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• IIS7 + WCF + Silverlight problems

  - by Eanna

  Hey, I've been building a silverlight application and a WCF service for a while now and recently tried to host them in IIS7. I installed IIS7 on Windows Server 2008 R2 and added these two application to my default website. I am having a number of problems so im hoping one of you can help out... 1) The silverlight and WCF service applications do not work with pass-through authentication. I need to "connect as" the administrator server account when setting up the application. I read online that you should only need to use the "connect as" field when you are connecting to another computer. If i dont supply the admin credentials i get this error. Do i have to set up permissions somewhere else? HTTP Error 500.19 - Internal Server Error The requested page cannot be accessed because the related configuration data for the page is invalid. Detailed Error Information Module IIS Web Core Notification BeginRequest Handler Not yet determined Error Code 0x80070005 Config Error Cannot read configuration file due to insufficient permissions Config File \?\C:\Users\Administrator\Documents\My Dropbox\Research Masters\Project\WCFService\Website\web.config Requested URL http:://localhost:80/WCFService/Service.svc Physical Path C:\Users\Administrator\Documents\My Dropbox\Research Masters\Project\WCFService\Website\Service.svc Logon Method Not yet determined Logon User Not yet determined Config Source -1: 0: Links and More Information This error occurs when there is a problem reading the configuration file for the Web server or Web application. In some cases, the event logs may contain more information about what caused this error. 2) Visual studio generated 2 webpages to run my silverlight application (.html and .aspx). When I am running the silverlight application (connected as admin) I can navigate to the .html page, no problem. When I try to open the .aspx file i get the following error Server Error in '/Platform' Application. Access is denied. Description: An error occurred while accessing the resources required to serve this request. You might not have permission to view the requested resources. Error message 401.3: You do not have permission to view this directory or page using the credentials you supplied (access denied due to Access Control Lists). Ask the Web server's administrator to give you access to 'C:\Users\Administrator\Documents\My Dropbox\Research Masters\Project\Platform\Website\PlatformTestPage.aspx'. Version Information: Microsoft .NET Framework Version:4.0.30128; ASP.NET Version:4.0.30128.1 3) The WCF service runs fine (again, connected as admin) until i restart the server. When i try to run the WCF service after a reboot, the mysql assembly seems to be missing from the solution. If i just rebuilt the solution and run the service again... it works (until next restart). Whats causing this error? Solution here - http://tinypic.com/view.php?pic=5yasqx&s=5 Server Error in '/WCFService' Application. Could not load file or assembly 'MySql.Data, Version=6.2.2.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' or one of its dependencies. Access is denied. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.IO.FileLoadException: Could not load file or assembly 'MySql.Data, Version=6.2.2.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' or one of its dependencies. Access is denied. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Assembly Load Trace: The following information can be helpful to determine why the assembly 'MySql.Data, Version=6.2.2.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' could not be loaded. WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog]. Stack Trace: [FileLoadException: Could not load file or assembly 'MySql.Data, Version=6.2.2.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' or one of its dependencies. Access is denied.] System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0 System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection, Boolean suppressSecurityChecks) +567 System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +192 System.Reflection.Assembly.Load(String assemblyString) +35 System.ServiceModel.Activation.ServiceHostFactory.CreateServiceHost(String constructorString, Uri[] baseAddresses) +243 System.ServiceModel.HostingManager.CreateService(String normalizedVirtualPath) +1423 System.ServiceModel.HostingManager.ActivateService(String normalizedVirtualPath) +50 System.ServiceModel.HostingManager.EnsureServiceAvailable(String normalizedVirtualPath) +1132 [ServiceActivationException: The service '/WCFService/Service.svc' cannot be activated due to an exception during compilation. The exception message is: Could not load file or assembly 'MySql.Data, Version=6.2.2.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d' or one of its dependencies. Access is denied..] System.Runtime.AsyncResult.End(IAsyncResult result) +889824 System.ServiceModel.Activation.HostedHttpRequestAsyncResult.End(IAsyncResult result) +179150 System.Web.AsyncEventExecutionStep.OnAsyncEventCompletion(IAsyncResult ar) +107 Version Information: Microsoft .NET Framework Version:4.0.30128; ASP.NET Version:4.0.30128.1 Thats about it, hope someone reads this message, I wasted most of the weekend trying to fix these problems on my own... thanks

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• Drupal Migration Problem

  - by Gok Demir

  After migrating my Drupal (6.16) installation from shared hosting to Linode VPS (Ubunto 10.04 32 bit). Whenever I click a URL it shows only the homepage. I put ?q=user at the end of the URL to login as an admin. When I logged in it is the same. I couldn't navigate to any URL. It shows only homepage. I forgot to clean Drupal cache before migration. Is it because of this? I couldn't navigate to Administer Site configuration Performance to clean cache, nothing works. By the way .htaccess Rewrite on enabled as shown below. apache2 apache2-doc apache2-utils libapache2-mod-php5 php5 php-pear php5-xcache php5-suhosin php5-mysql packages are installed. What can I do? # # Apache/PHP/Drupal settings: # # Protect files and directories from prying eyes. <FilesMatch "\.(engine|inc|info|install|make|module|profile|test|po|sh|.*sql|theme|tpl(\.php)?|xtmpl|svn-base)$|^(code-style\.pl|Entries.*|Repository|Root|Tag|Template|all-wcprops|entries|format)$"> Order allow,deny </FilesMatch> # Don't show directory listings for URLs which map to a directory. Options -Indexes # Follow symbolic links in this directory. Options +FollowSymLinks # Make Drupal handle any 404 errors. ErrorDocument 404 /index.php # Force simple error message for requests for non-existent favicon.ico. <Files favicon.ico> # There is no end quote below, for compatibility with Apache 1.3. ErrorDocument 404 "The requested file favicon.ico was not found. </Files> # Set the default handler. DirectoryIndex index.php # Override PHP settings. More in sites/default/settings.php # but the following cannot be changed at runtime. # PHP 4, Apache 1. <IfModule mod_php4.c> php_value magic_quotes_gpc 0 php_value register_globals 0 php_value session.auto_start 0 php_value mbstring.http_input pass php_value mbstring.http_output pass php_value mbstring.encoding_translation 0 </IfModule> # PHP 4, Apache 2. <IfModule sapi_apache2.c> php_value magic_quotes_gpc 0 php_value register_globals 0 php_value session.auto_start 0 php_value mbstring.http_input pass php_value mbstring.http_output pass php_value mbstring.encoding_translation 0 </IfModule> # PHP 5, Apache 1 and 2. <IfModule mod_php5.c> php_value magic_quotes_gpc 0 php_value register_globals 0 php_value session.auto_start 0 php_value mbstring.http_input pass php_value mbstring.http_output pass php_value mbstring.encoding_translation 0 </IfModule> # Requires mod_expires to be enabled. <IfModule mod_expires.c> # Enable expirations. ExpiresActive On # Cache all files for 2 weeks after access (A). ExpiresDefault A1209600 <FilesMatch \.php$> # Do not allow PHP scripts to be cached unless they explicitly send cache # headers themselves. Otherwise all scripts would have to overwrite the # headers set by mod_expires if they want another caching behavior. This may # fail if an error occurs early in the bootstrap process, and it may cause # problems if a non-Drupal PHP file is installed in a subdirectory. ExpiresActive Off </FilesMatch> </IfModule> # Various rewrite rules. <IfModule mod_rewrite.c> RewriteEngine on # If your site can be accessed both with and without the 'www.' prefix, you # can use one of the following settings to redirect users to your preferred # URL, either WITH or WITHOUT the 'www.' prefix. Choose ONLY one option: # # To redirect all users to access the site WITH the 'www.' prefix, # (http://example.com/... will be redirected to http://www.example.com/...) # adapt and uncomment the following: # RewriteCond %{HTTP_HOST} ^example\.com$ [NC] # RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301] # # To redirect all users to access the site WITHOUT the 'www.' prefix, # (http://www.example.com/... will be redirected to http://example.com/...) # uncomment and adapt the following: # RewriteCond %{HTTP_HOST} ^www\.example\.com$ [NC] # RewriteRule ^(.*)$ http://example.com/$1 [L,R=301] # Modify the RewriteBase if you are using Drupal in a subdirectory or in a # VirtualDocumentRoot and the rewrite rules are not working properly. # For example if your site is at http://example.com/drupal uncomment and # modify the following line: # RewriteBase /drupal # # If your site is running in a VirtualDocumentRoot at http://example.com/, # uncomment the following line: # RewriteBase / # Rewrite URLs of the form 'x' to the form 'index.php?q=x'. RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_URI} !=/favicon.ico RewriteRule ^(.*)$ index.php?q=$1 [L,QSA] </IfModule>

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• Boost::Interprocess Container Container Resizing No Default Constructor

  - by CuppM

  Hi, After combing through the Boost::Interprocess documentation and Google searches, I think I've found the reason/workaround to my issue. Everything I've found, as I understand it, seems to be hinting at this, but doesn't come out and say "do this because...". But if anyone can verify this I would appreciate it. I'm writing a series of classes that represent a large lookup of information that is stored in memory for fast performance in a parallelized application. Because of the size of data and multiple processes that run at a time on one machine, we're using Boost::Interprocess for shared memory to have a single copy of the structures. I looked at the Boost::Interprocess documentation and examples, and they typedef classes for shared memory strings, string vectors, int vector vectors, etc. And when they "use" them in their examples, they just construct them passing the allocator and maybe insert one item that they've constructed elsewhere. Like on this page: http://www.boost.org/doc/libs/1_42_0/doc/html/interprocess/allocators_containers.html So following their examples, I created a header file with typedefs for shared memory classes: namespace shm { namespace bip = boost::interprocess; // General/Utility Types typedef bip::managed_shared_memory::segment_manager segment_manager_t; typedef bip::allocator<void, segment_manager_t> void_allocator; // Integer Types typedef bip::allocator<int, segment_manager_t> int_allocator; typedef bip::vector<int, int_allocator> int_vector; // String Types typedef bip::allocator<char, segment_manager_t> char_allocator; typedef bip::basic_string<char, std::char_traits<char>, char_allocator> string; typedef bip::allocator<string, segment_manager_t> string_allocator; typedef bip::vector<string, string_allocator> string_vector; typedef bip::allocator<string_vector, segment_manager_t> string_vector_allocator; typedef bip::vector<string_vector, string_vector_allocator> string_vector_vector; } Then for one of my lookup table classes, it's defined something like this: class Details { public: Details(const shm::void_allocator & alloc) : m_Ids(alloc), m_Labels(alloc), m_Values(alloc) { } ~Details() {} int Read(BinaryReader & br); private: shm::int_vector m_Ids; shm::string_vector m_Labels; shm::string_vector_vector m_Values; }; int Details::Read(BinaryReader & br) { int num = br.ReadInt(); m_Ids.resize(num); m_Labels.resize(num); m_Values.resize(num); for (int i = 0; i < num; i++) { m_Ids[i] = br.ReadInt(); m_Labels[i] = br.ReadString().c_str(); int count = br.ReadInt(); m_Value[i].resize(count); for (int j = 0; j < count; j++) { m_Value[i][j] = br.ReadString().c_str(); } } } But when I compile it, I get the error: 'boost::interprocess::allocator<T,SegmentManager>::allocator' : no appropriate default constructor available And it's due to the resize() calls on the vector objects. Because the allocator types do not have a empty constructor (they take a const segment_manager_t &) and it's trying to create a default object for each location. So in order for it to work, I have to get an allocator object and pass a default value object on resize. Like this: int Details::Read(BinaryReader & br) { shm::void_allocator alloc(m_Ids.get_allocator()); int num = br.ReadInt(); m_Ids.resize(num); m_Labels.resize(num, shm::string(alloc)); m_Values.resize(num, shm::string_vector(alloc)); for (int i = 0; i < num; i++) { m_Ids[i] = br.ReadInt(); m_Labels[i] = br.ReadString().c_str(); int count = br.ReadInt(); m_Value[i].resize(count, shm::string(alloc)); for (int j = 0; j < count; j++) { m_Value[i][j] = br.ReadString().c_str(); } } } Is this the best/correct way of doing it? Or am I missing something. Thanks!

