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Search found 523 results on 21 pages for 'callbacks'.

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  • Why do you need "extern C" for in C++ callbacks to C functions?

    - by Artyom
    Hello, I find such examples in Boost code. namespace boost { namespace { extern "C" void *thread_proxy(void *f) { .... } } // anonymous void thread::thread_start(...) { ... pthread_create(something,0,&thread_proxy,something_else); ... } } // boost Why do you actually need this extern "C"? It is clear that thread_proxy function is private internal and I do not expect that it would be mangled as "thread_proxy" because I actually do not need it mangled at all. In fact in all my code that I had written and that runs on may platforms I never used extern "C" and this had worked as-as with normal functions. Why extern "C" is added? My problem is that extern "C" function pollute global name-space and they do not actually hidden as author expects. This is not duplicate! I'm not talking about mangling and external linkage. It is obvious in this code that external linkage is unwanted!

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  • Why do you need "extern C" for C++ callbacks to C functions?

    - by Artyom
    Hello, I find such examples in Boost code. namespace boost { namespace { extern "C" void *thread_proxy(void *f) { .... } } // anonymous void thread::thread_start(...) { ... pthread_create(something,0,&thread_proxy,something_else); ... } } // boost Why do you actually need this extern "C"? It is clear that thread_proxy function is private internal and I do not expect that it would be mangled as "thread_proxy" because I actually do not need it mangled at all. In fact in all my code that I had written and that runs on may platforms I never used extern "C" and this had worked as-as with normal functions. Why extern "C" is added? My problem is that extern "C" function pollute global name-space and they do not actually hidden as author expects. This is not duplicate! I'm not talking about mangling and external linkage. It is obvious in this code that external linkage is unwanted! Answer: Calling convention of C and C++ functions are not necessary the same, so you need to create one with C calling convention. See 7.5 (p4) of C++ standard.

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  • Serious problem with WCF, GridViews, Callbacks and ExecuteReaders exceptions.

    - by barjed
    Hi, I have this problem that is driving me insane. I have a project to deliver before Thursday. Basically an app consiting of three components that communicate with each other in WCF. I have one console app and one Windows Forms app. The console app is a server that's connected to the database. You can add records to it via the Windows Forms client that connectes with the server through the WCF. The code for the client: namespace BankAdministratorClient { [CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Single, UseSynchronizationContext = false)] public partial class Form1 : Form, BankServverReference.BankServerCallback { private BankServverReference.BankServerClient server = null; private SynchronizationContext interfaceContext = null; public Form1() { InitializeComponent(); interfaceContext = SynchronizationContext.Current; server = new BankServverReference.BankServerClient(new InstanceContext(this), "TcpBinding"); server.Open(); server.Subscribe(); refreshGridView(""); } public void refreshClients(string s) { SendOrPostCallback callback = delegate(object state) { refreshGridView(s); }; interfaceContext.Post(callback, s); } public void refreshGridView(string s) { try { userGrid.DataSource = server.refreshDatabaseConnection().Tables[0]; } catch (Exception ex) { MessageBox.Show(ex.ToString()); } } private void buttonAdd_Click(object sender, EventArgs e) { server.addNewAccount(Int32.Parse(inputPIN.Text), Int32.Parse(inputBalance.Text)); } private void Form1_FormClosing(object sender, FormClosingEventArgs e) { try { server.Unsubscribe(); server.Close(); }catch{} } } } The code for the server: namespace SSRfinal_tcp { class Program { static void Main(string[] args) { Console.WriteLine(MessageHandler.dataStamp("The server is starting up")); using (ServiceHost server = new ServiceHost(typeof(BankServer))) { server.Open(); Console.WriteLine(MessageHandler.dataStamp("The server is running")); Console.ReadKey(); } } } [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single, InstanceContextMode = InstanceContextMode.PerCall, IncludeExceptionDetailInFaults = true)] public class BankServer : IBankServerService { private static DatabaseLINQConnectionDataContext database = new DatabaseLINQConnectionDataContext(); private static List<IBankServerServiceCallback> subscribers = new List<IBankServerServiceCallback>(); public void Subscribe() { try { IBankServerServiceCallback callback = OperationContext.Current.GetCallbackChannel<IBankServerServiceCallback>(); if (!subscribers.Contains(callback)) subscribers.Add(callback); Console.WriteLine(MessageHandler.dataStamp("A new Bank Administrator has connected")); } catch { Console.WriteLine(MessageHandler.dataStamp("A Bank Administrator has failed to connect")); } } public void Unsubscribe() { try { IBankServerServiceCallback callback = OperationContext.Current.GetCallbackChannel<IBankServerServiceCallback>(); if (subscribers.Contains(callback)) subscribers.Remove(callback); Console.WriteLine(MessageHandler.dataStamp("A Bank Administrator has been signed out from the connection list")); } catch { Console.WriteLine(MessageHandler.dataStamp("A Bank Administrator has failed to sign out from the connection list")); } } public DataSet refreshDatabaseConnection() { var q = from a in database.GetTable<Account>() select a; DataTable dt = q.toTable(rec => new object[] { q }); DataSet data = new DataSet(); data.Tables.Add(dt); Console.WriteLine(MessageHandler.dataStamp("A Bank Administrator has requested a database data listing refresh")); return data; } public void addNewAccount(int pin, int balance) { Account acc = new Account() { PIN = pin, Balance = balance, IsApproved = false }; database.Accounts.InsertOnSubmit(acc); database.SubmitChanges(); database.addNewAccount(pin, balance, false); subscribers.ForEach(delegate(IBankServerServiceCallback callback) { callback.refreshClients("New operation is pending approval."); }); } } } This is really simple and it works for a single window. However, when you open multiple instances of the client window and try to add a new record, the windows that is performing the insert operation crashes with the ExecuteReader error and the " requires an open and available connection. the connection's current state is connecting" bla bla stuff. I have no idea what's going on. Please advise.

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  • compass-rails 1.03 - TypeError: can't convert nil into String

