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• Can I host multiple sites with one Amazon EC2 instance [duplicate]

  - by user22

  This question already has an answer here: Can you help me with my capacity planning? 2 answers I currently have VPS server and I pay around $75 per month and I get: 40GB HD 2Gb RAM 100GB BW 6 core cpu (but i dont use much) I have only one live website running and traffic is only max 100 user visit per day. I mostly do the my testing stuff and some of my inter sites for playing with coding. But I do need one server. I am thinking of moving to Amazon EC2 if the price diff is not so much because then I can learn some more stuff. I am thinking of getting the 3 years Heavy utilization Reserved instance because my server will be running all day and night. I tried their online caluclator with Medium Instance Heavy reserved for 3 years for EC2 it comes $31 per month(effective price) and for EBS and S3 , I think even if thats it $40 for all other stuff. I will be at no loss for what I am getting at present. Am i correct or I missed something?? Now In my current VPS I have Apache for PHP sites and MOD wsgi for python sites. I am not sure if I will be able to do all that stuff in Amazon EC2. Can I host python and PHP sites both in Amazon EC2 instance using Named Virtual Hosts and Ngnix

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• Methods and practices for managing a network that has no internet connection

  - by FaultyJuggler

  Originally asked in Super User but realized this belongs here. Long story short, I am setting up a network with 32 servers of varying specs that will be used for testing and development. We will be using RedHat Linux, we also do not have a router as of yet and were looking into making one of the servers act as our router/DHCP etc. The small cluster will be on an isolated network with no internet. I can use external harddrives and discs to transfer anything from external sources into machines on the network, so this isn't a locked down secure network, it just won't have a direct connection to the outside world. I've worked on such setups before, but always long after they were setup. So I'm reaching out to see what everyone knows as far as how groups have handled initial setup and maintenance of such a situation. What is the best way to get them all configured and up to date? What are the best ways to automate updates, network wide installs, etc. With the only given that I have large multi-terabyte external hard drives that would be used to drop whatever files are needed onto a central server, how do i then distribute those files and install their contents? I've done perl scripting, some teammates have played with puppet, so we aren't completely in the dark, I just wanted to avoid reinventing the wheel since this is a common challenge.

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• moving from WinXP to WinServer in VmWare

  - by Alex

  I have a Vmware machine for.Net application testing. Current setup: Host OS: win7 Guest OS: Right now the guest OS is Win Xp Pro x64, which runs great with just 1 gigabyte of RAM and 10 gigs of disk space. * This part can be skipped * As I said, there was a program that I needed to test, but unfortunately, by default, Vmware installs crappy display drivers(called SVGA II) on XP machines and there is NO way to upgrade them! This resulted in my program's error (the program used SlimDX (DirectX wrapper) to do some stuff..). Eventually I found out that display drivers most certainly is the problem. For example, Windows 7 virtual machine uses SVGA 3D drivers and I have NO problems running my SlimDX-based program. Now, regarding Windows Server 2008! Apparently, WDDM driver is supported by WS2008, which means that I'll be able to install SVGA 3D and to test my DX apps. * end of skip * The questions are: Will WS2008 be as smooth with just 1 gig of RAM just like Win XP was? Will 10 gigs of HDD be enough? Or the server requires more? Will I be able to install .Net ver. 4 on WS2008? Are there any limitations that I need to be aware of as a .Net programmer? EDIT: I was hoping that WS2008 is XP-based, not Vista-vased/W7-based. In comparison, W7 virtual machine with 2 gigs of RAM and 2 proc cores nearly kills my Host OS. Whereas, WinXp runs extremely fast even with 1 core and 1 gig of RAM. That's the main reason why I want to try WS2008..

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• Raspberry Pi how to format HDD

  - by Speed

  Hi I am very new to Raspberry Pi environment, so looking for a bit of help to format a usb hard disk drive. I ran lsblk and got sda 8:0 0 37.3G 0 disk sda1 8:1 0 37.3G 0 part looking on web, if tried the following "sudo mkfs.ext4 /dev/sda1 -L USB40gb" it did something but when I tried to mount the drive again, it still showed the files that were there before and I can not create new file/folder "Error creating directory: Permission denied" I am writing this from my windows 8.1 pc so can not cut and paste from the pi. trying to format its output is a bit hard. Oh, there is Nothing written after the word "part" above. There use to be /media/USB40gb so I have done something because this has disappeared. I am using PCManFM 0.9.10 It does not have a format option, which would make life a lot easier, but then its not windows. I think I am running the basic linux os for the pi. It boots to a graphic environment, but I do not know how to advise what it is. I think its OpenBox 2.0.4 Thanks in advance Speed PS: I reran the format string above but this time I changed the label to read USB37gb. I did this to confirm that I was in fact formatting the right drive. Low and behold, it actually formatted the drive, wiping everything from it. Great ... testing it by creating a new folder on the drive and get error msg Permission Denied! So I have fixed the formatting issue by trial and error but still can't use the drive... Suggestions anyone?

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• what is best multi-server configuration with OpenVPN

  - by sebut

  We have a number of Database severs running MongoDB on Debian plus a number of Application servers also on Debian. The db servers hold replicating db clusters, so they need to talk to each other. Application servers need to talk to all db servers (for reasons of fault tolerance). The servers are potentially spread across multiple hosting centers, so we need secure channels between all servers. The number of servers is bound to grow, so we need a VPN solution that's easy to maintain and expand. This is why I feel that SSH that we use for testing might not be up to the task and OpenVPN seems the way to go. I have ruled out TAP, since I understand that this would mean all traffic going to all the servers - perhaps this is a misunderstanding and TAP acts more like a switch? With TUN devices I imagine that all DB servers would live in their own separate subnet, they would also need a client configured to be able to connect to each of their peers. The application servers could live in a common subnet range with a client config only. Does this sound like a reasonable setup? Strangely, on the web I did not find anything about multi-server with OpenVPN. Thanks for all insights and ideas!

