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• What exactly is a reentrant function?

  - by eSKay

  Most of the times, the definition of reentrance is quoted from Wikipedia: A computer program or routine is described as reentrant if it can be safely called again before its previous invocation has been completed (i.e it can be safely executed concurrently). To be reentrant, a computer program or routine: Must hold no static (or global) non-constant data. Must not return the address to static (or global) non-constant data. Must work only on the data provided to it by the caller. Must not rely on locks to singleton resources. Must not modify its own code (unless executing in its own unique thread storage) Must not call non-reentrant computer programs or routines. How is safely defined? If a program can be safely executed concurrently, does it always mean that it is reentrant? What exactly is the common thread between the six points mentioned that I should keep in mind while checking my code for reentrant capabilities? Also, Are all recursive functions reentrant? Are all thread-safe functions reentrant? Are all recursive and thread-safe functions reentrant? While writing this question, one thing comes to mind: Are the terms like reentrance and thread safety absolute at all i.e. do they have fixed concrete definations? For, if they are not, this question is not very meaningful. Thanks!

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• Windows 7 versus Windows XP multithreading - Delphi app not acting right

  - by Robert Oschler

  I'm having a problem with a Delphi Pro 6 application that I wrote on my Windows XP machine when it runs on Windows 7. I don't have Windows 7 to test yet and I'm trying to see if Windows 7 might be the source of the trouble. Is there a fundamental difference between the way Windows 7 handles threads compared to Windows XP? I am seeing things happen out of sequence in my error logs on Windows 7 and it's causing problems. For example, objects that should have been initialized are uninitialized when running on Windows 7, yet those objects are initialized on Windows XP by the time they are needed. Some questions: 1) Are there any core differences that could cause threads/processes to behave differently between the two operating system versions? 2) I know this next question may seem absurd, but does Windows 7 attempt to split/fork threads that aren't split/forked on Windows XP? 3) And lastly, are there any known issues with FPU handling that can cause XP programs trouble when run on Windows 7 due to operational differences in wait state handling or register storage, or perhaps something like Exception mask settings, etc? 4) Any 32-bit versus 64-bit issues that could be creating trouble here? -- roschler

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• Database contents setting themselves to 0

  - by Luis Armando

  I have a Database that contains 4 tables, however I'm using 1 of them which is separated from the others. In this table I have 4 fields which are varchar and the rest are ints (11 other fields), when the users fill up the DB everything gets saved correctly, however it has happened 3 times so far that the database values for the int's reset to 0 without any apparent reason. At first, I thought, it was because those fields (where the numbers should go) were varchars not ints. However since I changed it, it happened again. I've already double checked my code and I have nothing that even updates or inserts a 0 value. Also I'm using codeigniter and active records which protect against SQL injections AND have XSS filtering enabled, could anyone point out something I might be missing or a reason for this to be happening? Also, I'm pretty sure about the answer of this but, is there ANY way to recover some data?? Other than having to ask everyone to fill in everything again.. =/ ** EDIT ** The Storage Engine is MyISAM and Collation is latin1_swedish_ci, Pack Keys are default, for all intents and purposes it's a normal DB

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• Indices instead of pointers in STL containers?

  - by zvrba

  Due to specific requirements [*], I need a singly-linked list implementation that uses integer indices instead of pointers to link nodes. The indices are always interpreted with respect to a vector containing the list nodes. I thought I might achieve this by defining my own allocator, but looking into the gcc's implementation of , they explicitly use pointers for the link fields in the list nodes (i.e., they do not use the pointer type provided by the allocator): struct _List_node_base { _List_node_base* _M_next; ///< Self-explanatory _List_node_base* _M_prev; ///< Self-explanatory ... } (For this purpose, the allocator interface is also deficient in that it does not define a dereference function; "dereferencing" an integer index always needs a pointer to the underlying storage.) Do you know a library of STL-like data structures (i am mostly in need of singly- and doubly-linked list) that use indices (wrt. a base vector) instead of pointers to link nodes? [*] Saving space: the lists will contain many 32-bit integers. With two pointers per node (STL list is doubly-linked), the overhead is 200%, or 400% on 64-bit platform, not counting the overhead of the default allocator.

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• What is the minimal licensable source code?

