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• Is it better to alloc/dealloc new UIBarButtonItems when toggling Edit/Done? Why?

  - by cambria

  Apple's documentation implies that for a UITableView editable with an "Edit/Done" button, you should create and destroy the button each time it's toggled. Here's a snippet of code "BonjourWeb" sample code project that does this: if (editing) { // Add the "done" button to the navigation bar UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(doneAction:)]; self.navigationItem.leftBarButtonItem = doneButton; [doneButton release]; [self addAddButton:YES]; } else { if ([self.customs count]) { // Add the "edit" button to the navigation bar UIBarButtonItem *editButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemEdit target:self action:@selector(editAction:)]; self.navigationItem.leftBarButtonItem = editButton; [editButton release]; } Is this really better than just editing the title of the button? Is there some performance optimisation that I'm not seeing? Or is this just bad example source?

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• Converting a macro to an inline function

  - by Rob

  I am using some Qt code that adds a VERIFY macro that looks something like this: #define VERIFY(cond) \ { \ bool ok = cond; \ Q_ASSERT(ok); \ } The code can then use it whilst being certain the condition is actually evaluated, e.g.: Q_ASSERT(callSomeFunction()); // callSomeFunction not evaluated in release builds! VERIFY(callSomeFunction()); // callSomeFunction is always evaluated Disliking macros, I would instead like to turn this into an inline function: inline VERIFY(bool condition) { Q_ASSERT(condition); } However, in release builds I am worried that the compiler would optimise out all calls to this function (as Q_ASSERT wouldn't actually do anything.) I am I worrying unnecessarily or is this likely depending on the optimisation flags/compiler/etc.? I guess I could change it to: inline VERIFY(bool condition) { condition; Q_ASSERT(condition); } But, again, the compiler may be clever enough to ignore the call. Is this inline alternative safe for both debug and release builds?

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• Inline template efficiency

  - by Darryl Gove

  I like inline templates, and use them quite extensively. Whenever I write code with them I'm always careful to check the disassembly to see that the resulting output is efficient. Here's a potential cause of inefficiency. Suppose we want to use the mis-named Leading Zero Detect (LZD) instruction on T4 (this instruction does a count of the number of leading zero bits in an integer register - so it should really be called leading zero count). So we put together an inline template called lzd.il looking like: .inline lzd lzd %o0,%o0 .end And we throw together some code that uses it: int lzd(int); int a; int c=0; int main() { for(a=0; a<1000; a++) { c=lzd(c); } return 0; } We compile the code with some amount of optimisation, and look at the resulting code: $ cc -O -xtarget=T4 -S lzd.c lzd.il $ more lzd.s .L77000018: /* 0x001c 11 */ lzd %o0,%o0 /* 0x0020 9 */ ld [%i1],%i3 /* 0x0024 11 */ st %o0,[%i2] /* 0x0028 9 */ add %i3,1,%i0 /* 0x002c */ cmp %i0,999 /* 0x0030 */ ble,pt %icc,.L77000018 /* 0x0034 */ st %i0,[%i1] What is surprising is that we're seeing a number of loads and stores in the code. Everything could be held in registers, so why is this happening? The problem is that the code is only inlined at the code generation stage - when the actual instructions are generated. Earlier compiler phases see a function call. The called functions can do all kinds of nastiness to global variables (like 'a' in this code) so we need to load them from memory after the function call, and store them to memory before the function call. Fortunately we can use a #pragma directive to tell the compiler that the routine lzd() has no side effects - meaning that it does not read or write to memory. The directive to do that is #pragma no_side_effect(<routine name), and it needs to be placed after the declaration of the function. The new code looks like: int lzd(int); #pragma no_side_effect(lzd) int a; int c=0; int main() { for(a=0; a<1000; a++) { c=lzd(c); } return 0; } Now the loop looks much neater: /* 0x0014 10 */ add %i1,1,%i1 ! 11 ! { ! 12 ! c=lzd(c); /* 0x0018 12 */ lzd %o0,%o0 /* 0x001c 10 */ cmp %i1,999 /* 0x0020 */ ble,pt %icc,.L77000018 /* 0x0024 */ nop

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• Why are MVC & TDD not employed more in game architecture?

