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  • unable to start regionservers in HBase

    - by amsal
    I have a problem starting regionservers on slave PCs. When I enlist only master PC in conf/regionservers everything works fine but when I add two more slaves to it the hbase does not start. If I delete all hbase folders in the tmp folder from all PCs and then start regionserver (with 3 regionservers enlisted) the hbase gets started but when I try to create a table it again fails (gets stuck). I am using hadoop 0.20.0 which is working fine and hbase 0.92.0. I have 3 PCs in cluster, one master and two slaves. Also tell that is DNS (both forward and backward lookup working) necessary for hbase in my case? Is there any way to replicate hbase table to all region servers? I.e. I want to have a copy of table at each PC and want to access them locally (when I execute map task they should use their local copy of hbase table).

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  • Database Context and Singleton injection with IoC

    - by zaitsman
    All of the below relates to a ASP.NET c# app. I have a Singleton Settings MemoryCache that reads values from database on first access and caches these, then invalidates them using SQL Service Broker message and re-reads as required. For the purposes of standard controllers, i create my Db Context in a request scope. However, this obviously means that i can't use the same context in the Settings Cache class, since that is a singleton and we have a scope collision. At the moment, i ended up with two db contexts - the Controllers get it via IoC container, whereas a Singleton just creates it's own. However, i am not satisfied with this approach (mostly due to the way i feel about two contexts, the cache doesn't set anything on the db hence concurrency is not an issue as much). What is a better way to do it?

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  • What is the difference from the push and pull development models?

    - by michelpm
    I was reading Extreme Programming Explained, Second Edition and in the chapter 11 "The Theory of Constraints" the authors talk about the old and obsolete "push" development model and the XP way, the "pull" development model. It looks like a quite important concept, but it takes only a very small paragraph and two images that are mere illustrations of the "waterfall" and iterative process, nothing specific about these models except by the image caption. I searched and it doesn't go any further about it in the rest of the book. I couldn't find any further explanations or discussions about it in the Internet either. If the only difference about those is that one is "waterfall" and the other is iterative, them why push and why pull? Does anyone understand what is really the difference between those two and give some good examples?

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  • Update Manager Partitions

    - by user170585
    Perhaps this is completely stupid, but here's my inquiry: I have Ubuntu 12.04 installed on an external hard drive. On that HD there are 4 partitions. Two for operating systems, two for swap (unnecessary but I like it that way). The actual computer itself has Windows 7. If I use the Update manager to update to 12.10 or even 13.04, would the new Ubuntu install itself on the same partition it already was on? The other operating system I'm running on the Hard Drive is Lubuntu, for when I need to run Linux on older computers, if that matters. Thanks, Adam

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  • Developing a search algorithm

    - by Richart Bremer
    I want to create a basic search engine, and I want you to give me some ideas how to filter out the best results for my visitors. I have three fields regarding a product the user can search in: Title Category Description I came up with these ideas and I ask you to either competently criticize them or add to them. If the search term occurs in all three fields it should be among the first results. If it is in two of the fields it is below the results of 1. Combine the amount of occurences and output a value in per cent. For instance if in all fields together the term clock appeared 50 times and in all fields together there are 200 words, then the per cent value is 50/200*100 = 25%. Another product entry amounts to say 20% so product one having 25% is listed before product two having 20%.

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  • What would you choose for your project between .NET and Java at this point in time ?

    - by Basic
    You are just starting a new project and you have these two technologies to choose from, Java and .NET. The project you are working doesn't involve having features that would make it easy to choose between the two technologies (e.g. .NET has this that I need and Java does not) and both of them should work just fine for you (though you only need one of course). Take into account: Performance Tools available (even 3rd party tools) Cross platform compatibility Libraries (especially 3rd party libraries) Cost (Oracle seems to try and monetize Java) Development process (Easiest/Fastest) Also keep in mind that Linux is not your main platform but you would like to port your project to Linux/MacOs as well. You should definitely keep in mind the trouble that has been revolving around Oracle and the Java community and the limitations of Mono and Java as well. It would be much appreciated if people with experience in both can give an overview and their own subjective view about which they would choose and why.

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  • What is the best taxonomy from Google's perspective?

    - by ZakGottlieb
    I was wondering what the best way is to structure a new website in Google's eyes. Currently, it contains two top-level categories (X & Y), and clicking a term under either one will result in the URL: www.nameofsite.com/X/X type term, or /Y/Y type term Technically, it is correct to group all "X type terms" under X and "Y type terms" under Y, but we could probably be more granular and break all articles into 5-6 top-level categories by breaking Y up into more specific categories. Given that the current URL structure will eventually result in 1000's of "X type terms" and "Y type terms" under just two top-level categories, would it be more advisable to have several of these, as suggested? Thank you in advance.

