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• Persistent (purely functional) Red-Black trees on disk performance

  - by Waneck

  I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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• Move options between multiple dropdown lists

  - by Martha

  We currently have a form with the standard multi-select functionality of "here are the available options, here are the selected options, here are some buttons to move stuff back and forth." However, the client now wants the ability to not just select certain items, but to also categorize them. For example, given a list of books, they want to not just select the ones they own, but also the ones they've read, the ones they would like to read, and the ones they've heard about. (All examples fictional.) Thankfully, a selected item can only be in one category at a time. I can find many examples of moving items between listboxes, but not a single one for moving items between multiple listboxes. To add to the complication, the form needs to have two sets of list+categories, e.g. a list of movies that need to be categorized in addition to the aforementioned books. An additional problem is that sorting between lists is all well and good in the javascript-enabled world, but I can't really think of a good fallback interface for, say, mobile browsers. Maybe a pseudo-listbox with radio buttons next to each item? The master list of items will in general be very long - over 100 items, certainly, possibly many more. Any given category will most likely contain one or two selected items, but the possibility exists for a category to have dozens of selected items, or zero selected items. As far as OS and stuff, the site is in classic asp (quit snickering!), the server-side code is VBScript, and so far we've avoided the various Javascript libraries by the simple expedient of almost never using client-side scripting. This one form for this one client is currently the big exception. Give 'em an inch and they want a mile... Oh, and I have to add: I suck at Javascript, or really at any C-descendant language. Curly braces give me hives. I'd really, really like something I can just copy & paste into my page, maybe tweak some variable names, and never look at it again. A girl can dream, can't she? :)

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• Square Peg Web: Gets you the traffic to where it matters most: Your Website!

  - by demetriusalwyn

  Have you decided to start your business online or is your business not reaching the targeted audience? Come to Square Peg Web; where you will find what you want to make your business reach new heights. The team at Square Peg Web is professionals who understand what you want and make sure you get it right. Our confidence stems from the fact of thousands of satisfied clients who keep referring friends and business associates to us and we do not let our clients down. Many companies promise the sky but how far is does their work live up to the promises? We do not know about the others however, we are sure that we strive to put together all our ideas and thoughts to make your website rank among the top. Web hosting is something that needs to have a personal touch; Square Peg Web customizes everything to suit your requirements so that you do not have to look further. With Square Peg Web you have a host of features to make your Business go viral. Some of the product details that are offered with Square Peg Web are unlimited product options/ variants/ properties giving you an option on price modifiers. You get unlimited customized input fields for your products and you can also Customer-define the prices. Square Peg Web provides you an option of using multiple product images with zoom features and one can also list a particular product in several categories. There are other aspects which make Square Peg Web the best choice for your website needs; every sale of yours’ is important to you and to us. We make sure that each sale is tracked by the product and also the list of bestsellers that appeal to the audience. Other comprehensive statistics of Square Peg Web includes searchable order data, an interface for shipments and order fulfillments, export sales & customer data for usage in a spreadsheet and the ability to export orders to QuickBooks format. With Square Peg Web; Admin Panel is a lot simpler. Administrative access is completely password protected and any changes done are all in real-time. You can have absolute control on the cart from anywhere around the world using your web browser and the topping on the cake is the unlimited amount of admin accounts that can be created for you. Square Peg Web offers you a world of experience with the options of choosing from marketing websites to e-commerce and from customized applications to community oriented sites. Some of the projects which appear in the portfolio of Square Peg Web are Online Marketing Web Sites, E-Commerce Web Sites, customized web applications, Blog designing and programming, video sharing and the option of downloading web sites, online advertisements, flash animation, customer and product support web sites, web site re-designing and planning and complete information architecture.

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• How to initiate chatting between two clients and two clients only, using applets and servlets?

  - by mithun1538

  Hello everyone, I first need to apologize for my earlier questions. (You can check my profile for them)They seemed to ask more questions than give answers. Hence, I am laying down the actual question that started all them absurd questions. I am trying to design a chat applet. Till now, I have coded the applet, servlet and communication between the applet and the servlet. The code in the servlet side is such that I was able to establish chatting between clients using the applets, but the code was more like a broadcast all feature, i.e. all clients would be chatting with each other. That was my first objective when I started designing the chat applet. The second step is chatting between only two specific users, much like any other chat application we have. So this was my idea for it: I create an instance of the servlet that has the 'broadcast-all' code. I then pass the address of this instance to the respective clients. 2 client applets use the address to then chat. Technically the code is 'broadcast-all', but since only 2 clients are connected to it, it gives the chatting between two clients feature. Thus, groups of 2 clients have different instances of the same servlet, and each instance handles chatting between two clients at a max. However, as predicted, the idea didn't materialize! I tried to create an instance of the servlet but the only solution for that was using sessions on the servlet side, and I don't know how to use this session for later communications. I then tried to modify my broadcast-all code. In that code, I was using classes that implemented Observer and Observable interfaces. So the next idea that I got was: Create a new object of the Observable class(say class_1). This object be common to 2 clients. 2 clients that wish to chat will use same object of the class_1. 2 other clients will use a different object of class_1. But the problem here lies with the class that implements the Observer interface(say class_2). Since this has observers monitoring the same type of class, namely class_1, how do I establish an observer monitoring one object of class_1 and another observer monitoring another object of the same class class_1 (Because notifyObservers() would notify all the observers and I can't assign a particular observer to a particular object)? I first decided to ask individual problems, like how to create instances of servlets, using objects of observable and observer and so on in stackoverflow... but I got confused even more. Can anyone give me an idea how to establish chatting between two clients only?(I am using Http and not sockets or RMI). Regards, Mithun. P.S. Thanks to all who replied to my previous (absurd) queries. I should have stated the purpose earlier so that you guys could help me better.

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• Is it a oop good design ?

  - by remi bourgarel

  Hi all, I'd like to know what you think about this part of our program is realized : We have in our database a list of campsite. Partners call us to get all the campsites near a GPS location or all the campsites which provide a bar (we call it a service). So how I realized it ? Here is our database : Campsite - ID - NAME - GPS_latitude - GPS_longitude CampsiteServices -Campsite_ID -Services_ID So my code (c# but it's not relevant, let say it's an OO language) looks like this public class SqlCodeCampsiteFilter{ public string SqlCode; public Dictionary<string, object> Parameters; } interface ISQLCampsiteFilter{ SqlCodeEngineCore CreateSQLCode(); } public class GpsLocationFilter : ISQLCampsiteFilter{ public float? GpsLatitude; public float? GpsLongitude; public SqlCodeEngineCore CreateSQLCode() { --return an sql code to filter on the gps location like dbo.getDistance(@gpsLat,@gpsLong,campsite.GPS_latitude,campsite.GPS_longitude) with the parameters } } public class ServiceFilter : : ISQLCampsiteFilter{ public int[] RequiredServicesID; public SqlCodeEngineCore CreateSQLCode() { --return an sql code to filter on the services "where ID IN (select CampsiteServices.Service_ID FROm CampsiteServices WHERE Service_ID in ...) } } So in my webservice code : List<ISQLFilterEngineCore> filters = new List<ISQLFilterEngineCore>(); if(gps_latitude.hasvalue && gps_longitude.hasvalue){ filters.Add (new GpsLocationFilter (gps_latitude.value,gps_longitude.value)); } if(required_services_id != null){ filters.Add (new ServiceFilter (required_services_id )); } string sql = "SELECT ID,NAME FROM campsite where 1=1" foreach(ISQLFilterEngineCore aFilter in filters){ SqlCodeCampsiteFilter code = aFilter.CreateSQLCode(); sql += code.SqlCode; mySqlCommand.AddParameters(code.Parameters);//add all the parameters to the sql command } return mySqlCommand.GetResults(); 1/ I don't use ORM for the simple reason that the system exists since 10 years and the only dev who is here since the beginning is starting to learn about difference between public and private. 2/ I don't like SP because : we can do override, and t-sql is not so funny to use :) So what do you think ? Is it clear ? Do you have any pattern that I should have a look to ? If something is not clear please ask

