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  • Java reflection appropriateness

    - by jsn
    This may be a fairly subjective question, but maybe not. My application contains a bunch of forms that are displayed to the user at different times. Each form is a class of its own. Typically the user clicks a button, which launches a new form. I have a convenience function that builds these buttons, you call it like this: buildButton( "button text", new SelectionAdapter() { @Override public void widgetSelected( SelectionEvent e ) { showForm( new TasksForm( args... ) ); } } ); I do this dozens of times, and it's really cumbersome having to make a SelectionAdapter every time. Really all I need for the button to know is what class to instantiate when it's clicked and what arguments to give the constructor, so I built a function that I call like this instead: buildButton( "button text", TasksForm.class, args... ); Where args is an arbitrary list of objects that you could use to instantiate TasksForm normally. It uses reflection to get a constructor from the class, match the argument list, and build an instance when it needs to. Most of the time I don't have to pass any arguments to the constructor at all. The downside is obviously that if I'm passing a bad set of arguments, it can't detect that at compilation time, so if it fails, a dialog is displayed at runtime. But it won't normally fail, and it'll be easy to debug if it does. I think this is much cleaner because I come from languages where the use of function and class literals is pretty common. But if you're a normal Java programmer, would seeing this freak you out, or would you appreciate not having to scan a zillion SelectionAdapters?

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  • Microsoft JScript runtime error Object doesn't support this property or method

    - by Darxval
    So i am trying to call this function in my javascript but it gives me the error of "Microsoft JScript runtime error Object doesn't support this property or method" and i cant figure out why. It is occuring when trying to call hmacObj.getHMAC. This is from the jsSHA website: http://jssha.sourceforge.net/ to use the hmac-sha1 algorithm encryption. Thank you! hmacObj = new jsSHA(signature_base_string,"HEX"); signature = hmacObj.getHMAC("hgkghk","HEX","SHA-1","HEX"); Above this i have copied the code from sha.js snippet: function jsSHA(srcString, inputFormat) { /* * Configurable variables. Defaults typically work */ jsSHA.charSize = 8; // Number of Bits Per character (8 for ASCII, 16 for Unicode) jsSHA.b64pad = ""; // base-64 pad character. "=" for strict RFC compliance jsSHA.hexCase = 0; // hex output format. 0 - lowercase; 1 - uppercase var sha1 = null; var sha224 = null; The function it is calling (inside of the jsSHA function) (snippet) this.getHMAC = function (key, inputFormat, variant, outputFormat) { var formatFunc = null; var keyToUse = null; var blockByteSize = null; var blockBitSize = null; var keyWithIPad = []; var keyWithOPad = []; var lastArrayIndex = null; var retVal = null; var keyBinLen = null; var hashBitSize = null; // Validate the output format selection switch (outputFormat) { case "HEX": formatFunc = binb2hex; break; case "B64": formatFunc = binb2b64; break; default: return "FORMAT NOT RECOGNIZED"; }

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  • MapView EXC_BAD_ACCESS (SIGSEGV) and KERN_INVALID_ADDRESS

