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• Problem when trying to use simple Shaders + VBOs

  - by Mr.Gando

  Hello I'm trying to convert the following functions to a VBO based function for learning purposes, it displays a static texture on screen. I'm using OpenGL ES 2.0 with shaders on the iPhone (should be almost the same than regular OpenGL in this case), this is what I got working: //Works! - (void) drawAtPoint:(CGPoint)point depth:(CGFloat)depth { GLfloat coordinates[] = { 0, 1, 1, 1, 0, 0, 1, 0 }; GLfloat width = (GLfloat)_width * _maxS, height = (GLfloat)_height * _maxT; GLfloat vertices[] = { -width / 2 + point.x, -height / 2 + point.y, width / 2 + point.x, -height / 2 + point.y, -width / 2 + point.x, height / 2 + point.y, width / 2 + point.x, height / 2 + point.y, }; glBindTexture(GL_TEXTURE_2D, _name); //Attrib position and attrib_tex coord are handles for the shader attributes glVertexAttribPointer(ATTRIB_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertices); glEnableVertexAttribArray(ATTRIB_POSITION); glVertexAttribPointer(ATTRIB_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, coordinates); glEnableVertexAttribArray(ATTRIB_TEXCOORD); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); } I tried to do this to convert to a VBO however I don't see anything displaying on-screen with this version: //Doesn't display anything - (void) drawAtPoint:(CGPoint)point depth:(CGFloat)depth { GLfloat width = (GLfloat)_width * _maxS, height = (GLfloat)_height * _maxT; GLfloat position[] = { -width / 2 + point.x, -height / 2 + point.y, width / 2 + point.x, -height / 2 + point.y, -width / 2 + point.x, height / 2 + point.y, width / 2 + point.x, height / 2 + point.y, }; //Texture on-screen position ( each vertex is x,y in on-screen coords ) GLfloat coordinates[] = { 0, 1, 1, 1, 0, 0, 1, 0 }; // Texture coords from 0 to 1 glBindVertexArrayOES(vao); glGenVertexArraysOES(1, &vao); glGenBuffers(2, vbo); //Buffer 1 glBindBuffer(GL_ARRAY_BUFFER, vbo[0]); glBufferData(GL_ARRAY_BUFFER, 8 * sizeof(GLfloat), position, GL_STATIC_DRAW); glEnableVertexAttribArray(ATTRIB_POSITION); glVertexAttribPointer(ATTRIB_POSITION, 2, GL_FLOAT, GL_FALSE, 0, position); //Buffer 2 glBindBuffer(GL_ARRAY_BUFFER, vbo[1]); glBufferData(GL_ARRAY_BUFFER, 8 * sizeof(GLfloat), coordinates, GL_DYNAMIC_DRAW); glEnableVertexAttribArray(ATTRIB_TEXCOORD); glVertexAttribPointer(ATTRIB_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, coordinates); //Draw glBindVertexArrayOES(vao); glBindTexture(GL_TEXTURE_2D, _name); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); } In both cases I'm using this simple Vertex Shader //Vertex Shader attribute vec2 position;//Bound to ATTRIB_POSITION attribute vec4 color; attribute vec2 texcoord;//Bound to ATTRIB_TEXCOORD varying vec2 texcoordVarying; uniform mat4 mvp; void main() { //You CAN'T use transpose before in glUniformMatrix4fv so... here it goes. gl_Position = mvp * vec4(position.x, position.y, 0.0, 1.0); texcoordVarying = texcoord; } The gl_Position is equal to product of mvp * vec4 because I'm simulating glOrthof in 2D with that mvp And this Fragment Shader //Fragment Shader uniform sampler2D sampler; varying mediump vec2 texcoordVarying; void main() { gl_FragColor = texture2D(sampler, texcoordVarying); } I really need help with this, maybe my shaders are wrong for the second case ? thanks in advance.

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• Concurrency and Calendar classes

  - by fbielejec

  I have a thread (class implementing runnable, called AnalyzeTree) organised around a hash map (ConcurrentMap slicesMap). The class goes through the data (called trees here) in the large text file and parses the geographical coordinates from it to the HashMap. The idea is to process one tree at a time and add or grow the values according to the key (which is just a Double value representing time). The relevant part of code looks like this: // grow map entry if key exists if (slicesMap.containsKey(sliceTime)) { double[] imputedLocation = imputeValue( location, parentLocation, sliceHeight, nodeHeight, parentHeight, rate, useTrueNoise, currentTreeNormalization, precisionArray); slicesMap.get(sliceTime).add( new Coordinates(imputedLocation[1], imputedLocation[0], 0.0)); // start new entry if no such key in the map } else { List<Coordinates> coords = new ArrayList<Coordinates>(); double[] imputedLocation = imputeValue( location, parentLocation, sliceHeight, nodeHeight, parentHeight, rate, useTrueNoise, currentTreeNormalization, precisionArray); coords.add(new Coordinates(imputedLocation[1], imputedLocation[0], 0.0)); slicesMap.putIfAbsent(sliceTime, coords); // slicesMap.put(sliceTime, coords); }// END: key check And the class is called like this (executor is ExecutorService executor = Executors.newFixedThreadPool(NTHREDS) ): mrsd = new SpreadDate(mrsdString); int readTrees = 1; while (treesImporter.hasTree()) { currentTree = (RootedTree) treesImporter.importNextTree(); executor.submit(new AnalyzeTree(currentTree, precisionString, coordinatesName, rateString, numberOfIntervals, treeRootHeight, timescaler, mrsd, slicesMap, useTrueNoise)); // new AnalyzeTree(currentTree, precisionString, // coordinatesName, rateString, numberOfIntervals, // treeRootHeight, timescaler, mrsd, slicesMap, // useTrueNoise).run(); readTrees++; }// END: while has trees Now this is running into troubles when executed in parallel (the commented part running sequentially is fine), I thought it might throw a ConcurrentModificationException, but apparently the problem is in mrsd (instance of SpreadDate object, which is simply a class for date related calculations). The SpreadDate class looks like this: public class SpreadDate { private Calendar cal; private SimpleDateFormat formatter; private Date stringdate; public SpreadDate(String date) throws ParseException { // if no era specified assume current era String line[] = date.split(" "); if (line.length == 1) { StringBuilder properDateStringBuilder = new StringBuilder(); date = properDateStringBuilder.append(date).append(" AD") .toString(); } formatter = new SimpleDateFormat("yyyy-MM-dd G", Locale.US); stringdate = formatter.parse(date); cal = Calendar.getInstance(); } public long plus(int days) { cal.setTime(stringdate); cal.add(Calendar.DATE, days); return cal.getTimeInMillis(); }// END: plus public long minus(int days) { cal.setTime(stringdate); cal.add(Calendar.DATE, -days); //line 39 return cal.getTimeInMillis(); }// END: minus public long getTime() { cal.setTime(stringdate); return cal.getTimeInMillis(); }// END: getDate } And the stack trace from when exception is thrown: java.lang.ArrayIndexOutOfBoundsException: 58 at sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate(BaseCalendar.java:454) at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2098) at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2013) at java.util.Calendar.setTimeInMillis(Calendar.java:1126) at java.util.GregorianCalendar.add(GregorianCalendar.java:1020) at utils.SpreadDate.minus(SpreadDate.java:39) at templates.AnalyzeTree.run(AnalyzeTree.java:88) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) at java.util.concurrent.FutureTask.run(FutureTask.java:166) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:636) If a move the part initializing mrsd to the AnalyzeTree class it runs without any problems - however it is not very memory efficient to initialize class each time this thread is running, hence my concerns. How can it be remedied?

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• flex using tweenmax library

  - by Nishant

  Hello, I am currently using flex transition effects on state change. Is there a way I can use tweenmax library for that? Update: In the code below, I have transitions from state one to state two. I would like to replace that code tweenermax library. <?xml version="1.0" encoding="utf-8"?> <s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955" minHeight="600"> <s:states> <s:State name="one" /> <s:State name="two" /> </s:states> <s:transitions> <s:Transition fromState="one" toState="two"> <s:Parallel targets="{one, two}"> <s:Fade /> </s:Parallel> </s:Transition> <s:Transition fromState="two" toState="one"> <s:Parallel targets="{one, two}"> <s:Fade /> </s:Parallel> </s:Transition> </s:transitions> <component:one id="one" /> <component:one id="two" /> </s:Application>

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• C#/.NET Little Wonders: Interlocked CompareExchange()

