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  • How to implement Session timeout in Web Server Side?

    - by Morgan Cheng
    I beheld a web framework implementing in-memory session in this way. The session object is added to Cache with timeout. When the time is out, the session is removed from Cache automatically. To protect race condition, each request should acquire lock on given session object to proceed. Each request will "touch" the session in Cache to refresh the timeout. Everything looks fine, until this scenario is discovered. Say, one operation takes a long time, longer than timeout. Another request comes and wait on session lock which is currently hold by the long-time request. Finally, the long-time request is over, it releases the lock. But, since it already takes longer time than timeout, the session object is already removed from Cache. This is obvious because the only request holding the lock doesn't have a chance to "touch" the session object in cache. The second request gets the lock but cannot retrieve the expired Session object. Oops... To fix this issue, the second request has to re-create the Session object. But, this is just like digging a buried dead body from tomb and try to bring it back to life. It causes buggy code. I'm wondering what's the best way to implement timeout in session to handle such scenario. I know that current platform must have good session mechanism. I just want to know the under-the-hood how.

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  • scala currying by nested functions or by multiple parameter lists

    - by Morgan Creighton
    In Scala, I can define a function with two parameter lists. def myAdd(x :Int)(y :Int) = x + y This makes it easy to define a partially applied function. val plusFive = myAdd(5) _ But, I can accomplish something similar by defining and returning a nested function. def myOtherAdd(x :Int) = { def f(y :Int) = x + y f _ } Cosmetically, I've moved the underscore, but this still feels like currying. val otherPlusFive = myOtherAdd(5) What criteria should I use to prefer one approach over the other?

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  • How does session_start lock in PHP?

    - by Morgan Cheng
    Originally, I just want to verify that session_start locks on session. So, I create a PHP file as below. Basically, if the pageview is even, the page sleeps for 10 seconds; if the pageview is odd, it doesn't. And, session_start is used to obtain the page view in $_SESSION. I tried to access the page in two tabs of one browser. It is not surprising that the first tab takes 10 seconds since I explicitly let it sleep. The second tab would not sleep, but it should be blocked by sessiont_start. That works as expected. To my surprise, the output of the second page shows that session_start takes almost no time. Actually, the whole page seems takes no time to load. But, the page does take 10 seconds to show in browser. obtained lock Cost time: 0.00016689300537109 Start 1269739162.1997 End 1269739162.1998 allover time elpased : 0.00032305717468262 The page views: 101 Does PHP extract session_start out of PHP page and execute it before other PHP statements? This is the code. <?php function float_time() { list($usec, $sec) = explode(' ', microtime()); return (float)$sec + (float)$usec; } $allover_start_time = float_time(); $start_time = float_time(); session_start(); echo "obtained lock<br/>"; $end_time = float_time(); $elapsed_time = $end_time - $start_time; echo "Cost time: $elapsed_time <br>"; echo "Start $start_time<br/>"; echo "End $end_time<br/>"; ob_flush(); flush(); if (isset($_SESSION['views'])) { $_SESSION['views'] += 1; } else { $_SESSION['views'] = 0; } if ($_SESSION['views'] % 2 == 0) { echo "sleep 10 seconds<br/>"; sleep(10); } $allover_end_time = float_time(); echo "allover time elpased : " . ($allover_end_time - $allover_start_time) . "<br/>"; echo "The page views: " . $_SESSION['views']; ?>

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  • How to build Graceful Degradation AJAX web page?

    - by Morgan Cheng
    I want to build web page with "Graceful Degradation". That is, the web page functions even javascript is disabled. Now I have to make design decision on the format of AJAX response. If javascript is disabled, each HTTP request to server will generate HTML as response. The browser refreshes with the returned HTML. That's fine. If javascript is enabled, each AJAX HTTP request to server will generate ... well, JSON or HTML. If it is HTML, it is easy to implement. Just have javascript to replace part of page with the returned HTML. And, in server side, not much code change is needed. If it is JSON, then I have to implement JSON-to-html logic in javascript again which is almost duplicate of server side logic. Duplication is evil. I really don't like it. The benefit is that the bandwidth usage is better than HTML, which brings better performance. So, what's the best solution to Graceful Degradation? AJAX request better to return JSON or HTML?