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• SSH very slow when connecting from external [closed]

  - by wnstnsmth

  Possible Duplicate: ssh delay when connecting We have a CentOS server that we use for internal testing purposes, which has sshd enabled. When I (as a developer) am at the company, I use ssh [email protected] to connect to it - and it works flawlessly. Now, in order to work from home, accessing the server via the company's static IP, we set up another port for ssh, 2020. So I execute ssh -p 2020 [email protected] and am immediately granted for a password. After entering the password, it takes up to 30 seconds until I can access the server. Same is with SFTP (i.e. uploading files takes about 30 seconds until it begins to transfer). As you can imagine, if you have to regularly upload files to a webserver via SFTP, this is very tedious. So I looked at similar questions and thus edited the sshd_config file on the server, setting UseDNS to "no" and GSSAPIAuthentication to "no" (this one also in ssh_config on the client) - it did not work.. Please have a look at the -vvv output when externally accessing the server: ssh -p 2020 -vvv [email protected] PasteBin: ssh What could it be? Do you need more info?

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• Mysql: Working With 192 Trillion Records... (Yes, 192 Trillion)

  - by Sarah

  Here's the question... Considering 192 trillion records, what should my considerations be? My main concern is speed. Here's the table... CREATE TABLE `ref` ( `id` INTEGER(13) AUTO_INCREMENT DEFAULT NOT NULL, `rel_id` INTEGER(13) NOT NULL, `p1` INTEGER(13) NOT NULL, `p2` INTEGER(13) DEFAULT NULL, `p3` INTEGER(13) DEFAULT NULL, `s` INTEGER(13) NOT NULL, `p4` INTEGER(13) DEFAULT NULL, `p5` INTEGER(13) DEFAULT NULL, `p6` INTEGER(13) DEFAULT NULL, PRIMARY KEY (`id`), KEY (`s`), KEY (`rel_id`), KEY (`p3`), KEY (`p4`) ); Here's the queries... SELECT id, s FROM ref WHERE red_id="$rel_id" AND p3="$p3" AND p4="$p4" SELECT rel_id, p1, p2, p3, p4, p5, p6 FROM ref WHERE id="$id" INSERT INTO rel (rel_id, p1, p2, p3, s, p4, p5, p6) VALUES ("$rel_id", "$p1", "$p2", "$p3", "$s", "$p4", "$p5", "$p6") Here's some notes... The SELECT's will be done much more frequently than the INSERT. However, occasionally I want to add a few hundred records at a time. Load-wise, there will be nothing for hours then maybe a few thousand queries all at once. Don't think I can normalize any more (need the p values in a combination) The database as a whole is very relational. This will be the largest table by far (next largest is about 900k) UPDATE (08/11/2010) Interestingly, I've been given a second option... Instead of 192 trillion I could store 2.6*10^16 (15 zeros, meaning 26 Quadrillion)... But in this second option I would only need to store one bigint(18) as the index in a table. That's it - just the one column. So I would just be checking for the existence of a value. Occasionally adding records, never deleting them. So that makes me think there must be a better solution then mysql for simply storing numbers... Given this second option, should I take it or stick with the first... [edit] Just got news of some testing that's been done - 100 million rows with this setup returns the query in 0.0004 seconds [/edit]

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• How many VPS do I need for my website? [duplicate]

  - by michael

  This question already has an answer here: How do you do load testing and capacity planning for web sites? 3 answers I made a website which aims at simulating a trading market. There are a list of prices and corresponding volumes that people want to purchase. Users can purchase at any price any time. My website retrieves the prices and volumes from my database every 2 seconds (I have to update the user's browser frequently to allow them to see the current market). Users' database INSERT query can be sent any time if they purchase. I used ajax to post or get data from my database (sometimes nested ajax calls). So, every 2 seconds, each user will send or retrieve data by using more than 20 database queries (in order to show a users the current prices and volumes). Also, I may have 200 users at a time. I was not using VPS before, and I got banned because of using too much CPU resources on my host. Now, I've purchased VPS*2 from a hosting servers. I have: CPU Speed: 2000 Mhz Memory: 2048 MB Disk Space: 20000 MB Bandwidth: 2000 GB Connection: 40 Mb/s Dedicated IP's 2 IP's Is this enough for my 200 users? Also, which VPS OS is suitable for me? Thank you.

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• How do I correctly Re-render a Recaptcha in ASP.NET MVC 2 after an AJAX POST

  - by Eoin Campbell

  Ok... I've downloaded and implemented this Recaptcha implementation for MVC which uses the ModelState to confirm the validity of the captcha control. It works brilliantly... except when I start to use it in an AJAX Form. In a nutshell, when a div is re-rendered with AJAX, the ReCaptcha that it should contain does not appear, even though the relevant <scripts> are in the source after the partial render. Code Below. using (Ajax.BeginForm("CreateComment", "Blog", new AjaxOptions() { HttpMethod = "POST", UpdateTargetId = "CommentAdd", OnComplete="ReloadRecaptcha", OnSuccess = "ShowComment", OnFailure = "ShowComment", OnBegin = "HideComment" })) {%> <fieldset class="comment"> <legend>Add New Comment</legend> <%= Html.ValidationSummary()%> <table class="postdetails"> <tbody> <tr> <td rowspan="3" id="blahCaptcha"> <%= Html.CreateRecaptcha("recaptcha", "blackglass") %> </td> .... Remainder of Form Omitted for Brevity I've confirmed the Form is perfectly functional when the Recaptcha Control is not present and the Javascript calls in the AjaxOptions are all working fine. The problem is that if the ModelState is Invalid as a result of the Recaptcha or some other validation, then the ActionResult returns the View to reshow the form. [RecaptchaFilter(IgnoreOnMobile = true)] [HttpPost] public ActionResult CreateComment(Comment c) { if (ModelState.IsValid) { try { //Code to insert Comment To DB return Content("Thank You"); } catch { ModelState.AddRuleViolations(c.GetRuleViolations()); } } else { ModelState.AddRuleViolations(c.GetRuleViolations()); } return View("CreateComment", c); } When it's InValid and the form posts back, for some reason the ReCaptcha Control does not re-render. I've checked the source and the <script> & <noscript> blocks are present in the HTML so the HTML Helper function below is obviously working <%= Html.CreateRecaptcha("recaptcha", "blackglass") %> I assume this has something to do with scripts injected into the DOM by AJAX are not re-executed. As you can see from the HTML snippet above, I've tried to add an OnComplete= javascript function to re-create the Captcha on the client side, but although the script executes with no errors, it doesn't work. OnComplete Function is. function ReloadRecaptcha() { Recaptcha.create("my-pub-key", 'blahCaptcha', { //blahCaptcha is the ID of the <td> where the ReCaptcha should go. theme: 'blackglass' }); } Can anyone shed any light on this ? Thanks, Eoin C