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• Big smart ViewModels, dumb Views, and any model, the best MVVM approach?

  - by Edward Tanguay

  The following code is a refactoring of my previous MVVM approach (Fat Models, skinny ViewModels and dumb Views, the best MVVM approach?) in which I moved the logic and INotifyPropertyChanged implementation from the model back up into the ViewModel. This makes more sense, since as was pointed out, you often you have to use models that you either can't change or don't want to change and so your MVVM approach should be able to work with any model class as it happens to exist. This example still allows you to view the live data from your model in design mode in Visual Studio and Expression Blend which I think is significant since you could have a mock data store that the designer connects to which has e.g. the smallest and largest strings that the UI can possibly encounter so that he can adjust the design based on those extremes. Questions: I'm a bit surprised that I even have to "put a timer" in my ViewModel since it seems like that is a function of INotifyPropertyChanged, it seems redundant, but it was the only way I could get the XAML UI to constantly (once per second) reflect the state of my model. So it would be interesting to hear anyone who may have taken this approach if you encountered any disadvantages down the road, e.g. with threading or performance. The following code will work if you just copy the XAML and code behind into a new WPF project. XAML: <Window x:Class="TestMvvm73892.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:TestMvvm73892" Title="Window1" Height="300" Width="300"> <Window.Resources> <ObjectDataProvider x:Key="DataSourceCustomer" ObjectType="{x:Type local:CustomerViewModel}" MethodName="GetCustomerViewModel"/> </Window.Resources> <DockPanel DataContext="{StaticResource DataSourceCustomer}"> <StackPanel DockPanel.Dock="Top" Orientation="Horizontal"> <TextBlock Text="{Binding Path=FirstName}"/> <TextBlock Text=" "/> <TextBlock Text="{Binding Path=LastName}"/> </StackPanel> <StackPanel DockPanel.Dock="Top" Orientation="Horizontal"> <TextBlock Text="{Binding Path=TimeOfMostRecentActivity}"/> </StackPanel> </DockPanel> </Window> Code Behind: using System; using System.Windows; using System.ComponentModel; using System.Threading; namespace TestMvvm73892 { public partial class Window1 : Window { public Window1() { InitializeComponent(); } } //view model public class CustomerViewModel : INotifyPropertyChanged { private string _firstName; private string _lastName; private DateTime _timeOfMostRecentActivity; private Timer _timer; public string FirstName { get { return _firstName; } set { _firstName = value; this.RaisePropertyChanged("FirstName"); } } public string LastName { get { return _lastName; } set { _lastName = value; this.RaisePropertyChanged("LastName"); } } public DateTime TimeOfMostRecentActivity { get { return _timeOfMostRecentActivity; } set { _timeOfMostRecentActivity = value; this.RaisePropertyChanged("TimeOfMostRecentActivity"); } } public CustomerViewModel() { _timer = new Timer(CheckForChangesInModel, null, 0, 1000); } private void CheckForChangesInModel(object state) { Customer currentCustomer = CustomerViewModel.GetCurrentCustomer(); MapFieldsFromModeltoViewModel(currentCustomer, this); } public static CustomerViewModel GetCustomerViewModel() { CustomerViewModel customerViewModel = new CustomerViewModel(); Customer currentCustomer = CustomerViewModel.GetCurrentCustomer(); MapFieldsFromModeltoViewModel(currentCustomer, customerViewModel); return customerViewModel; } public static void MapFieldsFromModeltoViewModel(Customer model, CustomerViewModel viewModel) { viewModel.FirstName = model.FirstName; viewModel.LastName = model.LastName; viewModel.TimeOfMostRecentActivity = model.TimeOfMostRecentActivity; } public static Customer GetCurrentCustomer() { return Customer.GetCurrentCustomer(); } //INotifyPropertyChanged implementation public event PropertyChangedEventHandler PropertyChanged; private void RaisePropertyChanged(string property) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(property)); } } } //model public class Customer { public string FirstName { get; set; } public string LastName { get; set; } public DateTime TimeOfMostRecentActivity { get; set; } public static Customer GetCurrentCustomer() { return new Customer { FirstName = "Jim", LastName = "Smith", TimeOfMostRecentActivity = DateTime.Now }; } } }

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• Random Page Cost and Planning

  - by Dave Jarvis

  A query (see below) that extracts climate data from weather stations within a given radius of a city using the dates for which those weather stations actually have data. The query uses the table's only index, rather effectively: CREATE UNIQUE INDEX measurement_001_stc_idx ON climate.measurement_001 USING btree (station_id, taken, category_id); Reducing the server's configuration value for random_page_cost from 2.0 to 1.1 had a massive performance improvement for the given range (nearly an order of magnitude) because it suggested to PostgreSQL that it should use the index. While the results now return in 5 seconds (down from ~85 seconds), problematic lines remain. Bumping the query's end date by a single year causes a full table scan: sc.taken_start >= '1900-01-01'::date AND sc.taken_end <= '1997-12-31'::date AND How do I persuade PostgreSQL to use the indexes regardless of years between the two dates? (A full table scan against 43 million rows is probably not the best plan.) Find the EXPLAIN ANALYSE results below the query. Thank you! Query SELECT extract(YEAR FROM m.taken) AS year, avg(m.amount) AS amount FROM climate.city c, climate.station s, climate.station_category sc, climate.measurement m WHERE c.id = 5182 AND earth_distance( ll_to_earth(c.latitude_decimal,c.longitude_decimal), ll_to_earth(s.latitude_decimal,s.longitude_decimal)) / 1000 <= 30 AND s.elevation BETWEEN 0 AND 3000 AND s.applicable = TRUE AND sc.station_id = s.id AND sc.category_id = 1 AND sc.taken_start >= '1900-01-01'::date AND sc.taken_end <= '1996-12-31'::date AND m.station_id = s.id AND m.taken BETWEEN sc.taken_start AND sc.taken_end AND m.category_id = sc.category_id GROUP BY extract(YEAR FROM m.taken) ORDER BY extract(YEAR FROM m.taken) 1900 to 1996: Index "Sort (cost=1348597.71..1348598.21 rows=200 width=12) (actual time=2268.929..2268.935 rows=92 loops=1)" " Sort Key: (date_part('year'::text, (m.taken)::timestamp without time zone))" " Sort Method: quicksort Memory: 32kB" " -> HashAggregate (cost=1348586.56..1348590.06 rows=200 width=12) (actual time=2268.829..2268.886 rows=92 loops=1)" " -> Nested Loop (cost=0.00..1344864.01 rows=744510 width=12) (actual time=0.807..2084.206 rows=134893 loops=1)" " Join Filter: ((m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (sc.station_id = m.station_id))" " -> Nested Loop (cost=0.00..12755.07 rows=1220 width=18) (actual time=0.502..521.937 rows=23 loops=1)" " Join Filter: ((sec_to_gc(cube_distance((ll_to_earth((c.latitude_decimal)::double precision, (c.longitude_decimal)::double precision))::cube, (ll_to_earth((s.latitude_decimal)::double precision, (s.longitude_decimal)::double precision))::cube)) / 1000::double precision) <= 30::double precision)" " -> Index Scan using city_pkey1 on city c (cost=0.00..2.47 rows=1 width=16) (actual time=0.014..0.015 rows=1 loops=1)" " Index Cond: (id = 5182)" " -> Nested Loop (cost=0.00..9907.73 rows=3659 width=34) (actual time=0.014..28.937 rows=3458 loops=1)" " -> Seq Scan on station_category sc (cost=0.00..970.20 rows=3659 width=14) (actual time=0.008..10.947 rows=3458 loops=1)" " Filter: ((taken_start >= '1900-01-01'::date) AND (taken_end <= '1996-12-31'::date) AND (category_id = 1))" " -> Index Scan using station_pkey1 on station s (cost=0.00..2.43 rows=1 width=20) (actual time=0.004..0.004 rows=1 loops=3458)" " Index Cond: (s.id = sc.station_id)" " Filter: (s.applicable AND (s.elevation >= 0) AND (s.elevation <= 3000))" " -> Append (cost=0.00..1072.27 rows=947 width=18) (actual time=6.996..63.199 rows=5865 loops=23)" " -> Seq Scan on measurement m (cost=0.00..25.00 rows=6 width=22) (actual time=0.000..0.000 rows=0 loops=23)" " Filter: (m.category_id = 1)" " -> Bitmap Heap Scan on measurement_001 m (cost=20.79..1047.27 rows=941 width=18) (actual time=6.995..62.390 rows=5865 loops=23)" " Recheck Cond: ((m.station_id = sc.station_id) AND (m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (m.category_id = 1))" " -> Bitmap Index Scan on measurement_001_stc_idx (cost=0.00..20.55 rows=941 width=0) (actual time=5.775..5.775 rows=5865 loops=23)" " Index Cond: ((m.station_id = sc.station_id) AND (m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (m.category_id = 1))" "Total runtime: 2269.264 ms" 1900 to 1997: Full Table Scan "Sort (cost=1370192.26..1370192.76 rows=200 width=12) (actual time=86165.797..86165.809 rows=94 loops=1)" " Sort Key: (date_part('year'::text, (m.taken)::timestamp without time zone))" " Sort Method: quicksort Memory: 32kB" " -> HashAggregate (cost=1370181.12..1370184.62 rows=200 width=12) (actual time=86165.654..86165.736 rows=94 loops=1)" " -> Hash Join (cost=4293.60..1366355.81 rows=765061 width=12) (actual time=534.786..85920.007 rows=139721 loops=1)" " Hash Cond: (m.station_id = sc.station_id)" " Join Filter: ((m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end))" " -> Append (cost=0.00..867005.80 rows=43670150 width=18) (actual time=0.009..79202.329 rows=43670079 loops=1)" " -> Seq Scan on measurement m (cost=0.00..25.00 rows=6 width=22) (actual time=0.001..0.001 rows=0 loops=1)" " Filter: (category_id = 1)" " -> Seq Scan on measurement_001 m (cost=0.00..866980.80 rows=43670144 width=18) (actual time=0.008..73312.008 rows=43670079 loops=1)" " Filter: (category_id = 1)" " -> Hash (cost=4277.93..4277.93 rows=1253 width=18) (actual time=534.704..534.704 rows=25 loops=1)" " -> Nested Loop (cost=847.87..4277.93 rows=1253 width=18) (actual time=415.837..534.682 rows=25 loops=1)" " Join Filter: ((sec_to_gc(cube_distance((ll_to_earth((c.latitude_decimal)::double precision, (c.longitude_decimal)::double precision))::cube, (ll_to_earth((s.latitude_decimal)::double precision, (s.longitude_decimal)::double precision))::cube)) / 1000::double precision) <= 30::double precision)" " -> Index Scan using city_pkey1 on city c (cost=0.00..2.47 rows=1 width=16) (actual time=0.012..0.014 rows=1 loops=1)" " Index Cond: (id = 5182)" " -> Hash Join (cost=847.87..1352.07 rows=3760 width=34) (actual time=6.427..35.107 rows=3552 loops=1)" " Hash Cond: (s.id = sc.station_id)" " -> Seq Scan on station s (cost=0.00..367.25 rows=7948 width=20) (actual time=0.004..23.529 rows=7949 loops=1)" " Filter: (applicable AND (elevation >= 0) AND (elevation <= 3000))" " -> Hash (cost=800.87..800.87 rows=3760 width=14) (actual time=6.416..6.416 rows=3552 loops=1)" " -> Bitmap Heap Scan on station_category sc (cost=430.29..800.87 rows=3760 width=14) (actual time=2.316..5.353 rows=3552 loops=1)" " Recheck Cond: (category_id = 1)" " Filter: ((taken_start >= '1900-01-01'::date) AND (taken_end <= '1997-12-31'::date))" " -> Bitmap Index Scan on station_category_station_category_idx (cost=0.00..429.35 rows=6376 width=0) (actual time=2.268..2.268 rows=6339 loops=1)" " Index Cond: (category_id = 1)" "Total runtime: 86165.936 ms"

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• Am I crazy? (How) should I create a jQuery content editor?

