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• How to store and collect data for mining such information as most viewed for last 24 hours, last 7 d

  - by Kirzilla

  Hello, Let's imagine that we have high traffic project (a tube site) which should provide sorting using this options (NOT IN REAL TIME). Number of videos is about 200K and all information about videos is stored in MySQL. Number of daily video views is about 1.5KK. As instruments we have Hard Disk Drive (text files), MySQL, Redis. Views top viewed top viewed last 24 hours top viewed last 7 days top viewed last 30 days top rated last 365 days How should I store such information? The first idea is to log all visits to text files (single file per hour, for example visits_20080101_00.log). At the beginning of each hour calculate views per video for previous hour and insert this information into MySQL. Then recalculate totals (for last 24 hours) and update statistics in tables. At the beginning of every day we have to do the same but recalculate for last 7 days, last 30 days, last 365 days. This method seems to be very poor for me because we have to store information about last 365 days for each video to make correct calculations. Is there any other good methods? Probably, we have to choose another instruments for this? Thank you.

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• implementation musical instrument using audio unit

  - by Develop.Kim

  post same question at apple developer forum ,too hi first sorry that my english is poor.. i want develop iphone application that playing musical instrument like 'ocarina' but don't need blow mic features. so first i tried to find that how implementation 'virtual musical instrument ' in iphone development. the during the decide implementation using 'Audio Unit' to report this article (link) so i want two kind of questions. i recognize that the 'musical instrument' can be divided into three sound that 'attack', 'sustain' , 'release'. 'decay' maybe included (link) . How implementation when audio unit base 'AUInstrumentBase' each sound ? i download sample 'SinSynth' (link) . i want play note this instrument unit for analyze source and study. Is there way to using AULab? expected the way using MIDI input . but i don't have MIDI. in addition, i wonder that i would think it right the way. to ask the advice... thank for reading poor english my article.

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• Running an application from an USB device...

  - by Workshop Alex

  I'm working on a proof-of-concept application, containing a WCF service with console host and client, both on a single USB device. On the same device I will also have the client application which will connect to this service. The service uses the entity framework to connect to the database, which in this POC will just return a list of names. If it works, it will be used for a larger project. Creating the client and service was easy and this works well from USB. But getting the service to connect to the database isn't. I've found this site, suggesting that I should modify machine.config but that stops the XCopy deployment. This project cannot change any setting of the PC, so this suggestion is bad. I cannot create a deployment setup either. The whole thing just needs to run from USB disk. So, how do I get it to run? (The service just selects a list of names from the database, which it returns to the client. If this POC works, it will do far more complex things!)

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• rake db:migrate fails when trying to do inserts

  - by anthony

  I'm trying to get a database populate so I can begin working on a project. THis project is already built and I'm being brought in to helpwith front-end work. Problem is I can't get rake db:migrate to do any inserts. Every time I run rake db:migrate I get this: ... == 20081220084043 CreateTimeDimension: migrating ============================== -- create_table(:time_dimension) - 0.0870s INSERT time_dimension(time_key, year, month, day, day_of_week, weekend, quarter) VALUES(20080101, 2008, 1, 1, 'Tuesday', false, 1) rake aborted! Could not load driver (uninitialized constant Mysql::Driver) ... I'm building on a MBP with Snow Leopard. I've installed XCode from the disk that comes with the mac. I've updated ruby, installed rails and all the needed gems. I have the 64 bit version of MySQL installed. I've tried the 32 bit version of MySQL and I've even tried installing from macports (via http://www.robbyonrails.com/articles/2010/02/08/installing-ruby-on-rails-passenger-postgresql-mysql-oh-my-zsh-on-snow-leopard-fourth-edition) The mysql gemis installed using: sudo env ARCHFLAGS="-arch x86_64" gem install mysql -- --with-mysql-config=/path/to/mysql/bin/mysql_config the migrate creates the tables just fine but it dies every. single. time. it trys an insert. Any help would be great

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• Is it OK to set state within Event Raising methods?