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  • Game of life in F# with accelerator

    - by jpalmer
    I'm trying to write life in F# using accelerator v2, but for some odd reason my output isn't square despite all my arrays being square - It appears that everything but a rectangular area in the top left of the matrix is being set to false. I've got no idea how this could be happening as all my operations should treat the entire array equally. Any ideas? open Microsoft.ParallelArrays open System.Windows.Forms open System.Drawing type IPA = IntParallelArray type BPA = BoolParallelArray type PAops = ParallelArrays let RNG = new System.Random() let size = 1024 let arrinit i = Array2D.init size size (fun x y -> i) let target = new DX9Target() let threearr = new IPA(arrinit 3) let twoarr = new IPA(arrinit 2) let onearr = new IPA(arrinit 1) let zeroarr = new IPA(arrinit 0) let shifts = [|-1;-1|]::[|-1;0|]::[|-1;1|]::[|0;-1|]::[|0;1|]::[|1;-1|]::[|1;0|]::[|1;1|]::[] let progress (arr:BPA) = let sums = shifts //adds up whether a neighbor is on or not |> List.fold (fun (state:IPA) t ->PAops.Add(PAops.Cond(PAops.Rotate(arr,t),onearr,zeroarr),state)) zeroarr PAops.Or(PAops.CompareEqual(sums,threearr),PAops.And(PAops.CompareEqual(sums,twoarr),arr)) //rule for life let initrandom () = Array2D.init size size (fun x y -> if RNG.NextDouble() > 0.5 then true else false) type meform () as self= inherit Form() let mutable array = new BoolParallelArray(initrandom()) let timer = new System.Timers.Timer(1.0) //redrawing timer do base.DoubleBuffered <- true do base.Size <- Size(size,size) do timer.Elapsed.Add(fun _ -> self.Invalidate()) do timer.Start() let draw (t:Graphics) = array <- array |> progress let bmap = new System.Drawing.Bitmap(size,size) target.ToArray2D array |> Array2D.iteri (fun x y t -> if not t then bmap.SetPixel(x,y,Color.Black)) t.DrawImageUnscaled(bmap,0,0) do self.Paint.Add(fun t -> draw t.Graphics) do Application.Run(new meform())

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  • Unpacking Argument Lists and Instantiating WTForms objects from web.py

    - by Morris Cornell-Morgan
    After a bit of searching, I've found that it's possible to instantiate a WTForms object in web.py using the following code: form = my_form(**web.input()) web.input() returns a "dictionary-like" web.storage object, but without the double asterisks WTForms will raise an exception: TypeError: formdata should be a multidict-type wrapper that supports the 'getlist' method From the Python documentation I understand that the two asterisks are used to unpack a dictionary of named arguments. That said, I'm still a bit confused about exactly what is going on. What makes the web.storage object returned by web.input() "dictionary-like" enough that it can be unpacked by ** but not "dictionary-like" enough that it can be passed as-is to the WTForms constructor? I know that this is an extremely basic question, but any advice to help a novice programmer would be greatly appreciated!

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  • In terms of loss of volume or corruption, is failure probability of an Amazon EBS volume 'x', indepe

    - by Tony Morgan
    In terms of loss of volume or corruption, is failure probability of an Amazon EBS* volume 'x', independent of the failure of another volume 'y'. Amazon states[1] AFR** of between 0.1%-0.5%, lets say 0.5%, 0.005. To restate the question is the AFR composed of two EBSs mirrored actually 0.005*0.005 = 0.000025? To be clear I'm not interested in high availability here, just very high durability. *EBS = elastic block storage (amazons persistant disks) **AFR = annual failure rate. [1] http://aws.amazon.com/ebs/

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  • Making my XNA sprite jump properly

    - by Matthew Morgan
    I have been having great trouble getting my sprite to jump. So far I have a section of code which with a single tap of "W" will send the sprite in a constant velocity upwards. I need to be able to make my sprite come back down to the ground a certain time or height after begining the jump. There is also a constant pull of velocity 2 on the sprite to simulate some kind of gravity. // Walking = true when there is collision detected between the sprite and ground if (Walking == true) if (keystate.IsKeyDown(Keys.W)) { Jumping = true; } if (Jumping == true) { spritePosition.Y -= 10; } Any ideas and help would be appreciated but I'd prefer a modified version of my code posted if at all possible.