  - by Hernán Eche

  Let's suppose I want to "protect" this code about being used without attribution, patenting it, or through any open source licence... #include<stdio.h> int main (void) { int version=2; printf("\r\n.Hello world, ver:(%d).", version); return 0; } It's a little obvious or just a language definition example.. When a source stop being "trivial, banal, commonplace, obvious", and start to be something that you may claim "rights"? Perhaps it depends on who read it, something that could be great geniality for someone that have never programmed, could be just obvious for an expert. It's easy when watching two sources there are 10000 same lines of code, that's a theft.. but that's not always so obvious. How to measure amount of "ownness", it's about creativity? line numbers? complexity? I can't imagine objetive answers for that, only some patches. For example perhaps the complexity, It's not fair to replace "years of engeneering" with "copy and paste". But is there any objetive index for objetive determination of this subject? (In a funny way I imagine this criterion: If the licence is longer than the code, then there is no owner, just to punish not caring storage space and world resources =P)

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• rails2 and aws-simple (simpledb): data cannot be deleted from amazon simpledb?

  - by z3cko

  i am developing a ruby on rails (2.3.8) application with data storage amazon simpledb. i am using the aws-sdb gem in the version aws-sdb (0.3.1) there are a few bugs, but the problems are outlined in the comments of this tutorial from amazon: http://developer.amazonwebservices.com/connect/entry.jspa?externalID=1242 i am wondering if it is a bug of the gem or maybe a proxy issue, but i cannot delete any data from simpledb. anyone else experienced this or has a clue? >> t=Team.find(:first) => #<Team:0x329f718 @prefix_options={}, @attributes={"updated_at"=>Fri May 28 16:33:17 UTC 2010, "id"=>0}> >> t.destroy => #<Net::HTTPOK 200 OK readbody=true> >> t=Team.find(:first) => #<Team:0x321ad38 @prefix_options={}, @attributes={"updated_at"=>Fri May 28 16:33:17 UTC 2010, "id"=>0}> the team model is a normal ActiveResource Model, according to said tutorial. class Team < ActiveResource::Base self.site = "http://localhost:8888" # Proxy host + port self.prefix = "/fb2010_dev/" # SDB domain end

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• populate uipicker view with results from core data DB using an NSArray

  - by Chris

  I am trying to populate a UIPickerView with the results of a NSFetchRequest. The results of the NSFetchRequest are then stored in an NSArray. I am using Core Data to interact with the SQLite DB. I have a simple class file that contains a UIPickerView that is associated with a storyboard scene in my project. The header file for the class looks like the following, ViewControllerUsers.h #import <UIKit/UIKit.h> #import "AppDelegate.h" @interface ViewControllerUsers : UIViewController <NSFetchedResultsControllerDelegate, UIPickerViewDelegate, UIPickerViewDataSource> { NSArray *dictionaries; } @property (nonatomic, strong) NSFetchedResultsController *fetchedResultsController; // Core Data @property (strong, nonatomic) NSManagedObjectContext *managedObjectContext; @property (nonatomic, strong) NSArray *users; @property (strong, nonatomic) IBOutlet UIPickerView *uiPickerViewUsers; @property (weak, nonatomic) IBOutlet UIBarButtonItem *btnDone; @property (weak, nonatomic) IBOutlet UIButton *btnChangePin; // added for testing purposes @property (nonatomic, strong) NSArray *usernames; - (IBAction)dismissScene:(id)sender; - (IBAction)changePin:(id)sender; @end The implementation file looks like the following, ViewControllerUsers.m #import "ViewControllerUsers.h" @interface ViewControllerUsers () @end @implementation ViewControllerUsers // Core Data @synthesize managedObjectContext = _managedObjectContext; @synthesize uiPickerViewUsers = _uiPickerViewUsers; @synthesize usernames = _usernames; - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. // Core Data if (_managedObjectContext == nil) { _managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; NSLog(@"After _managedObjectContext: %@", _managedObjectContext); } NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Account"]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Account" inManagedObjectContext:_managedObjectContext]; request.resultType = NSDictionaryResultType; request.propertiesToFetch = [NSArray arrayWithObject:[[entity propertiesByName] objectForKey:@"username"]]; request.returnsDistinctResults = YES; _usernames = [_managedObjectContext executeFetchRequest:request error:nil]; NSLog (@"names: %@",_usernames); } -(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView { //One column return 1; } -(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component { //set number of rows return _usernames.count; } -(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component { //set item per row return [_usernames objectAtIndex:row]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } - (void)viewDidUnload { [self setBtnDone:nil]; [self setUiPickerViewUsers:nil]; [self setBtnChangePin:nil]; [super viewDidUnload]; } - (IBAction)dismissScene:(id)sender { [self dismissModalViewControllerAnimated:YES]; } - (IBAction)changePin:(id)sender { } @end The current code is causing the app to crash, but the NSLog is show the results of the NSFetchRequest in the NSArray. I currently think that I am not formatting the results of the NSFetchRequest in the NSArray properly if I had to take a guess. The crash log looks like the following, 2013-06-26 16:49:24.219 KegCop[41233:c07] names: ( { username = blah; }, { username = chris; }, { username = root; } ) 2013-06-26 16:49:24.223 KegCop[41233:c07] -[NSKnownKeysDictionary1 isEqualToString:]: unrecognized selector sent to instance 0xe54d9a0 2013-06-26 16:49:24.223 KegCop[41233:c07] Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSKnownKeysDictionary1 isEqualToString:]: unrecognized selector sent to instance 0xe54d9a0' First throw call stack:

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• Is DB logging more secure than file logging for my PHP web app?