    - by Romiko
    I am running: ruby 1.9.3p392 (2013-02-22) [i386-mingw32] compass-rails 1.0.3 I used the Windows RailsInstaller to install Ruby on Rails Gemfile group :assets do gem 'sass-rails', '~> 3.2.3' gem 'coffee-rails', '~> 3.2.1' gem 'compass-rails','~> 1.0.2' # See https://github.com/sstephenson/execjs#readme for more supported runtimes # gem 'therubyracer', :platforms => :ruby gem 'uglifier', '>= 1.0.3' end I am currently experiencing issues importing sprites. My sprites are in: assets/images/source in my _shared.scss file I have: //Sprites @import "./source/*.png"; $source-sprite-dimensions: true; In my application.scss I have: /* * This is a manifest file that'll be compiled into application.css, which will include all the files * listed below. * * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets, * or vendor/assets/stylesheets of plugins, if any, can be referenced here using a relative path. * * You're free to add application-wide styles to this file and they'll appear at the top of the * compiled file, but it's generally better to create a new file per style scope. * *= require_self */ @import "_shared.scss"; @import "baseline.scss"; @import "global.scss"; @import "normalize.scss"; @import "print.scss"; @import "desktop.scss"; @import "tablet.scss"; @import "home.css.scss"; I am also using rails server and not compass watcher. However when I browse to the page at localhost:3000/assets/application.css, I get the following error: body:before { font-weight: bold; content: "\000a TypeError: can't convert nil into String\000a (in c:\002f RangerRomOnRails\002f RangerRom\002f app\002f assets\002f stylesheets\002f desktop.scss)"; } body:after { content: "\000a C:\002f RailsInstaller\002f Ruby1.9.3\002f lib\002f ruby\002f gems\002f 1.9.1\002f gems\002f compass-0.12.2\002f lib\002f compass\002f sass_extensions\002f functions\002f image_size.rb:17:in `extname'"; } Here is the full stack trace: compass (0 .12.2) lib/compass/sass_extensions/functions/image_size.rb:17:in `extname' compass (0.12.2) lib/compass/sass_extensions/functions/image_size.rb:17:in `initialize' compass (0.12.2) lib/compass/sass_extensions/functions/image_size.rb:50:in `new' compass (0.12.2) lib/compass/sass_extensions/functions/image_size.rb:50:in `image_dimensions' compass (0.12.2) lib/compass/sass_extensions/functions/image_size.rb:4:in `image_width' sass (3.2.9) lib/sass/script/funcall.rb:112:in `_perform' sass (3.2.9) lib/sass/script/node.rb:40:in `perform' sass (3.2.9) lib/sass/tree/visitors/perform.rb:298:in `visit_prop' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:100:in `visit' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `map' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:109:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:121:in `with_environment' sass (3.2.9) lib/sass/tree/visitors/perform.rb:108:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `block in visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:320:in `visit_rule' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:100:in `visit' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `map' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:109:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:121:in `with_environment' sass (3.2.9) lib/sass/tree/visitors/perform.rb:108:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `block in visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:320:in `visit_rule' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:100:in `visit' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `map' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:109:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:121:in `with_environment' sass (3.2.9) lib/sass/tree/visitors/perform.rb:108:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `block in visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:362:in `visit_media' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:100:in `visit' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `map' sass (3.2.9) lib/sass/tree/visitors/base.rb:53:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:109:in `block in visit_children' sass (3.2.9) lib/sass/tree/visitors/perform.rb:121:in `with_environment' sass (3.2.9) lib/sass/tree/visitors/perform.rb:108:in `visit_children' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `block in visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:128:in `visit_root' sass (3.2.9) lib/sass/tree/visitors/base.rb:37:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:100:in `visit' sass (3.2.9) lib/sass/tree/visitors/perform.rb:7:in `visit' sass (3.2.9) lib/sass/tree/root_node.rb:20:in `render' sass (3.2.9) lib/sass/engine.rb:315:in `_render' sass (3.2.9) lib/sass/engine.rb:262:in `render' sass-rails (3.2.6) lib/sass/rails/template_handlers.rb:106:in `evaluate' tilt (1.4.1) lib/tilt/template.rb:103:in `render' sprockets (2.2.2) lib/sprockets/context.rb:193:in `block in evaluate' sprockets (2.2.2) lib/sprockets/context.rb:190:in `each' sprockets (2.2.2) lib/sprockets/context.rb:190:in `evaluate' sprockets (2.2.2) lib/sprockets/processed_asset.rb:12:in `initialize' sprockets (2.2.2) lib/sprockets/base.rb:249:in `new' sprockets (2.2.2) lib/sprockets/base.rb:249:in `block in build_asset' sprockets (2.2.2) lib/sprockets/base.rb:270:in `circular_call_protection' sprockets (2.2.2) lib/sprockets/base.rb:248:in `build_asset' sprockets (2.2.2) lib/sprockets/index.rb:93:in `block in build_asset' sprockets (2.2.2) lib/sprockets/caching.rb:19:in `cache_asset' sprockets (2.2.2) lib/sprockets/index.rb:92:in `build_asset' sprockets (2.2.2) lib/sprockets/base.rb:169:in `find_asset' sprockets (2.2.2) lib/sprockets/index.rb:60:in `find_asset' sprockets (2.2.2) lib/sprockets/processed_asset.rb:111:in `block in resolve_dependencies' sprockets (2.2.2) lib/sprockets/processed_asset.rb:105:in `each' sprockets (2.2.2) lib/sprockets/processed_asset.rb:105:in `resolve_dependencies' sprockets (2.2.2) lib/sprockets/processed_asset.rb:97:in `build_required_assets' sprockets (2.2.2) lib/sprockets/processed_asset.rb:16:in `initialize' sprockets (2.2.2) lib/sprockets/base.rb:249:in `new' sprockets (2.2.2) lib/sprockets/base.rb:249:in `block in build_asset' sprockets (2.2.2) lib/sprockets/base.rb:270:in `circular_call_protection' sprockets (2.2.2) lib/sprockets/base.rb:248:in `build_asset' sprockets (2.2.2) lib/sprockets/index.rb:93:in `block in build_asset' sprockets (2.2.2) lib/sprockets/caching.rb:19:in `cache_asset' sprockets (2.2.2) lib/sprockets/index.rb:92:in `build_asset' sprockets (2.2.2) lib/sprockets/base.rb:169:in `find_asset' sprockets (2.2.2) lib/sprockets/index.rb:60:in `find_asset' sprockets (2.2.2) lib/sprockets/bundled_asset.rb:38:in `init_with' sprockets (2.2.2) lib/sprockets/asset.rb:24:in `from_hash' sprockets (2.2.2) lib/sprockets/caching.rb:15:in `cache_asset' sprockets (2.2.2) lib/sprockets/index.rb:92:in `build_asset' sprockets (2.2.2) lib/sprockets/base.rb:169:in `find_asset' sprockets (2.2.2) lib/sprockets/index.rb:60:in `find_asset' sprockets (2.2.2) lib/sprockets/environment.rb:78:in `find_asset' sprockets (2.2.2) lib/sprockets/base.rb:177:in `[]' actionpack (3.2.13) lib/sprockets/helpers/rails_helper.rb:126:in `asset_for' actionpack (3.2.13) lib/sprockets/helpers/rails_helper.rb:44:in `block in stylesheet_link_tag' actionpack (3.2.13) lib/sprockets/helpers/rails_helper.rb:43:in `collect' actionpack (3.2.13) lib/sprockets/helpers/rails_helper.rb:43:in `stylesheet_link_tag' app/views/layouts/application.html.erb:16:in `_app_views_layouts_application_html_erb___824639613_33845076' actionpack (3.2.13) lib/action_view/template.rb:145:in `block in render' activesupport (3.2.13) lib/active_support/notifications.rb:125:in `instrument' actionpack (3.2.13) lib/action_view/template.rb:143:in `render' actionpack (3.2.13) lib/action_view/renderer/template_renderer.rb:59:in `render_with_layout' actionpack (3.2.13) lib/action_view/renderer/template_renderer.rb:45:in `render_template' actionpack (3.2.13) lib/action_view/renderer/template_renderer.rb:18:in `render' actionpack (3.2.13) lib/action_view/renderer/renderer.rb:36:in `render_template' actionpack (3.2.13) lib/action_view/renderer/renderer.rb:17:in `render' actionpack (3.2.13) lib/abstract_controller/rendering.rb:110:in `_render_template' actionpack (3.2.13) lib/action_controller/metal/streaming.rb:225:in `_render_template' actionpack (3.2.13) lib/abstract_controller/rendering.rb:103:in `render_to_body' actionpack (3.2.13) lib/action_controller/metal/renderers.rb:28:in `render_to_body' actionpack (3.2.13) lib/action_controller/metal/compatibility.rb:50:in `render_to_body' actionpack (3.2.13) lib/abstract_controller/rendering.rb:88:in `render' actionpack (3.2.13) lib/action_controller/metal/rendering.rb:16:in `render' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:40:in `block (2 levels) in render' activesupport (3.2.13) lib/active_support/core_ext/benchmark.rb:5:in `block in ms' C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/benchmark.rb:295:in `realtime' activesupport (3.2.13) lib/active_support/core_ext/benchmark.rb:5:in `ms' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:40:in `block in render' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:83:in `cleanup_view_runtime' activerecord (3.2.13) lib/active_record/railties/controller_runtime.rb:24:in `cleanup_view_runtime' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:39:in `render' actionpack (3.2.13) lib/action_controller/metal/implicit_render.rb:10:in `default_render' actionpack (3.2.13) lib/action_controller/metal/implicit_render.rb:5:in `send_action' actionpack (3.2.13) lib/abstract_controller/base.rb:167:in `process_action' actionpack (3.2.13) lib/action_controller/metal/rendering.rb:10:in `process_action' actionpack (3.2.13) lib/abstract_controller/callbacks.rb:18:in `block in process_action' activesupport (3.2.13) lib/active_support/callbacks.rb:414:in `_run__956028316__process_action__416811168__callbacks' activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback' activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks' activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks' actionpack (3.2.13) lib/abstract_controller/callbacks.rb:17:in `process_action' actionpack (3.2.13) lib/action_controller/metal/rescue.rb:29:in `process_action' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action' activesupport (3.2.13) lib/active_support/notifications.rb:123:in `block in instrument' activesupport (3.2.13) lib/active_support/notifications/instrumenter.rb:20:in `instrument' activesupport (3.2.13) lib/active_support/notifications.rb:123:in `instrument' actionpack (3.2.13) lib/action_controller/metal/instrumentation.rb:29:in `process_action' actionpack (3.2.13) lib/action_controller/metal/params_wrapper.rb:207:in `process_action' activerecord (3.2.13) lib/active_record/railties/controller_runtime.rb:18:in `process_action' actionpack (3.2.13) lib/abstract_controller/base.rb:121:in `process' actionpack (3.2.13) lib/abstract_controller/rendering.rb:45:in `process' actionpack (3.2.13) lib/action_controller/metal.rb:203:in `dispatch' actionpack (3.2.13) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch' actionpack (3.2.13) lib/action_controller/metal.rb:246:in `block in action' actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `call' actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:73:in `dispatch' actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:36:in `call' journey (1.0.4) lib/journey/router.rb:68:in `block in call' journey (1.0.4) lib/journey/router.rb:56:in `each' journey (1.0.4) lib/journey/router.rb:56:in `call' actionpack (3.2.13) lib/action_dispatch/routing/route_set.rb:612:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call' rack (1.4.5) lib/rack/etag.rb:23:in `call' rack (1.4.5) lib/rack/conditionalget.rb:25:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/head.rb:14:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/params_parser.rb:21:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/flash.rb:242:in `call' rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context' rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/cookies.rb:341:in `call' activerecord (3.2.13) lib/active_record/query_cache.rb:64:in `call' activerecord (3.2.13) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call' activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `_run__360878605__call__248365880__callbacks' activesupport (3.2.13) lib/active_support/callbacks.rb:405:in `__run_callback' activesupport (3.2.13) lib/active_support/callbacks.rb:385:in `_run_call_callbacks' activesupport (3.2.13) lib/active_support/callbacks.rb:81:in `run_callbacks' actionpack (3.2.13) lib/action_dispatch/middleware/callbacks.rb:27:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/reloader.rb:65:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/remote_ip.rb:31:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call' railties (3.2.13) lib/rails/rack/logger.rb:32:in `call_app' railties (3.2.13) lib/rails/rack/logger.rb:16:in `block in call' activesupport (3.2.13) lib/active_support/tagged_logging.rb:22:in `tagged' railties (3.2.13) lib/rails/rack/logger.rb:16:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/request_id.rb:22:in `call' rack (1.4.5) lib/rack/methodoverride.rb:21:in `call' rack (1.4.5) lib/rack/runtime.rb:17:in `call' activesupport (3.2.13) lib/active_support/cache/strategy/local_cache.rb:72:in `call' rack (1.4.5) lib/rack/lock.rb:15:in `call' actionpack (3.2.13) lib/action_dispatch/middleware/static.rb:63:in `call' railties (3.2.13) lib/rails/engine.rb:479:in `call' railties (3.2.13) lib/rails/application.rb:223:in `call' rack (1.4.5) lib/rack/content_length.rb:14:in `call' railties (3.2.13) lib/rails/rack/log_tailer.rb:17:in `call' rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service' C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service' C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run' C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

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  • Assign C++ instance method to a global-function-pointer ?

