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• Soft lockup after upgrade - cannot install from live CD

  - by nbm

  I dual-boot MacIntel Core 2 duo. nVidia graphics. Ran upgrade from ubuntu 13.10 to 14.04 (64 bit). On restart ran into {numbers} Bug: soft lockup - CPU#0 stuck for 22s! [swapper/0:1] Tried loading earlier kernel: same problem Tried re-installing ubuntu from a liveCD that has worked in the past: version 13.04. Same problem. Tried re-partitioning hard drive using Mac OS X disk utility and then installing ubuntu 14.04LTS from liveCD. Same problem. Not possible to verify liveCD disk (creates same "soft lockup" bug.) Tried installing from the liveCD with version 13.04 that I know works (that's how I got Ubuntu on this machine in the first place.) Same problem. I know this is not a hardware problem as OS X works just fine, I am using it right now on the same machine. I have been using various versions of Ubuntu for 2 years. Things I cannot do: Open a terminal Verify CD image Start ubuntu from CD (same soft lockup problem) This problem is similar to some other questions, none of which have been satisfactorily answered: Ubuntu 14.04 soft lockup on Vostro 3500 Cannot do fresh install of Ubuntu 13.04 while booting from DVD: "soft lockup" bug Live CD stalls when installing Ubuntu 13.10 UPDATE 6/11/14: Following some much-appreciated advice from bain (see below) I burned a 12.04LTS disk and started with kernel parameters: noapic, no1apic, acpi=off, nomodeset, elevator=deadline, and clocksource=jiffies. With all of these parameters I was able to load the 12.04LTS CD ("Try without installing"). It worked fine. However, as soon as I tried to install Ubuntu from the CD, my wired ethernet (eth0) connection would hang. There are already various askubuntu questions and bug reports about this problem, none of which had answers for me. (E.g., dhclient eth0 does nothing, none of the various reset commands does anything, manually setting IP &etc does nothing. I could reliably kill the ethernet connection by clicking "install ubuntu" every single time.) I could go ahead and install 12.04 without an internet connection, but the install would freeze after mostly completing (I tried several times.) There were some relevant error messages in the details of the install output script that, IIRC, had to do with searching for missing files and not being able to access eth0 (internet) to get them. To be honest I gave up at that point and I'm not sure I wrote those down. If I find some notes I will post them. At this point I no longer have Ubuntu on my system. I wiped the partitions and am using exclusively OS X. I am leaving this question in case it helps anyone else with similar problems. I love open source and I love Linux, and the next machine I get I will probably just build from Arch. At the moment I miss repositories and a lot of other things about Ubuntu, but the OS X terminal is 'nix, I can pretty much use all the open source apps I like, and while I am not a fan of the Apple software it gets the job done for me. Unlike Ubuntu, which can't even install. I realize this isn't necessarily a place for a soapbox speech, but when I first installed 12.04 several years ago there were already people in the community complaining that Canonical was going too "commercial". But I loved it. Several years later and all I've seen is Canonical adding more not-so-useful bells and whistles to Ubuntu while continually failing to fix basic problems on upgrades. With a dual-boot (and sometimes triple-boot) system it always took me some tweaking to get an upgrade to work, and to some extent that is okay. But at this point I feel like Canonical ought to just put a price tag on Ubuntu. All I see is more commercialism and advertising and product tie-ins, and ongoing problems do not get fixed. I am a big fan of open-source, not-for profit enterprise. I am also a big fan of for-profit enterprise, which certainly has its place and usefulness. I am not a fan of companies who pretend to be in favor of open source but really are just out to make a buck, and IMNSHO that is what Canonical has become. This is a great community and I wish you all the best, but my next install of Linux will not be Ubuntu.

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• Cloud Computing Forces Better Design Practices

  - by Herve Roggero

  Is cloud computing simply different than on premise development, or is cloud computing actually forcing you to create better applications than you normally would? In other words, is cloud computing merely imposing different design principles, or forcing better design principles?  A little while back I got into a discussion with a developer in which I was arguing that cloud computing, and specifically Windows Azure in his case, was forcing developers to adopt better design principles. His opinion was that cloud computing was not yielding better systems; just different systems. In this blog, I will argue that cloud computing does force developers to use better design practices, and hence better applications. So the first thing to define, of course, is the word “better”, in the context of application development. Looking at a few definitions online, better means “superior quality”. As it relates to this discussion then, I stipulate that cloud computing can yield higher quality applications in terms of scalability, everything else being equal. Before going further I need to also outline the difference between performance and scalability. Performance and scalability are two related concepts, but they don’t mean the same thing. Scalability is the measure of system performance given various loads. So when developers design for performance, they usually give higher priority to a given load and tend to optimize for the given load. When developers design for scalability, the actual performance at a given load is not as important; the ability to ensure reasonable performance regardless of the load becomes the objective. This can lead to very different design choices. For example, if your objective is to obtains the fastest response time possible for a service you are building, you may choose the implement a TCP connection that never closes until the client chooses to close the connection (in other words, a tightly coupled service from a connectivity standpoint), and on which a connection session is established for faster processing on the next request (like SQL Server or other database systems for example). If you objective is to scale, you may implement a service that answers to requests without keeping session state, so that server resources are released as quickly as possible, like a REST service for example. This alternate design would likely have a slower response time than the TCP service for any given load, but would continue to function at very large loads because of its inherently loosely coupled design. An example of a REST service is the NO-SQL implementation in the Microsoft cloud called Azure Tables. Now, back to cloud computing… Cloud computing is designed to help you scale your applications, specifically when you use Platform as a Service (PaaS) offerings. However it’s not automatic. You can design a tightly-coupled TCP service as discussed above, and as you can imagine, it probably won’t scale even if you place the service in the cloud because it isn’t using a connection pattern that will allow it to scale [note: I am not implying that all TCP systems do not scale; I am just illustrating the scalability concepts with an imaginary TCP service that isn’t designed to scale for the purpose of this discussion]. The other service, using REST, will have a better chance to scale because, by design, it minimizes resource consumption for individual requests and doesn’t tie a client connection to a specific endpoint (which means you can easily deploy this service to hundreds of machines without much trouble, as long as your pockets are deep enough). The TCP and REST services discussed above are both valid designs; the TCP service is faster and the REST service scales better. So is it fair to say that one service is fundamentally better than the other? No; not unless you need to scale. And if you don’t need to scale, then you don’t need the cloud in the first place. However, it is interesting to note that if you do need to scale, then a loosely coupled system becomes a better design because it can almost always scale better than a tightly-coupled system. And because most applications grow overtime, with an increasing user base, new functional requirements, increased data and so forth, most applications eventually do need to scale. So in my humble opinion, I conclude that a loosely coupled system is not just different than a tightly coupled system; it is a better design, because it will stand the test of time. And in my book, if a system stands the test of time better than another, it is of superior quality. Because cloud computing demands loosely coupled systems so that its underlying service architecture can be leveraged, developers ultimately have no choice but to design loosely coupled systems for the cloud. And because loosely coupled systems are better… … the cloud forces better design practices. My 2 cents.