    - by user768113
    I'm having some 'issues' with my application... well, it crashes in an UIViewController that is presented modally, there the user enters information through UITextFields and his location is tracked by a MapView. Lets call this view controller "MapViewController" When the user submits the form, I call a different ViewController - modally again - that processes this info and a third one answers accordingly, then go back to a MenuVC using unwinding segues, which then calls MapViewController and so on. This sequence is repeated many times, but it always crashes in MapViewController. Looking at the crash log, I think that the MapView can be the problem of this or some element in the UI (because of the UIKit framework). I tried to use NSZombie in order to track a memory issue but it doesn't give me a clue about whats happening. Here is the crash log Hardware Model: iPad3,4 Process: MyApp [2253] OS Version: iOS 6.1.3 (10B329) Report Version: 104 Exception Type: EXC_BAD_ACCESS (SIGSEGV) Exception Codes: KERN_INVALID_ADDRESS at 0x00000044 Crashed Thread: 0 Thread 0 name: Dispatch queue: com.apple.main-thread Thread 0 Crashed: 0 IMGSGX554GLDriver 0x328b9be0 0x328ac000 + 56288 1 IMGSGX554GLDriver 0x328b9b8e 0x328ac000 + 56206deallocated instance 2 IMGSGX554GLDriver 0x328bc2f2 0x328ac000 + 66290 3 IMGSGX554GLDriver 0x328baf44 0x328ac000 + 61252 4 libGPUSupportMercury.dylib 0x370f86be 0x370f6000 + 9918 5 GLEngine 0x34ce8bd2 0x34c4f000 + 629714 6 GLEngine 0x34cea30e 0x34c4f000 + 635662 7 GLEngine 0x34c8498e 0x34c4f000 + 219534 8 GLEngine 0x34c81394 0x34c4f000 + 205716 9 VectorKit 0x3957f4de 0x394c7000 + 754910 10 VectorKit 0x3955552e 0x394c7000 + 582958 11 VectorKit 0x394d056e 0x394c7000 + 38254 12 VectorKit 0x394d0416 0x394c7000 + 37910 13 VectorKit 0x394cb7ca 0x394c7000 + 18378 14 VectorKit 0x394c9804 0x394c7000 + 10244 15 VectorKit 0x394c86a2 0x394c7000 + 5794 16 QuartzCore 0x354a07a4 0x35466000 + 239524 17 QuartzCore 0x354a06fc 0x35466000 + 239356 18 IOMobileFramebuffer 0x376f8fd4 0x376f4000 + 20436 19 IOKit 0x344935aa 0x34490000 + 13738 20 CoreFoundation 0x33875888 0x337e9000 + 575624 21 CoreFoundation 0x338803e4 0x337e9000 + 619492 22 CoreFoundation 0x33880386 0x337e9000 + 619398 23 CoreFoundation 0x3387f20a 0x337e9000 + 614922 24 CoreFoundation 0x337f2238 0x337e9000 + 37432 25 CoreFoundation 0x337f20c4 0x337e9000 + 37060 26 GraphicsServices 0x373ad336 0x373a8000 + 21302 27 UIKit 0x3570e2b4 0x356b7000 + 357044 28 MyApp 0x000ea12e 0xe9000 + 4398 29 MyApp 0x000ea0e4 0xe9000 + 4324 I think thats all, additionally, I would like to ask you: if you are using unwind segues then you are releasing view controllers from the memory heap, right? Meanwhile, performing segues let you instantiate those controllers. Technically, MenuVC should be the only VC alive in the heap during the app life cycle if you understand me.

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  • C/C++ I18N mbstowcs question

    - by bogertron
    I am working on internationalizing the input for a C/C++ application. I have currently hit an issue with converting from a multi-byte string to wide character string. The code needs to be cross platform compatible, so I am using mbstowcs and wcstombs as much as possible. I am currently working on a WIN32 machine and I have set the locale to a non-english locale (Japanese). When I attempt to convert a multibyte character string, I seem to be having some conversion issues. Here is an example of the code: int main(int argc, char** argv) { wchar_t *wcsVal = NULL; char *mbsVal = NULL; /* Get the current code page, in my case 932, runs only on windows */ TCHAR szCodePage[10]; int cch= GetLocaleInfo( GetSystemDefaultLCID(), LOCALE_IDEFAULTANSICODEPAGE, szCodePage, sizeof(szCodePage)); /* verify locale is set */ if (setlocale(LC_CTYPE, "") == 0) { fprintf(stderr, "Failed to set locale\n"); return 1; } mbsVal = argv[1]; /* validate multibyte string and convert to wide character */ int size = mbstowcs(NULL, mbsVal, 0); if (size == -1) { printf("Invalid multibyte\n"); return 1; } wcsVal = (wchar_t*) malloc(sizeof(wchar_t) * (size + 1)); if (wcsVal == NULL) { printf("memory issue \n"); return 1; } mbstowcs(wcsVal, szVal, size + 1); wprintf(L"%ls \n", wcsVal); return 0; } At the end of execution, the wide character string does not contain the converted data. I believe that there is an issue with the code page settings, because when i use MultiByteToWideChar and have the current code page sent in EX: MultiByteToWideChar( CP_ACP, 0, mbsVal, -1, wcsVal, size + 1 ); in place of the mbstowcs calls, the conversion succeeds. My question is, how do I use the generic mbstowcs call instead of teh MuliByteToWideChar call?