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• MKMap showing detail of annotations

  - by yeohchan

  I have encountered a problem of populating the description for each annotation. Each annotation works, but there is somehow an area when trying to click on it. Here is the code. the one in bold is the one that has the problem. -(void)viewDidLoad{ FlickrFetcher *fetcher=[FlickrFetcher sharedInstance]; NSArray *rec=[fetcher recentGeoTaggedPhotos]; for(NSDictionary *dic in rec){ NSLog(@"%@",dic); NSDictionary *string = [fetcher locationForPhotoID:[dic objectForKey:@"id"]]; double latitude = [[string objectForKey:@"latitude"] doubleValue]; double longitude = [[string objectForKey:@"longitude"]doubleValue]; if(latitude !=0 && latitude != 0 ){ CLLocationCoordinate2D coordinate1 = { latitude,longitude }; **NSDictionary *adress=[NSDictionary dictionaryWithObjectsAndKeys:[dic objectForKey:@"owner"],[dic objectForKey:@"title"],nil];** MKPlacemark *anArea=[[MKPlacemark alloc]initWithCoordinate:coordinate1 addressDictionary:adress]; [mapView addAnnotation:anArea]; } } } Here is what the Flickr class does: #import <Foundation/Foundation.h> #define TEST_HIGH_NETWORK_LATENCY 0 typedef enum { FlickrFetcherPhotoFormatSquare, FlickrFetcherPhotoFormatLarge } FlickrFetcherPhotoFormat; @interface FlickrFetcher : NSObject { NSManagedObjectModel *managedObjectModel; NSManagedObjectContext *managedObjectContext; NSPersistentStoreCoordinator *persistentStoreCoordinator; } // Returns the 'singleton' instance of this class + (id)sharedInstance; // // Local Database Access // // Checks to see if any database exists on disk - (BOOL)databaseExists; // Returns the NSManagedObjectContext for inserting and fetching objects into the store - (NSManagedObjectContext *)managedObjectContext; // Returns an array of objects already in the database for the given Entity Name and Predicate - (NSArray *)fetchManagedObjectsForEntity:(NSString*)entityName withPredicate:(NSPredicate*)predicate; // Returns an NSFetchedResultsController for a given Entity Name and Predicate - (NSFetchedResultsController *)fetchedResultsControllerForEntity:(NSString*)entityName withPredicate:(NSPredicate*)predicate; // // Flickr API access // NOTE: these are blocking methods that wrap the Flickr API and wait on the results of a network request // // Returns an array of Flickr photo information for photos with the given tag - (NSArray *)photosForUser:(NSString *)username; // Returns an array of the most recent geo-tagged photos - (NSArray *)recentGeoTaggedPhotos; // Returns a dictionary of user info for a given user ID. individual photos contain a user ID keyed as "owner" - (NSString *)usernameForUserID:(NSString *)userID; // Returns the photo for a given server, id and secret - (NSData *)dataForPhotoID:(NSString *)photoID fromFarm:(NSString *)farm onServer:(NSString *)server withSecret:(NSString *)secret inFormat:(FlickrFetcherPhotoFormat)format; // Returns a dictionary containing the latitue and longitude where the photo was taken (among other information) - (NSDictionary *)locationForPhotoID:(NSString *)photoID; @end

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• Getting RSSIValue from IOBluetoothHostController

  - by Tanner Ezell

  I'm trying to write a simple application that gathers the RSSIValue and displays it via NSLog, my code is as follows: #import <Foundation/Foundation.h> #import <Cocoa/Cocoa.h> #import <IOBluetooth/objc/IOBluetoothDeviceInquiry.h> #import <IOBluetooth/objc/IOBluetoothDevice.h> #import <IOBluetooth/objc/IOBluetoothHostController.h> #import <IOBluetooth/IOBluetoothUtilities.h> @interface getRSSI: NSObject {} -(void) readRSSIForDeviceComplete:(id)controller device:(IOBluetoothDevice*)device info:(BluetoothHCIRSSIInfo*)info error:(IOReturn)error; @end @implementation getRSSI - (void) readRSSIForDeviceComplete:(id)controller device:(IOBluetoothDevice*)device info:(BluetoothHCIRSSIInfo*)info error:(IOReturn)error { if (error != kIOReturnSuccess) { NSLog(@"readRSSIForDeviceComplete return error"); CFRunLoopStop(CFRunLoopGetCurrent()); } if (info->handle == kBluetoothConnectionHandleNone) { NSLog(@"readRSSIForDeviceComplete no handle"); CFRunLoopStop(CFRunLoopGetCurrent()); } NSLog(@"RSSI = %i dBm ", info->RSSIValue); [NSThread sleepUntilDate: [NSDate dateWithTimeIntervalSinceNow: 5]]; [device closeConnection]; [device openConnection]; [controller readRSSIForDevice:device]; } @end int main (int argc, const char * argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSLog(@"start"); IOBluetoothHostController *hci = [IOBluetoothHostController defaultController]; NSString *addrStr = @"xx:xx:xx:xx:xx:xx"; BluetoothDeviceAddress addr; IOBluetoothNSStringToDeviceAddress(addrStr, &addr); IOBluetoothDevice *device = [[IOBluetoothDevice alloc] init]; device = [IOBluetoothDevice withAddress:&addr]; [device retain]; [device openConnection]; getRSSI *rssi = [[getRSSI alloc] init]; [hci setDelegate:rssi]; [hci readRSSIForDevice:device]; CFRunLoopRun(); [hci release]; [rssi release]; [pool release]; return 0; } The problem I am facing is that the readRSSIForDeviceComplete seems to work just fine, info passes along a value. The problem is that the RSSI value is drastically different from the one I can view from OS X via option clicking the bluetooth icon at the top. It is typical for my application to print off 1,2,-1,-8,etc while the menu displays -64 dBm, -66, -70, -42, etc. I would really appreciate some guidance.