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  • How to troubleshoot PHP session file empty issue?

    - by Morgan Cheng
    I have a very simple test page for PHP session. <?php session_start(); if (isset($_SESSIONS['views'])) { $_SESSIONS['views'] = $_SESSIONS['pv'] + 1; } else { $_SESSIONS['views'] = 0; } var_dump($_SESSIONS); ?> After refreshing the page, it always show array 'views' => int 0 The environment is XAMPP 1.7.3. I checked phpInfo(). The session is enabled. Session Support enabled Registered save handlers files user sqlite Registered serializer handlers php php_binary wddx Directive Local Value Master Value session.auto_start Off Off session.bug_compat_42 On On When the page is accessed, there is session file sess_lnrk7ttpai8187v9q6iok74p20 created in my "D:\xampp\tmp" folder. But the content is empty. With Firebug, I can see cookies about the session. Cookie PHPSESSID=lnrk7ttpai8187v9q6iok74p20 It seems session data is not flushed to files. Is there any way or direction to trouble shoot this issue? Thanks.

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  • Is it necessary to "escape" character "<" and ">" for javascript string?

    - by Morgan Cheng
    Sometimes, server side will generate strings to be embedded in inline JavaScript code. For example, if "UserName" should be generated by ASP.NET. Then it looks like. <script> var username = "<%UserName%>"; </script> This is not safe, because a user can have his/her name to be </script><script>alert('bug')</script></script> It is XSS vulnerability. So, basically, the code should be: <script> var username = "<% JavascriptEncode(UserName)%>"; </script> What JavascriptEncode does is to add charater "\" before "/" and "'" and """. So, the output html is like. var username = "<\/scriptalert(\'bug\')<\/script<\/script"; Browser will not interpret "<\/script" as end of script block. So, XSS in avoided. However, there are still "<" and "" there. It is suggested to escape these two characters as well. First of all, I don't believe it is a good idea to change "<" to "&lt;" and "" to "&gt;" here. And, I'm not sure changing "<" to "\<" and "" to "\" is recognizable to all browsers. It seems it is not necessary to do further encoding for "<" and "". Is there any suggestion on this? Thanks.

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  • Setting ModerationInformation.Status from Approved back to pending removes

    - by Gavin Morgan
    Seeing if anyone else has had this problem and a resolution to it. I have a visual studio sequential workflow on a list (not a library) which does NOT use tasks, the approval process is done through the Approve/Reject OOTB buttons on the list item. The approval is a 2 stage approval, whereby if the 1st stage is completed (via clicking the Approve OOTB button), i reset the ModerationInformation.Status from Approved back to pending then send an email to the 2nd stage approver. My problem is, when i set the the ModerationInformation.Status back to Pending from Approved so there is never an approved version, the Creator loses permissions to view the item, and i get the "cannot find item" error from SharePoint for the person who created the item. The 1st and 2nd level approvers and anyone with approve rights CAN still see the item. Some more background information. the code i am using to update the moderationinformation is I get the properties from the workflow event and get a hook into the listitem properties.Item.ModerationInformation.Status = SPModerationStatusType.Pending; properties.Item.Update(); can anyone help.

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  • c# .net change label text

    - by Morgan
    Hello for I trying to use this code but for some reason it doesn't work. Really need help with this. The problem is that the label doesn't change name from "label" when I enter the site. <asp:Label ID="Label1" runat="server" Text= label'></asp:Label> <% Label1.Text = "test"; if (Request.QueryString["ID"] != null) { string test = Request.QueryString["ID"]; Label1.Text = "Du har nu lånat filmen:" + test; } %>

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  • Custom validation summary

    - by Robert Morgan
    I'm using the UpdateModel method for validation. How do I specify the text for the error messages as they appear in the validation summary? Sorry, I wasn't entirely clear. When I call UpdateModel(), if there is parsing error, for example if a string value is specified for a double field, a "SomeProperty is invalid" error message is automatically added to the ModelState. How do I specify the text for said automatically generated error message? If I implement IDataErrorInfo as suggested, it's error message property gets called for every column, regardless of whether the default binder deems it valid or not. I'd have to reimplement the parse error catching functionality that I get for free with the default binder. Incidentally, the default "SomeProperty is invalid" error messages seem to have mysteriously dissappeared in the RC. A validation summary appears and the relevant fields are highlighted but the text is missing! Any idea why this is? Thanks again and I hope all this waffle makes sense!