  - by Greg

  I ran across this pattern in the code of a library I'm using. It sets state within the event raising method, but only if the event is not null. protected virtual void OnMyEvent(EventArgs e) { if(MyEvent != null) { State = "Executing"; // Only sets state if MyEvent != null. MyEvent(this,e); } } Which means that the state is not set when overriding the method: protected override void OnMyEvent(EventArgs e) { base.OnMyEvent(e); Debug.Assert( State == "Executing" ); // This fails } but is only set when handling the event: foo.MyEvent += (o, args) => Debug.Assert(State == "Executing"); // This passes Setting state within the if(MyEvent != null) seems like bad form, but I've checked the Event Design Guidelines and it doesn't mention this. Do you think this code is incorrect? If so, why? (Reference to design guidelines would be helpful). Edit for Context: It's a Control, I'm trying to create subclass of it, and the state that it's setting is calling EnsureChildControls() conditionally based upon there being an event handler. I can call EnsureChildControls() myself, but I consider that something of a hack.

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• Best solution for __autoload

  - by tpk

  As our PHP5 OO application grew (in both size and traffic), we decided to revisit the __autoload() strategy. We always name the file by the class definition it contains, so class Customer would be contained within Customer.php. We used to list the directories in which a file can potentially exist, until the right .php file was found. This is quite inefficient, because you're potentially going through a number of directories which you don't need to, and doing so on every request (thus, making loads of stat() calls). Solutions that come to my mind... -use a naming convention that dictates the directory name (similar to PEAR). Disadvantages: doesn't scale too great, resulting in horrible class names. -come up with some kind of pre-built array of the locations (propel does this for its __autoload). Disadvantage: requires a rebuild before any deploy of new code. -build the array "on the fly" and cache it. This seems to be the best solution, as it allows for any class names and directory structure you want, and is fully flexible in that new files just get added to the list. The concerns are: where to store it and what about deleted/moved files. For storage we chose APC, as it doesn't have the disk I/O overhead. With regards to file deletes, it doesn't matter, as you probably don't wanna require them anywhere anyway. As to moves... that's unresolved (we ignore it as historically it didn't happen very often for us). Any other solutions?

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• Caching vector addition over changing collections

  - by DRMacIver

  I have the following setup: I have a largish number of uuids (currently about 10k but expected to grow unboundedly - they're user IDs) and a function f : id - sparse vector with 32-bit integer values (no need to worry about precision). The function is reasonably expensive (not outrageously so, but probably on the order of a few 100ms for a given id). The dimension of the sparse vectors should be assumed to be infinite, as new dimensions can appear over time, but in practice is unlikely to ever exceed about 20k (and individual results of f are unlikely to have more than a few hundred non-zero values). I want to support the following operations efficiently: add a new ID to the collection invalidate an existing ID retrieve sum f(id) in O(changes since last retrieval) i.e. I want to cache the sum of the vectors in a way that's reasonable to do incrementally. One option would be to support a remove ID operation and treat invalidation as a remove followed by an add. The problem with this is that it requires us to keep track of all the old values of f, which is expensive in space. I potentially need to use many instances of this sort of cached structure, so I would like to avoid that. The likely usage pattern is that new IDs are added at a fairly continuous rate and are frequently invalidated at first. Ids which have been invalidated recently are much more likely to be invalidated again than ones which have remained valid for a long time, but in principle an old Id can still be invalidated. Ideally I don't want to do this in memory (or at least I want a way that lets me save the result to disk efficiently), so an idea which lets me piggyback off an existing DB implementation of some sort would be especially appreciated.

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• Android SDK: Hello World won't run !