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  • How to get an embedded function to run multiple times

    - by Guy Montag
    The question I have is how to I get multiple instances of a function to run. Here is my function below - A simple fade function. Problem I'm having is that when it is called a second time it abandons the first call. So if a user clicks on a button it will display a message which fades. If the user clicks on another button the previous fading message just stops at the current opacity level. Try it here - www.arcmarks.com ( please do not repost this domain name) click on SignUp and than quickly click on SignIn with out typing anything. You will see the previous message simply halts. ? What is the stopping mechanism? Where did the previous function go? The function function newEffects(element, direction, max_time ) { newEffects.arrayHold = []; newEffects.arrayHold[element.id] = 0; function next() { newEffects.arrayHold[element.id] += 10; if ( direction === 'up' ) { element.style.opacity = newEffects.arrayHold[element.id] / max_time; } else if ( direction === 'down' ) { element.style.opacity = ( max_time - newEffects.arrayHold[element.id] ) / max_time; } if ( newEffects.arrayHold[element.id] <= max_time ) { setTimeout( next, 10 ); } } next(); return true; }; The Call newEffects(this.element, 'down', 4000 );

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  • Nhibernate Fluent domain Object with Id(x => x.id).GeneratedBy.Assigned not saveable

    - by urpcor
    Hi there, I am using for some legacy db the corresponding domainclasses with mappings. Now the Ids of the entities are calculated by some stored Procedure in the DB which gives back the Id for the new row.(Its legacy, I cant change this) Now I create the new entity , set the Id and Call Save. But nothing happens. no exeption. Even NH Profiler does not say a bit. its as the Save call does nothing. I expect that NH thinks that the record is already in the db because its got an Id already. But I am using Id(x = x.id).GeneratedBy.Assigned() and intetionally the Session.Save(object) method. I am confused. I saw so many samples there it worked. does any body have any ideas about it? public class Appendix { public virtual int id { get; set; } public virtual AppendixHierarchy AppendixHierachy { get; set; } public virtual byte[] appendix { get; set; } } public class AppendixMap : ClassMap<Appendix> { public AppendixMap () { WithTable("appendix"); Id(x => x.id).GeneratedBy.Assigned(); References(x => x.AppendixHierachy).ColumnName("appendixHierarchyId"); Map(x => x.appendix); } }

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  • How would a user stay logged in to a REST-based website?

    - by unforgiven3
    A year or so ago I asked this question: Can you help me understand this? “Common REST Mistakes: Sessions are irrelevant”. My question was essentially this: Okay, I get that HTTP authentication is done automatically on every message - but how? Is the username/password sent with every request? Doesn't that just increase attack surface area? I feel like I'm missing part of the puzzle. The answers I received made perfect sense in the context of a mobile (iPhone, Android, WP7) app - when talking to a REST service, the app would just send user credentials along with each request. That worked great for me. But now, I would like to better understand how one would secure a REST-like website, like StackOverflow itself or something like Reddit. How would things work if it was a user logged in via a web browser instead of logged in via an iPhone app? What happens when a user logs in? Are the credentials saved in the browser somehow? How would the browser know what credentials to send with subsequent REST requests? What if it's a JavaScript call to a webservice? How would the JavaScript call include user credentials? I'll be quite frank: my understanding of security when it comes to websites is pretty limited. I enjoyed working with REST services from an app perspective, but now I want to try and build a website that is based on REST principles, and I'm finding myself to be pretty lost. If there is anything in the above question that is unclear that you'd like me to clarify, please leave a comment and I'll address it.

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  • Multiple leaf methods problem in composite pattern

    - by Ondrej Slinták
    At work, we are developing an PHP application that would be later re-programmed into Java. With some basic knowledge of Java, we are trying to design everything to be easily re-written, without any headaches. Interesting problem came out when we tried to implement composite pattern with huge number of methods in leafs. What are we trying to achieve (not using interfaces, it's just an example): class Composite { ... } class LeafOne { public function Foo( ); public function Moo( ); } class LeafTwo { public function Bar( ); public function Baz( ); } $c = new Composite( Array( new LeafOne( ), new LeafTwo( ) ) ); // will call method Foo in all classes in composite that contain this method $c->Foo( ); It seems like pretty much classic Composite pattern, but problem is that we will have quite many leaf classes and each of them might have ~5 methods (of which few might be different than others). One of our solutions, which seems to be the best one so far and might actually work, is using __call magic method to call methods in leafs. Unfortunately, we don't know if there is an equivalent of it in Java. So the actual question is: Is there a better solution for this, using code that would be eventually easily re-coded into Java? Or do you recommend any other solution? Perhaps there's some different, better pattern I could use here. In case there's something unclear, just ask and I'll edit this post.

