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• Getting a handle on GIS math, where do I start?

  - by Joshua

  I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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• What makes this "declarator invalid"? C++

  - by nieldw

  I have Vertex template in vertex.h. From my graph.h: 20 template<class edgeDecor, class vertexDecor, bool dir> 21 class Vertex; which I use in my Graph template. I've used the Vertex template successfully throughout my Graph, return pointers to Vertices, etc. Now for the first time I am trying to declare and instantiate a Vertex object, and gcc is telling me that my 'declarator' is 'invalid'. How can this be? 81 template<class edgeDecor, class vertexDecor, bool dir> 82 Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const 83 { 84 /* Construct new Graph with apropriate decorators */ 85 Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); 86 span.E.reserve(this->E.size()); 87 88 typename Vertex<edgeDecor,int,dir> v = new Vertex(INT_MAX); 89 span.V = new vector<Vertex<edgeDecor,int,dir> >(this->V.size,v); 90 }; And gcc is saying: graph.h: In member function ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool) const’: graph.h:88: error: invalid declarator before ‘v’ graph.h:89: error: ‘v’ was not declared in this scope I know this is probably another noob question, but I'll appreciate any help.

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• How to classify NN/NNP/NNS obtained from POS tagged document as a product feature

  - by Shweta .......

  I'm planning to perform sentiment analysis on reviews of product features (collected from Amazon dataset). I have extracted review text from the dataset and performed POS tagging on that. I'm able to extract NN/NNP as well. But my doubt is how do I come to know that extracted words classify as features of the products? I know there are classifiers in nltk but I don't know how I should use it for my project. I'm assuming there are 2 ways of finding whether the extracted word is a product feature or not. One is to compare with a bag of words and find out if my word exists in that. Doubt: How do I create/get bag of words? Second way is to implement some kind of apriori algorithm to find out frequently occurring words as features. I would like to know which method is good and how to go about implementing it. Some pointers to available softwares or code snippets would be helpful! Thanks!

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• Having trouble with confusing behaviour of error between debug and release modes in Xcode

  - by Cocorico

  Hi guys, I am confused over something (what is new!). I have an iPhone program I am writing and using some sqlite in a certain method, and there is some error which is giving me a message that says "Program received signal: “EXC_BAD_ACCESS” Okay, so I am trying to hunt down why this is doing this, and I notice something: When I run the program in debug mode, it gives me this error every single time I access this method (I test on the device). However when I run the program in release mode, I can access this method 2 times, and then it will give me this error the third time. So I mean, can someone just give me an explanation of what might cause this, I think that maybe deep-down I am not that smart on the difference in XCode of debug and release modes. I think that release mode does optimizing, and I guess the actual assembly machine code comes out different, yes? I AM A BIG NEWBIE USER UNFORTUNATELY! I am not clear on a lot of things like this, or whether it needs for I to remove nslog commands in the release build and such. Maybe I should just post the actual code in separate Stack OVerflow post, and see if people can see the error, then maybe this all become clear to me.

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• SQL Query to return maximums over decades

