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• Delay android PlusClient login request

  - by jamesakadamingo

  I am trying to implement the new PlayServices API within my android application to use a +1 button. I have it working nicely, all the expected functionality is there. However it has one rather annoying feature (seriously google!). When you instance the plusclient: mPlusClient = new PlusClient(this, this, this, Scopes.PLUS_PROFILE); Your user is presented with a "Pick your account" dialog (if they have more than one account) followed by a "grant access" dialog. I understand the need for these steps, however they really get in the way of the user experience! My initial activity (post splash screen) now has the +1 button, which means that you have to instance the PlusClient. Doing so in the onCreate() method (as google suggests) means that my user is given the "authorisation" screen before they even know what is going on! What I want to do it delay that untill they actually click the +1 button. That way they will know why they are being asked to authorise access to their account! Any ideas? I have tried using an onClick listener on the +1 button to instance but it didn't work.

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• How would you update 100+ variables if something is changed in a different class?

  - by N. Lucas

  I have a class Grid which produces a graph paper like grid on in the drawing area. I then have 5 other classes for different shapes to draw with; Line, Polygon, Ellipse, Curve, Arc Now, these 5 classes use an instance of Grid because Grid has a resolution and a scale. Inside Grid I have: public function set resolution(x:Number):void { _gap = (modBy10(x) / 10); _scale = (modBy10(x) / (this.resolution * _scale)); draw(); } public function get resolution():Number { return (_gap * 10); } public function set scale(x:Number):void { _scale = (this.resolution / x); } public function get scale():Number { return _scale; } /**/ public function scaleLength(x:Number):Number { return (x * this.scale); } public function scaleLengthDown(x:Number):Number { return (x / this.scale); } public function scaleArea(x:Number):Number { return (x / Math.pow(this.scale, 2)); } I'm just lost for a solution on how to update every instance of my 5 drawing classes when Grid is changed. For instance, Polygon is made up of multiple instances of Line, Line(length, angle) where "length" is in either in, ft, cm, or m. If the user wishes to change the scale from say 10ft per 100px resolution.. Is there an easier way than re-drawing every Line inside Polygon?

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• Entity Framework: Detect DBSchema for licensing

  - by Program.X

  We're working on a product that may or may not have differing license schema for different databases. In particular, a lower-tier product would run on SQLExpress, but we don't want the end user to be able to use a "full-fat" SQL install - benefiting from the price cut. Clearly this must also be the case for other DBs, so Oracle may command a higher price than SQL, for instance (hypothetically). We're using Entity Framework. Obviously this hides all the neatness of accessing the core schema and using sp_version or whatever it is. We'd rather not pre-load the condition by running a series of SQL commands (one for each platform) and see what comes back, as this would limit our DB options. But if necassary, we're prepared to do it. So, is it possible to get this using EF itself? DBContext.COnnection.ServerVersion only returns something like "9.00.1234" (for SQL Server 2005). I would assume (though haven't yet checked - need to install an instance) SQLExpress would return something similar - "pretending" it is full-fat. Obviously, we have no Oracle/MySQL/etc. instance so can't establish whether that returns text "Oracle" or whatever.

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• ASP.NET DynamicData: Whats happening during an update?

  - by Jens A.

  I am using ASP.NET DynamicData (based on LINQ to SQL) on my site for basic scaffolding. On one table I have added additional properties, that are not stored in the table, but are retrieved from somewhere else. (Profile information for a user account, in this case). They are displayed just fine, but when editing these values and pressing "Update", they are not changed. Here's what the properties look like, the table is the standard aspnet_Users table: public String Address { get { UserProfile profile = UserProfile.GetUserProfile(UserName); return profile.Address; } set { UserProfile profile = UserProfile.GetUserProfile(UserName); profile.Address = value; profile.Save(); } } When I fired up the debugger, I've noticed that for each update the set accessor is called three times. Once with the new value, but on a newly created instance of user, then once with the old value, again on an new instance, and finally with the old value on the existing instance. Wondering a bit, I checked with the properties created by the designer, and they, too, are called three times in (almost) the same fashion. The only difference is, that the last call contains the new value for the property. I am a bit stumped here. Why three times, and why are my new properties behaving differently? I'd be grateful for any help on that matter! =)

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• How to run stored procedures and ad-hoc scripts asynchronously with "loosely" connected SQL Server 2

  - by sanga

  Is there a way to initiate a script against an instance of SQL server when it is not connected then have it run on the instance the next time it connects? This needs to happen without any intervention from me. Background situation if you are interested: We have about 120 machines each with their own instance of SQL Server 2000. Most of them are laptops. We have merge replication set up with each one. From time to time, there is a need to delete "rogue" guids from some tables in some instances that overwrite legitimate records on the main publisher as well as perform administrative tasks via stored procedure or adhoc sql statements. The problem is there is no telling when each machine is going to be connected to the network. Some folks turn their machines completely off at the end of the day. Others disconnect their machines and take them on business trips, home for the weekend etc. Did I mention that about 35 of these machines are in utility trucks and "attempt" to sync over a wireless connection. Thanks in advance for any assistance or suggestions. Sanga

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• Rewrite C++ code into Objective C

  - by Phil_M

  Hello I got some C++ Sourcecode that I would like to rewrite into Objective C. It would help me alot if someone could write me a header file for this Code. When I get the Headerfile I would be able to rewrite the rest of the Sourcecode. It would be very nice if someone could help me please. Thanks I will poste the sourcecode here: #include <stdlib.h> #include <iostream.h> #define STATES 5 int transitionTable[STATES][STATES]; // function declarations: double randfloat (void); int chooseNextEventFromTable (int current, int table[STATES][STATES]); int chooseNextEventFromTransitionTablee (int currentState); void setTable (int value, int table[STATES][STATES]); ////////////////////////////////////////////////////////////////////////// int main(void) { int i; // for demo purposes: transitionTable[0][0] = 0; transitionTable[0][1] = 20; transitionTable[0][2] = 30; transitionTable[0][3] = 50; transitionTable[0][4] = 0; transitionTable[1][0] = 35; transitionTable[1][1] = 25; transitionTable[1][2] = 20; transitionTable[1][3] = 30; transitionTable[1][4] = 0; transitionTable[2][0] = 70; transitionTable[2][1] = 0; transitionTable[2][2] = 15; transitionTable[2][3] = 0; transitionTable[2][4] = 15; transitionTable[3][0] = 0; transitionTable[3][1] = 25; transitionTable[3][2] = 25; transitionTable[3][3] = 0; transitionTable[3][4] = 50; transitionTable[4][0] = 13; transitionTable[4][1] = 17; transitionTable[4][2] = 22; transitionTable[4][3] = 48; transitionTable[4][4] = 0; int currentState = 0; for (i=0; i<10; i++) { std::cout << currentState << " "; currentState = chooseNextEventFromTransitionTablee(currentState); } return 0; }; ////////////////////////////////////////////////////////////////////////// ////////////////////////////// // // chooseNextEventFromTransitionTable -- choose the next note. // int chooseNextEventFromTransitionTablee(int currentState) { int targetSum = 0; int sum = 0; int targetNote = 0; int totalevents = 0; int i; currentState = currentState % STATES; // remove any octave value for (i=0; i<STATES; i++) { totalevents += transitionTable[currentState][i]; } targetSum = (int)(randfloat() * totalevents + 0.5); while (targetNote < STATES && sum+transitionTable[currentState][targetNote] < targetSum) { sum += transitionTable[currentState][targetNote]; targetNote++; } return targetNote; } ////////////////////////////// // // randfloat -- returns a random number between 0.0 and 1.0. // double randfloat(void) { return (double)rand()/RAND_MAX; } ////////////////////////////// // // setTable -- set all values in the transition table to the given value. // void setTable(int value, int table[STATES][STATES]) { int i, j; for (i=0; i<STATES; i++) { for (j=0; j<STATES; j++) { table[i][j] = value; } } }