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  • Visual Studio 2008 linker wants all symbols to be resolved, not only used ones

    - by user343011
    We recently upgraded to Visual Studio 2008 from 2005, and I think those error started after that. In our solution, we have a multitude of projects. Many of those are utility projects, or projects containing core functionality used by other projects. The output of those is lib files that are linked to when building the projects generating the final binaries using the "Project dependencies..." option. One of the other projects---Let us call it ResultLib---generates a DLL, and it needs one single function from the core project. This function uses only static function from its own source file, but the project in its entirety uses a lot of low-level Windows functions and also imports a DLL---Let us call it Driver.dll. Our problem is that when building ExtLib, the linker complains about a multitude of unresolved externals, for example all functions exported from Driver.dll, since its lib file is not specified when linking. If we try to fix this by adding all lib files used by other projects that use all of the core project, our resulting ResultLib DLL ends up importing Driver.dll and also exporting all functions defined in it. How do we tell Visual Studio to only try to resolve symbols that are actually used?

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  • System Calls in windows & Native API?

    - by claws
    Recently I've been using lot of Assembly language in *NIX operating systems. I was wondering about the windows domain. Calling convention in linux: mov $SYS_Call_NUM, %eax mov $param1 , %ebx mov $param2 , %ecx int $0x80 Thats it. That is how we should make a system call in linux. Reference of all system calls in linux: Regarding which $SYS_Call_NUM & which parameters we can use this reference : http://docs.cs.up.ac.za/programming/asm/derick_tut/syscalls.html OFFICIAL Reference : http://kernel.org/doc/man-pages/online/dir_section_2.html Calling convention in Windows: ??? Reference of all system calls in Windows: ??? Unofficial : http://www.metasploit.com/users/opcode/syscalls.html , but how do I use these in assembly unless I know the calling convention. OFFICIAL : ??? If you say, they didn't documented it. Then how is one going to write libc for windows without knowing system calls? How is one gonna do Windows Assembly programming? Atleast in the driver programming one needs to know these. right? Now, whats up with the so called Native API? Is Native API & System calls for windows both are different terms referring to same thing? In order to confirm I compared these from two UNOFFICIAL Sources System Calls: http://www.metasploit.com/users/opcode/syscalls.html Native API: http://undocumented.ntinternals.net/aindex.html My observations: All system calls are beginning with letters Nt where as Native API is consisting of lot of functions which are not beginning with letters Nt. System Call of windows are subset of Native API. System calls are just part of Native API. Can any one confirm this and explain.

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  • Which Visual Studio 2010 edition for sole developer

    - by bufferz
    I am the sole .net developer for a small company. My projects span many .net technologies including WinForms, WPF, SQL, XNA, Linq, WCF, WTF?, and others. I struggle staying on top of all these projects so I'm looking to make my life easier with the release of VS2010. Without a mentor I rely heavily on StackOverflow and whatever else Google comes up with. Should I convince my company to get an edition with an MSDN subscription? Is it one of those things where once you have it, you can't imagine life without it? What about the source control that comes with VS2010, do you all find it better than an SVN server? We're looking to hire another programmer this year, would I be best off getting a Team edition of VS2010 to be best prepared for that hire? Thanks!

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  • how to convert video from one format to another using php

    - by Meena
    hi i want to include the vedio download option in my webpage. I am using ffmpeg, but it seems to work very slow. Is there is any other way to do this or how to spead up the ffmpeg. i am using this code to get the frames from the vedio. to convert the vedio $call="ffmpeg -i ".$_SESSION['video_to_convert']." -vcodec libvpx -r 30 -b ".$quality." -acodec libvorbis -ab 128000 -ar ".$audio." -ac 2 -s ".$size." ".$converted_vids.$name.".".$type." -y 2> log/".$name.".txt"; $convert = (popen("start /b ".$call, "r")); pclose($convert); to get the frame from the vedio exec("ffmpeg -vframes 1 -ss ".$time_in_seconds." -i $converted_vids video_images.jpg -y 2>); but this code does not generate any error its loading continously.