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Two posts ago, I discussed the Interlocked Add(), Increment(), and Decrement() methods (here) for adding and subtracting values in a thread-safe, lightweight manner.  Then, last post I talked about the Interlocked Read() and Exchange() methods (here) for safely and efficiently reading and setting 32 or 64 bit values (or references).  This week, we’ll round out the discussion by talking about the Interlocked CompareExchange() method and how it can be put to use to exchange a value if the current value is what you expected it to be. Dirty reads can lead to bad results Many of the uses of Interlocked that we’ve explored so far have centered around either reading, setting, or adding values.  But what happens if you want to do something more complex such as setting a value based on the previous value in some manner? Perhaps you were creating an application that reads a current balance, applies a deposit, and then saves the new modified balance, where of course you’d want that to happen atomically.  If you read the balance, then go to save the new balance and between that time the previous balance has already changed, you’ll have an issue!  Think about it, if we read the current balance as $400, and we are applying a new deposit of $50.75, but meanwhile someone else deposits $200 and sets the total to $600, but then we write a total of $450.75 we’ve lost $200! Now, certainly for int and long values we can use Interlocked.Add() to handles these cases, and it works well for that.  But what if we want to work with doubles, for example?  Let’s say we wanted to add the numbers from 0 to 99,999 in parallel.  We could do this by spawning several parallel tasks to continuously add to a total: 1: double total = 0; 2:  3: Parallel.For(0, 10000, next => 4: { 5: total += next; 6: }); Were this run on one thread using a standard for loop, we’d expect an answer of 4,999,950,000 (the sum of all numbers from 0 to 99,999).  But when we run this in parallel as written above, we’ll likely get something far off.  The result of one of my runs, for example, was 1,281,880,740.  That is way off!  If this were banking software we’d be in big trouble with our clients.  So what happened?  The += operator is not atomic, it will read in the current value, add the result, then store it back into the total.  At any point in all of this another thread could read a “dirty” current total and accidentally “skip” our add.   So, to clean this up, we could use a lock to guarantee concurrency: 1: double total = 0.0; 2: object locker = new object(); 3:  4: Parallel.For(0, count, next => 5: { 6: lock (locker) 7: { 8: total += next; 9: } 10: }); Which will give us the correct result of 4,999,950,000.  One thing to note is that locking can be heavy, especially if the operation being locked over is trivial, or the life of the lock is a high percentage of the work being performed concurrently.  In the case above, the lock consumes pretty much all of the time of each parallel task – and the task being locked on is relatively trivial. Now, let me put in a disclaimer here before we go further: For most uses, lock is more than sufficient for your needs, and is often the simplest solution!    So, if lock is sufficient for most needs, why would we ever consider another solution?  The problem with locking is that it can suspend execution of your thread while it waits for the signal that the lock is free.  Moreover, if the operation being locked over is trivial, the lock can add a very high level of overhead.  This is why things like Interlocked.Increment() perform so well, instead of locking just to perform an increment, we perform the increment with an atomic, lockless method. As with all things performance related, it’s important to profile before jumping to the conclusion that you should optimize everything in your path.  If your profiling shows that locking is causing a high level of waiting in your application, then it’s time to consider lighter alternatives such as Interlocked. CompareExchange() – Exchange existing value if equal some value So let’s look at how we could use CompareExchange() to solve our problem above.  The general syntax of CompareExchange() is: T CompareExchange<T>(ref T location, T newValue, T expectedValue) If the value in location == expectedValue, then newValue is exchanged.  Either way, the value in location (before exchange) is returned. Actually, CompareExchange() is not one method, but a family of overloaded methods that can take int, long, float, double, pointers, or references.  It cannot take other value types (that is, can’t CompareExchange() two DateTime instances directly).  Also keep in mind that the version that takes any reference type (the generic overload) only checks for reference equality, it does not call any overridden Equals(). So how does this help us?  Well, we can grab the current total, and exchange the new value if total hasn’t changed.  This would look like this: 1: // grab the snapshot 2: double current = total; 3:  4: // if the total hasn’t changed since I grabbed the snapshot, then 5: // set it to the new total 6: Interlocked.CompareExchange(ref total, current + next, current); So what the code above says is: if the amount in total (1st arg) is the same as the amount in current (3rd arg), then set total to current + next (2nd arg).  This check and exchange pair is atomic (and thus thread-safe). This works if total is the same as our snapshot in current, but the problem, is what happens if they aren’t the same?  Well, we know that in either case we will get the previous value of total (before the exchange), back as a result.  Thus, we can test this against our snapshot to see if it was the value we expected: 1: // if the value returned is != current, then our snapshot must be out of date 2: // which means we didn't (and shouldn't) apply current + next 3: if (Interlocked.CompareExchange(ref total, current + next, current) != current) 4: { 5: // ooops, total was not equal to our snapshot in current, what should we do??? 6: } So what do we do if we fail?  That’s up to you and the problem you are trying to solve.  It’s possible you would decide to abort the whole transaction, or perhaps do a lightweight spin and try again.  Let’s try that: 1: double current = total; 2:  3: // make first attempt... 4: if (Interlocked.CompareExchange(ref total, current + i, current) != current) 5: { 6: // if we fail, go into a spin wait, spin, and try again until succeed 7: var spinner = new SpinWait(); 8:  9: do 10: { 11: spinner.SpinOnce(); 12: current = total; 13: } 14: while (Interlocked.CompareExchange(ref total, current + i, current) != current); 15: } 16:  This is not trivial code, but it illustrates a possible use of CompareExchange().  What we are doing is first checking to see if we succeed on the first try, and if so great!  If not, we create a SpinWait and then repeat the process of SpinOnce(), grab a fresh snapshot, and repeat until CompareExchnage() succeeds.  You may wonder why not a simple do-while here, and the reason it’s more efficient to only create the SpinWait until we absolutely know we need one, for optimal efficiency. Though not as simple (or maintainable) as a simple lock, this will perform better in many situations.  Comparing an unlocked (and wrong) version, a version using lock, and the Interlocked of the code, we get the following average times for multiple iterations of adding the sum of 100,000 numbers: 1: Unlocked money average time: 2.1 ms 2: Locked money average time: 5.1 ms 3: Interlocked money average time: 3 ms So the Interlocked.CompareExchange(), while heavier to code, came in lighter than the lock, offering a good compromise of safety and performance when we need to reduce contention. CompareExchange() - it’s not just for adding stuff… So that was one simple use of CompareExchange() in the context of adding double values -- which meant we couldn’t have used the simpler Interlocked.Add() -- but it has other uses as well. If you think about it, this really works anytime you want to create something new based on a current value without using a full lock.  For example, you could use it to create a simple lazy instantiation implementation.  In this case, we want to set the lazy instance only if the previous value was null: 1: public static class Lazy<T> where T : class, new() 2: { 3: private static T _instance; 4:  5: public static T Instance 6: { 7: get 8: { 9: // if current is null, we need to create new instance 10: if (_instance == null) 11: { 12: // attempt create, it will only set if previous was null 13: Interlocked.CompareExchange(ref _instance, new T(), (T)null); 14: } 15:  16: return _instance; 17: } 18: } 19: } So, if _instance == null, this will create a new T() and attempt to exchange it with _instance.  If _instance is not null, then it does nothing and we discard the new T() we created. This is a way to create lazy instances of a type where we are more concerned about locking overhead than creating an accidental duplicate which is not used.  In fact, the BCL implementation of Lazy<T> offers a similar thread-safety choice for Publication thread safety, where it will not guarantee only one instance was created, but it will guarantee that all readers get the same instance.  Another possible use would be in concurrent collections.  Let’s say, for example, that you are creating your own brand new super stack that uses a linked list paradigm and is “lock free”.  We could use Interlocked.CompareExchange() to be able to do a lockless Push() which could be more efficient in multi-threaded applications where several threads are pushing and popping on the stack concurrently. Yes, there are already concurrent collections in the BCL (in .NET 4.0 as part of the TPL), but it’s a fun exercise!  So let’s assume we have a node like this: 1: public sealed class Node<T> 2: { 3: // the data for this node 4: public T Data { get; set; } 5:  6: // the link to the next instance 7: internal Node<T> Next { get; set; } 8: } Then, perhaps, our stack’s Push() operation might look something like: 1: public sealed class SuperStack<T> 2: { 3: private volatile T _head; 4:  5: public void Push(T value) 6: { 7: var newNode = new Node<int> { Data = value, Next = _head }; 8:  9: if (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next) 10: { 11: var spinner = new SpinWait(); 12:  13: do 14: { 15: spinner.SpinOnce(); 16: newNode.Next = _head; 17: } 18: while (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next); 19: } 20: } 21:  22: // ... 23: } Notice a similar paradigm here as with adding our doubles before.  What we are doing is creating the new Node with the data to push, and with a Next value being the original node referenced by _head.  This will create our stack behavior (LIFO – Last In, First Out).  Now, we have to set _head to now refer to the newNode, but we must first make sure it hasn’t changed! So we check to see if _head has the same value we saved in our snapshot as newNode.Next, and if so, we set _head to newNode.  This is all done atomically, and the result is _head’s original value, as long as the original value was what we assumed it was with newNode.Next, then we are good and we set it without a lock!  If not, we SpinWait and try again. Once again, this is much lighter than locking in highly parallelized code with lots of contention.  If I compare the method above with a similar class using lock, I get the following results for pushing 100,000 items: 1: Locked SuperStack average time: 6 ms 2: Interlocked SuperStack average time: 4.5 ms So, once again, we can get more efficient than a lock, though there is the cost of added code complexity.  Fortunately for you, most of the concurrent collection you’d ever need are already created for you in the System.Collections.Concurrent (here) namespace – for more information, see my Little Wonders – The Concurent Collections Part 1 (here), Part 2 (here), and Part 3 (here). Summary We’ve seen before how the Interlocked class can be used to safely and efficiently add, increment, decrement, read, and exchange values in a multi-threaded environment.  In addition to these, Interlocked CompareExchange() can be used to perform more complex logic without the need of a lock when lock contention is a concern. The added efficiency, though, comes at the cost of more complex code.  As such, the standard lock is often sufficient for most thread-safety needs.  But if profiling indicates you spend a lot of time waiting for locks, or if you just need a lock for something simple such as an increment, decrement, read, exchange, etc., then consider using the Interlocked class’s methods to reduce wait. Technorati Tags: C#,CSharp,.NET,Little Wonders,Interlocked,CompareExchange,threading,concurrency