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• Ajax comments form in ASP.NET MVC2

  - by Artiom Chilaru

  I've been playing around with different aspects of MVC for some time now, and I've reached a situation where I'm not sure what would be the best way to solve a problem. I'm hoping that the SO community will help me out here :P I've seen a number of examples of Ajax.BeginForm on the internet, and it seems like a very nifty idea. E.g. you have a dropdown where you select a customer - and on selecting one it will load this client's details in some placeholder on the page. This works perfectly fine. But what to do if you want to tie in some validation in the box? Just hypothetically, imagine an article page, and user comments in the bottom. Below the comments area there's an ajax-y "Add comment" box. When a user adds a comment, it will appear in the comments area, below the last comment there. If I set the Ajax.BeginForm to Append the result of the call to the Comments area, it will work fine. But what if the data posted is not valid? Instead of appending a "successful" comment to the comments area I have to show the user validation errors. At this point I decided that the area INSIDE the Ajax.BeginForm will be inside a partial, and the form's submits will return this partial. Validation works fine. On each submit we reload the contents inside the form element. But how to add the successful comment to the top? Other things to consider: The comment form also has a "Preview" button. When the user clicks on Preview, I should load the rendered comment into a preview box. This will probably be inside the form area as well. I was thinking of using Json results instead. When the user submits the form, the server code will generate a Json object with a Success value, and html rendered partials as some properties. Something like { "success": true, "form": "<html form data>", "comment": "successful comment html to inject into the page" } This would be a perfect solution, except there's no way in MVC to render a partial into a string, inside the controller (separation of context, remember?). So.. what should I do then? Any "correct" way to implement this?

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• Reliable way of generating unique hardware ID

  - by mr.b

  Question: what's the best way to accomplish following. I have to come up with unique ID for each networked client, such that: it (ID) should persist once client software is installed on target computer, and should continue to persist if software is re-installed on same computer and same OS installment, it should not change if hardware configuration is modified in most ways (except changing the motherboard) When hard drive with client software installed is cloned to another computer with identical hardware configuration (or, as similar as possible), client software should be aware of that change. A little bit of explanation and some back-story: This question is basically age old question that also touches topic of software copy-protection, as some of mechanisms used in that area are mentioned here. I should be clear at this point that I'm not looking for a copy-protection scheme. Please, read on. :) I'm working on a client-server software that is supposed to work in local network. One of problems I have to solve is to identify each unique client in network (not so much of a problem), so that I can apply certain attributes to every specific client, retain and enforce those attributes during deployment lifetime of a specific client. While I was looking for a solution, I was aware of following: Windows activation system uses some kind of heavy fingerprinting mechanism, that is extremely sensitive to hardware modifications, Disk imaging software copies along all Volume IDs (tied to each partition when formatted), and custom, uniquely generated IDs during installation process, during first run, or in any other way, that is strictly software in its nature, and stored in registry or on hard drive, so it's very easy to confuse two Obvious choice for this kind of problem would be to find out BIOS identifiers (not 100% sure if this is unique through identical motherboard models, though), as that's the only thing I can rely on, that isn't duplicated, transferred by cloning, and that can't be changed (at least not by using some user-space program). Everything else fails as either being not reliable (MAC cloning, anyone?), or too demanding (in terms that it's too sensitive to configuration changes). Am I missing something obvious here? Sub-question that I'd like to ask is, am I doing it correctly, architecture-wise? Perhaps there is a better tool for task that I have to accomplish... Another approach I had in mind is something similar to handshake mechanism, where server maintains internal lookup table of connected client IDs (which can be even completely software-based and non-unique at any given moment), and tells client to come up with different ID during handshake, if duplicate ID is provided upon connection. That approach, unfortunately, doesn't play nicely with one of requirements to tie attributes to specific client during lifetime.

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• Is MVVM pointless?

  - by joebeazelman

  Is orthodox MVVM implementation pointless? I am creating a new application and I considered Windows Forms and WPF. I chose WPF because it's future-proof and offer lots of flexibility. There is less code and easier to make significant changes to your UI using XAML. Since the choice for WPF is obvious, I figured that I may as well go all the way by using MVVM as my application architecture since it offers blendability, separation concerns and unit testability. Theoretically, it seems beautiful like the holy grail of UI programming. This brief adventure; however, has turned into a real headache. As expected in practice, I’m finding that I’ve traded one problem for another. I tend to be an obsessive programmer in that I want to do things the right way so that I can get the right results and possibly become a better programmer. The MVVM pattern just flunked my test on productivity and has just turned into a big yucky hack! The clear case in point is adding support for a Modal dialog box. The correct way is to put up a dialog box and tie it to a view model. Getting this to work is difficult. In order to benefit from the MVVM pattern, you have to distribute code in several places throughout the layers of your application. You also have to use esoteric programming constructs like templates and lamba expressions. Stuff that makes you stare at the screen scratching your head. This makes maintenance and debugging a nightmare waiting to happen as I recently discovered. I had an about box working fine until I got an exception the second time I invoked it, saying that it couldn’t show the dialog box again once it is closed. I had to add an event handler for the close functionality to the dialog window, another one in the IDialogView implementation of it and finally another in the IDialogViewModel. I thought MVVM would save us from such extravagant hackery! There are several folks out there with competing solutions to this problem and they are all hacks and don’t provide a clean, easily reusable, elegant solution. Most of the MVVM toolkits gloss over dialogs and when they do address them, they are just alert boxes that don’t require custom interfaces or view models. I’m planning on giving up on the MVVM view pattern, at least its orthodox implementation of it. What do you think? Has it been worth the trouble for you if you had any? Am I just a incompetent programmer or does MVVM not what it's hyped up to be?

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• Client-side policy error using JacORB (Java/CORBA) with SSL

  - by jason

  I'm trying to add SSL to an existing CORBA app, and I keep getting this error: org.omg.CORBA.NO_PERMISSION: Client-side policy requires SSL/TLS, but server doesn't support it vmcid: 0x0 minor code: 0 completed: No at org.jacorb.orb.iiop.ClientIIOPConnection.checkSSL(ClientIIOPConnection.java:535) at org.jacorb.orb.iiop.ClientIIOPConnection.connect(ClientIIOPConnection.java:144) at org.jacorb.orb.giop.GIOPConnection.sendMessage(GIOPConnection.java:835) at org.jacorb.orb.giop.GIOPConnection.sendRequest(GIOPConnection.java:805) at org.jacorb.orb.giop.ClientConnection.sendRequest(ClientConnection.java:302) at org.jacorb.orb.giop.ClientConnection.sendRequest(ClientConnection.java:282) at org.jacorb.orb.Delegate.invoke_internal(Delegate.java:919) at org.jacorb.orb.Delegate.invoke(Delegate.java:868) at org.jacorb.orb.Delegate.is_a(Delegate.java:1268) at org.omg.CORBA.portable.ObjectImpl._is_a(ObjectImpl.java:112) at databridge.autogen.ILoginManagerHelper.narrow(ILoginManagerHelper.java:57) at databridge.test.Client.main(Client.java:59) I have generated keystores for both client and server and exchanged the keys between the two. Using this setup, I can get the demo application that came in the JacORB download to run successfully. The only difference I can tell is that my test is using the Tie method to get the POA. There are some policies that go into that, but I can't find any information on what policies need to go in there to enable SSL, if any. I'm not even sure that's the problem as the JacORB demo doesn't set any policies on the server or poa. When I run the -Djavax.net.debug=ssl, I can see the keystores load up the trusted certs on both the client and the server. I'm just not sure what policies are being referred to here, but it's odd that the demo works and the test doesn't using the exact same keystores and properties. I've emailed the mailing list, but I'm not holding out much hope as that doesn't seem to be very active. Any help would be greatly appreciated. Below are my properties files. Server Props: jacorb.security.support_ssl=on jacorb.security.ssl.server.supported_options=60 jacorb.security.ssl.server.required_options=20 jacorb.ssl.socket_factory=org.jacorb.security.ssl.sun_jsse.SSLSocketFactory jacorb.ssl.server_socket_factory=org.jacorb.security.ssl.sun_jsse.SSLServerSocketFactory jacorb.security.keystore=dbserver.jks jacorb.security.keystore_password=dbsslserver_pass jacorb.security.jsse.trustees_from_ks=on jacorb.security.jsse.log.verbosity=4 jacorb.implname=StandardImplName client props jacorb.security.support_ssl=on jacorb.security.ssl.client.supported_options=60 jacorb.security.ssl.client.required_options=20 jacorb.ssl.socket_factory=org.jacorb.security.ssl.sun_jsse.SSLSocketFactory jacorb.security.keystore=dbclient.jks jacorb.security.keystore_password=dbsslclient_pass jacorb.security.jsse.trustees_from_ks=on jacorb.security.jsse.log.verbosity=4 jacorb.implname=StandardImplName