  - by iama

  I would like to log errors/informational and warning messages from within my web application to a log. I was initially thinking of logging all of these onto a text file. However, my PHP web app will need write access to the log files and the folder housing this log file may also need write access if log file rotation is desired which my web app currently does not have. The alternative is for me to log the messages to the MySQL database since my web app is already using the MySQL database for all its data storage needs. However, this got me thinking that going with the MySQL option is much better than the file option since I already have a configuration file with the database access information protected using file system permissions. If I now go with the log file option I need to tinker the file and folder access permissions and this will only make my application less secure and defeats the whole purpose of logging. Is this correct? I am using XAMPP for development and am a newbie to LAMP. Please let me know your recommendations for logging. Thanks.

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• Which MySQL Fork/Version to Pick??

  - by Drew

  As most of you know, Sun acquired MySQL (and later Oracle acquired Sun), and during these acquisitions, there were a lot of FUD in MySQL community which resulted in creation of various forks. Today we have MySQL from MySQL, Percona (XtraDB) MySQL, OurDelta MySQL, MariaDB, Drizzle to name a few. Which brings us to the source of the problem. We are in the process of upgrading our databases (hardware/software) and I would like to know which one of the forks should I go with. Each has their own set of pros/cons. We are currently using MySQL 5.0.x from MySQL/Linux on an 8-core machine. Our new hardware is a monster with 32 cores and 32GB of memory connecting to a fast NetApp Storage via FC. I would like to stick with MySQL from MySQL but I have heard horror stories on how badly MySQL 5.1 performs on many cores. I have also heard that MySQL 5.4 performs better on multi-core machines but that's still not production ready. In addition, I have also heard a lot of good things about Percona builds. This is what I know so far: MySQL 5.1 from MySQL: Reliable choice, but doesn't scale well on a big machine Percona: Scales well, good backing company. I don't have much experience with it MariaDB: Don't know much about it besides that it was founded by Original MySQL developers (including Monty) OurDelta: Don't know much Drizzle: Mostly optimized for cloud computing I would like to know what's the general notion about this problem. Which build/version should I go with? How are you guys picking your builds/versions? Thanks!

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• Lockless queue implementation ends up having a loop under stress

  - by Fozi

  I have lockless queues written in C in form of a linked list that contains requests from several threads posted to and handled in a single thread. After a few hours of stress I end up having the last request's next pointer pointing to itself, which creates an endless loop and locks up the handling thread. The application runs (and fails) on both Linux and Windows. I'm debugging on Windows, where my COMPARE_EXCHANGE_PTR maps to InterlockedCompareExchangePointer. This is the code that pushes a request to the head of the list, and is called from several threads: void push_request(struct request * volatile * root, struct request * request) { assert(request); do { request->next = *root; } while(COMPARE_EXCHANGE_PTR(root, request, request->next) != request->next); } This is the code that gets a request from the end of the list, and is only called by a single thread that is handling them: struct request * pop_request(struct request * volatile * root) { struct request * volatile * p; struct request * request; do { p = root; while(*p && (*p)->next) p = &(*p)->next; // <- loops here request = *p; } while(COMPARE_EXCHANGE_PTR(p, NULL, request) != request); assert(request->next == NULL); return request; } Note that I'm not using a tail pointer because I wanted to avoid the complication of having to deal with the tail pointer in push_request. However I suspect that the problem might be in the way I find the end of the list. There are several places that push a request into the queue, but they all look generaly like this: // device->requests is defined as struct request * volatile requests; struct request * request = malloc(sizeof(struct request)); if(request) { // fill out request fields push_request(&device->requests, request); sem_post(device->request_sem); } The code that handles the request is doing more than that, but in essence does this in a loop: if(sem_wait_timeout(device->request_sem, timeout) == sem_success) { struct request * request = pop_request(&device->requests); // handle request free(request); } I also just added a function that is checking the list for duplicates before and after each operation, but I'm afraid that this check will change the timing so that I will never encounter the point where it fails. (I'm waiting for it to break as I'm writing this.) When I break the hanging program the handler thread loops in pop_request at the marked position. I have a valid list of one or more requests and the last one's next pointer points to itself. The request queues are usually short, I've never seen more then 10, and only 1 and 3 the two times I could take a look at this failure in the debugger. I thought this through as much as I could and I came to the conclusion that I should never be able to end up with a loop in my list unless I push the same request twice. I'm quite sure that this never happens. I'm also fairly sure (although not completely) that it's not the ABA problem. I know that I might pop more than one request at the same time, but I believe this is irrelevant here, and I've never seen it happening. (I'll fix this as well) I thought long and hard about how I can break my function, but I don't see a way to end up with a loop. So the question is: Can someone see a way how this can break? Can someone prove that this can not? Eventually I will solve this (maybe by using a tail pointer or some other solution - locking would be a problem because the threads that post should not be locked, I do have a RW lock at hand though) but I would like to make sure that changing the list actually solves my problem (as opposed to makes it just less likely because of different timing).