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  • How to troubleshoot memcache set method always fail issue?

    - by Morgan Cheng
    I have XAMPP 1.7.3 installed on Windows 7. The PHP version is 5.3.1. I have successfully installed memcache for win32 from http://www.splinedancer.com/memcached-win32. I got PHP extension php_memcache.dll from http://downloads.php.net/pierre. Restarting apache and checking phpinfo() shows memcache is OK. When I test it with below PHP page. It always fail in set method. <?php $memcache = new Memcache; $memcache->connect('127.0.0.1', 11211) or die ("Could not connect"); $version = $memcache->getVersion(); echo "Server's version: ".$version." \n"; $tmp_object = new stdClass; $tmp_object->str_attr = 'test'; $tmp_object->int_attr = 123; $memcache->set('key', $tmp_object, false, 10) or die ("Failed to save data at the server"); echo "Store data in the cache (data will expire in 10 seconds)\n"; $get_result = $memcache->get('key'); echo "Data from the cache: \n" ?> The set method always return false so it constantly output Server's version: Failed to save data at the server I'm stuck. I don't know which way to trouble shoot this issue. Anybody has any idea about possible direction? Thanks.

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  • usort - more parameters

    - by pgfonline
    Hallo, how can I pass more parameters to usort? I have different functions, which are very similar in structure, I want to have just one function: <?php $arr = array( array('number' => 100, 'string'=>'aaa'), array('number'=>50, 'string'=>'bdef'), array('number'=>150, 'string'=>'cbba') ); usort($arr, 'sortNumberDesc'); //How can I use just a single function? //How can I pass further parameters to usort? function sortNumberDesc($a, $b){ $a = $a['number']; $b = $b['number']; if ($a == $b) return 0; return ($a > $b) ? -1 : +1; } function sortNumberAsc($a, $b){ $a = $a['number']; $b = $b['number']; if ($a == $b) return 0; return ($a < $b) ? -1 : +1; } //I want to do the same with just one function: //Sort ID is the search index, reverse DESC or ASC function sort($a, $b, $sortId='number', $reverse = 0){ $a = $a[$sortId]; $b = $b[$sortId]; if ($a == $b) return 0; if($reverse == false) return ($a > $b) ? -1 : +1; else return ($a < $b) ? -1 : +1; } print_r($arr); ?>

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  • What Are Basic Tools For A New Project?

    - by Morgan Cheng
    For a long time, I thought that to start a new project we only need 3 basic tools. 1) A Build System (e.g. Maven & CruiseControl) 2) A Version Control System (e.g. CVS & SVN & GIT) 3) A Bug Tracking System (e.g. Bugzilla) Yesterday, a senior guy told me that we need at least one thing more. That is KPI(Key Performance Index). Without KPI, it is impossible to measure whether the project is progressing well or not. KPI is kind of SOFT tool compared to Maven/SVN/Bugzilla. I believe since I missed SOFT tools, there must be some other kind of tools I missed. So, anybody get some ideas what other basic tools necessary for a new project?

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  • Does PHP session conflict with Share-Nothing-Architecture?

    - by Morgan Cheng
    When I first meet PHP, I'm amazed by the idea Sharing-Nothing-Architecture. I once in a project whose scalaiblity suffers from sharing data among different HTTP requests. However, as I proceed my PHP learning. I found that PHP has sessions. This looks conflict with the idea of sharing nothing. So, PHP session is just invented to make counterpart technology of ASP/ASP.NET/J2EE? Should high scalable web sites use PHP session?