  - by RedRoses

  Hello, This is a very very beginner question regarding Android Development I am trying to create and run the Hello world example from the Android SDK website, but I can't see anything appearing on the screen. It appears to me that Eclipse just hangs at this point: [2010-11-05 09:55:47 - HelloAndroid] ------------------------------ [2010-11-05 09:55:47 - HelloAndroid] Android Launch! [2010-11-05 09:55:47 - HelloAndroid] adb is running normally. [2010-11-05 09:55:47 - HelloAndroid] Performing com.example.helloandroid.HelloAndroid activity launch [2010-11-05 09:55:48 - HelloAndroid] Automatic Target Mode: launching new emulator with compatible AVD 'AVD2' [2010-11-05 09:55:48 - HelloAndroid] Launching a new emulator with Virtual Device 'AVD2' [2010-11-05 09:55:51 - HelloAndroid] New emulator found: emulator-5554 [2010-11-05 09:55:51 - HelloAndroid] Waiting for HOME ('android.process.acore') to be launched... [2010-11-05 09:57:10 - HelloAndroid] WARNING: Application does not specify an API level requirement! [2010-11-05 09:57:10 - HelloAndroid] Device API version is 8 (Android 2.2) [2010-11-05 09:57:10 - HelloAndroid] HOME is up on device 'emulator-5554' [2010-11-05 09:57:10 - HelloAndroid] Uploading HelloAndroid.apk onto device 'emulator-5554' [2010-11-05 09:57:12 - HelloAndroid] Installing HelloAndroid.apk... [2010-11-05 09:59:33 - HelloAndroid] Success! [2010-11-05 09:59:33 - HelloAndroid] Starting activity com.example.helloandroid.HelloAndroid on device emulator-5554 So it says "Starting activity ..." but nothing ever starts and it's already been more than 30 mins. What could be wrong?? Thanks !

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• Design for fastest page download

  - by mexxican

  I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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• mod_rewrite: no access to real files and directories

  - by tshabalala

  Hello. I use mod_rewrite/.htaccess for pretty URLs. I forward all the requests to my index.php, like this: RewriteRule ^/?([a-zA-Z0-9/-]+)/?$ /index.php [NC,L] The index.php then handles the requests. I'm also using this condition/rule to eliminate trailing slashes (or rather rewrite them to the URL without a trailing slash, with a 301 redirect; I'm doing this to avoid duplicate content and because I like no trailing slashes better): RewriteCond %{HTTP_HOST} !^\.localhost$ [NC] RewriteRule ^(.+)/$ http://%{HTTP_HOST}/$1 [R=301,L] This works well, except that I now get an infinite loop when trying to access a (real) directory (the rewrite rule removes the trailing slash, the server adds it again, ...). I solved this by setting the DirectorySlash directive to Off: DirectorySlash Off I don't know how good this solution is, I don't feel too confident about it tbh. Anyway, what I'd like to do is completely ignore "real" files and directories, since I don't need them and I only use pretty URLs with "virtual" files/directories anyway. This would allow me to avoid the DirectorySlash workaround/hack too. Is this possible? Thanks!

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• C++ Dynamic object construction

  - by Rajesh Subramanian

  I have a base class, class Msg { ParseMsg() { ParseMsgData(); ParseTrailer(); } virtual void ParseMsgData() = 0; ParseTrailer(); }; and derived classes, class InitiateMsg { void ParseMsgData() { ... } }; class ReadOperationMsg { void ParseMsgData() { ... } }; class WriteOperationMsg { void ParseMsgData() { ... } }; and the scenario is below, void UsageFunction(string data) { Msg* msg = ParseHeader(data); ParseMsg } Msg* ParseHeader(string data) { Msg *msg = NULL; .... switch() { case 1: msg = new InitiateMsg(); break; case 2: msg = new ReadOperationMsg{(); break; case 3: msg = new WriteOperationMsg{(); break; .... } return msg; } based on the data ParseHeader method will decide which object has to be created, So I have implemented ParseHeader function outside the class where I am using. How can I make the ParseHeader function inside the Msg class and then use it? In C# the same is achieved by defining ParseHeader method as static with in class and use it from outside,

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• 2-column table with two foreign keys. Performance/design question.