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• Red Gate Coder interviews: Alex Davies

  - by Michael Williamson

  Alex Davies has been a software engineer at Red Gate since graduating from university, and is currently busy working on .NET Demon. We talked about tackling parallel programming with his actors framework, a scientific approach to debugging, and how JavaScript is going to affect the programming languages we use in years to come. So, if we start at the start, how did you get started in programming? When I was seven or eight, I was given a BBC Micro for Christmas. I had asked for a Game Boy, but my dad thought it would be better to give me a proper computer. For a year or so, I only played games on it, but then I found the user guide for writing programs in it. I gradually started doing more stuff on it and found it fun. I liked creating. As I went into senior school I continued to write stuff on there, trying to write games that weren’t very good. I got a real computer when I was fourteen and found ways to write BASIC on it. Visual Basic to start with, and then something more interesting than that. How did you learn to program? Was there someone helping you out? Absolutely not! I learnt out of a book, or by experimenting. I remember the first time I found a loop, I was like “Oh my God! I don’t have to write out the same line over and over and over again any more. It’s amazing!” When did you think this might be something that you actually wanted to do as a career? For a long time, I thought it wasn’t something that you would do as a career, because it was too much fun to be a career. I thought I’d do chemistry at university and some kind of career based on chemical engineering. And then I went to a careers fair at school when I was seventeen or eighteen, and it just didn’t interest me whatsoever. I thought “I could be a programmer, and there’s loads of money there, and I’m good at it, and it’s fun”, but also that I shouldn’t spoil my hobby. Now I don’t really program in my spare time any more, which is a bit of a shame, but I program all the rest of the time, so I can live with it. Do you think you learnt much about programming at university? Yes, definitely! I went into university knowing how to make computers do anything I wanted them to do. However, I didn’t have the language to talk about algorithms, so the algorithms course in my first year was massively important. Learning other language paradigms like functional programming was really good for breadth of understanding. Functional programming influences normal programming through design rather than actually using it all the time. I draw inspiration from it to write imperative programs which I think is actually becoming really fashionable now, but I’ve been doing it for ages. I did it first! There were also some courses on really odd programming languages, a bit of Prolog, a little bit of C. Having a little bit of each of those is something that I would have never done on my own, so it was important. And then there are knowledge-based courses which are about not programming itself but things that have been programmed like TCP. Those are really important for examples for how to approach things. Did you do any internships while you were at university? Yeah, I spent both of my summers at the same company. I thought I could code well before I went there. Looking back at the crap that I produced, it was only surpassed in its crappiness by all of the other code already in that company. I’m so much better at writing nice code now than I used to be back then. Was there just not a culture of looking after your code? There was, they just didn’t hire people for their abilities in that area. They hired people for raw IQ. The first indicator of it going wrong was that they didn’t have any computer scientists, which is a bit odd in a programming company. But even beyond that they didn’t have people who learnt architecture from anyone else. Most of them had started straight out of university, so never really had experience or mentors to learn from. There wasn’t the experience to draw from to teach each other. In the second half of my second internship, I was being given tasks like looking at new technologies and teaching people stuff. Interns shouldn’t be teaching people how to do their jobs! All interns are going to have little nuggets of things that you don’t know about, but they shouldn’t consistently be the ones who know the most. It’s not a good environment to learn. I was going to ask how you found working with people who were more experienced than you… When I reached Red Gate, I found some people who were more experienced programmers than me, and that was difficult. I’ve been coding since I was tiny. At university there were people who were cleverer than me, but there weren’t very many who were more experienced programmers than me. During my internship, I didn’t find anyone who I classed as being a noticeably more experienced programmer than me. So, it was a shock to the system to have valid criticisms rather than just formatting criticisms. However, Red Gate’s not so big on the actual code review, at least it wasn’t when I started. We did an entire product release and then somebody looked over all of the UI of that product which I’d written and say what they didn’t like. By that point, it was way too late and I’d disagree with them. Do you think the lack of code reviews was a bad thing? I think if there’s going to be any oversight of new people, then it should be continuous rather than chunky. For me I don’t mind too much, I could go out and get oversight if I wanted it, and in those situations I felt comfortable without it. If I was managing the new person, then maybe I’d be keener on oversight and then the right way to do it is continuously and in very, very small chunks. Have you had any significant projects you’ve worked on outside of a job? When I was a teenager I wrote all sorts of stuff. I used to write games, I derived how to do isomorphic projections myself once. I didn’t know what the word was so I couldn’t Google for it, so I worked it out myself. It was horrifically complicated. But it sort of tailed off when I started at university, and is now basically zero. If I do side-projects now, they tend to be work-related side projects like my actors framework, NAct, which I started in a down tools week. Could you explain a little more about NAct? It is a little C# framework for writing parallel code more easily. Parallel programming is difficult when you need to write to shared data. Sometimes parallel programming is easy because you don’t need to write to shared data. When you do need to access shared data, you could just have your threads pile in and do their work, but then you would screw up the data because the threads would trample on each other’s toes. You could lock, but locks are really dangerous if you’re using more than one of them. You get interactions like deadlocks, and that’s just nasty. Actors instead allows you to say this piece of data belongs to this thread of execution, and nobody else can read it. If you want to read it, then ask that thread of execution for a piece of it by sending a message, and it will send the data back by a message. And that avoids deadlocks as long as you follow some obvious rules about not making your actors sit around waiting for other actors to do something. There are lots of ways to write actors, NAct allows you to do it as if it was method calls on other objects, which means you get all the strong type-safety that C# programmers like. Do you think that this is suitable for the majority of parallel programming, or do you think it’s only suitable for specific cases? It’s suitable for most difficult parallel programming. If you’ve just got a hundred web requests which are all independent of each other, then I wouldn’t bother because it’s easier to just spin them up in separate threads and they can proceed independently of each other. But where you’ve got difficult parallel programming, where you’ve got multiple threads accessing multiple bits of data in multiple ways at different times, then actors is at least as good as all other ways, and is, I reckon, easier to think about. When you’re using actors, you presumably still have to write your code in a different way from you would otherwise using single-threaded code. You can’t use actors with any methods that have return types, because you’re not allowed to call into another actor and wait for it. If you want to get a piece of data out of another actor, then you’ve got to use tasks so that you can use “async” and “await” to await asynchronously for it. But other than that, you can still stick things in classes so it’s not too different really. Rather than having thousands of objects with mutable state, you can use component-orientated design, where there are only a few mutable classes which each have a small number of instances. Then there can be thousands of immutable objects. If you tend to do that anyway, then actors isn’t much of a jump. If I’ve already built my system without any parallelism, how hard is it to add actors to exploit all eight cores on my desktop? Usually pretty easy. If you can identify even one boundary where things look like messages and you have components where some objects live on one side and these other objects live on the other side, then you can have a granddaddy object on one side be an actor and it will parallelise as it goes across that boundary. Not too difficult. If we do get 1000-core desktop PCs, do you think actors will scale up? It’s hard. There are always in the order of twenty to fifty actors in my whole program because I tend to write each component as actors, and I tend to have one instance of each component. So this won’t scale to a thousand cores. What you can do is write data structures out of actors. I use dictionaries all over the place, and if you need a dictionary that is going to be accessed concurrently, then you could build one of those out of actors in no time. You can use queuing to marshal requests between different slices of the dictionary which are living on different threads. So it’s like a distributed hash table but all of the chunks of it are on the same machine. That means that each of these thousand processors has cached one small piece of the dictionary. I reckon it wouldn’t be too big a leap to start doing proper parallelism. Do you think it helps if actors get baked into the language, similarly to Erlang? Erlang is excellent in that it has thread-local garbage collection. C# doesn’t, so there’s a limit to how well C# actors can possibly scale because there’s a single garbage collected heap shared between all of them. When you do a global garbage collection, you’ve got to stop all of the actors, which is seriously expensive, whereas in Erlang garbage collections happen per-actor, so they’re insanely cheap. However, Erlang deviated from all the sensible language design that people have used recently and has just come up with crazy stuff. You can definitely retrofit thread-local garbage collection to .NET, and then it’s quite well-suited to support actors, even if it’s not baked into the language. Speaking of language design, do you have a favourite programming language? I’ll choose a language which I’ve never written before. I like the idea of Scala. It sounds like C#, only with some of the niggles gone. I enjoy writing static types. It means you don’t have to writing tests so much. When you say it doesn’t have some of the niggles? C# doesn’t allow the use of a property as a method group. It doesn’t have Scala case classes, or sum types, where you can do a switch statement and the compiler checks that you’ve checked all the cases, which is really useful in functional-style programming. Pattern-matching, in other words. That’s