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• kick off a map reduce job from my java/mysql webapp

  - by Brian

  Hi guys, I need a bit of archecture advice. I have a java based webapp, with a JPA based ORM backed onto a mysql relational database. Now, as part of the application I have a batch job that compares thousands of database records with each other. This job has become too time consuming and needs to be parallelized. I'm looking at using mapreduce and hadoop in order to do this. However, I'm not too sure about how to integrate this into my current architecture. I think the easiest initial solution is to find a way to push data from mysql into hadoop jobs. I have done some initial research on this and found the following relevant information and possibilities: 1) https://issues.apache.org/jira/browse/HADOOP-2536 this gives an interesting overview of some inbuilt JDBC support 2) This article http://architects.dzone.com/articles/tools-moving-sql-database describes some third party tools to move data from mysql to hadoop. To be honest I'm just starting out with learning about hbase and hadoop but I really don't know how to integrate this into my webapp. Any advice is greatly appreciated. cheers, Brian

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• System.InvalidOperationException in Output Window

  - by user318068

  I constantly get the following message in my output/debug windows. The app doesn't crash but I was wondering what the deal with it is: A first chance exception of type 'System.InvalidOperationException' occurred in System.dll my code :sol.cs using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ConsoleApplication1 { class Sol { public LinkedList<int> tower1 = new LinkedList<int>(); public LinkedList<int> tower2 = new LinkedList<int>(); public LinkedList<int> tower3 = new LinkedList<int>(); public static LinkedList<string> BFS = new LinkedList<string>(); public static LinkedList<string> DFS = new LinkedList<string>(); public static LinkedList<string> IDS = new LinkedList<string>(); public int depth; public LinkedList<Sol> neighbors; public Sol() { } public Sol(LinkedList<int> tower1, LinkedList<int> tower2, LinkedList<int> tower3) { this.tower1 = tower1; this.tower2 = tower2; this.tower3 = tower3; neighbors = new LinkedList<Sol>(); } public virtual void getneighbors() { Sol temp = this.copy(); Sol neighbor1 = this.copy(); Sol neighbor2 = this.copy(); Sol neighbor3 = this.copy(); Sol neighbor4 = this.copy(); Sol neighbor5 = this.copy(); Sol neighbor6 = this.copy(); if (temp.tower1.Count != 0) { if (neighbor1.tower2.Count != 0) { if (neighbor1.tower1.First.Value < neighbor1.tower2.First.Value) { neighbor1.tower2.AddFirst(neighbor1.tower1.First); neighbor1.tower1.RemoveFirst(); neighbors.AddLast(neighbor1); } } else { neighbor1.tower2.AddFirst(neighbor1.tower1.First); neighbor1.tower1.RemoveFirst(); neighbors.AddLast(neighbor1); } if (neighbor2.tower3.Count != 0) { if (neighbor2.tower1.First.Value < neighbor2.tower3.First.Value) { neighbor2.tower3.AddFirst(neighbor2.tower1.First); neighbor2.tower1.RemoveFirst(); neighbors.AddLast(neighbor2); } } else { neighbor2.tower3.AddFirst(neighbor2.tower1.First); neighbor2.tower1.RemoveFirst(); neighbors.AddLast(neighbor2); } } //------------- if (temp.tower2.Count != 0) { if (neighbor3.tower1.Count != 0) { if (neighbor3.tower2.First.Value < neighbor3.tower1.First.Value) { neighbor3.tower1.AddFirst(neighbor3.tower2.First); neighbor3.tower2.RemoveFirst(); neighbors.AddLast(neighbor3); } } else { neighbor3.tower1.AddFirst(neighbor3.tower2.First); neighbor3.tower2.RemoveFirst(); neighbors.AddLast(neighbor3); } if (neighbor4.tower3.Count != 0) { if (neighbor4.tower2.First.Value < neighbor4.tower3.First.Value) { neighbor4.tower3.AddFirst(neighbor4.tower2.First); neighbor4.tower2.RemoveFirst(); neighbors.AddLast(neighbor4); } } else { neighbor4.tower3.AddFirst(neighbor4.tower2.First); neighbor4.tower2.RemoveFirst(); neighbors.AddLast(neighbor4); } } //------------------------ if (temp.tower3.Count() != 0) { if (neighbor5.tower1.Count() != 