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• Unable to Connect to Management Studio Server

  - by Phil Hilliard

  I have a nasty situation. I am using Microsoft SQL Server Management Studio Express edition locally on my pc for testing, and once tested I upload database changes to a remote server. I have a situation where I deleted the Default Database on my local machine, and instead of searching hard enough to find an answer to that problem, I uninstalled and reinstalled Management Studio. Since then Management Studio has not been able to connect to the server. Is there any help (or hope for me for that matter), out there????? The following is the detailed error message: =================================== Cannot connect to LENOVO-E7A54767\SQLEXPRESS. =================================== A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) (.Net SqlClient Data Provider) ------------------------------ For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=-1&LinkId=20476 ------------------------------ Error Number: -1 Severity: 20 State: 0 ------------------------------ Program Location: at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity, SqlConnection owningObject) at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, Int64 timerExpire, SqlConnection owningObject) at System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(String host, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, Int64 timerStart) at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance) at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance) at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup) at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) at System.Data.SqlClient.SqlConnection.Open() at Microsoft.SqlServer.Management.UI.VSIntegration.ObjectExplorer.ObjectExplorer.ValidateConnection(UIConnectionInfo ci, IServerType server) at Microsoft.SqlServer.Management.UI.ConnectionDlg.Connector.ConnectionThreadUser()

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• Why can’t I create a database in an empty ASP MVC 2 project using Project->Add->New Item->SQL Server

  - by Dr Dork

  I'm diving head first into ASP MVC and am playing around with creating and manipulating a database. I did a search and found this tutorial for creating a database, however when I follow it, I get this error right at the start when trying to add a new database to my fresh, empty ASP MVC 2 project... A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) The only requirement the tutorial mentioned was SQL Server Express, but when I went to download it, it said it was already installed. I'm assuming it was part of the VS 2010 RC I installed and am running. So I don't know what else I need if I am missing something. This is all new to me, so I'm sure I'm missing something obvious here and after I'm done posting this question, I plan to do some more research into the topic of databases and how they work with ASP MVC. In the meantime, I was you could help me answer a couple high level questions... What am I missing/forgetting to do that is causing this error? Any suggestions for good resources/tutorials that focus on using databases with ASP MVC? I've done a lot of database programming in the past, so I'm familiar with the concepts of relational databases and the SQL language. I wish I could find a good resource for learning how to work with them in an ASP dev environment, as well as a good breakdown of all the related technologies used for working with them (i.e. LINQ to SQL). Thanks so much in advance for all your help! I'm going to start researching these questions right now.

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• Switching between 2 UINavigationControllers

  - by Smikey

  Hi all, I seem to have a problem switching between 2 UINavigationControllers, i.e. one which controls the main (selection) menu of my application, and the second which controls the main session (i.e. the user can't go back to the selection menu once they're started a new session). The first works just fine, but I get into trouble when trying to load the second. I have a class called GameViewController which contains the second UINavigationController instance. I set this up as usual, linking it as an IBOutlet to the delegate and setting up the NavController in the GameViewController.xib file with its 'Class' property pointing at GameScreenViewController (my main game screen), and its NIB Name property pointing to the GameScreenViewController nib file. I then create a new instance of GameViewController and load it. In IB, the navigation controller looks fine, with its View 'loaded from "GameScreenViewController"', however when the NavigationController is loaded in the game, it actually loads the GameViewController's UIWindow instance (just a blank window). I'm not sure how to make it load the Navigation Controller's view rather than its own window? Also, another quick question. When I load the second navigation controller from the first, which makes more sense to use: [self.view addSubview:gameViewController.view]; or [self presentModalViewController:gameViewController animated:YES]; Thanks for any help, much appreciated :D Michael

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• visual studio attaching to a process in debug mode

  - by user1612986

  i have a strange problem. the dll that i built (lets call it my.dll) in c++ visual studio 2010 uses a third party library (say tp.lib) which in turn calls a third party dll (say tp.dll). for debugging prupose i have in configurationProperties-debugging-command: Excel.exe and configurationProperties-debugging-commandArguments: "$(TargetPath)" in my computer i also set PATH variable to the directory where tp.dll resides now when i hit the F5 in visual studio excel opens up with my.dll and crashes giving me a "cannot open in dos mode" error. the reason this happens is tp.dll is not deployed when debug version of my.dll is deployed. when i open an instance of excel seperately and manually drop the debug version of my.dll then everything works fine and i can see all my functions that i wrote in my.dll the only issue is now i do not know how to debug becuase i do not know how to attach visual studio to the instance of excel i opened up seperately. my question is: 1 how can i attach visual studio to an already opened instance of Excel or 2 how can i hit F5 and still make Excel pick up the required tp.dll from the directory specified in the PATH variable before it starts to deploy my.dll. any of these two will allow my to step through the code for the purpose of debugging. thanks in advance.