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• Ember Data Sycn - LocalStorage+REST+RealTime+Online/Offline

  - by Miguel Madero

  We have a combination of requirements in terms o data access. Pre-load some reference data. We need reference data to survive browser restarts instead of just living in memory to avoid loading it all the time. I'm currently using the LocalStorageAdapter for that. Once we have it, we would like to sync changes (polling or using Socket.IO in the background and updating the LocalStorage could do the trick) There're other models that are more transactional, where we would need to directly go to the Server and get/save them. It would be nice to use something like the RESTAdapter for that. Lastly, there're some operations that should work off-line and changes should be synced later. To make it more concrete: * We pre-load vendor and "favorite products" into Local Storage. We work offline with those. * We need to sync server changes to vendor and product information. * If they search the full catalog, that requires them to be online. * When offline, we need to allow users to add something to their cart or even submit and order. We would like to queue this action and submit it when they have an Internet Connection. So a few questions are derived from this: * Is there a way to user RESTAdapter in combination with LocalStorage? * Is there some Socket.IO support? (Happy to do this part manually) * Is there Queueing support? Ideally at the Ember-Data level. I know we will have to do a lot of this manually and pull together the different lego pieces, but I wanted to ask for some perspective from experience Ember devs.

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• temporary tables within stored procedures on slave servers with readonly set

  - by lau

  Hi, We have set up a replication scheme master/slave and we've had problems lately because some users wrote directly on the slave instead of the master, making the whole setup inconsistent. To prevent these problems from happening again, we've decided to remove the insert, delete, update, etc... rights from the users accessing the slave. Problems is that some stored procedure (for reading) require temporary tables. I read that changing the global variable read_only to true would do what I want and allow the stored procedures to work correctly ( http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_read_only ) but I keep getting the error : The MySQL server is running with the --read-only option so it cannot execute this statement (1290) The stored procedure that I used (for testing purpose) is this one : DELIMITER $$ DROP PROCEDURE IF EXISTS test_readonly $$ CREATE DEFINER=dbuser@% PROCEDURE test_readonly() BEGIN CREATE TEMPORARY TABLE IF NOT EXISTS temp ( BT_INDEX int(11), BT_DESC VARCHAR(10) ); INSERT INTO temp (BT_INDEX, BT_DESC) VALUES (222,'walou'), (111,'bidouille'); DROP TABLE temp; END $$ DELIMITER ; The create temporary table and the drop table work fine with the readonly flag - if I comment the INSERT line, it runs fine- but whenever I want to insert or delete from that temporary table, I get the error message. I use Mysql 5.1.29-rc. My default storage engine is InnoDB. Thanks in advance, this problem is really driving me crazy.

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• Document management, SCM ?

  - by tsunade

  Hello, This might not be a hard core programming question, but it's related to some of the tools used by programmers I suspect. So we're a bunch of people each with a bunch of documents and a bunch of different computers on a bunch of operating systems (well, only 2, linux and windows). The best way these documents can be stored/managed is if they were available offline (the laptop might not always be online) but also synchronized between all the machines. Having a server with extra reliable storage be a "base repository" seems like a good idea to me. Using a SCM comes to my mind and I've tried Subversion, and it seems to be a good thing that it uses a centralized repository - but: When checking out the total size of the checkout is roughly double the original size. Big files or big repositories seem to slow it down. Also I've tried rsync, which might work - but it's a bit rough when it comes to the potential conflict. Finally I've tried Unison (which is a wrapping of rsync, I think) and while it works it becomes horribly slow for the big directories we have here since it has to scan everything. So the question is - is there a SCM tool out there that is actually practial to use for a big bunch of both small and big files? If thats a NO - does anyone know other tools that do this job? Thanks for reading :)