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• Crash in OS X Core Data Utility Tutorial

  - by vinogradov

  I'm trying to follow Apple's Core Data utility Tutorial. It was all going nicely, until... The tutorial uses a custom sub-class of NSManagedObject, called 'Run'. Run.h looks like this: #import <Foundation/Foundation.h> #import <CoreData/CoreData.h> @interface Run : NSManagedObject { NSInteger processID; } @property (retain) NSDate *date; @property (retain) NSDate *primitiveDate; @property NSInteger processID; @end Now, in Run.m we have an accessor method for the processID variable: - (void)setProcessID:(int)newProcessID { [self willChangeValueForKey:@"processID"]; processID = newProcessID; [self didChangeValueForKey:@"processID"]; } In main.m, we use functions to set up a managed object model and context, instantiate an entity called run, and add it to the context. We then get the current NSprocessInfo, in preparation for setting the processID of the run object. NSManagedObjectContext *moc = managedObjectContext(); NSEntityDescription *runEntity = [[mom entitiesByName] objectForKey:@"Run"]; Run *run = [[Run alloc] initWithEntity:runEntity insertIntoManagedObjectContext:moc]; NSProcessInfo *processInfo = [NSProcessInfo processInfo]; Next, we try to call the accessor method defined in Run.m to set the value of processID: [run setProcessID:[processInfo processIdentifier]]; And that's where it's crashing. The object run seems to exist (I can see it in the debugger), so I don't think I'm messaging nil; on the other hand, it doesn't look like the setProcessID: message is actually being received. I'm obviously still learning this stuff (that's what tutorials are for, right?), and I'm probably doing something really stupid. However, any help or suggestions would be gratefully received! ===MORE INFORMATION=== Following up on Jeremy's suggestions: The processID attribute in the model is set up like this: NSAttributeDescription *idAttribute = [[NSAttributeDescription alloc]init]; [idAttribute setName:@"processID"]; [idAttribute setAttributeType:NSInteger32AttributeType]; [idAttribute setOptional:NO]; [idAttribute setDefaultValue:[NSNumber numberWithInteger:-1]]; which seems a little odd; we are defining it as a scalar type, and then giving it an NSNumber object as its default value. In the associated class, Run, processID is defined as an NSInteger. Still, this should be OK - it's all copied directly from the tutorial. It seems to me that the problem is probably in there somewhere. By the way, the getter method for processID is defined like this: - (int)processID { [self willAccessValueForKey:@"processID"]; NSInteger pid = processID; [self didAccessValueForKey:@"processID"]; return pid; } and this method works fine; it accesses and unpacks the default int value of processID (-1). Thanks for the help so far!

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• EXC_BAD_ACCESS when I change moviePlayer contentURL

  - by Bruno

  Hello, In few words, my application is doing that : 1) My main view (MovieListController) has some video thumbnails and when I tap on one, it displays the moviePlayer (MoviePlayerViewController) : MovieListController.h : @interface MoviePlayerViewController : UIViewController <UITableViewDelegate>{ UIView *viewForMovie; MPMoviePlayerController *player; } @property (nonatomic, retain) IBOutlet UIView *viewForMovie; @property (nonatomic, retain) MPMoviePlayerController *player; - (NSURL *)movieURL; @end MovieListController.m : MoviePlayerViewController *controllerTV = [[MoviePlayerViewController alloc] initWithNibName:@"MoviePlayerViewController" bundle:nil]; controllerTV.delegate = self; controllerTV.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal; [self presentModalViewController: controllerTV animated: YES]; [controllerTV release]; 2) In my moviePlayer, I initialize the video I want to play MoviePlayerViewController.m : @implementation MoviePlayerViewController @synthesize player; @synthesize viewForMovie; - (void)viewDidLoad { NSLog(@"start"); [super viewDidLoad]; self.player = [[MPMoviePlayerController alloc] init]; self.player.view.frame = self.viewForMovie.bounds; self.player.view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight; [self.viewForMovie addSubview:player.view]; self.player.contentURL = [self movieURL]; } - (void)dealloc { NSLog(@"dealloc TV"); [player release]; [viewForMovie release]; [super dealloc]; } -(NSURL *)movieURL { NSBundle *bundle = [NSBundle mainBundle]; NSString *moviePath = [bundle pathForResource:@"FR_Tribord_Surf camp_100204" ofType:@"mp4"]; if (moviePath) { return [NSURL fileURLWithPath:moviePath]; } else { return nil; } } - It's working good, my movie is display My problem : When I go back to my main view : - (void) returnToMap: (MoviePlayerViewController *) controller { [self dismissModalViewControllerAnimated: YES]; } And I tap in a thumbnail to display again the moviePlayer (MoviePlayerViewController), I get a *Program received signal: “EXC_BAD_ACCESS”.* In my debugger I saw that it's stopping on the thread "main" : // // main.m // MoviePlayer // // Created by Eric Freeman on 3/27/10. // Copyright Apple Inc 2010. All rights reserved. // #import <UIKit/UIKit.h> int main(int argc, char *argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; int retVal = UIApplicationMain(argc, argv, nil, nil); //EXC_BAD_ACCESS [pool release]; return retVal; } If I comment self.player.contentURL = [self movieURL]; it's working, but when I let it, iI have this problem. I read that it's due to null pointer or memory problem but I don't understand why it's working the first time and not the second time. I release my object in dealloc method. Thanks for your help ! Bruno.

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• Expression Too Complex In Access 2007

  - by Jazzepi

  When I try to run this query in Access through the ODBC interface into a MySQL database I get an "Expression too complex in query expression" error. The essential thing I'm trying to do is translate abbreviated names of languages into their full body English counterparts. I was curious if there was some way to "trick" access into thinking the expression is smaller with sub queries, or if someone else had a better idea of how to solve this problem. I thought about making a temporary table and doing a join on it, but that's not supported in Access SQL. Just as an FYI, the query worked fine until I added the big long IFF chain. I tested the query on a smaller IFF chain for three languages, and that wasn't an issue, so the problem definitely stems from the huge IFF chain (It's 26 deep). Also, I might be able to drop some of the options (like combining the different forms of Chinese or Portuguese) As a test, I was able to get the SQL query to work after paring it down to 14 IFF() statements, but that's a far cry from the 26 languages I'd like to represent. SELECT TOP 5 Count( * ) AS [Number of visits by language], IIf(login.lang="ar","Arabic",IIf(login.lang="bg","Bulgarian",IIf(login.lang="zh_CN","Chinese (Simplified Han)",IIf(login.lang="zh_TW","Chinese (Traditional Han)",IIf(login.lang="cs","Czech",IIf(login.lang="da","Danish",IIf(login.lang="de","German",IIf(login.lang="en_US","United States English",IIf(login.lang="en_GB","British English",IIf(login.lang="es","Spanish",IIf(login.lang="fr","French",IIf(login.lang="el","Greek",IIf(login.lang="it","Italian",IIf(login.lang="ko","Korean",IIf(login.lang="hu","Hungarian",IIf(login.lang="nl","Dutch",IIf(login.lang="pl","Polish",IIf(login.lang="pt_PT","European Portuguese",IIf(login.lang="pt_BR","Brazilian Portuguese",IIf(login.lang="ru","Russian",IIf(login.lang="sk","Slovak",IIf(login.lang="sl","Slovenian","IIf(login.lang="fi","Finnish",IIf(login.lang="sv","Swedish",IIf(login.lang="tr","Turkish","Unknown")))))))))))))))))))))))))) AS [Language] FROM login, reservations, reservation_users, schedules WHERE (reservations.start_date Between DATEDIFF('s','1970-01-01 00:00:00',[Starting Date in the Following Format YYYY/MM/DD]) And DATEDIFF('s','1970-01-01 00:00:00',[Ending Date in the Following Format YYYY/MM/DD])) And reservations.is_blackout=0 And reservation_users.memberid=login.memberid And reservation_users.resid=reservations.resid And reservation_users.invited=0 And reservations.scheduleid=schedules.scheduleid And scheduletitle=[Schedule Title] GROUP BY login.lang ORDER BY Count( * ) DESC; @ Michael Todd I completely agree. The list of languages should have been a table in the database and the login.lang should have been a FK into that table. Unfortunately this isn't how the database was written, and it's not really mine to modify. The languages are placed into the login.lang field by the PHP running on top of the database.

