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• How can I make hundreds of simultaneously running processes communicate with a database through one

  - by Olfan

  Long speech short: How can I make hundreds of simultaneously running processes communicate with a database through one or few permanent sessions? The whole story: I once built a number crunching engine that handles vast amounts of large data files by forking off one child after another giving each a small number of files to work on. File locking, progress monitoring and result propagation happen in an Oracle database which all (sub-)processes access at various times using an application-specific module which encapsulates DBI. This worked well at first, but now with higher volumes of input data, the number of database sessions (one per child, and they can be very short-lived) constantly being opened and closed is becoming an issue. I now want to centralise database access so that there are only one or few fixed database sessions which handle all database access for all the (sub-)processes. The presence of the database abstraction module should make the changes easy because the function calls in the worker instances can stay the same. My problem is that I cannot think of a suitable way to enhance said module in order to establish communication between all the processes and the database connector(s). I thought of message queueing, but couldn't come up with a way of connecting a large herd of requestors with one or few database connectors in a way so that bidirectional communication is possible (for collecting the query result). An asynchronous approach could help here in that all requests are written to the same queue and the database connector servicing the request will "call back" to submit the result. But my mind fails me in generating an image clear enough so that I can paint into code. Threading instead of forking might have given me an easier start, but this would now require massive changes to the code base that I'm not prepared to do to a live system. The more I think of it, the more the base idea looks like a pre-forked web server to me only that it doesn't serve web pages but database queries. Any ideas on what to dig into, and where? Sample (pseudo) code to inspire me, links to possibly related articles, ready solutions on CPAN maybe?

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• Displaying count for current_user 'likes' on a 'question' in questions/show.html.erb view

  - by bgadoci

  I have an application that allows for users to create questions, create answers to questions, and 'like' answers of others. When a current_user lands on the /views/questions/show.html.erb page I am trying to display the total 'likes' for all answers on that question, for the current_user. In my Likes table I am collecting the question_id, site_id and the user_id and I have the appropriate associations set up between user, question, answers and likes. I think I just need to call this information the right way, which I can't seem to figure out. All of the below is taking place in the /views/questions/show.html.erb page. I have tried the following: <% div_for current_user do %> You have liked this question <%= @question.likes.count %> times <% end %> Which returns all the 'likes' for the question but not filtered by current_user You have liked this question <%= current_user.question.likes.count %> times Which gives an error of 'undefined method `question' You have liked this question <%= @question.current_user.likes.count %> times Which gives an error of 'undefined method `current_user' I have tried a couple of other things but they don't make as much sense as the above to me. What am I missing?

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• Database (MySQL) structuring: pros and cons of multiple tables

  - by Gideon

  I am collecting data and storing it MySQL, for: 75 variables 55 countries Each year I have, at this stage since I am building this tool created a single table, of variables / countries (storing 1 year worth of data). Next year (and for several years after that) a new set of data will be input for each country. There are therefore 3 variables in controlling data returned to a user reviewing all collected data. The general form of any query would be: Show me these specifics variables, for these specific countries, for these specific years. (Show me average age and weight, for USA and Canada, for 2012 and 2009, for example) My question is, it seems that I have two options for arranging this data: -Multiple tables where I create a table of country / variable for each year data is collected - Single table and simply add a column (field) for the year that data relates to. As far as I can tell I could make these database calls with either sructure, but is one more powerful / efficient / quicker, and why? Thanks for your consideration. It's a PDO / PHP interface if that is relevent.

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• Database solution for 200million writes/day, monthly summarization queries

  - by sb

  Hello. I'm looking for help deciding on which database system to use. (I've been googling and reading for the past few hours; it now seems worthwhile to ask for help from someone with firsthand knowledge.) I need to log around 200 million rows (or more) per 8 hour workday to a database, then perform weekly/monthly/yearly summary queries on that data. The summary queries would be for collecting data for things like billing statements, eg. "How many transactions of type A did each user run this month?" (could be more complex, but that's the general idea). I can spread the database amongst several machines, as necessary, but I don't think I can take old data offline. I'll definitely need to be able to query a month's worth of data, maybe a year. These queries would be for my own use, and wouldn't need to be generated in real-time for an end-user (they could run overnight, if needed). Does anyone have any suggestions as to which databases would be a good fit? P.S. Cassandra looks like it would have no problem handling the writes, but what about the huge monthly table scans? Is anyone familiar with Cassandra/Hadoop MapReduce performance?

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• Is 4-5 years the “Midlife Crisis” for a programming career?

  - by Jeff

  I’ve been programming C# professionally for a bit over 4 years now. For the past 4 years I’ve worked for a few small/medium companies ranging from “web/ads agencies”, small industry specific software shops to a small startup. I've been mainly doing "business apps" that involves using high-level programming languages (garbage collected) and my overall experience was that all of the works I’ve done could have been more professional. A lot of the things were done incorrectly (in a rush) mainly due to cost factor that people always wanted something “now” and with the smallest amount of spendable money. I kept on thinking maybe if I could work for a bigger companies or a company that’s better suited for programmers, or somewhere that's got the money and time to really build something longer term and more maintainable I may have enjoyed more in my career. I’ve never had a “mentor” that guided me through my 4 years career. I am pretty much blog / google / self taught programmer other than my bachelor IT degree. I’ve also observed another issue that most so called “senior” programmer in “my working environment” are really not that senior skill wise. They are “senior” only because they’ve been a long time programmer, but the code they write or the decisions they make are absolutely rubbish! They don't want to learn, they don't want to be better they just want to get paid and do what they've told to do which make sense and most of us are like that. Maybe that’s why they are where they are now. But I don’t want to become like them I want to be better. I’ve run into a mental state that I no longer intend to be a programmer for my future career. I started to think maybe there are better things out there to work on. The more blogs I read, the more “best practices” I’ve tried the more I feel I am drifting away from “my reality”. But I am not a great programmer otherwise I don't think I am where I am now. I think 4-5 years is a stage that can be a step forward career wise or a step out of where you are. I just wanted to hear what other have to say about what I’ve mentioned above and whether you’ve experienced similar situation in your past programming career and how you dealt with it. Thanks.