  - by Emanuel

  Hello everyone! I recently ran into a quite complex problem and after looking around a lot I couldn't find a solution to it. I've found answers to my questions many times before on stackoverflow.com, so I decided to post here. So I'm making a user/group managment system for a web-based project, and I'm storing all related data into a postgreSQL database. This system relies on three tables: USERS GROUPS GROUP_USERS The two first tables simply define all the users and all the groups on the site, and the last table, GROUP_USERS, stores the groups every user is part of. It only has two columns: USER_ID GROUP_ID Since every user can be a member of several groups, I decided to make a separate table for this purpose, rather than storing a comma separated column in the USERS-table. Now, both columns are foreign keys, and I want to make them both primary keys as well, this since each combination of USER_ID and GROUP_ID has to be unique, and if I give them the constraint UNIQUE pgAdmin tells me that each table should have at least one Primary key. But now I am stuck with what seems to be a lot of indexes and relations to a very small table only containing numbers. In the end, I want this table to be as fast as possible, even if containing tens of thousands of rows. Size on disk shouldn't be a problem since its just all numbers anyway, but it feels quite stupid to have a full-sized index refering to a smaller table. Should I stick with my current solution, store comma-separated values in a column in the USERS-table or is there any other solution I should be aware of. PS. I don't want to use an array-column, even if they are supported by postgreSQL. I want to be as generic as possible so I can switch database later on, if necessary. EDIT: I other words, will using a compound primary key and two foreign keys in one table with only two columns have a negative impact on performance rather than the opposite due to the size of the generated index? Thank you!

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• Why does a MFC application behaves mysteriously in encrypted hard drive environment.

  - by MauriceL

  I'm working on a bug where I have an MFC application that does weird things when installed in when Sophos Safeguard hard drive encryption is installed. I'm sorry to be so vague here, but I'm writing this away from the office so this is all from my (poor) memory. Three things I've noticed: AfxGetResourceHandle() doesn't return a consistent resource handle. There is a single case where we try to load a string resource, and for some reason, the resource handle that we get from this method is different to all the other stings. Can't construct a CDocumentTemplate. There is a trace error which I cant seem to recall. Will edit and post when I'm in tomorrow. This behaviour appears to manifest in a Visual Studio 2005 version of the project, but not a Visual Studio 2008 version. Unfortunately moving to the 2008 version is not an option. The bug is not always reproducable if I step through with a debugger. Also, bringing up debug message boxes changes the behaviuor, which leads me to think that either there is some kind of race condition going on with the way MFC events are being handled, but I'm not sure how I'll ever know for sure, or even what I can do about it if I did. I think there's some underlying reason that the app is behaving weirdly, but what I've posted are more symptoms. Can anyone think of what I should check for? I've run Windows update on the test environment to ensure everything was up to date, and I've examined the process in procmon to see if the disk encryption stuff was getting in the way and conflicting with files - it didn't appear to be, but it does appear to be involved in some way as our app accesses Sophos related paths in the temp directory.

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• Image does not update when file name remains the same in XCode 3.1.2

  - by vman049

  Hi Everyone, I'm using XCode version 3.1.2 and am developing for iPhone using the Simulator with iOS 2.2.1 on Leopard. I had an image file named "img.jpg" in my project which I decided to switch for a different file. After adding the new file into the XCode Resources folder, I removed the first file and renamed the new file to the same name as the previous one, "img.jpg." When I run my program, however, the Simulator loads the old image instead of the new one, even though the old one has been deleted from disk (not just the reference). I tried changing the name of the file to "img2.jpg," and it worked like it should - loading the new image, but I want to keep the name "img.jpg." I ran a search with Spotlight for "img.jpg" to see if there was another copy stored somewhere that XCode was using, but it only returned my new image file. I have tried uninstalling the app from the Simulator and running the application again, but that also does not fix the problem. What must I do for XCode to recognize that I want to use the new image file and not the old one? Thanks for your help!!

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• Windows: Does something temporarily grab the com ports on startup?