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• IQueryable and lazy loading

  - by Nelson

  I'm having a hard time determining the best way to handle this... With Entity Framework (and L2S), LINQ queries return IQueryable. I have read various opinions on whether the DAL/BLL should return IQueryable, IEnumerable or IList. Assuming we go with IList, then the query is run immediately and that control is not passed on to the next layer. This makes it easier to unit test, etc. You lose the ability to refine the query at higher levels, but you could simply create another method that allows you to refine the query and still return IList. And there are many more pros/cons. So far so good. Now comes Entity Framework and lazy loading. I am using POCO objects with proxies in .NET 4/VS 2010. In the presentation layer I do: foreach (Order order in bll.GetOrders()) { foreach (OrderLine orderLine in order.OrderLines) { // Do something } } In this case, GetOrders() returns IList so it executes immediately before returning to the PL. But in the next foreach, you have lazy loading which executes multiple SQL queries as it gets all the OrderLines. So basically, the PL is running SQL queries "on demand" in the wrong layer. Is there any sensible way to avoid this? I could turn lazy loading off, but then what's the point of having this "feature" that everyone was complaining EF1 didn't have? And I'll admit it is very useful in many scenarios. So I see several options: Somehow remove all associations in the entities and add methods to return them. This goes against the default EF behavior/code generation and makes it harder to do some composite (multiple entity) LINQ queries. It seems like a step backwards. I vote no. If we have lazy loading anyway which makes it hard to unit test, then go all the way and return IQueryable. You'll have more control farther up the layers. I still don't think this is a good option because IQueryable ties you to L2S, L2E, or your own full implementation of IQueryable. Lazy loading may run queries "on demand", but doesn't tie you to any specific interface. I vote no. Turn off lazy loading. You'll have to handle your associations manually. This could be with eager loading's .Include(). I vote yes in some specific cases. Keep IList and lazy loading. I vote yes in many cases, only due to the troubles with the others. Any other options or suggestions? I haven't found an option that really convinces me.

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• Unmanaged Code calling leads to heavy memory leak!!

  - by konnychen

  Maybe I need change the title as "Unmanaged Code calling leads to heavy memory leak!" The leak is around 30M/hour I think maybe I need complete my code here because the memory leak maybe not from a static string whereas my real code derive this string from external device (see new code attached). so I handle also unmanaged code. Could it be possible the leak comes from unmanaged code? But I freed the resouce by Marshal.FreeCoTaskMem(pos); oThread2 = new Thread(new ThreadStart(Cyclic_Call)); oThread2.Start(); delegate void SetText_lab_Statubar(string text); private void m_SetText_lab_Statubar(string text) { if (this.lab_Statubar.InvokeRequired) { SetText_lab_Statubar d = new SetText_lab_Statubar(m_SetText_lab_Statubar); this.Invoke(d, new object[] { text }); } else { this.lab_Statubar.Text = text; } } private void Cyclic_Call() { do { //... ... ReadMatrixCode(Station6, 0, str_Code); this.m_SetText_lab_Statubar(str_Code[4]); Thread.Sleep(100); } while (!b_AbortThraed); } private void ReadMatrixCode(Station st, int ItemNr, string[] str_Code) { IntPtr pItemStates = IntPtr.Zero; IntPtr pErrors = IntPtr.Zero; int NumItems = itemServerHandles.Length; m_SyncIO.Read(DataSrc, NumItems, itemServerHandles, out pItemStates, out pErrors); // This calls external dll which has some of "out IntPtr" errors = new int[NumItems]; Marshal.Copy(pErrors, errors, 0, NumItems); IntPtr pos = pItemStates; // Now get the read values and check errors for (int dwCount = 0; dwCount < NumItems; dwCount++) { result[dwCount] = (ITEMSTATE)Marshal.PtrToStructure(pos, typeof(ITEMSTATE)); pos = (IntPtr)(pos.ToInt32() + Marshal.SizeOf(typeof(ITEMSTATE))); } // Free allocated COM-ressouces Marshal.FreeCoTaskMem(pItemStates); Marshal.FreeCoTaskMem(pErrors); pItemStates = IntPtr.Zero; pErrors = IntPtr.Zero; } m_syncIO is a class and finally it will call COM component which is defined below [Guid("39C12B52-011E-11D0-9675-1020AFD8ADB3")] [InterfaceType(1)] [ComConversionLoss] public interface ISyncIO { void Read(DATASOURCE dwSource, int dwCount, int[] phServer, out IntPtr ppItemValues, out IntPtr ppErrors); void Write(int dwCount, int[] phServer, object[] pItemValues, out IntPtr ppErrors); }

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• What am I not getting about this abstract class implementation?

  - by Schnapple

  PREFACE: I'm relatively inexperienced in C++ so this very well could be a Day 1 n00b question. I'm working on something whose long term goal is to be portable across multiple operating systems. I have the following files: Utilities.h #include <string> class Utilities { public: Utilities() { }; virtual ~Utilities() { }; virtual std::string ParseString(std::string const& RawString) = 0; }; UtilitiesWin.h (for the Windows class/implementation) #include <string> #include "Utilities.h" class UtilitiesWin : public Utilities { public: UtilitiesWin() { }; virtual ~UtilitiesWin() { }; virtual std::string ParseString(std::string const& RawString); }; UtilitiesWin.cpp #include <string> #include "UtilitiesWin.h" std::string UtilitiesWin::ParseString(std::string const& RawString) { // Magic happens here! // I'll put in a line of code to make it seem valid return ""; } So then elsewhere in my code I have this #include <string> #include "Utilities.h" void SomeProgram::SomeMethod() { Utilities *u = new Utilities(); StringData = u->ParseString(StringData); // StringData defined elsewhere } The compiler (Visual Studio 2008) is dying on the instance declaration c:\somepath\somecode.cpp(3) : error C2259: 'Utilities' : cannot instantiate abstract class due to following members: 'std::string Utilities::ParseString(const std::string &)' : is abstract c:\somepath\utilities.h(9) : see declaration of 'Utilities::ParseString' So in this case what I'm wanting to do is use the abstract class (Utilities) like an interface and have it know to go to the implemented version (UtilitiesWin). Obviously I'm doing something wrong but I'm not sure what. It occurs to me as I'm writing this that there's probably a crucial connection between the UtilitiesWin implementation of the Utilities abstract class that I've missed, but I'm not sure where. I mean, the following works #include <string> #include "UtilitiesWin.h" void SomeProgram::SomeMethod() { Utilities *u = new UtilitiesWin(); StringData = u->ParseString(StringData); // StringData defined elsewhere } but it means I'd have to conditionally go through the different versions later (i.e., UtilitiesMac(), UtilitiesLinux(), etc.) What have I missed here?

