is the interface contract, the expression that uses the higher-order is the injector that, in this particular case, injects the implementation (\x -> (mod x 2) == 0) of the contract. More in general, can one relate higher-order functions and their usage pattern in functional programming to the dependency injection pattern in object-oriented languages? Or in the inverse direction, can dependency injection be compared to using some kind of higher-order function?

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• Origin of common list-processing function names

  - by Heatsink

  Some higher-order functions for operating on lists or arrays have been repeatedly adopted or reinvented. The functions map, fold[l|r], and filter are found together in several programming languages, such as Scheme, ML, and Python, that don't seem to have a common ancestor. I'm going with these three names to keep the question focused. To show that the names are not universal, here is a sampling of names for equivalent functionality in other languages. C++ has transform instead of map and remove_if instead of filter (reversing the meaning of the predicate). Lisp has mapcar instead of map, remove-if-not instead of filter, and reduce instead of fold (Some modern Lisp variants have map but this appears to be a derived form.) C# uses Select instead of map and Where instead of filter. C#'s names came from SQL via LINQ, and despite the name changes, their functionality was influenced by Haskell, which was itself influenced by ML. The names map, fold, and filter are widespread, but not universal. This suggests that they were borrowed from an influential source into other contemporary languages. Where did these function names come from?

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• Should CV contain cases where certain party fools me and not pay salary? Is it "holiday" time or not?

  - by otto

  Suppose I am fooled to work in a start-up or a company that has been a very small over a long time, let say 10 years. I work them 3 months and I really enjoy the work -- I learn a lot of new skills such as Haskell, MapReduce, CouchDB and many other little things. Now the firm did not pay any salary: A) I may be unskilled, B) I did not meet some deadline (I don't know because I am not allowed to speak to the boss but I know that I am not getting any payment) or C) I was fooled. Some detail about C I heard that the firm have had similar cases from my friend, "The guy X was there and he said he does not trust the firm at all so he went to other firm". I don't know what the term "trust" mean here, anyway the firm consists of ignorant drop-outs that hires academic people, a bit irony. They hire people from student-organizations and let them work and promise ok -compensation but -- when you start working the co-employer starts all kind of instructions "Do not work so hard, do not work so long, do not work so much" -- it is like he is making sure you do not feel sad when he does not pay any salary (co-employer is an owner in the firm). Anyway, I learnt a ton in the company but it was very inefficient working. I worked only alone, not really working in a "company". Now should by resume contain references to the firm and the guy who did not pay me anything? Or should my resume read that I worked in XYZ -technologies -- but 1 year's NDA -- what can write here? Now I fear that if I put the firm to my resume: they will lie about my input to my next employer. I feel they are very dishonest. On the other hand, I want to make it sure that I have worked over the time. So: Should my CV contain the not-so-good or even awful employers that may be fooling people to work there? I am pretty sure everyone knows the firm and its habbits, circles are small but people are afraid to speak.

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• What does SVN do better than git?

  - by doug

  No question that the majority of debates over programmer tools distill to either personal choice (by the user) or design emphasis, i.e., optimizing design according to particular uses cases (by the tool builder). Text Editors are probably the most prominent example--a coder who works on a Windows at work and codes in Haskell on the Mac at home, values cross-platform and compiler integration and so chooses Emacs over Textmate, etc. It's less common that a newly introduced technology is genuinely, demonstrably superior to the extant options. I wonder if this is in fact the case with version-control systems, in particular, centralized VCS (CVS, SVN) versus distributed VCS (git, hg)? I used SVN for about five years, and SVN is currently used where I work. A little less than three years ago, I switched to git (and gitHub) for all of my personal projects. I can think of a number of advantages of git over subversion (and which for the most part abstract to advantages of distributed over centralized VCS), but I cannot think of one contra example--some task (that's relevant and arises in a programmers usual workflow) that subversion does better than git. The only conclusion I have drawn from this is that I don't have any data--not that git is better, etc. My guess is that such counter-examples exist, hence this question.

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