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Articles indexed Wednesday May 5 2010

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  • How does Linux blocking I/O actually work?

    - by tgguy
    In Linux, when you make a blocking i/o call like read or accept, what actually happens? My thoughts: the process get taken out of the run queue, put into a waiting or blocking state on some wait queue. Then when a tcp connection is made (for accept) or the hard drive is ready or something for a file read, a hardware interrupt is raised which lets those processes waiting to wake up and run (in the case of a file read, how does linux know what processes to awaken, as there could be lots of processes waiting on different files?). Or perhaps instead of hardware interrupts, the individual process itself polls to check availability. Not sure, help?

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  • Stored Procedure in postgresql, multiple queries w/ agreggates.

    - by fenix
    I'm trying to write a store procedure that can take some input parameters (obviously), run multiple queries against those, taking the output from those and doing calculations, and from those calculations and the original queries, outputting a formatted text string like: Number of Rows for max(Z) matching condition x and y of total rows matching x (x&y/x*100). To explain the max(Z) bit, this will be the username field, it won't matter which actual entry is picked, because the where clause will filter the results by user id, is there a saner way to do this?

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  • XMLHttpRequest progressive download?

    - by StackedCrooked
    Just for fun I was creating a JavaScript console for controlling my PC. It involves a small webserver that takes command strings and forwards those to the system using popen calls (to be more specific popen4 on a Ruby mongrel server). The stdout channels are redirected to the http response. The problem is that the response only arrives once the entire contents of stdout has been sent. This is ok for small commands, but not for a command like find / which lists all the files in the system. In such situations it would be nice to have the results shown progressively in the webview (just like in the regular terminal). I thought that using XMLHttpRequest synchronously might result in progressive downloading, but it doesn't seem so. Is there any way to make it work?

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  • isReachable in Java doesn't appear to be working quite the way it's supposed to

    - by Rayne
    I'm using Clojure, but I can read Java, so this isn't a Clojure specific question. This doesn't even seem to be working from Java. I'm trying to implement a bit of a 'ping' function using isReachable. The code I'm using is this: (.isReachable (java.net.InetAddress/getByName "www.microsoft.com") 5000) Translated to Java by a good friend of mine: public class NetTest { public static void main (String[] args) throws Exception{ String host = "acidrayne.net"; InetAddress a = InetAddress.getByName(host); System.out.println(a.isReachable(10000)); } } Both of these return false. I suppose I must be doin' it wrong, but Google research is telling me differently. I'm confuzzled!

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  • Hide header and footer when printing from Internet Explorer using Javascript or CSS

    - by molasses
    When I print a webpage from Internet Explorer it will automatically add a header and footer including the website title, URL, date, and page number. Is it possible to hide the header and footer programatically using Javascript or CSS? Requirements: works in IE 6 (no other browser support necessary as its for an Intranet) may use ActiveX, Java Applet, Javascript, CSS preferably not something that the user needs to install (eg. http://www.meadroid.com/scriptx). feel free to list other third party available plug-ins though as I think this may be the only option don't require the user to manually update their browser settings don't render the pages as PDF or Word document or any other format don't write to the registry (security prevents this) Thanks

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  • What is the best way of doing this? (WCF 4)

    - by Jason Porter
    I have a multith-threaded, continusly running application that connects with multiple devices via TCP/IP sockets and exposes a set of WCF API's for controlling, monitoring and reporting on these devices. I would like to host this on IIS for the ususal reasons of not having to worry about re-starting the app in case of errors. So the issue I have is the main application running in parallel with the WCF Servies. To accomplish this I use the static AppInitialize class to start a thread which has the main applicaiton loop. The WCF services mostly report or control the shared objects with this thread. There are two problems that I see with this approach. One is that if the thread dies, IIS has no clue to re-start it so I have to play some tricks with some WCF calls. The other is that the backrgound thread deals with potentially thousands of devices that are connected permanently (typically a thread per socket connection). So I am not sure if IIS is buying me anything in this case. Another approach that I am thinking is to use WF for the main application that deals with the sockets and host both the WF and my WCF services in IIS using AppFabric. Since I have not use WF or AppFabric I am reaching out to see if this would be good approach or there are better alternative.

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  • Horizontally Flip a One Bit Bitmap Line

    - by roygbiv
    I'm looking for an algorithm to flip a 1 Bit Bitmap line horizontally. Remember these lines are DWORD aligned! I'm currently unencoding an RLE stream to an 8 bit-per-pixel buffer, then re-encoding to a 1 bit line, however, I would like to try and keep it all in the 1 bit space in an effort to increase its speed. Profiling indicates this portion of the program to be relatively slow compared to the rest. Example line (Before Flip): FF FF FF FF 77 AE F0 00 Example line (After Flip): F7 5E EF FF FF FF F0 00

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  • How does a cmdlet know when it really should call WriteVerbose()?