0) { if (neighbor5.tower3.ElementAtOrDefault(0) < neighbor5.tower1.ElementAtOrDefault(0)) { neighbor5.tower1.AddFirst(neighbor5.tower3.First); neighbor5.tower3.RemoveFirst(); neighbors.AddLast(neighbor5); } } else { neighbor5.tower1.AddFirst(neighbor5.tower3.First); neighbor5.tower3.RemoveFirst(); neighbors.AddLast(neighbor5); } if (neighbor6.tower2.Count() != 0) { if (neighbor6.tower3.ElementAtOrDefault(0) < neighbor6.tower2.ElementAtOrDefault(0)) { neighbor6.tower2.AddFirst(neighbor6.tower3.First); neighbor6.tower3.RemoveFirst(); neighbors.AddLast(neighbor6); } } else { neighbor6.tower2.AddFirst(neighbor6.tower3.First); neighbor6.tower3.RemoveFirst(); neighbors.AddLast(neighbor6); } } } public override string ToString() { string str; str = "tower1" + tower1.ToString() + " tower2" + tower2.ToString() + " tower3" + tower3.ToString(); return str; } public Sol copy() { Sol So; LinkedList<int> l1 = new LinkedList<int>(); LinkedList<int> l2 = new LinkedList<int>(); LinkedList<int> l3 = new LinkedList<int>(); for (int i = 0; i <= this.tower1.Count() - 1; i++) { l1.AddLast(tower1.ElementAt(i)); } for (int i = 0; i <= this.tower2.Count - 1; i++) { l2.AddLast(tower2.ElementAt(i)); } for (int i = 0; i <= this.tower3.Count - 1; i++) { l3.AddLast(tower3.ElementAt(i)); } So = new Sol(l1, l2, l3); return So; } public bool Equals(Sol sol) { if (this.tower1.Equals(sol.tower1) & this.tower2.Equals(sol.tower2) & this.tower3.Equals(sol.tower3)) return true; return false; } public virtual bool containedin(Stack<Sol> vec) { bool found = false; for (int i = 0; i <= vec.Count - 1; i++) { if (vec.ElementAt(i).tower1.Equals(this.tower1) && vec.ElementAt(i).tower2.Equals(this.tower2) && vec.ElementAt(i).tower3.Equals(this.tower3)) { found = true; break; } } return found; } public virtual bool breadthFirst(Sol start, Sol goal) { Stack<Sol> nextStack = new Stack<Sol>(); Stack<Sol> traversed = new Stack<Sol>(); bool found = false; start.depth = 0; nextStack.Push(start); while (nextStack.Count != 0) { Sol sol = nextStack.Pop(); BFS.AddFirst("poped State:" + sol.ToString() + "level " + sol.depth); traversed.Push(sol); if (sol.Equals(goal)) { found = true; BFS.AddFirst("Goal:" + sol.ToString()); break; } else { sol.getneighbors(); foreach (Sol neighbor in sol.neighbors) { if (!neighbor.containedin(traversed) && !neighbor.containedin(nextStack)) { neighbor.depth = (sol.depth + 1); nextStack.Push(neighbor); } } } } return found; } public virtual bool depthFirst(Sol start, Sol goal) { Stack<Sol> nextStack = new Stack<Sol>(); Stack<Sol> traversed = new Stack<Sol>(); bool found = false; start.depth = 0; nextStack.Push(start); while (nextStack.Count != 0) { //Dequeue next State for comparison //And add it 2 list of traversed States Sol sol = nextStack.Pop(); DFS.AddFirst("poped State:" + sol.ToString() + "level " + sol.depth); traversed.Push(sol); if (sol.Equals(goal)) { found = true; DFS.AddFirst("Goal:" + sol.ToString()); break; } else { sol.getneighbors(); foreach (Sol neighbor in sol.neighbors) { if (!neighbor.containedin(traversed) && !neighbor.containedin(nextStack)) { neighbor.depth = sol.depth + 1; nextStack.Push(neighbor); } } } } return found; } public virtual bool iterativedeepening(Sol start, Sol goal) { bool found = false; for (int level = 0; ; level++) { Stack<Sol> nextStack = new Stack<Sol>(); Stack<Sol> traversed = new Stack<Sol>(); start.depth = 0; nextStack.Push(start); while (nextStack.Count != 0) { Sol sol = nextStack.Pop(); IDS.AddFirst("poped State:" + sol.ToString() + "Level" + sol.depth); traversed.Push(sol); if (sol.Equals(goal)) { found = true; IDS.AddFirst("Goal:" + sol.ToString()); break; } else if (sol.depth < level) { sol.getneighbors(); foreach (Sol neighbor in sol.neighbors) { if (!neighbor.containedin(traversed) && !neighbor.containedin(nextStack)) { neighbor.depth = sol.depth + 1; nextStack.Push(neighbor); } //end if } //end for each } //end else if } // end while if (found == true) break; } // end for return found; } } } Just wondering if I may be doing something wrong somewhere or something.