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• Chuck Norris Be Thy Name

  - by Robz / Fervent Coder

  Chuck Norris doesn’t program with a keyboard. He stares the computer down until it does what he wants. All things need a name. We’ve tossed around a bunch of names for the framework of tools we’ve been working on, but one we kept coming back to was Chuck Norris. Why did we choose Chuck Norris? Well Chuck Norris sort of chose us. Everything we talked about, the name kept drawing us closer to it. We couldn’t escape Chuck Norris, no matter how hard we tried. So we gave in. Chuck Norris can divide by zero. What is the Chuck Norris Framework? @drusellers and I have been working on a variety of tools: WarmuP - http://github.com/chucknorris/warmup (Template your entire project/solution and create projects ready to code - From Zero to a Solution with everything in seconds. Your templates, your choices.) UppercuT - http://projectuppercut.org (Build with Conventions - Professional Builds in Moments, Not Days!) | Code also at http://github.com/chucknorris/uppercut DropkicK - http://github.com/chucknorris/dropkick (Deploy Fluently) RoundhousE - http://projectroundhouse.org (Professional Database Management with Versioning) | Code also at http://github.com/chucknorris/roundhouse SidePOP - http://sidepop.googlecode.com (Does your application need to check email?) HeadlocK - http://github.com/chucknorris/headlock (Hash a directory so you can later know if anything has changed) Others – still in concept or vaporware People ask why we choose such violent names for each tool of our framework? At first it was about whipping your code into shape, but after awhile the naming became, “How can we relate this to Chuck Norris?” People also ask why we uppercase the last letter of each name. Well, that’s more about making you ask questions…but there are a few reasons for it. Project managers never ask Chuck Norris for estimations…ever. The class object inherits from Chuck Norris Chuck Norris doesn’t need garbage collection because he doesn’t call .Dispose(), he calls .DropKick() So what are you waiting for? Join the Google group today, download and play with the tools. And lastly, welcome to Chuck Norris. Or should I say Chuck Norris welcomes you…

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• Inside Red Gate - Ricky Leeks

  - by Simon Cooper

  So, one of our profilers has a problem. Red Gate produces two .NET profilers - ANTS Performance Profiler (APP) and ANTS Memory Profiler (AMP). Both products help .NET developers solve problems they are virtually guaranteed to encounter at some point in their careers - slow code, and high memory usage, respectively. Everyone understands slow code - the symptoms are very obvious (an operation takes 2 hours when it should take 10 seconds), you know when you've solved it (the same operation now takes 15 seconds), and everyone understands how you can use a profiler like APP to help solve your particular problem. High memory usage is a much more subtle and misunderstood concept. How can .NET have memory leaks? The garbage collector, and how the CLR uses and frees memory, is one of the most misunderstood concepts in .NET. There's hundreds of blog posts out there covering various aspects of the GC and .NET memory, some of them helpful, some of them confusing, and some of them are just plain wrong. There's a lot of misconceptions out there. And, if you have got an application that uses far too much memory, it can be hard to wade through all the contradictory information available to even get an idea as to what's going on, let alone trying to solve it. That's where a memory profiler, like AMP, comes into play. Unfortunately, that's not the end of the issue. .NET memory management is a large, complicated, and misunderstood problem. Even armed with a profiler, you need to understand what .NET is doing with your objects, how it processes them, and how it frees them, to be able to use the profiler effectively to solve your particular problem. And that's what's wrong with AMP - even with all the thought, designs, UX sessions, and research we've put into AMP itself, some users simply don't have the knowledge required to be able to understand what AMP is telling them about how their application uses memory, and so they have problems understanding & solving their memory problem. Ricky Leeks This is where Ricky Leeks comes in. Created by one of the many...colourful...people in Red Gate, he headlines and promotes several tutorials, pages, and articles all with information on how .NET memory management actually works, with the goal to help educate developers on .NET memory management. And educating us all on how far you can push various vegetable-based puns. This, in turn, not only helps them understand and solve any memory issues they may be having, but helps them proactively code against such memory issues in their existing code. Ricky's latest outing is an interview on .NET Rocks, providing information on the Top 5 .NET Memory Management Gotchas, along with information on a free ebook on .NET Memory Management. Don't worry, there's loads more vegetable-based jokes where those came from...

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• clear explanation sought: throw() and stack unwinding

  - by Jerry Gagelman

  I'm not a programmer but have learned a lot watching others. I am writing wrapper classes to simplify things with a really technical API that I'm working with. Its routines return error codes, and I have a function that converts those to strings: static const char* LibErrString(int errno); For uniformity I decided to have member of my classes throw an exception when an error is encountered. I created a class: struct MyExcept : public std::exception { const char* errstr_; const char* what() const throw() {return errstr_;} MyExcept(const char* errstr) : errstr_(errstr) {} }; Then, in one of my classes: class Foo { public: void bar() { int err = SomeAPIRoutine(...); if (err != SUCCESS) throw MyExcept(LibErrString(err)); // otherwise... } }; The whole thing works perfectly: if SomeAPIRoutine returns an error, a try-catch block around the call to Foo::bar catches a standard exception with the correct error string in what(). Then I wanted the member to give more information: void Foo::bar() { char adieu[128]; int err = SomeAPIRoutine(...); if (err != SUCCESS) { std::strcpy(adieu,"In Foo::bar... "); std::strcat(adieu,LibErrString(err)); throw MyExcept((const char*)adieu); } // otherwise... } However, when SomeAPIRoutine returns an error, the what() string returned by the exception contains only garbage. It occurred to me that the problem could be due to adieu going out of scope once the throw is called. I changed the code by moving adieu out of the member definition and making it an attribute of the class Foo. After this, the whole thing worked perfectly: a try-call block around a call to Foo::bar that catches an exception has the correct (expanded) string in what(). Finally, my question: what exactly is popped off the stack (in sequence) when the exception is thrown in the if-block when the stack "unwinds?" As I mentioned above, I'm a mathematician, not a programmer. I could use a really lucid explanation of what goes onto the stack (in sequence) when this C++ gets converted into running machine code.