  - by Brendon Muir

  Ok, so I created a CMS mainly aimed at Primary Schools. It's getting fairly popular in New Zealand but the one thing I hate with a passion is the largely bad quality of in browser WYSIWYG editors. I've been using KTML (made by InterAKT which was purchased by Adobe a few years ago). In my opinion this editor does a lot of great things (image editing/management, thumbnailing and pretty good content editing). Unfortunately time has had its nasty way with this product and new browsers are beginning to break features and generally degrade the performance of this tool. It's also quite scary basing my livelihood on a defunct product! I've been hunting, in fact I regularly hunt around to see if anything has changed in the WYSIWYG arena. The closest thing I've seen that excites me is the WYSIHAT framework, but they've decided to ignore a pretty relevant editing paradigm which I'm going to outline below. This is the idea for my proposed editor, and I don't know of any existing products that can do this properly: Right, so the traditional model for editing let's say a Page in a CMS is to log into a 'back end' and click edit on the page. This will then load another screen with the editor in it and perhaps a few other fields. More advanced CMS's will maybe have several editing boxes that are for different portions of the page. Anyway, the big problem with this way of doing things is that the user is editing a document outside of the final context it will appear in. In the simplest terms, this means the page template. Many things can be wrong, e.g. the with of the editing area might be different to the width of the actual template area. The height is nearly always fixed because existing editors always seem to use IFRAMES for backward compatibility. And there are plenty of other beefs which I'm sure you're quite aware of if you're in this development area. Here's my editor utopia: You click 'Edit Page': The actual page (with its actual template) displays. Portions of the page have been marked as editable via a class name. You click on one of these areas (in my case it'd just be the big 'body' area in the middle of the template) and a editing bar drops down from the top of the screen with all your standard controls (bold, italic, insert image etc...). Iframes are never used, instead we rely on setting contentEditable to true on the DIV's in question. Firefox 2 and IE6 can go away, let's move on. You can edit the page knowing exactly how it will look when you save it. Because all the styles for this template are loaded, your headings will look correct, everything will be just dandy. Is this such a radical concept? Why are we still content with TinyMCE and that other editor that is too embarrassing to use because it sounds like a swear word!? Let's face the facts: I'm a JavaScript novice. I did once play around in this area using the Javascript Anthology from SitePoint as a guide. It was quite a cool learning experience, but they of course used the IFRAME to make their lives easier. I tried to go a different route and just use contentEditable and even tried to sidestep the native content editing routines (execCommand) and instead wrote my own. They kind of worked but there were always issues. Now we have jQuery, and a few libraries that abstract things like IE's lack of Range support. I'm wondering, am I crazy, or is it actually a good idea to try and build an editor around this editing paradigm using jQuery and relevant plugins to make the job easier? My actual questions: Where would you start? What plugins do you know of that would help the most? Is it worth it, or is there a magical project that already exists that I should join in on? What are the biggest hurdles to overcome in a project like this? Am I crazy? I hope this question has been posted on the right board. I figured it is a technical question as I'm wanting to know specific hurdles and pitfalls to watch out for and also if it is technically feasible with todays technology. Looking forward to hearing peoples thoughts and opinions.

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• Need some help understanding IO Statistics

  - by Abe Miessler

  I have a query that has a very costly INDEX SEEK operation in the execution plan. In order to track down the cause i set IO STATISTICS on and ran it. In the problem section it gave the following statistics: Table '#TempStudents_Enrollment2_____________________________________000000004D5F'. Scan count 0, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#TempRace2______________________________________________000000004D58'. Scan count 1, logical reads 1, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'RefRace'. Scan count 120, logical reads 240, physical reads 1, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'RefFedEnctyRaceCatg'. Scan count 18, logical reads 36, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#43B0BA0F'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#42BC95D6'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#41C8719D'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#40D44D64'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#LEA2_________________________________________________000000004D56'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#39332B9C'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#School2________________________________________________000000004D57'. Scan count 1, logical reads 29164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#GenderKey______________________________________________000000004D5A'. Scan count 1, logical reads 29164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#LangAcqKey_____________________________________________000000004D5B'. Scan count 1, logical reads 29164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#TransferCatKey___________________________________________000000004D5C'. Scan count 1, logical reads 29164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#ResCatKey______________________________________________000000004D5D'. Scan count 1, logical reads 29164, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'RPT_SnapShot_1_4_StuPgm_Denorm'. Scan count 2344954, logical reads 4992518, physical reads 16, read-ahead reads 8, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#3FE0292B'. Scan count 1, logical reads 2344954, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table 'RPT_SnapShot_1_4_StuEnrlmt_Denorm'. Scan count 20, logical reads 87679, physical reads 0, read-ahead reads 87425, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. Table '#GradeKey_______________________________________________000000004D59'. Scan count 1, logical reads 1, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0. What should I look for in here when i'm looking to improve the performance? The line with over 2 million for the Scan count looked suspicious to me but I really don't know. Does anyone see anything here that i should look into in more detail?

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• Convert XML namespace prefixes with C#?

  - by jrista

  I have run into an exasperating problem getting a Java service client to communicate successfully with a WCF service. I have overcome many hurdles, and I believe that this is my last one. The problem boils down to how Java Axis + WSS4J seem to handle xml namespaces. The Java platform seem to be very rigid in what they expect for xml namespace prefixes, and as such, do not understand the WCF reply messages. My problem in a nutshell is as follows. I have an xml response similar to the following from my WCF service: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" xmlns:a="http://www.w3.org/2005/08/addressing" xmlns:u="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"> <s:Header> <a:Action s:mustUnderstand="1" u:Id="_3">http://tempuri.org/IProcessor/DoProcessingResponse</a:Action> <h:CorrelationID xmlns:h="http://tempuri.org/">1234</h:CorrelationID> <a:RelatesTo u:Id="_4">uuid:40f800a0-9613-4f4a-96c5-b9fd98085deb</a:RelatesTo> <o:Security s:mustUnderstand="1" xmlns:o="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"> <!-- WS-Security header stuff --> </o:Security> </s:Header> <s:Body u:Id="_1"> <e:EncryptedData Id="_2" Type="http://www.w3.org/2001/04/xmlenc#Content" xmlns:e="http://www.w3.org/2001/04/xmlenc#"> <e:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/> <e:CipherData> <e:CipherValue>NfA6XunmyLlT2ucA+5QneoawHm+imcaCltDAJC1mRZOSxoB6YGpDLY1FyVykPbPGDoFGUESLsmvvbD62sNnRrgE+AuKPo+1CD3DF4LfurRcEv9A50ba9V+ViqlrhydhK</e:CipherValue> </e:CipherData> </e:EncryptedData> </s:Body> </s:Envelope> This response uses simple one-character namespace prefixes for most things, such as 's' for SOAP Envelope, 'a' for WS-Addressing, 'o' for 'WS-Security', etc. The Java client, namely WSS4J, seems to expect the following: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://www.w3.org/2005/08/addressing" xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"> <soap:Header> <wsa:Action soap:mustUnderstand="1" wsu:Id="_3">http://tempuri.org/IProcessor/DoProcessingResponse</wsa:Action> <h:CorrelationID xmlns:h="http://tempuri.org/">1234</h:CorrelationID> <wsa:RelatesTo wsu:Id="_4">uuid:40f800a0-9613-4f4a-96c5-b9fd98085deb</a:RelatesTo> <wsse:Security soap:mustUnderstand="1" xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd"> <!-- WS-Security header stuff --> </wsse:Security> </soap:Header> <soap:Body u:Id="_1"> <xenc:EncryptedData Id="_2" Type="http://www.w3.org/2001/04/xmlenc#Content" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"> <xenc:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes128-cbc"/> <xenc:CipherData> <xenc:CipherValue>NfA6XunmyLlT2ucA+5QneoawHm+imcaCltDAJC1mRZOSxoB6YGpDLY1FyVykPbPGDoFGUESLsmvvbD62sNnRrgE+AuKPo+1CD3DF4LfurRcEv9A50ba9V+ViqlrhydhK</xenc:CipherValue> </xenc:CipherData> </xenc:EncryptedData> </soap:Body> </soap:Envelope> Upon receipt of my response message, the Java client and WSS4J seem to want to look up elements by their own internal xml aliases, such as 'wsa' for WS-Addressing, and 'wsse' for WS-Security Extensions. Since neither of those namespaces are present in the actual response xml, exceptions are thrown. I am wondering if there is any simple way to transform an xml document from one set of namespaces to another set using C#, .NET, and the System.Xml namespace. I've poked around with XmlNamespaceManager a bit, but it does not seem to fully support what I need...or at least, I have been unable to find any really useful examples, and am not fully sure how it works. I am trying to avoid having to write some heavy-duty process to handle this manually myself, as I do not want to drastically impact the performance of our services when called by a Java Axis/WSS4J client.

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• Approaches for generic, compile-time safe lazy-load methods

  - by Aaronaught

  Suppose I have created a wrapper class like the following: public class Foo : IFoo { private readonly IFoo innerFoo; public Foo(IFoo innerFoo) { this.innerFoo = innerFoo; } public int? Bar { get; set; } public int? Baz { get; set; } } The idea here is that the innerFoo might wrap data-access methods or something similarly expensive, and I only want its GetBar and GetBaz methods to be invoked once. So I want to create another wrapper around it, which will save the values obtained on the first run. It's simple enough to do this, of course: int IFoo.GetBar() { if ((Bar == null) && (innerFoo != null)) Bar = innerFoo.GetBar(); return Bar ?? 0; } int IFoo.GetBaz() { if ((Baz == null) && (innerFoo != null)) Baz = innerFoo.GetBaz(); return Baz ?? 0; } But it gets pretty repetitive if I'm doing this with 10 different properties and 30 different wrappers. So I figured, hey, let's make this generic: T LazyLoad<T>(ref T prop, Func<IFoo, T> loader) { if ((prop == null) && (innerFoo != null)) prop = loader(innerFoo); return prop; } Which almost gets me where I want, but not quite, because you can't ref an auto-property (or any property at all). In other words, I can't write this: int IFoo.GetBar() { return LazyLoad(ref Bar, f => f.GetBar()); // <--- Won't compile } Instead, I'd have to change Bar to have an explicit backing field and write explicit getters and setters. Which is fine, except for the fact that I end up writing even more redundant code than I was writing in the first place. Then I considered the possibility of using expression trees: T LazyLoad<T>(Expression<Func<T>> propExpr, Func<IFoo, T> loader) { var memberExpression = propExpr.Body as MemberExpression; if (memberExpression != null) { // Use Reflection to inspect/set the property } } This plays nice with refactoring - it'll work great if I do this: return LazyLoad(f => f.Bar, f => f.GetBar()); But it's not actually safe, because someone less clever (i.e. myself in 3 days from now when I inevitably forget how this is implemented internally) could decide to write this instead: return LazyLoad(f => 3, f => f.GetBar()); Which is either going to crash or result in unexpected/undefined behaviour, depending on how defensively I write the LazyLoad method. So I don't really like this approach either, because it leads to the possibility of runtime errors which would have been prevented in the first attempt. It also relies on Reflection, which feels a little dirty here, even though this code is admittedly not performance-sensitive. Now I could also decide to go all-out and use DynamicProxy to do method interception and not have to write any code, and in fact I already do this in some applications. But this code is residing in a core library which many other assemblies depend on, and it seems horribly wrong to be introducing this kind of complexity at such a low level. Separating the interceptor-based implementation from the IFoo interface by putting it into its own assembly doesn't really help; the fact is that this very class is still going to be used all over the place, must be used, so this isn't one of those problems that could be trivially solved with a little DI magic. The last option I've already thought of would be to have a method like: T LazyLoad<T>(Func<T> getter, Action<T> setter, Func<IFoo, T> loader) { ... } This option is very "meh" as well - it avoids Reflection but is still error-prone, and it doesn't really reduce the repetition that much. It's almost as bad as having to write explicit getters and setters for each property. Maybe I'm just being incredibly nit-picky, but this application is still in its early stages, and it's going to grow substantially over time, and I really want to keep the code squeaky-clean. Bottom line: I'm at an impasse, looking for other ideas. Question: Is there any way to clean up the lazy-loading code at the top, such that the implementation will: Guarantee compile-time safety, like the ref version; Actually reduce the amount of code repetition, like the Expression version; and Not take on any significant additional dependencies? In other words, is there a way to do this just using regular C# language features and possibly a few small helper classes? Or am I just going to have to accept that there's a trade-off here and strike one of the above requirements from the list?