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• Java Copy/Paste org.w3c.dom.Node between two running copies of the same program

  - by Jay

  I have a program that shows a tree representation of an XML file. Using a number of sources online I have Copy/Paste within a single instance of the program working. I am using the system Clipboard. What I need though is to be able to copy a node from one instance of the program and paste to a different instance of the same program. I have tried a number of different options, all resulting in the same behavior. When pasting from within the same application the clipboardContent contains a "transferable" object with the correct data along with an isLocal set to "true". When I perform the copy and then attempt the paste from another instance of the same program running the clipboardContent contains a "flavorsToData" HashMap and "flavors" values, the check for isDataFlavorSupported fails (never hits my custom class that represents the new flavor). I have tried using different values for the requestor object in the getContents() call. Likewise I have tried a few different ClipboardOwners for the setContent() call. Neither seem to change the behavior in any way. I am sorely tempted to convert the node that is being copied back into a textual XML format, and then on the paste convert back to the DOM model, but would rather not if possible. This class is used to define the DataFlavor and transferable object: import java.awt.datatransfer.*; import org.w3c.dom.Node; public class NodeCopyPaste implements Transferable { static public DataFlavor NodeFlavor; private DataFlavor [] supportedFlavors = {NodeFlavor}; public Node aNode; public NodeCopyPaste (Node paraNode) { aNode = paraNode; try { NodeFlavor = new DataFlavor (Class.forName ("org.w3c.dom.Node"), "Node"); } catch (ClassNotFoundException e) { e.printStackTrace (); } } public synchronized DataFlavor [] getTransferDataFlavors () { return (supportedFlavors); } public boolean isDataFlavorSupported (DataFlavor nodeFlavor) { return (nodeFlavor.equals (NodeFlavor)); } public synchronized Object getTransferData (DataFlavor nFlavor) throws UnsupportedFlavorException { if (nFlavor.equals (NodeFlavor)) return (this); else throw new UnsupportedFlavorException (nFlavor); } public void lostOwnership (Clipboard parClipboard, Transferable parTransferable) { } } I define a Clipboard object from the main application screen and then tie in copy and paste handlers for the mouse clicks: During initialization I assign the system clipboard: clippy = Toolkit.getDefaultToolkit().getSystemClipboard(); Copy Handler Node copyNode = ((CLIInfo) node.getUserObject()).DOMNode.cloneNode(true); NodeCopyPaste contents = new NodeCopyPaste(copyNode); clippy.setContents (contents, null); Paste Handler Transferable clipboardContent = clippy.getContents (null); Node clonedNode = null; if ((clipboardContent != null) && (clipboardContent.isDataFlavorSupported (NodeCopyPaste.NodeFlavor))) { try { NodeCopyPaste tempNCP = (NodeCopyPaste) clipboardContent.getTransferData (NodeCopyPaste.NodeFlavor); clonedNode = tempNCP.aNode.cloneNode(true); } catch (Exception e) { e.printStackTrace (); } Thanks!

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• Ajax comments form in ASP.NET MVC2, howto?

  - by Artiom Chilaru

  I've been playing around with different aspects of MVC for some time now, and I've reached a situation where I'm not sure what would be the best way to solve a problem. I'm hoping that the SO community will help me out here :P I've seen a number of examples of Ajax.BeginForm on the internet, and it seems like a very nifty idea. E.g. you have a dropdown where you select a customer - and on selecting one it will load this client's details in some placeholder on the page. This works perfectly fine. But what to do if you want to tie in some validation in the box? Just hypothetically, imagine an article page, and user comments in the bottom. Below the comments area there's an ajax-y "Add comment" box. When a user adds a comment, it will appear in the comments area, below the last comment there. If I set the Ajax.BeginForm to Append the result of the call to the Comments area, it will work fine. But what if the data posted is not valid? Instead of appending a "successful" comment to the comments area I have to show the user validation errors. At this point I decided that the area INSIDE the Ajax.BeginForm will be inside a partial, and the form's submits will return this partial. Validation works fine. On each submit we reload the contents inside the form element. But how to add the successful comment to the top? Other things to consider: The comment form also has a "Preview" button. When the user clicks on Preview, I should load the rendered comment into a preview box. This will probably be inside the form area as well. I was thinking of using Json results instead. When the user submits the form, the server code will generate a Json object with a Success value, and html rendered partials as some properties. Something like { "success": true, "form": "<html form data>", "comment": "successful comment html to inject into the page" } This would be a perfect solution, except there's no way in MVC to render a partial into a string, inside the controller (separation of context, remember?). So.. what should I do then? Any "correct" way to implement this? Anyone???

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• WPF 4 Datagrid with ComboBox

  - by Doug

  I have a WPF 4 app with a ComboBox embedded in a DataGrid. The ComboBox is in a template column that displays the combobox when in edit mode but just a TextBlock otherwise. If I edit the cell and pick a new value from the combobox, when leaving the cell, the TextBlock in view mode does not reflect the new value. Ultimately, the new value gets saved and is displayed when the window is refreshed but it does not happen while still editing in the grid. Here are the parts that are making this more complicated. The grid and the combobox are bound to different ItemsSource from the EnityFramework which is tied to my database. For this problem, the grid is displaying project members. The project member name can be picked from the combobox which gives a list of all company employees. Any ideas on how to tie the view mode of the DataGridColumnTemplate to the edit value when they are pointing to different DataSources? Relevant XAML <Window.Resources> <ObjectDataProvider x:Key="EmployeeODP" /> </Window.Resources> <StackPanel> <DataGrid Name="teamProjectGrid" AutoGenerateColumns="false" ItemsSource="{Binding Path=ProjectMembers}" <DataGrid.Columns> <DataGridTemplateColumn Header="Name" x:Name="colProjectMember"> <DataGridTemplateColumn.CellTemplate> <DataTemplate> <TextBlock Text="{Binding Path=ProjectMemberFullName}" /> </DataTemplate> </DataGridTemplateColumn.CellTemplate> <DataGridTemplateColumn.CellEditingTemplate> <DataTemplate> <ComboBox x:Name="ProjectMemberCombo" IsReadOnly="True" DisplayMemberPath="FullName" SelectedValue="{Binding Path=Employee}" ItemsSource="{Binding Source={StaticResource EmployeeODP}}" /> </DataTemplate> </DataGridTemplateColumn.CellEditingTemplate> </DataGridTemplateColumn> <DataGridTextColumn x:Name="colProjectRole" Binding="{Binding Path=ProjectRole}" Header="Role" /> </DataGrid.Columns> </DataGrid> </StackPanel> Relevant Code Behind this.DataContext = new MyEntityLibrary.MyProjectEntities(); ObjectDataProvider EmployeeODP= (ObjectDataProvider)FindResource("EmployeeODP"); if (EmployeeODP != null) { EmployeeODP.ObjectInstance = this.DataContext.Employees; }

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• Cross field validation in jsf h:datatable using p:calendar