actually the major niggle. C# is pretty good, and I’m quite happy with C#. And what about going even further with the type system to remove the need for tests to something like Haskell? Or is that a step too far? I’m quite a pragmatist, I don’t think I could deal with trying to write big systems in languages with too few other users, especially when learning how to structure things. I just don’t know anyone who can teach me, and the Internet won’t teach me. That’s the main reason I wouldn’t use it. If I turned up at a company that writes big systems in Haskell, I would have no objection to that, but I wouldn’t instigate it. What about things in C#? For instance, there’s contracts in C#, so you can try to statically verify a bit more about your code. Do you think that’s useful, or just not worthwhile? I’ve not really tried it. My hunch is that it needs to be built into the language and be quite mathematical for it to work in real life, and that doesn’t seem to have ended up true for C# contracts. I don’t think anyone who’s tried them thinks they’re any good. I might be wrong. On a slightly different note, how do you like to debug code? I think I’m quite an odd debugger. I use guesswork extremely rarely, especially if something seems quite difficult to debug. I’ve been bitten spending hours and hours on guesswork and not being scientific about debugging in the past, so now I’m scientific to a fault. What I want is to see the bug happening in the debugger, to step through the bug happening. To watch the program going from a valid state to an invalid state. When there’s a bug and I can’t work out why it’s happening, I try to find some piece of evidence which places the bug in one section of the code. From that experiment, I binary chop on the possible causes of the bug. I suppose that means binary chopping on places in the code, or binary chopping on a stage through a processing cycle. Basically, I’m very stupid about how I debug. I won’t make any guesses, I won’t use any intuition, I will only identify the experiment that’s going to binary chop most effectively and repeat rather than trying to guess anything. I suppose it’s quite top-down. Is most of the time then spent in the debugger? Absolutely, if at all possible I will never debug using print statements or logs. I don’t really hold much stock in outputting logs. If there’s any bug which can be reproduced locally, I’d rather do it in the debugger than outputting logs. And with SmartAssembly error reporting, there’s not a lot that can’t be either observed in an error report and just fixed, or reproduced locally. And in those other situations, maybe I’ll use logs. But I hate using logs. You stare at the log, trying to guess what’s going on, and that’s exactly what I don’t like doing. You have to just look at it and see does this look right or wrong. We’ve covered how you get to grip with bugs. How do you get to grips with an entire codebase? I watch it in the debugger. I find little bugs and then try to fix them, and mostly do it by watching them in the debugger and gradually getting an understanding of how the code works using my process of binary chopping. I have to do a lot of reading and watching code to choose where my slicing-in-half experiment is going to be. The last time I did it was SmartAssembly. The old code was a complete mess, but at least it did things top to bottom. There wasn’t too much of some of the big abstractions where flow of control goes all over the place, into a base class and back again. Code’s really hard to understand when that happens. So I like to choose a little bug and try to fix it, and choose a bigger bug and try to fix it. Definitely learn by doing. I want to always have an aim so that I get a little achievement after every few hours of debugging. Once I’ve learnt the codebase I might be able to fix all the bugs in an hour, but I’d rather be using them as an aim while I’m learning the codebase. If I was a maintainer of a codebase, what should I do to make it as easy as possible for you to understand? Keep distinct concepts in different places. And name your stuff so that it’s obvious which concepts live there. You shouldn’t have some variable that gets set miles up the top of somewhere, and then is read miles down to choose some later behaviour. I’m talking from a very much SmartAssembly point of view because the old SmartAssembly codebase had tons and tons of these things, where it would read some property of the code and then deal with it later. Just thousands of variables in scope. Loads of things to think about. If you can keep concepts separate, then it aids me in my process of fixing bugs one at a time, because each bug is going to more or less be understandable in the one place where it is. And what about tests? Do you think they help at all? I’ve never had the opportunity to learn a codebase which has had tests, I don’t know what it’s like! What about when you’re actually developing? How useful do you find tests in finding bugs or regressions? Finding regressions, absolutely. Running bits of code that would be quite hard to run otherwise, definitely. It doesn’t happen very often that a test finds a bug in the first place. I don’t really buy nebulous promises like tests being a good way to think about the spec of the code. My thinking goes something like “This code works at the moment, great, ship it! Ah, there’s a way that this code doesn’t work. Okay, write a test, demonstrate that it doesn’t work, fix it, use the test to demonstrate that it’s now fixed, and keep the test for future regressions.” The most valuable tests are for bugs that have actually happened at some point, because bugs that have actually happened at some point, despite the fact that you think you’ve fixed them, are way more likely to appear again than new bugs are. Does that mean that when you write your code the first time, there are no tests? Often. The chance of there being a bug in a new feature is relatively unaffected by whether I’ve written a test for that new feature because I’m not good enough at writing tests to think of bugs that I would have written into the code. So not writing regression tests for all of your code hasn’t affected you too badly? There are different kinds of features. Some of them just always work, and are just not flaky, they just continue working whatever you throw at them. Maybe because the type-checker is particularly effective around them. Writing tests for those features which just tend to always work is a waste of time. And because it’s a waste of time I’ll tend to wait until a feature has demonstrated its flakiness by having bugs in it before I start trying to test it. You can get a feel for whether it’s going to be flaky code as you’re writing it. I try to write it to make it not flaky, but there are some things that are just inherently flaky. And very occasionally, I’ll think “this is going to be flaky” as I’m writing, and then maybe do a test, but not most of the time. How do you think your programming style has changed over time? I’ve got clearer about what the right way of doing things is. I used to flip-flop a lot between different ideas. Five years ago I came up with some really good ideas and some really terrible ideas. All of them seemed great when I thought of them, but they were quite diverse ideas, whereas now I have a smaller set of reliable ideas that are actually good for structuring code. So my code is probably more similar to itself than it used to be back in the day, when I was trying stuff out. I’ve got more disciplined about encapsulation, I think. There are operational things like I use actors more now than I used to, and that forces me to use immutability more than I used to. The first code that I wrote in Red Gate was the memory profiler UI, and that was an actor, I just didn’t know the name of it at the time. I don’t really use object-orientation. By object-orientation, I mean having n objects of the same type which are mutable. I want a constant number of objects that are mutable, and they should be different types. I stick stuff in dictionaries and then have one thing that owns the dictionary and puts stuff in and out of it. That’s definitely a pattern that I’ve seen recently. I think maybe I’m doing functional programming. Possibly. It’s plausible. If you had to summarise the essence of programming in a pithy sentence, how would you do it? Programming is the form of art that, without losing any of the beauty of architecture or fine art, allows you to produce things that people love and you make money from. So you think it’s an art rather than a science? It’s a little bit of engineering, a smidgeon of maths, but it’s not science. Like architecture, programming is on that boundary between art and engineering. If you want to do it really nicely, it’s mostly art. You can get away with doing architecture and programming entirely by having a good engineering mind, but you’re not going to produce anything nice. You’re not going to have joy doing it if you’re an engineering mind. Architects who are just engineering minds are not going to enjoy their job. I suppose engineering is the foundation on which you build the art. Exactly. How do you think programming is going to change over the next ten years? There will be an unfortunate shift towards dynamically-typed languages, because of JavaScript. JavaScript has an unfair advantage. JavaScript’s unfair advantage will cause more people to be exposed to dynamically-typed languages, which means other dynamically-typed languages crop up and the best features go into dynamically-typed languages. Then people conflate the good features with the fact that it’s dynamically-typed, and more investment goes into dynamically-typed languages. They end up better, so people use them. What about the idea of compiling other languages, possibly statically-typed, to JavaScript? It’s a reasonable idea. I would like to do it, but I don’t think enough people in the world are going to do it to make it pick up. The hordes of beginners are the lifeblood of a language community. They are what makes there be good tools and what makes there be vibrant community websites. And any particular thing which is the same as JavaScript only with extra stuff added to it, although it might be technically great, is not going to have the hordes of beginners. JavaScript is always to be quickest and easiest way for a beginner to start programming in the browser. And dynamically-typed languages are great for beginners. Compilers are pretty scary and beginners don’t write big code. And having your errors come up in the same place, whether they’re statically checkable errors or not, is quite nice for a beginner. If someone asked me to teach them some programming, I’d teach them JavaScript. If dynamically-typed languages are great for beginners, when do you think the benefits of static typing start to kick in? The value of having a statically typed program is in the tools that rely on the static types to produce a smooth IDE experience rather than actually telling me my compile errors. And only once you’re experienced enough a programmer that having a really smooth IDE experience makes a blind bit of difference, does static typing make a blind bit of difference. So it’s not really about size of codebase. If I go and write up a tiny program, I’m still going to get value out of writing it in C# using ReSharper because I’m experienced with C# and ReSharper enough to be able to write code five times faster if I have that help. Any other visions of the future? Nobody’s going to use actors. Because everyone’s going to be running on single-core VMs connected over network-ready protocols like JSON over HTTP. So, parallelism within one operating system is going to die. But until then, you should use actors. More Red Gater Coder interviews

