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  • Thread-safe data structure design

    - by Inso Reiges
    Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of "exists" call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? EDIT: I have a better example. Suppose that element retrieval returns either a reference or a pointer to the stored element and not it's copy. How can a caller be protected to safely use this pointer\reference after the call returns? If you think that not returning copies is a problem, then think about deep copies, i.e. objects that should also copy another objects they point to internally. Thank you.

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  • Multiple websites, Single sign-on design

    - by Yannis
    Hi all, I have a question. A client I have been doing some work recently has a range of websites with different login mechanisms. He is looking to slowly migrate to a single sign-on mechanism for his websites (all written in asp.net mvc). I am looking at my options here, so here is a list of requirements: 1) It has to be secure (duh) 2) It needs to support extra user properties over and above the usual name, address stuff (such as money or credits for a user) 3) It has to provide a centralized user management web console for his convenience (I understand that this will be a small project on top of whatever design solution I choose to go for) 4) It has to integrate with the existing websites without re-engineering the whole product (I understand that this depends on the current product implementation). 5) It has to deal with emailing the user when he registers (in order for him to activate his account) 6) It has to deal with activating the user when he clicks the activate me link in the email (I understand that 5 and 6 require some form of email templating system to support different emails per application) I was thinking of creating a library working together with forms authentication that exposes whatever methods are required (e.g. login, logout, activate, etc. and a small restful service to implement activation from email, registration processing etc. Taking into account that loads of things have been left out to make this question brief and to the point, does this sound like a good design? But this looks like a very common problem so arent there any existing projects that I could use? Thanks for reading.

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  • MUD (game) design concept question about timed events.

    - by mudder
    I'm trying my hand at building a MUD (multiplayer interactive-fiction game) I'm in the design/conceptualizing phase and I've run into a problem that I can't come up with a solution for. I'm hoping some more experienced programmers will have some advice. Here's the problem as best I can explain it. When the player decides to perform an action he sends a command to the server. the server then processes the command, determines whether or not the action can be performed, and either does it or responds with a reason as to why it could not be done. One reason that an action might fail is that the player is busy doing something else. For instance, if a player is mid-fight and has just swung a massive broadsword, it might take 3 seconds before he can repeat this action. If the player attempts to swing again to soon, the game will respond indicating that he must wait x seconds before doing that. Now, this I can probably design without much trouble. The problem I'm having is how I can replicate this behavior from AI creatures. All of the events that are being performed by the server ON ITS OWN, aka not as an immediate reaction to something a player has done, will have to be time sensitive. Some evil monster has cast a spell on you but must wait 30 seconds before doing it again... I think I'll probably be adding all these events to some kind of event queue, but how can I make that event queue time sensitive?

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  • Framework or design pattern for mailing all users of a webapp

    - by Todd Owen
    My app takes care of user registration (with the option to receive email announcements), and can easily handle the actual template-based rendering of email for a given user. JavaMail provides the mail transport layer. But how should I design the application layer between the business objects (e.g. User) and the mail transport? The straightforward approach would be a simple, synchronous loop: iterate through the users, queue the emails, and be done with it. "Queue" might mean sending them straight to the MTA (mail server), or to an in-memory queue to be consumed by another thread. However, I also plan to implement features like throttling the rate of emails, processing bounced emails (NDRs), and maintaining status across application restarts. My intuition is that a good design would decouple this from both the business layer and the mail transport layer as much as possible. I wondered if others had solved this problem before, but after much searching I haven't found any Java libraries which seem to fit this problem. Standalone mail apps such as James or list servers are too large in scope; packages like Spring's MailSender or Commons Email are too small in scope (being basically drop-in replacements for JavaMail). For other languages I haven't found anything appropriate either. I'm curious about how other developers have gone about adding bulk mailing to their applications.

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  • Complex SQL design, help/advice needed

    - by eugeneK
    Hi, i have few questions for SQL gurus in here ... Briefly this is ads management system where user can define campaigns for different countries, categories, languages. I have few questions in mind so help me with what you can. Generally i'm using ASP.NET and i want to cache all result set of certain user once he asks for statistics for the first time, this way i will avoid large round-trips to server. any help is welcomed Click here for diagram with all details you need for my questions 1.Main issue of this application is to show to the user how many clicks/impressions were and how much money he spent on campaign. What is the easiest way to get this information for him? I will also include filtering by date, date ranges and few other params in this statistics table. 2.Other issue is what happens when user will try to edit campaign. Old campaign will die this means if user set 0.01$ as campaignPPU (pay-per-unit) and next day updates it to 0.05$ all will be reset to 0.05$. 3.If you could re-design some parts of table design so it would be more flexible and easier to modify, how would you do it? Thanks... sorry for so large job but it may interest some SQL guys in here