  - by Matt Broekhuis

  I noticed this question was asked, but it has not been answered correctly. I have a datatable that has two columns start date and end date. Both contain primefaces p:calendar controls in them. I need to ensure that for each row that the date in column1 is not after the date in column2. I would like to tie this into the JSF validation framework, but I'm having trouble. i've tried marking the datatable rowStatePreserved="true" , this allows me to get the values, but something is still wrong as when it fails, all the values in the first row overwrite all the other values. What am I doing wrong, or should I be using a completely different strategy? xhtml code <h:form> <f:event type="postValidate" listener="#{bean.doCrossFieldValidation}"/> <p:dataTable id="eventDaysTable" value="#{course.courseSchedules}" var="_eventDay" styleClass="compactDataTable" > <p:column id="eventDayStartColumn"> <f:facet name="header"> Start </f:facet> <p:calendar id="startDate" required="true" value="#{_eventDay.startTime}" pattern="MM/dd/yyyy hh:mm a"/> </p:column> <p:column id="eventDayEndColumn"> <f:facet name="header"> End </f:facet> <p:calendar id="endDate" required="true" value="#{_eventDay.endTime}" pattern="MM/dd/yyyy hh:mm a"/> </p:column> </p:dataTable> </h:form> validationCode public void doCrossFieldValidation(ComponentSystemEvent cse) { UIData eventsDaysStable = (UIData) cse.getComponent().findComponent("eventDaysTable"); if (null != eventsDaysStable && eventsDaysStable.isRendered()) { Iterator<UIComponent> startDateCalendarIterator = eventsDaysStable.findComponent("eventDayStartColumn").getChildren().iterator(); Iterator<UIComponent> endDateCalendarIterator = eventsDaysStable.findComponent("eventDayEndColumn").getChildren().iterator(); while (startDateCalendarIterator.hasNext() && endDateCalendarIterator.hasNext()) { org.primefaces.component.calendar.Calendar startDateComponent = (org.primefaces.component.calendar.Calendar) startDateCalendarIterator.next(); org.primefaces.component.calendar.Calendar endDateComponent = (org.primefaces.component.calendar.Calendar) endDateCalendarIterator.next(); Date startDate = (Date) startDateComponent.getValue(); Date endDate = (Date) endDateComponent.getValue(); if (null != startDate && null != endDate && startDate.after(endDate)) { eventScheduleChronologyOk = false; startDateComponent.setValid(false); endDateComponent.setValid(false); } } if (!eventScheduleChronologyOk) { showErrorMessage(ProductManagementMessage.PRODUCT_SCHEDULE_OUT_OF_ORDER); } } }

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• navigator.onLine

  - by cf_PhillipSenn

  I'm playing with the incomplete example found at http://www.w3.org/TR/offline-webapps/ But I'm distressed to see comments in it like: "renders the note somewhere", and "report error", and "// …" So, will someone please help me write a valid example? Here's what I've got so far: <!DOCTYPE HTML> <html manifest="cache-manifest"> <head> <script> var db = openDatabase("notes", "", "The Example Notes App!", 1048576); function renderNote(row) { // renders the note somewhere } function reportError(source, message) { // report error } function renderNotes() { db.transaction(function(tx) { tx.executeSql('CREATE TABLE IF NOT EXISTS Notes(title TEXT, body TEXT)', []); tx.executeSql(‘SELECT * FROM Notes’, [], function(tx, rs) { for(var i = 0; i < rs.rows.length; i++) { renderNote(rs.rows[i]); } }); }); } function insertNote(title, text) { db.transaction(function(tx) { tx.executeSql('INSERT INTO Notes VALUES(?, ?)', [ title, text ], function(tx, rs) { // … }, function(tx, error) { reportError('sql', error.message); }); }); } </script> <style> label { display:block; } </style> </head> <body> <form> <label for="mytitle">Title:</label> <input name="mytitle"> <label for="mytext">Text:</label> <textarea name="mytext"></textarea> <!-- There is no submit button because I want to save the info on every keystroke --> </form> </body> </html> I also know that I have to incorporate this in there somewhere: if (navigator.onLine) { // Send data using XMLHttpRequest } else { // Queue data locally to send later } But I'm not sure what even I would tie that too.

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• C# Detect Localhost Port Usage

  - by ThaKidd

  In advance, thank you for your advice. I am currently working on a program which uses Putty to create a SSH connection with a server that uses local port forwarding to enable a client, running my software, to access the service behind the SSH server via localhost. IE: client:20100 - Internet - Remote SSH server exposed via router/firewall - Local Intranet - Intranet Web POP3 Server:110. Cmd Line: "putty -ssh -2 -P 22 -C -L 20100:intranteIP:110 -pw sshpassword sshusername@sshserver" Client would use putty to create a SSH connection with the SSH server specifying in the connection string that it would like to tie port 110 of the Intranet POP3 Server to port 20100 on the client system. Therefore the client would be able to open up a mail client to localhost:20100 and interact with the Internal POP3 server over the SSH tunnel. The above is a general description. I already know what I am trying to do will work without a problem so am not looking for debate on the above. The question is this...How can I ensure the local port (I cannot use dynamic ports, so it must be static) on localhost is not being used or listened to by any other application? I am currently executing this code in my C# app: private bool checkPort(int port) { try { //Create a socket on the current IPv4 address Socket TestSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); // Create an IP end point IPEndPoint localIP = new IPEndPoint(IPAddress.Parse("127.0.0.1"), port); // Bind that port TestSocket.Bind(localIP); // Cleanup TestSocket.Close(); return false; } catch (Exception e) { // Exception occurred. Port is already bound. return true; } } I am currently calling this function starting with a specific port in a for loop to get the 'false' return at the first available port. The first port I try is actually being listened to by uTorrent. The above code does not catch this and my connection fails. What is the best method to ensure a port is truly free? I do understand some other program may grab the port during/after I have tested it. I just need to find something that will ensure it is not currently in use AT ALL when the test is executed. If there is a way to truly reserve the localhost port during the test, I would love to hear about it.

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• IQueryable and lazy loading

  - by Nelson

  I'm having a hard time determining the best way to handle this... With Entity Framework (and L2S), LINQ queries return IQueryable. I have read various opinions on whether the DAL/BLL should return IQueryable, IEnumerable or IList. Assuming we go with IList, then the query is run immediately and that control is not passed on to the next layer. This makes it easier to unit test, etc. You lose the ability to refine the query at higher levels, but you could simply create another method that allows you to refine the query and still return IList. And there are many more pros/cons. So far so good. Now comes Entity Framework and lazy loading. I am using POCO objects with proxies in .NET 4/VS 2010. In the presentation layer I do: foreach (Order order in bll.GetOrders()) { foreach (OrderLine orderLine in order.OrderLines) { // Do something } } In this case, GetOrders() returns IList so it executes immediately before returning to the PL. But in the next foreach, you have lazy loading which executes multiple SQL queries as it gets all the OrderLines. So basically, the PL is running SQL queries "on demand" in the wrong layer. Is there any sensible way to avoid this? I could turn lazy loading off, but then what's the point of having this "feature" that everyone was complaining EF1 didn't have? And I'll admit it is very useful in many scenarios. So I see several options: Somehow remove all associations in the entities and add methods to return them. This goes against the default EF behavior/code generation and makes it harder to do some composite (multiple entity) LINQ queries. It seems like a step backwards. I vote no. If we have lazy loading anyway which makes it hard to unit test, then go all the way and return IQueryable. You'll have more control farther up the layers. I still don't think this is a good option because IQueryable ties you to L2S, L2E, or your own full implementation of IQueryable. Lazy loading may run queries "on demand", but doesn't tie you to any specific interface. I vote no. Turn off lazy loading. You'll have to handle your associations manually. This could be with eager loading's .Include(). I vote yes in some specific cases. Keep IList and lazy loading. I vote yes in many cases, only due to the troubles with the others. Any other options or suggestions? I haven't found an option that really convinces me.