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• Back-sliding into Unmanaged Code

  - by Laila

  It is difficult to write about Microsoft's ambivalence to .NET without mentioning clichés about dog food.  In case you've been away a long time, you'll remember that Microsoft surprised everyone with the speed and energy with which it introduced and evangelised the .NET Framework for managed code. There was good reason for this. Once it became obvious to all that it had sleepwalked into third place as a provider of development languages, behind Borland and Sun, it reacted quickly to attract the best talent in the industry to produce a windows version of the Java runtime, with Bounds-checking, Automatic Garbage collection, structures exception handling and common data types. To develop applications for this managed runtime, it produced several excellent languages, and more are being provided. The only thing Microsoft ever got wrong was to give it a stupid name. The logical step for Microsoft would be to base the entire operating system on the .NET framework, and to re-engineer its own applications. In 2002, Bill Gates, then Microsoft Chairman and Chief Software Architect said about their plans for .NET, "This is a long-term approach. These things don't happen overnight." Now, eight years later, we're still waiting for signs of the 'long-term approach'. Microsoft's vision of an entirely managed operating system has subsided since the Vista fiasco, but stays alive yet dormant as Midori, still being developed by Microsoft Research. This is an Internet-centric fork of the singularity operating system, a research project started in 2003 to build a highly-dependable operating system in which the kernel, device drivers, and applications are all written in managed code. Midori is predicated on the prevalence of connected systems, with provisions for distributed concurrency where application components exist 'in the cloud', and supports a programming model that can tolerate cancellation, intermittent connectivity and latency. It features an entirely new security model that sandboxes applications for increased security. So have Microsoft converted its existing applications to the .NET framework? It seems not. What Windows applications can run on Mono? Very few, it seems. We all thought that .NET spelt the end of DLL Hell and the need for COM interop, but it looks as if Bill Gates' idea of 'not overnight' might stretch to a decade or more. The Operating System has shown only minimal signs of migrating to .NET. Even where the use of .NET has come to dominate, when used for server applications with IIS, IIS itself is still entirely developed in unmanaged code. This is an irritation to Microsoft's greatest supporters who committed themselves fully to the NET framework, only to find parts of the Ambivalent Microsoft Empire quietly backsliding into unmanaged code and the awful C++. It is a strategic mistake that the invigorated Apple didn't make with the Mac OS X Architecture. Cheers, Laila

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• Can one draw a cube using different method/drawing mode?

  - by den-javamaniac

  Hi. I've just started learning gamedev (in particular android EGL based) and have ran over a code from Pro Android Games 2 that looks as follows: /* * Copyright (C) 2007 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package opengl.scenes.cubes; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.IntBuffer; import javax.microedition.khronos.opengles.GL10; public class Cube { public Cube(){ int one = 0x10000; int vertices[] = { -one, -one, -one, one, -one, -one, one, one, -one, -one, one, -one, -one, -one, one, one, -one, one, one, one, one, -one, one, one, }; int colors[] = { 0, 0, 0, one, one, 0, 0, one, one, one, 0, one, 0, one, 0, one, 0, 0, one, one, one, 0, one, one, one, one, one, one, 0, one, one, one, }; byte indices[] = { 0, 4, 5, 0, 5, 1, 1, 5, 6, 1, 6, 2, 2, 6, 7, 2, 7, 3, 3, 7, 4, 3, 4, 0, 4, 7, 6, 4, 6, 5, 3, 0, 1, 3, 1, 2 }; // Buffers to be passed to gl*Pointer() functions // must be direct, i.e., they must be placed on the // native heap where the garbage collector cannot vbb.asIntBuffer() // move them. // // Buffers with multi-byte datatypes (e.g., short, int, float) // must have their byte order set to native order ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4); vbb.order(ByteOrder.nativeOrder()); mVertexBuffer = vbb.asIntBuffer(); mVertexBuffer.put(vertices); mVertexBuffer.position(0); ByteBuffer cbb = ByteBuffer.allocateDirect(colors.length*4); cbb.order(ByteOrder.nativeOrder()); mColorBuffer = cbb.asIntBuffer(); mColorBuffer.put(colors); mColorBuffer.position(0); mIndexBuffer = ByteBuffer.allocateDirect(indices.length); mIndexBuffer.put(indices); mIndexBuffer.position(0); } public void draw(GL10 gl) { gl.glFrontFace(GL10.GL_CW); gl.glVertexPointer(3, GL10.GL_FIXED, 0, mVertexBuffer); gl.glColorPointer(4, GL10.GL_FIXED, 0, mColorBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, 36, GL10.GL_UNSIGNED_BYTE, mIndexBuffer); } private IntBuffer mVertexBuffer; private IntBuffer mColorBuffer; private ByteBuffer mIndexBuffer;} So it suggests to draw a cube using triangles. My question is: can I draw the same cube using GL_TPOLYGON? If so, isn't that an easier/more understandable way to do things?