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• Python error after installing libboost-all-dev on debian [migrated]

  - by Cameron Metzke

  A friend of mine wanted the liboost libraries installed on our shared computer so after installing libboost-all-dev 1.49.0.1 ( A debian wheezy machine ), I get this error when using the "pydoc modules" command on the commandline. It spits out the following error -- root@debian:/usr/include/c++/4.7# pydoc modules Please wait a moment while I gather a list of all available modules... **[debian:49065] [[INVALID],INVALID] ORTE_ERROR_LOG: A system-required executable either could not be found or was not executable by this user in file ../../../../../../orte/mca/ess/singleton/ess_singleton_module.c at line 357 [debian:49065] [[INVALID],INVALID] ORTE_ERROR_LOG: A system-required executable either could not be found or was not executable by this user in file ../../../../../../orte/mca/ess/singleton/ess_singleton_module.c at line 230 [debian:49065] [[INVALID],INVALID] ORTE_ERROR_LOG: A system-required executable either could not be found or was not executable by this user in file ../../../orte/runtime/orte_init.c at line 132 -------------------------------------------------------------------------- It looks like orte_init failed for some reason; your parallel process is likely to abort. There are many reasons that a parallel process can fail during orte_init; some of which are due to configuration or environment problems. This failure appears to be an internal failure; here's some additional information (which may only be relevant to an Open MPI developer): orte_ess_set_name failed --> Returned value A system-required executable either could not be found or was not executable by this user (-127) instead of ORTE_SUCCESS -------------------------------------------------------------------------- -------------------------------------------------------------------------- It looks like MPI_INIT failed for some reason; your parallel process is likely to abort. There are many reasons that a parallel process can fail during MPI_INIT; some of which are due to configuration or environment problems. This failure appears to be an internal failure; here's some additional information (which may only be relevant to an Open MPI developer): ompi_mpi_init: orte_init failed --> Returned "A system-required executable either could not be found or was not executable by this user" (-127) instead of "Success" (0) -------------------------------------------------------------------------- *** The MPI_Init() function was called before MPI_INIT was invoked. *** This is disallowed by the MPI standard. *** Your MPI job will now abort. [debian:49065] Abort before MPI_INIT completed successfully; not able to guarantee that all other processes were killed!** root@debian:/usr/include/c++/4.7# I tried looking into the problem and ended up uninstalling the following to get it to work again. openmpi common all 1.4.5-1 libibverbs-dev amd64 1.1.6-1 libopenmpi-dev amd64 1.4.5-1 mpi-default-dev amd64 1.0.1 libboost-mpi-python1.49.0 although pydoc works again, I'm assuming the packages I removed are gunna hurt somethiong else down the track ? As you guessed im not a c/c++ programmer. So I guess my question is, will this hurt something later ? is their a way to install those packages without hurting python ?

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• Cant access a remote server due mistake by setting firewall rule

  - by LMIT

  I need help due a my silly mistake! So for long time i have a dedicate server hosted by register.it Usually i access remotly to this server (Windows 2008 server) by Terminal Server. Today i wanted to block one site that continually send request to my server. So i was adding a new rule in the firewall (the native firewall on windows 2008 server), as i did many time, but this time, probably i was sleeping with my brain i add a general rules that stop everything! So i cant access to the server anymore, as no any users can browse the sites, nothing is working because this rule block everything. I know that is a silly mistake, no need to tell me :) so please what i can do ? The only 1 thing that my provider let me is reboot the server by his control panel, but this not help me in any way because the firewall block me again. i have administrator username and password, so what i really can do ? there are some trick some tecnique, some expert guru that can help me in this very bad situation ? UPDATE i follow the Tony suggest and i did a NMAP to check if some ports are open but look like all closed: NMAP RESULT Starting Nmap 6.00 ( http://nmap.org ) at 2012-05-29 22:32 W. Europe Daylight Time NSE: Loaded 93 scripts for scanning. NSE: Script Pre-scanning. Initiating Parallel DNS resolution of 1 host. at 22:32 Completed Parallel DNS resolution of 1 host. at 22:33, 13.00s elapsed Initiating SYN Stealth Scan at 22:33 Scanning xxx.xxx.xxx.xxx [1000 ports] SYN Stealth Scan Timing: About 29.00% done; ETC: 22:34 (0:01:16 remaining) SYN Stealth Scan Timing: About 58.00% done; ETC: 22:34 (0:00:44 remaining) Completed SYN Stealth Scan at 22:34, 104.39s elapsed (1000 total ports) Initiating Service scan at 22:34 Initiating OS detection (try #1) against xxx.xxx.xxx.xxx Retrying OS detection (try #2) against xxx.xxx.xxx.xxx Initiating Traceroute at 22:34 Completed Traceroute at 22:35, 6.27s elapsed Initiating Parallel DNS resolution of 11 hosts. at 22:35 Completed Parallel DNS resolution of 11 hosts. at 22:35, 13.00s elapsed NSE: Script scanning xxx.xxx.xxx.xxx. Initiating NSE at 22:35 Completed NSE at 22:35, 0.00s elapsed Nmap scan report for xxx.xxx.xxx.xxx Host is up. All 1000 scanned ports on xxx.xxx.xxx.xxx are filtered Too many fingerprints match this host to give specific OS details TRACEROUTE (using proto 1/icmp) HOP RTT ADDRESS 1 ... ... ... 13 ... 30 NSE: Script Post-scanning. Read data files from: D:\Program Files\Nmap OS and Service detection performed. Please report any incorrect results at http://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 145.08 seconds Raw packets sent: 2116 (96.576KB) | Rcvd: 61 (4.082KB) Question: The provider locally can access by username and password ?

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• Benchmark MySQL Cluster using flexAsynch: No free node id found for mysqld(API)?

  - by quanta

  I am going to benchmark MySQL Cluster using flexAsynch follow this guide, details as below: mkdir /usr/local/mysqlc732/ cd /usr/local/src/mysql-cluster-gpl-7.3.2 cmake . -DCMAKE_INSTALL_PREFIX=/usr/local/mysqlc732/ -DWITH_NDB_TEST=ON make make install Everything works fine until this step: # /usr/local/mysqlc732/bin/flexAsynch -t 1 -p 80 -l 2 -o 100 -c 100 -n FLEXASYNCH - Starting normal mode Perform benchmark of insert, update and delete transactions 1 number of concurrent threads 80 number of parallel operation per thread 100 transaction(s) per round 2 iterations Load Factor is 80% 25 attributes per table 1 is the number of 32 bit words per attribute Tables are with logging Transactions are executed with hint provided No force send is used, adaptive algorithm used Key Errors are disallowed Temporary Resource Errors are allowed Insufficient Space Errors are disallowed Node Recovery Errors are allowed Overload Errors are allowed Timeout Errors are allowed Internal NDB Errors are allowed User logic reported Errors are allowed Application Errors are disallowed Using table name TAB0 NDBT_ProgramExit: 1 - Failed ndb_cluster.log: WARNING -- Failed to allocate nodeid for API at 127.0.0.1. Returned eror: 'No free node id found for mysqld(API).' I also have recompiled with -DWITH_DEBUG=1 -DWITH_NDB_DEBUG=1. How can I run flexAsynch in the debug mode? # /usr/local/mysqlc732/bin/flexAsynch -h FLEXASYNCH Perform benchmark of insert, update and delete transactions Arguments: -t Number of threads to start, default 1 -p Number of parallel transactions per thread, default 32 -o Number of transactions per loop, default 500 -l Number of loops to run, default 1, 0=infinite -load_factor Number Load factor in index in percent (40 -> 99) -a Number of attributes, default 25 -c Number of operations per transaction -s Size of each attribute, default 1 (PK is always of size 1, independent of this value) -simple Use simple read to read from database -dirty Use dirty read to read from database -write Use writeTuple in insert and update -n Use standard table names -no_table_create Don't create tables in db -temp Create table(s) without logging -no_hint Don't give hint on where to execute transaction coordinator -adaptive Use adaptive send algorithm (default) -force Force send when communicating -non_adaptive Send at a 10 millisecond interval -local 1 = each thread its own node, 2 = round robin on node per parallel trans 3 = random node per parallel trans -ndbrecord Use NDB Record -r Number of extra loops -insert Only run inserts on standard table -read Only run reads on standard table -update Only run updates on standard table -delete Only run deletes on standard table -create_table Only run Create Table of standard table -drop_table Only run Drop Table on standard table -warmup_time Warmup Time before measurement starts -execution_time Execution Time where measurement is done -cooldown_time Cooldown time after measurement completed -table Number of standard table, default 0

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• Why cant I use two or more keyboards/ mouse parallely on one computer?

  - by rainbow365

  Hi, This is just a question of curiosity. Why cannot I use two keyboards parallely in windows? for eg. typing in notepad using 2 keyboards in real parallel mode. what prevents windows to accomdate such feature? is there any multitasking or parallel processing OS that can do it?

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• Why can't I use two or more keyboards/mice at the same time on one computer?

  - by rainbow365

  This is just a question of curiosity. Why cannot I use two keyboards at the same time in Windows? For example, typing in Notepad using 2 keyboards in real parallel mode. what prevents Windows from accommodating such a feature? Is there any multitasking or parallel processing OS that can do it?

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• ZeroDowntime deployment of configuration in Tomcat 7

  - by pagid

  looking at the things which can be done with the Parallel deployments in Tomcat 7, I wonder how new or changed configuration could be provided to these various versions of the application. In a nutshell - what parallel deployment offers is that pushing a new version of a war file to the webapps dir (with filenames like "App##01.war, "App##02.war") and ever user with a new session will get the newer version, all others stay with the old version. So how could one provide different or additional configuration (properties) to the various versions? Cheers.

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• Enable ReadyBoost on a second internal HDD?

  - by kd304

  I have two SATA HDDs in my desktop PC (one for daily activity, one for storage and backup). I can finely use ReadyBoost with pendrives, but I wonder, Is there a way I could use my underutilized second HDD to participate in the cacheing mechanism (same concept as having two CPU cores crunch things in parallel: have two HDDs fetch data in parallel)? Clearly speaking: I want to enable ReadyBoost on my separate D: drive.