    - by Roman Kuzmin
    How does a cmdlet know when it really should call WriteVerbose(), WriteDebug() and etc.? Perhaps I miss something simple but I cannot find the answer. All cmdlet implementations I have seen so far just call WriteVerbose() without any hesitation. I know that it is correct to do so, but it is not effective. Performance suffers when verbose mode is off but a cmdlet still prepares data for WriteVerbose() call, that is, for nothing. In other words, in a cmdlet I would like to be able to: if (<VerboseMode>) { .... data preparation, sometimes expensive ... WriteVerbose(...); } But I don't know how to get this if (<VerboseMode>). Any ideas?

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  • Java application return codes

    - by doele
    I have a Java program that processes one file at a time. This Java program is called from a wrapper script which logs the return code from the Java program. There are 2 types of errors. Expected errors and unexpected errors. In both cases I just need to log them. My wrapper knows about 3 different states. 0-OK, 1-PROCESSING_FAILED, 2- ERROR. Is this a valid approach? Here is my approach: enum ReturnCodes {OK,PROCESSING_FAILED,ERROR}; public static void main(String[] args) { ... proc.processMyFile(); ... System.exit(ReturnCodes.OK.ordinal()); } catch (Throwable t) { ... System.exit(ReturnCodes.ERROR.ordinal()); } private void processMyFile() { try { ... }catch( ExpectedException e) { ... System.exit(ReturnCodes.PROCESSING_FAILED.ordinal()); } }

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  • explain md's raid10,f2

    - by xenoterracide
    I know how most of the various RAID's work. But I stumbled on the recommended raid10,f2 mode while researching linux software raid. I don't really understand how it works on 2 or 3 disks. could someone explain it to me? or point me to a really good article that explains it?

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  • MySQL doesn't talk to PHP anymore (EasyPHP)

    - by Matt Ellen
    I've just upgraded from Windows XP to Windows 7 (64 bit) I was using EasyPHP 5.3.1 to develop my website, but since I've upgraded I can't get PHP to talk to MySQL. Even the PHPMyAdmin page doesn't load. I've tried installing the latest 64bit version of MySQL in place of the supplied version of MySQL, but that hasn't helped. The queries just don't seem to reach MySQL. I have verified that the DB for my database works by running mysql on the command line. PHPMyAdmin doesn't display an error, just a blank page. The error coming up from my website is: Warning: PDO::__construct() [pdo.--construct]: [2002] A connection attempt failed because the connected party did not (trying to connect via tcp://localhost:3306) in E:\services\EasyPHP-5.3.1\www\IdeaWeb\classes\Security.inc on line 14 Fatal error: Maximum execution time of 60 seconds exceeded in E:\services\EasyPHP-5.3.1\www\IdeaWeb\classes\Security.inc on line 0 Does anyone know how to solve this? (i.e. get MySQL talking to PHP.)

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  • How can I get Visual Studio 2010 to show Chinese comments properly

    - by Joe H
    I have some code from a Chinese business partner, but all of the comments in the code which are in Chinese. However, Visual Studio displays them as gibberish. How can I get them to display properly. Here is a code example with some comments converted to gibberish: //Á¬½Óµ½·þÎñÆ÷ void CTestAPIDlg::OnBnClickedButton2() { UpdateData(TRUE); //ÉèÖÃÊÇ·ñ¼Ç¼ÈÕÖ¾ m_ObjRSI->EnableLog(m_bIsOnLogReg,m_bIsOnLogComm); //ÅжÏÊÇ·ñÆôÓôúÀí if (m_bIsOnProxy) { //´úÀí²ÎÊý char proxyIP[64]; char proxyUserName[64]; char proxyUserPwd[64]; ZeroMemory(proxyIP,sizeof(proxyIP)); ZeroMemory(proxyUserName,sizeof(proxyUserName)); ZeroMemory(proxyUserPwd,sizeof(proxyUserPwd)); //×¢£º´Ë´¦ÒòΪÊÇʹÓÃunicode±àÒ룬ËùÒÔÒª×Ö·ûת»»£¬ÏÂͬ. WideCharToMultiByte(CP_ACP,0,m_strProxyIP,-1,proxyIP,64,NULL,NULL); WideCharToMultiByte(CP_ACP,0,m_strProxyUserName,-1,proxyUserName,64,NULL,NULL); WideCharToMultiByte(CP_ACP,0,m_strProxyPwd,-1,proxyUserPwd,64,NULL,NULL); //ÉèÖôúÀí²ÎÊý m_ObjRSI->SetProxyParam(proxyIP,m_iProxyPort,proxyUserName,proxyUserPwd,m_iProxyType); } //Á¬½Ó²ÎÊý char szIp[64]; ZeroMemory(szIp,sizeof(szIp)); WideCharToMultiByte(CP_ACP,0,m_strIP,-1,szIp,64,NULL,NULL); //Á¬½Ó·þÎñÆ÷ m_ObjRSI->SetCommParam(szIp,m_iPort,m_iCheckIDPort); m_ObjRSI->StartService(); //ÉèÖð´Å¥×´Ì¬ ((CButton*)GetDlgItem(IDC_CHECK2))->EnableWindow(FALSE); ((CButton*)GetDlgItem(IDC_CHECK3))->EnableWindow(FALSE); } Thanks in advance for any help...