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• Global State and Singletons Dependency injection

  - by Manu

  this is a problem i face lot of times when i am designing a new app i'll use a sample problem to explain this think i am writing simple game.so i want to hold a list of players. i have few options.. 1.use a static field in some class private static ArrayList<Player> players = new ArrayList<Integer>(); public Player getPlayer(int i){ return players.get(i); } but this a global state 2.or i can use a singleton class PlayerList{ private PlayerList instance; private PlayerList(){...} public PlayerList getInstance() { if(instance==null){ ... } return instance; } } but this is bad because it's a singleton 3.Dependency injection class Game { private PlayerList playerList; public Game(PlayerList list) { this.list = list; } public PlayerList getPlayerList() { return playerList; } } this seems good but it's not, if any object outside Game need to look at PlayerList (which is the usual case) i have to use one of the above methods to make the Game class available globally. so I just add another layer to the problem. didn't actually solve anything. what is the optimum solution ? (currently i use Singleton approach)

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• help me to parse JSON value using JSONTouch

  - by EquinoX

  I have the following json: http://www.adityaherlambang.me/webservice.php?user=2&num=10&format=json I would like to get all the name in this data by the following code, but it gives an error. How can I fix it? NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding]; NSDictionary *results = [responseString JSONValue]; NSDictionary *users = [results objectForKey:@"users"] objectForKey:@"user"]; for (NSDictionary *user in users){ //NSLog(@"key:%@, value:%@", user, [user objectForKey:user]); NSString *title = [users objectForKey:@"NAME"]; NSLog(@"%@", title); } Error: 2011-01-29 00:18:50.386 NeighborMe[7763:207] -[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0xb618840 2011-01-29 00:18:50.388 NeighborMe[7763:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0xb618840' *** Call stack at first throw: ( 0 CoreFoundation 0x027d9b99 __exceptionPreprocess + 185 1 libobjc.A.dylib 0x0292940e objc_exception_throw + 47 2 CoreFoundation 0x027db6ab -[NSObject(NSObject) doesNotRecognizeSelector:] + 187 3 CoreFoundation 0x0274b2b6 ___forwarding___ + 966 4 CoreFoundation 0x0274ae72 _CF_forwarding_prep_0 + 50 5 NeighborMe 0x0000bd75 -[NeighborListViewController connectionDidFinishLoading:] + 226 6 Foundation 0x0007cb96 -[NSURLConnection(NSURLConnectionReallyInternal) sendDidFinishLoading] + 108 7 Foundation 0x0007caef _NSURLConnectionDidFinishLoading + 133 8 CFNetwork 0x02d8d72f _ZN19URLConnectionClient23_clientDidFinishLoadingEPNS_26ClientConnectionEventQueueE + 285 9 CFNetwork 0x02e58fcf _ZN19URLConnectionClient26ClientConnectionEventQueue33processAllEventsAndConsumePayloadEP20XConnectionEventInfoI12XClientEvent18XClientEventParamsEl + 389 10 CFNetwork 0x02e5944b _ZN19URLConnectionClient26ClientConnectionEventQueue33processAllEventsAndConsumePayloadEP20XConnectionEventInfoI12XClientEvent18XClientEventParamsEl + 1537 11 CFNetwork 0x02d82968 _ZN19URLConnectionClient13processEventsEv + 100 12 CFNetwork 0x02d827e5 _ZN17MultiplexerSource7performEv + 251 13 CoreFoundation 0x027bafaf __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15 14 CoreFoundation 0x0271939b __CFRunLoopDoSources0 + 571 15 CoreFoundation 0x02718896 __CFRunLoopRun + 470 16 CoreFoundation 0x02718350 CFRunLoopRunSpecific + 208 17 CoreFoundation 0x02718271 CFRunLoopRunInMode + 97 18 GraphicsServices 0x030b800c GSEventRunModal + 217 19 GraphicsServices 0x030b80d1 GSEventRun + 115 20 UIKit 0x002e9af2 UIApplicationMain + 1160 21 NeighborMe 0x00001c34 main + 102 22 NeighborMe 0x00001bc5 start + 53 23 ??? 0x00000001 0x0 + 1 ) terminate called after throwing an instance of 'NSException' I really just wanted to be able to iterate through the names

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• UIViewController maintains state after being nilled

  - by Eric

  In my app, I made a BookViewController class that displays and animates the pages of a book and a MainMenuViewController class that displays a set of books the user can read. In the latter class, when the user taps on one of the books, a function is called that should create a completely new instance of BookViewController, but for some reason the instance maintains its state (i.e. it resumes from the page the user left off). How can this be if I set it to nil? What am I missing here? (Note that I'm using ARC). MainMenuViewController.m @interface MainMenuViewController () @property (strong) BookViewController *bookViewController; @end @implementation MainMenuViewController @synthesize bookViewController; -(void)bookTapped:(UIButton *)sender{ NSString *bookTitle; if(sender == book1button) bookTitle = @"book1"; else if(sender == book2button) bookTitle = @"book2"; bookViewController = nil; bookViewController = [[BookViewController alloc] initWithBookTitle:bookTitle]; [self presentViewController:bookViewController animated:YES completion:nil]; } BookViewController.h @interface BookViewController : UIViewController -(id)initWithBookTitle:(NSString *)bookTitle; @end BookViewController.m @implementation BookViewController -(id)initWithBookTitle:(NSString *)theBookTitle{ self = [super init]; if(self){ bookTitle = [NSString stringWithFormat:@"%@", theBookTitle]; [self setModalTransitionStyle:UIModalTransitionStyleCrossDissolve]; NSLog(@"init a BookViewController with bookTitle: %@", bookTitle); } return self; } Every time a book is tapped, bookTapped: is called, and thee console always prints: 2012-08-31 16:29:51.750 AppName[25713:c07] init a BookViewController with bookTitle: book1 So if a new instance of BookViewController is being created, how come it seems to be returning the old one?

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• Create table class as a singleton

  - by Mark

  I got a class that I use as a table. This class got an array of 16 row classes. These row classes all have 6 double variables. The values of these rows are set once and never change. Would it be a good practice to make this table a singleton? The advantage is that it cost less memory, but the table will be called from multiple threads so I have to synchronize my code which way cause a bit slower application. However lookups in this table are probably a very small portion of the total code that is executed. EDIT: This is my code, are there better ways to do this or is this a good practice? Removed synchronized keyword according to recommendations in this question. final class HalfTimeTable { private HalfTimeRow[] table = new HalfTimeRow[16]; private static final HalfTimeTable instance = new HalfTimeTable(); private HalfTimeTable() { if (instance != null) { throw new IllegalStateException("Already instantiated"); } table[0] = new HalfTimeRow(4.0, 1.2599, 0.5050, 1.5, 1.7435, 0.1911); table[1] = new HalfTimeRow(8.0, 1.0000, 0.6514, 3.0, 1.3838, 0.4295); //etc } @Override @Deprecated public Object clone() throws CloneNotSupportedException { throw new CloneNotSupportedException(); } public static HalfTimeTable getInstance() { return instance; } public HalfTimeRow getRow(int rownumber) { return table[rownumber]; } }

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• Run SQL Scripts from C# application across domains

  - by Saravanan AR

  To run sql script files from my C# application, I referred this. http://social.msdn.microsoft.com/Forums/en/adodotnetdataproviders/thread/43e8bc3a-1132-453b-b950-09427e970f31 it works perfectly when my machine and DB server are in the same domain. my problem now is, i'm executing this console application from a machine (name: X, user id: abc, domain D1). the SQL server is in another machine (name: Y, domain: D2). I use VPN to connect to machine Y with user id 'abc' and work on SQL in remote desktop. how can i run sql scripts across domains? I use this in a custom activity in my TFS build template as the last step to run the scripts in the target database which is in domain D2. i'm getting this error: "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)" is it possible to connect to the DB using the admin user ID of machine Y in domain D2?