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• Enabling "USB Printing Support" in Windows 7

  - by Kevin Dente

  I'm trying to use an old parallel-port based printer with a USB-to-parallel port adapter on Windows 7. When I plug it into the USB port on the computer it's listed as an unrecognized device. I know that these cables typically use the "USB Printing Support" driver with makes USB ports show up as printer ports in the printer dialog. Is there a way to manually add USB Printing Support to Windows 7, since it isn't being added automatically?

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• Enabling "USB Printing Support" in Windows 7

  - by Kevin Dente

  I'm trying to use an old parallel-port based printer with a USB-to-parallel port adapter on Windows 7. When I plug it into the USB port on the computer it's listed as an unrecognized device. I know that these cables typically use the "USB Printing Support" driver with makes USB ports show up as printer ports in the printer dialog. Is there a way to manually add USB Printing Support to Windows 7, since it isn't being added automatically?

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• Linux software RAID6: 3 drives offline - how to force online?

  - by Ole Tange

  This is similar to 3 drives fell out of Raid6 mdadm - rebuilding? except that it is not due to a failing cable. Instead the 3rd drive fell offline during rebuild of another drive. The drive failed with: kernel: end_request: I/O error, dev sdc, sector 293732432 kernel: md/raid:md0: read error not correctable (sector 293734224 on sdc). After rebooting both these sectors and the sectors around them are fine. This leads me to believe the error is intermittent and thus the device simply took too long to error correct the sector and remap it. I expect that no data was written to the RAID after it failed. Therefore I hope that if I can kick the last failing device online that the RAID is fine and that the xfs_filesystem is OK, maybe with a few missing recent files. Taking a backup of the disks in the RAID takes 24 hours, so I would prefer that the solution works the first time. I have therefore set up a test scenario: export PRE=3 parallel dd if=/dev/zero of=/tmp/raid${PRE}{} bs=1k count=1000k ::: 1 2 3 4 5 parallel mknod /dev/loop${PRE}{} b 7 ${PRE}{} \; losetup /dev/loop${PRE}{} /tmp/raid${PRE}{} ::: 1 2 3 4 5 mdadm --create /dev/md$PRE -c 4096 --level=6 --raid-devices=5 /dev/loop${PRE}[12345] cat /proc/mdstat mkfs.xfs -f /dev/md$PRE mkdir -p /mnt/disk2 umount -l /mnt/disk2 mount /dev/md$PRE /mnt/disk2 seq 1000 | parallel -j1 mkdir -p /mnt/disk2/{}\;cp /bin/* /mnt/disk2/{}\;sleep 0.5 & mdadm --fail /dev/md$PRE /dev/loop${PRE}3 /dev/loop${PRE}4 cat /proc/mdstat # Assume reboot so no process is using the dir kill %1; sync & kill %1; sync & # Force fail one too many mdadm --fail /dev/md$PRE /dev/loop${PRE}1 parallel --tag -k mdadm -E ::: /dev/loop${PRE}? | grep Upda # loop 2,5 are newest. loop1 almost newest => force add loop1 Next step is to add loop1 back - and this is where I am stuck. After that do a xfs-consistency check. When that works, check that the solution also works on real devices (such a 4 USB sticks).

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• Android GPS timeout

  - by Scott Saunders

  I'm writing an Android application that, among other things, needs to send the current GPS coordinates to a server when the user tells it to. From a context menu, I run the service below. The service is a LocationListener and requests updates from the LocationManager. When it gets a location (onLocationChanged()), it removes itself as a listener and sends the coordinates off to the server. All of this is working. However, if GPS coordinates are not quickly available, my service just keeps running until it gets some. It holds up the UI with a progress dialog, which is annoying. Worse, if the user has moved since starting the service, the first GPS coordinates might be wrong and the app will send bad data to the server. I need a timeout on the service. Is there a good way to do that? I'm not very experienced with threads. I think I can run a Runnable in the onStartCommand() method that will somehow count down 30 seconds and then, if there is no GPS result yet, call my service's stop() method. Does that sound like the best way to do this? Alternatively, is it possible to tell if the GPS cannot get a fix? How would I go about doing that? Edit: To further clarify, I'm looking for the best way to "give up" on getting a Location after some amount of time. public class AddCurrentLocation extends Service implements LocationListener { Application app; LocationManager mLocManager; ProgressDialog mDialog; @Override public int onStartCommand(Intent intent, int arg0, int arg1) { app = getApplication(); // show progress dialog if (app.getScreen() != null) { mDialog = ProgressDialog.show(app.getScreen(), "", "Adding Location. Please wait...", true); } // find GPS service and start listening Criteria criteria = new Criteria(); criteria.setAccuracy(Criteria.ACCURACY_FINE); mLocManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); String bestProvider = mLocManager.getBestProvider(criteria, true); mLocManager.requestLocationUpdates(bestProvider, 2000, 0, this); return START_NOT_STICKY; } private void stop() { mLocManager.removeUpdates(this); if (mDialog != null) { mDialog.dismiss(); } stopSelf(); } @Override public void onLocationChanged(Location location) { // done with GPS stop listening mLocManager.removeUpdates(this); sendLocation(location); // method to send info to server stop(); } // other required methods and sendLocation() ... }

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• Get coords of an oval in Tkinter

  - by Baddie

  I can't seem to figure out how to reterive the x,y position of an oval created on a Tkinter canvas using Python via c.create_oval(x0, y0, x1, y2) I understand that Tkinter creates the oval inside the box specified by x0,y0,x1,y2 and if I can get those coordinates that would also work. I need the coordinates to move the oval by an offset equal to the mouse coords and the actual oval.

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• How I can add JScroll bar to NavigableImagePanel which is an Image panel with an small navigation vi