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  • Drools - Doing Complex Stuff inside a Rule Condition or Consequence

    - by mfcabrera
    Hello, In my company we are planning to use Drools a BRE for couple of projects. Now we trying to define some best-practices. My question is what should be and shouldn't be done inside a Rule Condition/Consequence. Given that we can write Java directly or call methods (for example From a Global object in the Working Memory). Example. Given a Rule that evaluates a generic Object (e.g. Person) have property set to true. Now, that specific propertie can only be defined for that Object going to the database and fetching that info. So we have two ways of implementing that: Alternative A: Go to the database and fetch the object property (true/false, a code) Insert the Object in the working memory Evaluate the rule Alternative B: Insert a Global Object that has a method that connects to the database and check for the property for the given object. Insert the Object to eval in Working Memory In the rule, call the Global Object and perform the access to the database Which of those is considered better? I really like A, but sometimes B is more straightforward, however what would happen if something like a Exception from the Database is raised? I have seen the alternative B implemented in the Drools 5.0 Book from Packt Publishing,however they are doing a mocking and they don't talk about the actual implications of going to the database at all. Thank you,

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  • Pass arguments to a parameter class object

    - by David R
    This is undoubtedly a simple question. I used to do this before, but it's been around 10 years since I worked in C++ so I can't remember properly and I can't get a simple constructor call working. The idea is that instead of parsing the args in main, main would create an object specifically designed to parse the arguments and return them as required. So: Parameters params = new Parameters(argc, argv) then I can call things like params.getfile() Only problem is I'm getting a complier error in Visual Studio 2008 and I'm sure this is simple, but I think my mind is just too rusty. What I've got so far is really basic: In the main: #include "stdafx.h" #include "Parameters.h" int _tmain(int argc, _TCHAR* argv[]) { Parameters params = new Parameters(argc, argv); return 0; } Then in the Parameters header: #pragma once class Parameters { public: Parameters(int, _TCHAR*[]); ~Parameters(void); }; Finally in the Parameters class: include "Stdafx.h" #include "Parameters.h" Parameters::Parameters(int argc, _TCHAR* argv[]) { } Parameters::~Parameters(void) { } I would appreciate if anyone could see where my ageing mind has missed the really obvious. Thanks in advance.

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  • Member function overloading/template specialization issue

    - by Ferruccio
    I've been trying to call the overloaded table::scan_index(std::string, ...) member function without success. For the sake of clarity, I have stripped out all non-relevant code. I have a class called table which has an overloaded/templated member function named scan_index() in order to handle strings as a special case. class table : boost::noncopyable { public: template <typename T> void scan_index(T val, std::function<bool (uint recno, T val)> callback) { // code } void scan_index(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code } }; Then there is a hitlist class which has a number of templated member functions which call table::scan_index(T, ...) class hitlist { public: template <typename T> void eq(uint fieldno, T value) { table* index_table = db.get_index_table(fieldno); // code index_table->scan_index<T>(value, [&](uint recno, T n)->bool { // code }); } }; And, finally, the code which kicks it all off: hitlist hl; // code hl.eq<std::string>(*fieldno, p1.to_string()); The problem is that instead of calling table::scan_index(std::string, ...), it calls the templated version. I have tried using both overloading (as shown above) and a specialized function template (below), but nothing seems to work. After staring at this code for a few hours, I feel like I'm missing something obvious. Any ideas? template <> void scan_index<std::string>(std::string val, std::function<bool (uint recno, std::string val)> callback) { // code }

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  • Internal Java code best practice for dealing with invalid REST API parameters