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• ASP.NET MVC2: Getting textbox data from a view to a controller

  - by mr_plumley

  Hi, I'm having difficulty getting data from a textbox into a Controller. I've read about a few ways to accomplish this in Sanderson's book, Pro ASP.NET MVC Framework, but haven't had any success. Also, I've ran across a few similiar questions online, but haven't had any success there either. Seems like I'm missing something rather fundamental. Currently, I'm trying to use the action method parameters approach. Can someone point out where I'm going wrong or provide a simple example? Thanks in advance! Using Visual Studio 2008, ASP.NET MVC2 and C#: What I would like to do is take the data entered in the "Investigator" textbox and use it to filter investigators in the controller. I plan on doing this in the List method (which is already functional), however, I'm using the SearchResults method for debugging. Here's the textbox code from my view, SearchDetails: <h2>Search Details</h2> <% using (Html.BeginForm()) { %> <fieldset> <%= Html.ValidationSummary() %> <h4>Investigator</h4> <p> <%=Html.TextBox("Investigator")%> <%= Html.ActionLink("Search", "SearchResults")%> </p> </fieldset> <% } %> Here is the code from my controller, InvestigatorsController: private IInvestigatorsRepository investigatorsRepository; public InvestigatorsController(IInvestigatorsRepository investigatorsRepository) { //IoC: this.investigatorsRepository = investigatorsRepository; } public ActionResult List() { return View(investigatorsRepository.Investigators.ToList()); } public ActionResult SearchDetails() { return View(); } public ActionResult SearchResults(SearchCriteria search) { string test = search.Investigator; return View(); } I have an Investigator class: [Table(Name = "INVESTIGATOR")] public class Investigator { [Column(IsPrimaryKey = true, IsDbGenerated = false, AutoSync=AutoSync.OnInsert)] public string INVESTID { get; set; } [Column] public string INVEST_FNAME { get; set; } [Column] public string INVEST_MNAME { get; set; } [Column] public string INVEST_LNAME { get; set; } } and created a SearchCriteria class to see if I could get MVC to push the search criteria data to it and grab it in the controller: public class SearchCriteria { public string Investigator { get; set; } } } I'm not sure if project layout has anything to do with this either, but I'm using the 3 project approach suggested by Sanderson: DomainModel, Tests, and WebUI. The Investigator and SearcCriteria classes are in the DomainModel project and the other items mentioned here are in the WebUI project. Thanks again for any hints, tips, or simple examples! Mike

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• WPF Converter and NotifyOnTargetUpdated exclusive in a binding ?

  - by Mathieu Garstecki

  Hi, I have a problem with a databinding in WPF. When I try to use a value converter and set the NotifyOnTargetUpdated=True property to True, I get an XamlParseException with the following message: 'System.Windows.Data.BindingExpression' value cannot be assigned to property 'Contenu' of object 'View.UserControls.ShadowedText'. Value cannot be null. Parameter name: textToFormat Error at object 'System.Windows.Data.Binding' in markup file 'View.UserControls;component/saletotal.xaml' Line 363 Position 95. The binding is pretty standard: <my:ShadowedText Contenu="{Binding Path=Total, Converter={StaticResource CurrencyToStringConverter}, NotifyOnTargetUpdated=True}" TargetUpdated="MontantTotal_TargetUpdated"> </my:ShadowedText> (Styling properties removed for conciseness) The converter exists in the resources and works correctly when NotifyOnTargetUpdated=True is removed. Similarly, the TargetUpdated event is called and implemented correctly, and works when the converter is removed. Note: This binding is defined in a ControlTemplate, though I don't think that is relevant to the problem. Can anybody explain me what is happening ? Am I defining the binding wrong ? Are those features mutually exclusive (and in this case, can you explain why it is so) ? Thanks in advance. More info: Here is the content of the TargetUpdated handler: private void MontantTotal_TargetUpdated(object sender, DataTransferEventArgs e) { ShadowedText textBlock = (ShadowedText)e.TargetObject; double textSize = textBlock.Taille; double delta = 5; double defaultTaille = 56; double maxWidth = textBlock.MaxWidth; while (true) { FormattedText newFormat = new FormattedText(textBlock.Contenu, CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Calibri"), textSize, (SolidColorBrush) Resources["RougeVif"]); if (newFormat.Width < textBlock.MaxWidth && textSize <= defaultTaille) { if ((Math.Round(newFormat.Width) + delta) >= maxWidth || textSize == defaultTaille) { break; } textSize++; } else { if ((Math.Round(newFormat.Width) - delta) <= maxWidth && textSize <= defaultTaille) { break; } textSize--; } } textBlock.Taille = textSize; } The role of the handler is to resize the control based on the length of the content. It is quite ugly but I want to have the functional part working before refactoring.