  - by Abraham Lincoln

  My question is the following. I have a baseball database, and in that baseball database there is a master table which lists every player that has ever played. There is also a batting table, which tracks every players' batting statistics. I created a view to join those two together; hence the masterplusbatting table. CREATE TABLE `Master` ( `lahmanID` int(9) NOT NULL auto_increment, `playerID` varchar(10) NOT NULL default '', `nameFirst` varchar(50) default NULL, `nameLast` varchar(50) NOT NULL default '', PRIMARY KEY (`lahmanID`), KEY `playerID` (`playerID`), ) ENGINE=MyISAM AUTO_INCREMENT=18968 DEFAULT CHARSET=latin1; CREATE TABLE `Batting` ( `playerID` varchar(9) NOT NULL default '', `yearID` smallint(4) unsigned NOT NULL default '0', `teamID` char(3) NOT NULL default '', `lgID` char(2) NOT NULL default '', `HR` smallint(3) unsigned default NULL, PRIMARY KEY (`playerID`,`yearID`,`stint`), KEY `playerID` (`playerID`), KEY `team` (`teamID`,`yearID`,`lgID`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; Anyway, my first query involved finding the most home runs hit every year since baseball began, including ties. The query to do that is the following.... select f.yearID, f.nameFirst, f.nameLast, f.HR from ( select yearID, max(HR) as HOMERS from masterplusbatting group by yearID )as x inner join masterplusbatting as f on f.yearID = x.yearId and f.HR = x.HOMERS This worked great. However, I now want to find the highest HR hitter in each decade since baseball began. Here is what I tried. select f.yearID, truncate(f.yearid/10,0) as decade,f.nameFirst, f.nameLast, f.HR from ( select yearID, max(HR) as HOMERS from masterplusbatting group by yearID )as x inner join masterplusbatting as f on f.yearID = x.yearId and f.HR = x.HOMERS group by decade You can see that I truncated the yearID in order to get 187, 188, 189 etc instead of 1897, 1885,. I then grouped by the decade, thinking that it would give me the highest per decade, but it is not returning the correct values. For example, it's giving me Adrian Beltre with 48 HR's in 2004 but everyone knows that Barry Bonds hit 73 HR in 2001. Can anyone give me some pointers?

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• Design of std::ifstream class

  - by Nawaz

  Those of us who have seen the beauty of STL try to use it as much as possible, and also encourage others to use it wherever we see them using raw pointers and arrays. Scott Meyers have written a whole book on STL, with title Effective STL. Yet what happened to the developers of ifstream that they preferred char* over std::string. I wonder why the first parameter of ifstream::open() is of type const char*, instead of const std::string &. Please have a look at it's signature: void open(const char * filename, ios_base::openmode mode = ios_base::in ); Why this? Why not this: void open(const string & filename, ios_base::openmode mode = ios_base::in ); Is this a serious mistake with the design? Or this design is deliberate? What could be the reason? I don't see any reason why they have preferred char* over std::string. Note we could still pass char* to the latter function that takes std::string. That's not a problem! By the way, I'm aware that ifstream is a typedef, so no comment on my title.:P. It looks short that is why I used it. The actual class template is : template<class _Elem,class _Traits> class basic_ifstream;

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• selecting a row by means of a button ... using didSelectRowAtIndexPath

  - by John Smith

  hey people , I have a question concerning a button I would like to create which selects my previous selected row. This is what I came up so far but since I'm new with the functionality and such I could definately use some pointers I created a toolbar with a button and behind this button is the following action. -(void)clickRow { selectedRow = [self.tableView indexPathForSelectedRow]; [self.tableView:[self tableView] didSelectRowAtIndexPath:selectedRow]; } in my didSelectRowAtIndexPath there is a rootViewController being pushed rvController = [RootViewController alloc] ...etc So what I would like is my function clickRow to select the row and push the new rootviewcontroller (which has the right info since I'm using a tree ). I tried something like this as well -(void)clickRow { NSDictionary *dictionary = [self.tableDataSource objectAtIndex:indexPath.row]; NSArray *Children = [dictionary objectForKey:@"Children"]; rvController = [[RootViewController alloc] initWithNibName:@"RootViewController" bundle:[NSBundle mainBundle]]; rvController.CurrentLevel += 1; rvController.CurrentTitle = [dictionary objectForKey:@"Title"]; [self.navigationController pushViewController:rvController animated:YES]; rvController.tableDataSource = Children; [rvController release]; } The last function works a little but a little is not enough;) For instance if I press the middle row or any other it constantly selects the toprow. thnx all for those of you reading and trying to help

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• Working with complex objects in Prevayler commands