    - by umanga
    Greetings, My project structure is as follows: \- base (C static library) callbacks.h callbacks.c paint_node.c . . * libBase.a \-app (C++ application) main.cpp In C library 'base' , I have declared global-function-pointer as: in singleheader file callbacks.h #ifndef CALLBACKS_H_ #define CALLBACKS_H_ extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); #endif /* CALLBACKS_H_ */ in single C file they are initialized as callbacks.c #include "callbacks.h" void (*putPixelCallBack)(); void (*putImageCallBack)(); Other C files access this callback-functions as: paint_node.c #include "callbacks.h" void paint_node(node *node,int index){ //Call callbackfunction . . putPixelCallBack(node->x,node->y,index); } I compile these C files and generate a static library 'libBase.a' Then in C++ application, I want to assign C++ instance method to this global function-pointer: I did something like follows : in Sacm.cpp file #include "Sacm.h" extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); void Sacm::doDetection() { putPixelCallBack=(void(*)())&paintPixel; //call somefunctions in 'libBase' C library } void Sacm::paintPixel(int x,int y,int index) { qpainter.begin(this); qpainter.drawPoint(x,y); qpainter.end(); } But when compiling it gives the error: sacmtest.cpp: In member function ‘void Sacm::doDetection()’: sacmtest.cpp:113: error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function. Say ‘&Sacm::paintPixel’ sacmtest.cpp:113: error: converting from ‘void (Sacm::)(int, int, int)’ to ‘void ()()’ Any tips?

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  • Missing a constant on load.. how can i get around this? (Rails::Plugin::OpenID)

    - by Chris Kimpton
    I have a Rails 2 project that I am trying to upgrade to Rails 3, but getting some issues with bundler. When I run "rake", it runs the tests just fine. But when I run "bundle exec rake" it fails to find a constant. The error is this: /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/dependencies.rb:131:in `const_missing': uninitialized constant Rails::Plugin::OpenID (NameError) from /Users/kimptoc/Documents/ruby/borisbikes/borisbikestats.pre3/vendor/plugins/open_id_authentication/init.rb:16:in `evaluate_init_rb' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:182:in `call' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:182:in `evaluate_method' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:166:in `call' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:90:in `run' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:90:in `each' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:90:in `send' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:90:in `run' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/activesupport-2.3.9/lib/active_support/callbacks.rb:276:in `run_callbacks' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/actionpack-2.3.9/lib/action_controller/dispatcher.rb:51:in `send' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/actionpack-2.3.9/lib/action_controller/dispatcher.rb:51:in `run_prepare_callbacks' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/rails-2.3.9/lib/initializer.rb:631:in `prepare_dispatcher' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/rails-2.3.9/lib/initializer.rb:185:in `process' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/rails-2.3.9/lib/initializer.rb:113:in `send' from /Users/kimptoc/.rvm/gems/ruby-1.8.7-p330@p-borisbikestats-pre-rails3/gems/rails-2.3.9/lib/initializer.rb:113:in `run' from /Users/kimptoc/Documents/ruby/borisbikes/borisbikestats.pre3/config/environment.rb:9 from ./test/test_helper.rb:2:in `require' from ./test/test_helper.rb:2 I have these gems installed: $ gem list *** LOCAL GEMS *** actionmailer (2.3.9) actionpack (2.3.9) activerecord (2.3.9) activeresource (2.3.9) activesupport (2.3.9) authlogic (2.1.3) bundler (1.0.7) gravtastic (2.2.0) linecache (0.43) mocha (0.9.10) newrelic_rpm (2.13.4) parseexcel (0.5.2) rack (1.1.0) rack-openid (1.1.1) rails (2.3.9) rake (0.8.7) ruby-debug-base (0.10.5.jb2, 0.10.4) ruby-debug-ide (0.4.15) ruby-openid (2.1.8, 2.1.7, 2.0.4) sqlite3-ruby (1.3.2) The bundler Gemfile is as follows: source 'http://rubygems.org' #gem 'rails', '3.0.3' gem "rails", "2.3.9" gem "activesupport", "2.3.9" gem "ruby-openid", "2.1.7", :require => "openid" #gem "authlogic-oid", "1.0.4" # Bundle edge Rails instead: # gem 'rails', :git => 'git://github.com/rails/rails.git' gem 'sqlite3-ruby', :require => 'sqlite3' gem "authlogic", "= 2.1.3" gem "newrelic_rpm" # gem "facebooker" gem "parseexcel" gem 'gravtastic', '= 2.2.0' gem "rack-openid", '=1.1.1', :require => 'rack/openid' # not sure what this does... gem "mocha" I have these plugins installed: 2dc_jqgrid authlogic_openid open_id_authentication squirrel I see these similar questions: Missing a constant on load.. how can i get around this? and Requiring gem in Rails 3 Controller failing with "Constant Missing" But their solutions dont seem to work for my situation. I am guessing the issue is around the plugins, but my ruby-foo is too weak. Thanks in advance, Chris

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  • No method error in controller create action

    - by user2799827
    I have read a number of Q&As on SO in search of some help on this but have so far not solved my issue. I am trying to teach myself ruby/rails, and as a test project, I want to create a list of tvshows and a list of characters where each tvshow has_many characters and each character belongs_to a specific show. I am sure I am doing something basic incorrectly. Any assistance would be greatly appreciated. here is the characters controller: class CharactersController < ApplicationController before_action :set_character, only: [:show, :edit, :update, :destroy] # GET /characters # GET /characters.json def index @characters = Character.all end # GET /characters/1 # GET /characters/1.json def show end # GET /characters/new def new @character = Character.new end # GET /characters/1/edit def edit end # POST /characters # POST /characters.json def create @character = @tvshow.characters.create(params[:character]) respond_to do |format| if @character.save format.html { redirect_to @character, notice: 'Character was successfully created.' } format.json { render action: 'show', status: :created, location: @character } else format.html { render action: 'new' } format.json { render json: @character.errors, status: :unprocessable_entity } end end end # PATCH/PUT /characters/1 # PATCH/PUT /characters/1.json def update respond_to do |format| if @character.update(character_params) format.html { redirect_to @character, notice: 'Character was successfully updated.' } format.json { head :no_content } else format.html { render action: 'edit' } format.json { render json: @character.errors, status: :unprocessable_entity } end end end # DELETE /characters/1 # DELETE /characters/1.json def destroy @character.destroy respond_to do |format| format.html { redirect_to characters_url } format.json { head :no_content } end end private # Use callbacks to share common setup or constraints between actions. def set_character @character = Character.find(params[:id]) end # Never trust parameters from the scary internet, only allow the white list through. def character_params params.require(:character).permit(:first_name, :last_name, :bio) end end character model: class Character < ActiveRecord::Base belongs_to :tvshow default_scope -> { order('created_at DESC') } validates :tvshow_id, presence: true end tvshow model: class Tvshow < ActiveRecord::Base has_many :characters, dependent: :destroy end error gets returned when I attempt to create a character. here is the full trace: app/controllers/characters_controller.rb:27:in `create' actionpack (4.0.0) lib/action_controller/metal/implicit_render.rb:4:in `send_action' actionpack (4.0.0) lib/abstract_controller/base.rb:189:in `process_action' actionpack (4.0.0) lib/action_controller/metal/rendering.rb:10:in `process_action' actionpack (4.0.0) lib/abstract_controller/callbacks.rb:18:in `block in process_action' activesupport (4.0.0) lib/active_support/callbacks.rb:413:in `_run__1211653665462320621__process_action__callbacks' activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks' actionpack (4.0.0) lib/abstract_controller/callbacks.rb:17:in `process_action' actionpack (4.0.0) lib/action_controller/metal/rescue.rb:29:in `process_action' actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action' activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument' activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument' activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument' actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:30:in `process_action' actionpack (4.0.0) lib/action_controller/metal/params_wrapper.rb:245:in `process_action' activerecord (4.0.0) lib/active_record/railties/controller_runtime.rb:18:in `process_action' actionpack (4.0.0) lib/abstract_controller/base.rb:136:in `process' actionpack (4.0.0) lib/abstract_controller/rendering.rb:44:in `process' actionpack (4.0.0) lib/action_controller/metal.rb:195:in `dispatch' actionpack (4.0.0) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch' actionpack (4.0.0) lib/action_controller/metal.rb:231:in `block in action' actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `call' actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `dispatch' actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:48:in `call' actionpack (4.0.0) lib/action_dispatch/journey/router.rb:71:in `block in call' actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `each' actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `call' actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:655:in `call' rack (1.5.2) lib/rack/etag.rb:23:in `call' rack (1.5.2) lib/rack/conditionalget.rb:35:in `call' rack (1.5.2) lib/rack/head.rb:11:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call' rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context' rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call' activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call' activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call' activerecord (4.0.0) lib/active_record/migration.rb:369:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call' activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__2792846465963916895__call__callbacks' activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks' actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call' railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app' railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call' activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged' activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged' activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged' railties (4.0.0) lib/rails/rack/logger.rb:21:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call' rack (1.5.2) lib/rack/methodoverride.rb:21:in `call' rack (1.5.2) lib/rack/runtime.rb:17:in `call' activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call' rack (1.5.2) lib/rack/lock.rb:17:in `call' actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call' railties (4.0.0) lib/rails/engine.rb:511:in `call' railties (4.0.0) lib/rails/application.rb:97:in `call' rack (1.5.2) lib/rack/lock.rb:17:in `call' rack (1.5.2) lib/rack/content_length.rb:14:in `call' rack (1.5.2) lib/rack/handler/webrick.rb:60:in `service' /Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service' /Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run' /Users/dariusgoore/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

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  • How is this paradigm/style called?