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• Is there an equivalent to Java's ClassFileTransformer in .NET? (a way to replace a class)

  - by Alix

  I've been searching for this for quite a while with no luck so far. Is there an equivalent to Java's ClassFileTransformer in .NET? Basically, I want to create a class CustomClassFileTransformer (which in Java would implement the interface ClassFileTransformer) that gets called whenever a class is loaded, and is allowed to tweak it and replace it with the tweaked version. I know there are frameworks that do similar things, but I was looking for something more straightforward, like implementing my own ClassFileTransformer. Is it possible? EDIT #1. More details about why I need this: Basically, I have a C# application and I need to monitor the instructions it wants to run in order to detect read or write operations to fields (operations Ldfld and Stfld) and insert some instructions before the read/write takes place. I know how to do this (except for the part where I need to be invoked to replace the class): for every method whose code I want to monitor, I must: Get the method's MethodBody using MethodBase.GetMethodBody() Transform it to byte array with MethodBody.GetILAsByteArray(). The byte[] it returns contains the bytecode. Analyse the bytecode as explained here, possibly inserting new instructions or deleting/modifying existing ones by changing the contents of the array. Create a new method and use the new bytecode to create its body, with MethodBuilder.CreateMethodBody(byte[] il, int count), where il is the array with the bytecode. I put all these tweaked methods in a new class and use the new class to replace the one that was originally going to be loaded. An alternative to replacing classes would be somehow getting notified whenever a method is invoked. Then I'd replace the call to that method with a call to my own tweaked method, which I would tweak only the first time is invoked and then I'd put it in a dictionary for future uses, to reduce overhead (for future calls I'll just look up the method and invoke it; I won't need to analyse the bytecode again). I'm currently investigating ways to do this and LinFu looks pretty interesting, but if there was something like a ClassFileTransformer it would be much simpler: I just rewrite the class, replace it, and let the code run without monitoring anything. An additional note: the classes may be sealed. I want to be able to replace any kind of class, I cannot impose restrictions on their attributes. EDIT #2. Why I need to do this at runtime. I need to monitor everything that is going on so that I can detect every access to data. This applies to the code of library classes as well. However, I cannot know in advance which classes are going to be used, and even if I knew every possible class that may get loaded it would be a huge performance hit to tweak all of them instead of waiting to see whether they actually get invoked or not. POSSIBLE (BUT PRETTY HARDCORE) SOLUTION. In case anyone is interested (and I see the question has been faved, so I guess someone is), this is what I'm looking at right now. Basically I'd have to implement the profiling API and I'll register for the events that I'm interested in, in my case whenever a JIT compilation starts. An extract of the blogpost: In your ICorProfilerCallback2::ModuleLoadFinished callback, you call ICorProfilerInfo2::GetModuleMetadata to get a pointer to a metadata interface on that module. QI for the metadata interface you want. Search MSDN for "IMetaDataImport", and grope through the table of contents to find topics on the metadata interfaces. Once you're in metadata-land, you have access to all the types in the module, including their fields and function prototypes. You may need to parse metadata signatures and this signature parser may be of use to you. In your ICorProfilerCallback2::JITCompilationStarted callback, you may use ICorProfilerInfo2::GetILFunctionBody to inspect the original IL, and ICorProfilerInfo2::GetILFunctionBodyAllocator and then ICorProfilerInfo2::SetILFunctionBody to replace that IL with your own. The great news: I get notified when a JIT compilation starts and I can replace the bytecode right there, without having to worry about replacing the class, etc. The not-so-great news: you cannot invoke managed code from the API's callback methods, which makes sense but means I'm on my own parsing the IL code, etc, as opposed to be able to use Cecil, which would've been a breeze. I don't think there's a simpler way to do this without using AOP frameworks (such as PostSharp). If anyone has any other idea please let me know. I'm not marking the question as answered yet.

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• Using only alphanumeric characters(a-z) inside toCharArray

  - by Aaron

  Below you will find me using toCharArray in order to send a string to array. I then MOVE the value of the letter using a for statement... for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } However, when I use shiftCode to move the value such as... a shifted by -1; I get a symbol @. Is there a way to send the string to shiftCode or tell shiftCode to ONLY use letters? I need it to see my text, like "aaron", and when I use the for statement iterate through a-z only and ignore all symbols and numbers. I THINK it is as simple as... letter=codeWord.toCharArray(a,z); But trying different forms of that and googling it didn't give me any results. Perhaps it has to do with regex or something? Below you will find a complete copy of my program; it works exactly how I want it to do; but it iterates through letters and symbols. I also tried finding instructions online for toCharArray but if there exists any arguments I can't locate them. My program... import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* * Aaron L. Jones * CS219 * AaronJonesProg3 * * This program is designed to - * Work as a Ceasar Cipher */ /** * * Aaron Jones */ public class AaronJonesProg3 { static String codeWord; static int shiftCode; static int i; static char[] letter; /** * @param args the command line arguments */ public static void main(String[] args) throws IOException { // Instantiating that Buffer Class // We are going to use this to read data from the user; in buffer // For performance related reasons BufferedReader reader; // Building the reader variable here // Just a basic input buffer (Holds things for us) reader = new BufferedReader(new InputStreamReader(System.in)); // Java speaks to us here / We get it to query our user System.out.print("Please enter text to encrypt: "); // Try to get their input here try { // Get their codeword using the reader codeWord = reader.readLine(); // Make that input upper case codeWord = codeWord.toUpperCase(); // Cut the white space out codeWord = codeWord.replaceAll("\\s",""); // Make it all a character array letter = codeWord.toCharArray(); } // If they messed up the input we let them know here and end the prog. catch(Throwable t) { System.out.println(t.toString()); System.out.println("You broke it. But you impressed me because" + "I don't know how you did it!"); } // Java Speaks / Lets get their desired shift value System.out.print("Please enter the shift value: "); // Try for their input try { // We get their number here shiftCode = Integer.parseInt(reader.readLine()); } // Again; if the user broke it. We let them know. catch(java.lang.NumberFormatException ioe) { System.out.println(ioe.toString()); System.out.println("How did you break this? Use a number next time!"); } for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } System.out.println(); /**************************************************************** **************************************************************** ***************************************************************/ // Java speaks to us here / We get it to query our user System.out.print("Please enter text to decrypt: "); // Try to get their input here try { // Get their codeword using the reader codeWord = reader.readLine(); // Make that input upper case codeWord = codeWord.toUpperCase(); // Cut the white space out codeWord = codeWord.replaceAll("\\s",""); // Make it all a character array letter = codeWord.toCharArray(); } // If they messed up the input we let them know here and end the prog. catch(Throwable t) { System.out.println(t.toString()); System.out.println("You broke it. But you impressed me because" + "I don't know how you did it!"); } // Java Speaks / Lets get their desired shift value System.out.print("Please enter the shift value: "); // Try for their input try { // We get their number here shiftCode = Integer.parseInt(reader.readLine()); } // Again; if the user broke it. We let them know. catch(java.lang.NumberFormatException ioe) { System.out.println(ioe.toString()); System.out.println("How did you break this? Use a number next time!"); } for(i = 0; i < letter.length; i++){ letter[i] += (shiftCode); System.out.print(letter[i]); } System.out.println(); } }

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• How to associate Wi-Fi beacon info with a virtual "location"?

  - by leander

  We have a piece of embedded hardware that will sense 802.11 beacons, and we're using this to make a map of currently visible bssid -> signalStrength. Given this map, we would like to make a determination: Is this likely to be a location I have been to before? If so, what is its ID? If not, I should remember this location: generate a new ID. Now what should I store (and how should I store it) to make future determinations easier? This is for an augmented-reality app/game. We will be using it to associate particular characters and events with "locations". The device does not have internet or cellular access, so using a geolocation service is out of consideration for the time being. (We don't really need to know where we are in reality, just be able to determine if we return there.) It isn't crucial that it be extremely accurate, but it would be nice if it was tolerant to signal strength changes or the occasional missing beacon. It should be usable in relatively low numbers of access points (e.g. rural house with one wireless router) or many (wandering around a dense metropolis). In the case of a city, it should change location every few minutes of walking (continuously-overlapping signals make this a bit more tricky in naive code). A reasonable number of false positives (match a location when we aren't actually there) is acceptable. The wrong character/event showing up just adds a bit of variety. False negatives (no location match) are a bit more troublesome: this will tend to add a better-matching new location to the saved locations, masking the old one. While we will have additional logic to ensure locations that the device hasn't seen in a while will "orphan" any associated characters or events (if e.g. you move to a different country), we'd prefer not to mask and eventually orphan locations you do visit regularly. Some technical complications: signalStrength is returned as 1-4; presumably it's related to dB, but we are not sure exactly how; in my experiments it tends to stick to either 1 or 4, but occasionally we see numbers in between. (Tech docs on the hardware are sparse.) The device completes a scan of one-quarter of the channel space every second; so it takes about 4-5 seconds to get a complete picture of what's around. The list isn't always complete. (We are making strides to fix this using some slight sampling period randomization, as recommended by the library docs. We're also investigating ways to increase the number of scans without killing our performance; the hardware/libs are poorly behaved when it comes to saturating the bus.) We have only kilobytes to store our history. We have a "working" impl now, but it is relatively naive, and flaky in the face of real-world Wi-Fi behavior. Rough pseudocode: // recordLocation() -- only store strength 4 locations m_savedLocations[g_nextId++] = filterForStrengthGE( m_currentAPs, 4 ); // determineLocation() bestPoints = -inf; foreach ( oldLoc in m_savedLocations ) { points = 0.0; foreach ( ap in m_currentAPs ) { if ( oldLoc.has( ap ) ) { switch ( ap.signalStrength ) { case 3: points += 1.0; break; case 4: points += 2.0; break; } } } points /= oldLoc.numAPs; if ( points > bestPoints ) { bestLoc = oldLoc; bestPoints = points; } } if ( bestLoc && bestPoints > 1.0 ) { if ( bestPoints >= (2.0 - epsilon) ) { // near-perfect match. // update location with any new high-strength APs that have appeared bestLoc.addAPs( filterForStrengthGE( m_currentAPs, 4 ) ); } return bestLoc; } else { return NO_MATCH; } We record a location currently only when we have NO_MATCH and the app determines it's time for a new event. (The "near-perfect match" code above would appear to make it harder to match in the future... It's mostly to keep new powerful APs from being associated with other locations, but you'd think we'd need something to counter this if e.g. an AP doesn't show up in the next 10 times I match a location.) I have a feeling that we're missing some things from set theory or graph theory that would assist in grouping/classification of this data, and perhaps providing a better "confidence level" on matches, and better robustness against missed beacons, signal strength changes, and the like. Also it would be useful to have a good method for mutating locations over time. Any useful resources out there for this sort of thing? Simple and/or robust approaches we're missing?