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  • Touchpad stop working

    - by Diegov
    I'm in a HP 430 PC-Notebook using Oneiric. And sometimes my touchpad just stop working :(... I haven't installed anything, just safe playing with terminal following linuxcommand.org BTW my touchpad has a "hole" that in Windows, it works like this: two touch, block touchpad, two touch, unblock. And as far as I now, Ubuntu hasn't recognize this function so I think that the "hole" is not the problem... Also, I'm pretty sure that I haven't touch a little that... PD: Spanish speaker, sorry if "hole" is not the appropriate term haha.. Thanks!

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  • TFS 2012 API Create Alert Subscriptions

    - by Bob Hardister
    Originally posted on: http://geekswithblogs.net/BobHardister/archive/2013/07/24/tfs-2012-api-create-alert-subscriptions.aspxThere were only a few post on this and I felt like really important information was left out: What the defaults are How to create the filter string Here’s the code to create the subscription. Get the Collection public TfsTeamProjectCollection GetCollection(string collectionUrl) { try { //connect to the TFS collection using the active user TfsTeamProjectCollection tpc = new TfsTeamProjectCollection(new Uri(collectionUrl)); tpc.EnsureAuthenticated(); return tpc; } catch (Exception) { return null; } } Use Impersonation Because my app is used to create “support tickets” as stories in TFS, I use impersonation so the subscription is setup for the “requester.”  That way I can take all the defaults for the subscription delivery preferences. public TfsTeamProjectCollection GetCollectionImpersonation(string collectionUrl, string impersonatingUserAccount) { // see: http://blogs.msdn.com/b/taylaf/archive/2009/12/04/introducing-tfs-impersonation.aspx try { TfsTeamProjectCollection tpc = GetCollection(collectionUrl); if (!(tpc == null)) { //get the TFS identity management service (v2 is 2012 only) IIdentityManagementService2 ims = tpc.GetService<IIdentityManagementService2>(); //look up the user we want to impersonate TeamFoundationIdentity identity = ims.ReadIdentity(IdentitySearchFactor.AccountName, impersonatingUserAccount, MembershipQuery.None, ReadIdentityOptions.None); //create a new connection using the impersonated user account //note: do not ensure authentication because the impersonated user may not have //windows authentication at execution if (!(identity == null)) { TfsTeamProjectCollection itpc = new TfsTeamProjectCollection(tpc.Uri, identity.Descriptor); return itpc; } else { //the user account is not found return null; } } else { return null; } } catch (Exception) { return null; } } Create the Alert Subscription public bool SetWiAlert(string collectionUrl, string projectName, int wiId, string emailAddress, string userAccount) { bool setSuccessful = false; try { //use impersonation so the event service creating the subscription will default to //the correct account: otherwise domain ambiguity could be a problem TfsTeamProjectCollection itpc = GetCollectionImpersonation(collectionUrl, userAccount); if (!(itpc == null)) { IEventService es = itpc.GetService(typeof(IEventService)) as IEventService; DeliveryPreference deliveryPreference = new DeliveryPreference(); //deliveryPreference.Address = emailAddress; deliveryPreference.Schedule = DeliverySchedule.Immediate; deliveryPreference.Type = DeliveryType.EmailHtml; //the following line does not work for two reasons: //string filter = string.Format("\"ID\" = '{0}' AND \"Authorized As\" <> '[Me]'", wiId); //1. the create fails because there is a space between Authorized As //2. the explicit query criteria are all incorrect anyway // see uncommented line for what does work: you have to create the subscription mannually // and then get it to view what the filter string needs to be (see following commented code) //this works string filter = string.Format("\"CoreFields/IntegerFields/Field[Name='ID']/NewValue\" = '12175'" + " AND \"CoreFields/StringFields/Field[Name='Authorized As']/NewValue\"" + " <> '@@MyDisplayName@@'", projectName, wiId); string eventName = string.Format("<PT N=\"ALM Ticket for Work Item {0}\"/>", wiId); es.SubscribeEvent("WorkItemChangedEvent", filter, deliveryPreference, eventName); ////use this code to get existing subscriptions: you can look at manually created ////subscriptions to see what the filter string needs to be //IIdentityManagementService2 ims = itpc.GetService<IIdentityManagementService2>(); //TeamFoundationIdentity identity = ims.ReadIdentity(IdentitySearchFactor.AccountName, // userAccount, // MembershipQuery.None, // ReadIdentityOptions.None); //var existingsubscriptions = es.GetEventSubscriptions(identity.Descriptor); setSuccessful = true; return setSuccessful; } else { return setSuccessful; } } catch (Exception) { return setSuccessful; } }