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• SQL 2008 R2 login/network issue

  - by martinjd

  I have a Windows Server 2008 R2 new clean install , not a VM, that I have added to a Windows Server 2003 based domain using my account which has domain admin rights. The domain functional level is 2003. I performed a clean install of SQL Server 2008 R2 using my account which has domain admin rights. The installation completed without any errors. I logged into SSMS locally and attempted to add another domain account by clicking Search, Advanced and finding the user in the domain. When I return to the "Dialog - New" window and click OK I receive the following error: Create failed for Login 'Domain\User'. (Microsoft.SqlServer.Smo) An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo) Windows NT user or group 'Domain\User' not found. Check the name again. (Microsoft SQL Server, Error: 15401) I have verified that the firewall is off, tried adding a different domain user, tried using SA to add a user, installed the hotfix for KB 976494 and verified that the Local Security Policy for Domain Member: Digitally encrypt or sign secure channel Domain Member: Digitally encrypt secure channel Domain Member: Digitally sign secure channel are disabled none of which have made a difference. I can RDP to a Server 2003 server running SQL 2008 and add the same domain user without issue. Also if I try to connect with SSMS to the sql server from another system on the domain using my account I get the following error: Login failed. The login is from an untrusted domain and cannot be used with Windows authentication. (Microsoft SQL Server, Error: 18452) and on the database server I see the following in the security event log: An account failed to log on. Subject: Security ID: NULL SID Account Name: - Account Domain: - Logon ID: 0x0 Logon Type: 3 Account For Which Logon Failed: Security ID: NULL SID Account Name: myUserName Account Domain: MYDOMAIN Failure Information: Failure Reason: An Error occured during Logon. Status: 0xc000018d Sub Status: 0x0 Process Information: Caller Process ID: 0x0 Caller Process Name: - Network Information: Workstation Name: MYWKS Source Network Address: - Source Port: - Detailed Authentication Information: Logon Process: NtLmSsp Authentication Package: NTLM Transited Services: - Package Name (NTLM only): - Key Length: 0 I am sure that the "NULL SID" has some significant meaning but have no idea at this point what the issue could be.

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• Configuration problems with django and mod_wsgi

  - by Jimbo

  Hi, I've got problems on getting django to work on apache 2.2 with mod_wsgi. Django is installed and mod_wsgi too. I can even see a 404 page when accessing the path and I can login to django admin. But if I want to install the tagging module I get the following error: Traceback (most recent call last): File "setup.py", line 49, in <module> version_tuple = __import__('tagging').VERSION File "/home/jim/django-tagging/tagging/__init__.py", line 3, in <module> from tagging.managers import ModelTaggedItemManager, TagDescriptor File "/home/jim/django-tagging/tagging/managers.py", line 5, in <module> from django.contrib.contenttypes.models import ContentType File "/usr/lib/python2.5/site-packages/django/contrib/contenttypes/models.py", line 1, in <module> from django.db import models File "/usr/lib/python2.5/site-packages/django/db/__init__.py", line 10, in <module> if not settings.DATABASE_ENGINE: File "/usr/lib/python2.5/site-packages/django/utils/functional.py", line 269, in __getattr__ self._setup() File "/usr/lib/python2.5/site-packages/django/conf/__init__.py", line 40, in _setup self._wrapped = Settings(settings_module) File "/usr/lib/python2.5/site-packages/django/conf/__init__.py", line 75, in __init__ raise ImportError, "Could not import settings '%s' (Is it on sys.path? Does it have syntax errors?): %s" % (self.SETTINGS_MODULE, e) ImportError: Could not import settings 'mysite.settings' (Is it on sys.path? Does it have syntax errors?): No module named mysite.settings My httpd.conf: Alias /media/ /home/jim/django/mysite/media/ <Directory /home/jim/django/mysite/media> Order deny,allow Allow from all </Directory> Alias /admin/media/ "/usr/lib/python2.5/site-packages/django/contrib/admin/media/" <Directory "/usr/lib/python2.5/site-packages/django/contrib/admin/media/"> Order allow,deny Allow from all </Directory> WSGIScriptAlias /dj /home/jim/django/mysite/apache/django.wsgi <Directory /home/jim/django/mysite/apache> Order deny,allow Allow from all </Directory> My django.wsgi: import sys, os sys.path.append('/home/jim/django') sys.path.append('/home/jim/django/mysite') os.chdir('/home/jim/django/mysite') os.environ['DJANGO_SETTINGS_MODULE'] = 'mysite.settings' import django.core.handlers.wsgi application = django.core.handlers.wsgi.WSGIHandler() I try to get this to work since a few days and have read several blogs and answers here on so but nothing worked.

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• jQuery UI Tabs Not Working

  - by Christopher

  I just downloaded jQuery UI Tabs. In the included index.html file, it works fine, CSS and all, with no customization. I copied the files over to my web server, keeping the directory structure intact, and copied the content code to my already-existing index.html, but it does not work. My Header Code <script type="text/javascript" src="js/jquery-1.4.2.min.js"></script> <link type="text/css" href="css/start/jquery-ui-1.8.custom.css" rel="stylesheet" /> <script type="text/javascript" src="js/jquery-ui-1.8.custom.min.js"></script> <script type="text/javascript"> $(function(){ // Tabs $('#tabs').tabs(); }); </script> My Body Code <div id="tabs"> <ul> <li><a href="#tabs-1">First</a></li> <li><a href="#tabs-2">Second</a></li> <li><a href="#tabs-3">Third</a></li> </ul> <div id="tabs-1">Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</div> <div id="tabs-2">Phasellus mattis tincidunt nibh. Cras orci urna, blandit id, pretium vel, aliquet ornare, felis. Maecenas scelerisque sem non nisl. Fusce sed lorem in enim dictum bibendum.</div> <div id="tabs-3">Nam dui erat, auctor a, dignissim quis, sollicitudin eu, felis. Pellentesque nisi urna, interdum eget, sagittis et, consequat vestibulum, lacus. Mauris porttitor ullamcorper augue.</div> </div> My Output * First * Second * Third Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Phasellus mattis tincidunt nibh. Cras orci urna, blandit id, pretium vel, aliquet ornare, felis. Maecenas scelerisque sem non nisl. Fusce sed lorem in enim dictum bibendum. Nam dui erat, auctor a, dignissim quis, sollicitudin eu, felis. Pellentesque nisi urna, interdum eget, sagittis et, consequat vestibulum, lacus. Mauris porttitor ullamcorper augue. All of the files are referenced correctly, and it is all copied and pasted directly from a fully functional file., but it will not work.