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• Oracle Tutor: *** CAUTION to Word .docx Users ***

  - by [email protected]

  Microsoft released a security update KB969604 for Office 2007 (around June 2009) This update causes document variables within Word docx files to be scrambled. This update might still be pushed out via Office 2007 updates DO NOT save files as docx using MS OFFICE 2007 until you apply the MS hotfix # 970942 available here If you are using Windows XP with Office 2003 or Office 2000 and have installed an older Office 2007 compatibility pack, documents saved as docx may also cause the scrambled document variables. Installing the 2007 compatibility pack published on 1/6/2010 (version 4) will prevent the document variables from becoming corrupt. Those on Windows 2000 may not be able to install the latest compatibility pack, or the compatibility pack may not function properly. This situation will hopefully be rectified in the coming months. What is a document variable? Document variables store data inside the document, invisible to the user. The Tutor software uses them when converting the document to HTML and when creating the flowchart, just to name a couple of uses. How will you know if a document's variables are scrambled? The difficulty in diagnosing the issue is that the symptoms can take myriad forms. There isn't a single error message or a single feature that one can point to and say, "test for the problem by doing this." The best clue about the error is seeing any kind of string in an error message that has garbage characters, question marks, xml code snippets, or just nonsense. Such as "Language ?????????????xlr;lwlerkjl could not be found." It is also possible to see the corrupted data in the footers of the Word docs. And, just because the footers look correct does not mean that the document variables are not corrupted. The corruption problem does not occur in every document variable in the document, just some of them. Often it is less than a quarter of them. What is the difference between docx files and doc files? Office 2007 uses Office Open XML formats with .docx and .docm filename extensions. - Docx is an Office Open XML word document. - Docm is a macro enabled Office Open XML document. This means the file structure behind the scenes is quite different from the binary file formats used prior to Office 2007 such as .doc, .dot, .xls, and .ppt. Solution Summary: For Windows XP and Word 2007: Install the hotfix, or save files as *.doc For Windows XP and Word 2000 and 2003: Install the latest compatibility pack or save files as *.doc For Windows 2000 with Word 2000 or 2003, do not use any compatibility pack, save files as *.doc Emily Chorba Principle Product Manager for Oracle Tutor

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• Are there deprecated practices for multithread and multiprocessor programming that I should no longer use?

  - by DeveloperDon

  In the early days of FORTRAN and BASIC, essentially all programs were written with GOTO statements. The result was spaghetti code and the solution was structured programming. Similarly, pointers can have difficult to control characteristics in our programs. C++ started with plenty of pointers, but use of references are recommended. Libraries like STL can reduce some of our dependency. There are also idioms to create smart pointers that have better characteristics, and some version of C++ permit references and managed code. Programming practices like inheritance and polymorphism use a lot of pointers behind the scenes (just as for, while, do structured programming generates code filled with branch instructions). Languages like Java eliminate pointers and use garbage collection to manage dynamically allocated data instead of depending on programmers to match all their new and delete statements. In my reading, I have seen examples of multi-process and multi-thread programming that don't seem to use semaphores. Do they use the same thing with different names or do they have new ways of structuring protection of resources from concurrent use? For example, a specific example of a system for multithread programming with multicore processors is OpenMP. It represents a critical region as follows, without the use of semaphores, which seem not to be included in the environment. th_id = omp_get_thread_num(); #pragma omp critical { cout << "Hello World from thread " << th_id << '\n'; } This example is an excerpt from: http://en.wikipedia.org/wiki/OpenMP Alternatively, similar protection of threads from each other using semaphores with functions wait() and signal() might look like this: wait(sem); th_id = get_thread_num(); cout << "Hello World from thread " << th_id << '\n'; signal(sem); In this example, things are pretty simple, and just a simple review is enough to show the wait() and signal() calls are matched and even with a lot of concurrency, thread safety is provided. But other algorithms are more complicated and use multiple semaphores (both binary and counting) spread across multiple functions with complex conditions that can be called by many threads. The consequences of creating deadlock or failing to make things thread safe can be hard to manage. Do these systems like OpenMP eliminate the problems with semaphores? Do they move the problem somewhere else? How do I transform my favorite semaphore using algorithm to not use semaphores anymore?

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• Library to fake intermittent failures according to tester-defined policy?

  - by crosstalk

  I'm looking for a library that I can use to help mock a program component that works only intermittently - usually, it works fine, but sometimes it fails. For example, suppose I need to read data from a file, and my program has to avoid crashing or hanging when a read fails due to a disk head crash. I'd like to model that by having a mock data reader function that returns mock data 90% of the time, but hangs or returns garbage otherwise. Or, if I'm stress-testing my full program, I could turn on debugging code in my real data reader module to make it return real data 90% of the time and hang otherwise. Now, obviously, in this particular example I could just code up my mock manually to test against a random() routine. However, I was looking for a system that allows implementing any failure policy I want, including: Fail randomly 10% of the time Succeed 10 times, fail 4 times, repeat Fail semi-randomly, such that one failure tends to be followed by a burst of more failures Any policy the tester wants to define Furthermore, I'd like to be able to change the failure policy at runtime, using either code internal to the program under test, or external knobs or switches (though the latter can be implemented with the former). In pig-Java, I'd envision a FailureFaker interface like so: interface FailureFaker { /** Return true if and only if the mocked operation succeeded. Implementors should override this method with versions consistent with their failure policy. */ public boolean attempt(); } And each failure policy would be a class implementing FailureFaker; for example there would be a PatternFailureFaker that would succeed N times, then fail M times, then repeat, and a AlwaysFailFailureFaker that I'd use temporarily when I need to simulate, say, someone removing the external hard drive my data was on. The policy could then be used (and changed) in my mock object code like so: class MyMockComponent { FailureFaker faker; public void doSomething() { if (faker.attempt()) { // ... } else { throw new RuntimeException(); } } void setFailurePolicy (FailureFaker policy) { this.faker = policy; } } Now, this seems like something that would be part of a mocking library, so I wouldn't be surprised if it's been done before. (In fact, I got the idea from Steve Maguire's Writing Solid Code, where he discusses this exact idea on pages 228-231, saying that such facilities were common in Microsoft code of that early-90's era.) However, I'm only familiar with EasyMock and jMockit for Java, and neither AFAIK have this function, or something similar with different syntax. Hence, the question: Do such libraries as I've described above exist? If they do, where have you found them useful? If you haven't found them useful, why not?