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  • javax.naming.NameNotFoundException: Name [comp/env] is not bound in this Context. Unable to find [comp] error with java scheduler

    - by Morgan Azhari
    What I'm trying to do is to update my database after a period of time. So I'm using java scheduler and connection pooling. I don't know why but my code only working once. It will print: init success success javax.naming.NameNotFoundException: Name [comp/env] is not bound in this Context. Unable to find [comp]. at org.apache.naming.NamingContext.lookup(NamingContext.java:820) at org.apache.naming.NamingContext.lookup(NamingContext.java:168) at org.apache.naming.SelectorContext.lookup(SelectorContext.java:158) at javax.naming.InitialContext.lookup(InitialContext.java:411) at test.Pool.main(Pool.java:25) ---> line 25 is Context envContext = (Context)initialContext.lookup("java:/comp/env"); I don't know why it only works once. I already test it if I didn't running it without java scheduler and it works fine. No error whatsoerver. Don't know why i get this error if I running it using scheduler. Hope someone can help me. My connection pooling code: public class Pool { public DataSource main() { try { InitialContext initialContext = new InitialContext(); Context envContext = (Context)initialContext.lookup("java:/comp/env"); DataSource datasource = new DataSource(); datasource = (DataSource)envContext.lookup("jdbc/test"); return datasource; } catch (Exception ex) { ex.printStackTrace(); } return null; } } my web.xml: <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> <listener> <listener-class> package.test.Pool</listener-class> </listener> <resource-ref> <description>DB Connection Pooling</description> <res-ref-name>jdbc/test</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> </resource-ref> Context.xml: <?xml version="1.0" encoding="UTF-8"?> <Context path="/project" reloadable="true"> <Resource auth="Container" defaultReadOnly="false" driverClassName="com.mysql.jdbc.Driver" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory" initialSize="0" jdbcInterceptors="org.apache.tomcat.jdbc.pool.interceptor.ConnectionState;org.apache.tomcat.jdbc.pool.interceptor.StatementFinalizer" jmxEnabled="true" logAbandoned="true" maxActive="300" maxIdle="50" maxWait="10000" minEvictableIdleTimeMillis="300000" minIdle="30" name="jdbc/test" password="test" removeAbandoned="true" removeAbandonedTimeout="60" testOnBorrow="true" testOnReturn="false" testWhileIdle="true" timeBetweenEvictionRunsMillis="30000" type="javax.sql.DataSource" url="jdbc:mysql://localhost:3306/database?noAccessToProcedureBodies=true" username="root" validationInterval="30000" validationQuery="SELECT 1"/> </Context> my java scheduler public class Scheduler extends HttpServlet{ public void init() throws ServletException { System.out.println("init success"); try{ Scheduling_test test = new Scheduling_test(); ScheduledExecutorService executor = Executors.newScheduledThreadPool(100); ScheduledFuture future = executor.scheduleWithFixedDelay(test, 1, 60 ,TimeUnit.SECONDS); }catch(Exception e){ e.printStackTrace(); } } } Schedule_test public class Scheduling_test extends Thread implements Runnable{ public void run(){ Updating updating = new Updating(); updating.run(); } } updating public class Updating{ public void run(){ ResultSet rs = null; PreparedStatement p = null; StringBuilder sb = new StringBuilder(); Pool pool = new Pool(); Connection con = null; DataSource datasource = null; try{ datasource = pool.main(); con=datasource.getConnection(); sb.append("SELECT * FROM database"); p = con.prepareStatement(sb.toString()); rs = p.executeQuery(); rs.close(); con.close(); p.close(); datasource.close(); System.out.println("success"); }catch (Exception e){ e.printStackTrace(); } }

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  • How does twitter server get to know single tweet ID from URL fragment segment?

    - by Morgan Cheng
    Each tweet has a single URL such as http://twitter.com/#!/DeliciousHot/status/23189589820702720. The tweet identification (/DeliciousHot/status/23189589820702720) is in the URL fragment segment which is not actually sent to server. Originally, I thought it works this way: The URL response doesn't have this tweet specific info. It is JavaScript module that extracts tweet id from current browser URL and fetch tweet payload with AJAX. The page content is then updated with the tweet payload. To my surprise, it is doesn't work this way! With Firebug, you can view that response of http://twitter.com/#!/DeliciousHot/status/23189589820702720 has tweet payload "10 Signs of a True Gentleman" text in inline JavaScript. The tweet payload is not fetched by another AJAX. So, how does Twitter server get to know the expected tweet ID even it is in URL fragment segment?

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