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  • How safe is my safe rethrow?

    - by gustafc
    (Late edit: This question will hopefully be obsolete when Java 7 comes, because of the "final rethrow" feature which seems like it will be added.) Quite often, I find myself in situations looking like this: do some initialization try { do some work } catch any exception { undo initialization rethrow exception } In C# you can do it like this: InitializeStuff(); try { DoSomeWork(); } catch { UndoInitialize(); throw; } For Java, there's no good substitution, and since the proposal for improved exception handling was cut from Java 7, it looks like it'll take at best several years until we get something like it. Thus, I decided to roll my own: (Edit: Half a year later, final rethrow is back, or so it seems.) public final class Rethrow { private Rethrow() { throw new AssertionError("uninstantiable"); } /** Rethrows t if it is an unchecked exception. */ public static void unchecked(Throwable t) { if (t instanceof Error) throw (Error) t; if (t instanceof RuntimeException) throw (RuntimeException) t; } /** Rethrows t if it is an unchecked exception or an instance of E. */ public static <E extends Exception> void instanceOrUnchecked( Class<E> exceptionClass, Throwable t) throws E, Error, RuntimeException { Rethrow.unchecked(t); if (exceptionClass.isInstance(t)) throw exceptionClass.cast(t); } } Typical usage: public void doStuff() throws SomeException { initializeStuff(); try { doSomeWork(); } catch (Throwable t) { undoInitialize(); Rethrow.instanceOrUnchecked(SomeException.class, t); // We shouldn't get past the above line as only unchecked or // SomeException exceptions are thrown in the try block, but // we don't want to risk swallowing an error, so: throw new SomeException("Unexpected exception", t); } private void doSomeWork() throws SomeException { ... } } It's a bit wordy, catching Throwable is usually frowned upon, I'm not really happy at using reflection just to rethrow an exception, and I always feel a bit uneasy writing "this will not happen" comments, but in practice it works well (or seems to, at least). What I wonder is: Do I have any flaws in my rethrow helper methods? Some corner cases I've missed? (I know that the Throwable may have been caused by something so severe that my undoInitialize will fail, but that's OK.) Has someone already invented this? I looked at Commons Lang's ExceptionUtils but that does other things. Edit: finally is not the droid I'm looking for. I'm only interested to do stuff when an exception is thrown. Yes, I know catching Throwable is a big no-no, but I think it's the lesser evil here compared to having three catch clauses (for Error, RuntimeException and SomeException, respectively) with identical code. Note that I'm not trying to suppress any errors - the idea is that any exceptions thrown in the try block will continue to bubble up through the call stack as soon as I've rewinded a few things.

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  • Ajax, Callback, postback and Sys.WebForms.PageRequestManager.getInstance().add_beginRequest