  - by secoif

  I will preface this by saying I haven't looked a huge amount of game source, nor built much in the way of games. But coming from trying to employ 'enterprise' coding practices in web apps, looking at game source code seriously hurts my head: "What is this view logic doing in with business logic? this needs refactoring... so does this, refactor, refactorrr" This worries me as I'm about to start a game project, and I'm not sure whether trying to mvc/tdd the dev process is going to hinder us or help us, as I don't see many game examples that use this or much push for better architectural practices it in the community. The following is an extract from a great article on prototyping games, though to me it seemed exactly the attitude many game devs seem to use when writing production game code: Mistake #4: Building a system, not a game ...if you ever find yourself working on something that isn’t directly moving your forward, stop right there. As programmers, we have a tendency to try to generalize our code, and make it elegant and be able to handle every situation. We find that an itch terribly hard not scratch, but we need to learn how. It took me many years to realize that it’s not about the code, it’s about the game you ship in the end. Don’t write an elegant game component system, skip the editor completely and hardwire the state in code, avoid the data-driven, self-parsing, XML craziness, and just code the damned thing. ... Just get stuff on the screen as quickly as you can. And don’t ever, ever, use the argument “if we take some extra time and do this the right way, we can reuse it in the game”. EVER. is it because games are (mostly) visually oriented so it makes sense that the code will be weighted heavily in the view, thus any benefits from moving stuff out to models/controllers, is fairly minimal, so why bother? I've heard the argument that MVC introduces a performance overhead, but this seems to me to be a premature optimisation, and that there'd more important performance issues to tackle before you worry about MVC overheads (eg render pipeline, AI algorithms, datastructure traversal, etc). Same thing regarding TDD. It's not often I see games employing test cases, but perhaps this is due to the design issues above (mixed view/business) and the fact that it's difficult to test visual components, or components that rely on probablistic results (eg operate within physics simulations). Perhaps I'm just looking at the wrong source code, but why do we not see more of these 'enterprise' practices employed in game design? Are games really so different in their requirements, or is a people/culture issue (ie game devs come from a different background and thus have different coding habits)?

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• Unexplained CPU and Disk activity spikes in SQL Server 2005

  - by Philip Goh

  Before I pose my question, please allow me to describe the situation. I have a database server, with a number of tables. Two of the biggest tables contain over 800k rows each. The majority of rows are less than 10k in size, though roughly 1 in 100 rows will be 1 MB but <4 MB. So out of the 1.6 million rows, about 16000 of them will be these large rows. The reason they are this big is because we're storing zip files binary blobs in the database, but I'm digressing. We have a service that runs constantly in the background, trimming 10 rows from each of these 2 tables. In the performance monitor graph above, these are the little bumps (red for CPU, green for disk queue). Once ever minute we get a large spike of CPU activity together with a jump in disk activity, indicated by the red arrow in the screenshot. I've run the SQL Server profiler, and there is nothing that jumps out as a candidate that would explain this spike. My suspicion is that this spike occurs when one of the large rows gets deleted. I've fed the results of the profiler into the tuning wizard, and I get no optimisation recommendations (i.e. I assume this means my database is indexed correctly for my current workload). I'm not overly worried as the server is coping fine in all circumstances, even under peak load. However, I would like to know if there is anything else I can do to find out what is causing this spike? Update: After investigating this some more, the CPU and disk usage spike was down to SQL server's automatic checkpoint. The database uses the simple recovery model, and this truncates the log file at each checkpoint. We can see this demonstrated in the following graph. As described on MSDN, the checkpoints will occur when the transaction log becomes 70% full and we are using the simple recovery model. This has been enlightening and I've definitely learned something!

