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• Looking for a fast, compact, streamable, multi-language, strongly typed serialization format

  - by sanity

  I'm currently using JSON (compressed via gzip) in my Java project, in which I need to store a large number of objects (hundreds of millions) on disk. I have one JSON object per line, and disallow linebreaks within the JSON object. This way I can stream the data off disk line-by-line without having to read the entire file at once. It turns out that parsing the JSON code (using http://www.json.org/java/) is a bigger overhead than either pulling the raw data off disk, or decompressing it (which I do on the fly). Ideally what I'd like is a strongly-typed serialization format, where I can specify "this object field is a list of strings" (for example), and because the system knows what to expect, it can deserialize it quickly. I can also specify the format just by giving someone else its "type". It would also need to be cross-platform. I use Java, but work with people using PHP, Python, and other languages. So, to recap, it should be: Strongly typed Streamable (ie. read a file bit by bit without having to load it all into RAM at once) Cross platform (including Java and PHP) Fast Free (as in speech) Any pointers?

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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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• 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'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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• 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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• 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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• What is a NULL value

  - by Adi

  I am wondering , what exactly is stored in the memory when we say a particular variable pointer to be NULL. suppose I have a structure, say typdef struct MEM_LIST MEM_INSTANCE; struct MEM_LIST { char *start_addr; int size; MEM_INSTANCE *next; }; MEM_INSTANCE *front; front = (MEM_INSTANCE*)malloc(sizeof(MEM_INSTANCE*)); -1) If I make front=NULL. What will be the value which actually gets stored in the different fields of the front, say front-size ,front-start_addr. Is it 0 or something else. I have limited knowledge in this NULL thing. -2) If I do a free(front); It frees the memory which is pointed out by front. So what exactly free means here, does it make it NULL or make it all 0. -3) What can be a good strategy to deal with initialization of pointers and freeing them . Thanks in advance

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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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• Java SWT: wrapping syncExec and asyncExec to clean up code

  - by jonescb

  I have a Java Application using SWT as the toolkit, and I'm getting tired of all the ugly boiler plate code it takes to update a GUI element. Just to set a disabled button to be enabled I have to go through something like this: shell.getDisplay().asyncExec(new Runnable() { public void run() { buttonOk.setEnabled(true); } }); I prefer keeping my source code as flat as I possibly can, but I need a whopping 3 indentation levels just to do something simple. Is there some way I can wrap it? I would like a class like: public class UIUpdater { public static void updateUI(Shell shell, *function_ptr*) { shell.getDisplay().asyncExec(new Runnable() { public void run() { //Execute function_ptr } }); } } And can be used like so: UIUpdater.updateUI(shell, buttonOk.setEnabled(true)); Something like this would be great for hiding that horrible mess SWT seems to think is necessary to do anything. As I understand it, Java cannot do functions pointers. But Java 7 will have something called Closures which should be what I want. But in the meantime is there anything at all I can do to pass a function pointer or callback to another function to be executed? As an aside, I'm starting to think it'd be worth the effort to redo this application in Swing, and I don't have to put up with this ugly crap and non-cross-platformyness of SWT.

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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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• 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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• 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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• 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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• Using bash to copy file to spec folders

  - by Franko

  I have a folder with a fair amount of subfolders. In some of the subfolders do I have a folder.jpg picture. What I try to do find that folder(s) and copy it to all other subfolders that got the same artist and album information then continue on to the next album etc. The structure of all the folders are "artist - year - album - [encoding information]". I have made a really simple one liner that find the folders that got the file but there am I stuck. ls -F | grep / | while read folders;do find "$folders" -name folder.jpg; done Anyone have any good tip or ideas how to solve this or pointers how to proceed? Edit: First of all, i´m real new to this (like you cant tell) so please have patience. Ok, let me break it down even more. I have a folder structure that looks like this: artist1 - year - album - [flac] artist1 - year - album - [mp3] artist1 - year - album - [AAC] artist2 - year - album - [flac] etc I like to loop over the set of folders that have the same artist and album information and look for a folder.jpg file. When I find that file do I like to copy it to all of the other folders in the same set. Ex if I find one folder.jpg in artist1 - year - album - [flac] folder do I like to have that folder.jpg copied to artist1 - year - album - [mp3] & artist1 - year - album - [AAC] but not to artist2 - year - album - [flac]. The continue the loop until all the sets been processed. I really hope that makes it a bit more easy to understand what I try to do :)

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• Save object using variable with object name

  - by FBE

  I'm wondering what an easy way is to save an object in R, using a variable objectName with the name of the object to be saved. I want this to easy save objects, with their name in the file name. I tried to use get, but I didn't manage to save the object with it's original object name. Example: If I have the object called "temp", which I want to save in the directory "dataDir". I put the name of the object in the variable "objectName". Attempt 1: objectName<-"temp" save(get(objectName), file=paste(dataDir, objectName, ".RData", sep="")) load(paste(dataDir, objectName, ".RData", sep="")) This didn't work, because R tries to save an object called get(objectName), instead of the result of this call. So I tried the following: Attempt 2: objectName<-"temp" object<-get(objectName) save(object, file=paste(dataDir, objectName, ".RData", sep="")) load(paste(dataDir, objectName, ".RData", sep="")) This obviously didn't work, because R saves the object with name "object", and not with name "temp". After loading I have a copy of "object", instead of "temp". (Yes, with the same contents...but that is not what I want :) ). So I thought it should be something with pointers. So tried the following: Attempt 3: objectName<-"temp" object<<-get(objectName) save(object, file=paste(dataDir, objectName, ".RData", sep="")) load(paste(dataDir, objectName, ".RData", sep="")) Same result as attempt 2. But I'm not sure I'm doing what I think I'm doing. What is the solution for this?