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• Django Threaded Commenting System

  - by Yasin Ozel

  (and sorry for my english) I am learning Python and Django. Now, my challange is developing threaded generic comment system. There is two models, Post and Comment. -Post can be commented. -Comment can be commented. (endless/threaded) -Should not be a n+1 query problem in system. (No matter how many comments, should not increase the number of queries) My current models are like this: class Post(models.Model): title = models.CharField(max_length=100) content = models.TextField() child = generic.GenericRelation( 'Comment', content_type_field='parent_content_type', object_id_field='parent_object_id' ) class Comment(models.Model): content = models.TextField() child = generic.GenericRelation( 'self', content_type_field='parent_content_type', object_id_field='parent_object_id' ) parent_content_type = models.ForeignKey(ContentType) parent_object_id = models.PositiveIntegerField() parent = generic.GenericForeignKey( "parent_content_type", "parent_object_id") Are my models right? And how can i get all comment (with hierarchy) of post, without n+1 query problem? Note: I know mttp and other modules but I want to learn this system. Edit: I run "Post.objects.all().prefetch_related("child").get(pk=1)" command and this gave me post and its child comment. But when I wanna get child command of child command a new query is running. I can change command to ...prefetch_related("child__child__child...")... then still a new query running for every depth of child-parent relationship. Is there anyone who has idea about resolve this problem?

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• Literal ampersands in System.Uri query string

  - by Nathan Baulch

  I'm working on a client app that uses a restful service to look up companies by name. It's important that I'm able to include literal ampersands in my queries since this character is quite common in company names. However whenever I pass %26 (the URI escaped ampersand character) to System.Uri, it converts it back to a regular ampersand character! On closer inspection, the only two characters that aren't converted back are hash (%23) and percent (%25). Lets say I want to search for a company named "Pierce & Pierce": var endPoint = "http://localhost/companies?where=Name eq '{0}'"; var name = "Pierce & Pierce"; Console.WriteLine(new Uri(string.Format(endPoint, name))); Console.WriteLine(new Uri(string.Format(endPoint, Uri.EscapeUriString(name)))); Console.WriteLine(new Uri(string.Format(endPoint, Uri.EscapeDataString(name)))); All three of the above combinations return: http://localhost/companies?where=Name eq 'Pierce & Pierce' This causes errors on the server side since the ampersand is (correctly) interpreted as a query arg delimiter. What I really need it to return is the original string: http://localhost/companies?where=Name eq 'Pierce %26 Pierce' How can I work around this behavior without discarding System.Uri entirely? I can't replace all ampersands with %26 at the last moment because there will usually be multiple query args involved and I don't want to destroy their delimiters. Note: A similar problem was discussed in this question but I'm specifically referring to System.Uri.

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• updating system's time using .Net

  - by user62958

  I am trying to update my system time using the following: [StructLayout(LayoutKind.Sequential)] private struct SYSTEMTIME { public ushort wYear; public ushort wMonth; public ushort wDayOfWeek; public ushort wDay; public ushort wHour; public ushort wMinute; public ushort wSecond; public ushort wMilliseconds; } [DllImport("kernel32.dll", EntryPoint = "GetSystemTime", SetLastError = true)] private extern static void Win32GetSystemTime(ref SYSTEMTIME lpSystemTime); [DllImport("kernel32.dll", EntryPoint = "SetSystemTime", SetLastError = true)] private extern static bool Win32SetSystemTime(ref SYSTEMTIME lpSystemTime); public void SetTime() { TimeSystem correctTime = new TimeSystem(); DateTime sysTime = correctTime.GetSystemTime(); // Call the native GetSystemTime method // with the defined structure. SYSTEMTIME systime = new SYSTEMTIME(); Win32GetSystemTime(ref systime); // Set the system clock ahead one hour. systime.wYear = (ushort)sysTime.Year; systime.wMonth = (ushort)sysTime.Month; systime.wDayOfWeek = (ushort)sysTime.DayOfWeek; systime.wDay = (ushort)sysTime.Day; systime.wHour = (ushort)sysTime.Hour; systime.wMinute = (ushort)sysTime.Minute; systime.wSecond = (ushort)sysTime.Second; systime.wMilliseconds = (ushort)sysTime.Millisecond; Win32SetSystemTime(ref systime); } When I debug everything looks good and all the values are correct but when it calles the Win32SetSystemTime(ref systime) th actual time of system(display time) doesn't change and stays the same. The strange part is that when I call the Win32GetSystemTime(ref systime) it gives me the new updated time. Can someone give me some help on this?