  - by alexantd

  The demos included in the Prevayler distribution show how to pass in a couple strings (or something simple like that) into a command constructor in order to create or update an object. The problem is that I have an object called MyObject that has a lot of fields. If I had to pass all of them into the CreateMyObject command manually, it would be a pain. So an alternative I thought of is to pass my business object itself into the command, but to hang onto a clone of it (keeping in mind that I can't store the BO directly in the command). Of course after executing this command, I would need to make sure to dispose of the original copy that I passed in. public class CreateMyObject implements TransactionWithQuery { private MyObject object; public CreateMyObject(MyObject business_obj) { this.object = (MyObject) business_obj.clone(); } public Object executeAndQuery(...) throws Exception { ... } } The Prevayler wiki says: Transactions can't carry direct object references (pointers) to business objects. This has become known as the baptism problem because it's a common beginner pitfall. Direct object references don't work because once a transaction has been serialized to the journal and then deserialized for execution its object references no longer refer to the intended objects - - any objects they may have referred to at first will have been copied by the serialization process! Therefore, a transaction must carry some kind of string or numeric identifiers for any objects it wants to refer to, and it must look up the objects when it is executed. I think by cloning the passed-in object I will be getting around the "direct object pointer" problem, but I still don't know whether or not this is a good idea...

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• Low-Hanging Fruit: Obfuscating non-critical values in JavaScript

  - by Piskvor

  I'm making an in-browser game of the type "guess what place/monument/etc. is in this satellite/aerial view", using Google Maps JS API v3. However, I need to protect against cheaters - you have to pass a google.maps.LatLng and a zoom level to the map constructor, which means a cheating user only needs to view source to get to this data. I am already unsetting every value I possibly can without breaking the map (such as center and the manipulation functions like setZoom()), and initializing the map in an anonymous function (so the object is not visible in global namespace). Now, this is of course in-browser, client-side, untrusted JavaScript; I've read much of the obfuscation tag and I'm not trying to make the script bullet-proof (it's just a game, after all). I only need to make the obfuscation reasonably hard against the 1337 Java5kryp7 haxz0rz - "kid sister encryption", as Bruce Schneier puts it. Anything harder than base64 encoding would deter most cheaters by eliminating the lowest-hanging fruit - if the cheater is smart and determined enough to use a JS debugger, he can bypass anything I can do (as I need to pass the value to Google Maps API in plaintext), but that's unlikely to happen on a mass scale (there will also be other, not-code-related ways to prevent cheating). I've tried various minimizers and obfuscators, but those will mostly deal with code - the values are still shown verbatim. TL;DR: I need to obfuscate three values in JavaScript. I'm not looking for bullet-proof armor, just a sneeze-guard. What should I use?

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• Spree customize/extend user roles and permissions

  - by swapnil

  I am trying to specify some custom roles in Spree for example role 'client' and extend the permissions to access the admin section for this role. This user will be able to access only those Product created by that user. Concept is letting a user with role 'client' manage only products and other certain Models. To start with I added CanCan plugin and defined a RoleAbility Class in role_ability.rb Just following this post : Spree Custom Roles Permissions class RoleAbility include CanCan::Ability def initialize(user) user ||= User.new if user.has_role? 'admin' can :manage, :all elsif user.has_role? 'client_admin' can :read, Product can :admin, Product end end end Added this to an initializer : config/initializers/spree.rb Ability.register_ability(RetailerAbility) Also extended admin_products_controller_decorator.rb :app/controllersadmin_products_controller_decorator.rb Admin::ProductsController.class_eval do def authorize_admin authorize! :admin, Product authorize! params[:action].to_sym, Product end end But I am getting flash message 'Authorisation Failure' Trying to find some luck, I referred following links A github gist for Customizing Spree Roles : https://gist.github.com/1277326 Here's a similar issue what I am facing : http://groups.google.com/group/spree-user/browse_thread/thread/1e819e10410d03c5/23b269e09c7ed47e All efforts in vain... Any pointers of what is going on here highly appreciated ? Thanks in advance.