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• Haskell newbie on types

  - by garulfo

  I'm completely new to Haskell (and more generally to functional programming), so forgive me if this is really basic stuff. To get more than a taste, I try to implement in Haskell some algorithmic stuff I'm working on. I have a simple module Interval that implements intervals on the line. It contains the type data Interval t = Interval t t the helper function makeInterval :: (Ord t) => t -> t -> Interval t makeInterval l r | l <= r = Interval l r | otherwise = error "bad interval" and some utility functions about intervals. Here, my interest lies in multidimensional intervals (d-intervals), those objects that are composed of d intervals. I want to separately consider d-intervals that are the union of d disjoint intervals on the line (multiple interval) from those that are the union of d interval on d separate lines (track interval). With distinct algorithmic treatments in mind, I think it would be nice to have two distinct types (even if both are lists of intervals here) such as import qualified Interval as I -- Multilple interval newtype MInterval t = MInterval [I.Interval t] -- Track interval newtype TInterval t = TInterval [I.Interval t] to allow for distinct sanity checks, e.g. makeMInterval :: (Ord t) => [I.Interval t] -> MInterval t makeMInterval is = if foldr (&&) True [I.precedes i i' | (i, i') <- zip is (tail is)] then (MInterval is) else error "bad multiple interval" makeTInterval :: (Ord t) => [I.Interval t] -> TInterval t makeTInterval = TInterval I now get to the point, at last! But some functions are naturally concerned with both multiple intervals and track intervals. For example, a function order would return the number of intervals in a multiple interval or a track interval. What can I do? Adding -- Dimensional interval data DInterval t = MIntervalStuff (MInterval t) | TIntervalStuff (TInterval t) does not help much, since, if I understand well (correct me if I'm wrong), I would have to write order :: DInterval t -> Int order (MIntervalStuff (MInterval is)) = length is order (TIntervalStuff (TInterval is)) = length is and call order as order (MIntervalStuff is) or order (TIntervalStuff is) when is is a MInterval or a TInterval. Not that great, it looks odd. Neither I want to duplicate the function (I have many functions that are concerned with both multiple and track intevals, and some other d-interval definitions such as equal length multiple and track intervals). I'm left with the feeling that I'm completely wrong and have missed some important point about types in Haskell (and/or can't forget enough here about OO programming). So, quite a newbie question, what would be the best way in Haskell to deal with such a situation? Do I have to forget about introducing MInterval and TInterval and go with one type only? Thanks a lot for your help, Garulfo

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• Handling aces and finding a segfault in a blackjack program

  - by Bill Adams

  Here's what i have so far... I have yet to figure out how i'm going to handle the 11 / 1 situation with an ace, and when the player chooses an option for hit/stand, i get segfault. HELP!!! #include <stdio.h> #include <string.h> #include <stdlib.h> #include <time.h> #define DECKSIZE 52 #define VALUE 9 #define FACE 4 #define HANDSIZE 26 typedef struct { int value; char* suit; char* name; }Card; typedef struct { int value; char* suit; char* name; }dealerHand; typedef struct { int value; char* suit; char* name; }playerHand; Card cards[DECKSIZE]; dealerHand deal[HANDSIZE]; playerHand dealt[HANDSIZE]; char *faceName[]={"two","three", "four","five","six", "seven","eight","nine", "ten", "jack","queen", "king","ace"}; char *suitName[]={"spades","diamonds","clubs","hearts"}; void printDeck(){ int i; for(i=0;i<DECKSIZE;i++){ printf("%s of %s value = %d\n ",cards[i].name,cards[i].suit,cards[i].value); if((i+1)%13==0 && i!=0) printf("-------------------\n\n"); } } void shuffleDeck(){ srand(time(NULL)); int this; int that; Card temp; int c; for(c=0;c<10000;c++){ //c is the index for number of individual card shuffles should be set to c<10000 or more this=rand()%DECKSIZE; that=rand()%DECKSIZE; temp=cards[this]; cards[this]=cards[that]; cards[that]=temp; } } /*void hitStand(i,y){ // I dumped this because of a segfault i couldn't figure out. int k; printf(" Press 1 to HIT or press 2 to STAND:"); scanf("%d",k); if(k=1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } } */ int main(){ int suitCount=0; int faceCount=0; int i; int x; int y; int d; int p; int k; for(i=0;i<DECKSIZE;i++){ //this for statement builds the deck if(faceCount<9){ cards[i].value=faceCount+2; }else{ //assigns face cards as value 10 cards[i].value=10; } cards[i].suit=suitName[suitCount]; cards[i].name=faceName[faceCount++]; if(faceCount==13){ //this if loop increments suit count once cards[i].value=11; //all faces have been assigned, and also suitCount++; //assigns the ace as 11 faceCount=0; } //end building deck } /*printDeck(); //prints the deck in order shuffleDeck(); //shuffles the deck printDeck(); //prints the deck as shuffled This was used in testing, commented out to keep the deck hidden!*/ shuffleDeck(); x=0; y=0; for(i=0;i<4;i++){ //this for loop deals the first 4 cards, dealt[y].suit=cards[i].suit; //first card to player, second to dealer, dealt[y].name=cards[i].name; //as per standard dealing practice. dealt[y].value=cards[i].value; i++; y++; deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; } printf(" Dealer's hand is: %s of %s and XXXX of XXXX. (Second card is hidden!)\n",deal[0].name,deal[0].suit,deal[1].name,deal[1].suit); printf(" Player's hand is: %s of %s and %s of %s.\n",dealt[0].name,dealt[0].suit,dealt[1].name,dealt[1].suit); printf(" the current value of the index i=%d\n",i); //this line gave me the value of i for testing d=deal[0].value+deal[1].value; p=dealt[0].value+dealt[1].value; if(d==21){ printf(" The Dealer has Blackjack! House win!\n"); }else{ if(d>21){ printf(" The dealer is Bust! You win!\n"); }else{ if(d>17){ printf(" Press 1 to HIT or 2 to STAND"); scanf("%d",k); if(k==1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } }else{ if(d<17){ printf(" Dealer Hits!"); deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; i++; } } } } return 0; }