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• Four New Java Champions

  - by Tori Wieldt

  Four luminaries in the Java community have been selected as new Java Champions. The are Agnes Crepet, Lars Vogel, Yara Senger and Martijn Verburg. They were selected for their technical knowledge, leadership, inspiration, and tireless work for the community. Here is how they rock the Java world: Agnes Crepet Agnes Crepet (France) is a passionate technologist with over 11 years of software engineering experience, especially in the Java technologies, as a Developer, Architect, Consultant and Trainer. She has been using Java since 1999, implementing multiple kinds of applications (from 20 days to 10000 men days) for different business fields (banking, retail, and pharmacy). Currently she is a Java EE Architect for a French pharmaceutical company, the homeopathy world leader. She is also the co-founder, with other passionate Java developers, of a software company named Ninja Squad, dedicated to Software Craftsmanship. Agnes is the leader of two Java User Groups (JUG), the Lyon JUG Duchess France and the founder of the Mix-IT Conferenceand theCast-IT Podcast, two projects about Java and Agile Development. She speaks at Java and JUG conferences around the world and regularly writes articles about the Java Ecosystem for the French print Developer magazine Programmez! and for the Duchess Blog. Follow Agnes @agnes_crepet. Lars Vogel Lars Vogel (Germany) is the founder and CEO of the vogella GmbH and works as Java, Eclipse and Android consultant, trainer and book author. He is a regular speaker at international conferences, such as EclipseCon, Devoxx, Droidcon and O'Reilly's Android Open. With more than one million visitors per month, his website vogella.com is one of the central sources for Java, Eclipse and Android programming information. Lars is committer in the Eclipse project and received in 2010 the "Eclipse Top Contributor Award" and 2012 the "Eclipse Top Newcomer Evangelist Award." Follow Lars on Twitter @vogella. Yara Senger Yara Senger (Brazil) has been a tireless Java activist in Brazil for many years. She is President of SouJava and she is an alternate representative of the group on the JCP Executive Committee. Yara has led SouJava in many initiatives, from technical events to social activities. She is co-founder and director of GlobalCode, which trains developers throughout Brazil.  Last year, she was recipient of the Duke Choice's Award, for the JHome embedded environment.  Yara is also an active speaker, giving presentations in many countries, including JavaOne SF, JavaOne Latin Ameria, JavaOne India, JFokus, and JUGs throughout Brazil. Yara is editor of InfoQ Brasil and also frequently posts at http://blog.globalcode.com.br/search/label/Yara. Follow Yara @YaraSenger. Martijn Verburg Martijn Verburg (UK) is the CTO of jClarity (a Java/JVM performance cloud tooling start-up) and has over 12 years experience as a Java/JVM technology professional and OSS mentor in a variety of organisations from start-ups to large enterprises. He is the co-leader of the London Java Community (~2800 developers) and leads the global effort for the Java User Group "Adopt a JSR" and "Adopt OpenJDK" programmes. These programmes encourage day to day Java developer involvement with OpenJDK, Java standards (JSRs), an important relationship for keeping the Java ecosystem relevant to the 9 million Java developers out there today. As a leading expert on technical team optimisation, his talks and presentations are in high demand by major conferences (JavaOne, Devoxx, OSCON, QCon) where you'll often find him challenging the industry status quo via his alter ego "The Diabolical Developer." You can read more in the OTN ariticle "Challenging the Diabolical Developer: A Conversation with JavaOne Rock Star Martijn Verburg." Follow Martijn @karianna. The Java Champions are an exclusive group of passionate Java technology and community leaders who are community-nominated and selected under a project sponsored by Oracle. Java Champions get the opportunity to provide feedback, ideas, and direction that will help Oracle grow the Java Platform. Congratulations to these new Java Champions!

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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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• Perm SSIS Developer Urgently Required

  - by blakmk

    Job Role To provide dedicated data services support to the company, by designing, creating, maintaining and enhancing database objects, ensuring data quality, consistency and integrity. Migrating data from various sources to central SQL 2008 data warehouse will be the primary function. Migration of data from bespoke legacy database’s to SQL 2008 data warehouse. Understand key business requirements, Liaising with various aspects of the company. Create advanced transformations of data, with focus on data cleansing, redundant data and duplication. Creating complex business rules regarding data services, migration, Integrity and support (Best Practices). Experience ·         Minimum 3 year SSIS experience, in a project or BI Development role and involvement in at least 3 full ETL project life cycles, using the following methodologies and tools o    Excellent knowledge of ETL concepts including data migration & integrity, focusing on SSIS. o    Extensive experience with SQL 2005 products, SQL 2008 desirable. o    Working knowledge of SSRS and its integration with other BI products. o    Extensive knowledge of T-SQL, stored procedures, triggers (Table/Database), views, functions in particular coding and querying. o    Data cleansing and harmonisation. o    Understanding and knowledge of indexes, statistics and table structure. o    SQL Agent – Scheduling jobs, optimisation, multiple jobs, DTS. o    Troubleshoot, diagnose and tune database and physical server performance. o    Knowledge and understanding of locking, blocks, table and index design and SQL configuration. ·         Demonstrable ability to understand and analyse business processes. ·         Experience in creating business rules on best practices for data services. ·         Experience in working with, supporting and troubleshooting MS SQL servers running enterprise applications ·         Proven ability to work well within a team and liaise with other technical support staff such as networking administrators, system administrators and support engineers. ·         Ability to create formal documentation, work procedures, and service level agreements. ·         Ability to communicate technical issues at all levels including to a non technical audience. ·         Good working knowledge of MS Word, Excel, PowerPoint, Visio and Project.   Location Based in Crawley with possibility of some remote working Contact me for more info: http://sqlblogcasts.com/blogs/blakmk/contact.aspx      

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• Entity System with C++ templates