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• 10000's+ UI elements, bind or draw?

  - by jpiccolo

  I am drawing a header for a timeline control. It looks like this: I go to 0.01 millisecond per line, so for a 10 minute timeline I am looking at drawing 60000 lines + 6000 labels. This takes a while, ~10 seconds. I would like to offload this from the UI thread. My code is currently: private void drawHeader() { Header.Children.Clear(); switch (viewLevel) { case ViewLevel.MilliSeconds100: double hWidth = Header.Width; this.drawHeaderLines(new TimeSpan(0, 0, 0, 0, 10), 100, 5, hWidth); //Was looking into background worker to off load UI //backgroundWorker = new BackgroundWorker(); //backgroundWorker.DoWork += delegate(object sender, DoWorkEventArgs args) // { // this.drawHeaderLines(new TimeSpan(0, 0, 0, 0, 10), 100, 5, hWidth); // }; //backgroundWorker.RunWorkerAsync(); break; } } private void drawHeaderLines(TimeSpan timeStep, int majorEveryXLine, int distanceBetweenLines, double headerWidth) { var currentTime = new TimeSpan(0, 0, 0, 0, 0); const int everyXLine100 = 10; double currentX = 0; var currentLine = 0; while (currentX < headerWidth) { var l = new Line { ToolTip = currentTime.ToString(@"hh\:mm\:ss\.fff"), StrokeThickness = 1, X1 = 0, X2 = 0, Y1 = 30, Y2 = 25 }; if (((currentLine % majorEveryXLine) == 0) && currentLine != 0) { l.StrokeThickness = 2; l.Y2 = 15; var textBlock = new TextBlock { Text = l.ToolTip.ToString(), FontSize = 8, FontFamily = new FontFamily("Tahoma"), Foreground = new SolidColorBrush(Color.FromRgb(255, 255, 255)) }; Canvas.SetLeft(textBlock, (currentX - 22)); Canvas.SetTop(textBlock, 0); Header.Children.Add(textBlock); } if ((((currentLine % everyXLine100) == 0) && currentLine != 0) && (currentLine % majorEveryXLine) != 0) { l.Y2 = 20; var textBlock = new TextBlock { Text = string.Format(".{0}", TimeSpan.Parse(l.ToolTip.ToString()).Milliseconds), FontSize = 8, FontFamily = new FontFamily("Tahoma"), Foreground = new SolidColorBrush(Color.FromRgb(192, 192, 192)) }; Canvas.SetLeft(textBlock, (currentX - 8)); Canvas.SetTop(textBlock, 8); Header.Children.Add(textBlock); } l.Stroke = new SolidColorBrush(Color.FromRgb(255, 255, 255)); Header.Children.Add(l); Canvas.SetLeft(l, currentX); currentX += distanceBetweenLines; currentLine++; currentTime += timeStep; } } I had looked into BackgroundWorker, except you can't create UI elements on a non-UI thread. Is it possible at all to do drawHeaderLines in a non-UI thread? Could I use data binding for drawing the lines? Would this help with UI responsiveness? I would imagine I can use databinding, but the Styling is probably beyond my current WPF ability (coming from winforms and trying to learn what all these style objects are and binding them). Would anyone be able to supply a starting point for tempting this out? Or Google a tutorial that would get me started?

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• [SOLVED]Django - Passing variables to template based on db

  - by George 'Griffin

  I am trying to add a feature to my app that would allow me to enable/disable the "Call Me" button based on whether or not I am at [home|the office]. I created a model in the database called setting, it looks like this: class setting(models.Model): key = models.CharField(max_length=200) value = models.CharField(max_length=200) Pretty simple. There is currently one row, available, the value of it is the string True. I want to be able to transparently pass variables to the templates like this: {% if available %} <!-- Display button --> {% else %} <!-- Display grayed out button --> {% endif %} Now, I could add logic to every view that would check the database, and pass the variable to the template, but I am trying to stay DRY. What is the best way to do this? UPDATE I created a context processor, and added it's path to the TEMPLATE_CONTEXT_PROCESSORS, but it is not being passed to the template def available(request): available = Setting.objects.get(key="available") if open.value == "True": return {"available":True} else: return {} UPDATE TWO If you are using the shortcut render_to_response, you need to pass an instance of RequestContext to the function. from the django documentation: If you're using Django's render_to_response() shortcut to populate a template with the contents of a dictionary, your template will be passed a Context instance by default (not a RequestContext). To use a RequestContext in your template rendering, pass an optional third argument to render_to_response(): a RequestContext instance. Your code might look like this: def some_view(request): # ... return render_to_response('my_template.html', my_data_dictionary, context_instance=RequestContext(request)) Many thanks for all the help!

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• Window manipulation and inctences control

  - by touki

  In my application there are only 2 windows — win_a & win_b, on each of these windows there is button that call another window, e.g. click on btn1 of win_a will call win_b, click on btn2 of win_b will show win_a. Desired behaviour: 1. Only one instance of object is premitted at the same time, e.g. situation, where 2 instances of win_a running at the same time is not permitted. When you click on button that calls windows that already exist this action will only change a focus to needed window. If you call a window that previously had been created, but after this has been closed this action will create a new instance of this window. E.g. there are 2 running windows. you close one of them and after try to call this window back, so related button will create it. How to write it in WPF (XAML + C#). For the moment I wrote a version that can create a lot of instances of the same window (no number of instances control implemented), but I want to see only one instance of the same window, as we can see it in a lot of applications. Example of my code: Window win = new Window(); win.Show(); Thanks.

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• grails services :: multiple projects

  - by naveen

  PROBLEM : I have multiple grails projects (lets say appA, appB and appC) : services to be precise I want to run them in a single grails-app.. probably a war deployment, how can i do this? REQUIREMENTS : I want this to be a single app since i am deploying it on cloud and i don't have enough memory to hold all these service instances individually. The reason for multiple grails project is scalability. So that if later on i want to run 10 instance of appA, 3 instance of appB, and 1 instance of aapC; i should be able to do that. EDIT : Can i use something like 0mq, will that be helpful in keeping the services separated from each other. How will i package my service? And reading the docs of 0mq seems that it can work with both inprocess and external process. Will async grails requests on HTTP work with 0mq in process/ external mq calls. Haven't used 0mq, but from the initial doc it seems to work. Need some experience calls in this scenario. Are there any other alternatives or mq alternatives?