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• Sharing same vector control between different places

  - by Alexander K

  Hi everyone, I'm trying to implement the following: I have an Items Manager, that has an Item class inside. Item class can store two possible visual representations of it - BitmapImage(bitmap) and UserControl(vector). Then later, in the game, I need to share the same image or vector control between all possible places it takes place. For example, consider 10 trees on the map, and all point to the same vector control. Or in some cases this can be bitmap image source. So, the problem is that BitmapImage source can be easily shared in the application by multiple UIElements. However, when I try to share vector control, it fails, and says Child Element is already a Child element of another control. I want to know how to organize this in the best way. For example replace UserControl with other type of control, or storage, however I need to be sure it supports Storyboard animations inside. The code looks like this: if (bi.item.BitmapSource != null) { Image previewImage = new Image(); previewImage.Source = bi.item.BitmapSource; itemPane.ItemPreviewCanvas.Children.Add(previewImage); } else if (bi.item.VectorSource != null) { UserControl previewControl = bi.item.VectorSource; itemPane.ItemPreviewCanvas.Children.Add(previewControl); } Thanks in advance

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• How to upload Image on Android?

  - by Mattiah85

  I havve to upload image from my SD card to PHP server. I have read a lot of articles and topics but I have some problems... First I have use that code: HttpURLConnection connection = null; DataOutputStream outputStream = null; //DataInputStream inputStream = null; String urlServer = hostName+"Upload"; String lineEnd = "\r\n"; String twoHyphens = "--"; String boundary = "*****"; String serverResponseMessage; //int serverResponseCode; int bytesRead, bytesAvailable, bufferSize; byte[] buffer; int maxBufferSize = 1*1024*1024; try { showLog("uploading file: " + file); FileInputStream fileInputStream = new FileInputStream(new File(pictureFileDir+"/"+file) ); URL url = new URL(urlServer); connection = (HttpURLConnection) url.openConnection(); // Allow Inputs &amp; Outputs. connection.setDoInput(true); connection.setDoOutput(true); connection.setUseCaches(false); // Set HTTP method to POST. connection.setRequestMethod("POST"); connection.setRequestProperty("Connection", "Keep-Alive"); connection.setRequestProperty("Content-Type", "multipart/form-data;boundary="+boundary); outputStream = new DataOutputStream( connection.getOutputStream() ); outputStream.writeBytes(twoHyphens + boundary + lineEnd); outputStream.writeBytes("Content-Disposition: form-data; name=\"uploaded_file\";filename=\"" + file +"\"" + lineEnd); outputStream.writeBytes(lineEnd); bytesAvailable = fileInputStream.available(); bufferSize = Math.min(bytesAvailable, maxBufferSize); buffer = new byte[bufferSize]; // Read file bytesRead = fileInputStream.read(buffer, 0, bufferSize); while (bytesRead > 0) { outputStream.write(buffer, 0, bufferSize); bytesAvailable = fileInputStream.available(); bufferSize = Math.min(bytesAvailable, maxBufferSize); bytesRead = fileInputStream.read(buffer, 0, bufferSize); } outputStream.writeBytes(lineEnd); outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd); // Responses from the server (code and message) //serverResponseCode = connection.getResponseCode(); serverResponseMessage = connection.getResponseMessage(); showLog("server response: " + serverResponseMessage); fileInputStream.close(); outputStream.flush(); outputStream.close(); } catch (Exception ex) { ex.printStackTrace(); } but server response 200/OK and no file was on destination server... After i have read about Multipart: try { HttpParams params = new BasicHttpParams(); params.setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1); DefaultHttpClient mHttpClient = new DefaultHttpClient(params); File image = new File(pictureFileDir + "/" + filename); HttpPost httppost = new HttpPost(hostName+"Upload"); MultipartEntity multipartEntity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE); multipartEntity.addPart("Image", new FileBody(image)); httppost.setEntity(multipartEntity); mHttpClient.execute(httppost, new PhotoUploadResponseHandler()); } catch (Exception e) { e.printStackTrace(); } but then a i have such LOG in LogCat and nothing else... 06-04 06:50:52.277: D/dalvikvm(1584): DexOpt: couldn't find static field Lorg/apache/http/message/BasicHeaderValueParser;.INSTANCE 06-04 06:50:52.277: W/dalvikvm(1584): VFY: unable to resolve static field 6688 (INSTANCE) in Lorg/apache/http/message/BasicHeaderValueParser; 06-04 06:50:52.277: D/dalvikvm(1584): VFY: replacing opcode 0x62 at 0x001b ServerSide Script: $target_path = "uploads"; $target_path = $target_path . basename( $_FILES['Image']); if(move_uploaded_file($_FILES['tmp_name'], $file_path)) { echo "success"; } else{ echo "fail"; } why? What is the simplest way to upload image?