  - by tommaisey

  I've been getting interested in the Entity/Component style of game programming, and I've come up with a design in C++ which I'd like a critique of. I decided to go with a fairly pure Entity system, where entities are simply an ID number. Components are stored in a series of vectors - one for each Component type. However, I didn't want to have to add boilerplate code for every new Component type I added to the game. Nor did I want to use macros to do this, which frankly scare me. So I've come up with a system based on templates and type hinting. But there are some potential issues I'd like to check before I spend ages writing this (I'm a slow coder!) All Components derive from a Component base class. This base class has a protected constructor, that takes a string parameter. When you write a new derived Component class, you must initialise the base with the name of your new class in a string. When you first instantiate a new DerivedComponent, it adds the string to a static hashmap inside Component mapped to a unique integer id. When you subsequently instantiate more Components of the same type, no action is taken. The result (I think) should be a static hashmap with the name of each class derived from Component that you instantiate at least once, mapped to a unique id, which can by obtained with the static method Component::getTypeId ("DerivedComponent"). Phew. The next important part is TypedComponentList<typename PropertyType>. This is basically just a wrapper to an std::vector<typename PropertyType> with some useful methods. It also contains a hashmap of entity ID numbers to slots in the array so we can find Components by their entity owner. Crucially TypedComponentList<> is derived from the non-template class ComponentList. This allows me to maintain a list of pointers to ComponentList in my main ComponentManager, which actually point to TypedComponentLists with different template parameters (sneaky). The Component manager has template functions such as: template <typename ComponentType> void addProperty (ComponentType& component, int componentTypeId, int entityId) and: template <typename ComponentType> TypedComponentList<ComponentType>* getComponentList (int componentTypeId) which deal with casting from ComponentList to the correct TypedComponentList for you. So to get a list of a particular type of Component you call: TypedComponentList<MyComponent>* list = componentManager.getComponentList<MyComponent> (Component::getTypeId("MyComponent")); Which I'll admit looks pretty ugly. Bad points of the design: If a user of the code writes a new Component class but supplies the wrong string to the base constructor, the whole system will fail. Each time a new Component is instantiated, we must check a hashed string to see if that component type has bee instantiated before. Will probably generate a lot of assembly because of the extensive use of templates. I don't know how well the compiler will be able to minimise this. You could consider the whole system a bit complex - perhaps premature optimisation? But I want to use this code again and again, so I want it to be performant. Good points of the design: Components are stored in typed vectors but they can also be found by using their entity owner id as a hash. This means we can iterate them fast, and minimise cache misses, but also skip straight to the component we need if necessary. We can freely add Components of different types to the system without having to add and manage new Component vectors by hand. What do you think? Do the good points outweigh the bad?

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• What is the most platform- and Python-version-independent way to make a fast loop for use in Python?

  - by Statto

  I'm writing a scientific application in Python with a very processor-intensive loop at its core. I would like to optimise this as far as possible, at minimum inconvenience to end users, who will probably use it as an uncompiled collection of Python scripts, and will be using Windows, Mac, and (mainly Ubuntu) Linux. It is currently written in Python with a dash of NumPy, and I've included the code below. Is there a solution which would be reasonably fast which would not require compilation? This would seem to be the easiest way to maintain platform-independence. If using something like Pyrex, which does require compilation, is there an easy way to bundle many modules and have Python choose between them depending on detected OS and Python version? Is there an easy way to build the collection of modules without needing access to every system with every version of Python? Does one method lend itself particularly to multi-processor optimisation? (If you're interested, the loop is to calculate the magnetic field at a given point inside a crystal by adding together the contributions of a large number of nearby magnetic ions, treated as tiny bar magnets. Basically, a massive sum of these.) # calculate_dipole # ------------------------- # calculate_dipole works out the dipole field at a given point within the crystal unit cell # --- # INPUT # mu = position at which to calculate the dipole field # r_i = array of atomic positions # mom_i = corresponding array of magnetic moments # --- # OUTPUT # B = the B-field at this point def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) #4pi / mu0 (at the front of the dipole eqn) A = 1e-7 #initalise dipole field B = zeros(3,float) for i in range(len(relative)): #work out the dipole field and add it to the estimate so far B += A*(3*dot(mom_i[i],r_unit[i])*r_unit[i] - mom_i[i]) / sqrt(dot(relative[i],relative[i]))**3 return B

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• Asymptotic complexity of a compiler

  - by Meinersbur

  What is the maximal acceptable asymptotic runtime of a general-purpose compiler? For clarification: The complexity of compilation process itself, not of the compiled program. Depending on the program size, for instance, the number of source code characters, statements, variables, procedures, basic blocks, intermediate language instructions, assembler instructions, or whatever. This is highly depending on your point of view, so this is a community wiki. See this from the view of someone who writes a compiler. Will the optimisation level -O4 ever be used for larger programs when one of its optimisations takes O(n^6)? Related questions: When is superoptimisation (exponential complexity or even incomputable) acceptable? What is acceptable for JITs? Does it have to be linear? What is the complexity of established compilers? GCC? VC? Intel? Java? C#? Turbo Pascal? LCC? LLVM? (Reference?) If you do not know what asymptotic complexity is: How long are you willing to wait until the compiler compiled your project? (scripting languages excluded)

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• Neural Network settings for fast training