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• iPhone: Problems releasing UIViewController in a multithreaded environment

  - by bart-simpson

  Hi! I have a UIViewController and in that controller, i am fetching an image from a URL source. The image is fetched in a separate thread after which the user-interface is updated on the main thread. This controller is displayed as a page in a UIScrollView parent which is implemented to release controllers that are not in view anymore. When the thread finishes fetching content before the UIViewController is released, everything works fine - but when the user scrolls to another page before the thread finishes, the controller is released and the only handle to the controller is owned by the thread making releaseCount of the controller equals to 1. Now, as soon as the thread drains NSAutoreleasePool, the controller gets releases because the releaseCount becomes 0. At this point, my application crashes and i get the following error message: bool _WebTryThreadLock(bool), 0x4d99c60: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now... The backtrace reveals that the application crashed on the call to [super dealloc] and it makes total sense because the dealloc function must have been triggered by the thread when the pool was drained. My question is, how i can overcome this error and release the controller without leaking memory? One solution that i tried was to call [self retain] before the pool is drained so that retainCount doesn't fall to zero and then using the following code to release controller in the main thread: [self performSelectorOnMainThread:@selector(autorelease) withObject:nil waitUntilDone:NO]; Unfortunately, this did not work out. Below is the function that is executed on a thread: - (void)thread_fetchContent { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSURL *imgURL = [NSURL URLWithString:@"http://www.domain.com/image.png"]; // UIImage *imgHotspot is declared as private - The image is retained // here and released as soon as it is assigned to UIImageView imgHotspot = [[[UIImage alloc] initWithData: [NSData dataWithContentsOfURL: imgURL]] retain]; if ([self retainCount] == 1) { [self retain]; // increment retain count ~ workaround [pool drain]; // drain pool // this doesn't work - i get the same error [self performSelectorOnMainThread:@selector(autorelease) withObject:nil waitUntilDone:NO]; } else { // show fetched image on the main thread - this works fine! [self performSelectorOnMainThread:@selector(showImage) withObject:nil waitUntilDone:NO]; [pool drain]; } } Please help! Thank you in advance.

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• Unique_ptr compiler errors

  - by Godric Seer

  I am designing and entity-component system for a project, and C++ memory management is giving me a few issues. I just want to make sure my design is legitimate. So to start I have an Entity class which stores a vector of Components: class Entity { private: std::vector<std::unique_ptr<Component> > components; public: Entity() { }; void AddComponent(Component* component) { this -> components.push_back(std::unique_ptr<Component>(component)); } ~Entity(); }; Which if I am not mistaken means that when the destructor is called (even the default, compiler created one), the destructor for the Entity, will call ~components, which will call ~std::unique_ptr for each element in the vector, and lead to the destruction of each Component, which is what I want. The component class has virtual methods, but the important part is its constructor: Component::Component(Entity parent) { parent.addComponent(this) // I am not sure if this would work like I expect // Other things here } As long as passing this to the method works, this also does what I want. My confusion is in the factory. What I want to do is something along the lines of: std::shared_ptr<Entity> createEntity() { std::shared_ptr<Entity> entityPtr(new Entity()); new Component(*parent); // Initialize more, and other types of Components return entityPtr; } Now, I believe that this setup will leave the ownership of the Component in the hands of its Parent Entity, which is what I want. First a small question, do I need to pass the entity into the Component constructor by reference or pointer or something? If I understand C++, it would pass by value, which means it gets copied, and the copied entity would die at the end of the constructor. The second, and main question is that code based on this sample will not compile. The complete error is too large to print here, however I think I know somewhat of what is going on. The compiler's error says I can't delete an incomplete type. My Component class has a purely virtual destructor with an implementation: inline Component::~Component() { }; at the end of the header. However since the whole point is that Component is actually an interface. I know from here that a complete type is required for unique_ptr destruction. The question is, how do I work around this? For reference I am using gcc 4.4.6.

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• How can i convert this to a factory/abstract factory?

  - by Amitd

  I'm using MigraDoc to create a pdf document. I have business entities similar to the those used in MigraDoc. public class Page{ public List<PageContent> Content { get; set; } } public abstract class PageContent { public int Width { get; set; } public int Height { get; set; } public Margin Margin { get; set; } } public class Paragraph : PageContent{ public string Text { get; set; } } public class Table : PageContent{ public int Rows { get; set; } public int Columns { get; set; } //.... more } In my business logic, there are rendering classes for each type public interface IPdfRenderer<T> { T Render(MigraDoc.DocumentObjectModel.Section s); } class ParagraphRenderer : IPdfRenderer<MigraDoc.DocumentObjectModel.Paragraph> { BusinessEntities.PDF.Paragraph paragraph; public ParagraphRenderer(BusinessEntities.PDF.Paragraph p) { paragraph = p; } public MigraDoc.DocumentObjectModel.Paragraph Render(MigraDoc.DocumentObjectModel.Section s) { var paragraph = s.AddParagraph(); // add text from paragraph etc return paragraph; } } public class TableRenderer : IPdfRenderer<MigraDoc.DocumentObjectModel.Tables.Table> { BusinessEntities.PDF.Table table; public TableRenderer(BusinessEntities.PDF.Table t) { table =t; } public MigraDoc.DocumentObjectModel.Tables.Table Render(Section obj) { var table = obj.AddTable(); //fill table based on table } } I want to create a PDF page as : var document = new Document(); var section = document.AddSection();// section is a page in pdf var page = GetPage(1); // get a page from business classes foreach (var content in page.Content) { //var renderer = createRenderer(content); // // get Renderer based on Business type ?? // renderer.Render(section) } For createRenderer() i can use switch case/dictionary and return type. How can i get/create the renderer generically based on type ? How can I use factory or abstract factory here? Or which design pattern better suits this problem?

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• idiomatic property changed notification in scala?