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• Best way to create a SPARQL endpoint for a RDBMS (MySQL database)

  - by Ankur

  I am doing (want to do) some experiments with Linked Open Datasets particularly those put out by governments. I have a RDBMS (more specifically MySQL). I designed it with semantic web ideas in mind i.e. I have a information stored as objects, predicates and classes which define objects. In turn all objects are related to each other though statements of the form subject -- predicate -- object (where the subjects are from the objects table). I want to be able to query other RDF triple stores from my application and let other triple stores query my data. Is it possible to "set something up" so that this is possible? I have looked at Jena. Using Jena seems to mean I have to it as a storage application rather than MySQL - the only problem with this is that I include a new concept called a category (which I don't think is part of the semantic web languages). I will use categories to help with displaying information (they don't have any other meaning) but using Jena seems to mean that I can't organise predicates under categories for more convenient viewing. I am using Java so a JAVA API is preferred. It's also possible I misunderstood the purpose of Jena, and maybe that can be of use, but I am not sure how. I am sure four days from now this question will seem rather silly, but at the moment I am somewhat confused about how to proceed.

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• Database abstraction/adapters for ruby

  - by Stiivi

  What are the database abstractions/adapters you are using in Ruby? I am mainly interested in data oriented features, not in those with object mapping (like active record or data mapper). I am currently using Sequel. Are there any other options? I am mostly interested in: simple, clean and non-ambiguous API data selection (obviously), filtering and aggregation raw value selection without field mapping: SELECT col1, col2, col3 = [val1, val2, val3] not hash of { :col1 = val1 ...} API takes into account table schemas 'some_schema.some_table' in a consistent (and working) way; also reflection for this (get schema from table) database reflection: get list of table columns, their database storage types and perhaps adaptor's abstracted types table creation, deletion be able to work with other tables (insert, update) in a loop enumerating selection from another table without requiring to fetch all records from table being enumerated Purpose is to manipulate data with unknown structure at the time of writing code, which is the opposite to object mapping where structure or most of the structure is usually well known. I do not need the object mapping overhead. What are the options, including back-ends for object-mapping libraries?

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• Firefox extension js object initialization

  - by Michael

  Note: this is about Firefox extension, not a js general question. In Firefox extension project I need my javascript object to be initialized just once per Firefox window. Otherwise each time I open my window a new timers will be engaged, new properties will be used, so everything will start from scratch. hope example below will demystify my question :) var StupidExtension { statusBarValue: "Not Initialized Yet", startup: function () { ... // Show statusBarValue in Status Bar Panel }, initTimerToRetrieveStatusBarValueFromNetwork: function () { ... } } so each time you hit Ctrl+N a new window you will see "Not Initialized Yet" and then new timer will be fired, so after some time it retrieve data from network you will see value also on second window and so on. Ideally would be to have just a single timer function running and updating all status bar panels in all Firefox windows. Of course I can do some caching, like saving the value in prefs or some other storage, then show it from there. But I feel like this is artificial. So the question will be is there "native" technique of making static some parts of the object among all Firefox window instances?

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• MS SQL - Multi-Column substring matching

  - by hamlin11

  One of my clients is hooked on multi-column substring matching. I understand that Contains and FreeText search for words (and at least in the case of Contains, word prefixes). However, based upon my understanding of this MSDN book, neither of these nor their variants are capable of searching substrings. I have used LIKE rather extensively (Select * from A where A.B Like '%substr%') Sample table A: ID | Col1 | Col2 | Col3 | ------------------------------------- 1 | oklahoma | colorado | Utah | 2 | arkansas | colorado | oklahoma | 3 | florida | michigan | florida | ------------------------------------- The following code will give us row 1 and row 2: select * from A where Col1 like '%klah%' or Col2 like '%klah%' or Col3 like '%klah%' This is rather ugly, probably slow, and I just don't like it very much. Probably because the implementations that I'm dealing with have 10+ columns that need searched. The following may be a slight improvement as code readability goes, but as far as performance, we're still in the same ball park. select * from A where (Col1 + ' ' + Col2 + ' ' + Col3) like '%klah%' I have thought about simply adding insert, update, and delete triggers that simply add the concatenated version of the above columns into a separate table that shadows this table. Sample Shadow_Table: ID | searchtext | --------------------------------- 1 | oklahoma colorado Utah | 2 | arkansas colorado oklahoma | 3 | florida michigan florida | --------------------------------- This would allow us to perform the following query to search for '%klah%' select * from Shadow_Table where searchtext like '%klah%' I really don't like having to remember that this shadow table exists and that I'm supposed to use it when I am performing multi-column substring matching, but it probably yields pretty quick reads at the expense of write and storage space. My gut feeling tells me there there is an existing solution built into SQL Server 2008. However, I don't seem to be able to find anything other than research papers on the subject. Any help would be appreciated.