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  • ASP.NET GridView And TreeList: 2 Export Improvements v2010 vol 1

    Two very useful export enhancements have been added to the ASPxGridView and ASPxTreeList. Starting with DXperience v2010.1, you can change the exported column width size and export to the Excel 2007 XLSX document format: 1. Change Column Width To change the column width before exporting, use the ExportWidth property. This property has been added to both the GridViewColumn and TreeListDataColumn classes. 2. Excel XLSX Format Two new methods have been added to the ASPxGridViewExporter and ASPxTreeListExporter...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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  • And just like that, there went February

    - by Enrique Lima
    The best intentions were having me at perhaps posting more than twice a month, and here we are and … well it has been busy. There has been a lot of SharePoint 2010 already in this first number of weeks of the year, a good amount of TFS 2010, but even better working quite actively on two topics that I enjoy quite a bit … Windows Azure and Application Lifecycle Management.  And there is more to come around those two. Through the influencers program with Geekswithblogs and Discountasp.net I got access to a hosted TFS solution that I am currently testing and will be posting my findings and documenting a good amount of information on that process. Another great resource has been fpweb.net, and there will be more details on this too.  Pretty exciting stuff! That is what is going on and what will be coming on here shortly.

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  • What book do you recommend for the OCAJP certification (1Z0-803) and OCPJP (1Z0-804) [on hold]

    - by Muhammad Gelbana
    I find completely contradicting reviews for the VERY same book on amazon and even some book writers are rewarding people for good reviews so basically most of the reviews are totally fake ! You can even figure it out from the reviewer name, which you'll similar to the writer's name and assume that they could actually be from the same country and the reviewer is just being helpful, to the book writer of course ! I can't make my mind for which book I should buy ! I only need a book or two that covers the Java associate and professional topics very well, not just an overview, I need a material that covers everything from A to Z. Even though I've been developing in Java for around 4.5 years but I must not know a detail or two. Would someone kindly shed some light on a good book based on actual experience with the book ? THANK YOU !

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  • How is WPF Data Binding using Object Data Source in Visual Studio 2010 done?

    - by Rob Perkins
    This is probably mostly a question about how to use the VS 2010 IDE tools in a way the Microsofties didn't specifically intend. But since this is something I immediately tried without success. I have defined a .NET 4.0 WPF Application project with a simple class that looks like this: Public Class Class1 Public Property One As String = "OneString" Public Property Two As String = "TwoString" End Class I then defined it as an "Object Data Source" in VS2010, using the IDE's "Add New Data Source..." feature. This exposes the class members in a GUI element in the IDE as given in this image: Dragging "Class1" from that tool to the surface of "Window1.xaml" in a default "WPF Application" results in the design view looking like this: And generated XAML like this: <Window x:Class="Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="133" Width="170" xmlns:my="clr-namespace:WpfApplication1" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" > <Window.Resources> <CollectionViewSource x:Key="Class1ViewSource" d:DesignSource="{d:DesignInstance my:Class1, CreateList=True}" /> </Window.Resources> <Grid DataContext="{StaticResource Class1ViewSource}" HorizontalAlignment="Left" Name="Grid1" VerticalAlignment="Top"> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto" /> <ColumnDefinition Width="Auto" /> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto" /> <RowDefinition Height="Auto" /> </Grid.RowDefinitions> <Label Content="One:" Grid.Column="0" Grid.Row="0" HorizontalAlignment="Left" Margin="3" VerticalAlignment="Center" /> <TextBlock Grid.Column="1" Grid.Row="0" Height="23" HorizontalAlignment="Left" Margin="3" Name="OneTextBlock" Text="{Binding Path=One}" VerticalAlignment="Center" /> <Label Content="Two:" Grid.Column="0" Grid.Row="1" HorizontalAlignment="Left" Margin="3" VerticalAlignment="Center" /> <TextBlock Grid.Column="1" Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="3" Name="TwoTextBlock" Text="{Binding Path=Two}" VerticalAlignment="Center" /> </Grid> Note the data bindings Text="{Binding Path=One}" and Text="{Binding Path=Two}" in the TextBlock elements. Code-behind for Window1.xaml has this in Window_Loaded: Class Window1 Private m_c1 As New Class1 Private Sub Window1_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded Dim Class1ViewSource As System.Windows.Data.CollectionViewSource = CType(Me.FindResource("Class1ViewSource"), System.Windows.Data.CollectionViewSource) 'Load data by setting the CollectionViewSource.Source property: 'Class1ViewSource.Source = [generic data source] Me.DataContext = m_c1 End Sub End Class Running the application produces this output: The expected result was that "OneString" would appear next to "One" and "TwoString" next to "Two" in the running window. The question is: Why didn't this work? What will work instead? If I put bindings in a DataTemplate, it works. Blend, with its sample data stuff, implied that this should work, but it doesn't. I know I'm missing something pretty fundamental here; what is it?