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  • OOP design issue: Polymorphism

    - by Graham Phillips
    I'm trying to solve a design issue using inheritance based polymorphism and dynamic binding. I have an abstract superclass and two subclasses. The superclass contains common behaviour. SubClassA and SubClassB define some different methods: SubClassA defines a method performTransform(), but SubClassB does not. So the following example 1 var v:SuperClass; 2 var b:SubClassB = new SubClassB(); 3 v = b; 4 v.performTransform(); would cause a compile error on line 4 as performTransform() is not defined in the superclass. We can get it to compile by casting... (v as SubClassA).performTransform(); however, this will cause a runtime exception to be thrown as v is actually an instance of SubClassB, which also does not define performTransform() So we can get around that by testing the type of an object before casting it: if( typeof v == SubClassA) { (cast v to SubClassA).performTransform(); } That will ensure that we only call performTransform() on v's that are instances of SubClassA. That's a pretty inelegant solution to my eyes, but at least its safe. I have used interface based polymorphism (interface meaning a type that can't be instantiated and defines the API of classes that implement it) in the past, but that also feels clunky. For the above case, if SubClassA and SubClassB implemented ISuperClass that defined performTransform, then they would both have to implement performTransform(). If SubClassB had no real need for a performTransform() you would have to implement an empty function. There must be a design pattern out there that addresses the issue.

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  • QTCreator 3.1 design tab not working

    - by user3112140
    I’m currently using QtCreator 3.1 and qt-everywhere-opensource-src-5.2.1 on Ubuntu 12.04 My project is correctly working, i.e., i can build it and run without any trouble. But i’ve got some problems with the design tab inside Qtcreator. First, on all qml file (even with example projects), i have an error message “Using Qt Quick code model instead of Qt Quick2 (M324) (4:1)” and i can’t use the design editor. Second, on qml files with other import than QtQuick 2.2 (for me QtQml.Models 2.1 and QtQuick.Controls 1.1), the import is underlined in red with the error message “QML module not found”. I’ve tried to edit the .pro file by adding QML2_IMPORT_PATH=/home/user/qt-everywhere-opensource-src-5.2.1/qtquickcontrols/qml/QtQuick/Controls/ (also tried with QML_IMPORT_PATH), it doesn’t work. Then, I tried to add it to my path in a terminal using “export QML_IMPORT_PATH=/home/user/qt-everywhere-opensource-src-5.2.1/qtquickcontrols/qml/QtQuick/Controls/” and this time, in the error message, i can see the added path in the error message, but it still doesn’t work. Anyone has an idea to help me ? Thx !

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  • Complicated .NET factory design

    - by Tom W
    Hello SO; I'm planning to ask a fairly elaborate question that is also something of a musing here, so bear with me... I'm trying to design a factory implementation for a simulation application. The simulation will consist of different sorts of entities i.e. it is not a homogenous simulation in any respect. As a result, there will be numerous very different concrete implementations and only the very general properties will be abstracted at the top level. What I'd like to be able to do is create new simulation entities by calling a method on the model with a series of named arguments representing the parameters of the entity, and have the model infer what type of object is being described by the inbound parameters (from the names of the parameters and potentially the sequence they occur in) and call a factory method on the appropriate derived class. For example, if I pass the model a pair of parameters (Param1=5000, Param2="Bacon") I would like it to infer that the names Param1 and Param2 'belong' to the class "Blob1" and call a shared function "getBlob1" with named parameters Param1:=5000, Param2:="Bacon" whereas if I pass the model (Param1=5000, Param3=50) it would call a similar factory method for Blob2; because Param1 and Param3 in that order 'belong' to Blob2. I foresee several issues to resolve: Whether or not I can reflect on the available types with string parameter names and how to do this if it's possible Whether or not there's a neat way of doing the appropriate constructor inference from the combinatoric properties of the argument list or whether I'm going to have to bodge something to do it 'by hand'. If possible I'd like the model class to be able to accept parameters as parameters rather than as some collection of keys and values, which would require the model to expose a large number of parametrised methods at runtime without me having to code them explicitly - presumably one for every factory method available in the relevant namespace. What I'm really asking is how you'd go about implementing such a system, rather than whether or not it's fundamentally possible. I don't have the foresight or experience with .NET reflection to be able to figure out a way by myself. Hopefully this will prove an informative discussion.