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• Making swap faster, easier to use and exception-safe

  - by FredOverflow

  I could not sleep last night and started thinking about std::swap. Here is the familiar C++98 version: template <typename T> void swap(T& a, T& b) { T c(a); a = b; b = c; } If a user-defined class Foo uses external ressources, this is inefficient. The common idiom is to provide a method void Foo::swap(Foo& other) and a specialization of std::swap<Foo>. Note that this does not work with class templates since you cannot partially specialize a function template, and overloading names in the std namespace is illegal. The solution is to write a template function in one's own namespace and rely on argument dependent lookup to find it. This depends critically on the client to follow the "using std::swap idiom" instead of calling std::swap directly. Very brittle. In C++0x, if Foo has a user-defined move constructor and a move assignment operator, providing a custom swap method and a std::swap<Foo> specialization has little to no performance benefit, because the C++0x version of std::swap uses efficient moves instead of copies: #include <utility> template <typename T> void swap(T& a, T& b) { T c(std::move(a)); a = std::move(b); b = std::move(c); } Not having to fiddle with swap anymore already takes a lot of burden away from the programmer. Current compilers do not generate move constructors and move assignment operators automatically yet, but as far as I know, this will change. The only problem left then is exception-safety, because in general, move operations are allowed to throw, and this opens up a whole can of worms. The question "What exactly is the state of a moved-from object?" complicates things further. Then I was thinking, what exactly are the semantics of std::swap in C++0x if everything goes fine? What is the state of the objects before and after the swap? Typically, swapping via move operations does not touch external resources, only the "flat" object representations themselves. So why not simply write a swap template that does exactly that: swap the object representations? #include <cstring> template <typename T> void swap(T& a, T& b) { unsigned char c[sizeof(T)]; memcpy( c, &a, sizeof(T)); memcpy(&a, &b, sizeof(T)); memcpy(&b, c, sizeof(T)); } This is as efficient as it gets: it simply blasts through raw memory. It does not require any intervention from the user: no special swap methods or move operations have to be defined. This means that it even works in C++98 (which does not have rvalue references, mind you). But even more importantly, we can now forget about the exception-safety issues, because memcpy never throws. I can see two potential problems with this approach: First, not all objects are meant to be swapped. If a class designer hides the copy constructor or the copy assignment operator, trying to swap objects of the class should fail at compile-time. We can simply introduce some dead code that checks whether copying and assignment are legal on the type: template <typename T> void swap(T& a, T& b) { if (false) // dead code, never executed { T c(a); // copy-constructible? a = b; // assignable? } unsigned char c[sizeof(T)]; std::memcpy( c, &a, sizeof(T)); std::memcpy(&a, &b, sizeof(T)); std::memcpy(&b, c, sizeof(T)); } Any decent compiler can trivially get rid of the dead code. (There are probably better ways to check the "swap conformance", but that is not the point. What matters is that it's possible). Second, some types might perform "unusual" actions in the copy constructor and copy assignment operator. For example, they might notify observers of their change. I deem this a minor issue, because such kinds of objects probably should not have provided copy operations in the first place. Please let me know what you think of this approach to swapping. Would it work in practice? Would you use it? Can you identify library types where this would break? Do you see additional problems? Discuss!

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• Dynamic object property populator (without reflection)

  - by grenade

  I want to populate an object's properties without using reflection in a manner similar to the DynamicBuilder on CodeProject. The CodeProject example is tailored for populating entities using a DataReader or DataRecord. I use this in several DALs to good effect. Now I want to modify it to use a dictionary or other data agnostic object so that I can use it in non DAL code --places I currently use reflection. I know almost nothing about OpCodes and IL. I just know that it works well and is faster than reflection. I have tried to modify the CodeProject example and because of my ignorance with IL, I have gotten stuck on two lines. One of them deals with dbnulls and I'm pretty sure I can just lose it, but I don't know if the lines preceding and following it are related and which of them will also need to go. The other, I think, is the one that pulled the value out of the datarecord before and now needs to pull it out of the dictionary. I think I can replace the "getValueMethod" with my "property.Value" but I'm not sure. I'm open to alternative/better ways of skinning this cat too. Here's the code so far (the commented out lines are the ones I'm stuck on): using System; using System.Collections.Generic; using System.Reflection; using System.Reflection.Emit; public class Populator<T> { private delegate T Load(Dictionary<string, object> properties); private Load _handler; private Populator() { } public T Build(Dictionary<string, object> properties) { return _handler(properties); } public static Populator<T> CreateBuilder(Dictionary<string, object> properties) { //private static readonly MethodInfo getValueMethod = typeof(IDataRecord).GetMethod("get_Item", new [] { typeof(int) }); //private static readonly MethodInfo isDBNullMethod = typeof(IDataRecord).GetMethod("IsDBNull", new [] { typeof(int) }); Populator<T> dynamicBuilder = new Populator<T>(); DynamicMethod method = new DynamicMethod("Create", typeof(T), new[] { typeof(Dictionary<string, object>) }, typeof(T), true); ILGenerator generator = method.GetILGenerator(); LocalBuilder result = generator.DeclareLocal(typeof(T)); generator.Emit(OpCodes.Newobj, typeof(T).GetConstructor(Type.EmptyTypes)); generator.Emit(OpCodes.Stloc, result); int i = 0; foreach (var property in properties) { PropertyInfo propertyInfo = typeof(T).GetProperty(property.Key, BindingFlags.Public | BindingFlags.Instance | BindingFlags.IgnoreCase | BindingFlags.FlattenHierarchy | BindingFlags.Default); Label endIfLabel = generator.DefineLabel(); if (propertyInfo != null && propertyInfo.GetSetMethod() != null) { generator.Emit(OpCodes.Ldarg_0); generator.Emit(OpCodes.Ldc_I4, i); //generator.Emit(OpCodes.Callvirt, isDBNullMethod); generator.Emit(OpCodes.Brtrue, endIfLabel); generator.Emit(OpCodes.Ldloc, result); generator.Emit(OpCodes.Ldarg_0); generator.Emit(OpCodes.Ldc_I4, i); //generator.Emit(OpCodes.Callvirt, getValueMethod); generator.Emit(OpCodes.Unbox_Any, property.Value.GetType()); generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod()); generator.MarkLabel(endIfLabel); } i++; } generator.Emit(OpCodes.Ldloc, result); generator.Emit(OpCodes.Ret); dynamicBuilder._handler = (Load)method.CreateDelegate(typeof(Load)); return dynamicBuilder; } } EDIT: Using Marc Gravell's PropertyDescriptor implementation (with HyperDescriptor) the code is simplified a hundred-fold. I now have the following test: using System; using System.Collections.Generic; using System.ComponentModel; using Hyper.ComponentModel; namespace Test { class Person { public int Id { get; set; } public string Name { get; set; } } class Program { static void Main() { HyperTypeDescriptionProvider.Add(typeof(Person)); var properties = new Dictionary<string, object> { { "Id", 10 }, { "Name", "Fred Flintstone" } }; Person person = new Person(); DynamicUpdate(person, properties); Console.WriteLine("Id: {0}; Name: {1}", person.Id, person.Name); Console.ReadKey(); } public static void DynamicUpdate<T>(T entity, Dictionary<string, object> properties) { foreach (PropertyDescriptor propertyDescriptor in TypeDescriptor.GetProperties(typeof(T))) if (properties.ContainsKey(propertyDescriptor.Name)) propertyDescriptor.SetValue(entity, properties[propertyDescriptor.Name]); } } } Any comments on performance considerations for both TypeDescriptor.GetProperties() & PropertyDescriptor.SetValue() are welcome...

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• PHP MVC Framework Structure

  - by bigstylee

  I am sorry about the amount of code here. I have tried to show enough for understanding while avoiding confusion (I hope). I have included a second copy of the code at Pastebin. (The code does execute without error/notice/warning.) I am currently creating a Content Management System while trying to implement the idea of Model View Controller. I have only recently come across the concept of MVC (within the last week) and trying to implement this into my current project. One of the features of the CMS is dynamic/customisable menu areas and each feature will be represented by a controller. Therefore there will be multiple versions of the Controller Class, each with specific extended functionality. I have looked at a number of tutorials and read some open source solutions to the MVC Framework. I am now trying to create a lightweight solution for my specific requirements. I am not interested in backwards compatibility, I am using PHP 5.3. An advantage of the Base class is not having to use global and can directly access any loaded class using $this->Obj['ClassName']->property/function();. Hoping to get some feedback using the basic structure outlined (with performance in mind). Specifically; a) Have I understood/implemented the concept of MVC correctly? b) Have I understood/implemented Object Orientated techniques with PHP 5 correctly? c) Should the class propertise of Base be static? d) Improvements? Thank you very much in advance! <?php /* A "Super Class" that creates/stores all object instances */ class Base { public static $Obj = array(); // Not sure this is the correct use of the "static" keyword? public static $var; static public function load_class($directory, $class) { echo count(self::$Obj)."\n"; // This does show the array is getting updated and not creating a new array :) if (!isset(self::$Obj[$class]) && !is_object(self::$Obj[$class])) //dont want to load it twice { /* Locate and include the class file based upon name ($class) */ return self::$Obj[$class] = new $class(); } return TRUE; } } /* Loads general configuration objects into the "Super Class" */ class Libraries extends Base { public function __construct(){ $this->load_class('library', 'Database'); $this->load_class('library', 'Session'); self::$var = 'Hello World!'; //testing visibility /* Other general funciton classes */ } } class Database extends Base { /* Connects to the the database and executes all queries */ public function query(){} } class Session extends Base { /* Implements Sessions in database (read/write) */ } /* General functionality of controllers */ abstract class Controller extends Base { protected function load_model($class, $method) { /* Locate and include the model file */ $this->load_class('model', $class); call_user_func(array(self::$Obj[$class], $method)); } protected function load_view($name) { /* Locate and include the view file */ #include('views/'.$name.'.php'); } } abstract class View extends Base { /* ... */ } abstract class Model extends Base { /* ... */ } class News extends Controller { public function index() { /* Displays the 5 most recent News articles and displays with Content Area */ $this->load_model('NewsModel', 'index'); $this->load_view('news', 'index'); echo $this->var; } public function menu() { /* Displays the News Title of the 5 most recent News articles and displays within the Menu Area */ $this->load_model('news/index'); $this->load_view('news/index'); } } class ChatBox extends Controller { /* ... */ } /* Lots of different features extending the controller/view/model class depending upon request and layout */ class NewsModel extends Model { public function index() { echo $this->var; self::$Obj['Database']->query(/*SELECT 5 most recent news articles*/); } public function menu() { /* ... */ } } $Libraries = new Libraries; $controller = 'News'; // Would be determined from Query String $method = 'index'; // Would be determined from Query String $Content = $Libraries->load_class('controller', $controller); //create the controller for the specific page if (in_array($method, get_class_methods($Content))) { call_user_func(array($Content, $method)); } else { die('Bad Request'. $method); } $Content::$var = 'Goodbye World'; echo $Libraries::$var . ' - ' . $Content::$var; ?> /* Ouput */ 0 1 2 3 Goodbye World! - Goodbye World

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• PHP Fatal error, trying to request method inside model multiple times