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• In an extension method how do a create an object based on the implementation class

  - by Greg

  Hi, In an extension method how do a create an object based on the implementation class. So in the code below I wanted to add an "AddRelationship" extension method, however I'm not sure how within the extension method I can create an Relationship object? i.e. don't want to tie the extension method to this particular implementation of relationship public static class TopologyExtns { public static void AddNode<T>(this ITopology<T> topIf, INode<T> node) { topIf.Nodes.Add(node.Key, node); } public static INode<T> FindNode<T>(this ITopology<T> topIf, T searchKey) { return topIf.Nodes[searchKey]; } public static bool AddRelationship<T>(this ITopology<T> topIf, INode<T> parentNode, INode<T> childNode) { var rel = new RelationshipImp(); // ** How do I create an object from teh implementation // Add nodes to Relationship // Add relationships to Nodes } } public interface ITopology<T> { //List<INode> Nodes { get; set; } Dictionary<T, INode<T> > Nodes { get; set; } } public interface INode<T> { // Properties List<IRelationship<T>> Relationships { get; set; } T Key { get; } } public interface IRelationship<T> { // Parameters INode<T> Parent { get; set; } INode<T> Child { get; set; } } namespace TopologyLibrary_Client { class RelationshipsImp : IRelationship<string> { public INode<string> Parent { get; set; } public INode<string> Child { get; set; } } } public class TopologyImp<T> : ITopology<T> { public Dictionary<T, INode<T>> Nodes { get; set; } public TopologyImp() { Nodes = new Dictionary<T, INode<T>>(); } } thanks

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• Hide a base class method from derived class, but still visible outside of assembly

  - by clintp

  This is a question about tidyness. The project is already working, I'm satisfied with the design but I have a couple of loose ends that I'd like to tie up. My project has a plugin architecture. The main body of the program dispatches work to the plugins that each reside in their own AppDomain. The plugins are described with an interface, which is used by the main program (to get the signature for invoking DispatchTaskToPlugin) and by the plugins themselves as an API contract: namespace AppServer.Plugin.Common { public interface IAppServerPlugin { void Register(); void DispatchTaskToPlugin(Task t); // Other methods omitted } } In the main body of the program Register() is called so that the plugin can register its callback methods with the base class, and then later DispatchTaskToPlugin() is called to get the plugin running. The plugins themselves are in two parts. There's a base class that implements the framework for the plugin (setup, housekeeping, teardown, etc..). This is where DispatchTaskToPlugin is actually defined: namespace AppServer.Plugin { abstract public class BasePlugin : MarshalByRefObject, AppServer.Plugin.Common.IAppServerPlugin { public void DispatchTaskToPlugin(Task t) { // ... // Eventual call to actual plugin code // } // Other methods omitted } } The actual plugins themselves only need to implement a Register() method (to give the base class the delegates to call eventually) and then their business logic. namespace AppServer.Plugin { public class Plugin : BasePlugin { override public void Register() { // Calls a method in the base class to register itself. } // Various callback methods, business logic, etc... } } Now in the base class (BasePlugin) I've implemented all kinds of convenience methods, collected data, etc.. for the plugins to use. Everything's kosher except for that lingering method DispatchTaskToPlugin(). It's not supposed to be callable from the Plugin class implementations -- they have no use for it. It's only needed by the dispatcher in the main body of the program. How can I prevent the derived classes (Plugin) from seeing the method in the base class (BasePlugin/DispatchTaskToPlugin) but still have it visible from outside of the assembly? I can split hairs and have DispatchTaskToPlugin() throw an exception if it's called from the derived classes, but that's closing the barn door a little late. I'd like to keep it out of Intellisense or possibly have the compiler take care of this for me. Suggestions?

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• Implementing coroutines in Java

  - by JUST MY correct OPINION

  This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines currently available in Java, what would be required to implement them? As I said in that question, I know about the following: You can implement "coroutines" as threads/thread pools behind the scenes. You can do tricksy things with JVM bytecode behind the scenes to make coroutines possible. The so-called "Da Vinci Machine" JVM implementation has primitives that make coroutines doable without bytecode manipulation. There are various JNI-based approaches to coroutines also possible. I'll address each one's deficiencies in turn. Thread-based coroutines This "solution" is pathological. The whole point of coroutines is to avoid the overhead of threading, locking, kernel scheduling, etc. Coroutines are supposed to be light and fast and to execute only in user space. Implementing them in terms of full-tilt threads with tight restrictions gets rid of all the advantages. JVM bytecode manipulation This solution is more practical, albeit a bit difficult to pull off. This is roughly the same as jumping down into assembly language for coroutine libraries in C (which is how many of them work) with the advantage that you have only one architecture to worry about and get right. It also ties you down to only running your code on fully-compliant JVM stacks (which means, for example, no Android) unless you can find a way to do the same thing on the non-compliant stack. If you do find a way to do this, however, you have now doubled your system complexity and testing needs. The Da Vinci Machine The Da Vinci Machine is cool for experimentation, but since it is not a standard JVM its features aren't going to be available everywhere. Indeed I suspect most production environments would specifically forbid the use of the Da Vinci Machine. Thus I could use this to make cool experiments but not for any code I expect to release to the real world. This also has the added problem similar to the JVM bytecode manipulation solution above: won't work on alternative stacks (like Android's). JNI implementation This solution renders the point of doing this in Java at all moot. Each combination of CPU and operating system requires independent testing and each is a point of potentially frustrating subtle failure. Alternatively, of course, I could tie myself down to one platform entirely but this, too, makes the point of doing things in Java entirely moot. So... Is there any way to implement coroutines in Java without using one of these four techniques? Or will I be forced to use the one of those four that smells the least (JVM manipulation) instead?

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• MATLAB arbitrary code execution

  - by aristotle2600

  I am writing an automatic grader program under linux. There are several graders written in MATLAB, so I want to tie them all together and let students run a program to do an assignment, and have them choose the assignment. I am using a C++ main program, which then has mcc-compiled MATLAB libraries linked to it. Specifically, my program reads a config file for the names of the various matlab programs, and other information. It then uses that information to present choices to the student. So, If an assignment changes, is added or removed, then all you have to do is change the config file. The idea is that next, the program invokes the correct matlab library that has been compiled with mcc. But, that means that the libraries have to be recompiled if a grader gets changed. Worse, the whole program must be recompiled if a grader is added or removed. So, I would like one, simple, unchanging matlab library function to call the grader m-files directly. I currently have such a library, that uses eval on a string passed to it from the main program. The problem is that when I do this, apparently, mcc absorbs the grader m-code into itself; changing the grader m code after compilation has no effect. I would like for this not to happen. It was brought to my attention that Mathworks may not want me to be able to do this, since it could bypass matlab entirely. That is not my intention, and I would be happy with a solution that requires a full matlab install. My possible solutions are to use a mex file for the main program, or have the main program call a mcc library, which then calls a mex file, which then calls the proper grader. The reason I am hesitant about the first solution is that I'm not sure how many changes I would have to make to my code to make it work; my code is C++, not C, which I think makes things more complicated. The 2nd solution, though, may just be more complicated and ultimately have the same problem. So, any thoughts on this situation? How should I do this?

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• How can a C/C++ program put itself into background?

  - by Larry Gritz

  What's the best way for a running C or C++ program that's been launched from the command line to put itself into the background, equivalent to if the user had launched from the unix shell with '&' at the end of the command? (But the user didn't.) It's a GUI app and doesn't need any shell I/O, so there's no reason to tie up the shell after launch. But I want a shell command launch to be auto-backgrounded without the '&' (or on Windows). Ideally, I want a solution that would work on any of Linux, OS X, and Windows. (Or separate solutions that I can select with #ifdef.) It's ok to assume that this should be done right at the beginning of execution, as opposed to somewhere in the middle. One solution is to have the main program be a script that launches the real binary, carefully putting it into the background. But it seems unsatisfying to need these coupled shell/binary pairs. Another solution is to immediately launch another executed version (with 'system' or CreateProcess), with the same command line arguments, but putting the child in the background and then having the parent exit. But this seems clunky compared to the process putting itself into background. Edited after a few answers: Yes, a fork() (or system(), or CreateProcess on Windows) is one way to sort of do this, that I hinted at in my original question. But all of these solutions make a SECOND process that is backgrounded, and then terminate the original process. I was wondering if there was a way to put the EXISTING process into the background. One difference is that if the app was launched from a script that recorded its process id (perhaps for later killing or other purpose), the newly forked or created process will have a different id and so will not be controllable by any launching script, if you see what I'm getting at. Edit #2: fork() isn't a good solution for OS X, where the man page for 'fork' says that it's unsafe if certain frameworks or libraries are being used. I tried it, and my app complains loudly at runtime: "The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec()." I was intrigued by daemon(), but when I tried it on OS X, it gave the same error message, so I assume that it's just a fancy wrapper for fork() and has the same restrictions. Excuse the OS X centrism, it just happens to be the system in front of me at the moment. But I am indeed looking for a solution to all three platforms.