    - by McMannus
    I have the following situation: I'm developing an add-in for a UML modeling tool. The models that can be created by the user are stored inside the main application and a limited access to the models is given through its API. However, the add-in has a lot of callbacks for events that are triggered by the main application, when changes to the model occur by the user. Since the models are already stored once in the main application, I considered it not practicable to duplicate the models in the add-in, which leads to the fact that I have only behavior in the add-in, rather than having a state. This behavior is mainly expressed by static functions, that are organized in functional cohesive classes. The callbacks for the events have always references to the model elements relevant for the specifc event that ocurred. First, it seemed to me that this is a procedural style in general, but procedural style doesn't consider events/callbacks, so this boils down to the question. How is this programming style called?

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  • How to delete/edit files from readonly filesystem

    - by Santosh Linkha
    I am having problem with my memory device (actually a memory card that act external memory device like pendrive). experimentx@workmateX:/var/www/zendtest$ sudo rm /media/A88F-8788/python-2.7.1-docs-html.zip rm: cannot remove `/media/A88F-8788/python-2.7.1-docs-html.zip': Read-only file system I tried to change the file permission of the system but that doesn't work experimentx@workmateX:/var/www/zendtest$ sudo chmod 0777 /media/A88F-8788/python-2.7.1-docs-html.zip chmod: changing permissions of `/media/A88F-8788/python-2.7.1-docs-html.zip': Read-only file system But it perfectly works on windows. UPDATE On opening the drive and running command sudo mount -o remount,rw /media/A88F-8788 /var/log/syslog: Mar 23 15:29:48 workmateX kernel: [18042.257407] fat_get_cluster: 11 callbacks suppressed Mar 23 15:29:48 workmateX kernel: [18042.257414] FAT: Filesystem error (dev sdb1) Mar 23 15:29:48 workmateX kernel: [18042.257418] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:29:48 workmateX kernel: [18042.257425] FAT: Filesystem has been set read-only Mar 23 15:29:48 workmateX kernel: [18042.258187] FAT: Filesystem error (dev sdb1) Mar 23 15:29:48 workmateX kernel: [18042.258194] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.333787] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.333795] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.335949] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.335957] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.354903] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.354911] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.357213] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.357221] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.359547] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.359555] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.361929] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.361936] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.377416] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.377424] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.379384] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.379392] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.381898] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.381906] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.383764] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.383772] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.569747] fat_get_cluster: 11 callbacks suppressed Mar 23 15:31:40 workmateX kernel: [18154.569754] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.569758] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.569765] FAT: Filesystem has been set read-only Mar 23 15:31:40 workmateX kernel: [18154.572022] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.572029] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.582933] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.582941] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.585921] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.585929] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.587819] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.587827] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.597547] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.597555] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.599503] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.599511] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.602896] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.602905] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.615338] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.615346] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.618574] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.618581] fat_get_cluster: invalid cluster chain (i_pos 0) var/log/message: Mar 23 15:29:48 workmateX kernel: [18042.257407] fat_get_cluster: 11 callbacks suppressed Mar 23 15:31:40 workmateX kernel: [18154.569747] fat_get_cluster: 11 callbacks suppressed

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  • Is it appropriate to try to control the order of finalization?

    - by Strilanc
    I'm writing a class which is roughly analogous to a CancellationToken, except it has a third state for "never going to be cancelled". At the moment I'm trying to decide what to do if the 'source' of the token is garbage collected without ever being set. It seems that, intuitively, the source should transition the associated token to the 'never cancelled' state when it is about to be collected. However, this could trigger callbacks who were only kept alive by their linkage from the token. That means what those callbacks reference might now in the process of finalization. Calling them would be bad. In order to "fix" this, I wrote this class: public sealed class GCRoot { private static readonly GCRoot MainRoot = new GCRoot(); private GCRoot _next; private GCRoot _prev; private object _value; private GCRoot() { this._next = this._prev = this; } private GCRoot(GCRoot prev, object value) { this._value = value; this._prev = prev; this._next = prev._next; _prev._next = this; _next._prev = this; } public static GCRoot Root(object value) { return new GCRoot(MainRoot, value); } public void Unroot() { lock (MainRoot) { _next._prev = _prev; _prev._next = _next; this._next = this._prev = this; } } } intending to use it like this: Source() { ... _root = GCRoot.Root(callbacks); } void TransitionToNeverCancelled() { _root.Unlink(); ... } ~Source() { TransitionToNeverCancelled(); } but now I'm troubled. This seems to open the possibility for memory leaks, without actually fixing all cases of sources in limbo. Like, if a source is closed over in one of its own callbacks, then it is rooted by the callback root and so can never be collected. Presumably I should just let my sources be collected without a peep. Or maybe not? Is it ever appropriate to try to control the order of finalization, or is it a giant warning sign?

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  • What determines which Javascript functions are blocking vs non-blocking?

    - by Sean
    I have been doing web-based Javascript (vanilla JS, jQuery, Backbone, etc.) for a few years now, and recently I've been doing some work with Node.js. It took me a while to get the hang of "non-blocking" programming, but I've now gotten used to using callbacks for IO operations and whatnot. I understand that Javascript is single-threaded by nature. I understand the concept of the Node "event queue". What I DON'T understand is what determines whether an individual javascript operation is "blocking" vs. "non-blocking". How do I know which operations I can depend on to produce an output synchronously for me to use in later code, and which ones I'll need to pass callbacks to so I can process the output after the initial operation has completed? Is there a list of Javascript functions somewhere that are asynchronous/non-blocking, and a list of ones that are synchronous/blocking? What is preventing my Javascript app from being one giant race condition? I know that operations that take a long time, like IO operations in Node and AJAX operations on the web, require them to be asynchronous and therefore use callbacks - but who is determining what qualifies as "a long time"? Is there some sort of trigger within these operations that removes them from the normal "event queue"? If not, what makes them different from simple operations like assigning values to variables or looping through arrays, which it seems we can depend on to finish in a synchronous manner? Perhaps I'm not even thinking of this correctly - hoping someone can set me straight. Thanks!

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  • RSpec test failing looking for a new set of eyes

    - by TheDelChop
    Guys, Here my issuse: I've got two models: class User < ActiveRecord::Base # Setup accessible (or protected) attributes for your model attr_accessible :email, :username has_many :tasks end class Task < ActiveRecord::Base belongs_to :user end with this simple routes.rb file TestProj::Application.routes.draw do |map| resources :users do resources :tasks end end this schema: ActiveRecord::Schema.define(:version => 20100525021007) do create_table "tasks", :force => true do |t| t.string "name" t.integer "estimated_time" t.datetime "created_at" t.datetime "updated_at" t.integer "user_id" end create_table "users", :force => true do |t| t.string "email" t.string "password" t.string "password_confirmation" t.datetime "created_at" t.datetime "updated_at" t.string "username" end add_index "users", ["email"], :name => "index_users_on_email", :unique => true add_index "users", ["username"], :name => "index_users_on_username", :unique => true end and this controller for my tasks: class TasksController < ApplicationController before_filter :load_user def new @task = @user.tasks.new end private def load_user @user = User.find(params[:user_id]) end end Finally here is my test: require 'spec_helper' describe TasksController do before(:each) do @user = Factory(:user) @task = Factory(:task) end #GET New describe "GET New" do before(:each) do User.stub!(:find).with(@user.id.to_s).and_return(@user) @user.stub_chain(:tasks, :new).and_return(@task) end it "should return a new Task" do @user.tasks.should_receive(:new).and_return(@task) get :new, :user_id => @user.id end end end This test fails with the following output: 1) TasksController GET New should return a new Task Failure/Error: get :new, :user_id => @user.id undefined method `abstract_class?' for Object:Class # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:1234:in `class_of_active_record_descendant' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:900:in `base_class' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:655:in `reset_table_name' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:647:in `table_name' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:932:in `arel_table' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:927:in `unscoped' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/named_scope.rb:30:in `scoped' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activerecord/lib/active_record/base.rb:405:in `find' # ./app/controllers/tasks_controller.rb:15:in `load_user' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/callbacks.rb:431:in `_run__1954900289__process_action__943997142__callbacks' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/callbacks.rb:405:in `send' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/callbacks.rb:405:in `_run_process_action_callbacks' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/callbacks.rb:88:in `send' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/callbacks.rb:88:in `run_callbacks' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/abstract_controller/callbacks.rb:17:in `process_action' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/action_controller/metal/rescue.rb:8:in `process_action' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/abstract_controller/base.rb:113:in `process' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/abstract_controller/rendering.rb:39:in `sass_old_process' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/gems/haml-3.0.0.beta.3/lib/sass/plugin/rails.rb:26:in `process' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/action_controller/metal/testing.rb:12:in `process_with_new_base_test' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/action_controller/test_case.rb:390:in `process' # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/actionpack/lib/action_controller/test_case.rb:328:in `get' # ./spec/controllers/tasks_controller_spec.rb:20 # /home/chopper/.rvm/gems/ruby-1.8.7-p249@rails3/bundler/gems/rails-16a5e918a06649ffac24fd5873b875daf66212ad-master/activesupport/lib/active_support/dependencies.rb:209:in `inject' Can anybody help me understand what's going on here? It seems to be an RSpec problem since the controller action actually works, but I could be wrong. Thanks, Joe

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  • Why do I get a WCF timeout even though my service call and callback are successful?