  - by Tim

  I have a WPF/C# app that is launched as part of the "Startup" group on a Windows Embedded Standard machine. One of the first things the app does (in its static App() method) is create a new SerialPort object for COM1. COM1 is a hardwired serial port, not a USB virtual port or anything like that. My problem is that every so often (maybe 1 out of 12) on startup, I get an exception: System.UnauthorizedAccessException: Access to the port 'COM1' is denied. There are no other applications using this port. Also, when I relaunch the app following this error, it grabs the port just fine. It's as if the com port isn't ready/set up for my app sometimes. I'm clueless on this one! Any insight is appreciated! UPDATE: I added a call to SerialPort.GetPortNames() and printout all available ports before attempting to open the port. In the failure case COM1 is indeed THERE! So, it's not that the port isn't ready. It looks like something in Windows is actually grabbing the port temporarily and blocking me.

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• Events + Adapter Pattern

  - by Stretto

  I have an adapter pattern on a generic class that essentially adapts between types: class A<T> { event EventHandler e; } class Aadapter<T1, T2> : A<T1> { A<T2> a; Aadapter(A<T2> _a) { a = _a; } } The problem is that A contains an event. I effectively want all event handlers assigned to Adapter to fall through to a. It would be awesome if I could assign the a's event handler to adapter's event handler but this is impossible? The idea here is that A is almost really just A but we need a way to adapt the them. Because of the way event's work I can't how to efficiently do it except manually add two event handlers and when they are called they "relay" the to the other event. This isn't pretty though and it would seem much nicer if I could have something like class A<T> { event EventHandler e; } class Aadapter<T1, T2> : A<T1> { event *e; A<T2> a; Aadapter(A<T2> _a) { a = _a; e = a.e; } } in a sense we have a pointer to the event that we can assign a2's event to. I doubt there is any simple way but maybe someone has some idea to make it work. (BTW, I realize this is possible with virtual events but I'd like to avoid this if at all possible)

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• Implementing a Version check between an Abstract class and it's implementation

  - by Michael Stum

  I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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• How to secure connection strings in VS?

  - by salvationishere

  I see several others have posted this question, however, none of the solutions I've tried have fixed this yet. I have a 32-bit XP running VS 2008 and I am trying to encrypt my connection string in my web.config file. But I am getting the error: The configuration section '...' was not found. Failed! The command I give it: C:\Program Files\Microsoft Visual Studio 9.0\VCAspnet_regiis.exe -pe "system.we b/AdventureWorksConnectionString2" -app "/Documents and Settings/Admin/My Docume nts/Visual Studio 2008/Projects/AddFileToSQL2" Also, how does -app map virtual directory? In other words the path above is the directory right below c:. Is this the correct path to use? And AddFileToSQL2 is the name of my project, although it is part of the AddFileToSQL solution. I have this folder web shared with all of the permissions. And the relevant part of my web.config file: <add name="AdventureWorksConnectionString2" connectionString="Data Source=SIDEKICK;Initial Catalog=AdventureWorks;Persist Security Info=true; User ID=AdventureWorks;Password=sqlMagic" providerName="System.Data.SqlClient" />

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• [PHP] Local/Dev/Live deployment - best workflow

  - by Adam Kiss

  Hello, situation We our little company with 3 people, each has a localhost webserver and most projects (previous and current) are on one PC network shared disk. We have virtual server, where some of our clients' sites and our site. Our standard workflow is: Coder PC ? Programmer localhost ? dev domain (client.company.com) ? live version (client.com) It often happens, that there are two or three guys working on same projects at the same time - one is on dev version, two are on localhost. When finished, we try to synchronize the files on dev version and ideally not to mess up any files, which *knock knock * doesn't happen often. And then one of us deploys dev version on live webserver. question we are looking for a way to simplify this workflow while updating websites - ideally some sort of diff uploader or VCS probably (Git/SVN/VCS/...), but we are not completely sure where to begin or what way would be ideal, therefore I ask you, fellow stackoverflowers for your experience with website / application deployment and recommended workflow. We probably will also need to use Mac in process, so if it won't be a problem, that would be even better. Thank you