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• Module not found

  - by TMP

  Hi There! I've been working on this one quite a bit and haven't gotten any closer to a solution. I juut dug up my old copy of the WindowsHookLib again - It's available with source at http://www.codeproject.com/KB/DLL/WindowsHookLib.aspx. This library allows Global Windows Mouse/Keyboard/Clipboard Hooks, which is very useful. I'm trying to use the Mouse Hook in here to Capture Mouse-Motion (I could use a Timer that always polls Cursor.Position, but I plan on using more features of WindowsHookLib later). Code as follows: MouseHook mh = new MouseHook(); mh.InstallHook(); mh.MouseMove += new EventHandler<WindowsHookLib.MouseEventArgs>(mh_MouseMove); But on the call to InstallHook(), I get an Exception: "The specified Module could not be found". Strange. Searching, I found that someone thought this occurs because a DLL is not in a place included in the Windows PATH variable, and because placing it in system32 didn't help I went the whole hog and translated the thing to C# for inclusion directly in my project (I was curious how it works). However the error was obstinately persistent, so I dug a bit on this, and found the Code in the Library that is responsible: In InstallHook(), we have IntPtr hinstDLL = Marshal.GetHINSTANCE(Assembly.GetExecutingAssembly().GetModules()[0]); this._hMouseHook = UnsafeNativeMethods.SetWindowsHookEx(14, this._mouseProc, hinstDLL, 0); if (this._hMouseHook == IntPtr.Zero) { throw new MouseHookException(new Win32Exception(Marshal.GetLastWin32Error()).Message); } And this (after modification and recompile) tells me that what I'm really getting is a Windows error "ERROR_MOD_NOT_FOUND"! Now, Here I'm stumped. Didn't I just compile the Hook Library directly into my project? (UnsafeMethods.SetWindowsHookEx is just a DllImported Method from user32) Any Answers, or Prods in the right direction, or any hints, pointers or similar are very much appreciated!

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• Reflecting over classes in .NET produces methods only differing by a modifier

  - by mrjoltcola

  I'm a bit boggled by something, I hope the CLR gearheads can help. Apparently my gears aren't big enough. I have a reflector utility that generates assembly stubs for Cola for .NET, and I find classes have methods that only differ by a modifier, such as virtual. Example below, from Oracle.DataAccess.dll, method GetType(): class OracleTypeException : System.SystemException { virtual string ToString (); virtual System.Exception GetBaseException (); virtual void set_Source (string value); virtual void GetObjectData (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context); virtual System.Type GetType (); // here virtual bool Equals (object obj); virtual int32 GetHashCode (); System.Type GetType (); // and here } What is this? I have not been able to reproduce this with C# and it causes trouble for Cola as it thinks GetType() is a redefinition, since the signature is identical. My method reflector starts like this: static void DisplayMethod(MethodInfo m) { if ( // Filter out things Cola cannot yet import, like generics, pointers, etc. m.IsGenericMethodDefinition || m.ContainsGenericParameters || m.ReturnType.IsGenericType || !m.ReturnType.IsPublic || m.ReturnType.IsArray || m.ReturnType.IsPointer || m.ReturnType.IsByRef || m.ReturnType.IsPointer || m.ReturnType.IsMarshalByRef || m.ReturnType.IsImport ) return; // generate stub signature // [snipped] }

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• Using Python to get a CSV output for the following example.

  - by Az

  Hi there, I'm back again with my ongoing saga of Student-Project Allocation questions. Thanks to Moron (who does not match his namesake) I've got a bit of direction for an evaluation portion of my project. Going with the idea of the Assignment Problem and Hungarian Algorithm I would like to express my data in the form of a .csv file which would end up looking like this in spreadsheet form. This is based on the structure I saw here. | | Project 1 | Project 2 | Project 3 | |----------|-----------|-----------|-----------| |Student1 | | 2 | 1 | |----------|-----------|-----------|-----------| |Student2 | 1 | 2 | 3 | |----------|-----------|-----------|-----------| |Student3 | 1 | 3 | 2 | |----------|-----------|-----------|-----------| To make it less cryptic: the rows are the Students/Agents and the columns represent Projects/Task. Obviously ONE project can be assigned to ONE student. That, in short, is what my project is about. The fields represent the preference weights the students have placed upon the projects (ranging from 1 to 10). If blank, that student does not want that project and there's no chance of him/her being assigned such. Anyway, my data is stored within dictionaries. Specifically the students and projects dictionaries such that: students[student_id] = Student(student_id, student_name, alloc_proj, alloc_proj_rank, preferences) where preferences is in the form of a dictionary such that preferences[rank] = {project_id} and projects[project_id] = Project(project_id, project_name) I'm aware that sorted(students.keys()) will give me a sorted list of all the student IDs which will populate the row labels and sorted(projects.keys()) will give me the list I need to populate the column labels. Thus for each student, I'd go into their preferences dictionary and match the applicable projects to ranks. I can do that much. Where I'm failing is understanding how to create a .csv file. Any help, pointers or good tutorials will be highly appreciated.