  - by danpalmer

  I am creating a tool for predicting the time and cost of software projects based on past data. The tool uses a neural network to do this and so far, the results are promising, but I think I can do a lot more optimisation just by changing the properties of the network. There don't seem to be any rules or even many best-practices when it comes to these settings so if anyone with experience could help me I would greatly appreciate it. The input data is made up of a series of integers that could go up as high as the user wants to go, but most will be under 100,000 I would have thought. Some will be as low as 1. They are details like number of people on a project and the cost of a project, as well as details about database entities and use cases. There are 10 inputs in total and 2 outputs (the time and cost). I am using Resilient Propagation to train the network. Currently it has: 10 input nodes, 1 hidden layer with 5 nodes and 2 output nodes. I am training to get under a 5% error rate. The algorithm must run on a webserver so I have put in a measure to stop training when it looks like it isn't going anywhere. This is set to 10,000 training iterations. Currently, when I try to train it with some data that is a bit varied, but well within the limits of what we expect users to put into it, it takes a long time to train, hitting the 10,000 iteration limit over and over again. This is the first time I have used a neural network and I don't really know what to expect. If you could give me some hints on what sort of settings I should be using for the network and for the iteration limit I would greatly appreciate it. Thank you!

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• Optional Member Objects

  - by David Relihan

  Okay, so you have a load of methods sprinkled around your systems main class. So you do the right thing and refactor by creating a new class and perform move method(s) into a new class. The new class has a single responsibility and all is right with the world again: class Feature { public: Feature(){}; void doSomething(); void doSomething1(); void doSomething2(); }; So now your original class has a member variable of type object: Feature _feature; Which you will call in the main class. Now if you do this many times, you will have many member-objects in your main class. Now these features may or not be required based on configuration so in a way it's costly having all these objects that may or not be needed. Can anyone suggest a way of improving this? At the moment I plan to test in the newly created class if the feature is enabled - so the when a call is made to method I will return if it is not enabled. I could have a pointer to the object and then only call new if feature is enabled - but this means I will have to test before I call a method on it which would be potentially dangerous and not very readable. Would having an auto_ptr to the object improve things: auto_ptr<Feature> feature; Or am I still paying the cost of object invokation even though the object may\or may not be required. BTW - I don't think this is premeature optimisation - I just want to consider the possibilites.

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• Passing data between ViewControllers versus doing local Fetch in each VC

  - by Tofrizer

  Hi All, I'm developing an iPhone app using Core Data and I'm looking for some general advice and recommendations on whether its acceptable to pass data between ViewControllers versus doing a local fetch in each ViewController as you navigate to it. Ordinarily I would say it all depends on various factors (e.g. performance etc) but the passing data approach is so prevalent in my app and I'm spooked by all the stories about Apple rejecting apps because of not conforming to their standard guidelines. So let me put another way -- is it non-standard to pass data between VC's? The reason I pass data so much is because each ViewController is just another view on to data present in my object model / graph. Once I have a handle on my first object in the first view controller (which I of course do have to fetch), I can use the existing object composition / relationships to drill down into the next level of detail into data and so I just pass these objects to the next VC. Separately, one possible downside with this passing-data-to-each-VC approach is I don't benefit from (what I perceive to be) the optimisation/benefits that NSFetchedResultsController provides in terms of efficient memory usage and section handling. My app is read-only but I do have one table with 5000 rows and I'm curious if I am missing out on NSFetchedResultsController benefits. Any thoughts on this as well? Can I somehow still benefit from NSFetchedResultsController goodness without having to do a full fetch (as I would have already passed in the data from my previous VC)? Thanks a lot.

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• Destructors not called when native (C++) exception propagates to CLR component

  - by Phil Nash

  We have a large body of native C++ code, compliled into DLLs. Then we have a couple of dlls containing C++/CLI proxy code to wrap the C++ interfaces. On top of that we have C# code calling into the C++/CLI wrappers. Standard stuff, so far. But we have a lot of cases where native C++ exceptions are allowed to propagate to the .Net world and we rely on .Net's ability to wrap these as System.Exception objects and for the most part this works fine. However we have been finding that destructors of objects in scope at the point of the throw are not being invoked when the exception propagates! After some research we found that this is a fairly well known issue. However the solutions/ workarounds seem less consistent. We did find that if the native code is compiled with /EHa instead of /EHsc the issue disappears (at least in our test case it did). However we would much prefer to use /EHsc as we translate SEH exceptions to C++ exceptions ourselves and we would rather allow the compiler more scope for optimisation. Are there any other workarounds for this issue - other than wrapping every call across the native-managed boundary in a (native) try-catch-throw (in addition to the C++/CLI layer)?

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• What is different about C++ math.h abs() compared to my abs()

  - by moka

  I am currently writing some glsl like vector math classes in c++, and I just implemented an abs() function like this: template<class T> static inline T abs(T _a) { return _a < 0 ? -_a : _a; } I compared its speed to the default c++ abs from math.h like this: clock_t begin = clock(); for(int i=0; i<10000000; ++i) { float a = abs(-1.25); }; clock_t end = clock(); unsigned long time1 = (unsigned long)((float)(end-begin) / ((float)CLOCKS_PER_SEC/1000.0)); begin = clock(); for(int i=0; i<10000000; ++i) { float a = myMath::abs(-1.25); }; end = clock(); unsigned long time2 = (unsigned long)((float)(end-begin) / ((float)CLOCKS_PER_SEC/1000.0)); std::cout<<time1<<std::endl; std::cout<<time2<<std::endl; Now the default abs takes about 25ms while mine takes 60. I guess there is some low level optimisation going on. Does anybody know how math.h abs works internally? The performance difference is nothing dramatic, but I am just curious!