    - by user338262
    Hi, I have a user control which encapsulates a NumericUpDownExtender. This UserControl implements the interface ICallbackEventHandler, because I want that when a user changes the value of the textbox associated a custom event to be raised in the server. By the other hand each time an async postback is done I shoe a message of loading and disable the whole screen. This works perfect when something is changed in for example an UpdatePanel through this lines of code: Sys.WebForms.PageRequestManager.getInstance().add_beginRequest( function (sender, args) { var modalPopupBehavior = $find('programmaticSavingLoadingModalPopupBehavior'); modalPopupBehavior.show(); } ); The UserControl is placed inside a detailsview which is inside an UpdatePanel in an aspx. When the custom event is raised I want another textbox in the aspx to change its value. So far, When I click on the UpDownExtender, it goes correctly to the server and raises the custom event, and the new value of the textbox is assigned in the server. but it is not changed in the browser. I suspect that the problem is the callback, since I have the same architecture for a UserControl with an AutoCompleteExtender which implement IPostbackEventHandler and it works. Any clues how can I solve this here to make the UpDownNumericExtender user control to work like the AutComplete one? This is the code of the user control and the parent: using System; using System.Web.UI; using System.ComponentModel; using System.Text; namespace Corp.UserControls { [Themeable(true)] public partial class CustomNumericUpDown : CorpNumericUpDown, ICallbackEventHandler { protected void Page_PreRender(object sender, EventArgs e) { if (!Page.IsPostBack) { currentInstanceNumber = CorpAjaxControlToolkitUserControl.getNextInstanceNumber(); } registerControl(this.HFNumericUpDown.ClientID, currentInstanceNumber); string strCallServer = "NumericUpDownCallServer" + currentInstanceNumber.ToString(); // If this function is not written the callback to get the disponibilidadCliente doesn't work if (!Page.ClientScript.IsClientScriptBlockRegistered("ReceiveServerDataNumericUpDown")) { StringBuilder str = new StringBuilder(); str.Append("function ReceiveServerDataNumericUpDown(arg, context) {}").AppendLine(); Page.ClientScript.RegisterClientScriptBlock(typeof(CorpNumericUpDown), "ReceiveServerDataNumericUpDown", str.ToString(), true); } nudeNumericUpDownExtender.BehaviorID = "NumericUpDownEx" + currentInstanceNumber.ToString(); ClientScriptManager cm = Page.ClientScript; String cbReference = cm.GetCallbackEventReference(this, "arg", "ReceiveServerDataNumericUpDown", ""); String callbackScript = "function " + strCallServer + "(arg, context)" + Environment.NewLine + "{" + Environment.NewLine + cbReference + ";" + Environment.NewLine + "}" + Environment.NewLine; cm.RegisterClientScriptBlock(typeof(CustomNumericUpDown), strCallServer, callbackScript, true); base.Page_PreRender(sender,e); } [System.ComponentModel.Browsable(true)] [System.ComponentModel.Bindable(true)] public Int64 Value { get { return (string.IsNullOrEmpty(HFNumericUpDown.Value) ? Int64.Parse("1") : Int64.Parse(HFNumericUpDown.Value)); } set { HFNumericUpDown.Value = value.ToString(); //txtAutoCompleteCliente_AutoCompleteExtender.ContextKey = value.ToString(); // TODO: Change the text of the textbox } } [System.ComponentModel.Browsable(true)] [System.ComponentModel.Bindable(true)] [Description("The text of the numeric up down")] public string Text { get { return txtNumericUpDown.Text; } set { txtNumericUpDown.Text = value; } } public delegate void NumericUpDownChangedHandler(object sender, NumericUpDownChangedArgs e); public event NumericUpDownChangedHandler numericUpDownEvent; [System.ComponentModel.Browsable(true)] [System.ComponentModel.Bindable(true)] [System.ComponentModel.Description("Raised after the number has been