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• Programming Language, Turing Completeness and Turing Machine

  - by Amumu

  A programming language is said to be Turing Completeness if it can successfully simulate a universal TM. Let's take functional programming language for example. In functional programming, function has highest priority over anything. You can pass functions around like any primitives or objects. This is called first class function. In functional programming, your function does not produce side effect i.e. output strings onto screen, change the state of variables outside of its scope. Each function has a copy of its own objects if the objects are passed from the outside, and the copied objects are returned once the function finishes its job. Each function written purely in functional style is completely independent to anything outside of it. Thus, the complexity of the overall system is reduced. This is referred as referential transparency. In functional programming, each function can have its local variables kept its values even after the function exits. This is done by the garbage collector. The value can be reused the next time the function is called again. This is called memoization. A function usually should solve only one thing. It should model only one algorithm to answer a problem. Do you think that a function in a functional language with above properties simulate a Turing Machines? Functions (= algorithms = Turing Machines) are able to be passed around as input and returned as output. TM also accepts and simulate other TMs Memoization models the set of states of a Turing Machine. The memorized variables can be used to determine states of a TM (i.e. which lines to execute, what behavior should it take in a give state ...). Also, you can use memoization to simulate your internal tape storage. In language like C/C++, when a function exits, you lose all of its internal data (unless you store it elsewhere outside of its scope). The set of symbols are the set of all strings in a programming language, which is the higher level and human-readable version of machine code (opcode) Start state is the beginning of the function. However, with memoization, start state can be determined by memoization or if you want, switch/if-else statement in imperative programming language. But then, you can't Final accepting state when the function returns a value, or rejects if an exception happens. Thus, the function (= algorithm = TM) is decidable. Otherwise, it's undecidable. I'm not sure about this. What do you think? Is my thinking true on all of this? The reason I bring function in functional programming because I think it's closer to the idea of TM. What experience with other programming languages do you have which make you feel the idea of TM and the ideas of Computer Science in general? Can you specify how you think?

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• Is there a pedagogical game engine?

  - by K.G.

  I'm looking for a book, website, or other resource that gives modern 3D game engines the same treatment as Operating Systems: Design and Implementation gave operating systems. I have read Jason Gregory's Game Engine Architecture, which I enjoyed. However, by intent the author treated components of the architecture as atomic units, whereas what I'm interested in is the plumbing between those units that makes a coherent whole out of ideally loosely coupled parts. In books such as these, one usually reads that "that's academic," but that's the point! I have also read Julian Gold's Object-oriented Game Development, which likewise was good, but I feel is beginning to show its age. Since even mobile platforms these days are multicore and have fast video memory, those kinds of things (concurrency, display item buffering) would ideally be covered. There are other resources, such as the Doom 3 source code, which is highly instructive for its being a shipped product. The problem with those is as follows: float Q_rsqrt( float number ) { long i; float x2, y; const float threehalfs = 1.5F; x2 = number * 0.5F; y = number; i = * ( long * ) &y; // evil floating point bit level hacking i = 0x5f3759df - ( i >> 1 ); // what the f***? y = * ( float * ) &i; y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration // y = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed return y; } To wit, while brilliant, this kind of source requires more enlightenment than I can usually muster upon first read. In summary, here's my white whale: For an adult reader with experience in programming. I wish I could save all the trees killed by every. Single. Game Programming book ever devoting the first two chapters to "Now just what is a variable anyway?" In C or C++, very preferably C++. Languages that are more concise are fantastic for teaching, except for when what you want to learn is how to cope with a verbose language. There is also the benefit of the guardrails that C++ doesn't provide, such as garbage collection. Platform agnostic. I'm sincerely afraid that this book is out there and it's Visual C++/DirectX oriented. I'm a Linux guy, and I'd do what it takes, but I would very much like to be able to use OpenGL. Thanks for everything! Before anyone gets on my case about it, Fast inverse square root was from Quake III Arena, not Doom 3!

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• A brief note for customers running SOA Suite on AIX platforms

  - by christian

  When running Oracle SOA Suite with IBM JVMs on the AIX platform, we have seen performance slowdowns and/or memory leaks. On occasion, we have even encountered some OutOfMemoryError conditions and the concomittant Java coredump. If you are experiencing this issue, the resolution may be to configure -Dsun.reflect.inflationThreshold=0 in your JVM startup parameters. https://www.ibm.com/developerworks/java/library/j-nativememory-aix/ contains a detailed discussion of the IBM AIX JVM memory model, but I will summarize my interpretation and understanding of it in the context of SOA Suite, below. Java ClassLoaders on IBM JVMs are allocated a native memory area into which they are anticipated to map such things as jars loaded from the filesystem. This is an excellent memory optimization, as the file can be loaded into memory once and then shared amongst many JVMs on the same host, allowing for excellent horizontal scalability on AIX hosts. However, Java ClassLoaders are not used exclusively for loading files from disk. A performance optimization by the Oracle Java language developers enables reflectively accessed data to optimize from a JNI call into Java bytecodes which are then amenable to hotspot optimizations, amongst other things. This performance optimization is called inflation, and it is executed by generating a sun.reflect.DelegatingClassLoader instance dynamically to inject the Java bytecode into the virtual machine. It is generally considered an excellent optimization. However, it interacts very negatively with the native memory area allocated by the IBM JVM, effectively locking out memory that could otherwise be used by the Java process. SOA Suite and WebLogic are both very large users of reflection code. They reflectively use many code paths in their operation, generating lots of DelegatingClassLoaders in normal operation. The IBM JVM slowdown and subsequent OutOfMemoryError are as a direct result of the Java memory consumed by the DelegatingClassLoader instances generated by SOA Suite and WebLogic. Java garbage collection runs more frequently to try and keep memory available, until it can no longer do so and throws OutOfMemoryError. The setting sun.reflect.inflationThreshold=0 disables this optimization entirely, never allowing the JVM to generate the optimized reflection code. IBM JVMs are susceptible to this issue primarily because all Java ClassLoaders have this native memory allocation, which is shared with the regular Java heap. Oracle JVMs don't automatically give all ClassLoaders a native memory area, and my understanding is that jar files are never mapped completely from shared memory in the same way as IBM does it. This results in different behaviour characteristics on IBM vs Oracle JVMs.