  - by Jeremy Bell

  I'm trying to find a cleaner alternative (that is idiomatic to Scala) to the kind of thing you see with data-binding in WPF/silverlight data-binding - that is, implementing INotifyPropertyChanged. First, some background: In .Net WPF or silverlight applications, you have the concept of two-way data-binding (that is, binding the value of some element of the UI to a .net property of the DataContext in such a way that changes to the UI element affect the property, and vise versa. One way to enable this is to implement the INotifyPropertyChanged interface in your DataContext. Unfortunately, this introduces a lot of boilerplate code for any property you add to the "ModelView" type. Here is how it might look in Scala: trait IDrawable extends INotifyPropertyChanged { protected var drawOrder : Int = 0 def DrawOrder : Int = drawOrder def DrawOrder_=(value : Int) { if(drawOrder != value) { drawOrder = value OnPropertyChanged("DrawOrder") } } protected var visible : Boolean = true def Visible : Boolean = visible def Visible_=(value: Boolean) = { if(visible != value) { visible = value OnPropertyChanged("Visible") } } def Mutate() : Unit = { if(Visible) { DrawOrder += 1 // Should trigger the PropertyChanged "Event" of INotifyPropertyChanged trait } } } For the sake of space, let's assume the INotifyPropertyChanged type is a trait that manages a list of callbacks of type (AnyRef, String) = Unit, and that OnPropertyChanged is a method that invokes all those callbacks, passing "this" as the AnyRef, and the passed-in String). This would just be an event in C#. You can immediately see the problem: that's a ton of boilerplate code for just two properties. I've always wanted to write something like this instead: trait IDrawable { val Visible = new ObservableProperty[Boolean]('Visible, true) val DrawOrder = new ObservableProperty[Int]('DrawOrder, 0) def Mutate() : Unit = { if(Visible) { DrawOrder += 1 // Should trigger the PropertyChanged "Event" of ObservableProperty class } } } I know that I can easily write it like this, if ObservableProperty[T] has Value/Value_= methods (this is the method I'm using now): trait IDrawable { // on a side note, is there some way to get a Symbol representing the Visible field // on the following line, instead of hard-coding it in the ObservableProperty // constructor? val Visible = new ObservableProperty[Boolean]('Visible, true) val DrawOrder = new ObservableProperty[Int]('DrawOrder, 0) def Mutate() : Unit = { if(Visible.Value) { DrawOrder.Value += 1 } } } // given this implementation of ObservableProperty[T] in my library // note: IEvent, Event, and EventArgs are classes in my library for // handling lists of callbacks - they work similarly to events in C# class PropertyChangedEventArgs(val PropertyName: Symbol) extends EventArgs("") class ObservableProperty[T](val PropertyName: Symbol, private var value: T) { protected val propertyChanged = new Event[PropertyChangedEventArgs] def PropertyChanged: IEvent[PropertyChangedEventArgs] = propertyChanged def Value = value; def Value_=(value: T) { if(this.value != value) { this.value = value propertyChanged(this, new PropertyChangedEventArgs(PropertyName)) } } } But is there any way to implement the first version using implicits or some other feature/idiom of Scala to make ObservableProperty instances function as if they were regular "properties" in scala, without needing to call the Value methods? The only other thing I can think of is something like this, which is more verbose than either of the above two versions, but is still less verbose than the original: trait IDrawable { private val visible = new ObservableProperty[Boolean]('Visible, false) def Visible = visible.Value def Visible_=(value: Boolean): Unit = { visible.Value = value } private val drawOrder = new ObservableProperty[Int]('DrawOrder, 0) def DrawOrder = drawOrder.Value def DrawOrder_=(value: Int): Unit = { drawOrder.Value = value } def Mutate() : Unit = { if(Visible) { DrawOrder += 1 } } }

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• generated service mock: everything but RhinoMocks fails?

  - by hko

  I have the "quest" to search for the next Mocking Framework for my company, and basically it's down to NSubstitute (simplest syntax, but no strict mocks), FakeItEasy(best reviews, Roy Osherove bonus, and slightly better lib support than NSubstitute), Moq (best "other libs support", biggest featureset, downside: mock.Object). We definitely want to move on from RhinoMocks, e.g. because of the unusefull interactiontest error messages (it should tell me what the parameter was instead, when a verification fails). So I was pretty surprised the other day (that was yesterday) when I found out RhinoMocks could do a thing where every other mock framework fails at: Mocking an autogenerated SomethingService (a typical VS autogenerated service with a default construtor in a partial class). Please don't argue about the design.. I intend to write lightweight integration tests (and some unit tests), and I can't mess around with the service, the product is installed on too many customers system. See this code: // here the NSubstitute and FakeItEasy equivalents throw an exception.. see below TicketStoreService fakeTicketStoreService = MockRepository.GenerateMock<TicketStoreService>(); fakeTicketStoreService.Expect(service => service.DoSomething(Arg.Is(new Guid())).Return(new Guid()); fakeTicketStoreService.DoSomething(Arg.Is(new Guid())); fakeTicketStoreService.VerifyAllExpectations(); Note that DoSomething is a non-virtual methodcall in an autogenerated class. So it shouldn't work, according to common knowledge. But it does. Problem is that it's the only (non commercial) framework that can do this: Rhino.Mocks works, and verification works too FakeItEasy says it doesn't find a default constructor (probably just wrong exception message): No default constructor was found on the type SomeNamespace.TicketStoreService Moq gives something sane and understandable: Invalid setup on a non-virtual (overridable in VB) member: service=> service.DoSomething Nsubstitute gives a message System.NotSupportedException: Cannot serialize member System.ComponentModel.Component.Site of type System.ComponentModel.ISite because it is an interface. I'm really wondering what's going on here with the frameworks, except Moq. The "fancy new" frameworks seem to have an initial perf hit too, probably preparing some Type cache and serializing stuff, whilst RhinoMocks somehow manages to create a very "slim" mock without recursion. I have to admit I didn't like RhinoMocks very well, but here it shines.. unfortunately. So, is there a way to get that to work with newer (non-commercial!) mocking frameworks, or somehow get a sane error message out of Rhino.Mocks? And why can Rhino.Mocks achieve this, when clearly every Mocking framework states it can only work with virtual methods when given a concrete class? Let's not derail the discussion by talking about alternative approaches like Extract&Override or runtime-proxy Mocking frameworks like JustMock/TypeMock/Moles or the new Fakes framework, I know these, but that would be less ideal solutions, for reasons beyond this topic. Any help appreciated..