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• Class Inside Structure

  - by Knvn

  Could some one please explain, What happens when a reference type is defined inside the value type. I write the following code: namespace ClassInsideStruct { class ClassInsideStruct { static void Main(string[] args) { ValueType ObjVal = new ValueType(10); ObjVal.Display(); ValueType.ReferenceType ObjValRef = new ValueType.ReferenceType(10); ObjValRef.Display(); Test(ObjVal, ObjValRef); ObjVal.Display(); ObjValRef.Display(); Console.ReadKey(); } private static void Test(ValueType v, ValueType.ReferenceType r) { v.SValue = 50; r.RValue = 50; } } struct ValueType { int StructNum; ReferenceType ObjRef; public ValueType(int i) { StructNum = i; ObjRef = new ReferenceType(i); } public int SValue { get { return StructNum; } set { StructNum = value; ObjRef.RValue = value; } } public void Display() { Console.WriteLine("ValueType: " + StructNum); Console.Write("ReferenceType Inside ValueType Instance: "); ObjRef.Display(); } public class ReferenceType { int ClassNum; public ReferenceType(int i) { ClassNum = i; } public void Display() { Console.WriteLine("Reference Type: " + ClassNum); } public int RValue { get { return ClassNum; } set { ClassNum = value; } } } } } Which outputs: ValueType: 10 ReferenceType Inside ValueType Instance: Reference Type: 10 Reference Type: 10 ValueType: 10 ReferenceType Inside ValueType Instance: Reference Type: 50 Reference Type: 50 I'm curious to know, after calling the method Test(ObjVal, ObjValRef), how the values of ReferenceType is changed to 50 which resides inside the ValueType who's value is not changed?

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• Changing Value of Array Pointer When Passed to a Function

  - by ZAX

  I have a function which receives both the array, and a specific instance of the array. I try to change the specific instance of the array by accessing one of its members "color", but it does not actually change it, as can be seen by debugging (checking the value of color after function runs in the main program). I am hoping someone can help me to access this member and change it. Essentially I need the instance of the array I'm specifying to be passed by reference if nothing else, but I'm hoping there is an easier way to accomplish what I'm trying to do. Here's the structures: typedef struct adjEdge{ int vertex; struct adjEdge *next; } adjEdge; typedef struct vertex{ int sink; int source; int color; //0 will be white, 1 will be grey, 5 will be black int number; adjEdge *nextVertex; } vertex; And here is the function: void walk(vertex *vertexArray, vertex v, int source, maxPairing *head) { int i; adjEdge *traverse; int moveVertex; int sink; traverse = vertexArray[v.number-1].nextVertex; if(v.color != 5 && v.sink == 5) { sink = v.number; v.color = 5; addMaxPair(head, source, sink); } else { walk(vertexArray, vertexArray[traverse->vertex-1], source, head); } } In particular, v.color needs to be changed to a 5, that way later after recursion the if condition blocks it.

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• JS best practice for member functions

  - by MickMalone1983

  I'm writing a little mobile games library, and I'm not sure the best practice for declaring member functions of instantiated function objects. For instance, I might create a simple object with one property, and a method to print it: function Foo(id){ this.id = id; this.print = function(){ console.log(this.id); }; }; However, a function which does not need access to 'private' members of the function does not need to be declared in the function at all. I could equally have written: function print(){ console.log(this.id); }; function Foo(id){ this.id = id; this.print = print; }; When the function is invoked through an instance of Foo, the instance becomes the context for this, so the output is the same in either case. I'm not entirely sure how memory is allocated with JS, and I can't find anything that I can understand about something this specific, but it seems to me that with the first example all members of Foo, including the print function, are duplicated each time it is instantiated - but with the second, it just gets a pointer to one, pre-declared function, which would save any more memory having to be allocated as more instances of Foo are created. Am I correct, and if I am, is there any memory/performance benefit to doing this?

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• Passing multiple simple POST Values to ASP.NET Web API