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• Visual studio 2010 colourizers, intellisense and the rest. Where to start!!

  - by Owen

  Ok, before I begin I realize that there is a lot of documentation on this subject but I have thus far failed to get even basic colourization working for VS2010. My goal is to simply get to a point where I can open a document and everything is coloured red, from here I can implement the relevant parsing logic. Here's what I have tried/found: 1) Downloaded all the relevent SDK's and such- Found the ook sample (http://code.msdn.microsoft.com/ookLanguage) - didn't build, didn't work. 2) Knowing almost nothing about MEF read through "Implementing a Language Service By Using the Managed Package Framework" - http://msdn.microsoft.com/en-us/library/bb166533(v=VS.100).aspx This was pretty much a copy and paste of all the basic stuff here, and also updating some references which were out of date with the sample see: http://social.msdn.microsoft.com/Forums/en-US/vsx/thread/a310fe67-afd2-4592-b295-3fc86fec7996 Now, I have got to a point where when running the package MEF appears to have hooked up correctly (I know this because with the debugger open I can see that the packages initialize and FDoIdle methods are being hit). When I open a file of the extension I have registered with the ProvideLanguageExtensionAttribute everything dies as if in an endless loop, yet no debug symbols hit (though they are loaded). Looking at the ook sample and the MEF examples they seem to be totally different approaches to the same problem. In the ook sample there are notions of Clasifications and Completion controllers which aren't mentioned in the MEF example. Also, they don't seem to create a Package or Language service, so I have no idea how it should work? With the MEF example, my assumption is that I need to hook into the "IScanner.ScanTokenAndProvideInfoAboutIt" to provide syntax highlighting? Which would be fine if I could ever hit this method. So my first question I guess is which approach should I be taking here? Or do they both somehow tie together? My second questions is, where can I find a basic fully working project that implements bog standard basic syntax highlighting and intellisense or VS2010? Thirdly, in the MEF example when I created a Package there were a bunch of test projects created for me. I appears that the integration tests launch the VS2010 test rig somehow, but the test fails. It would be good to write my service with tests but I have no idea what/how I can test each interaction so any references to testing Language services would be helpful. Finally, please throw any resource/book links my way that I may find useful. Cheers, Chris. N.B. Sorry I realize this is part question part rant, but I have never been so confused.

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• Local and global variables in javascript

  - by caramel1991

  Today,I started to code a page that prompt the user to choose their PC spec,and the code is as follow <html> <title>Computer Specification Chooser</title> <head> <script type="text/javascript"> var compSpec = document.compChooser; function processorUnavailable_onclick() { alert("Sorry that processor speed is currently unavailable"); compSpec.processor[2].checked = true; } </script> </head> <body> <form name="compChooser"> <p>Tick all components you wan included on your computer</p> <p> DVD-ROM <input type="checkbox" name="chkDVD" value="DVD-ROM" /> <br /> CD-ROM <input type="checkbox" name="chkCD" value="CD-ROM" /> <br /> Zip Drive <input type="checkbox" name="chkZIP" value="ZIP DRIVE" /> </p> <p> Select the processor speed you require <br /> <input type="radio" name="processor" value="3.8" /> 3.8 GHZ <input type="radio" name="processor" value="4.8" onclick="processorUnavailable_onclick()" /> 4.8 GHZ <input type="radio" name="processor" value="6" /> 6 GHZ </p> <input type="button" name="btnCheck" value="Check Form" /> </form> </body> </html> The problem I'm facing is on the function that I've tie to the event handler,when I try to choose the radio button of the processor value 4.8 GHZ,yes it alert me with the message inside the function,but after that,it doest not execute the next statement inside the function,that is to check the next processor value 6 GHZ. I've try my effort to change it and test on it,and find out when I set the var compSpec = document.compChooser as a local variable inside the function instead of a global variable,the next statement could be executed. But I thought for a global variable,it is accessible in everywhere on the page and also inside a function.But why now I can't accesses it inside my function??Any idea?? Besides,I stumble upon a weird article while googling,it says that when a global variable is created,it is added to window object.I just curious why this happen??And what's the benefits and uses of it?? THANK YOU

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• Quetion regarding local and global variable in javascript

  - by caramel1991

  Today,I started to code a page that prompt the user to choose their PC spec,and the code is as follow <html> <title>Computer Specification Chooser</title> <head> <script type="text/javascript"> var compSpec = document.compChooser; function processorUnavailable_onclick() { alert("Sorry that processor speed is currently unavailable"); compSpec.processor[2].checked = true; } </script> </head> <body> <form name="compChooser"> <p>Tick all components you wan included on your computer</p> <p> DVD-ROM <input type="checkbox" name="chkDVD" value="DVD-ROM" /> <br /> CD-ROM <input type="checkbox" name="chkCD" value="CD-ROM" /> <br /> Zip Drive <input type="checkbox" name="chkZIP" value="ZIP DRIVE" /> </p> <p> Select the processor speed you require <br /> <input type="radio" name="processor" value="3.8" /> 3.8 GHZ <input type="radio" name="processor" value="4.8" onclick="processorUnavailable_onclick()" /> 4.8 GHZ <input type="radio" name="processor" value="6" /> 6 GHZ </p> <input type="button" name="btnCheck" value="Check Form" /> </form> </body> </html> The problem I'm facing is on the function that I've tie to the event handler,when I try to choose the radio button of the processor value 4.8 GHZ,yes it alert me with the message inside the function,but after that,it doest not execute the next statement inside the function,that is to check the next processor value 6 GHZ,I've try my effort to change it and test on it,and find out when I set the var compSpec = document.compChooser as a local variable inside the function instead of a global variable,the next statement could be executed.But I thought for a global variable,it is accessible in everywhere on the page and also inside a function.But why now I can't accesses it inside my function??Any idea??Besides,I stumble upon a weird article while googling,it says that when a global variable is created,it is added to window object.I just curious why this happen??And what's the benefits and uses of it??THANK YOU

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• Can't get jQuery to get focus on cloned input fields

  - by Rebel1Moon

  I have a page that needs to create dynamic form fields as often as the user needs, and I am trying to use Ajax to tie it in to my database for faster form entry and to prevent user typos. So, I have put my Ajax returned data into popup div, the user selects, then the form field is filled in. The problem comes on the cloned fields. They don't seem to want to bring up the popup div when focused. I am thinking it is something to do with when they get created/added to the DOM. Here is my JS that creates the clones: $(document).ready(function() { var regex = /^(.*)(\d)+$/i; var cloneIndex = $(".clonedInput").length; $("button.clone").live("click", function(){ $(this).parents(".clonedInput").clone() .appendTo("#course_container") .attr("id", "clonedInput" + cloneIndex) .find("*").each(function() { var id = this.id || ""; var match = id.match(regex) || []; if (match.length == 3) { this.id = match[1] + (cloneIndex); } }); cloneIndex++; numClones=cloneIndex-1; //alert("numClones "+numClones); }); Here is where I expect to be able to get focus on the correct cloned field and call the popup. The baker_equiv0 id is original code, whereas baker_equiv1 is the first clone. $('#baker_equiv0').focus(function() { \\ THIS CODE WORKS $('.popup').fadeIn(500); $('#results').empty(); // document.enter_data.baker_equiv1.value="test"; THIS LINE WORKS //alert("numClones "+numClones); }); $('#baker_equiv1').focus(function() { // THIS DOESN'T EVER FIRE alert("numClones "+numClones); $('.popup').fadeIn(500); $('#results').empty(); }); Here is the HTML with the form: <label for="baker_equiv" class="">Baker Equivalent: <span class="requiredField">*</span></label> <input type="text" class="cinputsa" name="baker_equiv[]" id="baker_equiv0" size="8" ONKEYUP="get_equiv(this.value);"> If I put this in the HTML code above, it works fine: onfocus="alert(this.id)" I'd also be interested in how to adjust the JS code to work based on the id array created rather than having to copy code for each potential set of fields clones, i.e., baker_equiv[] rather than baker_equiv0, baker_equiv1, etc. Thanks all!