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• Suggestions on writing a TCP IP messaging system (Client/Server) using Delphi 2010

  - by Shane

  I would like to write a messaging system using TCP IP in Delphi 2010. I would like to hear what my best options are for using the standard delphi 2010 components/indy components for doing this. I would like to write a server which does the listening and forwarding of messages to all machines on the network running a client. 1.) a.) clients can send a message to server to be forwarded to all other clients b.) clients listen for messages from other senders (via server) and displays messages. 2.) a.) Server can send a message to all clients b.) Server forwards any messages from clients to all other clients thanks for any suggestions NOTE: I am not writing a instant messaging or chat program. This is merely a system where users can send alerts/messages to other users - they can not reply to each other! NO commercial, shareware, etc links - please! I would like to hear about how you would go about writing this type of system and what approachs you would take, and possibly the TCP IP messaging architecture you would use. Whether it be straight Winows API, Indy components, etc, etc.

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• Best way to implement plugin framework - are DLLs the only way (C/C++ project)?

  - by Microkernel

  Introduction: I am currently developing a document classifier software in C/C++ and I will be using Naive-Bayesian model for classification. But I wanted the users to use any algorithm that they want(or I want in the future), hence I went to separate the algorithm part in the architecture as a plugin that will be attached to the main app @ app start-up. Hence any user can write his own algorithm as a plugin and use it with my app. Problem Statement: The way I am intending to develop this is to have each of the algorithms that user wants to use to be made into a DLL file and put into a specific directory. And at the start, my app will search for all the DLLs in that directory and load them. My Questions: (1) What if a malicious code is made as a DLL (and that will have same functions mandated by plugin framework) and put into my plugins directory? In that case, my app will think that its a plugin and picks it and calls its functions, so the malicious code can easily bring down my entire app down (In the worst case could make my app as a malicious code launcher!!!). (2) Is using DLLs the only way available to implement plugin design pattern? (Not only for the fear of malicious plugin, but its a generic question out of curiosity :) ) (3) I think a lot of softwares are written with plugin model for extendability, if so, how do they defend against such attacks? (4) In general what do you think about my decision to use plugin model for extendability (do you think I should look at any other alternatives?) Thank you -MicroKernel :)

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• WPF C# Client/Server announcement system

  - by manemawanna

  I'm currently in the process of creating an announcement system at my place of work. The role of this system will be to replace all users email due to people misusing it and generally abusing the facility. The system will consist of: Web Portal: Will allow staff to enter any important announcements (this will be restricted via AD). SQL Server 2k5 DB: Will hold the announcements along with records of staff members and if they've read the announcements etc. Front End: Created in WPF & C# which is nearly complete, it will display the announcements to the users. Web Page: Client will contact every so often, which will return an xml file for the client to read. However my boss has now shifted the goal posts and would like the announcements to appear to the user once they are written to the database, rather than waiting on the client to contact the webpage. So now I'm a bit unsure as to how to go about this. I have one idea where I would create a small server application to monitor for new announcements then contact the clients to inform them to approach the website for the information they need. But I'm just looking to see if theres a better or more efficient way to do this or if someone else has a more appropriate idea or suggestion.

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• Magento - Add a button to system.xml with method attached to it

  - by vrnet

  Hi, I have created a module that has an "export like" method running regularly as defined in my module's cron area of the config.xml file. But I'd like to give the user the ability to run this export method on demand by adding a "Run now" button in the system configuration, thus using the system.xml file. It seems that the "frontend type" button may be working as I've tried and it adds a tiny clickable button in the config section. But I am not able to attach a method nor a label on the button itself. I thought about adding a button in the "Grid.php" file of the module but this not what I'd like to do as it does fit with my acl. Below is my system.xml file with the "button" frontend type. Does anyone have a clue on how to : add a label/value to the button add a class to the button add a method to call when the button is clicked Many thanks for your help ! <?xml version="1.0" encoding="UTF-8"?> <config> ... <fields> ... <run translate="label"> <label>Run now</label> <frontend_type>button</frontend_type> <backend_model>SOME BACKEND MODEL</backend_model> <sort_order>20</sort_order> <show_in_default>1</show_in_default> <show_in_website>1</show_in_website> <show_in_store>1</show_in_store> </run> </fields> ... </config>

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• mailing system DB structure, need help