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• UITabBarContrtoller achieve from a different class in iPhone

  - by baluedo

  Hi! I have the following problem: There is a class that includes five tabs in the following way: mainMenuClient.h #import <UIKit/UIKit.h> @interface MainMenuClient : UIViewController { UITabBarController *tabBarController; } @property (nonatomic, retain) UITabBarController *tabBarController; @end mainMenuClient.m -(void)viewDidLoad { UIView *contentView = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; contentView.backgroundColor = [UIColor blackColor]; self.view = contentView; [contentView release]; ContactListTab *contactTab = [[ContactListTab alloc] init]; ChatTab *chat = [[ChatTab alloc]init]; DialerTab *dialer = [[DialerTab alloc]init]; MenuTab *menu = [[MenuTab alloc]init]; TesztingFile *teszting = [[TesztingFile alloc]init]; contactTab.title = @"Contact List"; chat.title = @"Chat"; dialer.title = @"Dialer"; menu.title = @"Menu"; teszting.title = @"TesztTab"; contactTab.tabBarItem.image = [UIImage imageNamed:@"Contacts_icon.png"]; chat.tabBarItem.image = [UIImage imageNamed:@"Chat_icon.png"]; dialer.tabBarItem.image = [UIImage imageNamed:@"Dialer_icon.png"]; menu.tabBarItem.image = [UIImage imageNamed:@"Menu_icon.png"]; teszting.tabBarItem.image = [UIImage imageNamed:@"Contacts_icon.png"]; chat.tabBarItem.badgeValue = @"99"; tabBarController = [[UITabBarController alloc]init]; tabBarController.view.frame = CGRectMake(0, 0, 320, 460); [tabBarController setViewControllers:[NSArray arrayWithObjects:contactTab, chat, dialer, menu, teszting, nil]]; [contactTab release]; [chat release]; [dialer release]; [menu release]; [teszting release]; [self.view addSubview:tabBarController.view]; [super viewDidLoad]; } In the contactTab class there are a UITableViewController. contactTab.h - (void)updateCellData; - (void)configureCell:(UITableViewCell *)cell forIndexPath:(NSIndexPath *)indexPath; There is a third class, which I would like to achieve is a method of UITableViewController's (from ContactTab). So far I tried this: When I tried to achieve the UItabbarController: MainMenuClient *menu; UITabBarController *tabBarControllerchange = [[UITabBarController alloc] init]; tabBarControllerchange = menu.tabBarController; [tabBarControllerchange setSelectedIndex:0]; When I tried to achieve the UITableViewController: ContactListTab *contactListTab; [contactListTab updateCellData]; Does anybody have an idea for this problem? Thanks. Balazs.

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• Recommended textbook for machine-level programming?

  - by Norman Ramsey

  I'm looking at textbooks for an undergraduate course in machine-level programming. If the perfect book existed, this is what it would look like: Uses examples written in C or assembly language, or both. Covers machine-level operations such as two's-complement integer arithmetic, bitwise operations, and floating-point arithmetic. Explains how caches work and how they affect performance. Explains machine instructions or assembly instructions. Bonus if the example assembly language includes x86; triple bonus if it includes x86-64 (aka AMD64). Explains how C values and data structures are represented using hardware registers and memory. Explains how C control structures are translated into assembly language using conditional and unconditional branch instructions. Explains something about procedure calling conventions and how procedure calls are implemented at the machine level. Books I might be interested in would probably have the words "machine organization" or "computer architecture" in the title. Here are some books I'm considering but am not quite happy with: Computer Systems: A Programmer's Perspective by Randy Bryant and Dave O'Hallaron. This is quite a nice book, but it's a book for a broad, shallow course in systems programming, and it contains a great deal of material my students don't need. Also, it is just out in a second edition, which will make it expensive. Computer Organization and Design: The Hardware/Software Interface by Dave Patterson and John Hennessy. This is also a very nice book, but it contains way more information about how the hardware works than my students need. Also, the exercises look boring. Finally, it has a show-stopping bug: it is based very heavily on MIPS hardware and the use of a MIPS simulator. My students need to learn how to use DDD, and I can't see getting this to work on a simulator. Not to mention that I can't see them cross-compiling their code for the simulator, and so on and so forth. Another flaw is that the book mentions the x86 architecture only to sneer at it. I am entirely sympathetic to this point of view, but news flash! You guys lost! Write Great Code Vol I: Understanding the Machine by Randall Hyde. I haven't evaluated this book as thoroughly as the other two. It has a lot of what I need, but the translation from high-level language to assembler is deferred to Volume Two, which has mixed reviews. My students will be annoyed if I make them buy a two-volume series, even if the price of those two volumes is smaller than the price of other books. I would really welcome other suggestions of books that would help students in a class where they are to learn how C-language data structures and code are translated to machine-level data structures and code and where they learn how to think about performance, with an emphasis on the cache.

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• Windows 7 - pydoc from cmd

  - by Random_Person

  Okay, I'm having one of those moments that makes me question my ability to use a computer. This is not the sort of question I imagined asking as my first SO post, but here goes. Started on Zed's new "Learn Python the Hard Way" since I've been looking to get back into programming after a 10 year hiatus and python was always what I wanted. This book has really spoken to me. That being said, I'm having a serious issue with pydoc from the command. I've got all the directories in c:/python26 in my system path and I can execute pydoc from the command line just fine regardless of pwd - but it accepts no arguments. Doesn't matter what I type, I just get the standard pydoc output telling me the acceptable arguments. Any ideas? For what it's worth, I installed ActivePython as per Zed's suggestion. C:\Users\Chevee>pydoc file pydoc - the Python documentation tool pydoc.py <name> ... Show text documentation on something. <name> may be the name of a Python keyword, topic, function, module, or package, or a dotted reference to a class or function within a module or module in a package. If <name> contains a '\', it is used as the path to a Python source file to document. If name is 'keywords', 'topics', or 'modules', a listing of these things is displayed. pydoc.py -k <keyword> Search for a keyword in the synopsis lines of all available modules. pydoc.py -p <port> Start an HTTP server on the given port on the local machine. pydoc.py -g Pop up a graphical interface for finding and serving documentation. pydoc.py -w <name> ... Write out the HTML documentation for a module to a file in the current directory. If <name> contains a '\', it is treated as a filename; if it names a directory, documentation is written for all the contents. C:\Users\Chevee> EDIT: New information, pydoc works just fine in PowerShell. As a linux user, I have no idea why I'm trying to use cmd anyways--but I'd still love to figure out what's up with pydoc and cmd. EDIT 2: More new information. In cmd... c:\>python c:/python26/lib/pydoc.py file ...works just fine. Everything works just fine with just pydoc in PowerShell without me worrying about pwd, or extensions or paths.

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• Realtime Twitter Replies?

  - by ejunker

  I have created Twitter bots for many geographic locations. I want to allow users to @-reply to the Twitter bot with commands and then have the bot respond with the results. I would like to have the bot reply to the user as quickly as possible (realtime). Apparently, Twitter used to have an XMPP/Jabber interface that would provide this type of realtime feed of replies but it was shut down. As I see it my options are to use one of the following: REST API This would involve polling every X minutes for each bot. The problem with this is that it is not realtime and each Twitter account would have to be polled. Search API The search API does allow specifying a "-to" parameter in the search and replies to all bots could be aggregated in a search such as "-to bot1 OR -to bot2...". Though if you have hundreds of bots then the search string would get very long and probably exceed the maximum length of a GET request. Streaming API The streaming API looks very promising as it provides realtime results. The API allows you to specify a follow and track parameters. follow is not useful as the bot does not know who will be sending it commands. track allows you to specify keywords to track. This could possibly work by creating a daemon process that connects to the Streaming API and tracks all references to the bot's names. Once again since there are lots of bots to track the length and complexity of the query may be an issue. Another idea would be to track a special hashtag such as #botcommand and then a user could send a command using this syntax @bot1 weather #botcommand. Then by using the Streaming API to track all references to #botcommand would give you a realtime stream of all the commands. Further parsing could then be done to determine which bot to send the command to. Third-party service Are there any third-party companies that have access to the Twitter firehouse and offer realtime data? I haven't investigated these, but here are a few that I have found: Gnip Tweet.IM excla.im TwitterSpy - seems to use polling, not realtime I'm leaning towards using the Streaming API. Is there a better way to get near realtime @-replies for many (hundreds) of Twitter accounts?