increased or decreased")] protected virtual void OnNumericUpDownEvent(object sender, NumericUpDownChangedArgs e) { if (numericUpDownEvent != null) //check to see if anyone has attached to the event numericUpDownEvent(this, e); } #region ICallbackEventHandler Members public string GetCallbackResult() { return "";//throw new NotImplementedException(); } public void RaiseCallbackEvent(string eventArgument) { NumericUpDownChangedArgs nudca = new NumericUpDownChangedArgs(long.Parse(eventArgument)); OnNumericUpDownEvent(this, nudca); } #endregion } /// <summary> /// Class that adds the prestamoList to the event /// </summary> public class NumericUpDownChangedArgs : System.EventArgs { /// <summary> /// The current selected value. /// </summary> public long Value { get; private set; } public NumericUpDownChangedArgs(long value) { Value = value; } } } using System; using System.Collections.Generic; using System.Text; namespace Corp { /// <summary> /// Summary description for CorpAjaxControlToolkitUserControl /// </summary> public class CorpNumericUpDown : CorpAjaxControlToolkitUserControl { private Int16 _currentInstanceNumber; // This variable hold the instanceNumber assignated at first place. public short currentInstanceNumber { get { return _currentInstanceNumber; } set { _currentInstanceNumber = value; } } protected void Page_PreRender(object sender, EventArgs e) { const string strOnChange = "OnChange"; const string strCallServer = "NumericUpDownCallServer"; StringBuilder str = new StringBuilder(); foreach (KeyValuePair<String, Int16> control in controlsToRegister) { str.Append("function ").Append(strOnChange + control.Value).Append("(sender, eventArgs) ").AppendLine(); str.Append("{").AppendLine(); str.Append(" if (sender) {").AppendLine(); str.Append(" var hfield = document.getElementById('").Append(control.Key).Append("');").AppendLine(); str.Append(" if (hfield.value != eventArgs) {").AppendLine(); str.Append(" hfield.value = eventArgs;").AppendLine(); str.Append(" ").Append(strCallServer + control.Value).Append("(eventArgs, eventArgs);").AppendLine(); str.Append(" }").AppendLine(); str.Append(" }").AppendLine(); str.Append("}").AppendLine(); Page.ClientScript.RegisterClientScriptBlock(typeof(CorpNumericUpDown), Guid.NewGuid().ToString(), str.ToString(), true); } str = new StringBuilder(); foreach (KeyValuePair<String, Int16> control in controlsToRegister) { str.Append(" funcsPageLoad[funcsPageLoad.length] = function() { $find('NumericUpDownEx" + control.Value + "').add_currentChanged(").Append(strOnChange + control.Value).Append(");};").AppendLine(); str.Append(" funcsPageUnLoad[funcsPageUnLoad.length] = function() { $find('NumericUpDownEx" + control.Value + "').remove_currentChanged(").Append(strOnChange + control.Value).Append(");};").AppendLine(); } Page.ClientScript.RegisterClientScriptBlock(typeof(CorpNumericUpDown), Guid.NewGuid().ToString(), str.ToString(), true); } } } and to create the loading view I use this: //The beginRequest event is raised before the processing of an asynchronous postback starts and the postback is sent to the server. You can use this event to call custom script to set a request header or to start an animation that notifies the user that the postback is being processed. Sys.WebForms.PageRequestManager.getInstance().add_beginRequest( function (sender, args) { var modalPopupBehavior = $find('programmaticSavingLoadingModalPopupBehavior'); modalPopupBehavior.show(); } ); //The endRequest event is raised after an asynchronous postback is finished and control has been returned to the browser. You can use this event to provide a notification to users or to log errors. Sys.WebForms.PageRequestManager.getInstance().add_endRequest( function (sender, arg) { var modalPopupBehavior = $find('programmaticSavingLoadingModalPopupBehavior'); modalPopupBehavior.hide(); } ); Thanks in advance! Daniel.