    - by KallDrexx
    I'm playing around with hooking up an in-game console to a WCF interface, so an external application can send console commands and receive console output. To accomplish this I created the following service contracts: public interface IConsoleNetworkCallbacks { [OperationContract(IsOneWay = true)] void NewOutput(IEnumerable<string> text, string category); } [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(IConsoleNetworkCallbacks))] public interface IConsoleInterface { [OperationContract] void ProcessInput(string input); [OperationContract] void ChangeCategory(string category); } On the server I implemented it with: public class ConsoleNetworkInterface : IConsoleInterface, IDisposable { public ConsoleNetworkInterface() { ConsoleManager.Instance.RegisterOutputUpdateHandler(OutputHandler); } public void Dispose() { ConsoleManager.Instance.UnregisterOutputHandler(OutputHandler); } public void ProcessInput(string input) { ConsoleManager.Instance.ProcessInput(input); } public void ChangeCategory(string category) { ConsoleManager.Instance.UnregisterOutputHandler(OutputHandler); ConsoleManager.Instance.RegisterOutputUpdateHandler(OutputHandler, category); } protected void OutputHandler(IEnumerable<string> text, string category) { var callbacks = OperationContext.Current.GetCallbackChannel<IConsoleNetworkCallbacks>(); callbacks.NewOutput(text, category); } } On the client I implemented the callback with: public class Callbacks : IConsoleNetworkCallbacks { public void NewOutput(IEnumerable<string> text, string category) { MessageBox.Show(string.Format("{0} lines received for '{1}' category", text.Count(), category)); } } Finally, I establish the service host with the following class: public class ConsoleServiceHost : IDisposable { protected ServiceHost _host; public ConsoleServiceHost() { _host = new ServiceHost(typeof(ConsoleNetworkInterface), new Uri[] { new Uri("net.pipe://localhost") }); _host.AddServiceEndpoint(typeof(IConsoleInterface), new NetNamedPipeBinding(), "FrbConsolePipe"); _host.Open(); } public void Dispose() { _host.Close(); } } and use the following code on my client to establish the connection: protected Callbacks _callbacks; protected IConsoleInterface _proxy; protected void ConnectToConsoleServer() { _callbacks = new Callbacks(); var factory = new DuplexChannelFactory<IConsoleInterface>(_callbacks, new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/FrbConsolePipe")); _proxy = factory.CreateChannel(); _proxy.ProcessInput("Connected"); } So what happens is that my ConnectToConsoleServer() is called and then it gets all the way to _proxy.ProcessInput("Connected");. In my game (on the server) I immediately see the output caused by the ProcessInput call, but the client is still stalled on the _proxy.ProcessInput() call. After a minute my client gets a JIT TimeoutException however at the same time my MessageBox message appears. So obviously not only is my command being sent immediately, my callback is being correctly called. So why am I getting a timeout exception? Note: Even removing the MessageBox call, I still have this issue, so it's not an issue of the GUI blocking the callback response.

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  • What are the use cases for closures/callback functions in Javascript?

    - by Christopher Altman
    I was listening to Crockford's talk on Javascript closures and am convinced of the benefit of information hiding, but I do not have a firm understanding of when to use callback functions. It is mostly a true statement that a person could accomplish the same functionality with or without callbacks. As someone who is writing code, what heuristics or cues should I keep in mind when determining when to use callbacks/closures? I am not looking for the blanket statement 'Closures make more secure code', rather a list of practical examples or rules of thumb for when callbacks are the right idea. Crockford's Presentation: http://www.yuiblog.com/blog/2010/04/08/video-crockonjs-5/

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  • Designing for an algorithm that reports progress

    - by Stefano Borini
    I have an iterative algorithm and I want to print the progress. However, I may also want it not to print any information, or to print it in a different way, or do other logic. In an object oriented language, I would perform the following solutions: Solution 1: virtual method have the algorithm class MyAlgoClass which implements the algo. The class also implements a virtual reportIteration(iterInfo) method which is empty and can be reimplemented. Subclass the MyAlgoClass and override reportIteration so that it does what it needs to do. This solution allows you to carry additional information (for example, the file unit) in the reimplemented class. I don't like this method because it clumps together two functionalities that may be unrelated, but in GUI apps it may be ok. Solution 2: observer pattern the algorithm class has a register(Observer) method, keeps a list of the registered observers and takes care of calling notify() on each of them. Observer::notify() needs a way to get the information from the Subject, so it either has two parameters, one with the Subject and the other with the data the Subject may pass, or just the Subject and the Observer is now in charge of querying it to fetch the relevant information. Solution 3: callbacks I tend to see the callback method as a lightweight observer. Instead of passing an object, you pass a callback, which may be a plain function, but also an instance method in those languages that allow it (for example, in python you can because passing an instance method will remain bound to the instance). C++ however does not allow it, because if you pass a pointer to an instance method, this will not be defined. Please correct me on this regard, my C++ is quite old. The problem with callbacks is that generally you have to pass them together with the data you want the callback to be invoked with. Callbacks don't store state, so you have to pass both the callback and the state to the Subject in order to find it at callback execution, together with any additional data the Subject may provide about the event is reporting. Question My question is relative to the fact that I need to implement the opening problem in a language that is not object oriented, namely Fortran 95, and I am fighting with my usual reasoning which is based on python assumptions and style. I think that in Fortran the concept is similar to C, with the additional trouble that in C you can store a function pointer, while in Fortran 95 you can only pass it around. Do you have any comments, suggestions, tips, and quirks on this regard (in C, C++, Fortran and python, but also in any other language, so to have a comparison of language features that can be exploited on this regard) on how to design for an algorithm that must report progress to some external entity, using state from both the algorithm and the external entity ?

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  • DDD / Layers and legacy systems

    - by CSM
    I have to refactor a complex C# app (many dialogs, mixed logic and so on). There is a part managing the communication with special hardware equipments (sending commands and receive data via asynchronous c# callbacks). The code is "spaghetti" with mixed UI/Logic/Communication/etc and my task is to split the layers in a DDD sense. So, to which layer belongs a callback driver routine? The callbacks are creating "bubbles" in the system, up to the UI layer and because of this I cannot enforce the essential principle that any element of a layer depends only on other elements in the same layer or on elements of the layers "beneath" it. Thank you in advance.

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  • Can I load multiple UIViewControllers that each kick off their own NSURLConnections?

    - by RexOnRoids
    My Rootviewcontroller uses NSURLConnection to get data from a server, and then, based on this data, loads a bunch (like 7) of smaller UIViewControllers that each also use their own NSURLConnection to get some more specific data from the server. But, the problem is, only the RooTViewController is recieving callbacks from: - (void)connectionDidFinishLoading:(NSURLConnection *)theConnection the other UIViewControllers never get callbacks...

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  • callback pattern

    - by robUK
    Hello, gcc 4.4.3 c89 I am creating a client server application and I will need to implement some callback functions. However, I am not too experienced in callbacks. And I am wondering if anyone knowns some good reference material to follow when designing callbacks. Is there any design patterns that are used for c. I did look at some patterns but there where all c++. Many thanks for any suggestions,

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  • Using the West Wind Web Toolkit to set up AJAX and REST Services