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• Network authentication + roaming home directory - which technology should I look into using?

  - by Brian

  I'm looking into software which provides a user with a single identity across multiple computers. That is, a user should have the same permissions on each computer, and the user should have access to all of his or her files (roaming home directory) on each computer. There seem to be many solutions for this general idea, but I'm trying to determine the best one for me. Here are some details along with requirements: The network of machines are Amazon EC2 instances running Ubuntu. We access the machines with SSH. Some machines on this LAN may have different uses, but I am only discussing machines for a certain use (running a multi-tenancy platform). The system will not necessarily have a constant amount of machines. We may have to permanently or temporarily alter the amount of machines running. This is the the reason why I'm looking into centralized authentication/storage. The implementation of this effect should be a secure one. We're unsure if users will have direct shell access, but their software will potentially be running (under restricted Linux user names, of course) on our systems, which is as good as direct shell access. Let's assume that their software could potentially be malicious for the sake of security. I have heard of several technologies/combinations to achieve my goal, but I'm unsure of the ramifications of each. An older ServerFault post recommended NFS & NIS, though the combination has security problems according to this old article by Symantec. The article suggests moving to NIS+, but, as it is old, this Wikipedia article has cited statements suggesting a trending away from NIS+ by Sun. The recommended replacement is another thing I have heard of... LDAP. It looks like LDAP can be used to save user information in a centralized location on a network. NFS would still need to be used to cover the 'roaming home folder' requirement, but I see references of them being used together. Since the Symantec article pointed out security problems in both NIS and NFS, is there software to replace NFS, or should I heed that article's suggestions for locking it down? I'm tending toward LDAP because another fundamental piece of our architecture, RabbitMQ, has a authentication/authorization plugin for LDAP. RabbitMQ will be accessible in a restricted manner to users on the system, so I would like to tie the security systems together if possible. Kerberos is another secure authentication protocol that I have heard of. I learned a bit about it some years ago in a cryptography class but don't remember much about it. I have seen suggestions online that it can be combined with LDAP in several ways. Is this necessary? What are the security risks of LDAP without Kerberos? I also remember Kerberos being used in another piece of software developed by Carnegie Mellon University... Andrew File System, or AFS. OpenAFS is available for use, though its setup seems a bit complicated. At my university, AFS provides both requirements... I can log in to any machine, and my "AFS folder" is always available (at least when I acquire an AFS token). Along with suggestions for which path I should look into, does anybody have any guides which were particularly helpful? As the bold text pointed out, LDAP looks to be the best choice, but I'm particularly interested in the implementation details (Keberos? NFS?) with respect to security.

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• Run Your Tests With Any NUnit Version

  - by Alois Kraus

  I always thought that the NUnit test runners and the test assemblies need to reference the same NUnit.Framework version. I wanted to be able to run my test assemblies with the newest GUI runner (currently 2.5.3). Ok so all I need to do is to reference both NUnit versions the newest one and the official for the current project. There is a nice article form Kent Bogart online how to reference the same assembly multiple times with different versions. The magic works by referencing one NUnit assembly with an alias which does prefix all types inside it. Then I could decorate my tests with the TestFixture and Test attribute from both NUnit versions and everything worked fine except that this was ugly. After playing a little bit around to make it simpler I found that I did not need to reference both NUnit.Framework assemblies. The test runners do not require the TestFixture and Test attribute in their specific version. That is really neat since the test runners are instructed by attributes what to do in a declarative way there is really no need to tie the runners to a specific version. At its core NUnit has this little method hidden to find matching TestFixtures and Tests   public bool CanBuildFrom(Type type) {     if (!(!type.IsAbstract || type.IsSealed))     {         return false;     }     return (((Reflect.HasAttribute(type,           "NUnit.Framework.TestFixtureAttribute", true) ||               Reflect.HasMethodWithAttribute(type, "NUnit.Framework.TestAttribute"       , true)) ||               Reflect.HasMethodWithAttribute(type, "NUnit.Framework.TestCaseAttribute"   , true)) ||               Reflect.HasMethodWithAttribute(type, "NUnit.Framework.TheoryAttribute"     , true)); } That is versioning and backwards compatibility at its best. I tell NUnit what to do by decorating my tests classes with NUnit Attributes and the runner executes my intent without the need to bind me to a specific version. The contract between NUnit versions is actually a bit more complex (think of AssertExceptions) but this is also handled nicely by using not the concrete type but simply to check for the catched exception type by string. What can we learn from this? Versioning can be easy if the contract is small and the users of your library use it in a declarative way (Attributes). Everything beyond it will force you to reference several versions of the same assembly with all its consequences. Type equality is lost between versions so none of your casts will work. That means that you cannot simply use IBigInterface in two versions. You will need a wrapper to call the correct versioned one. To get out of this mess you can use one (and only one) version agnostic driver to encapsulate your business logic from the concrete versions. This is of course more work but as NUnit shows it can be easy. Simplicity is therefore not a nice thing to have but also requirement number one if you intend to make things more complex in version two and want to support any version (older and newer). Any interaction model above easy will not be maintainable. There are different approached to versioning. Below are my own personal observations how versioning works within the  .NET Framwork and NUnit.   Versioning Models 1. Bug Fixing and New Isolated Features When you only need to fix bugs there is no need to break anything. This is especially true when you have a big API surface. Microsoft did this with the .NET Framework 3.0 which did leave the CLR as is but delivered new assemblies for the features WPF, WCF and Windows Workflow Foundations. Their basic model was that the .NET 2.0 assemblies were declared as red assemblies which must not change (well mostly but each change was carefully reviewed to minimize the risk of breaking changes as much as possible) whereas the new green assemblies of .NET 3,3.5 did not have such obligations since they did implement new unrelated features which did not have any impact on the red assemblies. This is versioning strategy aimed at maximum compatibility and the delivery of new unrelated features. If you have a big API surface you should strive hard to do the same or you will break your customers code with every release. 2. New Breaking Features There are times when really new things need to be added to an existing product. The .NET Framework 4.0 did change the CLR in many ways which caused subtle different behavior although the API´s remained largely unchanged. Sometimes it is possible to simply recompile an application to make it work (e.g. changed method signature void Func() –> bool Func()) but behavioral changes need much more thought and cannot be automated. To minimize the impact .NET 2.0,3.0,3.5 applications will not automatically use the .NET 4.0 runtime when installed but they will keep using the “old” one. What is interesting is that a side by side execution model of both CLR versions (2 and 4) within one process is possible. Key to success was total isolation. You will have 2 GCs, 2 JIT compilers, 2 finalizer threads within one process. The two .NET runtimes cannot talk  (except via the usual IPC mechanisms) to each other. Both runtimes share nothing and run independently within the same process. This enables Explorer plugins written for the CLR 2.0 to work even when a CLR 4 plugin is already running inside the Explorer process. The price for isolation is an increased memory footprint because everything is loaded and running two times.   3. New Non Breaking Features It really depends where you break things. NUnit has evolved and many different Assert, Expect… methods have been added. These changes are all localized in the NUnit.Framework assembly which can be easily extended. As long as the test execution contract (TestFixture, Test, AssertException) remains stable it is possible to write test executors which can run tests written for NUnit 10 because the execution contract has not changed. It is possible to write software which executes other components in a version independent way but this is only feasible if the interaction model is relatively simple.   Versioning software is hard and it looks like it will remain hard since you suddenly work in a severely constrained environment when you try to innovate and to keep everything backwards compatible at the same time. These are contradicting goals and do not play well together. The easiest way out of this is to carefully watch what your customers are doing with your software. Minimizing the impact is much easier when you do not need to guess how many people will be broken when this or that is removed.