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• Call 32-bit or 64-bit program from bootloader

  - by user1002358

  There seems to be quite a lot of identical information on the Internet about writing the following 3 bootloaders: Infinite loop jmp $ Print a single character Print "Hello World". This is fantastic, and I've gone through these 3 variations with very little trouble. I'd like to write some 32- or 64-bit code in C and compile it, and call that code from the bootloader... basically a bootloader that, for example, sets the computer up to run some simple numerical simulation. I'll start by listing primes, for example, and then maybe some input/output from the user to maybe compute a Fourier transform. I don't know. I haven't found any information on how to do this, but I can already foresee some problems before I even begin. First of all, compiling a C program compiles it into one of several different files, depending on the target. For Windows, it's a PE file. For Linux, it's a .out file. These files are both quite different. In my instance, the target isn't Windows or Linux, it's just whatever I have written in the bootloader. Secondly, where would the actual code reside? The bootloader is exactly 512 bytes, but the program I write in C will certainly compile to something much larger. It will need to sit on my (virtual) hard disk, probably in some sort of file system (which I haven't even defined!) and I will need to load the information from this file into memory before I can even think about executing it. But from my understanding, all this is many, many orders of magnitude more complex than a 12-line "Hello World" bootloader. So my question is: How do I call a large 32- or 64-bit program (written in C/C++) from my 16-bit bootloader.

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• Iteration through the HtmlDocument.All collection stops at the referenced stylesheet?

  - by Jonas

  Since "bug in .NET" is often not the real cause of a problem, I wonder if I'm missing something here. What I'm doing feels pretty simple. I'm iterating through the elements in a HtmlDocument called doc like this: System.Diagnostics.Debug.WriteLine("*** " + doc.Url + " ***"); foreach (HtmlElement field in doc.All) System.Diagnostics.Debug.WriteLine(string.Format("Tag = {0}, ID = {1} ", field.TagName, field.Id)); I then discovered the debug window output was this: Tag = !, ID = Tag = HTML, ID = Tag = HEAD, ID = Tag = TITLE, ID = Tag = LINK, ID = ... when the actual HTML document looks like this: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <title>Protocol</title> <link rel="Stylesheet" type="text/css" media="all" href="ProtocolStyle.css"> </head> <body onselectstart="return false"> <table> <!-- Misc. table elements and cell values --> </table> </body> </html> Commenting out the LINK tag solves the issue for me, and the document is completely parsed. The ProtocolStyle.css file exist on disk and is loaded properly, if that would matter. Is this a bug in .NET 3.5 SP1, or what? For being such a web-oriented framework, I find it hard to believe there would be such a major bug in it.

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• One-to-many Associations Empty Columns Issue (Ext on Rails)

  - by Joe

  I'm playing with rewriting part of a web application in Rails + Ext. However, I'm having trouble getting an associated models' name to display in the grid view. I've been able to successfully convert several models and arrange the views nicely using tabs and Ext's layout helpers. However, I'm in the middle of setting up an association -- I've followed along with Jon Barket's tutorial on how to do this using Ext -- and I've made all the Rails and JS changes suggested (with appropriate name changes for my models,) the result being that the combo box is now being correctly populated with the names of the associated models, and changes are actually written correctly to database, BUT the data doesn't show up in the column, it's just empty. However, the correct data is there in the 'detail' view. Really just wondering if anyone else ran into this, or had any thoughts on what could be happening. Definitely willing to post code if requested; just note that (AFAIK) my changes follow the tutorial pretty closely. Thanks in advance! UPDATE: Alright, slight progress - kind of. I can get the associated model id # displaying properly -- just by modifying the column model slightly. But I can't get the virtual attribute displayed in the main table (in Jon's example it's country_name.) It still goes blank when I change the data source for that column from dataIndex: 'model[associated_model_id]' to dataIndex: 'virtual_attributes[associated_model_name]' ANOTHER UPDATE: Bump. Has NOBODY here tried integrating Ext with Rails?