  - by Tom

  The error message [23-Mar-2010 08:36:16] PHP Fatal error: Cannot redeclare humanize() (previously declared in /Users/tmclssns/Sites/nadar/nadar/trunk/webapp/application/filer/models/Filer/Aggregate.php:133) in /Users/tmclssns/Sites/nadar/nadar/trunk/webapp/application/filer/models/Filer/Aggregate.php on line 133 I have a "Filer" model which contains several methods to generate graphs. Each method in there related to generating graphs has the suffix "Graph" in the method name. As we have some performance issues, I try to render the graphs in advance (using cron) instead of rendering them on each request. The code below is what I came up with: public function generategraphsAction() { $this->_helper->viewRenderer->setNoRender(); $config = Zend_Registry::get('config'); $id = $this->_getParam('filerid'); $filer = new Filer($id); $filer_methods = get_class_methods($filer); foreach ($filer_methods as $filer_method) { if (preg_match('/^(.*)Graph$/i', $filer_method, $matches)) { $path = $config->imaging_caching_dir . "/$id/{$matches[1]}.png"; $filer->$matches[0]($path); } } // var_dump(get_class_methods($filer)); die; } The result from the var_dump(), when uncommented, is: array 0 => string '__construct' (length=11) 1 => string 'find_by_name' (length=12) 2 => string 'getPartner' (length=10) 3 => string 'getSlots' (length=8) 4 => string 'getGroups' (length=9) 5 => string 'grouplist' (length=9) 6 => string 'getAggregates' (length=13) 7 => string 'getVolumes' (length=10) 8 => string 'getAggregateVolumes' (length=19) 9 => string 'getShelves' (length=10) 10 => string 'getAutoSupportHistory' (length=21) 11 => string 'getAutoSupportMail' (length=18) 12 => string 'getOrphans' (length=10) 13 => string 'getAll' (length=6) 14 => string 'getDiskRevOverview' (length=18) 15 => string 'getDiskTypeOverview' (length=19) 16 => string 'getDiskTypeSizeFunctionOverview' (length=31) 17 => string 'getLicenses' (length=11) 18 => string 'removeGroup' (length=11) 19 => string 'addGroup' (length=8) 20 => string 'hasGroup' (length=8) 21 => string 'aggdefaultGraph' (length=15) 22 => string 'aggbarGraph' (length=11) 23 => string 'voldefaultGraph' (length=15) 24 => string 'volbarGraph' (length=11) 25 => string 'replicationGraph' (length=16) 26 => string 'getReplicationData' (length=18) 27 => string 'humanize' (length=8) 28 => string 'getFiler' (length=8) 29 => string 'getOptions' (length=10) 30 => string 'getCifsInfo' (length=11) 31 => string 'getCifsStats' (length=12) 32 => string '__get' (length=5) 33 => string 'tr' (length=2) 34 => string 'trs' (length=3) 35 => string 'fieldList' (length=9) The generategraphsAction() method finds the 'Graph' methods correctly: array 0 => string 'aggdefaultGraph' (length=15) 1 => string 'aggdefault' (length=10) array 0 => string 'aggbarGraph' (length=11) 1 => string 'aggbar' (length=6) array 0 => string 'voldefaultGraph' (length=15) 1 => string 'voldefault' (length=10) array 0 => string 'volbarGraph' (length=11) 1 => string 'volbar' (length=6) array 0 => string 'replicationGraph' (length=16) 1 => string 'replication' (length=11) However when the first graph is generated, it generates the above listed PHP fatal error. Anyone can come up with a solution to this? I tried to pass by reference or switch a few things around (like re declare the Filer model, $current_filer = new Filer($id); and unset() it again after the request, but resulted in the same error) without much success. The referenced method "humanize" isn't used for anything I'm doing at the moment, but belongs to the Model because it's used in several other places. Of course, removing the method is not really an option right now, and the model contains several other methods as well so I assume if I just move the humanize method around, it will generate an error on the next one. For reference, the humanize() method: public function humanize ($kbytes, $unit = null) { // KiloByte, Megabyte, GigaByte, TeraByte, PetaByte, ExaByte, ZettaByte, YottaByte $units = array('KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'); if (null !== $units) { $i = array_search(substr($unit, -2), $units); if (! $i) { $i = floor((strlen($kbytes) - 1) / 3); } } else { $i = floor((strlen($kbytes) - 1) / 3); } $newSize = round($kbytes / pow(1024, $i), 2); return $newSize . $units[$i]; } Thanks in advance for the help offered.

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• Help required in adding new methods, properties into existing classes dynamically

  - by Bepenfriends

  Hi All, I am not sure whether it is possible to achieve this kind of implementation in Dot Net. Below are the information Currently we are on an application which is done in COM+, ASP, XSL, XML technologies. It is a multi tier architecture application in which COM+ acts as the BAL. The execution steps for any CRUD operation will be defined using a seperate UI which uses XML to store the information. BAL reads the XML and understands the execution steps which are defined and executes corresponding methods in DLL. Much like EDM we have our custom model (using XML) which determines which property of object is searchable, retrievable etc. Based on this information BAL constructs queries and calls procedures to get the data. In the current application both BAL and DAL are heavily customizable without doing any code change. the results will be transmitted to presentation layer in XML format which constructs the UI based on the data recieved. Now I am creating a migration project which deals with employee information. It is also going to follow the N Tier architecture in which the presentation layer communicates with BAL which connects to DAL to return the Data. Here is the problem, In our existing version we are handling every information as XML in its native form (no converstion of object etc), but in the migration project, Team is really interested in utilizing the OOP model of development where every information which is sent from BAL need to be converted to objects of its respective types (example employeeCollection, Address Collection etc). If we have the static number of data returned from BAL we can have a class which contains those nodes as properties and we can access the same. But in our case the data returned from our BAL need to be customized. How can we handle the customization in presentation layer which is converting the result to an Object. Below is an example of the XML returned <employees> <employee> <firstName>Employee 1 First Name</firstName> <lastName>Employee 1 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>3</addressType> <StreetName>Street name3</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> <employee> <firstName>Employee 2 First Name</firstName> <lastName>Employee 2 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> </employees> If these are the only columns then i can write a class which is like public class Address{ public int AddressType {get;set;}; public string StreetName {get;set;}; public string RegionName {get;set;}; } public class Employee{ public string FirstName {get; set;} public string LastName {get; set;} public string AddressCollection {get; set;} } public class EmployeeCollection : List<Employee>{ public bool Add (Employee Data){ .... } } public class AddressCollection : List<Address>{ public bool Add (Address Data){ .... } } This class will be provided to customers and consultants as DLLs. We will not provide the source code for the same. Now when the consultants or customers does customization(example adding country to address and adding passport information object with employee object) they must be able to access those properties in these classes, but without source code they will not be able to do those modifications.which makes the application useless. Is there is any way to acomplish this in DotNet. I thought of using Anonymous classes but, the problem with Anonymous classes are we can not have methods in it. I am not sure how can i fit the collection objects (which will be inturn an anonymous class) Not sure about datagrid / user control binding etc. I also thought of using CODEDom to create classes runtime but not sure about the meory, performance issues. also the classes must be created only once and must use the same till there is another change. Kindly help me out in this problem. Any kind of help meterial/ cryptic code/ links will be helpful.

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• Watching setTimeout loops so that only one is running at a time.

  - by DA

  I'm creating a content rotator in jQuery. 5 items total. Item 1 fades in, pauses 10 seconds, fades out, then item 2 fades in. Repeat. Simple enough. Using setTimeout I can call a set of functions that create a loop and will repeat the process indefinitely. I now want to add the ability to interrupt this rotator at any time by clicking on a navigation element to jump directly to one of the content items. I originally started going down the path of pinging a variable constantly (say every half second) that would check to see if a navigation element was clicked and, if so, abandon the loop, then restart the loop based on the item that was clicked. The challenge I ran into was how to actually ping a variable via a timer. The solution is to dive into JavaScript closures...which are a little over my head but definitely something I need to delve into more. However, in the process of that, I came up with an alternative option that actually seems to be better performance-wise (theoretically, at least). I have a sample running here: http://jsbin.com/uxupi/14 (It's using console.log so have fireBug running) Sample script: $(document).ready(function(){ var loopCount = 0; $('p#hello').click(function(){ loopCount++; doThatThing(loopCount); }) function doThatOtherThing(currentLoopCount) { console.log('doThatOtherThing-'+currentLoopCount); if(currentLoopCount==loopCount){ setTimeout(function(){doThatThing(currentLoopCount)},5000) } } function doThatThing(currentLoopCount) { console.log('doThatThing-'+currentLoopCount); if(currentLoopCount==loopCount){ setTimeout(function(){doThatOtherThing(currentLoopCount)},5000); } } }) The logic being that every click of the trigger element will kick off the loop passing into itself a variable equal to the current value of the global variable. That variable gets passed back and forth between the functions in the loop. Each click of the trigger also increments the global variable so that subsequent calls of the loop have a unique local variable. Then, within the loop, before the next step of each loop is called, it checks to see if the variable it has still matches the global variable. If not, it knows that a new loop has already been activated so it just ends the existing loop. Thoughts on this? Valid solution? Better options? Caveats? Dangers? UPDATE: I'm using John's suggestion below via the clearTimeout option. However, I can't quite get it to work. The logic is as such: var slideNumber = 0; var timeout = null; function startLoop(slideNumber) { ...do stuff here to set up the slide based on slideNumber... slideFadeIn() } function continueCheck(){ if (timeout != null) { // cancel the scheduled task. clearTimeout(timeout); timeout = null; return false; }else{ return true; } }; function slideFadeIn() { if (continueCheck){ // a new loop hasn't been called yet so proceed... // fade in the LI $currentListItem.fadeIn(fade, function() { if(multipleFeatures){ timeout = setTimeout(slideFadeOut,display); } }); }; function slideFadeOut() { if (continueLoop){ // a new loop hasn't been called yet so proceed... slideNumber=slideNumber+1; if(slideNumber==features.length) { slideNumber = 0; }; timeout = setTimeout(function(){startLoop(slideNumber)},100); }; startLoop(slideNumber); The above kicks of the looping. I then have navigation items that, when clicked, I want the above loop to stop, then restart with a new beginning slide: $(myNav).click(function(){ clearTimeout(timeout); timeout = null; startLoop(thisItem); }) If I comment out 'startLoop...' from the click event, it, indeed, stops the initial loop. However, if I leave that last line in, it doesn't actually stop the initial loop. Why? What happens is that both loops seem to run in parallel for a period. So, when I click my navigation, clearTimeout is called, which clears it.

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• New hire expectations... (Am I being unreasonable?)

  - by user295841

  I work for a very small custom software shop. We currently consist me and my boss. My boss is an old FoxPro DOS developer and OOP makes him uncomfortable. He is planning on taking a back seat in the next few years to hopefully enjoy a “partial retirement”. I will be taking over the day to day operations and we are now desperately looking for more help. We tried Monster.com, Dice.com, and others a few years ago when we started our search. We had no success. We have tried outsourcing overseas (total disaster), hiring kids right out of college (mostly a disaster but that’s where I came from), interns (good for them, not so good for us) and hiring laid off “experienced” developers (there was a reason they were laid off). I have heard hiring practices discussed on podcasts, blogs, etc... and have tried a few. The “Fizz Buzz” test was a good one. One kid looked physically ill before he finally gave up. I think my problem is that I have grown so much as a developer since I started here that I now have a high standard. I hear/read very intelligent people podcasts and blogs and I know that there are lots of people out there that can do the job. I don’t want to settle for less than a “good” developer. Perhaps my expectations are unreasonable. I expect any good developer (entry level or experienced) to be billable (at least paying their own wage) in under one month. I expect any good developer to be able to be productive (at least dangerous) in any language or technology with only a few days of research/training. I expect any good developer to be able to take a project from initial customer request to completion with little or no help from others. Am I being unreasonable? What constitutes a valuable developer? What should be expected of an entry level developer? What should be expected of an experienced developer? I realize that everyone is different but there has to be some sort of expectations standard, right? I have been giving the test project below to potential canidates to weed them out. Good idea? Too much? Too little? Please let me know what you think. Thanks. Project ID: T00001 Description: Order Entry System Deadline: 1 Week Scope The scope of this project is to develop a fully function order entry system. Screen/Form design must be user friendly and promote efficient data entry and modification. User experience (Navigation, Screen/Form layouts, Look and Feel…) is at the developer’s discretion. System may be developed using any technologies that conform to the technical and system requirements. Deliverables Complete source code Database setup instructions (Scripts or restorable backup) Application installation instructions (Installer or installation procedure) Any necessary documentation Technical Requirements Server Platform – Windows XP / Windows Server 2003 / SBS Client Platform – Windows XP Web Browser (If applicable) – IE 8 Database – At developer’s discretion (Must be a relational SQL database.) Language – At developer’s discretion All data must be normalized. (+) All data must maintain referential integrity. (++) All data must be indexed for optimal performance. System must handle concurrency. System Requirements Customer Maintenance Customer records must have unique ID. Customer data will include Name, Address, Phone, etc. User must be able to perform all CRUD (Create, Read, Update, and Delete) operations on the Customer table. User must be able to enter a specific Customer ID to edit. User must be able to pull up a sortable/queryable search grid/utility to find a customer to edit. Validation must be performed prior to database commit. Customer record cannot be deleted if the customer has an order in the system. (++) Inventory Maintenance Part records must have unique ID. Part data will include Description, Price, UOM (Unit of Measure), etc. User must be able to perform all CRUD operations on the part table. User must be able to enter a specific Part ID to edit. User must be able to pull up a sortable/queryable search grid/utility to find a part to edit. Validation must be performed prior to database commit. Part record cannot be deleted if the part has been used in an order. (++) Order Entry Order records must have a unique auto-incrementing key (Order Number). Order data must be split into a header/detail structure. (+) Order can contain an infinite number of detail records. Order header data will include Order Number, Customer ID (++), Order Date, Order Status (Open/Closed), etc. Order detail data will include Part Number (++), Quantity, Price, etc. User must be able to perform all CRUD operations on the order tables. User must be able to enter a specific Order Number to edit. User must be able to pull up a sortable/queryable search grid/utility to find an order to edit. User must be able to print an order form from within the order entry form. Validation must be performed prior to database commit. Reports Customer Listing – All Customers in the system. Inventory Listing – All parts in the system. Open Order Listing – All open orders in system. Customer Order Listing – All orders for specific customer. All reports must include sorts and filter functions where applicable. Ex. Customer Listing by range of Customer IDs. Open Order Listing by date range.