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  • Invalidating the HTTP Cache on read only front servers

    - by Microserf
    We have a CMS system and in the production mode a number of servers only have read-only access to the content (with a few exceptions) and the editors for the site work on the content on servers behind it (which are not available to the public). We're caching the content quite a long time on the front servers, but sometimes we want the content the editors publish to be available for visitors instantly. What would the best way be to invalidate the cache in this situation, should we trigger it from our code?

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  • Sending data from one Protocol to another Protocol in Twisted?

    - by veb
    Hi! One of my protocols is connected to a server, and with the output of that I'd like to send it to the other protocol. I need to access the 'msg' method in ClassA from ClassB but I keep getting: exceptions.AttributeError: 'NoneType' object has no attribute 'write' Actual code: http://pastebin.com/MQPhduSY Any ideas please? :-)

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  • Pylons error handling

    - by TJ Huffington
    Hello, I am just getting started with Pylons and am confused as to how to account for exceptions. What is the proper way to error check user input (ensure a correct email address, check that it doesn't yet exist in the database, etc ...)? Should these checks go inside the model classes or somewhere else? Sample code would be great.

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  • ASP.NET Exception Handling in background threads

    - by Xodarap
    When I do ThreadPool.QueueUserWorkItem, I don't want unhandled exceptions to kill my entire process. So I do something like: ThreadPool.QueueUserWorkItem(delegate() { try { FunctionIActuallyWantToCall(); } catch { HandleException(); } }); Is this the recommended pattern? It seems like there should be a simpler way to do this. It's in an asp.net-mvc app, if that's relevant.

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  • Keyboard input with timeout in Python

    - by J. Pablo Fernández
    How would you prompt the user for some input but timing out after N seconds? Google is pointing to a mail thread about it at http://mail.python.org/pipermail/python-list/2006-January/533215.html but it seems not to work. The statement in which the timeout happens, no matter whether it is a sys.input.readline or timer.sleep(), I always get: <type 'exceptions.TypeError'>: [raw_]input expected at most 1 arguments, got 2 which somehow the except fails to catch.

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  • Client configuration to consume WCF JSON web service

    - by Grzenio
    Hi, I have configured the web service to use Json as described on this blog: http://www.west-wind.com/weblog/posts/164419.aspx and various other blogs, but I couldn't create a client to consume this service. I tried various things, but invariably I got meaningless exceptions. What is the correct way to implement the (WCF I should add) client?

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  • Good style for handling constructor failure of critical object

    - by mtlphil
    I'm trying to decide between two ways of instantiating an object & handling any constructor exceptions for an object that is critical to my program, i.e. if construction fails the program can't continue. I have a class SimpleMIDIOut that wraps basic Win32 MIDI functions. It will open a MIDI device in the constructor and close it in the destructor. It will throw an exception inherited from std::exception in the constructor if the MIDI device cannot be opened. Which of the following ways of catching constructor exceptions for this object would be more in line with C++ best practices Method 1 - Stack allocated object, only in scope inside try block #include <iostream> #include "simplemidiout.h" int main() { try { SimpleMIDIOut myOut; //constructor will throw if MIDI device cannot be opened myOut.PlayNote(60,100); //..... //myOut goes out of scope outside this block //so basically the whole program has to be inside //this block. //On the plus side, it's on the stack so //destructor that handles object cleanup //is called automatically, more inline with RAII idiom? } catch(const std::exception& e) { std::cout << e.what() << std::endl; std::cin.ignore(); return 1; } std::cin.ignore(); return 0; } Method 2 - Pointer to object, heap allocated, nicer structured code? #include <iostream> #include "simplemidiout.h" int main() { SimpleMIDIOut *myOut; try { myOut = new SimpleMIDIOut(); } catch(const std::exception& e) { std::cout << e.what() << std::endl; delete myOut; return 1; } myOut->PlayNote(60,100); std::cin.ignore(); delete myOut; return 0; } I like the look of the code in Method 2 better, don't have to jam my whole program into a try block, but Method 1 creates the object on the stack so C++ manages the object's life time, which is more in tune with RAII philosophy isn't it? I'm still a novice at this so any feedback on the above is much appreciated. If there's an even better way to check for/handle constructor failure in a siatuation like this please let me know.

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  • Error Handling for Application in PHP