    - by Rick Strahl
    I frequently get questions about which option to use for creating AJAX and REST backends for ASP.NET applications. There are many solutions out there to do this actually, but when I have a choice - not surprisingly - I fall back to my own tools in the West Wind West Wind Web Toolkit. I've talked a bunch about the 'in-the-box' solutions in the past so for a change in this post I'll talk about the tools that I use in my own and customer applications to handle AJAX and REST based access to service resources using the West Wind West Wind Web Toolkit. Let me preface this by saying that I like things to be easy. Yes flexible is very important as well but not at the expense of over-complexity. The goal I've had with my tools is make it drop dead easy, with good performance while providing the core features that I'm after, which are: Easy AJAX/JSON Callbacks Ability to return any kind of non JSON content (string, stream, byte[], images) Ability to work with both XML and JSON interchangeably for input/output Access endpoints via POST data, RPC JSON calls, GET QueryString values or Routing interface Easy to use generic JavaScript client to make RPC calls (same syntax, just what you need) Ability to create clean URLS with Routing Ability to use standard ASP.NET HTTP Stack for HTTP semantics It's all about options! In this post I'll demonstrate most of these features (except XML) in a few simple and short samples which you can download. So let's take a look and see how you can build an AJAX callback solution with the West Wind Web Toolkit. Installing the Toolkit Assemblies The easiest and leanest way of using the Toolkit in your Web project is to grab it via NuGet: West Wind Web and AJAX Utilities (Westwind.Web) and drop it into the project by right clicking in your Project and choosing Manage NuGet Packages from anywhere in the Project.   When done you end up with your project looking like this: What just happened? Nuget added two assemblies - Westwind.Web and Westwind.Utilities and the client ww.jquery.js library. It also added a couple of references into web.config: The default namespaces so they can be accessed in pages/views and a ScriptCompressionModule that the toolkit optionally uses to compress script resources served from within the assembly (namely ww.jquery.js and optionally jquery.js). Creating a new Service The West Wind Web Toolkit supports several ways of creating and accessing AJAX services, but for this post I'll stick to the lower level approach that works from any plain HTML page or of course MVC, WebForms, WebPages. There's also a WebForms specific control that makes this even easier but I'll leave that for another post. So, to create a new standalone AJAX/REST service we can create a new HttpHandler in the new project either as a pure class based handler or as a generic .ASHX handler. Both work equally well, but generic handlers don't require any web.config configuration so I'll use that here. In the root of the project add a Generic Handler. I'm going to call this one StockService.ashx. Once the handler has been created, edit the code and remove all of the handler body code. Then change the base class to CallbackHandler and add methods that have a [CallbackMethod] attribute. Here's the modified base handler implementation now looks like with an added HelloWorld method: using System; using Westwind.Web; namespace WestWindWebAjax { /// <summary> /// Handler implements CallbackHandler to provide REST/AJAX services /// </summary> public class SampleService : CallbackHandler { [CallbackMethod] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } } } Notice that the class inherits from CallbackHandler and that the HelloWorld service method is marked up with [CallbackMethod]. We're done here. Services Urlbased Syntax Once you compile, the 'service' is live can respond to requests. All CallbackHandlers support input in GET and POST formats, and can return results as JSON or XML. To check our fancy HelloWorld method we can now access the service like this: http://localhost/WestWindWebAjax/StockService.ashx?Method=HelloWorld&name=Rick which produces a default JSON response - in this case a string (wrapped in quotes as it's JSON): (note by default JSON will be downloaded by most browsers not displayed - various options are available to view JSON right in the browser) If I want to return the same data as XML I can tack on a &format=xml at the end of the querystring which produces: <string>Hello Rick. Time is: 11/1/2011 12:11:13 PM</string> Cleaner URLs with Routing Syntax If you want cleaner URLs for each operation you can also configure custom routes on a per URL basis similar to the way that WCF REST does. To do this you need to add a new RouteHandler to your application's startup code in global.asax.cs one for each CallbackHandler based service you create: protected void Application_Start(object sender, EventArgs e) { CallbackHandlerRouteHandler.RegisterRoutes<StockService>(RouteTable.Routes); } With this code in place you can now add RouteUrl properties to any of your service methods. For the HelloWorld method that doesn't make a ton of sense but here is what a routed clean URL might look like in definition: [CallbackMethod(RouteUrl="stocks/HelloWorld/{name}")] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } The same URL I previously used now becomes a bit shorter and more readable with: http://localhost/WestWindWebAjax/HelloWorld/Rick It's an easy way to create cleaner URLs and still get the same functionality. Calling the Service with $.getJSON() Since the result produced is JSON you can now easily consume this data using jQuery's getJSON method. First we need a couple of scripts - jquery.js and ww.jquery.js in the page: <!DOCTYPE html> <html> <head> <link href="Css/Westwind.css" rel="stylesheet" type="text/css" /> <script src="scripts/jquery.min.js" type="text/javascript"></script> <script src="scripts/ww.jquery.min.js" type="text/javascript"></script> </head> <body> Next let's add a small HelloWorld example form (what else) that has a single textbox to type a name, a button and a div tag to receive the result: <fieldset> <legend>Hello World</legend> Please enter a name: <input type="text" name="txtHello" id="txtHello" value="" /> <input type="button" id="btnSayHello" value="Say Hello (POST)" /> <input type="button" id="btnSayHelloGet" value="Say Hello (GET)" /> <div id="divHelloMessage" class="errordisplay" style="display:none;width: 450px;" > </div> </fieldset> Then to call the HelloWorld method a little jQuery is used to hook the document startup and the button click followed by the $.getJSON call to retrieve the data from the server. <script type="text/javascript"> $(document).ready(function () { $("#btnSayHelloGet").click(function () { $.getJSON("SampleService.ashx", { Method: "HelloWorld", name: $("#txtHello").val() }, function (result) { $("#divHelloMessage") .text(result) .fadeIn(1000); }); });</script> .getJSON() expects a full URL to the endpoint of our service, which is the ASHX file. We can either provide a full URL (SampleService.ashx?Method=HelloWorld&name=Rick) or we can just provide the base URL and an object that encodes the query string parameters for us using an object map that has a property that matches each parameter for the server method. We can also use the clean URL routing syntax, but using the object parameter encoding actually is safer as the parameters will get properly encoded by jQuery. The result returned is whatever the result on the server method is - in this case a string. The string is applied to the divHelloMessage element and we're done. Obviously this is a trivial example, but it demonstrates the basics of getting a JSON response back to the browser. AJAX Post Syntax - using ajaxCallMethod() The previous example allows you basic control over the data that you send to the server via querystring parameters. This works OK for simple values like short strings, numbers and boolean values, but doesn't really work if you need to pass something more complex like an object or an array back up to the server. To handle traditional RPC type messaging where the idea is to map server side functions and results to a client side invokation, POST operations can be used. The easiest way to use this functionality is to use ww.jquery.js and the ajaxCallMethod() function. ww.jquery wraps jQuery's AJAX functions and knows implicitly how to call a CallbackServer method with parameters and parse the result. Let's look at another simple example that posts a simple value but returns something more interesting. Let's start with the service method: [CallbackMethod(RouteUrl="stocks/{symbol}")] public StockQuote GetStockQuote(string symbol) { Response.Cache.SetExpires(DateTime.UtcNow.Add(new TimeSpan(0, 2, 0))); StockServer server = new StockServer(); var quote = server.GetStockQuote(symbol); if (quote == null) throw new ApplicationException("Invalid Symbol passed."); return quote; } This sample utilizes a small StockServer helper class (included in the sample) that downloads a stock quote from Yahoo's financial site via plain HTTP GET requests and formats it into a StockQuote object. Lets create a small HTML block that lets us query for the quote and display it: <fieldset> <legend>Single Stock Quote</legend> Please enter a stock symbol: <input type="text" name="txtSymbol" id="txtSymbol" value="msft" /> <input type="button" id="btnStockQuote" value="Get Quote" /> <div id="divStockDisplay" class="errordisplay" style="display:none; width: 450px;"> <div class="label-left">Company:</div> <div id="stockCompany"></div> <div class="label-left">Last Price:</div> <div id="stockLastPrice"></div> <div class="label-left">Quote Time:</div> <div id="stockQuoteTime"></div> </div> </fieldset> The final result looks something like this:   Let's hook up the button handler to fire the request and fill in the data as shown: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").show().fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, HH:mm EST")); }, onPageError); }); So we point at SampleService.ashx and the GetStockQuote method, passing a single parameter of the input symbol value. Then there are two handlers for success and failure callbacks.  The success handler is the interesting part - it receives the stock quote as a result and assigns its values to various 'holes' in the stock display elements. The data that comes back over the wire is JSON and it looks like this: { "Symbol":"MSFT", "Company":"Microsoft Corpora", "OpenPrice":26.11, "LastPrice":26.01, "NetChange":0.02, "LastQuoteTime":"2011-11-03T02:00:00Z", "LastQuoteTimeString":"Nov. 11, 2011 4:20pm" } which is an object representation of the data. JavaScript can evaluate this JSON string back into an object easily and that's the reslut that gets passed to the success function. The quote data is then applied to existing page content by manually selecting items and applying them. There are other ways to do this more elegantly like using templates, but here we're only interested in seeing how the data is returned. The data in the object is typed - LastPrice is a number and QuoteTime is a date. Note about the date value: JavaScript doesn't have a date literal although the JSON embedded ISO string format used above  ("2011-11-03T02:00:00Z") is becoming fairly standard for JSON serializers. However, JSON parsers don't deserialize dates by default and return them by string. This is why the StockQuote actually returns a string value of LastQuoteTimeString for the same date. ajaxMethodCallback always converts dates properly into 'real' dates and the example above uses the real date value along with a .formatDate() data extension (also in ww.jquery.js) to display the raw date properly. Errors and Exceptions So what happens if your code fails? For example if I pass an invalid stock symbol to the GetStockQuote() method you notice that the code does this: if (quote == null) throw new ApplicationException("Invalid Symbol passed."); CallbackHandler automatically pushes the exception message back to the client so it's easy to pick up the error message. Regardless of what kind of error occurs: Server side, client side, protocol errors - any error will fire the failure handler with an error object parameter. The error is returned to the client via a JSON response in the error callback. In the previous examples I called onPageError which is a generic routine in ww.jquery that displays a status message on the bottom of the screen. But of course you can also take over the error handling yourself: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); }, function (error, xhr) { $("#divErrorDisplay").text(error.message).fadeIn(1000); }); }); The error object has a isCallbackError, message and  stackTrace properties, the latter of which is only populated when running in Debug mode, and this object is returned for all errors: Client side, transport and server side errors. Regardless of which type of error you get the same object passed (as well as the XHR instance optionally) which makes for a consistent error retrieval mechanism. Specifying HttpVerbs You can also specify HTTP Verbs that are allowed using the AllowedHttpVerbs option on the CallbackMethod attribute: [CallbackMethod(AllowedHttpVerbs=HttpVerbs.GET | HttpVerbs.POST)] public string HelloWorld(string name) { … } If you're building REST style API's this might be useful to force certain request semantics onto the client calling. For the above if call with a non-allowed HttpVerb the request returns a 405 error response along with a JSON (or XML) error object result. The default behavior is to allow all verbs access (HttpVerbs.All). Passing in object Parameters Up to now the parameters I passed were very simple. But what if you need to send something more complex like an object or an array? Let's look at another example now that passes an object from the client to the server. Keeping with the Stock theme here lets add a method called BuyOrder that lets us buy some shares for a stock. Consider the following service method that receives an StockBuyOrder object as a parameter: [CallbackMethod] public string BuyStock(StockBuyOrder buyOrder) { var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } public class StockBuyOrder { public string Symbol { get; set; } public int Quantity { get; set; } public DateTime BuyOn { get; set; } public StockBuyOrder() { BuyOn = DateTime.Now; } } This is a contrived do-nothing example that simply echoes back what was passed in, but it demonstrates how you can pass complex data to a callback method. On the client side we now have a very simple form that captures the three values on a form: <fieldset> <legend>Post a Stock Buy Order</legend> Enter a symbol: <input type="text" name="txtBuySymbol" id="txtBuySymbol" value="GLD" />&nbsp;&nbsp; Qty: <input type="text" name="txtBuyQty" id="txtBuyQty" value="10" style="width: 50px" />&nbsp;&nbsp; Buy on: <input type="text" name="txtBuyOn" id="txtBuyOn" value="<%= DateTime.Now.ToString("d") %>" style="width: 70px;" /> <input type="button" id="btnBuyStock" value="Buy Stock" /> <div id="divStockBuyMessage" class="errordisplay" style="display:none"></div> </fieldset> The completed form and demo then looks something like this:   The client side code that picks up the input values and assigns them to object properties and sends the AJAX request looks like this: $("#btnBuyStock").click(function () { // create an object map that matches StockBuyOrder signature var buyOrder = { Symbol: $("#txtBuySymbol").val(), Quantity: $("#txtBuyQty").val() * 1, // number Entered: new Date() } ajaxCallMethod("SampleService.ashx", "BuyStock", [buyOrder], function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError); }); The code creates an object and attaches the properties that match the server side object passed to the BuyStock method. Each property that you want to update needs to be included and the type must match (ie. string, number, date in this case). Any missing properties will not be set but also not cause any errors. Pass POST data instead of Objects In the last example I collected a bunch of values from form variables and stuffed them into object variables in JavaScript code. While that works, often times this isn't really helping - I end up converting my types on the client and then doing another conversion on the server. If lots of input controls are on a page and you just want to pick up the values on the server via plain POST variables - that can be done too - and it makes sense especially if you're creating and filling the client side object only to push data to the server. Let's add another method to the server that once again lets us buy a stock. But this time let's not accept a parameter but rather send POST data to the server. Here's the server method receiving POST data: [CallbackMethod] public string BuyStockPost() { StockBuyOrder buyOrder = new StockBuyOrder(); buyOrder.Symbol = Request.Form["txtBuySymbol"]; ; int qty; int.TryParse(Request.Form["txtBuyQuantity"], out qty); buyOrder.Quantity = qty; DateTime time; DateTime.TryParse(Request.Form["txtBuyBuyOn"], out time); buyOrder.BuyOn = time; // Or easier way yet //FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } Clearly we've made this server method take more code than it did with the object parameter. We've basically moved the parameter assignment logic from the client to the server. As a result the client code to call this method is now a bit shorter since there's no client side shuffling of values from the controls to an object. $("#btnBuyStockPost").click(function () { ajaxCallMethod("SampleService.ashx", "BuyStockPost", [], // Note: No parameters - function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError, // Force all page Form Variables to be posted { postbackMode: "Post" }); }); The client simply calls the BuyStockQuote method and pushes all the form variables from the page up to the server which parses them instead. The feature that makes this work is one of the options you can pass to the ajaxCallMethod() function: { postbackMode: "Post" }); which directs the function to include form variable POST data when making the service call. Other options include PostNoViewState (for WebForms to strip out WebForms crap vars), PostParametersOnly (default), None. If you pass parameters those are always posted to the server except when None is set. The above code can be simplified a bit by using the FormVariableBinder helper, which can unbind form variables directly into an object: FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); which replaces the manual Request.Form[] reading code. It receives the object to unbind into, a string of properties to skip, and an optional prefix which is stripped off form variables to match property names. The component is similar to the MVC model binder but it's independent of MVC. Returning non-JSON Data CallbackHandler also supports returning non-JSON/XML data via special return types. You can return raw non-JSON encoded strings like this: [CallbackMethod(ReturnAsRawString=true,ContentType="text/plain")] public string HelloWorldNoJSON(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } Calling this method results in just a plain string - no JSON encoding with quotes around the result. This can be useful if your server handling code needs to return a string or HTML result that doesn't fit well for a page or other UI component. Any string output can be returned. You can also return binary data. Stream, byte[] and Bitmap/Image results are automatically streamed back to the client. Notice that you should set the ContentType of the request either on the CallbackMethod attribute or using Response.ContentType. This ensures the Web Server knows how to display your binary response. Using a stream response makes it possible to return any of data. Streamed data can be pretty handy to return bitmap data from a method. The following is a method that returns a stock history graph for a particular stock over a provided number of years: [CallbackMethod(ContentType="image/png",RouteUrl="stocks/history/graph/{symbol}/{years}")] public Stream GetStockHistoryGraph(string symbol, int years = 2,int width = 500, int height=350) { if (width == 0) width = 500; if (height == 0) height = 350; StockServer server = new StockServer(); return server.GetStockHistoryGraph(symbol,"Stock History for " + symbol,width,height,years); } I can now hook this up into the JavaScript code when I get a stock quote. At the end of the process I can assign the URL to the service that returns the image into the src property and so force the image to display. Here's the changed code: $("#btnStockQuote").click(function () { var symbol = $("#txtSymbol").val(); ajaxCallMethod("SampleService.ashx", "GetStockQuote", [symbol], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); // display a stock chart $("#imgStockHistory").attr("src", "stocks/history/graph/" + symbol + "/2"); },onPageError); }); The resulting output then looks like this: The charting code uses the new ASP.NET 4.0 Chart components via code to display a bar chart of the 2 year stock data as part of the StockServer class which you can find in the sample download. The ability to return arbitrary data from a service is useful as you can see - in this case the chart is clearly associated with the service and it's nice that the graph generation can happen off a handler rather than through a page. Images are common resources, but output can also be PDF reports, zip files for downloads etc. which is becoming increasingly more common to be returned from REST endpoints and other applications. Why reinvent? Obviously the examples I've shown here are pretty basic in terms of functionality. But I hope they demonstrate the core features of AJAX callbacks that you need to work through in most applications which is simple: return data, send back data and potentially retrieve data in various formats. While there are other solutions when it comes down to making AJAX callbacks and servicing REST like requests, I like the flexibility my home grown solution provides. Simply put it's still the easiest solution that I've found that addresses my common use cases: AJAX JSON RPC style callbacks Url based access XML and JSON Output from single method endpoint XML and JSON POST support, querystring input, routing parameter mapping UrlEncoded POST data support on callbacks Ability to return stream/raw string data Essentially ability to return ANYTHING from Service and pass anything All these features are available in various solutions but not together in one place. I've been using this code base for over 4 years now in a number of projects both for myself and commercial work and it's served me extremely well. Besides the AJAX functionality CallbackHandler provides, it's also an easy way to create any kind of output endpoint I need to create. Need to create a few simple routines that spit back some data, but don't want to create a Page or View or full blown handler for it? Create a CallbackHandler and add a method or multiple methods and you have your generic endpoints.  It's a quick and easy way to add small code pieces that are pretty efficient as they're running through a pretty small handler implementation. I can have this up and running in a couple of minutes literally without any setup and returning just about any kind of data. Resources Download the Sample NuGet: Westwind Web and AJAX Utilities (Westwind.Web) ajaxCallMethod() Documentation Using the AjaxMethodCallback WebForms Control West Wind Web Toolkit Home Page West Wind Web Toolkit Source Code © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  jQuery  AJAX   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Parallelism in .NET – Part 18, Task Continuations with Multiple Tasks