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  • Problem accessing private variables in jQuery like chainable design pattern

    - by novogeek
    Hi folks, I'm trying to create my custom toolbox which imitates jQuery's design pattern. Basically, the idea is somewhat derived from this post: http://stackoverflow.com/questions/2061501/jquery-plugin-design-pattern-common-practice-for-dealing-with-private-function (Check the answer given by "David"). So here is my toolbox function: (function(window){ var mySpace=function(){ return new PrivateSpace(); } var PrivateSpace=function(){ var testCache={}; }; PrivateSpace.prototype={ init:function(){ console.log('init this:', this); return this; }, ajax:function(){ console.log('make ajax calls here'); return this; }, cache:function(key,selector){ console.log('cache selectors here'); testCache[key]=selector; console.log('cached selector: ',testCache); return this; } } window.hmis=window.m$=mySpace(); })(window) Now, if I execute this function like: console.log(m$.cache('firstname','#FirstNameTextbox')); I get an error 'testCache' is not defined. I'm not able to access the variable "testCache" inside my cache function of the prototype. How should I access it? Basically, what I want to do is, I want to cache all my jQuery selectors into an object and use this object in the future.

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  • How to Load In Content with jQuery?

    - by ClarkSKent
    Hello, I am trying to add ajax functionality to my pagination so the content loads in the same page instead of the user having to navigate to another page when clicking the page links. I should mention that I am using this php pagination class. Being new to jquery, I am unsure of how to properly do this with the pagination class. This is what the main page looks like: <?php $categoryId=$_GET['category']; echo $categoryId; ?> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.1/jquery.min.js"></script> <script type="text/javascript" src="jquery_page.js"></script> <?php //Include the PS_Pagination class include('ps_pagination.php'); //Connect to mysql db $conn = mysql_connect('localhost', 'root', 'root'); mysql_select_db('ajax_demo',$conn); $sql = "select * from explore where category='$categoryId'"; //Create a PS_Pagination object $pager = new PS_Pagination($conn, $sql, 3, 11, 'param1=value1&param2=value2'); //The paginate() function returns a mysql //result set for the current page $rs = $pager->paginate(); //Loop through the result set echo "<table width='800px'>"; while($row = mysql_fetch_assoc($rs)) { echo "<tr>"; echo"<td>"; echo $row['id']; echo"</td>"; echo"<td>"; echo $row['site_description']; echo"</td>"; echo"<td>"; echo $row['site_price']; echo"</td>"; echo "</tr>"; } echo "</table>"; echo "<ul id='pagination'>"; echo "<li>"; //Display the navigation echo $pager->renderFullNav(); echo "</li>"; echo "</ul>"; ?> <div id="loading" ></div> <div id="content" ></div> <a href="#" class="category" id="marketing">Marketing</a> <a href="#" class="category" id="automotive">Automotive</a> <a href="#" class="category" id="sports">Sports</a> Any help on this would be great. Thanks.

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  • the possible solution to this design issue??

    - by Sachindra
    I need to know how to fix this issue in the designs of forms.. Getting this in firefox and this in IE... the color is not an issue.. juz need the alignment to be fixed... The code goes like this : <div class="content_form_box7_main"> <div class="content_form_box7_main1"> <input type="text" name="email" value="Comments" class="content_form_box7_inside"/> </div> </div> the style goes like : .content_form_box7_main{ float:left; color:#FFFFFF; padding:5px 0px 2px 0px; width:281px; } .content_form_box7_main1{ float:left; padding:0px 0px 0px 40px; } .content_form_box7_inside{ float:left; background-image:url(images/amcro_contact4.gif); width:206px; height:43px; background-repeat:no-repeat; border:none; background-color:#E0D1B4; vertical-align:top; } apologies if it looks complex ...

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  • SQL Table design question

    - by Projapati
    Please ignore this question if it sounds stupid to you. I have SQL table (SQL Server) for photo albums and it has 20+ columns & it will hold millions of albums. I need to designate some albums as Promoted and some as Featured every week. I also need a very efficient way to get these albums (page by page) when I show it to users. How should I design this? option 1: I can create another table just to store the ids of the promoted and featured albums like this and then join the main albums table to get the set of columns I need. table designated_albums: album_id promoted_featured 1 1 5 0 7 1 15 0 The query for promoted will return 1, 7 The query for featured will return 5, 15 Option 2: I can add 1 column store 1 if promoted and 0 if featured. Otherwise it is null I can then query to check for 1 in that column for promoted albums & 0 for featured. Option 3: I can add 2 bit columns: one for promoted (0/1) and one for featured(0/1) Which way would perform better? EDIT: The design should be efficient in SQL 2008 as well. Right now I have SQL 2005.