    - by user326389
    My colleague wrote the following stackoverflow question: other stack overflow question on this topic The question seems to have been misinterpreted and I want to find out the answer, so I'm starting this new question... hopefully a little more clear. Basically, we have a REST API. Users of our API call our methods with parameters. But sometimes users call them with the wrong parameters!! Maybe a mistake in their code, maybe they're just trying to play with us, maybe they're trying to see how we respond, who knows! We respond with HTTP status error codes and maybe a detailed description of the invalid parameter in the XML response. All is well. But internally we deal with these invalid parameters by throwing exceptions. For example, if someone looks up a Person object by giving us their profile id, but the profile id doesn't exist... we throw a PersonInvalidException when looking them up. Then we catch this exception in our API controller and send back an HTTP 400 status error code. Our question is... is this the best practice, throwing exceptions internally for this kind of user error? These exceptions never get propogated back to the user, this is a REST API. They only make our code cleaner. Otherwise we could have a validation method in each of our API controllers to make sure the parameters all make sense, but that seems inefficient. We have to look up things in our database potentially twice. Or we could return nulls and check for them, but that sucks... What are your thoughts?

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  • SQL Server 2008 Stored Proc suddenly returns -1

    - by aaginor
    I use the following stored procedure from my SQL Server 2008 database to return a value to my C#-Program ALTER PROCEDURE [dbo].[getArticleBelongsToCatsCount] @id int AS BEGIN SET NOCOUNT ON; DECLARE @result int; set @result = (SELECT COUNT(*) FROM art_in_cat WHERE child_id = @id); return @result; END I use a SQLCommand-Object to call this Stored Procedure public int ExecuteNonQuery() { try { return _command.ExecuteNonQuery(); } catch (Exception e) { Logger.instance.ErrorRoutine(e, "Text: " + _command.CommandText); return -1; } } Till recently, everything works fine. All of a sudden, the stored procedure returned -1. At first, I suspected, that the ExecuteNonQuery-Command would have caused and Exception, but when stepping through the function, it shows that no Exception is thrown and the return value comes directly from return _command.ExecuteNonQuery(); I checked following parameters and they were as expected: - Connection object was set to the correct database with correct access values - the parameter for the SP was there and contained the right type, direction and value Then I checked the SP via SQLManager, I used the same value for the parameter like the one for which my C# brings -1 as result (btw. I checked some more parameter values in my C' program and they ALL returned -1) but in the manager, the SP returns the correct value. It looks like the call from my C# prog is somehow bugged, but as I don't get any error (it's just the -1 from the SP), I have no idea, where to look for a solution.

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  • Problem with function calls [javascript]

    - by Samuel
    <script language="javascript"> function toggle(id) { alert('call'); if (document.getElementById(id).style.display == "none") { alert('now visible'); document.getElementById(id).style.display = ""; } else { alert('now invisible'); document.getElementById(id).style.display = "none"; } } </script> </head> <body onload="toggle('image1');alert('test_body');toggle('image2')"> <script language="javascript"> alert('test_pre_function'); toggle('image1'); alert('test_after_function'); toggle('image2'); </script> Looks like a lot of code but it's pretty simple so i think most of you won't have troubles with it. toggle() should toggle the display status of divs containing images. When the user enters the site the divs should hide, when everything is loaded the divs should show up. (onload) Strangely enough, the funtion in the body (not in the body tag) only work half, i get and alert 'test_pre_function' and i get an alert 'call' (out of the function), but that's it. The code in the body tag runs just fine. I find this weird because it's supposed to do exactly the same twice and one time it runs, another time not, so i guess i must have made some stupid mistake. Thanks for any help!

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  • merging two tables, while applying aggregates on the duplicates (max,min and sum)

    - by cloudraven
    I have a table (let's call it log) with a few millions of records. Among the fields I have Id, Count, FirstHit, LastHit. Id - The record id Count - number of times this Id has been reported FirstHit - earliest timestamp with which this Id was reported LastHit - latest timestamp with which this Id was reported This table only has one record for any given Id Everyday I get into another table (let's call it feed) with around half a million records with these fields among many others: Id Timestamp - Entry date and time. This table can have many records for the same id What I want to do is to update log in the following way. Count - log count value, plus the count() of records for that id found in feed FirstHit - the earliest of the current value in log or the minimum value in feed for that id LastHit - the latest of the current value in log or the maximum value in feed for that id. It should be noticed that many of the ids in feed are already in log. The simple thing that worked is to create a temporary table and insert into it the union of both as in Select Id, Min(Timestamp) As FirstHit, MAX(Timestamp) as LastHit, Count(*) as Count FROM feed GROUP BY Id UNION ALL Select Id, FirstHit,LastHit,Count FROM log; From that temporary table I do a select that aggregates Min(firsthit), max(lasthit) and sum(Count) Select Id, Min(FirstHit),Max(LastHit),Sum(Count) FROM @temp GROUP BY Id; and that gives me the end result. I could then delete everything from log and replace it with everything with temp, or craft an update for the common records and insert the new ones. However, I think both are highly inefficient. Is there a more efficient way of doing this. Perhaps doing the update in place in the log table?