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• How employable am I as a programmer?

  - by dsimcha

  I'm currently a Ph.D. student in Biomedical Engineering with a concentration in computational biology and am starting to think about what I want to do after graduate school. I feel like I've accumulated a lot of programming skills while in grad school, but taken a very non-traditional path to learning all this stuff. I'm wondering whether I would have an easy time getting hired as a programmer and could fall back on that if I can't find a good job directly in my field, and if so whether I would qualify for a more prestigious position than "code monkey". Things I Have Going For Me Approximately 4 years of experience programming as part of my research. I believe I have a solid enough grasp of the fundamentals that I could pick up new languages and technologies pretty fast, and could demonstrate this in an interview. Good math and statistics skills. An extensive portfolio of open source work (and the knowledge that working on these projects implies): I wrote a statistics library in D, mostly from scratch. I wrote a parallelism library (parallel map, reduce, foreach, task parallelism, pipelining, etc.) that is currently in review for adoption by the D standard library. I wrote a 2D plotting library for D against the GTK Cairo backend. I currently use it for most of the figures I make for my research. I've contributed several major performance optimizations to the D garbage collector. (Most of these were low-hanging fruit, but it still shows my knowledge of low-level issues like memory management, pointers and bit twiddling.) I've contributed lots of miscellaneous bug fixes to the D standard library and could show the change logs to prove it. (This demonstrates my ability read other people's code.) Things I Have Going Against Me Most of my programming experience is in D and Python. I have very little to virtually no experience in the more established, "enterprise-y" languages like Java, C# and C++, though I have learned a decent amount about these languages from small, one-off projects and discussions about language design in the D community. In general I have absolutely no knowledge of "enterprise-y" technlogies. I've never used a framework before, possibly because most reusable code for scientific work and for D tends to call itself a "library" instead. I have virtually no formal computer science/software engineering training. Almost all of my knowledge comes from talking to programming geek friends, reading blogs, forums, StackOverflow, etc. I have zero professional experience with the official title of "developer", "software engineer", or something similar.

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• How to refactor my design, if it seems to require multiple inheritance?

  - by Omega

  Recently I made a question about Java classes implementing methods from two sources (kinda like multiple inheritance). However, it was pointed out that this sort of need may be a sign of a design flaw. Hence, it is probably better to address my current design rather than trying to simulate multiple inheritance. Before tackling the actual problem, some background info about a particular mechanic in this framework: It is a simple game development framework. Several components allocate some memory (like pixel data), and it is necessary to get rid of it as soon as you don't need it. Sprites are an example of this. Anyway, I decided to implement something ala Manual-Reference-Counting from Objective-C. Certain classes, like Sprites, contain an internal counter, which is increased when you call retain(), and decreased on release(). Thus the Resource abstract class was created. Any subclass of this will obtain the retain() and release() implementations for free. When its count hits 0 (nobody is using this class), it will call the destroy() method. The subclass needs only to implement destroy(). This is because I don't want to rely on the Garbage Collector to get rid of unused pixel data. Game objects are all subclasses of the Node class - which is the main construction block, as it provides info such as position, size, rotation, etc. See, two classes are used often in my game. Sprites and Labels. Ah... but wait. Sprites contain pixel data, remember? And as such, they need to extend Resource. But this, of course, can't be done. Sprites ARE nodes, hence they must subclass Node. But heck, they are resources too. Why not making Resource an interface? Because I'd have to re-implement retain() and release(). I am avoiding this in virtue of not writing the same code over and over (remember that there are multiple classes that need this memory-management system). Why not composition? Because I'd still have to implement methods in Sprite (and similar classes) that essentially call the methods of Resource. I'd still be writing the same code over and over! What is your advice in this situation, then?

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• Ray Picking Problems

  - by A Name I Haven't Decided On

  I've read so many answers on here about how to do Ray Picking, that I thought I had the idea of it down. But when I try to implement it in my game, I get garbage. I'm working with LWJGL. Here's the code: public static Ray getPick(int mouseX, int mouseY){ glPushMatrix(); //Setting up the Mouse Clip Vector4f mouseClip = new Vector4f((float)mouseX * 2 / 960f - 1, 1 - (float)mouseY * 2 / 640f ,0 ,1); //Loading Matrices FloatBuffer modMatrix = BufferUtils.createFloatBuffer(16); FloatBuffer projMatrix = BufferUtils.createFloatBuffer(16); glGetFloat(GL_MODELVIEW_MATRIX, modMatrix); glGetFloat(GL_PROJECTION_MATRIX, projMatrix); //Assigning Matrices Matrix4f proj = new Matrix4f(); Matrix4f model = new Matrix4f(); model.load(modMatrix); proj.load(projMatrix); //Multiplying the Projection Matrix by the Model View Matrix Matrix4f tempView = new Matrix4f(); Matrix4f.mul(proj, model, tempView); tempView.invert(); //Getting the Camera Position in World Space. The 4th Column of the Model View Matrix. model.invert(); Point cameraPos = new Point(model.m30, model.m31, model.m32); //Theoretically getting the vector the Picking Ray goes Vector4f rayVector = new Vector4f(); Matrix4f.transform(tempView, mouseClip, rayVector); rayVector.translate((float)-cameraPos.getX(),(float) -cameraPos.getY(),(float) -cameraPos.getZ(), 0f); rayVector.normalise(); glPopMatrix(); //This Basically Spits out a value that changes as the Camera moves. //When the Mouse moves, the values change around 0.001 points from screen edge to edge. System.out.format("Vector: %f %f %f%n", rayVector.x, rayVector.y, rayVector.z); //return new Ray(cameraPos, rayVector); return null; } I don't really know why this isn't working. I was hoping some more experienced eyes might be able to help me out. I can get the camera position like a champ, it's the vector the rays going in that I can't seem to get right. Thanks.