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• Does my fat-client application belong in the MVC pattern?

  - by boatingcow

  The web-based application I’m currently working on is growing arms and legs! It’s basically an administration system which helps users to keep track of bookings, user accounts, invoicing etc. It can also be accessed via a couple of different websites using a fairly crude API. The fat-client design loosely follows the MVC pattern (or perhaps MVP) with a php/MySQL backend, Front Controller, several dissimilar Page Controllers, a liberal smattering of object-oriented and procedural Models, a confusing bunch of Views and templates, some JavaScripts, CSS files and Flash objects. The programmer in me is a big fan of the principle of “Separation of Concerns” and on that note, I’m currently trying to figure out the best way to separate and combine the various concerns as the project grows and more people contribute to it. The problem we’re facing is that although JavaScript (or Flash with ActionScript) is normally written with the template, hence part of the View and decoupled from the Controller and Model, we find that it actually encompasses the entire MVC pattern... Swap an image with an onmouseover event - that’s Behaviour. Render a datagrid - we’re manipulating the View. Send the result of reordering a list via AJAX - now we’re in Control. Check a form field to see if an email address is in a valid format - we’re consulting the Model. Is it wise to let the database people write up the validation Model with jQuery? Can the php programmers write the necessary Control structures in JavaScript? Can the web designers really write a functional AJAX form for their View? Should there be a JavaScript overlord for every project? If the MVC pattern could be applied to the people instead of the code, we would end up with this: Model - the database boffins - “SELECT * FROM mind WHERE interested IS NULL” Control - pesky programmers - “class Something extends NothingAbstractClass{…}” View - traditionally the domain of the graphic/web designer - “” …and a new layer: Behaviour - interaction and feedback designer - “CSS3 is the new black…” So, we’re refactoring and I’d like to stick to best practice design, but I’m not sure how to proceed. I don’t want to reinvent the wheel, so would anyone have any hints or tips as to what pattern I should be looking at or any code samples from someone who’s already done the dirty work? As the programmer guy, how can I rewrite the app for backend and front end whilst keeping the two separate? And before you ask, yes I’ve looked at Zend, CodeIgnitor, Symfony, etc., and no, they don’t seem to cross the boundary between server logic and client logic!

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• Code Golf: Evaluating Mathematical Expressions

  - by Noldorin

  Challenge Here is the challenge (of my own invention, though I wouldn't be surprised if it has previously appeared elsewhere on the web). Write a function that takes a single argument that is a string representation of a simple mathematical expression and evaluates it as a floating point value. A "simple expression" may include any of the following: positive or negative decimal numbers, +, -, *, /, (, ). Expressions use (normal) infix notation. Operators should be evaluated in the order they appear, i.e. not as in BODMAS, though brackets should be correctly observed, of course. The function should return the correct result for any possible expression of this form. However, the function does not have to handle malformed expressions (i.e. ones with bad syntax). Examples of expressions: 1 + 3 / -8 = -0.5 (No BODMAS) 2*3*4*5+99 = 219 4 * (9 - 4) / (2 * 6 - 2) + 8 = 10 1 + ((123 * 3 - 69) / 100) = 4 2.45/8.5*9.27+(5*0.0023) = 2.68... Rules I anticipate some form of "cheating"/craftiness here, so please let me forewarn against it! By cheating, I refer to the use of the eval or equivalent function in dynamic languages such as JavaScript or PHP, or equally compiling and executing code on the fly. (I think my specification of "no BODMAS" has pretty much guaranteed this however.) Apart from that, there are no restrictions. I anticipate a few Regex solutions here, but it would be nice to see more than just that. Now, I'm mainly interested in a C#/.NET solution here, but any other language would be perfectly acceptable too (in particular, F# and Python for the functional/mixed approaches). I haven't yet decided whether I'm going to accept the shortest or most ingenious solution (at least for the language) as the answer, but I would welcome any form of solution in any language, except what I've just prohibited above! My Solution I've now posted my C# solution here (403 chars). Update: My new solution has beaten the old one significantly at 294 chars, with the help of a bit of lovely regex! I suspected that this will get easily beaten by some of the languages out there with lighter syntax (particularly the funcional/dynamic ones), and have been proved right, but I'd be curious if someone could beat this in C# still. Update I've seen some very crafty solutions already. Thanks to everyone who has posted one. Although I haven't tested any of them yet, I'm going to trust people and assume they at least work with all of the given examples. Just for the note, re-entrancy (i.e. thread-safety) is not a requirement for the function, though it is a bonus. Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear/semi-obfuscated function: (code here) Any notes on the algorithm/clever shortcuts it takes.