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  • How to get IMediaControl.Run() to start a file playing with no delay

    - by MusiGenesis
    I am attempting to use DirectShow to play two AVI files consecutively (one after the other) so that there is no interruption in the audio or video when the player transitions from one file to the next. I have two custom controls on my form. Each one is pre-loaded with an AVI file, and before playback begins I set up all the DirectShow interfaces, set the video windows and resize them, call IMediaControl.Run(), then IMediaControl.Pause(), then IMediaSeeking.SetPositions to reset to frame 0, on both controls. On the form, you can see that both files are paused at their initial frames. I then call IMediaControl.Run() on the first control, and wait for it to complete before calling Run() on the second control. Initially, I hooked into the first video's EC_COMPLETE notification message, and used this to start the second. Thinking that this event might be slow to arrive (turns out it is, but for a weird reason), I tried two other approaches: Check the first video's current position inside a timer that goes off every second or so (using IMediaPosition.get_CurrentPosition). When the current position is within a second of the video's stop time (known in advance from IMediaPosition.get_StopTime), I go into a tight while loop and wait for the current position to equal the stop time, and then call Run() on the second video. Same as the first, except I replace the while loop with a call to timeSetEvent from winmm.dll, with a delay set so that it fires right when the first file is supposed to end. I use the callback to Run() the second file. Either of these two methods substantially cuts down the delay between the end of the first file and the beginning of the second, indicating that the EC_COMPLETE message doesn't arrive immediately after the file is complete (I also tried hooking the EC_SEGMENT_COMPLETE message, which is supposed to be used for looping within a file, but apparently nobody supports this - it never occurs on my machine, at least). Doing all of the above has cut the transition delay from as much as a second, down to a barely perceptible glitch; about a third of the time the files transition with no interruption at all, which suggests there's no fundamental reason I can't get this to work all the time. The slight delay is still unacceptable, unfortunately. I assume (and I could easily be wrong) that the remaining delay is due to a slight variable delay between the call to IMediaControl.Run() and when the video actually starts playing. Does anybody know anything I can do to eliminate this little lag? It would also help to be told this is fundamentally impossible for whatever reason, which wouldn't surprise me. I've never encountered a video player in Windows that doesn't have this problem, so it may not be doable. More info: the AVI files I'm playing are completely uncompressed (video and audio are uncompressed), so I don't think the lag is due to DirectShow's having to uncompress the video ahead of play start, although it may still buffer ahead as matter of course (and this may be the source of the problem). I would have though that starting play, pausing and then rewinding to the beginning would fix this. Also, the way I'm handling the transition is to actually have the second control underneath the first; when the first completes playing, I start the second and then call BringToFront on it, creating the appearance of a single video transitioning between the two originals. I don't think the glitch is due to this, because it works perfectly some of the time, and even if this were problematic, it wouldn't explain the matching audio glitch. Even more: I just tried starting the second video 30-50 milliseconds "early" and that seemed to eliminate even more of the gap, so I'm guessing that the lag in Run() is about that long. It appears to be variable, though, so this is still not where I need it to be.

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  • WebSphere Application Server EJB Optimization