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• This is a great job opportunity!!! [closed]

  - by Stuart Gordon

  ASP.NET MVC Web Developer / London / £450pd / £25-£50,000pa / Interested contact [email protected] ! As a web developer within the engineering department, you will work with a team of enthusiastic developers building a new ASP.NET MVC platform for online products utilising exciting cutting edge technologies and methodologies (elements of Agile, Scrum, Lean, Kanban and XP) as well as developing new stand-alone web products that conform to W3C standards. Key Responsibilities and Objectives: Develop ASP.NET MVC websites utilising Frameworks and enterprise search technology. Develop and expand content management and delivery solutions. Help maintain and extend existing products. Formulate ideas and visions for new products and services. Be a proactive part of the development team and provide support and assistance to others when required. Qualification/Experience Required: The ideal candidate will have a web development background and be educated to degree level in a Computer Science/IT related course plus ASP.NET MVC experience. The successful candidate needs to be able to demonstrate commercial experience in all or most of the following skills: Essential: ASP.NET MVC with C# (Visual Studio), Castle, nHibernate, XHTML and JavaScript. Experience of Test Driven Development (TDD) using tools such as NUnit. Preferable: Experience of Continuous Integration (TeamCity and MSBuild), SQL Server (T-SQL), experience of source control such as Subversion (plus TortioseSVN), JQuery. Learn: Fluent NHibernate, S#arp Architecture, Spark (View engine), Behaviour Driven Design (BDD) using MSpec. Furthermore, you will possess good working knowledge of W3C web standards, web usability, web accessibility and understand the basics of search engine optimisation (SEO). You will also be a quick learner, have good communication skills and be a self-motivated and organised individual.

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• gcc -finline-functions behaviour?

  - by user176168

  I'm using gcc with the -finline-functions optimization for release builds. In order to combat code bloat because I work on an embedded system I want to say don't inline particular functions. The obvious way to do this would be through function attributes ie attribute(noinline). The problem is this doesn't seem to work when I switch on the global -finline-functions optimisation which is part of the -O3 switch. It also has something to do with it being templated as a non templated version of the same function doesn't get inlined which is as expected. Has anybody any idea of how to control inlining when this global switch is on? Here's the code: #include <cstdlib> #include <iostream> using namespace std; class Base { public: template<typename _Type_> static _Type_ fooT( _Type_ x, _Type_ y ) __attribute__ (( noinline )); }; template<typename _Type_> _Type_ Base::fooT( _Type_ x, _Type_ y ) { asm(""); return x + y; } int main(int argc, char *argv[]) { int test = Base::fooT( 1, 2 ); printf( "test = %d\n", test ); system("PAUSE"); return EXIT_SUCCESS; }

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• Is there any point in using a volatile long?

  - by Adamski

  I occasionally use a volatile instance variable in cases where I have two threads reading from / writing to it and don't want the overhead (or potential deadlock risk) of taking out a lock; for example a timer thread periodically updating an int ID that is exposed as a getter on some class: public class MyClass { private volatile int id; public MyClass() { ScheduledExecutorService execService = Executors.newScheduledThreadPool(1); execService.scheduleAtFixedRate(new Runnable() { public void run() { ++id; } }, 0L, 30L, TimeUnit.SECONDS); } public int getId() { return id; } } My question: Given that the JLS only guarantees that 32-bit reads will be atomic is there any point in ever using a volatile long? (i.e. 64-bit). Caveat: Please do not reply saying that using volatile over synchronized is a case of pre-optimisation; I am well aware of how / when to use synchronized but there are cases where volatile is preferable. For example, when defining a Spring bean for use in a single-threaded application I tend to favour volatile instance variables, as there is no guarantee that the Spring context will initialise each bean's properties in the main thread.

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• C++, using one byte to store two variables

  - by 2di

  Hi All I am working on representation of the chess board, and I am planning to store it in 32 bytes array, where each byte will be used to store two pieces. (That way only 4 bits are needed per piece) Doing it in that way, results in a overhead for accessing particular index of the board. Do you think that, this code can be optimised or completely different method of accessing indexes can be used? c++ char getPosition(unsigned char* c, int index){ //moving pointer c+=(index>>1); //odd number if (index & 1){ //taking right part return *c & 0xF; }else { //taking left part return *c>>4; } } void setValue(unsigned char* board, char value, int index){ //moving pointer board+=(index>>1); //odd number if (index & 1){ //replace right part //save left value only 4 bits *board = (*board & 0xF0) + value; }else { //replacing left part *board = (*board & 0xF) + (value<<4); } } int main() { char* c = (char*)malloc(32); for (int i = 0; i < 64 ; i++){ setValue((unsigned char*)c, i % 8,i); } for (int i = 0; i < 64 ; i++){ cout<<(int)getPosition((unsigned char*)c, i)<<" "; if (((i+1) % 8 == 0) && (i > 0)){ cout<<endl; } } return 0; } I am equally interested in your opinions regarding chess representations, and optimisation of the method above, as a stand alone problem. Thanks a lot

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• Whether to put method code in a VB.Net data storage class, or put it in a separate class?