  - by Anna

  i have a system there user(sender) can write a note to friends(receivers), number of receivers=0. Text of the message is saved in DB and visible to sender and all receivers then they login to system. Sender can add more receivers at any time. More over any of receivers can edit the message and even remove it from DB. For this system i created 3 tables, shortly: users(userID, username, password) messages(messageID, text) list(id, senderID, receiverID, messageID) in table "list" each row corresponds to pair sender-receiver, like sender_x_ID -- receiver_1_ID -- message_1_ID sender_x_ID -- receiver_2_ID -- message_1_ID sender_x_ID -- receiver_3_ID -- message_1_ID Now the problem is: 1. if user deletes the message from table "messages" how to automatically delete all rows from table "list" which correspond to deleted message. Do i have to include some foreign keys? More important: 2. if sender has let say 3 receivers for his message1 (username1, username2 and username3) and at certain moment decides to add username4 and username5 and at the same time exclude username1 from the list of receivers. PHP code will get the new list of receivers (username2, username3, username4, username5) That means insert to table "list" sender_x_ID -- receiver_4_ID -- message_1_ID sender_x_ID -- receiver_5_ID -- message_1_ID and also delete from table "list" the row corresponding to user1 (which is not in the list or receivers any more) sender_x_ID -- receiver_1_ID -- message_1_ID which sql query to send from PHP to make it in an easy and intelligent way? Please help! Examples of sql queries would be perfect!

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• what patern is layerd architechture in asp.net ?

  - by haansi

  Hi, I am a asp.net developer and don't know much about patterns and architecture. I will very thankful if you can please guide me here. In my web applications I use 4 layers. Web site project (having web forms + code behind cs files, user controls + code behind cs files, master pages + code behind cs files) CustomTypesLayer a class library (having custom types, enumerations, DTOs, constructers, get, set and validations) BusinessLogicLayer a class library (having all business logic, rules and all calls to DAL functions) DataAccessLayer a class library( having just classes communicating to database.) -My user interface just calls BusinessLogicLayer. BusinessLogicLayer do proecessign in it self and for data it calls DataAccessLayer funtions. -Web forms do not calls directly DAL. -CustomTypesLayer is shared by all layers. Please guide me is this approach a pattern ? I though it may be MVC or MVP but pages have there code behind files as well which are confusing me. If it is no patren is it near to some patren ? pleaes guide thanks

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• Memory mapping of files and system cache behavior in WinXP

  - by Canopus

  Our application is memory intensive and deals with reading a large number of disk files. The total load can be more than 3 GB. There is a custom memory manager that uses memory mapped files to achieve reading of such a huge data. The files are mapped into the process memory space only when needed and with this the process memory is well under control. But what is observed is, with memory mapping, the system cache keeps on increasing until it occupies the available physical memory. This leads to the slowing down of the entire system. My question is how to prevent system cache from hogging the physical memory? I attempted to remove the file buffering (by using FILE_FLAG_NO_BUFFERING ), but with this, the read operations take considerable amount of time and slows down the application performance. How to achieve the scalability without sacrificing much on performance. What are the common techniques used in such cases? I dont have a good understanding of the WinXP OS caching behavior. Any good links explaining the same would also be helpful.

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• Failed to create a 'System.Windows.RoutedEventHandler' from the text 'Button_Click'

  - by ay89

  In my windows phone 8 application, while trying to create a dependency property I am always getting this exception. what I am doing wrong, plz guide me. {System.Windows.Markup.XamlParseException: Failed to create a 'System.Windows.RoutedEventHandler' from the text 'Button_Click'. [Line: 108 Position: 66] at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator) at com.sap.View.HomePage.InitializeComponent() at com.sap.View.HomePage..ctor()} this is code-behind of Header public static readonly DependencyProperty MenuClickProperty = DependencyProperty.Register("MenuClick", typeof(RoutedEventHandler), typeof(Header), new PropertyMetadata(OnMenuClickHandlerChanged)); public RoutedEventHandler MenuClick { get { return (RoutedEventHandler)GetValue(MenuClickProperty); } set { SetValue(MenuClickProperty, new RoutedEventHandler(value)); } } private static void OnMenuClickHandlerChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { Header header = d as Header; header.OnMenuClickHandlerPropertyChanged(e); } private void OnMenuClickHandlerPropertyChanged(DependencyPropertyChangedEventArgs e) { MenuButton.Click += MenuClick; } this is in my user control (Header) <Button Click="{Binding Path=MenuClick, Source={RelativeSource Mode=Self}}" /> this is how i am including control on my Page: <myControls:Header Title="{Binding Title}" MenuClick="Button_Click" /> this is in code-behind: public void Button_Click(object sender, RoutedEventArgs e) { OpenSettings(); }

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• Is it good practise to blank out inherited functionality that will not be used?