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  • Is multithreading the right way to go for my case?

    - by Julien Lebosquain
    Hello, I'm currently designing a multi-client / server application. I'm using plain good old sockets because WCF or similar technology is not what I need. Let me explain: it isn't the classical case of a client simply calling a service; all clients can 'interact' with each other by sending a packet to the server, which will then do some action, and possible re-dispatch an answer message to one or more clients. Although doable with WCF, the application will get pretty complex with hundreds of different messages. For each connected client, I'm of course using asynchronous methods to send and receive bytes. I've got the messages fully working, everything's fine. Except that for each line of code I'm writing, my head just burns because of multithreading issues. Since there could be around 200 clients connected at the same time, I chose to go the fully multithreaded way: each received message on a socket is immediately processed on the thread pool thread it was received, not on a single consumer thread. Since each client can interact with other clients, and indirectly with shared objects on the server, I must protect almost every object that is mutable. I first went with a ReaderWriterLockSlim for each resource that must be protected, but quickly noticed that there are more writes overall than reads in the server application, and switched to the well-known Monitor to simplify the code. So far, so good. Each resource is protected, I have helper classes that I must use to get a lock and its protected resource, so I can't use an object without getting a lock. Moreover, each client has its own lock that is entered as soon as a packet is received from its socket. It's done to prevent other clients from making changes to the state of this client while it has some messages being processed, which is something that will happen frequently. Now, I don't just need to protect resources from concurrent accesses. I must keep every client in sync with the server for some collections I have. One tricky part that I'm currently struggling with is the following: I have a collection of clients. Each client has its own unique ID. When a client connects, it must receive the IDs of every connected client, and each one of them must be notified of the newcomer's ID. When a client disconnects, every other client must know it so that its ID is no longer valid for them. Every client must always have, at a given time, the same clients collection as the server so that I can assume that everybody knows everybody. This way if I'm sending a message to client #1 telling "Client #2 has done something", I know that it will always be correctly interpreted: Client 1 will never wonder "but who is Client 2 anyway?". My first attempt for handling the connection of a new client (let's call it X) was this pseudo-code (remember that newClient is already locked here): lock (clients) { foreach (var client in clients) { lock (client) { client.Send("newClient with id X has connected"); } } clients.Add(newClient); newClient.Send("the list of other clients"); } Now imagine that in the same time, another client has sent a packet that translates into a message that must be broadcasted to every connected client, the pseudo-code will be something like this (remember that the current client - let's call it Y - is already locked here): lock (clients) { foreach (var client in clients) { lock (client) { client.Send("something"); } } } An obvious deadlock occurs here: on one thread X is locked, the clients lock has been entered, started looping through the clients, and at one moment must get Y's lock... which is already acquired on the second thread, itself waiting for the clients collection lock to be released! This is not the only case like this in the server application. There are other collections which must be kept in sync with the clients, some properties on a client can be changed by another one, etc. I tried other types of locks, lock-free mechanisms and a bunch of other things. Either there were obvious deadlocks when I'm using too much locks for safety, or obvious race conditions otherwise. When I finally find a good middle point between the two, it usually comes with very subtle race conditions / dead locks and other multi-threading issues... my head hurts very quickly since for any single line of code I'm writing I have to review almost the whole application to ensure everything will behave correctly with any number of threads. So here's my final question: how would you resolve this specific case, the general case, and more importantly: aren't I going the wrong way here? I have little problems with the .NET framework, C#, simple concurrency or algorithms in general. Still, I'm lost here. I know I could use only one thread processing the incoming requests and everything will be fine. However, that won't scale well at all with more clients... But I'm thinking more and more to go this simple way. What do you think? Thanks in advance to you, StackOverflow people which have taken the time to read this huge question. I really had to explain the whole context if I want to get some help.