  - by Alan K

  TLDR summary: (a) Should I include (lengthy) method code in classes which may spawn multiple objects at runtime, (b) does doing so cause memory usage bloat, (c) if so should I "outsource" the code to a class that is loaded only once and have the class methods call that, or alternatively (d) does the code get loaded only once with the object definition anyway and I'm worrying about nothing? ........ I don't know whether there's a good answer to this but if there is I haven't found it yet by searching in the usual places. In my VB.Net (2010 if it matters) WinForms project I have about a dozen or so class objects in an object model. Some of these are pretty simple and do little more than act as data storage repositories. The ones further up the object model, however, have an increasing number of methods. There can be a significant number of higher level objects in use though the exact number will be runtime dependent so I can't be more precise than that. As I was writing the method code for one of the top level ones I noticed that it was starting to get quite lengthy. Memory optimisation is something of a lost art given how much memory the average PC has these days but I don't want to make my application a resource hog. So my questions for anyone who knows .Net way better than I do (of which there will be many) are: Is the code loaded into memory with each instance of the class that's created? Alternatively is it loaded only once with the definition of the class, and all derived objects just refer to that definition? (I'm not really sure how that could be possible given that, for example, event handlers can be assigned dynamically, but no harm asking.) If the answer to the first one is yes, would it be more efficient to write the code in a "utility" object which is loaded only once and called from the real class' methods? Any thoughts appreciated.

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• Overhead of calling tiny functions from a tight inner loop? [C++]

  - by John

  Say you see a loop like this one: for(int i=0; i<thing.getParent().getObjectModel().getElements(SOME_TYPE).count(); ++i) { thing.getData().insert( thing.GetData().Count(), thing.getParent().getObjectModel().getElements(SOME_TYPE)[i].getName() ); } if this was Java I'd probably not think twice. But in performance-critical sections of C++, it makes me want to tinker with it... however I don't know if the compiler is smart enough to make it futile. This is a made up example but all it's doing is inserting strings into a container. Please don't assume any of these are STL types, think in general terms about the following: Is having a messy condition in the for loop going to get evaluated each time, or only once? If those get methods are simply returning references to member variables on the objects, will they be inlined away? Would you expect custom [] operators to get optimized at all? In other words is it worth the time (in performance only, not readability) to convert it to something like: ElementContainer &source = thing.getParent().getObjectModel().getElements(SOME_TYPE); int num = source.count(); Store &destination = thing.getData(); for(int i=0;i<num;++i) { destination.insert(thing.GetData().Count(), source[i].getName(); } Remember, this is a tight loop, called millions of times a second. What I wonder is if all this will shave a couple of cycles per loop or something more substantial? Yes I know the quote about "premature optimisation". And I know that profiling is important. But this is a more general question about modern compilers, Visual Studio in particular.

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• What influences running time of reading a bunch of images?

  - by remi

  I have a program where I read a handful of tiny images (50000 images of size 32x32). I read them using OpenCV imread function, in a program like this: std::vector<std::string> imageList; // is initialized with full path to the 50K images for(string s : imageList) { cv::Mat m = cv::imread(s); } Sometimes, it will read the images in a few seconds. Sometimes, it takes a few minutes to do so. I run this program in GDB, with a breakpoint further away than the loop for reading images so it's not because I'm stuck in a breakpoint. The same "erratic" behaviour happens when I run the program out of GDB. The same "erratic" behaviour happens with program compiled with/without optimisation The same "erratic" behaviour happens while I have or not other programs running in background The images are always at the same place in the hard drive of my machine. I run the program on a Linux Suse distrib, compiled with gcc. So I am wondering what could affect the time of reading the images that much?