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• Java @Contented annotation to help reduce false sharing

  - by Dave

  See this posting by Aleksey Shipilev for details -- @Contended is something we've wanted for a long time. The JVM provides automatic layout and placement of fields. Usually it'll (a) sort fields by descending size to improve footprint, and (b) pack reference fields so the garbage collector can process a contiguous run of reference fields when tracing. @Contended gives the program a way to provide more explicit guidance with respect to concurrency and false sharing. Using this facility we can sequester hot frequently written shared fields away from other mostly read-only or cold fields. The simple rule is that read-sharing is cheap, and write-sharing is very expensive. We can also pack fields together that tend to be written together by the same thread at about the same time. More generally, we're trying to influence relative field placement to minimize coherency misses. Fields that are accessed closely together in time should be placed proximally in space to promote cache locality. That is, temporal locality should condition spatial locality. Fields accessed together in time should be nearby in space. That having been said, we have to be careful to avoid false sharing and excessive invalidation from coherence traffic. As such, we try to cluster or otherwise sequester fields that tend to written at approximately the same time by the same thread onto the same cache line. Note that there's a tension at play: if we try too hard to minimize single-threaded capacity misses then we can end up with excessive coherency misses running in a parallel environment. Theres no single optimal layout for both single-thread and multithreaded environments. And the ideal layout problem itself is NP-hard. Ideally, a JVM would employ hardware monitoring facilities to detect sharing behavior and change the layout on the fly. That's a bit difficult as we don't yet have the right plumbing to provide efficient and expedient information to the JVM. Hint: we need to disintermediate the OS and hypervisor. Another challenge is that raw field offsets are used in the unsafe facility, so we'd need to address that issue, possibly with an extra level of indirection. Finally, I'd like to be able to pack final fields together as well, as those are known to be read-only.

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• Variable number of GUI Buttons

  - by Wakaka

  I have a generic HTML5 Canvas GUI Button class and a Scene class. The Scene class has a method called createButton(), which will create a new Button with onclick parameter and store it in a list of buttons. I call createButton() for all UI buttons when initializing the Scene. Because buttons can appear and disappear very often during rendering, Scene would first deactivate all buttons (temporarily remove their onclick, onmouseover etc property) before each render frame. During rendering, the renderer would then activate the required buttons for that frame. The problem is that part of the UI requires a variable number of buttons, and their onclick, onmouseover etc properties change frequently. An example is a buffs system. The UI will list all buffs as square sprites for the current unit selected, and mousing over each square will bring up a tooltip with some information on the buff. But the number of buffs is variable thus I won't know how many buttons to create at the start. What's the best way to solve this problem? P.S. My game is in Javascript, and I know I can use HTML buttons, but would like to make my game purely Canvas-based. Create buttons on-the-fly during rendering. Thus I will only have buttons when I require them. After the render frame these buttons would be useless and removed. Create a fixed set of buttons that I'm going to assume the number of buffs per unit won't exceed. During each render frame activate the buttons accordingly and set their onmouseover property. Assign a button to each Buff instance. This sounds wrong as the buff button is a part of the GUI which can only have one unit selected. Assigning a button to every single Buff in the game seems to be overkill. Also, I would need to change the button's position every render frame since its order in the unit's list of buffs matter. Any other solutions? I'm actually quite for idea (1) but am worried about the memory/time issues of creating a new Button() object every render frame. But this is in Javascript where object creation is oh-so-common ({} mainly) due to automatic garbage collection. What is your take on this? Thanks!

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• What are some of the best wireless routers for a price-conscious home power-user?

  - by Alain

  I'm extremely dissatisfied with the 'popular' choice for routers in homes and small offices. They are expensive (upwards of 60$), lack a great deal of useful configuration options, and seem to need to be restarted quite often. (Linksys comes to mind). I've been on the market for a good router lately, and slowly collecting a set of requirements I feel good routers should meet. Maximum number of TCP/IP connections. - This isn't something I see any routers advertise, but in terms of supporting torrent applications, I've been screwed by routers that support less than 20 here. From what I understand a fairly standard number is 200, but there are not so expensive routers that support thousands. Router configuration menu - Most have standard menu's that let you set up basic things like your wireless network encryption settings, uPnP, and maybe even DMZ (demilitarized zones). An absolute requirement for me, however, are routers with good enough firmware to support: Explicit Port forwarding Assigning static local ips to specific mac addresses, or at least Port forwarding by MAC address Port, IP and MAC filtering Dynamic DNS service for home users who want to set up a server but have a dynamic IP Traffic shaping (ideally) - giving priority to packets from certain machines or over certain ports. Strong wireless signal - If getting a reliable signal requires me to be so close to the router that I can connect an Ethernet cable, it's not good enough. As many Ethernet ports as possible. - Because I want to be able to switch from console gaming to PC gaming without visiting my router. So far, the best thing I've stumbled upon (in the bargain bin at staples) was a 20$ retail plus router. It was meant to be the cheapest alternative until I could find something better to purchase online, but I was actually blown away by the firmware capabilities. It supports defining reserved bandwidth for certain network traffic, dynamic DNS, reserving local IPs for specific MAC addresses, etc. At 2 am when my roommate is killing our Internet with their torrents, I can limit their bandwidth without outright blacklisting them. I have, however, met serious limitations when it comes to network traffic between local machines. It claims a 300Mbps connection, but I have trouble streaming videos from my PC to my console or other laptops wirelessly. It has a meltdown and needs to be reset once in a while (no more than a couple times a month), and it's got a 200 connection limit. There 4 Ethernet ports in the back but I'm pretty sure the first doesn't work. So some great answers to this question would be: Any metrics you use to compare routers, and requirements you have for new candidates. The best routers you've found for supporting home servers, file management systems, high volume torrent traffic, good price/feature ratio, etc. Good configuration advice (aside from 'use Ethernet whenever possible') Thanks for your feedback and experiences!