    - by Zubair1
    I was wondering if someone can show me a good way to handle errors in my PHP app, that i am also easily able to reuse in my codes. So far i have been using the following functions: Inline Errors function display_errors_for($fieldname) { global $errors; if (isset($errors[$fieldname])) { return '<label for="' .$fieldname. '" class="error">' . ucfirst($errors[$fieldname]). '</label>'; } else { return false; } } All Errrors function display_all_errors($showCounter = true) { global $errors; $counter = 0; foreach ($errors as $errorFieldName => $errorText) { if ($showCounter == true) { $counter++; echo '<li>' . $counter . ' - <label for="' .$errorFieldName. '">' .$errorText. '</label></li>'; } else { echo '<li><label for="' .$errorFieldName. '">' .$errorText. '</label></li>'; } } } I have a $errors = array(); defined on the top of my global file, so it is appended to all files. The way i use it is that if i encounter an error, i push a new error key/value to the $errors array holder, something like the following: if (strlen($username) < 3) { $errors['username'] = "usernames cannot be less then 3 characters."; } This all works great and all, But i wondering if some one has a better approach for this? with classes? i don't think i want to use Exceptions with try/catch seems like an overkill to me. I'm planning to make a new app, and i'll be getting my hands wet with OOP alot, though i have already made apps using OOP but this time i'm planning to go even deeper and use OOP approach more extensively. What i have in mind is something like this, though its just a basic class i will add further detail to it as i go deeper and deeper in my app to see what it needs. class Errors { public $errors = array(); public function __construct() { // Initialize Default Values // Initialize Methods } public function __destruct() { //nothing here too... } public function add($errorField, $errorDesc) { if (!is_string($errorField)) return false; if (!is_string($errorDesc)) return false; $this->errors[$errorField] = $errorDesc; } public function display($errorsArray) { // code to iterate through the array and display all errors. } } Please share your thoughts, if this is a good way to make a reusable class to store and display errors for an entire app, or is getting more familiar with exceptions and try/catch my only choice?

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  • Reliable session faulting for unknown reason

    - by Scarfman007
    I am trying to achieve the following - one client-side proxy instance (kept open) accessed by multiple threads using a reliable session. What I have managed so far is to have either A) a reliable session with a client-side proxy which is created and disposed per call or B) what I aim for, but without a reliable session. When I enable reliable sessions on my binding however, the following behaviour is exhibited: Client-side Upon application startup everything appears to work fine until roughly 18 messages in to the WCF session. I firstly get the proxy.InnerChannel.Faulted event raised, then an exception is caught at the point where I am calling the method on the proxy. The exception is a System.TimeoutException, with message: "The request channel timed out while waiting for a reply after 00:00:59.9062512. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout." The inner exception has a similar message: "The request operation did not complete within the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout." With the method at the top of the inner stack trace being: System.ServiceModel.Channels.ReliableRequestSessionChannel.SyncRequest.WaitForReply(TimeSpan timeout) I then call proxy.Close followed by proxy.Abort (catching and ignoring exceptions). If I utilize the default settings (i.e. have simply <reliableSession/>), then calling proxy. Close results in another System.Timeout exception (although this time the allotted timeout is 00:00:00), however if I override the defaults as specified above no exception is thrown. Service-side Utilizing WCF tracing I get a System.ServiceModel.CommunicationException, with message: "The sequence has been terminated by the remote endpoint. The session has stopped waiting for a particular reply. Because of this the reliable session cannot continue. The reliable session was faulted." And a stack trace ending at: System.ServiceModel.AsyncResult.End[TAsyncResult](IAsyncResult result) When remotely attaching to the server I get the same message, which occurs when code execution steps over the return statement of my service in the service call which causes the error. The puzzling thing to me is that the service is stable and runs with options A) or B) as decribed at the beginning of my post, and occurs after a varying number of messages (around 18). The former fact points to there being nothing wrong with the code (indeed I have checked that no exceptions are thrown), and the latter just serves to confuse me and is why I modified the settings on the reliable session binding. I am quite stuck on this. Can anyone suggest why the reliable session would fault in such a way?

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  • What's the best software development conventions document you have seen?

    - by Pavel Radzivilovsky
    Google C++ development conventions outlaw exceptions, RAII, RTTI and bans the default parameter in parseInt(number, radix=10). Qt API style guide is brilliant, but only covers interfaces. The Robert C. Martin series Clean Code has M104 galaxy on the cover, but it is 462 pages long and based on Java, with no simple "do this" digest. Assuming that it is important to synchronize style and best practices across the organization, what is the smartest, most pleasant and useful conventions document you have worked with?