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• Data access pattern

  - by andlju

  I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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• OSGI classcast exception on felix

  - by Nico

  Hi, i'm fairly new to osgi and am trying to get a functional proof of concept together. The setup is that my common api is created in a bundle creatively named common-api.jar with no bundle activator, but it exports all it's interfaces. the one of interest in this situation is DatabaseService.java. I then have a Second bundle called systemx-database-service. That implements the database service interface. this works fine as in the activator of the implementation bundle i test the connection to the database and select some arbitraty values. I also register the service i want to be available to the other bundle's like so: context.registerService(DatabaseService.class.getName(), new SystemDatabaseServiceImpl(context), new Properties()); The basic idea being when you look for a service reference for a Database service you'll get back the SystemDatabaseService implementation. When i do a inspect service the output it this: -> inspect s c 69 System Database Service (69) provides services: ---------------------------------------------- objectClass = za.co.xxx.xxx.common.api.DatabaseService service.id = 39 which would lead me to believe that if i do this in a test bundle: context.getService(context.getServiceReference(DatabaseService.class)); i should get back an instance of DatabaseService.class, but alas no such luck. it simply seems like it cannot find the service. stick with me here my story gets stranger. figuring there is no where to go but up i wrote this monstrosity: for (Bundle bundle : bundles) { if (bundle.getSymbolicName().equals("za.co.xxx.xxx.database-service")) { ServiceReference[] registeredServices = bundle.getRegisteredServices(); for (ServiceReference ref : registeredServices) { DatabaseService service = (DatabaseService) context.getService(ref); // use service here. } } } } now i can actually see the service reference, but i get this error java.lang.ClassCastException: za.co.xxx.xxx.database.service.impl.SystemDatabaseServiceImpl cannot be cast to za.co.xxx.xx.common.api.DatabaseService which is crazy since the implementation clearly implements the interface! Any help would be appreciated. Please keep in mind i'm very new at the osgi way of thinking so my whole approach here might be flawed. oh. if anyone wants the manifests i can post them. and i'm using the maven-bnd-plugin to build and executing on felix. thanks Nico

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• Gathering Staff anyone interested?

  - by kasene

  Thread Title - Gathering Staff Rush-Soft Game Design is currently looking for staff of a moderate skill level. Team Name - RushSoft Game Design Project Name - N/A We are gathering staff so that we can begin working on a new game. Target Aim - Freeware / Free Version - Paid Version With our first project our aim is to simply get our name out there. Generally we will be targeting a freeware distribution platform or a Free and Paid version. Compensation - Prehaps in the future but don't rely on it If in the future we start developing a game we intend to make any sort of sizable profit from then yes, there will be compensation however currently our low, low funding comes from generous donations. Any money that we make for now will go to the teams funding for things like engine licenses and company registration. Technology - C/C++ RSETech Our primary functional language will be C/C++ as most games are. We will be using a custom built library built on Direct3D called RSETech or RushSoft Engine Technology. Currently its is fully capable of being used for developing a game. The final version is made up of almost entirely C (No C++ or OOP). There is a C++ version currently in the works. Programming: - Microsoft Visual C++ 2008 / 2010 2D Art - Photoshop CS2 - GIMP Talent Needed - We currently are in need of x2 Programmers - With understanding of the following C/C ++ and game programming aspects: -If/Else Conditions -Functions/Methods -Arrays -Pointers (You don't need to fully understand these. Just know when they need to be used.) -Enums -Loops (For and While) -Structs (and How to use . and - syntax) -Classes (and how to call methods and access variables from a class) -State Machines -Switches -Include Guards -Understanding of how game loops work in general. (Init, Update, Render, Deinit) x2 Artists - As long as you have the means to and are able to draw 2D sprites and collab with a game designer to get a good result. 1 or more Game Designers - You can design levels (for platformers) as well as write game scripts and you can come up with good ideas and game mechanics. As long as you can do these things and are able to work well with artists and programmers you're golden. Business Consultant - Someone who knows the industry and how it works. Will inquire about possible distribution platforms as well as contact other developers, websites, and publishers on RushSofts behalf. Team Structure - Kasene Clark - Co-Founder/Lead Programmer/Game Designer Casey W - Co-Founder/Artist(GC/Animation)/Game Designer Nathan Mayworm - Game Designer. Website - RushSoft Websitek Contact - Kasene Clark [email protected] - [email protected] Phone - 12075181967 Feedback - Any Thank You! -Kasene

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• ANSI C blackjack assignment, linux GCC compiler, i'm stuck...