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• What's the best way to resolve this scope problem?

  - by Peter Stewart

  I'm writing a program in python that uses genetic techniques to optimize expressions. Constructing and evaluating the expression tree is the time consumer as it can happen billions of times per run. So I thought I'd learn enough c++ to write it and then incorporate it in python using cython or ctypes. I've done some searching on stackoverflow and learned a lot. This code compiles, but leaves the pointers dangling. I tried 'this_node = new Node(...' . It didn't seem to work. And I'm not at all sure how I'd delete all the references as there would be hundreds. I'd like to use variables that stay in scope, but maybe that's not the c++ way. What is the c++ way? class Node { public: char *cargo; int depth; Node *left; Node *right; } Node make_tree(int depth) { depth--; if(depth <= 0) { Node tthis_node("value",depth,NULL,NULL); return tthis_node; } else { Node this_node("operator" depth, &make_tree(depth), &make_tree(depth)); return this_node; } };

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• Fix hard-coded display setting without source (24-bit, need 32-bit)

  - by FerretallicA

  I wrote a program about 10 years ago in Visual Basic 6 which was basically a full-screen game similar to Breakout / Arkanoid but had 'demoscene'-style backgrounds. I found the program, but not the source code. Back then I hard-coded the display mode to 800x600x24, and the program crashes whenever I try to run it as a result. No virtual machine seems to support 24-bit display when the host display mode is 16/32-bit. It uses DirectX 7 so DOSBox is no use. I've tried all sorts of decompiler and at best they give me the form names and a bunch of assembly calls which mean nothing to me. The display mode setting was a DirectX 7 call but there's no clear reference to it in the decompilation. In this situation, is there any pointers on how I can: pin-point the function call in the program which is setting the display mode to 800x600x24 (ResHacker maybe?) and change the value being passed to it so it sets 800x600x32 view/intercept DirectX calls being made while it's running or if that's not possible, at least run the program in an environment that emulates a 24-bit display I don't need to recover the source code (as nice as it would be) so much as just want to get it running.

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• Best practices, PHP, tracking millions of impressions per day.

  - by John

  What do I have to do to make 20k mysql inserts per second possible (during peak hours around 1k/sec during slower times)? I've been doing some research and I've seen the "INSERT DELAYED" suggestion, writing to a flat file, "fopen(file,'a')", and then running a chron job to dump the "needed" data into mysql, etc. I've also heard you need multiple servers and "load balancers" which I've never heard of, to make something like this work. I've also been looking at these "cloud server" thing-a-ma-jigs, and their automatic scalability, but not sure about what's actually scalable. The application is just a tracker script, so if I have 100 websites that get 3 million page loads a day, there will be around 300 million inserts a day. The data will be ran through a script that will run every 15-30 minutes which will normalize the data and insert it into another mysql table. How do the big dogs do it? How do the little dogs do it? I can't afford a huge server anymore so any intuitive ways, if there are multiple ways of going at it, you smart people can think of.. please let me know :)

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• java - powermock whenNew doesnt seem to work, calls the actual constructor

  - by user1331243

  I have two final classes that are used in my unit test. I am trying to use whenNew on the constructor of a final class, but I see that it calls the actual constructor. The code is @PrepareForTest({A.class, B.class, Provider.class}) @Test public void testGetStatus() throws Exception { B b = mock(B.class); when(b.getStatus()).thenReturn(1); whenNew(B.class).withArguments(anyString()).thenReturn(b); Provider p = new Provider(); int val = p.getStatus(); assertTrue((val == 1)); } public class Provider { public int getStatus() { B b = new B("test"); return b.getStatus(); } } public final class A { private void init() { // ...do soemthing } private static A a; private A() { } public static A getInstance() { if (a == null) { a = new A(); a.init(); } return a; } } public final class B { public B() { } public B(String s) { this(A.getInstance(), s); } public B(A a, String s) { } public int getStatus() { return 0; } } On debug, I find that its the actual class B instance created and not the mock instance that is returned for new usage and assertion fails. Any pointers on how to get this working. Thanks