  - by Timo Kosig

  I'm wondering if I should change the software architecture of one of my projects. I'm developing software for a project where two sides (in fact a host and a device) use shared code. That helps because shared data, e.g. enums can be stored in one central place. I'm working with what we call a "channel" to transfer data between device and host. Each channel has to be implemented on device and host side. We have different kinds of channels, ordinary ones and special channels which transfer measurement data. My current solution has the shared code in an abstract base class. From there on code is split between the two sides. As it has turned out there are a few cases when we would have shared code but we can't share it, we have to implement it on each side. The principle of DRY (don't repeat yourself) says that you shouldn't have code twice. My thought was now to concatenate the functionality of e.g. the abstract measurement channel on the device side and the host side in an abstract class with shared code. That means though that once we create an actual class for either the device or the host side for that channel we have to hide the functionality that is used by the other side. Is this an acceptable thing to do: public abstract class MeasurementChannelAbstract { protected void MethodUsedByDeviceSide() { } protected void MethodUsedByHostSide() { } } public class DeviceMeasurementChannel : MeasurementChannelAbstract { public new void MethodUsedByDeviceSide() { base.MethodUsedByDeviceSide(); } } Now, DeviceMeasurementChannel is only using the functionality for the device side from MeasurementChannelAbstract. By declaring all methods/members of MeasurementChannelAbstract protected you have to use the new keyword to enable that functionality to be accessed from the outside. Is that acceptable or are there any pitfalls, caveats, etc. that could arise later when using the code?

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• Built in background-scheduling system in .NET?

  - by Lasse V. Karlsen

  I ask though I doubt there is any such system. Basically I need to schedule tasks to execute at some point in the future (usually no more than a few seconds or possibly minutes from now), and have some way of cancelling that request unless too late. Ie. code that would look like this: var x = Scheduler.Schedule(() => SomethingSomething(), TimeSpan.FromSeconds(5)); ... x.Dispose(); // cancels the request Is there any such system in .NET? Is there anything in TPL that can help me? I need to run such future-actions from various instances in a system here, and would rather avoid each such class instance to have its own thread and deal with this. Also note that I don't want this (or similar, for instance through Tasks): new Thread(new ThreadStart(() => { Thread.Sleep(5000); SomethingSomething(); })).Start(); There will potentially be a few such tasks to execute, they don't need to be executed in any particular order, except for close to their deadline, and it isn't vital that they have anything like a realtime performance concept. I just want to avoid spinning up a separate thread for each such action.

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• How to structure Javascript programs in complex web applications?

  - by mixedpickles

  Hi there. I have a problem, which is not easily described. I'm writing a web application that makes heavy usage of jquery and ajax calls. Now I don't have experience in designing the architecture for javascript programms, but I realize that my program has not a good structure. I think I have to many identifiers referring to the same (at least more or less) thing. Let's have an exemplary look at an arbitrary UI widget: The eventhandlers use DOM elements as parameters. The DOM element represents a widget in the browser. A lot of times I use jQuery objects (I think they are basically a wrapper around DOM elements) to do something with the widget. Sometimes they are used transiently, sometimes they are stored in a variable for later purposes. The ajax function calls use strings identifiers for these widgets. They are processed server side. Beside that I have a widget class whose instances represents a widget. It is instantiated through the new operator. Now I have somehow four different object identifiers for the same thing, which needs to be kept in sync until the page is loaded anew. This seems not to be a good thing. Any advice?

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• Abstract Design Pattern implementation

  - by Pathachiever11

  I started learning design patterns a while ago (only covered facade and abstract so far, but am enjoying it). I'm looking to apply the Abstract pattern to a problem I have. The problem is: Supporting various Database systems using one abstract class and a set of methods and properties, which then the underlying concrete classes (inheriting from abstract class) would be implementing. I have created a DatabaseWrapper abstract class and have create SqlClientData and MSAccessData concrete class that inherit from the DatabaseWrapper. However, I'm still a bit confused about how the pattern goes as far as implementing these classes on the Client. Would I do the following?: DatabaseWrapper sqlClient = new SqlClientData(connectionString); This is what I saw in an example, but that is not what I'm looking for because I want to encapsulate the concrete classes; I only want the Client to use the abstract class. This is so I can support for more database systems in the future with minimal changes to the Client, and creating a new concrete class for the implementations. I'm still learning, so there might be a lot of things wrong here. Please tell me how I can encapsulate all the concrete classes, and if there is anything wrong with my approach. Many Thanks! PS: I'm very excited to get into software architecture, but still am a beginner, so take it easy on me. :)

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• Mac OS on a Windows PC

  I've done a little bit of reading on the topic, but nothing too clear has turned up. Why is it so difficult to run Mac OS on a virtual machine on a PC? Some sources say it's because of hardware architecture. Is there a clear, definitive reason?