  - by Sarah Kho

  Hi, I have the following NavigableImagePanel, it is under BSD license and I found it in the web. What I want to do with this panel is as follow: I want to add a JScrollPane to it in order to show images in their full size and let the users to re-center the image using the small navigation panel. Right now, the panel resize the images to fit them in the current panel size. I want it to load the image in its real size and let users to navigate to different parts of the image using the navigation panel. Source code for the panel: import java.awt.AWTEvent; import java.awt.BorderLayout; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GraphicsEnvironment; import java.awt.Image; import java.awt.Point; import java.awt.Rectangle; import java.awt.RenderingHints; import java.awt.Toolkit; import java.awt.event.ComponentAdapter; import java.awt.event.ComponentEvent; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.event.MouseMotionListener; import java.awt.event.MouseWheelEvent; import java.awt.event.MouseWheelListener; import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException; import java.util.Arrays; import javax.imageio.ImageIO; import javax.swing.JFrame; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.SwingUtilities; /** * @author pxt * */ public class NavigableImagePanel extends JPanel { /** * <p>Identifies a change to the zoom level.</p> */ public static final String ZOOM_LEVEL_CHANGED_PROPERTY = "zoomLevel"; /** * <p>Identifies a change to the zoom increment.</p> */ public static final String ZOOM_INCREMENT_CHANGED_PROPERTY = "zoomIncrement"; /** * <p>Identifies that the image in the panel has changed.</p> */ public static final String IMAGE_CHANGED_PROPERTY = "image"; private static final double SCREEN_NAV_IMAGE_FACTOR = 0.15; // 15% of panel's width private static final double NAV_IMAGE_FACTOR = 0.3; // 30% of panel's width private static final double HIGH_QUALITY_RENDERING_SCALE_THRESHOLD = 1.0; private static final Object INTERPOLATION_TYPE = RenderingHints.VALUE_INTERPOLATION_BILINEAR; private double zoomIncrement = 0.2; private double zoomFactor = 1.0 + zoomIncrement; private double navZoomFactor = 1.0 + zoomIncrement; private BufferedImage image; private BufferedImage navigationImage; private int navImageWidth; private int navImageHeight; private double initialScale = 0.0; private double scale = 0.0; private double navScale = 0.0; private int originX = 0; private int originY = 0; private Point mousePosition; private Dimension previousPanelSize; private boolean navigationImageEnabled = true; private boolean highQualityRenderingEnabled = true; private WheelZoomDevice wheelZoomDevice = null; private ButtonZoomDevice buttonZoomDevice = null; /** * <p>Defines zoom devices.</p> */ public static class ZoomDevice { /** * <p>Identifies that the panel does not implement zooming, * but the component using the panel does (programmatic zooming method).</p> */ public static final ZoomDevice NONE = new ZoomDevice("none"); /** * <p>Identifies the left and right mouse buttons as the zooming device.</p> */ public static final ZoomDevice MOUSE_BUTTON = new ZoomDevice("mouseButton"); /** * <p>Identifies the mouse scroll wheel as the zooming device.</p> */ public static final ZoomDevice MOUSE_WHEEL = new ZoomDevice("mouseWheel"); private String zoomDevice; private ZoomDevice(String zoomDevice) { this.zoomDevice = zoomDevice; } public String toString() { return zoomDevice; } } //This class is required for high precision image coordinates translation. private class Coords { public double x; public double y; public Coords(double x, double y) { this.x = x; this.y = y; } public int getIntX() { return (int)Math.round(x); } public int getIntY() { return (int)Math.round(y); } public String toString() { return "[Coords: x=" + x + ",y=" + y + "]"; } } private class WheelZoomDevice implements MouseWheelListener { public void mouseWheelMoved(MouseWheelEvent e) { Point p = e.getPoint(); boolean zoomIn = (e.getWheelRotation() < 0); if (isInNavigationImage(p)) { if (zoomIn) { navZoomFactor = 1.0 + zoomIncrement; } else { navZoomFactor = 1.0 - zoomIncrement; } zoomNavigationImage(); } else if (isInImage(p)) { if (zoomIn) { zoomFactor = 1.0 + zoomIncrement; } else { zoomFactor = 1.0 - zoomIncrement; } zoomImage(); } } } private class ButtonZoomDevice extends MouseAdapter { public void mouseClicked(MouseEvent e) { Point p = e.getPoint(); if (SwingUtilities.isRightMouseButton(e)) { if (isInNavigationImage(p)) { navZoomFactor = 1.0 - zoomIncrement; zoomNavigationImage(); } else if (isInImage(p)) { zoomFactor = 1.0 - zoomIncrement; zoomImage(); } } else { if (isInNavigationImage(p)) { navZoomFactor = 1.0 + zoomIncrement; zoomNavigationImage(); } else if (isInImage(p)) { zoomFactor = 1.0 + zoomIncrement; zoomImage(); } } } } /** * <p>Creates a new navigable image panel with no default image and * the mouse scroll wheel as the zooming device.</p> */ public NavigableImagePanel() { setOpaque(false); addComponentListener(new ComponentAdapter() { public void componentResized(ComponentEvent e) { if (scale > 0.0) { if (isFullImageInPanel()) { centerImage(); } else if (isImageEdgeInPanel()) { scaleOrigin(); } if (isNavigationImageEnabled()) { createNavigationImage(); } repaint(); } previousPanelSize = getSize(); } }); addMouseListener(new MouseAdapter() { public void mousePressed(MouseEvent e) { if (SwingUtilities.isLeftMouseButton(e)) { if (isInNavigationImage(e.getPoint())) { Point p = e.getPoint(); displayImageAt(p); } } } public void mouseClicked(MouseEvent e){ if (e.getClickCount() == 2) { resetImage(); } } }); addMouseMotionListener(new MouseMotionListener() { public void mouseDragged(MouseEvent e) { if (SwingUtilities.isLeftMouseButton(e) && !isInNavigationImage(e.getPoint())) { Point p = e.getPoint(); moveImage(p); } } public void mouseMoved(MouseEvent e) { //we need the mouse position so that after zooming //that position of the image is maintained mousePosition = e.getPoint(); } }); setZoomDevice(ZoomDevice.MOUSE_WHEEL); } /** * <p>Creates a new navigable image panel with the specified image * and the mouse scroll wheel as the zooming device.</p> */ public NavigableImagePanel(BufferedImage image) throws IOException { this(); setImage(image); } private void addWheelZoomDevice() { if (wheelZoomDevice == null) { wheelZoomDevice = new WheelZoomDevice(); addMouseWheelListener(wheelZoomDevice); } } private void addButtonZoomDevice() { if (buttonZoomDevice == null) { buttonZoomDevice = new ButtonZoomDevice(); addMouseListener(buttonZoomDevice); } } private void removeWheelZoomDevice() { if (wheelZoomDevice != null) { removeMouseWheelListener(wheelZoomDevice); wheelZoomDevice = null; } } private void removeButtonZoomDevice() { if (buttonZoomDevice != null) { removeMouseListener(buttonZoomDevice); buttonZoomDevice = null; } } /** * <p>Sets a new zoom device.</p> * * @param newZoomDevice specifies the type of a new zoom device. */ public void setZoomDevice(ZoomDevice newZoomDevice) { if (newZoomDevice == ZoomDevice.NONE) { removeWheelZoomDevice(); removeButtonZoomDevice(); } else if (newZoomDevice == ZoomDevice.MOUSE_BUTTON) { removeWheelZoomDevice(); addButtonZoomDevice(); } else if (newZoomDevice == ZoomDevice.MOUSE_WHEEL) { removeButtonZoomDevice(); addWheelZoomDevice(); } } /** * <p>Gets the current zoom device.</p> */ public ZoomDevice getZoomDevice() { if (buttonZoomDevice != null) { return ZoomDevice.MOUSE_BUTTON; } else if (wheelZoomDevice != null) { return ZoomDevice.MOUSE_WHEEL; } else { return ZoomDevice.NONE; } } //Called from paintComponent() when a new image is set. private void initializeParams() { double xScale = (double)getWidth() / image.getWidth(); double yScale = (double)getHeight() / image.getHeight(); initialScale = Math.min(xScale, yScale); scale = initialScale; //An image is initially centered centerImage(); if (isNavigationImageEnabled()) { createNavigationImage(); } } //Centers the current image in the panel. private void centerImage() { originX = (int)(getWidth() - getScreenImageWidth()) / 2; originY = (int)(getHeight() - getScreenImageHeight()) / 2; } //Creates and renders the navigation image in the upper let corner of the panel. private void createNavigationImage() { //We keep the original navigation image larger than initially //displayed to allow for zooming into it without pixellation effect. navImageWidth = (int)(getWidth() * NAV_IMAGE_FACTOR); navImageHeight = navImageWidth * image.getHeight() / image.getWidth(); int scrNavImageWidth = (int)(getWidth() * SCREEN_NAV_IMAGE_FACTOR); int scrNavImageHeight = scrNavImageWidth * image.getHeight() / image.getWidth(); navScale = (double)scrNavImageWidth / navImageWidth; navigationImage = new BufferedImage(navImageWidth, navImageHeight, image.getType()); Graphics g = navigationImage.getGraphics(); g.drawImage(image, 0, 0, navImageWidth, navImageHeight, null); } /** * <p>Sets an image for display in the panel.</p> * * @param image an image to be set in the panel */ public void setImage(BufferedImage image) { BufferedImage oldImage = this.image; this.image = image; //Reset scale so that initializeParameters() is called in paintComponent() //for the new image. scale = 0.0; firePropertyChange(IMAGE_CHANGED_PROPERTY, (Image)oldImage, (Image)image); repaint(); } /** * <p>resets an image to the centre of the panel</p> * */ public void resetImage() { BufferedImage oldImage = this.image; this.image = image; //Reset scale so that initializeParameters() is called in paintComponent() //for the new image. scale = 0.0; firePropertyChange(IMAGE_CHANGED_PROPERTY, (Image)oldImage, (Image)image); repaint(); } /** * <p>Tests whether an image uses the standard RGB color space.</p> */ public static boolean isStandardRGBImage(BufferedImage bImage) { return bImage.getColorModel().getColorSpace().isCS_sRGB(); } //Converts this panel's coordinates into the original image coordinates private Coords panelToImageCoords(Point p) { return new Coords((p.x - originX) / scale, (p.y - originY) / scale); } //Converts the original image coordinates into this panel's coordinates private Coords imageToPanelCoords(Coords p) { return new Coords((p.x * scale) + originX, (p.y * scale) + originY); } //Converts the navigation image coordinates into the zoomed image coordinates private Point navToZoomedImageCoords(Point p) { int x = p.x * getScreenImageWidth() / getScreenNavImageWidth(); int y = p.y * getScreenImageHeight() / getScreenNavImageHeight(); return new Point(x, y); } //The user clicked within the navigation image and this part of the image //is displayed in the panel. //The clicked point of the image is centered in the panel. private void displayImageAt(Point p) { Point scrImagePoint = navToZoomedImageCoords(p); originX = -(scrImagePoint.x - getWidth() / 2); originY = -(scrImagePoint.y - getHeight() / 2); repaint(); } //Tests whether a given point in the panel falls within the image boundaries. private boolean isInImage(Point p) { Coords coords = panelToImageCoords(p); int x = coords.getIntX(); int y = coords.getIntY(); return (x >= 0 && x < image.getWidth() && y >= 0 && y < image.getHeight()); } //Tests whether a given point in the panel falls within the navigation image //boundaries. private boolean isInNavigationImage(Point p) { return (isNavigationImageEnabled() && p.x < getScreenNavImageWidth() && p.y < getScreenNavImageHeight()); } //Used when the image is resized. private boolean isImageEdgeInPanel() { if (previousPanelSize == null) { return false; } return (originX > 0 && originX < previousPanelSize.width || originY > 0 && originY < previousPanelSize.height); } //Tests whether the image is displayed in its entirety in the panel. private boolean isFullImageInPanel() { return (originX >= 0 && (originX + getScreenImageWidth()) < getWidth() && originY >= 0 && (originY + getScreenImageHeight()) < getHeight()); } /** * <p>Indicates whether the high quality rendering feature is enabled.</p> * * @return true if high quality rendering is enabled, false otherwise. */ public boolean isHighQualityRenderingEnabled() { return highQualityRenderingEnabled; } /** * <p>Enables/disables high quality rendering.</p> * * @param enabled enables/disables high quality rendering */ public void setHighQualityRenderingEnabled(boolean enabled) { highQualityRenderingEnabled = enabled; } //High quality rendering kicks in when when a scaled image is larger //than the original image. In other words, //when image decimation stops and interpolation starts. private boolean isHighQualityRendering() { return (highQualityRenderingEnabled && scale > HIGH_QUALITY_RENDERING_SCALE_THRESHOLD); } /** * <p>Indicates whether navigation image is enabled.<p> * * @return true when navigation image is enabled, false otherwise. */ public boolean isNavigationImageEnabled() { return navigationImageEnabled; } /** * <p>Enables/disables navigation with the navigation image.</p> * <p>Navigation image should be disabled when custom, programmatic navigation * is implemented.</p> * * @param enabled true when navigation image is enabled, false otherwise. */ public void setNavigationImageEnabled(boolean enabled) { navigationImageEnabled = enabled; repaint(); } //Used when the panel is resized private void scaleOrigin() { originX = originX * getWidth() / previousPanelSize.width; originY = originY * getHeight() / previousPanelSize.height; repaint(); } //Converts the specified zoom level to scale. private double zoomToScale(double zoom) { return initialScale * zoom; } /** * <p>Gets the current zoom level.</p> * * @return the current zoom level */ public double getZoom() { return scale / initialScale; } /** * <p>Sets the zoom level used to display the image.</p> * <p>This method is used in programmatic zooming. The zooming center is * the point of the image closest to the center of the panel. * After a new zoom level is set the image is repainted.</p> * * @param newZoom the zoom level used to display this panel's image. */ public void setZoom(double newZoom) { Point zoomingCenter = new Point(getWidth() / 2, getHeight() / 2); setZoom(newZoom, zoomingCenter); } /** * <p>Sets the zoom level used to display the image, and the zooming center, * around which zooming is done.</p> * <p>This method is used in programmatic zooming. * After a new zoom level is set the image is repainted.</p> * * @param newZoom the zoom level used to display this panel's image. */ public void setZoom(double newZoom, Point zoomingCenter) { Coords imageP = panelToImageCoords(zoomingCenter); if (imageP.x < 0.0) { imageP.x = 0.0; } if (imageP.y < 0.0) { imageP.y = 0.0; } if (imageP.x >= image.getWidth()) { imageP.x = image.getWidth() - 1.0; } if (imageP.y >= image.getHeight()) { imageP.y = image.getHeight() - 1.0; } Coords correctedP = imageToPanelCoords(imageP); double oldZoom = getZoom(); scale = zoomToScale(newZoom); Coords panelP = imageToPanelCoords(imageP); originX += (correctedP.getIntX() - (int)panelP.x); originY += (correctedP.getIntY() - (int)panelP.y); firePropertyChange(ZOOM_LEVEL_CHANGED_PROPERTY, new Double(oldZoom), new Double(getZoom())); repaint(); } /** * <p>Gets the current zoom increment.</p> * * @return the current zoom increment */ public double getZoomIncrement() { return zoomIncrement; } /** * <p>Sets a new zoom increment value.</p> * * @param newZoomIncrement new zoom increment value */ public void setZoomIncrement(double newZoomIncrement) { double oldZoomIncrement = zoomIncrement; zoomIncrement = newZoomIncrement; firePropertyChange(ZOOM_INCREMENT_CHANGED_PROPERTY, new Double(oldZoomIncrement), new Double(zoomIncrement)); } //Zooms an image in the panel by repainting it at the new zoom level. //The current mouse position is the zooming center. private void zoomImage() { Coords imageP = panelToImageCoords(mousePosition); double oldZoom = getZoom(); scale *= zoomFactor; Coords panelP = imageToPanelCoords(imageP); originX += (mousePosition.x - (int)panelP.x); originY += (mousePosition.y - (int)panelP.y); firePropertyChange(ZOOM_LEVEL_CHANGED_PROPERTY, new Double(oldZoom), new Double(getZoom())); repaint(); } //Zooms the navigation image private void zoomNavigationImage() { navScale *= navZoomFactor; repaint(); } /** * <p>Gets the image origin.</p> * <p>Image origin is defined as the upper, left corner of the image in * the panel's coordinate system.</p> * @return the point of the upper, left corner of the image in the panel's coordinates * system. */ public Point getImageOrigin() { return new Point(originX, originY); } /** * <p>Sets the image origin.</p> * <p>Image origin is defined as the upper, left corner of the image in * the panel's coordinate system. After a new origin is set, the image is repainted. * This method is used for programmatic image navigation.</p>