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• LsaAddAccountRights not working for me

  - by SteveL

  Using: Delphi 2010 and the JEDI Windows API and JWSCL I am trying to assign the Logon As A Service privilege to a user using LsaAddAccountRights function but it does not work ie. after the function returns, checking in Group Policy Editor shows that the user still does not have the above mentioned privilege. I'm running the application on Windows XP. Would be glad if someone could point out what is wrong in my code: unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, JwaWindows, JwsclSid; type TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); private { Private declarations } public { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} function AddPrivilegeToAccount(AAccountName, APrivilege: String): DWORD; var lStatus: TNTStatus; lObjectAttributes: TLsaObjectAttributes; lPolicyHandle: TLsaHandle; lPrivilege: TLsaUnicodeString; lSid: PSID; lSidLen: DWORD; lTmpDomain: String; lTmpDomainLen: DWORD; lTmpSidNameUse: TSidNameUse; lPrivilegeWStr: String; begin ZeroMemory(@lObjectAttributes, SizeOf(lObjectAttributes)); lStatus := LsaOpenPolicy(nil, lObjectAttributes, POLICY_LOOKUP_NAMES, lPolicyHandle); if lStatus <> STATUS_SUCCESS then begin Result := LsaNtStatusToWinError(lStatus); Exit; end; try lTmpDomainLen := DNLEN; // In 'clear code' this should be get by LookupAccountName SetLength(lTmpDomain, lTmpDomainLen); lSidLen := SECURITY_MAX_SID_SIZE; GetMem(lSid, lSidLen); try if LookupAccountName(nil, PChar(AAccountName), lSid, lSidLen, PChar(lTmpDomain), lTmpDomainLen, lTmpSidNameUse) then begin lPrivilegeWStr := APrivilege; lPrivilege.Buffer := PChar(lPrivilegeWStr); lPrivilege.Length := Length(lPrivilegeWStr) * SizeOf(Char); lPrivilege.MaximumLength := lPrivilege.Length; lStatus := LsaAddAccountRights(lPolicyHandle, lSid, @lPrivilege, 1); Result := LsaNtStatusToWinError(lStatus); end else Result := GetLastError; finally FreeMem(lSid); end; finally LsaClose(lPolicyHandle); end; end; procedure TForm1.Button1Click(Sender: TObject); begin AddPrivilegeToAccount('Sam', 'SeServiceLogonRight'); end; end. Thanks in advance.

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• Strange behavior of move with strings

  - by Umair Ahmed

  I am testing some enhanced string related functions with which I am trying to use move as a way to copy strings around for faster, more efficient use without delving into pointers. While testing a function for making a delimited string from a TStringList, I encountered a strange issue. The compiler referenced the bytes contained through the index when it was empty and when a string was added to it through move, index referenced the characters contained. Here is a small downsized barebone code sample:- unit UI; interface uses System.SysUtils, System.Types, System.UITypes, System.Rtti, System.Classes, System.Variants, FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.Layouts, FMX.Memo; type TForm1 = class(TForm) Results: TMemo; procedure FormCreate(Sender: TObject); end; var Form1: TForm1; implementation {$R *.fmx} function StringListToDelimitedString ( const AStringList: TStringList; const ADelimiter: String ): String; var Str : String; Temp1 : NativeInt; Temp2 : NativeInt; DelimiterSize : Byte; begin Result := ' '; Temp1 := 0; DelimiterSize := Length ( ADelimiter ) * 2; for Str in AStringList do Temp1 := Temp1 + Length ( Str ); SetLength ( Result, Temp1 ); Temp1 := 1; for Str in AStringList do begin Temp2 := Length ( Str ) * 2; // Here Index references bytes in Result Move ( Str [1], Result [Temp1], Temp2 ); // From here the index seems to address characters instead of bytes in Result Temp1 := Temp1 + Temp2; Move ( ADelimiter [1], Result [Temp1], DelimiterSize ); Temp1 := Temp1 + DelimiterSize; end; end; procedure TForm1.FormCreate(Sender: TObject); var StrList : TStringList; Str : String; begin // Test 1 : StringListToDelimitedString StrList := TStringList.Create; Str := ''; StrList.Add ( 'Hello1' ); StrList.Add ( 'Hello2' ); StrList.Add ( 'Hello3' ); StrList.Add ( 'Hello4' ); Str := StringListToDelimitedString ( StrList, ';' ); Results.Lines.Add ( Str ); StrList.Free; end; end. Please devise a solution and if possible, some explanation. Alternatives are welcome too.

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• Can I call make runtime decided method calls in Java?

  - by Catalin Marin

  I know there is an invoke function that does the stuff, I am overall interested in the "correctness" of using such a behavior. My issue is this: I have a Service Object witch contains methods which I consider services. What I want to do is alter the behavior of those services without later intrusion. For example: class MyService { public ServiceResponse ServeMeDonuts() { do stuff... return new ServiceResponse(); } after 2 months I find out that I need to offer the same service to a new client app and I also need to do certain extra stuff like setting a flag, or make or updating certain data, or encode the response differently. What I can do is pop it up and throw down some IFs. In my opinion this is not good as it means interaction with tested code and may result in un wanted behaviour for the previous service clients. So I come and add something to my registry telling the system that the "NewClient" has a different behavior. So I'll do something like this: public interface Behavior { public void preExecute(); public void postExecute(); } public class BehaviorOfMyService implements Behavior{ String method; String clientType; public void BehaviorOfMyService(String method,String clientType) { this.method = method; this.clientType = clientType; } public void preExecute() { Method preCall = this.getClass().getMethod("pre" + this.method + this.clientType); if(preCall != null) { return preCall.invoke(); } return false; } ...same for postExecute(); public void preServeMeDonutsNewClient() { do the stuff... } } when the system will do something like this if(registrySaysThereIs different behavior set for this ServiceObject) { Class toBeCalled = Class.forName("BehaviorOf" + usedServiceObjectName); Object instance = toBeCalled.getConstructor().newInstance(method,client); instance.preExecute(); ....call the service... instance.postExecute(); .... } I am not particularly interested in correctness of code as in correctness of thinking and approach. Actually I have to do this in PHP, witch I see as a kind of Pop music of programming which I have to "sing" for commercial reasons, even though I play POP I really want to sing by the book, so putting aside my more or less inspired analogy I really want to know your opinion on this matter for it's practical necessity and technical approach. Thanks

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