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• cache memory performance

  - by Krewie

  Hello, i just have a general question about cache memory. How would a program perform badly on a cache based system ? , since cache memory stores adresses from main memory that is requested, aswell as adresses that ranges around the same adress as the one copied from the main memory.

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• What's open-source commenting system are available?

  - by Shamoon

  My site has several listing pages and on each page, I'd like to enable a commenting mechanism, but I want it to be as open source as humanly possible. This means full use of OpenID's, Facebook connect, etc. Does such a system exist that'll allow users to post their comments on my listing pages? By the way, my site utilizes a LAMP architecture.

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• The best way to separate admin functionality from a public site?

  - by AndrewO

  I'm working on a site that's grown both in terms of user-base and functionality to the point where it's becoming evident that some of the admin tasks should be separate from the public website. I was wondering what the best way to do this would be. For example, the site has a large social component to it, and a public sales interface. But at the same time, there's back office tasks, bulk upload processing, dashboards (with long running queries), and customer relations tools in the admin section that I would like to not be effected by spikes in public traffic (or effect the public-facing response time). The site is running on a fairly standard Rails/MySQL/Linux stack, but I think this is more of an architecture problem than an implementation one: mainly, how does one keep the data and business logic in sync between these different applications? Some strategies that I'm evaluating: 1) Create a slave database of the public facing database on another machine. Extract out all of the model and library code so that it can be shared between the applications. Create new controllers and views for the admin interfaces. I have limited experience with replication and am not even sure that it's supposed to be used this way (most of the time I've seen it, it's been for scaling out the read capabilities of the same application, rather than having multiple different ones). I'm also worried about the potential for latency issues if the slave is not on the same network. 2) Create new more task/department-specific applications and use a message oriented middleware to integrate them. I read Enterprise Integration Patterns awhile back and they seemed to advocate this for distributed systems. (Alternatively, in some cases the basic Rails-style RESTful API functionality might suffice.) But, I have nightmares about data synchronization issues and the massive re-architecting that this would entail. 3) Some mixture of the two. For example, the only public information necessary for some of the back office tasks is a read-only completion time or status. Would it make sense to have that on a completely separate system and send the data to public? Meanwhile, the user/group admin functionality would be run on a separate system sharing the database? The downside is, this seems to keep many of the concerns I have with the first two, especially the re-architecting. I'm sure the answers are going to be highly dependent on a site's specific needs, but I'd love to hear success (or failure) stories.

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• Top-down or bottom-up design?

  - by Gabriel Šcerbák

  There are basically those two approaches to designing a system. What are the advantages and disadvantages? When should I use which? Should I combine those approaches? How?

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• Java portal architectural considerations

  - by Woot4Moo

  Currently there exists a need to create an application that will serve 5 different customers each requiring their own specific URL and content repository. My question is when designing this application what should my considerations be for protecting the content of the individual customers while meeting the requirements of the unique URL. The system will be sitting on Windows with a postgres database and java as the implementation language.

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• I need to understand why my server turned off