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• Will spreading your servers load not just consume more recourses

  - by Saif Bechan

  I am running a heavy real-time updating website. The amount of recourses needed per user are quite high, ill give you an example. Setup Every visit The application is php/mysql so on every visit static and dynamic content is loaded. Recourses: apache,php,mysql Every second (no more than a second will just be too long) The website needs to be updated real-time so every second there is an ajax call thats updates the website. Recourses: jQuery,apache,php,mysql Avarage spending for single user (spending one minute and visited 3 pages) Apache: +/- 63 requests / responsess serving static and dynamic content (img,css,js,html) php: +/- 63 requests / responses mysql: +/- 63 requests / responses jquery: +/- 60 requests / responses Optimization I want to optimize this process, but I think that maybe it would be just the same in the end. Before implementing and testing (which will take weeks) I wanted to have some second opinions from you guys. Every visit I want to start off with having nginx in the front and work as a proxy to deliver the static content. Recources: Dynamic: apache,php,mysql Static: nginx This will spread the load on apache a lot. Every Second For the script that loads every second I want to set up Node.js server side javascript with nginx in te front. I want to set it up that jquery makes a request ones a minute, and node.js streams the data to the client every second. Recources: jQuery,nginx,node.js,mysql Avarage spending for single user (spending one minute and visited 3 pages) Nginx: 4 requests / responsess serving mostly static conetent(img,css,js) Apache: 3 requests only the pages php: 3 requests only the pages node.js: 1 request / 60 responses jquery: 1 request / 60 responses mysql: 63 requests / responses Optimization As you can see in the optimisation the load from Apache and PHP are lifted and places on nginx and node.js. These are known for there light footprint and good performance. But I am having my doubts, because there are still 2 programs extra loaded in the memory and they consume cpu. So it it better to have less programs that do the job, or more. Before I am going to spend a lot of time setting this up I would like to know if it will be worth the while.

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• WordPress SEO Plugins to make your Blog Search Engine Friendly

  - by Vaibhav

  WordPress is the most common blogging system in use today and its use as a CMS is also wide spread. With hundreds of millions of sites using wordpress, getting correct SEO for your WordPress based Blog or Site is very important. We get regular queries from people who want Search Engine Optimisation for their site or blog which is made using wordpress. Here is a list of 16 of the best WordPress Plug-ins That can help you achieve better rankings: All in one SEO Pack This is most popular plugin among all SEO plugins for WordPress. It is easy to use and is compatible with most of the WordPress plugins. It works as a complete package of SEO plugin – automatically generating META tags and optimizing search engines for your titles and avoiding duplicate content. You can also include META tags manually (Met title, Meta description and Met keywords) for all pages and post in your website. HeadSpace2 HeasSpace2 is available in different languages , you can manage a wide range of SEO Tasks related with meta data, you can tag your posts, Custom descriptions and titles. So your page can rank the created relevancy on Search engines and you can load different settings for different pages. Platinum SEO plugin Automatic 301 redirects permalink changes, META tags generation, avoids duplicate content, and does SEO optimization of post and page titles and a lots of other features. TGFI.net SEO WordPress Plugin It’s a modified version of all-in-one SEO Pack. It has some unique feature over All-in-one SEO plugin, It generate titles, meta descriptions and meta keywords automatically when overrides are not present. Google XML Sitemaps Sitemaps Generated by this tool are supported by  Google,  Yahoo,  Bing, and Ask. We all know Sitemaps make indexing of web pages easier for web crawlers. Crawlers can retrieve complete structure of site and more information by sitemaps. They notify all major search engines about new posts every time you create a new post. Sitemap Generator You can generate highly customizable sitemap for your WordPress page. You can choose what to show and what not to show, you can list the items in your choice of orde. It supports pages and permalinks and multi-level categories. SEO Slugs They can generate more search engine friendly URLs for your site. Slugs are filename assigned to your post , this plugin removes all  common words like ‘a’, ‘the’, ‘in’, ‘what’, ‘you’ from slug which are assigned automatically to your post. SEO Post Links This is a similar plugin to SEO Slug, it removes unnecessary keywords from slug to make it short and SEO friendly and you can fix the number of characters in your post. Automatic SEO links With this tool you can create auto linking in your post. You can use this tool for inter linking or external linking too. Just select your words, anchor text target URL nature of links ( Do fallow / No follow ). This plugin will replace the matches found in post, WP Backlinks A helpful plugin for link exchange , whenever any webmaster submits a link for link exchange, the plugin will spider webmasters site for reciprocal link, and if everything is found good , your link will be exchanged. SEO Title Tag You can optimize your Title  tags of  Word press blog through this plugin . You can also override the title tag with custom titles , mass editing and title tags for 404 pages which are the main feature of this plugin. 404 SEO plugin With this Plugin you can customize 404 page of your site; you can give customized error message and links to relevant pages of your site. Redirection A powerful plugins to manage 301 redirection and logs related with redirection, with this plugin you can track 404 errors and track the log of all redirected URLs , this plugin can redirect  post automatically when URL changes for that post. AddToAny This plugin helps your readers to share, save, email and bookmark your posts and pages. It supports more than a hundred social bookmarking , networking and sharing sites. SEO Friendly Images You can make SEO friendly images available on your site with the help of this tool. It updates images with proper titles and ALT tags. Robots Meta A plugin which prevents Search engines to index comments on your post, login and admin pages. It also allows to add tags for individual pages.

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