  - by Rick Strahl

  A few weeks backs I posted a blog post  about what does and doesn't work with ASP.NET Web API when it comes to POSTing data to a Web API controller. One of the features that doesn't work out of the box - somewhat unexpectedly -  is the ability to map POST form variables to simple parameters of a Web API method. For example imagine you have this form and you want to post this data to a Web API end point like this via AJAX: <form> Name: <input type="name" name="name" value="Rick" /> Value: <input type="value" name="value" value="12" /> Entered: <input type="entered" name="entered" value="12/01/2011" /> <input type="button" id="btnSend" value="Send" /> </form> <script type="text/javascript"> $("#btnSend").click( function() { $.post("samples/PostMultipleSimpleValues?action=kazam", $("form").serialize(), function (result) { alert(result); }); }); </script> or you might do this more explicitly by creating a simple client map and specifying the POST values directly by hand:$.post("samples/PostMultipleSimpleValues?action=kazam", { name: "Rick", value: 1, entered: "12/01/2012" }, $("form").serialize(), function (result) { alert(result); }); On the wire this generates a simple POST request with Url Encoded values in the content:POST /AspNetWebApi/samples/PostMultipleSimpleValues?action=kazam HTTP/1.1 Host: localhost User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:15.0) Gecko/20100101 Firefox/15.0.1 Accept: application/json Connection: keep-alive Content-Type: application/x-www-form-urlencoded; charset=UTF-8 X-Requested-With: XMLHttpRequest Referer: http://localhost/AspNetWebApi/FormPostTest.html Content-Length: 41 Pragma: no-cache Cache-Control: no-cachename=Rick&value=12&entered=12%2F10%2F2011 Seems simple enough, right? We are basically posting 3 form variables and 1 query string value to the server. Unfortunately Web API can't handle request out of the box. If I create a method like this:[HttpPost] public string PostMultipleSimpleValues(string name, int value, DateTime entered, string action = null) { return string.Format("Name: {0}, Value: {1}, Date: {2}, Action: {3}", name, value, entered, action); }You'll find that you get an HTTP 404 error and { "Message": "No HTTP resource was found that matches the request URI…"} Yes, it's possible to pass multiple POST parameters of course, but Web API expects you to use Model Binding for this - mapping the post parameters to a strongly typed .NET object, not to single parameters. Alternately you can also accept a FormDataCollection parameter on your API method to get a name value collection of all POSTed values. If you're using JSON only, using the dynamic JObject/JValue objects might also work. ModelBinding is fine in many use cases, but can quickly become overkill if you only need to pass a couple of simple parameters to many methods. Especially in applications with many, many AJAX callbacks the 'parameter mapping type' per method signature can lead to serious class pollution in a project very quickly. Simple POST variables are also commonly used in AJAX applications to pass data to the server, even in many complex public APIs. So this is not an uncommon use case, and - maybe more so a behavior that I would have expected Web API to support natively. The question "Why aren't my POST parameters mapping to Web API method parameters" is already a frequent one… So this is something that I think is fairly important, but unfortunately missing in the base Web API installation. Creating a Custom Parameter Binder Luckily Web API is greatly extensible and there's a way to create a custom Parameter Binding to provide this functionality! Although this solution took me a long while to find and then only with the help of some folks Microsoft (thanks Hong Mei!!!), it's not difficult to hook up in your own projects. It requires one small class and a GlobalConfiguration hookup. Web API parameter bindings allow you to intercept processing of individual parameters - they deal with mapping parameters to the signature as well as converting the parameters to the actual values that are returned. Here's the implementation of the SimplePostVariableParameterBinding class:public class SimplePostVariableParameterBinding : HttpParameterBinding { private const string MultipleBodyParameters = "MultipleBodyParameters"; public SimplePostVariableParameterBinding(HttpParameterDescriptor descriptor) : base(descriptor) { } /// <summary> /// Check for simple binding parameters in POST data. Bind POST /// data as well as query string data /// </summary> public override Task ExecuteBindingAsync(ModelMetadataProvider metadataProvider, HttpActionContext actionContext, CancellationToken cancellationToken) { // Body can only be read once, so read and cache it NameValueCollection col = TryReadBody(actionContext.Request); string stringValue = null; if (col != null) stringValue = col[Descriptor.ParameterName]; // try reading query string if we have no POST/PUT match if (stringValue == null) { var query = actionContext.Request.GetQueryNameValuePairs(); if (query != null) { var matches = query.Where(kv => kv.Key.ToLower() == Descriptor.ParameterName.ToLower()); if (matches.Count() > 0) stringValue = matches.First().Value; } } object value = StringToType(stringValue); // Set the binding result here SetValue(actionContext, value); // now, we can return a completed task with no result TaskCompletionSource<AsyncVoid> tcs = new TaskCompletionSource<AsyncVoid>(); tcs.SetResult(default(AsyncVoid)); return tcs.Task; } private object StringToType(string stringValue) { object value = null; if (stringValue == null) value = null; else if (Descriptor.ParameterType == typeof(string)) value = stringValue; else if (Descriptor.ParameterType == typeof(int)) value = int.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(Int32)) value = Int32.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(Int64)) value = Int64.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(decimal)) value = decimal.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(double)) value = double.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(DateTime)) value = DateTime.Parse(stringValue, CultureInfo.CurrentCulture); else if (Descriptor.ParameterType == typeof(bool)) { value = false; if (stringValue == "true" || stringValue == "on" || stringValue == "1") value = true; } else value = stringValue; return value; } /// <summary> /// Read and cache the request body /// </summary> /// <param name="request"></param> /// <returns></returns> private NameValueCollection TryReadBody(HttpRequestMessage request) { object result = null; // try to read out of cache first if (!request.Properties.TryGetValue(MultipleBodyParameters, out result)) { // parsing the string like firstname=Hongmei&lastname=Ge result = request.Content.ReadAsFormDataAsync().Result; request.Properties.Add(MultipleBodyParameters, result); } return result as NameValueCollection; } private struct AsyncVoid { } }   The ExecuteBindingAsync method is fired for each parameter that is mapped and sent for conversion. This custom binding is fired only if the incoming parameter is a simple type (that gets defined later when I hook up the binding), so this binding never fires on complex types or if the first type is not a simple type. For the first parameter of a request the Binding first reads the request body into a NameValueCollection and caches that in the request.Properties collection. The request body can only be read once, so the first parameter request reads it and then caches it. Subsequent parameters then use the cached POST value collection. Once the form collection is available the value of the parameter is read, and the value is translated into the target type requested by the Descriptor. SetValue writes out the value to be mapped. Once you have the ParameterBinding in place, the binding has to be assigned. This is done along with all other Web API configuration tasks at application startup in global.asax's Application_Start:GlobalConfiguration.Configuration.ParameterBindingRules .Insert(0, (HttpParameterDescriptor descriptor) => { var supportedMethods = descriptor.ActionDescriptor.SupportedHttpMethods; // Only apply this binder on POST and PUT operations if (supportedMethods.Contains(HttpMethod.Post) || supportedMethods.Contains(HttpMethod.Put)) { var supportedTypes = new Type[] { typeof(string), typeof(int), typeof(decimal), typeof(double), typeof(bool), typeof(DateTime) }; if (supportedTypes.Where(typ => typ == descriptor.ParameterType).Count() > 0) return new SimplePostVariableParameterBinding(descriptor); } // let the default bindings do their work return null; });   The ParameterBindingRules.Insert method takes a delegate that checks which type of requests it should handle. The logic here checks whether the request is POST or PUT and whether the parameter type is a simple type that is supported. Web API calls this delegate once for each method signature it tries to map and the delegate returns null to indicate it's not handling this parameter, or it returns a new parameter binding instance - in this case the SimplePostVariableParameterBinding. Once the parameter binding and this hook up code is in place, you can now pass simple POST values to methods with simple parameters. The examples I showed above should now work in addition to the standard bindings. Summary Clearly this is not easy to discover. I spent quite a bit of time digging through the Web API source trying to figure this out on my own without much luck. It took Hong Mei at Micrsoft to provide a base example as I asked around so I can't take credit for this solution :-). But once you know where to look, Web API is brilliantly extensible to make it relatively easy to customize the parameter behavior. I'm very stoked that this got resolved  - in the last two months I've had two customers with projects that decided not to use Web API in AJAX heavy SPA applications because this POST variable mapping wasn't available. This might actually change their mind to still switch back and take advantage of the many great features in Web API. I too frequently use plain POST variables for communicating with server AJAX handlers and while I could have worked around this (with untyped JObject or the Form collection mostly), having proper POST to parameter mapping makes things much easier. I said this in my last post on POST data and say it again here: I think POST to method parameter mapping should have been shipped in the box with Web API, because without knowing about this limitation the expectation is that simple POST variables map to parameters just like query string values do. I hope Microsoft considers including this type of functionality natively in the next version of Web API natively or at least as a built-in HttpParameterBinding that can be just added. This is especially true, since this binding doesn't affect existing bindings. Resources SimplePostVariableParameterBinding Source on GitHub Global.asax hookup source Mapping URL Encoded Post Values in  ASP.NET Web API© Rick Strahl, West Wind Technologies, 2005-2012Posted in Web Api  AJAX   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Move Files from a Failing PC with an Ubuntu Live CD