  - by Dema

  Our organization was robbed and definitely it was inside job. I was set up. I work as a manager and as system administrator in this organization and everything goes against me. The only clue I have is that someone accidentally or intentionally turned of a server that is in the office indicating that some one was inside at the time that no one should be. This is the only evidence I have that can justify me.  I looked the log files and they show that the Power button was pressed. Can you help me to find out that that was not a bug or systems overheat? I will post the log files and if you will ask more I will gladly provide the information. Messages: Dec 24 21:43:14 jamx shutdown[27883]: shutting down for system halt Dec 24 21:43:15 jamx init: Switching to runlevel: 0 Dec 24 21:43:15 jamx smartd[3047]: smartd received signal 15: Terminated Dec 24 21:43:15 jamx smartd[3047]: smartd is exiting (exit status 0) Dec 24 21:43:15 jamx avahi-daemon[3015]: Got SIGTERM, quitting. Dec 24 21:43:15 jamx avahi-daemon[3015]: Leaving mDNS multicast group on interface eth0.IPv6 with address fe80::221:85ff:fe11:8221. Dec 24 21:43:15 jamx avahi-daemon[3015]: Leaving mDNS multicast group on interface eth0.IPv4 with address 82.207.41.239. Dec 24 21:43:15 jamx shutdown[27962]: shutting down for system halt Dec 24 21:43:15 jamx saslauthd[2983]: server_exit     : master exited: 2983 Dec 24 21:43:29 jamx nmbd[2921]: [2010/12/24 21:43:29, 0] nmbd/nmbd.c:terminate(58) Dec 24 21:43:29 jamx nmbd[2921]:   Got SIGTERM: going down... Dec 24 21:43:31 jamx clamd[2526]: Pid file removed. Dec 24 21:43:31 jamx clamd[2526]: --- Stopped at Fri Dec 24 21:43:31 2010 Dec 24 21:43:31 jamx clamd[2526]: Socket file removed. Dec 24 21:43:31 jamx mydns[2645]: jamx.org.ua up 9h44m48s (35088s) 117 questions (0/s) NOERROR=117 SERVFAIL=0 NXDOMAIN=0 NOTIMP=0 REFUSED=0 (100% TCP, 117 queries) Dec 24 21:43:31 jamx mydns[2645]: terminated Dec 24 21:43:34 jamx ntpd[2512]: ntpd exiting on signal 15 Dec 24 21:43:34 jamx hcid[2265]: Got disconnected from the system message bus Dec 24 21:43:35 jamx rpc.statd[2167]: Caught signal 15, un-registering and exiting. Dec 24 21:43:35 jamx portmap[28473]: connect from 127.0.0.1 to unset(status): request from unprivileged port Dec 24 21:43:35 jamx auditd[2021]: The audit daemon is exiting. Dec 24 21:43:35 jamx kernel: audit(1293219815.505:4044): audit_pid=0 old=2021 by auid=4294967295 Dec 24 21:43:35 jamx pcscd: pcscdaemon.c:572:signal_trap() Preparing for suicide Dec 24 21:43:36 jamx pcscd: hotplug_libusb.c:376:HPRescanUsbBus() Hotplug stopped Dec 24 21:43:36 jamx pcscd: readerfactory.c:1379:RFCleanupReaders() entering cleaning function Dec 24 21:43:36 jamx pcscd: pcscdaemon.c:532:at_exit() cleaning /var/run Dec 24 21:43:36 jamx kernel: Kernel logging (proc) stopped. Dec 24 21:43:36 jamx kernel: Kernel log daemon terminating. Dec 24 21:43:37 jamx exiting on signal 15 Acpid: [Fri Dec 24 21:43:14 2010] received event "button/power PWRF 00000080 00000001" [Fri Dec 24 21:43:14 2010] notifying client 2382[68:68] [Fri Dec 24 21:43:14 2010] executing action "/bin/ps awwux | /bin/grep gnome-power-manager | /bin/grep -qv grep || /sbin/shutdown -h now" [Fri Dec 24 21:43:14 2010] BEGIN HANDLER MESSAGES [Fri Dec 24 21:43:15 2010] END HANDLER MESSAGES [Fri Dec 24 21:43:15 2010] action exited with status 0 [Fri Dec 24 21:43:15 2010] completed event "button/power PWRF 00000080 00000001" [Fri Dec 24 21:43:15 2010] received event "button/power PWRF 00000080 00000002" [Fri Dec 24 21:43:15 2010] notifying client 2382[68:68] [Fri Dec 24 21:43:15 2010] executing action "/bin/ps awwux | /bin/grep gnome-power-manager | /bin/grep -qv grep || /sbin/shutdown -h now" [Fri Dec 24 21:43:15 2010] BEGIN HANDLER MESSAGES [Fri Dec 24 21:43:15 2010] END HANDLER MESSAGES [Fri Dec 24 21:43:15 2010] action exited with status 0 [Fri Dec 24 21:43:15 2010] completed event "button/power PWRF 00000080 00000002" [Fri Dec 24 21:43:34 2010] exiting

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• Should we write detailed architecture design or just an outline when designing a program?

  - by EpsilonVector

  When I'm doing design for a task, I keep fighting this nagging feeling that aside from being a general outline it's going to be more or less ignored in the end. I'll give you an example: I was writing a frontend for a device that has read/write operations. It made perfect sense in the class diagram to give it a read and a write function. Yet when it came down to actually writing them I realized they were literally the same function with just one line of code changed (read vs write function call), so to avoid code duplication I ended up implementing a do_io function with a parameter that distinguishes between operations. Goodbye original design. This is not a terribly disruptive change, but it happens often and can happen in more critical parts of the program as well, so I can't help but wondering if there's a point to design more detail than a general outline, at least when it comes to the program's architecture (obviously when you are specifying an API you have to spell everything out). This might be just the result of my inexperience in doing design, but on the other hand we have agile methodologies which sort of say "we give up on planning far ahead, everything is going to change in a few days anyway", which is often how I feel. So, how exactly should I "use" design?

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