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• How to compare a memory bits in C++?

  - by Trunet

  Hi, I need help with a memory bit comparison function. I bought a LED Matrix here with 4 x HT1632C chips and I'm using it on my arduino mega2560. There're no code available for this chipset(it's not the same as HT1632) and I'm writing on my own. I have a plot function that get x,y coordinates and a color and that pixel turn on. Only this is working perfectly. But I need more performance on my display so I tried to make a shadowRam variable that is a "copy" of my device memory. Before I plot anything on display it checks on shadowRam to see if it's really necessary to change that pixel. When I enabled this(getShadowRam) on plot function my display has some, just SOME(like 3 or 4 on entire display) ghost pixels(pixels that is not supposed to be turned on). If I just comment the prev_color if's on my plot function it works perfectly. Also, I'm cleaning my shadowRam array setting all matrix to zero. variables: #define BLACK 0 #define GREEN 1 #define RED 2 #define ORANGE 3 #define CHIP_MAX 8 byte shadowRam[63][CHIP_MAX-1] = {0}; getShadowRam function: byte HT1632C::getShadowRam(byte x, byte y) { byte addr, bitval, nChip; if (x>=32) { nChip = 3 + x/16 + (y>7?2:0); } else { nChip = 1 + x/16 + (y>7?2:0); } bitval = 8>>(y&3); x = x % 16; y = y % 8; addr = (x<<1) + (y>>2); if ((shadowRam[addr][nChip-1] & bitval) && (shadowRam[addr+32][nChip-1] & bitval)) { return ORANGE; } else if (shadowRam[addr][nChip-1] & bitval) { return GREEN; } else if (shadowRam[addr+32][nChip-1] & bitval) { return RED; } else { return BLACK; } } plot function: void HT1632C::plot (int x, int y, int color) { if (x<0 || x>X_MAX || y<0 || y>Y_MAX) return; if (color != BLACK && color != GREEN && color != RED && color != ORANGE) return; char addr, bitval; byte nChip; byte prev_color = HT1632C::getShadowRam(x,y); bitval = 8>>(y&3); if (x>=32) { nChip = 3 + x/16 + (y>7?2:0); } else { nChip = 1 + x/16 + (y>7?2:0); } x = x % 16; y = y % 8; addr = (x<<1) + (y>>2); switch(color) { case BLACK: if (prev_color != BLACK) { // compare with memory to only set if pixel is other color // clear the bit in both planes; shadowRam[addr][nChip-1] &= ~bitval; HT1632C::sendData(nChip, addr, shadowRam[addr][nChip-1]); shadowRam[addr+32][nChip-1] &= ~bitval; HT1632C::sendData(nChip, addr+32, shadowRam[addr+32][nChip-1]); } break; case GREEN: if (prev_color != GREEN) { // compare with memory to only set if pixel is other color // set the bit in the green plane and clear the bit in the red plane; shadowRam[addr][nChip-1] |= bitval; HT1632C::sendData(nChip, addr, shadowRam[addr][nChip-1]); shadowRam[addr+32][nChip-1] &= ~bitval; HT1632C::sendData(nChip, addr+32, shadowRam[addr+32][nChip-1]); } break; case RED: if (prev_color != RED) { // compare with memory to only set if pixel is other color // clear the bit in green plane and set the bit in the red plane; shadowRam[addr][nChip-1] &= ~bitval; HT1632C::sendData(nChip, addr, shadowRam[addr][nChip-1]); shadowRam[addr+32][nChip-1] |= bitval; HT1632C::sendData(nChip, addr+32, shadowRam[addr+32][nChip-1]); } break; case ORANGE: if (prev_color != ORANGE) { // compare with memory to only set if pixel is other color // set the bit in both the green and red planes; shadowRam[addr][nChip-1] |= bitval; HT1632C::sendData(nChip, addr, shadowRam[addr][nChip-1]); shadowRam[addr+32][nChip-1] |= bitval; HT1632C::sendData(nChip, addr+32, shadowRam[addr+32][nChip-1]); } break; } } If helps: The datasheet of board I'm using. On page 7 has the memory mapping I'm using. Also, I have a video of display working.

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• JSF : How to refresh required field in ajax request

  - by Tama

  Ok, here you are the core problem. The page. I have two required "input text". A command button that changes the bean value and reRenderes the "job" object. <a4j:form id="pervForm"> SURNAME:<h:inputText id="surname" label="Surname" value="#{prevManager.surname}" required="true" /> <br/> JOB:<h:inputText value="#{prevManager.job}" id="job" maxlength="10" size="10" label="#{msg.common_label_job}" required="true" /> <br/> <a4j:commandButton value="Set job to Programmer" ajaxSingle="true" reRender="job"> <a4j:actionparam name="jVal" value="Programmer" assignTo="#{prevManager.job}"/> </a4j:commandButton> <h:commandButton id="save" value="save" action="save" class="HATSBUTTON"/> </a4j:form> Here the simple manager: public class PrevManager { private String surname; private String job; public String getSurname() { return surname; } public void setSurname(String surname) { this.surname = surname; } public String getJob() { return job; } public void setJob(String job) { this.job = job; } public String save() { //do something } } Let's do this: Write something on the Job input text (such as "teacher"). Leave empty the surname. Save. Validation error appears (surname is mandatory). Press "Set job to Programmer": nothing happens. Checking the bean value, I discovered that it is correctly updated, indeed the component on the page is not updated! Well, according to the JBoss Docs I found: Ajax region is a key ajax component. It limits the part of the component tree to be processed on the server side when ajax request comes. Processing means invocation during Decode, Validation and Model Update phase. Most common reasons to use a region are: -avoiding the aborting of the JSF lifecycle processing during the validation of other form input unnecessary for given ajax request; -defining the different strategies when events will be delivered (immediate="true/false") -showing an individual indicator of an ajax status -increasing the performance of the rendering processing (selfRendered="true/false", renderRegionOnly="true/false") The following two examples show the situation when a validation error does not allow to process an ajax input. Type the name. The outputText component should reappear after you. However, in the first case, this activity will be aborted because of the other field with required="true". You will see only the error message while the "Job" field is empty. Here you are the example: <ui:composition xmlns="http://www.w3.org/1999/xhtml" xmlns:ui="http://java.sun.com/jsf/facelets" xmlns:h="http://java.sun.com/jsf/html" xmlns:f="http://java.sun.com/jsf/core" xmlns:a4j="http://richfaces.org/a4j" xmlns:rich="http://richfaces.org/rich"> <style> .outergridvalidationcolumn { padding: 0px 30px 10px 0px; } </style> <a4j:outputPanel ajaxRendered="true"> <h:messages style="color:red" /> </a4j:outputPanel> <h:panelGrid columns="2" columnClasses="outergridvalidationcolumn"> <h:form id="form1"> <h:panelGrid columns="2"> <h:outputText value="Name" /> <h:inputText value="#{userBean.name}"> <a4j:support event="onkeyup" reRender="outname" /> </h:inputText> <h:outputText value="Job" /> <h:inputText required="true" id="job2" value="#{userBean.job}" /> </h:panelGrid> </h:form> <h:form id="form2"> <h:panelGrid columns="2"> <h:outputText value="Name" /> <a4j:region> <h:inputText value="#{userBean.name}"> <a4j:support event="onkeyup" reRender="outname" /> </h:inputText> </a4j:region> <h:outputText value="Job" /> <h:inputText required="true" id="job1" value="#{userBean.job}" /> </h:panelGrid> </h:form> </h:panelGrid> <h:outputText id="outname" style="font-weight:bold" value="Typed Name: #{userBean.name}" /> <br /> </ui:composition> Form1: the behaviour is incorrect. I need to fill the job and then the name. Form2: the behaviour is correct. I do not need to fill the job to see the correct value. Unfortunately using Ajax region does not help (indeed I used it in a bad way ...) because my fields are both REQUIRED. That's the main different. Any idea? Many thanks.

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• Database file is inexplicably locked during SQLite commit

  - by sweeney

  Hello, I'm performing a large number of INSERTS to a SQLite database. I'm using just one thread. I batch the writes to improve performance and have a bit of security in case of a crash. Basically I cache up a bunch of data in memory and then when I deem appropriate, I loop over all of that data and perform the INSERTS. The code for this is shown below: public void Commit() { using (SQLiteConnection conn = new SQLiteConnection(this.connString)) { conn.Open(); using (SQLiteTransaction trans = conn.BeginTransaction()) { using (SQLiteCommand command = conn.CreateCommand()) { command.CommandText = "INSERT OR IGNORE INTO [MY_TABLE] (col1, col2) VALUES (?,?)"; command.Parameters.Add(this.col1Param); command.Parameters.Add(this.col2Param); foreach (Data o in this.dataTemp) { this.col1Param.Value = o.Col1Prop; this. col2Param.Value = o.Col2Prop; command.ExecuteNonQuery(); } } this.TryHandleCommit(trans); } conn.Close(); } } I now employ the following gimmick to get the thing to eventually work: private void TryHandleCommit(SQLiteTransaction trans) { try { trans.Commit(); } catch (Exception e) { Console.WriteLine("Trying again..."); this.TryHandleCommit(trans); } } I create my DB like so: public DataBase(String path) { //build connection string SQLiteConnectionStringBuilder connString = new SQLiteConnectionStringBuilder(); connString.DataSource = path; connString.Version = 3; connString.DefaultTimeout = 5; connString.JournalMode = SQLiteJournalModeEnum.Persist; connString.UseUTF16Encoding = true; using (connection = new SQLiteConnection(connString.ToString())) { //check for existence of db FileInfo f = new FileInfo(path); if (!f.Exists) //build new blank db { SQLiteConnection.CreateFile(path); connection.Open(); using (SQLiteTransaction trans = connection.BeginTransaction()) { using (SQLiteCommand command = connection.CreateCommand()) { command.CommandText = DataBase.CREATE_MATCHES; command.ExecuteNonQuery(); command.CommandText = DataBase.CREATE_STRING_DATA; command.ExecuteNonQuery(); //TODO add logging } trans.Commit(); } connection.Close(); } } } I then export the connection string and use it to obtain new connections in different parts of the program. At seemingly random intervals, though at far too great a rate to ignore or otherwise workaround this problem, I get unhandled SQLiteException: Database file is locked. This occurs when I attempt to commit the transaction. No errors seem to occur prior to then. This does not always happen. Sometimes the whole thing runs without a hitch. No reads are being performed on these files before the commits finish. I have the very latest SQLite binary. I'm compiling for .NET 2.0. I'm using VS 2008. The db is a local file. All of this activity is encapsulated within one thread / process. Virus protection is off (though I think that was only relevant if you were connecting over a network?). As per Scotsman's post I have implemented the following changes: Journal Mode set to Persist DB files stored in C:\Docs + Settings\ApplicationData via System.Windows.Forms.Application.AppData windows call No inner exception Witnessed on two distinct machines (albeit very similar hardware and software) Have been running Process Monitor - no extraneous processes are attaching themselves to the DB files - the problem is definitely in my code... Does anyone have any idea whats going on here? I know I just dropped a whole mess of code, but I've been trying to figure this out for way too long. My thanks to anyone who makes it to the end of this question! brian UPDATES: Thanks for the suggestions so far! I've implemented many of the suggested changes. I feel that we are getting closer to the answer...however... The code above technically works however it is non-deterministic! It is not guaranteed to do anything aside from spin in neutral forever. In practice it seems to work somewhere between the 1st and 10th iteration. If i batch my commits at a reasonable interval damage will be mitigated but I really do not want to leave things in this state... More suggestions welcome!