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• Why does the VS2005 debugger not report "base." values properly? (was "Why is this if statement fail

  - by Rawling

  I'm working on an existing class that is two steps derived from System.Windows.Forms.Combo box. The class overrides the Text property thus: public override string Text { get { return this.AccessibilityObject.Value; } set { if (base.Text != value) { base.Text = value; } } } The reason given for that "get" is this MS bug: http://support.microsoft.com/kb/814346 However, I'm more interested in the fact that the "if" doesn't work. There are times where "base.Text != value" is true and yet pressing F10 steps straight to the closing } of the "set" and the Text property is not changed. I've seen this both by just checking values in the debugger, and putting a conditional breakpoint on that only breaks when the "if" statement's predicate is true. How on earth can "if" go wrong? The class between this and ComboBox doesn't touch the Text property. The bug above shouldn't really be affecting anything - it says it's fixed in VS2005. Is the debugger showing different values than the program itself sees? Update I think I've found what is happening here. The debugger is reporting value incorrectly (including evaluating conditional breakpoints incorrectly). To see this, try the following pair of classes: class MyBase { virtual public string Text { get { return "BaseText"; } } } class MyDerived : MyBase { public override string Text { get { string test = base.Text; return "DerivedText"; } } } Put a breakpoint on the last return statement, then run the code and access that property. In my VS2005, hovering over base.Text gives the value "DerivedText", but the variable test has been correctly set to "BaseText". So, new question: why does the debugger not handle base properly, and how can I get it to?

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• Why can a public class not inherit from a less visible one?

  - by Dan Tao

  I apologize if this question has been asked before. I've searched SO somewhat and wasn't able to find it. I'm just curious what the rationale behind this design was/is. Obviously I understand that private/internal members of a base type cannot, nor should they, be exposed through a derived public type. But it seems to my naive thinking that the "hidden" parts could easily remain hidden while some base functionality is still shared and a new interface is exposed publicly. I'm thinking of something along these lines: Assembly X internal class InternalClass { protected virtual void DoSomethingProtected() { // Let's say this method provides some useful functionality. // Its visibility is quite limited (only to derived types in // the same assembly), but at least it's there. } } public class PublicClass : InternalClass { public void DoSomethingPublic() { // Now let's say this method is useful enough that this type // should be public. What's keeping us from leveraging the // base functionality laid out in InternalClass's implementation, // without exposing anything that shouldn't be exposed? } } Assembly Y public class OtherPublicClass : PublicClass { // It seems (again, to my naive mind) that this could work. This class // simply wouldn't be able to "see" any of the methods of InternalClass // from AssemblyX directly. But it could still access the public and // protected members of PublicClass that weren't inherited from // InternalClass. Does this make sense? What am I missing? }

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• Tracking down origin of I/O in multi-process server

  - by Craig Ringer

  I'm currently trying to track down some phantom I/O in a PostgreSQL build I'm testing. It's a multi-process server and it isn't simple to associate disk I/O back to a particular back-end and query. I thought Linux's perf tool would be ideal for this, but I'm struggling to capture block I/O performance counter metrics and associate them with user-space activity. It's easy to record block I/O requests and completions with, eg: sudo perf record -g -T -u postgres -e 'block:block_rq_*' and the user-space pid is recorded, but there's no kernel or user-space stack captured, or ability to snapshot bits of the user-space process's heap (say, query text) etc. So while you have the pid, you don't know what the process was doing at that point. Just perf script output like: postgres 7462 [002] 301125.113632: block:block_rq_issue: 8,0 W 0 () 208078848 + 1024 [postgres] If I add the -g flag to perf record it'll take snapshots of the kernel stack, but doesn't capture user-space state for perf events captured in the kernel. The user-space stack only goes up to the entry-point from userspace, like LWLockRelease, LWLockAcquire, memcpy (mmap'd IO), __GI___libc_write, etc. So. Any tips? Being able to capture a snapshot of the user-space stack in response to kernel events would be ideal.

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