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  • Making buttons - <button> or <div> ?

    - by user246114
    Hi, I'm wondering what html element to use for buttons on a web page - I'd like to style my 'buttons' like twitter does. For example: http://twitter.com/twitter the "more" button at the bottom of the tweet listing - is that a <button> element, or a <div> element? I'd like to know which to use. I think for either <button> or <div> we can supply rollover states and all that stuff to make it look pleasant? Thanks

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  • How can I use SVN to manage my Firefox Extension project?

    - by 4AM
    I'm using SVN to manage my Firefox extension project, and this project contains an XPCOM component. Firefox is loading directly from my working directory by placing a text file with the working directory's path in the ./extensions directory of my user profile. When Firefox starts, my extension fails to load & overlay; examining the Error Console, I see that the error states that ".svn cannot be loaded as a component" - a reference to the .svn directory inside my "components" directory of the plug-in structure. Is there any way to get Firefox to ignore this directory, or get SVN to generate a working copy without the .svn directories in it?

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  • Comet and Simultaneous Ajax request

    - by Amitd
    Hi , I am trying to use a COMET solution using ASP.NET . Trouble is i want to implement sending and notification part in the same page. On IE7, whenever i try to send a request ,it just gets queued up. After reading on internet and stackoverflow pages i found that i can only do 2 simultaneous asyn ajax requests per page. So until i close my comet Ajax request,my 2nd request doesnt get completed ,doesnt even go out from the browser. And when i checked with Firefox i just one Ajax comet request running all time..so doesnt that leave me one more ajax request? Also the solution uses IRequiressessionstate for Asynchronous HTTP Handler which i had removed.but still it creates problems on multiple instances of IE7. I had one work around which is stated here http://support.microsoft.com/kb/282402 it means we can increase the request limit from registry by default is 2. By changing "MaxConnectionsPer1_0Server" key in hive "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings" we can increase the number of requests. Basically i want to broadcast information to multiple clients connected to a server using Comet and the clients can also send messages to the Server. Broadcasting works but the send request back to server doesnt work. Im using IIS 6 and ASP.NET . Are there any more workarounds or ways to send more requests? References : http://stackoverflow.com/questions/561046/how-many-concurrent-ajax-xmlhttprequest-requests-are-allowed-in-popular-browser http://stackoverflow.com/questions/349381/ajax-php-sessions-and-simultaneous-requests http://stackoverflow.com/questions/2412807/jquery-ajax-request-blocked-by-long-running-ajax-request http://stackoverflow.com/questions/898190/jquery-making-simultaneous-ajax-requests-is-it-possible

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  • Scala Eclipse IDE suddenly ignoring breakpoints

    - by malsmith
    I've been using Scala 2.8RC1 and Scala Eclipse plugin for 2.8 RC1 happily for a few days. However, last night after adding a couple jar files to my environment (apache http client jars) the debugger just stopped stopping at breakpoints in scala code. Java code stops fine at breakpoints. I tried creating a new mimimal scala app breakpoints don't stop. I've tried switching to sun-jre-1.6.0.20 from the openjdk-1.6.18 I had been using. I've switched to the scala 2.8 nightly and also eclipse plugin for scala nightly builds. No luck. I would greatly appreciate ideas for fixes. Rather frustrating as the initial experience with 2.8 was really great.

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  • Get dialog input field IDs in CKEditor

    - by rt-uk
    Each input field in the CKEditor dialogs are renamed with a unique number, but the number changes depending on what options are visible. I need to reference 'txtUrl' which has an id something like #35_textInput. So far I have discovered that something like this should work: alert(CKEDITOR.instances.myElement.document.$.body.getId('txtUrl')); But it doesn't. Please help.

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  • Is something along the lines of nested memoization needed here?