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• Why is my new Phenom II 965 BE not significantly faster than my old Athlon 64 X2 4600+?

  - by Software Monkey

  I recently rebuilt my 5 year old computer. I upgraded all core components, in particular from an Athlon 64 X2 4600+ at 2.4 GHz with DDR2 800 to a Phenom II 965 BE (quad core) at 3.6 GHz with DDR3 1333 (actually 1600, but testing consistently detected memory errors at 1600). The motherboard is also much newer and better. The HDD's (x3), DVD writer and card reader are the same. The BIOS memory config is auto-everything except the base timing which I overrode to 1T instead of 2T. The BIOS CPU multiplier is slightly over-clocked to 3.6 GHz from the stock 3.4 GHz. I noticed compiling Java is slower than I expected. As it happens I have some (single-threaded) Java pattern-matching code which is CPU and memory bound and for which I have performance numbers recorded on a number of hardware platforms, including my old system. So I did a test run on the new equipment and was stunned to find that the numbers are only slightly better than my old system, about 25%. The data set it is operating on is a 148,975 character array, which should easily fit in caches, but in any event the new CPU has larger caches all around. The system was, of course, otherwise idle for the test and the test run is a timed 10 seconds to eliminate scheduling anomalies. A long while ago, when I upgraded only memory from DD2 667 to DDR2 800 there was no change in performance of this test, which subjectively supports that the test cycle does not need to (significantly) access main memory, but yes it is creating and garbage collecting a large number of objects in the process of this test (low millions of matches are found for the pattern set). I am about 99.999% certain the code hasn't changed since I last ran it on 2009-03-17 - but I can't easily retest the old hardware, because it is currently in pieces on my work-bench waiting to be built into a new computer for my kids. Note that Windows (XP) reports a CPU speed of 795 MHz unless I have some thing running. With stuff running it seems to jump all over the place each time I use ALT-Pause to display the system properties, everywhere from 795 MHz to 3.4 Ghz. So why might my shiny new hardware under-performing so badly? EDIT: The old memory was Mushkin DDR2 800 with timings set for auto which should have been 5-5-5-12. The new memory is Corsair DDR3 1600, running at 1333 with timings also auto which are 9-9-9-21. In both cases they are a paired set of dual channel DIMMs. I was waiting to ensure my system was stable before tweaking with memory timings.

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• Microsoft Office 2003 document (Excel and Word) intermitently, takes 30 seconds to load

  - by Julio Nobre

  I am trying to figure out why a simple .XLS EXCEL workbook is taking, randomly, 30 seconds to open. Before answering: Please, bear mind the following: Problem symptoms Hanging is intermitent and it takes exactly 30 seconds; During hanging there is no cpu or disk activity; It only happens during document load. Every runs smooth after that; Windows Explorer.exe hangs on folder, but all other folders, system and applications are still responsive; There are no consecutive hangings. I have to wait for while to reproduce this behaviour; All samples documents are located on a local drive (C:\BPI); The no document has has macros and have any addins usage; The problem does occurs on others files extensions like .PDF, for example; Office 2003 is being used for several years; The computer is running Windows XP; Computer has several network mapped drives, all addressed to main file server; Recently, main fileserver was replaced by Windows 2011 SBS Standard Edition What I have done so far I have traced machine Explorer.exe, using Process Monitor, added Duration column, and filtered by Duration 1. That's is how I found that hanging was taking exactly 30 seconds. For further information, please refer to Oliver Salzburg tutorial. Using Process Monitor, I have also figured out than five operations were taking most of sample collecting duration. Looking at sample image below, column Operation below you will notice that one single operation was taking 29 seconds; I have tried different documents (.xls and .doc), all of them smaller than 30 KB; I have, temporarily, removed all shortcuts on User Document's folder that were pointing to network drives or shares; I have runned CCleaner to fix registry issues; I made sure that there were no external links on tested workbook or word documents; I have reproduced this behaviour for hours; I have extensivelly researched for hours on the web; Process Monitor's collected and filtered data

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• iotop for Linux kernel 2.6.18

  - by Lightsauce

  So it has to come to my attention that iotop isn't availalbe for 2.6.18 since it's less than 2.6.20 and requires Python 2.6+. I've done some research and came across this article: http://lserinol.blogspot.com/2009/09/io-usage-per-process-on-linux.html According to this, if these process have io stats in /proc/pid#/io (where pid# is the process #) it's doable regardless of the kernel version. So, in reality, I could upgrade Python to 2.6 and test out iotop. However, my flavor of Linux, CentOS release 5.5 (Final), only supports Python 2.4.3-44.el5 currently. If I were to do uninstall from yum, it doesn't look so pretty. It ends up wanting to uninstall 235 packages, most of which are very important! I read in one place, online (I forget the URL from yesterday), that you can install Python 2.6+ parallel to this one, and have the rpm install for iotop use that. Well, I didn't choose that route. I figured, what the heck, lets write iotop (not copying it, but reverse engineering it without actually looking at it's code/it in use) in bash. I thought it would just grab the /proc/pid#/io file and parse stats. So I wrote a script to grab the top 10 rchar, wchar, read_bytes, and write_bytes by collecting all these stats from all the /proc/pid#/io files, sorting them by each metric, then grabbing the top 10 highest values. The conclusion, the data seems completely useless. Does anybody know any resources for advanced Linux where I can figure out how to take these /proc/pid#/ directories and figure out what the heck they are doing with io on the disk? My main goal is to figure out what exactly is causing high load on my disk. I just know it's on the / partition (/dev/sda2 in this case), and I'm not really sure how to narrow it down without the help of iotop. If I run iostat to grab metrics for 1 minute, every second, the first result it gives me shows a high 'kB_read/s', so that makes me think, it's reading mostly. However, if I watch the update it gives me every second, it's actually just showing values for kB_wrtn/s. This makes me think the initial value iostat gives me is misleading.

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