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  • incorrect height in Chrome when "-webkit-appearance: none" and value="" on <input> tag

    - by Avi Steiner
    In Chrome v17.0.963.79 on Windows 7, I seem to be having an inexplicable problem when applying the -webkit-appearance: none style to an <input> tag. The problem is as follows: I have a stylesheet, let's call it potatofoot.css, which consists of the code .tbl { display: table; } .tblRow { display: table-row; } .tblCell { display: table-cell; } input { -webkit-appearance: none; }? and I have an html file, let's call it blech.html, which contains the code <div class="tbl"> <div class="tblRow"> <label class="tblCell">Name</label> <input type="text" class="tblCell" value="I'M NOT EMPTY! OH, YEAH!"> </div><!--end tblRow--> </div><!--end tbl--> This displays fine (see this jsfiddle). But when I empty the value attribute, as in this jsfiddle, the entire table grows from a height of 26px to a height of 31px, the label moves to the bottom, and the input stays at the top. However, if I remove -webkit-appearance: none;, everything shows up the same with and without out the value attribute being filled. What's going on?

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  • Why is my JavaScript function "a" not defined?

    - by 4l3x
    When I call my JavaScript function B, the javascript console in firefox said that function A is not defined, but on chrome browser if defined. And when I call function "A" in body segment: <input type="button" onclick="A()" value=" ..A.. "> , firefox said that function B is not defined? :S <html> <head> <script language="javascript" type="text/javascript"> function B(){ alert(" hi B "); document.write('<br><br><input type="button" onClick="A()" value=" ..A..">'); }; function A(){ alert(" hi A"); document.write('<br><br><input type="button" onclick="B()" value=" ..b..">'); if (window.WebCL == undefined) { alert("Unfortunately your system does not support WebCL. "); return false; } } </script> </head> <body> <input type="button" onclick="B()" value=" ..B.. "> </body> </html>

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  • Javascript Instance Variable Syntax (AJAX page refresh)

    - by Rosarch
    I'm having difficulty with Javascript instance variables. I'm trying to make an easy way to refresh the chat page, looking for new messages. The AJAX call supplies a mid, or the lowest message id to be returned. This allows the call to only ask for the most recent messages, instead of all of them. MessageRefresher.prototype._latest_mid; function MessageRefresher(latest_mid) { this._latest_mid = latest_mid; // it thinks `this` refers to the MessageRefresher object } MessageRefresher.prototype.refresh = function () { refreshMessages(this._latest_mid); // it thinks `this` refers to the window this._latest_mid++; } function refreshMessages(latest_mid) { $.getJSON('API/read_messages', { room_id: $.getUrlVar('key'), mid: latest_mid }, function (messages) { for (var i = 0; i < messages[0].length; i++) { var newChild = sprintf("<li>%s: %s</li>", messages[1][i], messages[0][i]); $("#messages").append(newChild); } }); var messageRefresher = new MessageRefresher(0); setInterval(messageRefresher.refresh, 1000); This results in all the messages being printed out, over and over again. I know it has other bugs, but the main issue I'm trying to work out right now is the use of the instance variable. Or is there another way I should be going about doing this?

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  • Access is denied. Javascript error on request to secured page

    - by ihorko
    On SomePage.aspx page by javascript (XMLHttpRequest) I call SecuredPage.aspx used next code: var httpRequest = GetXmlHttp(); var url = "https://myhost.com/SecuredPage.aspx"; var params = "param1=" + document.getElementById('param1').value + "&param2=" + document.getElementById('param2').value; httpRequest.open("POST", url, true); httpRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded"); httpRequest.onreadystatechange = function() { //Call a function when the state changes. if (httpRequest.readyState == 4 && httpRequest.status == 200) { alert(httpRequest.responseText); } } httpRequest.send(params); // HERE ACCESS IS DENIED //--------------------------------------------- function GetXmlHttp() { var xmlhttp = false; if (window.XMLHttpRequest) { xmlhttp = new XMLHttpRequest(); } else if (window.ActiveXObject) // code for IE { try { xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); } catch (E) { xmlhttp = false; } } } return xmlhttp; } It throws Access is denied error. if send to http (http://myhost.com/SecuredPage.aspx), it works fine. How is it possible to resolve that problem. Thanks!

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  • Thread mutex behaviour

    - by Alberteddu
    Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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