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• Reverse geocode street name and city as text

  - by Taylor Satula

  Hello, I have been having some trouble finding a good way to output just the street name and city as text (Infinite Loop, Cupertino shown here) that can be displayed in my iPhone app. This needs to be able to dynamically change as you change streets and city. I don't have the slightest idea of how to do this, I hope someone can help. I have attached a very rough image of what I am trying to acheave. I have found this (http://code.google.com/apis/maps/documentation/javascript/services.html#Geocoding) for google maps about how to reverse geocode using javascript, but what I do not understand is how this would be done in a iPhone development setting. I work in web design and I see how it would be done in HTML but I am very new to iPhone development and don't have the slightest clue of how it would be done here. If someone could spell out how to do this I would be extremely grateful. I cannot seem to find what I am looking for by searching Google. Reference picture: http://www.threepixeldrift.com/images/deep-storage/reversegeocodeiphoneapp.jpg

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• Negative number representation across multiple architechture

  - by Donotalo

  I'm working with OKI 431 micro controller. It can communicate with PC with appropriate software installed. An EEPROM is connected in the I2C bus of the micro which works as permanent memory. The PC software can read from and write to this EEPROM. Consider two numbers, B and C, each is two byte integer. B is known to both the PC software and the micro and is a constant. C will be a number so close to B such that B-C will fit in a signed 8 bit integer. After some testing, appropriate value for C will be determined by PC and will be stored into the EEPROM of the micro for later use. Now the micro can store C in two ways: The micro can store whole two byte representing C The micro can store B-C as one byte signed integer, and can later derive C from B and B-C I think that two's complement representation of negative number is now universally accepted by hardware manufacturers. Still I personally don't like negative numbers to be stored in a storage medium which will be accessed by two different architectures because negative number can be represented in different ways. For you information, 431 also uses two's complement. Should I get rid of the headache that negative number can be represented in different ways and accept the one byte solution as my other team member suggested? Or should I stick to the decision of the two byte solution because I don't need to deal with negative numbers? Which one would you prefer and why?

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• java will this threading setup work or what can i be doing wrong

  - by Erik

  Im a bit unsure and have to get advice. I have the: public class MyApp extends JFrame{ And from there i do; MyServer = new MyServer (this); MyServer.execute(); MyServer is a: public class MyServer extends SwingWorker<String, Object> { MyServer is doing listen_socket.accept() in the doInBackground() and on connection it create a new class Connection implements Runnable { I have the belove DbHelper that are a singleton. It holds an Sqlite connected. Im initiating it in the above MyApp and passing references all the way in to my runnable: class Connection implements Runnable { My question is what will happen if there are two simultaneous read or `write? My thought here was the all methods in the singleton are synchronized and would put all calls in the queue waiting to get a lock on the synchronized method. Will this work or what can i change? public final class DbHelper { private boolean initalized = false; private String HomePath = ""; private File DBFile; private static final String SYSTEM_TABLE = "systemtable"; Connection con = null; private Statement stmt; private static final ContentProviderHelper instance = new ContentProviderHelper (); public static ContentProviderHelper getInstance() { return instance; } private DbHelper () { if (!initalized) { initDB(); initalized = true; } } private void initDB() { DBFile = locateDBFile(); try { Class.forName("org.sqlite.JDBC"); // create a database connection con = DriverManager.getConnection("jdbc:sqlite:J:/workspace/workComputer/user_ptpp"); } catch (SQLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } private File locateDBFile() { File f = null; try{ HomePath = System.getProperty("user.dir"); System.out.println("HomePath: " + HomePath); f = new File(HomePath + "/user_ptpp"); if (f.canRead()) return f; else { boolean success = f.createNewFile(); if (success) { System.out.println("File did not exist and was created " + HomePath); // File did not exist and was created } else { System.out.println("File already exists " + HomePath); // File already exists } } } catch (IOException e) { System.out.println("Maybe try a new directory. " + HomePath); //Maybe try a new directory. } return f; } public String getHomePath() { return HomePath; } private synchronized String getDate(){ SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date date = new Date(); return dateFormat.format(date); } public synchronized String getSelectedSystemTableColumn( String column) { String query = "select "+ column + " from " + SYSTEM_TABLE ; try { stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY); ResultSet rs = stmt.executeQuery(query); while (rs.next()) { String value = rs.getString(column); if(value == null || value == "") return ""; else return value; } } catch (SQLException e ) { e.printStackTrace(); return ""; } finally { } return ""; } }