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• Using tslib (touchscreen input) with DirectFB on embedded system (gumstix overo)

  - by emi1faber

  I'm attempting to use tslib with DirectFB on the gumstix Overo. Everything seems to be compiled correctly, as when DirectFB starts up, I get messages saying "Started 'tslib Input' ... DirectFB/Input: tslib touchscreen 0 0.1 (tslib)" etc. However, I haven't been able to find any example code showing how one reads the X-Y coordinates of a touchscreen press. Is there any example code out there to initialize the touchscreen and return the coordinates of a touchscreen press? Thanks in advance, Ben

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• Python performance: iteration and operations on nested lists

  - by J.J.

  Problem Hey folks. I'm looking for some advice on python performance. Some background on my problem: Given: A mesh of nodes of size (x,y) each with a value (0...255) starting at 0 A list of N input coordinates each at a specified location within the range (0...x, 0...y) Increment the value of the node at the input coordinate and the node's neighbors within range Z up to a maximum of 255. Neighbors beyond the mesh edge are ignored. (No wrapping) BASE CASE: A mesh of size 1024x1024 nodes, with 400 input coordinates and a range Z of 75 nodes. Processing should be O(x*y*Z*N). I expect x, y and Z to remain roughly around the values in the base case, but the number of input coordinates N could increase up to 100,000. My goal is to minimize processing time. Current results I have 2 current implementations: f1, f2 Running speed on my 2.26 GHz Intel Core 2 Duo with Python 2.6.1: f1: 2.9s f2: 1.8s f1 is the initial naive implementation: three nested for loops. f2 is replaces the inner for loop with a list comprehension. Code is included below for your perusal. Question How can I further reduce the processing time? I'd prefer sub-1.0s for the test parameters. Please, keep the recommendations to native Python. I know I can move to a third-party package such as numpy, but I'm trying to avoid any third party packages. Also, I've generated random input coordinates, and simplified the definition of the node value updates to keep our discussion simple. The specifics have to change slightly and are outside the scope of my question. thanks much! f1 is the initial naive implementation: three nested for loops. 2.9s def f1(x,y,n,z): rows = [] for i in range(x): rows.append([0 for i in xrange(y)]) for i in range(n): inputX, inputY = (int(x*random.random()), int(y*random.random())) topleft = (inputX - z, inputY - z) for i in xrange(max(0, topleft[0]), min(topleft[0]+(z*2), x)): for j in xrange(max(0, topleft[1]), min(topleft[1]+(z*2), y)): if rows[i][j] <= 255: rows[i][j] += 1 f2 is replaces the inner for loop with a list comprehension. 1.8s def f2(x,y,n,z): rows = [] for i in range(x): rows.append([0 for i in xrange(y)]) for i in range(n): inputX, inputY = (int(x*random.random()), int(y*random.random())) topleft = (inputX - z, inputY - z) for i in xrange(max(0, topleft[0]), min(topleft[0]+(z*2), x)): l = max(0, topleft[1]) r = min(topleft[1]+(z*2), y) rows[i][l:r] = [j+1 for j in rows[i][l:r] if j < 255]

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• Graph spacing algorithm

  - by David

  Hi, I am looking for an algorithm that would be useful for determining x y coordinates for a number objects to display on screen. Each object can be related to another object and there can be any number of relationships and there can be any number of these objects. There is no restriction on the overall size of area on which to display these object. I am writing this in php and would be looking to store the coordinates in an array.

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• Hadoop: Iterative MapReduce Performance

  - by S.N

  Is it correct to say that the parallel computation with iterative MapReduce can be justified only when the training data size is too large for the non-parallel computation for the same logic? I am aware that the there is overhead for starting MapReduce jobs. This can be critical for overall execution time when a large number of iterations is required. I can imagine that the sequential computation is faster than the parallel computation with iterative MapReduce as long as the memory allows to hold a data set in many cases. Is it the only benefit to use the iterative MapReduce? If not, what are the other benefits could be?

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• openmp in mex : stackoverflow error

  - by Edwin

  i have got the following fraction of code that getting me the stack overflow error #pragma omp parallel shared(Mo1, Mo2, sum_normalized_p_gn, Data, Mean_Out,Covar_Out,Prior_Out, det) private(i) num_threads( number_threads ) { //every thread has a new copy double* normalized_p_gn = (double*)malloc(NMIX*sizeof(double)); #pragma omp critical { int id = omp_get_thread_num(); int threads = omp_get_num_threads(); mexEvalString("drawnow"); } #pragma omp for //some parallel process..... } the variables declared in the shared are created by malloc. and they consumes with large amount of memory there are 2 questions regarding to the above code. 1) why this would generate the stack overflow error( i.e. segmentation fault) before it goes into the parallel for loop? it works fine when it runs in the sequential mode.... 2) am i right to dynamic allocate memory for each thread like "normalized_p_gn" above? Regards Edwin

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• Getting geospatial indexes to work in MongoDB 1.4.3

  - by Marcel J.

  I wanted to try geospatial indexes with MongoDB, but all I get is > db.map_nodes.find( { coodinate: { $near: [54, 10] } } ) error: { "$err" : "invalid operator: $near" } and > db.map_nodes.runCommand({geoNear:"coordinates", near:[50,50]}) { "errmsg" : "no such cmd", "bad cmd" : { "geoNear" : "coordinates", "near" : [ 50, 50 ] }, "ok" : 0 } I am using MongoDB 1.4.3. What am I doing wrong?

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• Transform GPS Co-Ordinates to Container Co-Ordinates.

  - by npinti

  Hi, I am looking for some service that can transform GPS coordinates into XY coordinates so that I can plot a point on an Image. Something like fromLatLngToContainerPixel would be great. Thanks in advance. P.S. I am developing a desktop application in java.

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