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  • XML Schema for a .NET type that inherits and implements

    - by John Ruiz
    Hi, Please consider the following three .NET types: I have an interface, an abstract class, and a concrete class. My question is how to write the XML Schema to include the properties from the interface and from the abstract class. public interface IStartable { bool RequiresKey { get; set; } void Start(object key); } public abstract class Vehicle { uint WheelCount { get; set; } } public class Car : Vehicle, IStartable { public bool RequiresKey { get; set; } public string Make { get; set; } publilc string Model { get; set; } public Car() {} public void Start(object key) { // start car with key } } I don't know how to complete this schema: <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="cars" xmlns="cars" xmlns:c="cars"> <!-- How do I get car to have vehicle's wheelcount AND IStartable's RequiresKey? --> <xs:element name="Car" type="c:Car" /> <xs:complexType name="Car"> <xs:complexContent> <xs:extension base="c:Vehicle"> <xs:group ref=c:CarGroup" /> </xs:extension> </xs:complexContent> </xs:complexType> <xs:group name="CarGroup"> <xs:sequence> <xs:element name="Make" type="xs:token" /> <xs:element name="Model" type="xs:token" /> </xs:sequence> </xs:group> <xs:complexType name="Vehicle"> <xs:sequence> <xs:element name="WheelCount" type="xs:unsignedInt" /> </xs:sequence> </xs:complexType> <xs:complexType name="IStartable"> <xs:sequence> <xs:element name="RequiresKey" type="xs:boolean" /> </xs:sequence> </xs:complexType> </xs:schema>

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  • Good infrastructure design questions for software developers?

    - by JakeRobinson
    Building on Jeff's blog post titled Vampires (Programmers) versus Werewolves (Sysadmins) From my perspective, the whole point of the company is to talk about what we're doing. Getting things done is important, of course, but we have to stop occasionally to write up what we're doing, how we're doing it, and why we're even doing it in the first place -- including all our doubts and misgivings and concerns. So, what are some questions you ask your software developers when they request a server?

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  • Domino Document data compression and design compression

    - by pipalia
    I was thinking of turning this on some large databases not just mail files - we have around 8 - 10GB of large databases as well as small databases of couple of hundred MB in size. But after reading this post I am not too sure: http://www-10.lotus.com/ldd/nd85forum.nsf/4b9931b774db788c85256bf0006b5e6d/1f4e67b569720e54852576c0003cb8ac?OpenDocument Can anyone confirm whether this is true? Are these any ill effects on performance by turning this feature on and if so what's the difference in performance? Thanks.

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  • Which laptop should I get for web design / development

    - by Mikey1010
    Hi, I require to buy a laptop, but I'm clueless really-need a laptop that will run the usual software for web work-photoshop,fireworks,dreamweaver,flash etc but also run php and .net, maybe most programs open at same time. My budget is between £400-£600 ($600-$900) please provide links if possible! Any help is very much appreciated.

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  • Which laptop should I get for web design / development

    - by Mikey1010
    Hi, I require to buy a laptop, but I'm clueless really-need a laptop that will run the usual software for web work-photoshop,fireworks,dreamweaver,flash etc but also run php and .net, maybe most programs open at same time. My budget is between £400-£600 ($600-$900) please provide links if possible! Any help is very much appreciated.

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  • Tomcat - Spring Framework - MySQL, Load balancing design

    - by Mat Banik
    Lets say I have Spring Framework App that is running on Tomcat and uses MySQL database: What would be the best solution in this instance that would allow for sociability (price/performance/integration time)? More precisely: What would be on the Web Load balancer box, and who should be the tomcat web server clustered? What would be on the Database Load balancer box and how should be the database servers clustered? And if at all possible specific technical integration links would be of great help.

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  • Better way to design a database

    - by cMinor
    I have a conceptual problem and I would like to get your ideas on how I'll be able to do what I am aiming. My goal is to create a database with information of persons who work at a place depending on their profession and skills,and keep control of salary and projects (how much would cost summing all the hours of work) I have 3 categories which can have subcategories: Outsourcing Technician welder turner assistant Administrative supervisor manager So each person has its information and the projects they are working on, also one person may do several jobs... I was thinking about having 5 tables (EMPLOYEE, SKILLS, PROYECTS, SALARY, PROFESSION) but I guess there is a better way of doing this. create table Employee ( PRIMARY KEY [Person_ID] int(10), [Name] varchar(30), [sex] varchar(10), [address] varchar(10), [profession] varchar(10), [Skills_ID] int(10), [Proyect_ID] int(10), [Salary_ID] int(10), [Salary] float ) create table Skills ( PRIMARY KEY [Skills_ID] int(10), FOREIGN KEY [Skills_name] varchar(10) REFERENCES Employee(Person_ID), [Skills_pay] float(10), [Comments] varchar(50) ) create table Proyects ( PRIMARY KEY [Proyect_ID] int(10), FOREIGN KEY [Skills_name] varchar(10) REFERENCES Employee(Person_ID) [Proyect_name] varchar(10), [working_Hours] float(10), [Comments] varchar(50) ) create table Salary ( PRIMARY KEY [Salary_ID] int(10), FOREIGN KEY [Skills_name] varchar(10) REFERENCES Employee(Person_ID) [Proyect_name] varchar(10), [working_Hours] float(10), [Comments] varchar(50) ) So to get the total amount of the cost of a project I would just sum the working hours of each employee envolved and sum some extra costs in an aggregate query. Is there a way to do this in a more efficient way? What to add or delete of this small model? I guess I am missing something in the salary - maybe I need another table for that?