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• Multithreaded linked list traversal

  - by Rob Bryce

  Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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• Including objects from external .js files

  - by Molle

  I have been searching for many hours over several days for this answer and though there are many topics on how to include files in a project (also here at Stack Overflow), I have not yet found THE solution to my problem. I'm working on a project where I want to include one single object at a time, from many different files (I do not want to include the files themselves, only their content). All the object in all the files have the same name, only the content is different. It is important that I do not get a SCRIPT tag in the head section of the page as all the content from the files will have the same names. None of the files will have functions anyways, only one single object, that will need to be loaded one at the time and then discarded when the next element is loaded. The objects will hold the data that will be shown on the page and they will be called from the menu by an 'onclick' event. function setMenu() // The menu is being build. { var html = ''; html += '<table border="0">'; for (var i = 0; i<menu.pages.length; i++) { html += '<tr class="menuPunkt"><td width="5"></td><td onclick="pageName(this)">'+ menu.pages[i] +'</td><td width="5"></td></tr>'; } // menu is a global object containing elements such as an array with // all the pages that needs to be shown and styling for the menu. html += '</table>'; document.getElementById("menu").innerHTML = html; style.setMenu(); // The menu is being positioned and styled. } Now, when I click on a menu item the pageName function is triggered and I'm sending the HTML element to the function as well, it is here that I want the content from my external file to be loaded into a local variable and used to display content on the page. ** The answer I want is "How to load the external obj into the function where I need it? (It may be an external file, but only in the term of not being included in the head section. I'm still loading the the file from my own local library.** function pageName(elm) // The element that I clicked is elm. { var page = info.innerHTML; // I need only the innerHTML from the element. var file = 'sites/' + page + '.js'; // The file to be loaded is created. var obj = ?? // Here I somehow want the object from the external file to be loaded. // Before doing stuff the the obj. style.content(); } The content from the external file could look like this: // The src for the external page: 'sites/page.js' var obj = new Object() { obj.innerHTML = 'Text to be shown'; obj.style = 'Not important for problem at hand'; obj.otherStuff = ' --||-- '; } Any help will be appreciated, Molle

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• Generating authentication header from azure table through objective-c

  - by user923370

  I'm fetching data from iCloud and for that I need to generate a header (azure table storage). I used the code below for that and it is generating the headers. But when I use these headers in my project it is showing "make sure that the value of authorization header is formed correctly including the signature." I googled a lot and tried many codes but in vain. Can anyone kindly please help me with where I'm going wrong in this code. -(id)generat{ NSString *messageToSign = [NSString stringWithFormat:@"%@/%@/%@", dateString,AZURE_ACCOUNT_NAME, tableName]; NSString *key = @"asasasasasasasasasasasasasasasasasasasasas=="; const char *cKey = [key cStringUsingEncoding:NSUTF8StringEncoding]; const char *cData = [messageToSign cStringUsingEncoding:NSUTF8StringEncoding]; unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH]; CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC); NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)]; NSString *hash = [Base64 encode:HMAC]; NSLog(@"Encoded hash: %@", hash); NSURL *url=[NSURL URLWithString: @"http://my url"]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; [request addValue:[NSString stringWithFormat:@"SharedKeyLite %@:%@",AZURE_ACCOUNT_NAME, hash] forHTTPHeaderField:@"Authorization"]; [request addValue:dateString forHTTPHeaderField:@"x-ms-date"]; [request addValue:@"application/atom+xml, application/xml"forHTTPHeaderField:@"Accept"]; [request addValue:@"UTF-8" forHTTPHeaderField:@"Accept-Charset"]; NSLog(@"Headers: %@", [request allHTTPHeaderFields]); NSLog(@"URL: %@", [[request URL] absoluteString]); return request; } -(NSString*)rfc1123String:(NSDate *)date { static NSDateFormatter *df = nil; if(df == nil) { df = [[NSDateFormatter alloc] init]; df.locale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]; df.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"]; df.dateFormat = @"EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'"; } return [df stringFromDate:date]; }

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