  - by Trevor Bekolay

  You’ve loaded the Ubuntu Live CD to salvage files from a failing system, but where do you store the recovered files? We’ll show you how to store them on external drives, drives on the same PC, a Windows home network, and other locations. We’ve shown you how to recover data like a forensics expert, but you can’t store recovered files back on your failed hard drive! There are lots of ways to transfer the files you access from an Ubuntu Live CD to a place that a stable Windows machine can access them. We’ll go through several methods, starting each section from the Ubuntu desktop – if you don’t yet have an Ubuntu Live CD, follow our guide to creating a bootable USB flash drive, and then our instructions for booting into Ubuntu. If your BIOS doesn’t let you boot using a USB flash drive, don’t worry, we’ve got you covered! Use a Healthy Hard Drive If your computer has more than one hard drive, or your hard drive is healthy and you’re in Ubuntu for non-recovery reasons, then accessing your hard drive is easy as pie, even if the hard drive is formatted for Windows. To access a hard drive, it must first be mounted. To mount a healthy hard drive, you just have to select it from the Places menu at the top-left of the screen. You will have to identify your hard drive by its size. Clicking on the appropriate hard drive mounts it, and opens it in a file browser. You can now move files to this hard drive by drag-and-drop or copy-and-paste, both of which are done the same way they’re done in Windows. Once a hard drive, or other external storage device, is mounted, it will show up in the /media directory. To see a list of currently mounted storage devices, navigate to /media by clicking on File System in a File Browser window, and then double-clicking on the media folder. Right now, our media folder contains links to the hard drive, which Ubuntu has assigned a terribly uninformative label, and the PLoP Boot Manager CD that is currently in the CD-ROM drive. Connect a USB Hard Drive or Flash Drive An external USB hard drive gives you the advantage of portability, and is still large enough to store an entire hard disk dump, if need be. Flash drives are also very quick and easy to connect, though they are limited in how much they can store. When you plug a USB hard drive or flash drive in, Ubuntu should automatically detect it and mount it. It may even open it in a File Browser automatically. Since it’s been mounted, you will also see it show up on the desktop, and in the /media folder. Once it’s been mounted, you can access it and store files on it like you would any other folder in Ubuntu. If, for whatever reason, it doesn’t mount automatically, click on Places in the top-left of your screen and select your USB device. If it does not show up in the Places list, then you may need to format your USB drive. To properly remove the USB drive when you’re done moving files, right click on the desktop icon or the folder in /media and select Safely Remove Drive. If you’re not given that option, then Eject or Unmount will effectively do the same thing. Connect to a Windows PC on your Local Network If you have another PC or a laptop connected through the same router (wired or wireless) then you can transfer files over the network relatively quickly. To do this, we will share one or more folders from the machine booted up with the Ubuntu Live CD over the network, letting our Windows PC grab the files contained in that folder. As an example, we’re going to share a folder on the desktop called ToShare. Right-click on the folder you want to share, and click Sharing Options. A Folder Sharing window will pop up. Check the box labeled Share this folder. A window will pop up about the sharing service. Click the Install service button. Some files will be downloaded, and then installed. When they’re done installing, you’ll be appropriately notified. You will be prompted to restart your session. Don’t worry, this won’t actually log you out, so go ahead and press the Restart session button. The Folder Sharing window returns, with Share this folder now checked. Edit the Share name if you’d like, and add checkmarks in the two checkboxes below the text fields. Click Create Share. Nautilus will ask your permission to add some permissions to the folder you want to share. Allow it to Add the permissions automatically. The folder is now shared, as evidenced by the new arrows above the folder’s icon. At this point, you are done with the Ubuntu machine. Head to your Windows PC, and open up Windows Explorer. Click on Network in the list on the left, and you should see a machine called UBUNTU in the right pane. Note: This example is shown in Windows 7; the same steps should work for Windows XP and Vista, but we have not tested them. Double-click on UBUNTU, and you will see the folder you shared earlier! As well as any other folders you’ve shared from Ubuntu. Double click on the folder you want to access, and from there, you can move the files from the machine booted with Ubuntu to your Windows PC. Upload to an Online Service There are many services online that will allow you to upload files, either temporarily or permanently. As long as you aren’t transferring an entire hard drive, these services should allow you to transfer your important files from the Ubuntu environment to any other machine with Internet access. We recommend compressing the files that you want to move, both to save a little bit of bandwidth, and to save time clicking on files, as uploading a single file will be much less work than a ton of little files. To compress one or more files or folders, select them, and then right-click on one of the members of the group. Click Compress…. Give the compressed file a suitable name, and then select a compression format. We’re using .zip because we can open it anywhere, and the compression rate is acceptable. Click Create and the compressed file will show up in the location selected in the Compress window. Dropbox If you have a Dropbox account, then you can easily upload files from the Ubuntu environment to Dropbox. There is no explicit limit on the size of file that can be uploaded to Dropbox, though a free account begins with a total limit of 2 GB of files in total. Access your account through Firefox, which can be opened by clicking on the Firefox logo to the right of the System menu at the top of the screen. Once into your account, press the Upload button on top of the main file list. Because Flash is not installed in the Live CD environment, you will have to switch to the basic uploader. Click Browse…find your compressed file, and then click Upload file. Depending on the size of the file, this could take some time. However, once the file has been uploaded, it should show up on any computer connected through Dropbox in a matter of minutes. Google Docs Google Docs allows the upload of any type of file – making it an ideal place to upload files that we want to access from another computer. While your total allocation of space varies (mine is around 7.5 GB), there is a per-file maximum of 1 GB. Log into Google Docs, and click on the Upload button at the top left of the page. Click Select files to upload and select your compressed file. For safety’s sake, uncheck the checkbox concerning converting files to Google Docs format, and then click Start upload. Go Online – Through FTP If you have access to an FTP server – perhaps through your web hosting company, or you’ve set up an FTP server on a different machine – you can easily access the FTP server in Ubuntu and transfer files. Just make sure you don’t go over your quota if you have one. You will need to know the address of the FTP server, as well as the login information. Click on Places > Connect to Server… Choose the FTP (with login) Service type, and fill in your information. Adding a bookmark is optional, but recommended. You will be asked for your password. You can choose to remember it until you logout, or indefinitely. You can now browse your FTP server just like any other folder. Drop files into the FTP server and you can retrieve them from any computer with an Internet connection and an FTP client. Conclusion While at first the Ubuntu Live CD environment may seem claustrophobic, it has a wealth of options for connecting to peripheral devices, local computers, and machines on the Internet – and this article has only scratched the surface. Whatever the storage medium, Ubuntu’s got an interface for it! Similar Articles Productive Geek Tips Backup Your Windows Live Writer SettingsMove a Window Without Clicking the Titlebar in UbuntuRecover Deleted Files on an NTFS Hard Drive from a Ubuntu Live CDCreate a Bootable Ubuntu USB Flash Drive the Easy WayReset Your Ubuntu Password Easily from the Live CD TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips Acronis Online Backup DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows Tech Fanboys Field Guide Check these Awesome Chrome Add-ons iFixit Offers Gadget Repair Manuals Online Vista style sidebar for Windows 7 Create Nice Charts With These Web Based Tools Track Daily Goals With 42Goals

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• Clustering Basics and Challenges