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• Should I return an NSMutableString in a method that returns NSString

  - by Casey Marshall

  Ok, so I have a method that takes an NSString as input, does an operation on the contents of this string, and returns the processed string. So the declaration is: - (NSString *) processString: (NSString *) str; The question: should I just return the NSMutableString instance that I used as my "work" buffer, or should I create a new NSString around the mutable one, and return that? So should I do this: - (NSString *) processString: (NSString *) str { NSMutableString *work = [NSMutableString stringWithString: str]; // process 'work' return work; } Or this: - (NSString *) processString: (NSString *) str { NSMutableString *work = [NSMutableString stringWithString: str]; // process 'work' return [NSString stringWithString: work]; // or [work stringValue]? } The second one makes another copy of the string I'm returning, unless NSString does smart things like copy-on-modify. But the first one is returning something the caller could, in theory, go and modify later. I don't care if they do that, since the string is theirs. But are there valid reasons for preferring the latter form over the former? And, is either stringWithString or stringValue preferred over the other?

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Modeling complex hierarchies

  - by jdn

  To gain some experience, I am trying to make an expert system that can answer queries about the animal kingdom. However, I have run into a problem modeling the domain. I originally considered the animal kingdom hierarchy to be drawn like -animal -bird -carnivore -hawk -herbivore -bluejay -mammals -carnivores -herbivores This I figured would allow me to make queries easily like "give me all birds", but would be much more expensive to say "give me all carnivores", so I rewrote the hierarchy to look like: -animal -carnivore -birds -hawk -mammals -xyz -herbivores -birds -bluejay -mammals But now it will be much slower to query "give me all birds." This is of course a simple example, but it got me thinking that I don't really know how to model complex relationships that are not so strictly hierarchical in nature in the context of writing an expert system to answer queries as stated above. A directed, cyclic graph seems like it could mathematically solve the problem, but storing this in a relational database and maintaining it (updates) would seem like a nightmare to me. I would like to know how people typically model such things. Explanations or pointers to resources to read further would be acceptable and appreciated.

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• Building asynchronous cache pattern with JSP

  - by merweirdo

  I have a JSP that will take some 8 minutes to render. The code logic itself can not be made more efficient (it will update often and be updated by basically a pointy haired boss). I tried wrapping it with a caching layer like <%@ taglib uri="/WEB-INF/classes/oscache.tld" prefix="oscache" %> <oscache:cache time="60"> <div class="pagecontent"> ..... my logic </div> </oscache:cache> This is nice until the 60 seconds is over. The next query after that blocks until the 8 minutes of rendering is done with again. I would need a way to build a pattern something like: If there is no version of the dynamic content in the cache run the actual logic (and populate the cache for subsequent requests) If there is a non-expired version of the dynamic content in the cache serve the output of the JSP logic from the cache If there is an expired version of the dynamic content in the cache serve the output of the JSP logic still from the cache AND run the JSP logic in the background so that the cache gets updated transparently to the user - avoiding the user have to wait for 8 minutes I found out that at least EHCache might be able to do some asynchronous cache updating but it did not sadly seem to apply to the JSP tags... Also I have to take in 10-20 parameters for the actual logic of the JSP and some of them should be used as a key for caching. Code example and/or pointers would be greatly appreciated. I do not frankly care if the solution provided is extremely ugly. I just want a simple 5 minute caching with asynchronous cache update taking into account some parameters as a key.