  - by Bill Adams

  Here's what i have so far... I have yet to figure out how i'm going to handle the 11 / 1 situation with an ace, and when the player chooses an option for hit/stand, i get segfault. HELP!!! #include <stdio.h> #include <string.h> #include <stdlib.h> #include <time.h> #define DECKSIZE 52 #define VALUE 9 #define FACE 4 #define HANDSIZE 26 typedef struct { int value; char* suit; char* name; }Card; typedef struct { int value; char* suit; char* name; }dealerHand; typedef struct { int value; char* suit; char* name; }playerHand; Card cards[DECKSIZE]; dealerHand deal[HANDSIZE]; playerHand dealt[HANDSIZE]; char *faceName[]={"two","three", "four","five","six", "seven","eight","nine", "ten", "jack","queen", "king","ace"}; char *suitName[]={"spades","diamonds","clubs","hearts"}; void printDeck(){ int i; for(i=0;i<DECKSIZE;i++){ printf("%s of %s value = %d\n ",cards[i].name,cards[i].suit,cards[i].value); if((i+1)%13==0 && i!=0) printf("-------------------\n\n"); } } void shuffleDeck(){ srand(time(NULL)); int this; int that; Card temp; int c; for(c=0;c<10000;c++){ //c is the index for number of individual card shuffles should be set to c<10000 or more this=rand()%DECKSIZE; that=rand()%DECKSIZE; temp=cards[this]; cards[this]=cards[that]; cards[that]=temp; } } /*void hitStand(i,y){ // I dumped this because of a segfault i couldn't figure out. int k; printf(" Press 1 to HIT or press 2 to STAND:"); scanf("%d",k); if(k=1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } } */ int main(){ int suitCount=0; int faceCount=0; int i; int x; int y; int d; int p; int k; for(i=0;i<DECKSIZE;i++){ //this for statement builds the deck if(faceCount<9){ cards[i].value=faceCount+2; }else{ //assigns face cards as value 10 cards[i].value=10; } cards[i].suit=suitName[suitCount]; cards[i].name=faceName[faceCount++]; if(faceCount==13){ //this if loop increments suit count once cards[i].value=11; //all faces have been assigned, and also suitCount++; //assigns the ace as 11 faceCount=0; } //end building deck } /*printDeck(); //prints the deck in order shuffleDeck(); //shuffles the deck printDeck(); //prints the deck as shuffled This was used in testing, commented out to keep the deck hidden!*/ shuffleDeck(); x=0; y=0; for(i=0;i<4;i++){ //this for loop deals the first 4 cards, dealt[y].suit=cards[i].suit; //first card to player, second to dealer, dealt[y].name=cards[i].name; //as per standard dealing practice. dealt[y].value=cards[i].value; i++; y++; deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; } printf(" Dealer's hand is: %s of %s and XXXX of XXXX. (Second card is hidden!)\n",deal[0].name,deal[0].suit,deal[1].name,deal[1].suit); printf(" Player's hand is: %s of %s and %s of %s.\n",dealt[0].name,dealt[0].suit,dealt[1].name,dealt[1].suit); printf(" the current value of the index i=%d\n",i); //this line gave me the value of i for testing d=deal[0].value+deal[1].value; p=dealt[0].value+dealt[1].value; if(d==21){ printf(" The Dealer has Blackjack! House win!\n"); }else{ if(d>21){ printf(" The dealer is Bust! You win!\n"); }else{ if(d>17){ printf(" Press 1 to HIT or 2 to STAND"); scanf("%d",k); if(k==1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } }else{ if(d<17){ printf(" Dealer Hits!"); deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; i++; } } } } return 0; }

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• Data access pattern, combining push and pull?

  - by andlju

  I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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• Scala actors: receive vs react

  - by jqno

  Let me first say that I have quite a lot of Java experience, but have only recently become interested in functional languages. Recently I've started looking at Scala, which seems like a very nice language. However, I've been reading about Scala's Actor framework in Programming in Scala, and there's one thing I don't understand. In chapter 30.4 it says that using react instead of receive makes it possible to re-use threads, which is good for performance, since threads are expensive in the JVM. Does this mean that, as long as I remember to call react instead of receive, I can start as many Actors as I like? Before discovering Scala, I've been playing with Erlang, and the author of Programming Erlang boasts about spawning over 200,000 processes without breaking a sweat. I'd hate to do that with Java threads. What kind of limits am I looking at in Scala as compared to Erlang (and Java)? Also, how does this thread re-use work in Scala? Let's assume, for simplicity, that I have only one thread. Will all the actors that I start run sequentially in this thread, or will some sort of task-switching take place? For example, if I start two actors that ping-pong messages to each other, will I risk deadlock if they're started in the same thread? According to Programming in Scala, writing actors to use react is more difficult than with receive. This sounds plausible, since react doesn't return. However, the book goes on to show how you can put a react inside a loop using Actor.loop. As a result, you get loop { react { ... } } which, to me, seems pretty similar to while (true) { receive { ... } } which is used earlier in the book. Still, the book says that "in practice, programs will need at least a few receive's". So what am I missing here? What can receive do that react cannot, besides return? And why do I care? Finally, coming to the core of what I don't understand: the book keeps mentioning how using react makes it possible to discard the call stack to re-use the thread. How does that work? Why is it necessary to discard the call stack? And why can the call stack be discarded when a function terminates by throwing an exception (react), but not when it terminates by returning (receive)? I have the impression that Programming in Scala has been glossing over some of the key issues here, which is a shame, because otherwise it's a truly excellent book.

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• Javascript code inside updatepanel usercontrol.

  - by Ed Woodcock

  Ok: I've got an updatepanel on an aspx page that contains a single Placeholder. Inside this placeholder I'm appending one of a selection of usercontrols depending on certain external conditions (this is a configuration page). In each of these usercontrols there is a bindUcEvents() javascript function that binds the various jQuery and javascript events to buttons and validators inside the usercontrol. The issue I'm having is that the usercontrol's javascript is not being recognised. Normally, javascript inside an updatepanel is executed when the updatepanel posts back, however none of this code can be found by the page (I've tried running the function manually via firebug's console, but it tells me it cannot find the function). Does anyone have any suggestions? Cheers, Ed. EDIT: cut down (but functional) example: Markup: <script src="/js/jquery-1.3.2.min.js"></script> <form id="form1" runat="server"> <div> <asp:ScriptManager ID="Script" runat="server" /> <asp:Button ID="Postback" runat="server" Text="Populate" OnClick="PopulatePlaceholder" /> <asp:UpdatePanel ID="UpdateMe" runat="server"> <Triggers> <asp:AsyncPostBackTrigger ControlID="Postback" EventName="Click" /> </Triggers> <ContentTemplate> <asp:Literal ID="Code" runat="server" /> <asp:PlaceHolder ID="PlaceMe" runat="server" /> </ContentTemplate> </asp:UpdatePanel> </div> </form> C#: protected void PopulatePlaceholder(object sender, EventArgs e) { Button button = new Button(); button.ID = "Push"; button.Text = "push"; button.OnClientClick = "javascript:return false;"; Code.Text = "<script type=\"text/javascript\"> function bindEvents() { $('#" + button.ClientID + "').click(function() { alert('hello'); }); } bindEvents(); </script>"; PlaceMe.Controls.Add(button); }

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