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  • Flexible virtualization infrastructure Design with libvirt

    - by Lessfoe
    I'm going to install a CentOS6 Server with Virtualization ( libvirtd ) capabilities on a DELL Server with Hardware RAID5 of around 6T of disk space ( It has 4x2T disks in a PERC700 RAID Controller ). I'm going then to install some guests which requires few resources except one that needs 500GB of disk space, 8/16GB of RAM and good performances. I was thinking about file images for guests storage but I'm not sure about the 500GB VM what needs good performances so that an LVM device could be better. So my question is what would be the best layout concerning: RAID setup ( RAID5, RAID1 + 1 disk for OS only. ) disk partitioning ( using the entire disk/ leave free space for future use and extending it with LVM ) guests storage management ( LVM devices or file images ( considering the 500GB VM that is performance demanding ) or mixed ) Where to put guests storage? /var/lib/libvirt/images or maybe in a custom dir separated from system /home/VMs Thanks in advance for any hint.

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  • how to design pound -> varnish -> jboss for ha + loadbalancing

    - by andreash
    Hello, I'm planning a new infrastructure for our web application. We have two JBossAS5 servers, running in a cluster. Session state will be replicated via JBoss Cache. In front of that, there should be some cache, to speed up delivery of static elements. However, most of the traffic to our app will be via HTTPS. So far, I had been thinking of two Varnish caches in front of the JBossASs, each being configured for loadbalancing to the two JBossASs via round-robin. Since Varnish doesn't handle HTTPS, then there would need to be two pound proxies in front of the Varnishs, dealing with the HTTPS. The two pounds would be made high-available with Heartbeat/LinuxHA. The traffic to www.example.com would then be going through our firewall, from there to the virtual IP of the pounds, from there to the Varnishs, and from there to the JBossASs. Question 1: Does this make sense? Or is it overly complicated, and the same goal can be reached with simpler methods? Question 2: If my layout is fine, how do I configure the pound - Varnish step? Should I a) make the Varnish service high-available through Heartbeat/LinuxHA as well and direct traffic from pound to the virtual IP of the Varnishs, or should I rather b) Configure two independent Varnishs and use load-balancing in pound to address the different Varnishs? Thanks a lot for your insight! Andreas.

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  • Throughput; capacity planning help for C10K like design

    - by z8000
    I am designing a network service in which clients connect and stay connected -- the model is not far off from IRC less the s2s connections. I could use some help understanding how to do capacity planning, in particular with the system resource costs associated with handling messages from/to clients. There's an article that tried to get 1 million clients connected to the same server [1]. Of course, most of these clients were completely idle in the test. If the clients sent a message every 5 seconds or so the system would surely be brought to its knees. But... How do you do less hand-waving and you know, measure such a breaking point? We're talking about messages being sent by a client over a TCP socket, into the kernel, and read by an application. The data is shuffled around in memory from one buffer to another. Do I need to consider memory throughput ("5 GT/s" [2], etc.)? I'm pretty sure I have the ability to measure the basic memory requirements due to TCP/IP buffers, expected bandwidth, and CPU resources required to process messages. I'm a little dim on what I'm calling "thoughput". Help! Also, does anyone really do this? Or, do most people sort of hand-wave and see what the real world offers, and then react appropriately? [1] http://www.metabrew.com/article/a-million-user-comet-application-with-mochiweb-part-3/ [2] http://en.wikipedia.org/wiki/GT/s

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  • [MacOS] Visio-like design software?

    - by OverTheRainbow
    Hello It's a software-related question but not development-related :-/ A friend of mine is looking for an equivalent on Macintosh to Visio or SmarDraw to draw plans for home improvements. I don't know anything about Macintosh, so would appreciate any feedback on good softwares for this type of applications. Thank you.

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