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  • StreamWriter not creating new file

    - by fearofawhackplanet
    I'm trying to create a new log file every hour with the following code running on a server. The first log file of the day is being created and written to fine, but no further log files that day get created. Any ideas what might be going wrong? No exceptions are thrown either. private void LogMessage(Message msg) { using (StreamWriter sw = File.AppendText(_logDirectory + DateTime.Today.ToString("yyyyMMddHH") + ".txt")) { sw.WriteLine(msg.ToString()); } }

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  • C# - Exception messages in English?

    - by Carra
    We are logging any exceptions that happen in our system by writing the Exception.Message to a file. However, they are written in the culture of the client. And Turkish errors don't mean a lot to me. So how can we log any error messages in English without changing the users culture?

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  • Access violation when running native C++ application that uses a /clr built DLL

    - by doobop
    I'm reorganzing a legacy mixed (managed and unmanaged DLLs) application so that the main application segment is unmanaged MFC and that will call a C++ DLL compiled with /clr flag that will bridge the communication between the managed (C# DLLs) and unmanaged code. Unfortuantely, my changed have resulted in an Access violation that occurs before the application InitInstance() is called. This makes it very difficult to debug. The only information I get is the following stack trace. > 64006108() ntdll.dll!_ZwCreateMutant@16() + 0xc bytes kernel32.dll!_CreateMutexW@12() + 0x7a bytes So, here are some sceanrios I've tried. - Turned on Exceptions-Win32 Exceptions-c0000005 Access Violation to break when Thrown. Still the most detail I get is from the above stack trace. I've tried the application with F10, but it fails before any breakpoints are hit and fails with the above stack trace. - I've stubbed out the bridge DLL so that it only has one method that returns a bool and that method is coded to just return false (no C# code called). bool DllPassthrough::IsFailed() { return false; } If the stubbed out DLL is compiled with the /clr flag, the application fails. If it is compiled without the /clr flag, the application runs. - I've created a stub MFC application using the Visual Studio wizard for multidocument applications and call DllPassthrough::IsFailed(). This succeeds even with the /clr flag used to compile the DLL. - I've tried doing a manual LoadLibrary on winmm.lib as outlined in the following note Access violation when using c++/cli. The application still fails. So, my questions are how to solve the problem? Any hints, strategies, or previous incidents. And, failing that, how can I get more information on what code segment or library is causing the access exception? If I try more involved workarounds like doing LoadLibrary calls, I'd like to narrow it to the failing libraries. Thanks. BTW, we are using Visual Studio 2008 and the project is being built against the .NET 2.0 framework for the managed sections.

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  • Is it against best practice to throw Exception on most JUnit tests?

    - by Chris Knight
    Almost all of my JUnit tests are written with the following signature: public void testSomething() throws Exception My reasoning is that I can focus on what I'm testing rather than exception handling which JUnit appears to give me for free. But am I missing anything by doing this? Is it against best practice? Would I gain anything by explicitly catching specific exceptions in my test and then fail()'ing on them?

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  • Get invalid user input with a Spring typeMismatch error

    - by TimmyJ
    I've implemented a ReloadableResourceBundleMessageSource in my Spring MVC application which I use to display prettier error messages for binding exceptions. The problem I'm having is that, due to a company policy, these errors must be displayed in the following format: [inputData] is not a valid [fieldName]. The field name is accessible by default in my message properties file (as the {0} argument), but I can't figure out a way to display the invalid user input. Is this possible?

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  • Exception handling protocol for methods

    - by athena
    Is there any specific protocol for handling exceptions in public methods? Consider this eg. public int someMethod() { try{ code that might throw an exception } catch(Exception e) { log the exception } } Say that this method might throw an ArrayIndexOutOfBoundsException. So, is it correct to handle this Exception in the method itself (as in the example) or throw it and assume that the calling method will handle the Exception?

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