    - by Daniel
    System.Transactions notoriously escalates transactions involving multiple connections to the same database to the DTC. The module and helper class, ConnectionContext, below are meant to prevent this by ensuring multiple connection requests for the same database return the same connection object. This is, in some sense, memoization, although there are multiple things being memoized and the second is dependent on the first. Is there some way to hide the synchronization and/or mutable state (perhaps using memoization) in this module, or perhaps rewrite it in a more functional style? (It may be worth nothing that there's no locking when getting the connection by connection string because Transaction.Current is ThreadStatic.) type ConnectionContext(connection:IDbConnection, ownsConnection) = member x.Connection = connection member x.OwnsConnection = ownsConnection interface IDisposable with member x.Dispose() = if ownsConnection then connection.Dispose() module ConnectionManager = let private _connections = new Dictionary<string, Dictionary<string, IDbConnection>>() let private getTid (t:Transaction) = t.TransactionInformation.LocalIdentifier let private removeConnection tid = let cl = _connections.[tid] for (KeyValue(_, con)) in cl do con.Close() lock _connections (fun () -> _connections.Remove(tid) |> ignore) let getConnection connectionString (openConnection:(unit -> IDbConnection)) = match Transaction.Current with | null -> new ConnectionContext(openConnection(), true) | current -> let tid = getTid current // get connections for the current transaction let connections = match _connections.TryGetValue(tid) with | true, cl -> cl | false, _ -> let cl = Dictionary<_,_>() lock _connections (fun () -> _connections.Add(tid, cl)) cl // find connection for this connection string let connection = match connections.TryGetValue(connectionString) with | true, con -> con | false, _ -> let initial = (connections.Count = 0) let con = openConnection() connections.Add(connectionString, con) // if this is the first connection for this transaction, register connections for cleanup if initial then current.TransactionCompleted.Add (fun args -> let id = getTid args.Transaction removeConnection id) con new ConnectionContext(connection, false)

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  • When accessing ResultSets in JDBC, is there an elegant way to distinguish between nulls and actual z

    - by Uri
    When using JDBC and accessing primitive types via a result set, is there a more elegant way to deal with the null/0 than the following: int myInt = rs.getInt(columnNumber) if(rs.wasNull())? { // Treat as null } else { // Treat as 0 } I personally cringe whenever I see this sort of code. I fail to see why ResultSet was not defined to return the boxed integer types (except, perhaps, performance) or at least provide both. Bonus points if anyone can convince me that the current API design is great :) My solution was to write a wrapper that returns an Integer (I care more about elegance of client code than performance), but I'm wondering if I'm missing a better way to do this.

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  • PHP: best practice. Do i save html tags in DB or store the html entity value?

    - by Matt
    Hi Guys, I was wondering about which way i should do the following. I am using the tiny MCE wysiwyg editor which formats the users data with the right html tags. Now, i need to save this data entered into the editor into a database table. Should i encode the html tags to their corresponding entities when inserting into the DB, then when i get the data back from the table, not have the encode it for XSS purposes but i'd still have to use eval for the html tags to format the text. OR Do i save the html tags into the database, then when i get the data back from the database encode the html tags to their entities, but then as the tags will appear to the user, i'd have to use the eval function to actually format the data as it was entered. My thoughts are with the first option, i just wondered on what you guys thought. Thanks M

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  • TSql Lookup function

    - by OldMan
    I have a bunch of dimension tables that have unique ID and Name fields. I need a T-SQL function that returns an ID when passed a table name and a value for the name field. I'm guessing the query would build a little query then execute it? Performance isn't an issue since this is a one time ETL thing.

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  • Can freetextbox display links that were not explicitly added?

    - by Joe
    I would like to display links that are pasted in as links rather than text but freetextbox does not seem to do this. For instance, if somebody pastes in http://www.stackoverflow.com it looks like a link but shows up only as text. Do I need to convert this myself or is there a setting in the editor to take care of this?

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  • Visual C++ overrides/mock objects for unit testing?

    - by Mark
    When I'm running unit tests, I want to be able to "stub out" or create a mock object, but I'm running into DLL Hell. For example: There are two DLL libraries built: A.dll and B.dll -- Classes in A.dll have calls to classes in B.dll so when A.dll was built, the link line was using B.lib for the defintions. My test driver (Foo.exe) is testing classes in A.dll, so it links against A.lib. However, I want to "stub out" some of the calls A.dll makes to B.dll with simple versions (return basic value, no DB look up, etc). I can't build an Override.dll that just overrides the needed methods (not entire classes) and replace B.dll because Foo.exe will A) complain that B.dll is missing if I just remove it and put Override.dll in it's place or B) if I rename Override.dll to B.dll, Foo.exe complains that there are unresolved symbols because Override.dll is not a complete implementation of B.dll. Is there a way to do this? Is there a way to statically link Foo.exe with A.lib, B.lib and Override.lib such that it will work without having to completely rebuild A.lib and B.lib to remove the __delcspec(dllexport)? Is there another option?

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