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• Array of templated structs

  - by Jakub Mertlik

  I have structs templated by int derived from a Base struct. struct Base { int i; double d; }; template< int N > struct Derv : base { static const int mN = N; }; I need to make an array of Derv< N where N can vary for each struct in that array. I know C/C++ does not allow arrays of objects of different types, but is there a way around this? I was thinking of separating the type information somehow (hints like pointers to Base struct or usage of union spring to my mind, but with all of these I don't know how to store the type information of each array element for usage DURING COMPILE TIME). As you can see, the memory pattern of each Derv< N is the same. I need to access the type of each array element for template specialization later in my code. The general aim of this all is to have a compile-time dispatch mechanism without the need to do a runtime "type switch" somewhere in the code. Thank you.

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• how to split a very large database on sql server

  - by ken jackson

  I have a 90 GB SQL Server database that I want to make more manageable. It stores stock data from 50+ different stocks from 2009 and 2010, and each stock is a separate table. Some tables have hundreds of millions of rows, and other have just a few million. What I want to do is somehow split the database, so that I don't have a single database file that is 90 GB. What I want is to be able to somehow magically split all the tables so that I can backup the 2009 data once and not have to keep on including it in the backup every time I backup the entire database, however, I would like the 2009 data to be included whenever I do a query. Is partitioning the database the way to go? Will it do the above for me, or will I need some other solution? I research partitioning, but I wasn't sure if that would solve all my problems. I wasn't able to find anything that would tell me whether or not it would migrate prexisting data, or whether it only worked for newly inserted data. Any help or pointers would be much appreciated. Thanks in advance, Ken

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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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• Generic callbacks

  - by bobobobo

  Extends So, I'm trying to learn template metaprogramming better and I figure this is a good exercise for it. I'm trying to write code that can callback a function with any number of arguments I like passed to it. // First function to call int add( int x, int y ) ; // Second function to call double square( double x ) ; // Third func to call void go() ; The callback creation code should look like: // Write a callback object that // will be executed after 42ms for "add" Callback<int, int, int> c1 ; c1.func = add ; c1.args.push_back( 2 ); // these are the 2 args c1.args.push_back( 5 ); // to pass to the "add" function // when it is called Callback<double, double> c2 ; c2.func = square ; c2.args.push_back( 52.2 ) ; What I'm thinking is, using template metaprogramming I want to be able to declare callbacks like, write a struct like this (please keep in mind this is VERY PSEUDOcode) <TEMPLATING ACTION <<ANY NUMBER OF TYPES GO HERE>> > struct Callback { double execTime ; // when to execute TYPE1 (*func)( TYPE2 a, TYPE3 b ) ; void* argList ; // a stored list of arguments // to plug in when it is time to call __func__ } ; So for when called with Callback<int, int, int> c1 ; You would automatically get constructed for you by < HARDCORE TEMPLATING ACTION > a struct like struct Callback { double execTime ; // when to execute int (*func)( int a, int b ) ; void* argList ; // this would still be void*, // but I somehow need to remember // the types of the args.. } ; Any pointers in the right direction to get started on writing this?

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• How to setup relationships in contact Database

  - by Walt

  I am currently embarking on a new venture to learn PHP and MySQL. I have done some simple databases in the past using Access, but this one is to be a web-centric database for tracking a myriad of data including contacts and project information. I will need to link the various tables in various relationships, and I am not sure the best way to do that. Since I am just starting out with PHP/MySQL I am researching online sources for learning as much as possible. If anyone has recommendations on books or websites, I would appreciate it. In setting up my tables, one major area that I am concerned with is contacts. I will have a variety of contacts that include: employees, clients, vendors, subcontractors, etc.. and a single contact can be multiple types and each type would have various additional fields that pertain to them. My thought was to have one contacts table that links to other tables for the various contact types. I'm not sure which field type or setup of table options are best... Thoughts? This scenario will likely play out in other areas of the database as well for projects and products. Any pointers/direction would be appreciated. WES

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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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• Error logging in C#

  - by rschuler

  I am making my switch from coding in C++ to C#. I need to replace my C++ error logging/reporting macro system with something similar in C#. In my C++ source I can write LOGERR("Some error"); or LOGERR("Error with inputs %s and %d", stringvar, intvar); The macro & supporting library code then passes the (possibly varargs) formatted message into a database along with the source file, source line, user name, and time. The same data is also stuffed into a data structure for later reporting to the user. Does anybody have C# code snippets or pointers to examples that do this basic error reporting/logging? Edit: At the time I asked this question I was really new to .NET and was unaware of System.Diagnostics.Trace. System.Diagnostics.Trace was what I needed at that time. Since then I have used log4net on projects where the logging requirements were larger and more complex. Just edit that 500 line XML configuration file and log4net will do everything you will ever need :)

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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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