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• Swing GUI using JNI crashes

  - by Div

  Hi, A java swing application(GUI) using JNI code to communicate with native C code. The Swing application launches properly and works fine. The GUI is used to start some customized system level tests(io,memory,cpu) and show their progress. The tests have to be left running at-least overnight to get the results. But, the next morning, GUI crashes and throws following message. Any pointers on source of the issue will be greatly appreciated. Java version: java 1.5 / java 1.6 OS: Solaris 10. Thanks, Div =============MESSAGES================== # uname -a SunOS Generic_127127-11 sun4v sparc SUNW, # # # # An unexpected error has been detected by HotSpot Virtual Machine: # # SIGSEGV (0xb) at pc=0xff268924, pid=9473, tid=272 # # Java VM: Java HotSpot(TM) Server VM (1.5.0_14-b03 mixed mode) # Problematic frame: # C [libc.so.1+0x68924] strstr+0x20 # # An error report file with more information is saved as hs_err_pid9473.log # # If you would like to submit a bug report, please visit: # HotSpot Virtual Machine Error Reporting Page # ============================= Another machine: # A fatal error has been detected by the Java Runtime Environment: # # SIGSEGV (0xb) at pc=0xff231fd0, pid=1406, tid=180 # # JRE version: 6.0_18-b07 # Java VM: Java HotSpot(TM) Server VM (16.0-b13 mixed mode solaris-sparc ) # Problematic frame: # C [libc.so.1+0x31fd0] strcpy+0x70 # # An error report file with more information is saved as: # /usr/sunvts/bin/hs_err_pid1406.log #

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• Kindle Fire Cant Fit My Webpage inside a Webview of specific size

  - by Madhavan Rangarao

  This is baffling to me. Please help, I could not figure it out ... In my sample html file I have set the meta tag to be <meta name="viewport" content="target-densitydpi=device-dpi, user-scalable=no"> to fit the webpage inside my webview of custom size say 800x600. In Android, I had to specify "target-densitydpi=device-dpi" and it did the job nicely. I tested my custom web page with nexus 7 tablet and the web page fits inside my web view correctly. The same code does not work in Kindle Fire. Only a part of my web page is shown and even if I set the 'initial-scale=1.0' did not help. I tried various settings programmatically but it did not help either. webview.getSettings().setBuiltInZoomControls(true); webview.getSettings().setSupportZoom(true); webview.getSettings().setLoadWithOverviewMode(true); webview.setInitialScale(1); webview.getSettings().setUseWideViewPort(true); Any pointers?

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• Point data structure for a sketching application

  - by bebraw

  I am currently developing a little sketching application based on HTML5 Canvas element. There is one particular problem I haven't yet managed to find a proper solution for. The idea is that the user will be able to manipulate existing stroke data (points) quite freely. This includes pushing point data around (ie. magnet tool) and manipulating it at whim otherwise (ie. altering color). Note that the current brush engine is able to shade by taking existing stroke data in count. It's a quick and dirty solution as it just iterates the points in the current stroke and checks them against a distance rule. Now the problem is how to do this in a nice manner. It is extremely important to be able to perform efficient queries that return all points within given canvas coordinate and radius. Other features, such as space usage, should be secondary to this. I don't mind doing some extra processing between strokes while the user is not painting. Any pointers are welcome. :)

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• A good solution for displaying galleries with lytebox and php

  - by Johann

  Hello I have thought for a while over an issue with the loading of images on a website-solution that I have programmed (For fun and the experience) The programming language used is PHP with MYSQL as the database language It also uses javascript, but not extensively I have recently realized that the engine I programmed, while it has it's smart solutions also carry a lot of flaws and redundant code. I have therefore decided to make a new one, now incorporating what I know, but didn't when I started the previous project. For the new system, there will be an option to add galleries to a site, and upload images to it. I have used the javascript image viewer Lytebox before. The screen goes dark and an image appears with a "Previous" and "next" button to view the other images. The problem is that I used groups with lytebox and the images themselves, resized as thumbs. This causes lytebox to work only when all the images have loaded. If you click a link before that, the image is shown as if you right click and choose "Show image" Information about these images is parsed from a database using a while statement with a counter that goes from 0 to sizeof() I'm thinking it probably isn't a good idea to have the images as the thumbs, even if you restrict the upload size. Likewise, adding thumbs at upload also seems like a hassle. It would be practical if the thumbs didn't show up before they were fully loaded. Has anyone got any good tips. Any help would be appreciated. Johann

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