  - by Karoly Vegh

  For upcoming posts it seemed to be a good idea to dedicate some time for cluster basic concepts and theory. This post misses a lot of details that would explode the articlesize, should you have questions, do not hesitate to ask them in the comments.  The goal here is to get some concepts straight. I can't promise to give you an overall complete definitions of cluster, cluster agent, quorum, voting, fencing, split brain condition, so the following is more of an explanation. Here we go. -------- Cluster, HA, failover, switchover, scalability -------- An attempted definition of a Cluster: A cluster is a set (2+) server nodes dedicated to keep application services alive, communicating through the cluster software/framework with eachother, test and probe health status of servernodes/services and with quorum based decisions and with switchover/failover techniques keep the application services running on them available. That is, should a node that runs a service unexpectedly lose functionality/connection, the other ones would take over the and run the services, so that availability is guaranteed. To provide availability while strictly sticking to a consistent clusterconfiguration is the main goal of a cluster.  At this point we have to add that this defines a HA-cluster, a High-Availability cluster, where the clusternodes are planned to run the services in an active-standby, or failover fashion. An example could be a single instance database. Some applications can be run in a distributed or scalable fashion. In the latter case instances of the application run actively on separate clusternodes serving servicerequests simultaneously. An example for this version could be a webserver that forwards connection requests to many backend servers in a round-robin way. Or a database running in active-active RAC setup.  -------- Cluster arhitecture, interconnect, topologies -------- Now, what is a cluster made of? Servers, right. These servers (the clusternodes) need to communicate. This of course happens over the network, usually over dedicated network interfaces interconnecting all the clusternodes. These connection are called interconnects.How many clusternodes are in a cluster? There are different cluster topologies. The most simple one is a clustered pair topology, involving only two clusternodes:  There are several more topologies, clicking the image above will take you to the relevant documentation. Also, to answer the question Solaris Cluster allows you to run up to 16 servers in a cluster. Where shall these clusternodes be placed? A very important question. The right answer is: It depends on what you plan to achieve with the cluster. Do you plan to avoid only a server outage? Then you can place them right next to eachother in the datacenter. Do you need to avoid DataCenter outage? In that case of course you should place them at least in different fire zones. Or in two geographically distant DataCenters to avoid disasters like floods, large-scale fires or power outages. We call this a stretched- or campus cluster, the clusternodes being several kilometers away from eachother. To cover really large distances, you probably need to move to a GeoCluster, which is a different kind of animal.  What is a geocluster? A Geographic Cluster in Solaris Cluster terms is actually a metacluster between two, separate (locally-HA) clusters.  -------- Cluster resource types, agents, resources, resource groups -------- So how does the cluster manage my applications? The cluster needs to start, stop and probe your applications. If you application runs, the cluster needs to check regularly if the application state is healthy, does it respond over the network, does it have all the processes running, etc. This is called probing. If the cluster deems the application is in a faulty state, then it can try to restart it locally or decide to switch (stop on node A, start on node B) the service. Starting, stopping and probing are the three actions that a cluster agent does. There are many different kinds of agents included in Solaris Cluster, but you can build your own too. Examples are an agent that manages (mounts, moves) ZFS filesystems, or the Oracle DB HA agent that cares about the database, or an agent that moves a floating IP address between nodes. There are lots of other agents included for Apache, Tomcat, MySQL, Oracle DB, Oracle Weblogic, Zones, LDoms, NFS, DNS, etc.We also need to clarify the difference between a cluster resource and the cluster resource group.A cluster resource is something that is managed by a cluster agent. Cluster resource types are included in Solaris cluster (see above, e.g. HAStoragePlus, HA-Oracle, LogicalHost). You can group cluster resources into cluster resourcegroups, and switch these groups together from one node to another. To stick to the example above, to move an Oracle DB service from one node to another, you have to switch the group between nodes, and the agents of the cluster resources in the group will do the following:  On node A Shut down the DB Unconfigure the LogicalHost IP the DB Listener listens on unmount the filesystem   Then, on node B: mount the FS configure the IP  startup the DB -------- Voting, Quorum, Split Brain Condition, Fencing, Amnesia -------- How do the clusternodes agree upon their action? How do they decide which node runs what services? Another important question. Running a cluster is a strictly democratic thing.Every node has votes, and you need the majority of votes to have the deciding power. Now, this is usually no problem, clusternodes think very much all alike. Still, every action needs to be governed upon in a productive system, and has to be agreed upon. Agreeing is easy as long as the clusternodes all behave and talk to eachother over the interconnect. But if the interconnect is gone/down, this all gets tricky and confusing. Clusternodes think like this: "My job is to run these services. The other node does not answer my interconnect communication, it must be down. I'd better take control and run the services!". The problem is, as I have already mentioned, clusternodes very much think alike. If the interconnect is gone, they all assume the other node is down, and they all want to mount the data backend, enable the IP and run the database. Double IPs, double mounts, double DB instances - now that is trouble. Also, in a 2-node cluster they both have only 50% of the votes, that is, they themselves alone are not allowed to run a cluster.  This is where you need a quorum device. According to Wikipedia, the "requirement for a quorum is protection against totally unrepresentative action in the name of the body by an unduly small number of persons.". They need additional votes to run the cluster. For this requirement a 2-node cluster needs a quorum device or a quorum server. If the interconnect is gone, (this is what we call a split brain condition) both nodes start to race and try to reserve the quorum device to themselves. They do this, because the quorum device bears an additional vote, that could ensure majority (50% +1). The one that manages to lock the quorum device (e.g. if it's an FC LUN, it SCSI reserves it) wins the right to build/run a cluster, the other one - realizing he was late - panics/reboots to ensure the cluster config stays consistent.  Losing the interconnect isn't only endangering the availability of services, but it also endangers the cluster configuration consistence. Just imagine node A being down and during that the cluster configuration changes. Now node B goes down, and node A comes up. It isn't uptodate about the cluster configuration's changes so it will refuse to start a cluster, since that would lead to cluster amnesia, that is the cluster had some changes, but now runs with an older cluster configuration repository state, that is it's like it forgot about the changes.  Also, to ensure application data consistence, the clusternode that wins the race makes sure that a server that isn't part of or can't currently join the cluster can access the devices. This procedure is called fencing. This usually happens to storage LUNs via SCSI reservation.  Now, another important question: Where do I place the quorum disk?  Imagine having two sites, two separate datacenters, one in the north of the city and the other one in the south part of it. You run a stretched cluster in the clustered pair topology. Where do you place the quorum disk/server? If you put it into the north DC, and that gets hit by a meteor, you lose one clusternode, which isn't a problem, but you also lose your quorum, and the south clusternode can't keep the cluster running lacking the votes. This problem can't be solved with two sites and a campus cluster. You will need a third site to either place the quorum server to, or a third clusternode. Otherwise, lacking majority, if you lose the site that had your quorum, you lose the cluster. Okay, we covered the very basics. We haven't talked about virtualization support, CCR, ClusterFilesystems, DID devices, affinities, storage-replication, management tools, upgrade procedures - should those be interesting for you, let me know in the comments, along with any other questions. Given enough demand I'd be glad to write a followup post too. Now I really want to move on to the second part in the series: ClusterInstallation.  Oh, as for additional source of information, I recommend the documentation: http://docs.oracle.com/cd/E23623_01/index.html, and the OTN Oracle Solaris Cluster site: http://www.oracle.com/technetwork/server-storage/solaris-cluster/index.html

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