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• Jquery mobile page structure

  - by Die 20

  I built a jquery mobile site a while back and I have recently been expanding on it and noticing performance issues. I believe it is because I constructed the site using a multi-page set up where a single php file houses the following pages: **ALL_PAGES.PHP** <html> <head> /* external css and js files */ </head> <body> <div date-role="page" id="main"> <div class="page_link"> page 1 </div> <div class="page_link"> page 2 </div> <div class="page_link"> page 3 </div> </div> <div date-role="page" id="page 1"> <div class="page_link"> main </div> <div class="page_link"> page 2 </div> <div class="page_link"> page 3 </div> </div> <div date-role="page" id="page 2"> <div class="page_link"> main </div> <div class="page_link"> page 1 </div> <div class="page_link"> page 3 </div> </div> <div date-role="page" id="page 3"> <div class="page_link"> main </div> <div class="page_link"> page 1 </div> <div class="page_link"> page 2 </div> </div> </body> </html> **end ALL_PAGES.PHP ** I want to break away from this multi-page setup on one php file, and move to a setup where each page is a separate php file. To accomplish this I took the html from each page and moved it to its own php page. Then I added href links in replace of the mobile.change() functions I used for the "page_link" classes. **MAIN.PHP** <html> <head> external css and js files </head> <body> <div date-role="page" id="page 1"> <a href="/main.php"> main </a> <a href="/page_2.php"> page 2 </a> <a href="/page_3.php"> page 3 </a> </div> </body> </html> **end MAIN.PHP** **PAGE_1.PHP** <div date-role="page" id="page 1"> <a href="/main.php"> main </a> <a href="/page_2.php"> page 2 </a> <a href="/page_3.php"> page 3 </a> </div> **end PAGE_1.PHP** **PAGE_2.PHP** <div date-role="page" id="page 2"> <a href="/main.php"> main </a> <a href="/page_1.php"> page 1 </a> <a href="/page_3.php"> page 3 </a> </div> **end PAGE_2.PHP** **PAGE_3.PHP** <div date-role="page" id="page 3"> <a href="/main.php"> main </a> <a href="/page_1.php"> page 1 </a> <a href="/page_2.php"> page 2 </a> </div> **end PAGE_3.PHP** The site works fine except when the user hits the refresh button in the browser. When that happens each page loses access to any external css and js files located on the main page. I am fairly new to JQM so any advice would be helpful.

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• Find the set of largest contiguous rectangles to cover multiple areas

  - by joelpt

  I'm working on a tool called Quickfort for the game Dwarf Fortress. Quickfort turns spreadsheets in csv/xls format into a series of commands for Dwarf Fortress to carry out in order to plot a "blueprint" within the game. I am currently trying to optimally solve an area-plotting problem for the 2.0 release of this tool. Consider the following "blueprint" which defines plotting commands for a 2-dimensional grid. Each cell in the grid should either be dug out ("d"), channeled ("c"), or left unplotted ("."). Any number of distinct plotting commands might be present in actual usage. . d . d c c d d d d c c . d d d . c d d d d d c . d . d d c To minimize the number of instructions that need to be sent to Dwarf Fortress, I would like to find the set of largest contiguous rectangles that can be formed to completely cover, or "plot", all of the plottable cells. To be valid, all of a given rectangle's cells must contain the same command. This is a faster approach than Quickfort 1.0 took: plotting every cell individually as a 1x1 rectangle. This video shows the performance difference between the two versions. For the above blueprint, the solution looks like this: . 9 . 0 3 2 8 1 1 1 3 2 . 1 1 1 . 2 7 1 1 1 4 2 . 6 . 5 4 2 Each same-numbered rectangle above denotes a contiguous rectangle. The largest rectangles take precedence over smaller rectangles that could also be formed in their areas. The order of the numbering/rectangles is unimportant. My current approach is iterative. In each iteration, I build a list of the largest rectangles that could be formed from each of the grid's plottable cells by extending in all 4 directions from the cell. After sorting the list largest first, I begin with the largest rectangle found, mark its underlying cells as "plotted", and record the rectangle in a list. Before plotting each rectangle, its underlying cells are checked to ensure they are not yet plotted (overlapping a previous plot). We then start again, finding the largest remaining rectangles that can be formed and plotting them until all cells have been plotted as part of some rectangle. I consider this approach slightly more optimized than a dumb brute-force search, but I am wasting a lot of cycles (re)calculating cells' largest rectangles and checking underlying cells' states. Currently, this rectangle-discovery routine takes the lion's share of the total runtime of the tool, especially for large blueprints. I have sacrificed some accuracy for the sake of speed by only considering rectangles from cells which appear to form a rectangle's corner (determined using some neighboring-cell heuristics which aren't always correct). As a result of this 'optimization', my current code doesn't actually generate the above solution correctly, but it's close enough. More broadly, I consider the goal of largest-rectangles-first to be a "good enough" approach for this application. However I observe that if the goal is instead to find the minimum set (fewest number) of rectangles to completely cover multiple areas, the solution would look like this instead: . 3 . 5 6 8 1 3 4 5 6 8 . 3 4 5 . 8 2 3 4 5 7 8 . 3 . 5 7 8 This second goal actually represents a more optimal solution to the problem, as fewer rectangles usually means fewer commands sent to Dwarf Fortress. However, this approach strikes me as closer to NP-Hard, based on my limited math knowledge. Watch the video if you'd like to better understand the overall strategy; I have not addressed other aspects of Quickfort's process, such as finding the shortest cursor-path that plots all rectangles. Possibly there is a solution to this problem that coherently combines these multiple strategies. Help of any form would be appreciated.

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• Which workaround to use for the following SQL deadlock?

  - by Marko

  I found a SQL deadlock scenario in my application during concurrency. I belive that the two statements that cause the deadlock are (note - I'm using LINQ2SQL and DataContext.ExecuteCommand(), that's where this.studioId.ToString() comes into play): exec sp_executesql N'INSERT INTO HQ.dbo.SynchronizingRows ([StudioId], [UpdatedRowId]) SELECT @p0, [t0].[Id] FROM [dbo].[UpdatedRows] AS [t0] WHERE NOT (EXISTS( SELECT NULL AS [EMPTY] FROM [dbo].[ReceivedUpdatedRows] AS [t1] WHERE ([t1].[StudioId] = @p0) AND ([t1].[UpdatedRowId] = [t0].[Id]) ))',N'@p0 uniqueidentifier',@p0='" + this.studioId.ToString() + "'; and exec sp_executesql N'INSERT INTO HQ.dbo.ReceivedUpdatedRows ([UpdatedRowId], [StudioId], [ReceiveDateTime]) SELECT [t0].[UpdatedRowId], @p0, GETDATE() FROM [dbo].[SynchronizingRows] AS [t0] WHERE ([t0].[StudioId] = @p0)',N'@p0 uniqueidentifier',@p0='" + this.studioId.ToString() + "'; The basic logic of my (client-server) application is this: Every time someone inserts or updates a row on the server side, I also insert a row into the table UpdatedRows, specifying the RowId of the modified row. When a client tries to synchronize data, it first copies all of the rows in the UpdatedRows table, that don't contain a reference row for the specific client in the table ReceivedUpdatedRows, to the table SynchronizingRows (the first statement taking part in the deadlock). Afterwards, during the synchronization I look for modified rows via lookup of the SynchronizingRows table. This step is required, otherwise if someone inserts new rows or modifies rows on the server side during synchronization I will miss them and won't get them during the next synchronization (explanation scenario to long to write here...). Once synchronization is complete, I insert rows to the ReceivedUpdatedRows table specifying that this client has received the UpdatedRows contained in the SynchronizingRows table (the second statement taking part in the deadlock). Finally I delete all rows from the SynchronizingRows table that belong to the current client. The way I see it, the deadlock is occuring on tables SynchronizingRows (abbreviation SR) and ReceivedUpdatedRows (abbreviation RUR) during steps 2 and 3 (one client is in step 2 and is inserting into SR and selecting from RUR; while another client is in step 3 inserting into RUR and selecting from SR). I googled a bit about SQL deadlocks and came to a conclusion that I have three options. Inorder to make a decision I need more input about each option/workaround: Workaround 1: The first advice given on the web about SQL deadlocks - restructure tables/queries so that deadlocks don't happen in the first place. Only problem with this is that with my IQ I don't see a way to do the synchronization logic any differently. If someone wishes to dwelve deeper into my current synchronization logic, how and why it is set up the way it is, I'll post a link for the explanation. Perhaps, with the help of someone smarter than me, it's possible to create a logic that is deadlock free. Workaround 2: The second most common advice seems to be the use of WITH(NOLOCK) hint. The problem with this is that NOLOCK might miss or duplicate some rows. Duplication is not a problem, but missing rows is catastrophic! Another option is the WITH(READPAST) hint. On the face of it, this seems to be a perfect solution. I really don't care about rows that other clients are inserting/modifying, because each row belongs only to a specific client, so I may very well skip locked rows. But the MSDN documentaion makes me a bit worried - "When READPAST is specified, both row-level and page-level locks are skipped". As I said, row-level locks would not be a problem, but page-level locks may very well be, since a page might contain rows that belong to multiple clients (including the current one). While there are lots of blog posts specifically mentioning that NOLOCK might miss rows, there seems to be none about READPAST (never) missing rows. This makes me skeptical and nervous to implement it, since there is no easy way to test it (implementing would be a piece of cake, just pop WITH(READPAST) into both statements SELECT clause and job done). Can someone confirm whether the READPAST hint can miss rows? Workaround 3: The final option is to use ALLOW_SNAPSHOT_ISOLATION and READ_COMMITED_SNAPSHOT. This would seem to be the only option to work 100% - at least I can't find any information that would contradict with it. But it is a little bit trickier to setup (I don't care much about the performance hit), because I'm using LINQ. Off the top of my head I probably need to manually open a SQL connection and pass it to the LINQ2SQL DataContext, etc... I haven't looked into the specifics very deeply. Mostly I would prefer option 2 if somone could only reassure me that READPAST will never miss rows concerning the current client (as I said before, each client has and only ever deals with it's own set of rows). Otherwise I'll likely have to implement option 3, since option 1 is probably impossible... I'll post the table definitions for the three tables as well, just in case: CREATE TABLE [dbo].[UpdatedRows]( [Id] [uniqueidentifier] NOT NULL ROWGUIDCOL DEFAULT NEWSEQUENTIALID() PRIMARY KEY CLUSTERED, [RowId] [uniqueidentifier] NOT NULL, [UpdateDateTime] [datetime] NOT NULL, ) ON [PRIMARY] GO CREATE NONCLUSTERED INDEX IX_RowId ON dbo.UpdatedRows ([RowId] ASC) WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO CREATE TABLE [dbo].[ReceivedUpdatedRows]( [Id] [uniqueidentifier] NOT NULL ROWGUIDCOL DEFAULT NEWSEQUENTIALID() PRIMARY KEY NONCLUSTERED, [UpdatedRowId] [uniqueidentifier] NOT NULL REFERENCES [dbo].[UpdatedRows] ([Id]), [StudioId] [uniqueidentifier] NOT NULL REFERENCES, [ReceiveDateTime] [datetime] NOT NULL, ) ON [PRIMARY] GO CREATE CLUSTERED INDEX IX_Studios ON dbo.ReceivedUpdatedRows ([StudioId] ASC) WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO CREATE TABLE [dbo].[SynchronizingRows]( [StudioId] [uniqueidentifier] NOT NULL [UpdatedRowId] [uniqueidentifier] NOT NULL REFERENCES [dbo].[UpdatedRows] ([Id]) PRIMARY KEY CLUSTERED ([StudioId], [UpdatedRowId]) ) ON [PRIMARY] GO PS! Studio = Client. PS2! I just noticed that the index definitions have ALLOW_PAGE_LOCK=ON. If I would turn it off, would that make any difference to READPAST? Are there any negative downsides for turning it off?

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