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• Silverlight Recruiting Application Part 4 - Navigation and Modules

  After our brief intermission (and the craziness of Q1 2010 release week), we're back on track here and today we get to dive into how we are going to navigate through our applications as well as how to set up our modules. That way, as I start adding the functionality- adding Jobs and Applicants, Interview Scheduling, and finally a handy Dashboard- you'll see how everything is communicating back and forth. This is all leading up to an eventual webinar, in which I'll dive into this process and give a honest look at the current story for MVVM vs. Code-Behind applications. (For a look at the future with SL4 and a little thing called MEF, check out what Ross is doing over at his blog!) Preamble... Before getting into really talking about this app, I've done a little bit of work ahead of time to create a ton of files that I'll need. Since the webinar is going to cover the Dashboard, it's not here, but otherwise this is a look at what the project layout looks like (and remember, this is both projects since they share the .Web): So as you can see, from an architecture perspective, the code-behind app is much smaller and more streamlined- aka a better fit for the one man shop that is me. Each module in the MVVM app has the same setup, which is the Module class and corresponding Views and ViewModels. Since the code-behind app doesn't need a go-between project like Infrastructure, each MVVM module is instead replaced by a single Silverlight UserControl which will contain all the logic for each respective bit of functionality. My Very First Module Navigation is going to be key to my application, so I figured the first thing I would setup is my MenuModule. First step here is creating a Silverlight Class Library named MenuModule, creatingthe View and ViewModel folders, and adding the MenuModule.cs class to handle module loading. The most important thing here is that my MenuModule inherits from IModule, which runs an Initialize on each module as it is created that, in my case, adds the views to the correct regions. Here's the MenuModule.cs code: public class MenuModule : IModule { private readonly IRegionManager regionManager; private readonly IUnityContainer container; public MenuModule(IUnityContainer container, IRegionManager regionmanager) { this.container = container; this.regionManager = regionmanager; } public void Initialize() { var addMenuView = container.Resolve<MenuView>(); regionManager.Regions["MenuRegion"].Add(addMenuView); } } Pretty straightforward here... We inject a container and region manager from Prism/Unity, then upon initialization we grab the view (out of our Views folder) and add it to the region it needs to live in. Simple, right? When the MenuView is created, the only thing in the code-behind is a reference to the set the MenuViewModel as the DataContext. I'd like to achieve MVVM nirvana and have zero code-behind by placing the viewmodel in the XAML, but for the reasons listed further below I can't. Navigation - MVVM Since navigation isn't the biggest concern in putting this whole thing together, I'm using the Button control to handle different options for loading up views/modules. There is another reason for this- out of the box, Prism has command support for buttons, which is one less custom command I had to work up for the functionality I would need. This comes from the Microsoft.Practices.Composite.Presentation assembly and looks as follows when put in code: <Button x:Name="xGoToJobs" Style="{StaticResource menuStyle}" Content="Jobs" cal:Click.Command="{Binding GoModule}" cal:Click.CommandParameter="JobPostingsView" /> For quick reference, 'menuStyle' is just taking care of margins and spacing, otherwise it looks, feels, and functions like everyone's favorite Button. What MVVM's this up is that the Click.Command is tying to a DelegateCommand (also coming fromPrism) on the backend. This setup allows you to tie user interaction to a command you setup in your viewmodel, which replaces the standard event-based setup you'd see in the code-behind app. Due to databinding magic, it all just works. When we get looking at the DelegateCommand in code, it ends up like this: public class MenuViewModel : ViewModelBase { private readonly IRegionManager regionManager; public DelegateCommand<object> GoModule { get; set; } public MenuViewModel(IRegionManager regionmanager) { this.regionManager = regionmanager; this.GoModule = new DelegateCommand<object>(this.goToView); } public void goToView(object obj) { MakeMeActive(this.regionManager, "MainRegion", obj.ToString()); } } Another for reference, ViewModelBase takes care of iNotifyPropertyChanged and MakeMeActive, which switches views in the MainRegion based on the parameters. So our public DelegateCommand GoModule ties to our command on the view, that in turn calls goToView, and the parameter on the button is the name of the view (which we pass with obj.ToString()) to activate. And how do the views get the names I can pass as a string? When I called regionManager.Regions[regionname].Add(view), there is an overload that allows for .Add(view, "viewname"), with viewname being what I use to activate views. You'll see that in action next installment, just wanted to clarify how that works. With this setup, I create two more buttons in my MenuView and the MenuModule is good to go. Last step is to make sure my MenuModule loads in my Bootstrapper: protected override IModuleCatalog GetModuleCatalog() { ModuleCatalog catalog = new ModuleCatalog(); // add modules here catalog.AddModule(typeof(MenuModule.MenuModule)); return catalog; } Clean, simple, MVVM-delicious. Navigation - Code-Behind Keeping with the history of significantly shorter code-behind sections of this series, Navigation will be no different. I promise. As I explained in a prior post, due to the one-project setup I don't have to worry about the same concerns so my menu is part of MainPage.xaml. So I can cheese-it a bit, though, since I've already got three buttons all set I'm just copying that code and adding three click-events instead of the command/commandparameter setup: <!-- Menu Region --> <StackPanel Grid.Row="1" Orientation="Vertical"> <Button x:Name="xJobsButton" Content="Jobs" Style="{StaticResource menuStyleCB}" Click="xJobsButton_Click" /> <Button x:Name="xApplicantsButton" Content="Applicants" Style="{StaticResource menuStyleCB}" Click="xApplicantsButton_Click" /> <Button x:Name="xSchedulingModule" Content="Scheduling" Style="{StaticResource menuStyleCB}" Click="xSchedulingModule_Click" /> </StackPanel> Simple, easy to use events, and no extra assemblies required! Since the code for loading each view will be similar, we'll focus on JobsView for now.The code-behind with this setup looks something like... private JobsView _jobsView; public MainPage() { InitializeComponent(); } private void xJobsButton_Click(object sender, RoutedEventArgs e) { if (MainRegion.Content.GetType() != typeof(JobsView)) { if (_jobsView == null) _jobsView = new JobsView(); MainRegion.Content = _jobsView; } } What am I doing here? First, for each 'view' I create a private reference which MainPage will hold on to. This allows for a little bit of state-maintenance when switching views. When a button is clicked, first we make sure the 'view' typeisn't active (why load it again if it is already at center stage?), then we check if the view has been created and create if necessary, then load it up. Three steps to switching views and is easy as pie. Part 4 Results The end result of all this is that I now have a menu module (MVVM) and a menu section (code-behind) that load their respective views. Since I'm using the same exact XAML (except with commands/events depending on the project), the end result for both is again exactly the same and I'll show a slightly larger image to show it off: Next time, we add the Jobs Module and wire up RadGridView and a separate edit page to handle adding and editing new jobs. That's when things get fun. And somewhere down the line, I'll make the menu look slicker. :) Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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