    - by Reed
    In my introduction to Task continuations I demonstrated how the Task class provides a more expressive alternative to traditional callbacks.  Task continuations provide a much cleaner syntax to traditional callbacks, but there are other reasons to switch to using continuations… Task continuations provide a clean syntax, and a very simple, elegant means of synchronizing asynchronous method results with the user interface.  In addition, continuations provide a very simple, elegant means of working with collections of tasks. Prior to .NET 4, working with multiple related asynchronous method calls was very tricky.  If, for example, we wanted to run two asynchronous operations, followed by a single method call which we wanted to run when the first two methods completed, we’d have to program all of the handling ourselves.  We would likely need to take some approach such as using a shared callback which synchronized against a common variable, or using a WaitHandle shared within the callbacks to allow one to wait for the second.  Although this could be accomplished easily enough, it requires manually placing this handling into every algorithm which requires this form of blocking.  This is error prone, difficult, and can easily lead to subtle bugs. Similar to how the Task class static methods providing a way to block until multiple tasks have completed, TaskFactory contains static methods which allow a continuation to be scheduled upon the completion of multiple tasks: TaskFactory.ContinueWhenAll. This allows you to easily specify a single delegate to run when a collection of tasks has completed.  For example, suppose we have a class which fetches data from the network.  This can be a long running operation, and potentially fail in certain situations, such as a server being down.  As a result, we have three separate servers which we will “query” for our information.  Now, suppose we want to grab data from all three servers, and verify that the results are the same from all three. With traditional asynchronous programming in .NET, this would require using three separate callbacks, and managing the synchronization between the various operations ourselves.  The Task and TaskFactory classes simplify this for us, allowing us to write: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAll( new[] {server1, server2, server3 }, (tasks) => { // Propogate exceptions (see below) Task.WaitAll(tasks); return this.CompareTaskResults( tasks[0].Result, tasks[1].Result, tasks[2].Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This is clean, simple, and elegant.  The one complication is the Task.WaitAll(tasks); statement. Although the continuation will not complete until all three tasks (server1, server2, and server3) have completed, there is a potential snag.  If the networkClass.GetResults method fails, and raises an exception, we want to make sure to handle it cleanly.  By using Task.WaitAll, any exceptions raised within any of our original tasks will get wrapped into a single AggregateException by the WaitAll method, providing us a simplified means of handling the exceptions.  If we wait on the continuation, we can trap this AggregateException, and handle it cleanly.  Without this line, it’s possible that an exception could remain uncaught and unhandled by a task, which later might trigger a nasty UnobservedTaskException.  This would happen any time two of our original tasks failed. Just as we can schedule a continuation to occur when an entire collection of tasks has completed, we can just as easily setup a continuation to run when any single task within a collection completes.  If, for example, we didn’t need to compare the results of all three network locations, but only use one, we could still schedule three tasks.  We could then have our completion logic work on the first task which completed, and ignore the others.  This is done via TaskFactory.ContinueWhenAny: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAny( new[] {server1, server2, server3 }, (firstTask) => { return this.ProcessTaskResult(firstTask.Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, instead of working with all three tasks, we’re just using the first task which finishes.  This is very useful, as it allows us to easily work with results of multiple operations, and “throw away” the others.  However, you must take care when using ContinueWhenAny to properly handle exceptions.  At some point, you should always wait on each task (or use the Task.Result property) in order to propogate any exceptions raised from within the task.  Failing to do so can lead to an UnobservedTaskException.

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  • Declaration, allocation and assignment of an array of pointers to function pointers

    - by manneorama
    Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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  • Issue with Callback method and maintaining CultureInfo and ASP.Net HttpRuntime

    - by Little Larry Sellers
    Hi All, Here is my issue. I am working on an E-commerce solution that is deployed to multiple European countries. We persist all exceptions within the application to SQL Server and I have found that there are records in the DB that have a DateTime in the future! We define the culture in the web.config, for example pt-PT, and the format expected is DD-MM-YYYY. After debugging I found the issue with these 'future' records in the DB is because of Callback methods we use. For example, in our Caching architecture we use Callbacks, as such - CacheItemRemovedCallback ReloadCallBack = new CacheItemRemovedCallback(OnRefreshRequest); When I check the current threads CultureInfo, on these Callbacks it is en-US instead of pt-PT and also the HttpContext is null. If an exception occurs on the Callback our exception manager reports it as MM-DD-YYYY and thus it is persisted to SQL Server incorrectly. Unfortunately, in the exception manager code, we use DateTime.Now, which is fine if it is not a callback. I can't change this code to be culture specific due to it being shared across other verticals. So, why don't callbacks into ASP.Net maintain context? Is there any way to maintain it on this callback thread? What are the best practices here? Thanks.

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  • Metro: Promises

    - by Stephen.Walther
    The goal of this blog entry is to describe the Promise class in the WinJS library. You can use promises whenever you need to perform an asynchronous operation such as retrieving data from a remote website or a file from the file system. Promises are used extensively in the WinJS library. Asynchronous Programming Some code executes immediately, some code requires time to complete or might never complete at all. For example, retrieving the value of a local variable is an immediate operation. Retrieving data from a remote website takes longer or might not complete at all. When an operation might take a long time to complete, you should write your code so that it executes asynchronously. Instead of waiting for an operation to complete, you should start the operation and then do something else until you receive a signal that the operation is complete. An analogy. Some telephone customer service lines require you to wait on hold – listening to really bad music – until a customer service representative is available. This is synchronous programming and very wasteful of your time. Some newer customer service lines enable you to enter your telephone number so the customer service representative can call you back when a customer representative becomes available. This approach is much less wasteful of your time because you can do useful things while waiting for the callback. There are several patterns that you can use to write code which executes asynchronously. The most popular pattern in JavaScript is the callback pattern. When you call a function which might take a long time to return a result, you pass a callback function to the function. For example, the following code (which uses jQuery) includes a function named getFlickrPhotos which returns photos from the Flickr website which match a set of tags (such as “dog” and “funny”): function getFlickrPhotos(tags, callback) { $.getJSON( "http://api.flickr.com/services/feeds/photos_public.gne?jsoncallback=?", { tags: tags, tagmode: "all", format: "json" }, function (data) { if (callback) { callback(data.items); } } ); } getFlickrPhotos("funny, dogs", function(data) { $.each(data, function(index, item) { console.log(item); }); }); The getFlickr() function includes a callback parameter. When you call the getFlickr() function, you pass a function to the callback parameter which gets executed when the getFlicker() function finishes retrieving the list of photos from the Flickr web service. In the code above, the callback function simply iterates through the results and writes each result to the console. Using callbacks is a natural way to perform asynchronous programming with JavaScript. Instead of waiting for an operation to complete, sitting there and listening to really bad music, you can get a callback when the operation is complete. Using Promises The CommonJS website defines a promise like this (http://wiki.commonjs.org/wiki/Promises): “Promises provide a well-defined interface for interacting with an object that represents the result of an action that is performed asynchronously, and may or may not be finished at any given point in time. By utilizing a standard interface, different components can return promises for asynchronous actions and consumers can utilize the promises in a predictable manner.” A promise provides a standard pattern for specifying callbacks. In the WinJS library, when you create a promise, you can specify three callbacks: a complete callback, a failure callback, and a progress callback. Promises are used extensively in the WinJS library. The methods in the animation library, the control library, and the binding library all use promises. For example, the xhr() method included in the WinJS base library returns a promise. The xhr() method wraps calls to the standard XmlHttpRequest object in a promise. The following code illustrates how you can use the xhr() method to perform an Ajax request which retrieves a file named Photos.txt: var options = { url: "/data/photos.txt" }; WinJS.xhr(options).then( function (xmlHttpRequest) { console.log("success"); var data = JSON.parse(xmlHttpRequest.responseText); console.log(data); }, function(xmlHttpRequest) { console.log("fail"); }, function(xmlHttpRequest) { console.log("progress"); } ) The WinJS.xhr() method returns a promise. The Promise class includes a then() method which accepts three callback functions: a complete callback, an error callback, and a progress callback: Promise.then(completeCallback, errorCallback, progressCallback) In the code above, three anonymous functions are passed to the then() method. The three callbacks simply write a message to the JavaScript Console. The complete callback also dumps all of the data retrieved from the photos.txt file. Creating Promises You can create your own promises by creating a new instance of the Promise class. The constructor for the Promise class requires a function which accepts three parameters: a complete, error, and progress function parameter. For example, the code below illustrates how you can create a method named wait10Seconds() which returns a promise. The progress function is called every second and the complete function is not called until 10 seconds have passed: (function () { "use strict"; var app = WinJS.Application; function wait10Seconds() { return new WinJS.Promise(function (complete, error, progress) { var seconds = 0; var intervalId = window.setInterval(function () { seconds++; progress(seconds); if (seconds > 9) { window.clearInterval(intervalId); complete(); } }, 1000); }); } app.onactivated = function (eventObject) { if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) { wait10Seconds().then( function () { console.log("complete") }, function () { console.log("error") }, function (seconds) { console.log("progress:" + seconds) } ); } } app.start(); })(); All of the work happens in the constructor function for the promise. The window.setInterval() method is used to execute code every second. Every second, the progress() callback method is called. If more than 10 seconds have passed then the complete() callback method is called and the clearInterval() method is called. When you execute the code above, you can see the output in the Visual Studio JavaScript Console. Creating a Timeout Promise In the previous section, we created a custom Promise which uses the window.setInterval() method to complete the promise after 10 seconds. We really did not need to create a custom promise because the Promise class already includes a static method for returning promises which complete after a certain interval. The code below illustrates how you can use the timeout() method. The timeout() method returns a promise which completes after a certain number of milliseconds. WinJS.Promise.timeout(3000).then( function(){console.log("complete")}, function(){console.log("error")}, function(){console.log("progress")} ); In the code above, the Promise completes after 3 seconds (3000 milliseconds). The Promise returned by the timeout() method does not support progress events. Therefore, the only message written to the console is the message “complete” after 10 seconds. Canceling Promises Some promises, but not all, support cancellation. When you cancel a promise, the promise’s error callback is executed. For example, the following code uses the WinJS.xhr() method to perform an Ajax request. However, immediately after the Ajax request is made, the request is cancelled. // Specify Ajax request options var options = { url: "/data/photos.txt" }; // Make the Ajax request var request = WinJS.xhr(options).then( function (xmlHttpRequest) { console.log("success"); }, function (xmlHttpRequest) { console.log("fail"); }, function (xmlHttpRequest) { console.log("progress"); } ); // Cancel the Ajax request request.cancel(); When you run the code above, the message “fail” is written to the Visual Studio JavaScript Console. Composing Promises You can build promises out of other promises. In other words, you can compose promises. There are two static methods of the Promise class which you can use to compose promises: the join() method and the any() method. When you join promises, a promise is complete when all of the joined promises are complete. When you use the any() method, a promise is complete when any of the promises complete. The following code illustrates how to use the join() method. A new promise is created out of two timeout promises. The new promise does not complete until both of the timeout promises complete: WinJS.Promise.join([WinJS.Promise.timeout(1000), WinJS.Promise.timeout(5000)]) .then(function () { console.log("complete"); }); The message “complete” will not be written to the JavaScript Console until both promises passed to the join() method completes. The message won’t be written for 5 seconds (5,000 milliseconds). The any() method completes when any promise passed to the any() method completes: WinJS.Promise.any([WinJS.Promise.timeout(1000), WinJS.Promise.timeout(5000)]) .then(function () { console.log("complete"); }); The code above writes the message “complete” to the JavaScript Console after 1 second (1,000 milliseconds). The message is written to the JavaScript console immediately after the first promise completes and before the second promise completes. Summary The goal of this blog entry was to describe WinJS promises. First, we discussed how promises enable you to easily write code which performs asynchronous actions. You learned how to use a promise when performing an Ajax request. Next, we discussed how you can create your own promises. You learned how to create a new promise by creating a constructor function with complete, error, and progress parameters. Finally, you learned about several advanced methods of promises. You learned how to use the timeout() method to create promises which complete after an interval of time. You also learned how to cancel promises and compose promises from other promises.

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