    - by Chris Aldrich
    We are working on developing a Java EE based application. Our application is Java 1.5 compatible and will be deployed to WAS ND 6.1.0.21 with EBJ 3.0 and Web Services feature packs. The configuration is currently one cell with two clusters. Each cluster will have two nodes. Our application, or our system, as I should rather say, comes in two or three parts. Part 1: An ear deployed to one cluster that contains 3rd party vendor code combined with customization code. Their code is EJB 2.0 compliant and has a lot of Remote Home interfaces. Part 2: An ear deployed to the same cluster as the first ear. This ear contains EBJ 3's that make calls into the EJB 2's supplied by the vendor and the custom code. These EJB 3's are used by the JSF UI also packaged with the EAR, and some of them are also exposed as web services (JAX-WS 2.0 with SOAP 1.2 compliance) for other clients. Part 3: There may be other services that do not depend on our vendor/custom code app. These services will be EJB 3.0's and web services that are deployed to the other cluster. Per a recommendation from some IBM staff on site here, communication between nodes in a cluster can be EJB RMI. But if we are going across clusters and/or other cells, then the communication should be web services. That said, some of us are wondering about performance and optimizing communication for speed of our applications that will use our web services and EJB's. Right now most EJB's are exposed as remote. (and our vendor set theirs up that way, rather than also exposing local home interfaces). We are wondering if WAS does any optimizations between apps in the same node/cluster node space. If two apps are installed in the same area and they call each other via remote home interface, is WAS smart enough to make it a local home interface call? Are their other optimization techniques? Should we consider them? Should we not? What are the costs/benefits? Here is the question from one of our team members as sent in their email: The question is: Supposing we develop our EJBs as remote EJBs, where our UI controller code is talking to our EXT java services via EJB3...what are our options for performance optimization when both the EJB server and client are running in the same container? As one point of reference, google has given me some oooooold websphere performance tuning documentation from 2000 that explains a tuning configuration you can set to enable Call By Reference for EJB communication when they're in the same application server JVM. It states the following: Because EJBs are inherently location independent, they use a remote programming model. Method parameters and return values are serialized over RMI-IIOP and returned by value. This is the intrinsic RMI "Call By Value" model. WebSphere provides the "No Local Copies" performance optimization for running EJBs and clients (typically servlets) in the same application server JVM. The "No Local Copies" option uses "Call By Reference" and does not create local proxies for called objects when both the client and the remote object are in the same process. Depending on your workload, this can result in a significant overhead savings. Configure "No Local Copies" by adding the following two command line parameters to the application server JVM: * -Djavax.rmi.CORBA.UtilClass=com.ibm.CORBA.iiop.Util * -Dcom.ibm.CORBA.iiop.noLocalCopies=true CAUTION: The "No Local Copies" configuration option improves performance by changing "Call By Value" to "Call By Reference" for clients and EJBs in the same JVM. One side effect of this is that the Java object derived (non-primitive) method parameters can actually be changed by the called enterprise bean. Consider Figure 16a: Also, we will also be using Process Server 6.2 and WESB 6.2 as well in the future. Any ideas? recommendations? Thanks

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  • Minimum-Waste Print Job Grouping Algorithm?

    - by Matt Mc
    I work at a publishing house and I am setting up one of our presses for "ganging", in other words, printing multiple jobs simultaneously. Given that different print jobs can have different quantities, and anywhere from 1 to 20 jobs might need to be considered at a time, the problem would be to determine which jobs to group together to minimize waste (waste coming from over-printing on smaller-quantity jobs in a given set, that is). Given the following stable data: All jobs are equal in terms of spatial size--placement on paper doesn't come into consideration. There are three "lanes", meaning that three jobs can be printed simultaneously. Ideally, each lane has one job. Part of the problem is minimizing how many lanes each job is run on. If necessary, one job could be run on two lanes, with a second job on the third lane. The "grouping" waste from a given set of jobs (let's say the quantities of them are x, y and z) would be the highest number minus the two lower numbers. So if x is the higher number, the grouping waste would be (x - y) + (x - z). Otherwise stated, waste is produced by printing job Y and Z (in excess of their quantities) up to the quantity of X. The grouping waste would be a qualifier for the given set, meaning it could not exceed a certain quantity or the job would simply be printed alone. So the question is stated: how to determine which sets of jobs are grouped together, out of any given number of jobs, based on the qualifiers of 1) Three similar quantities OR 2) Two quantities where one is approximately double the other, AND with the aim of minimal total grouping waste across the various sets. (Edit) Quantity Information: Typical job quantities can be from 150 to 350 on foreign languages, or 500 to 1000 on English print runs. This data can be used to set up some scenarios for an algorithm. For example, let's say you had 5 jobs: 1000, 500, 500, 450, 250 By looking at it, I can see a couple of answers. Obviously (1000/500/500) is not efficient as you'll have a grouping waste of 1000. (500/500/450) is better as you'll have a waste of 50, but then you run (1000) and (250) alone. But you could also run (1000/500) with 1000 on two lanes, (500/250) with 500 on two lanes and then (450) alone. In terms of trade-offs for lane minimization vs. wastage, we could say that any grouping waste over 200 is excessive. (End Edit) ...Needless to say, quite a problem. (For me.) I am a moderately skilled programmer but I do not have much familiarity with algorithms and I am not fully studied in the mathematics of the area. I'm I/P writing a sort of brute-force program that simply tries all options, neglecting any option tree that seems to have excessive grouping waste. However, I can't help but hope there's an easier and more efficient method. I've looked at various websites trying to find out more about algorithms in general and have been slogging my way through the symbology, but it's slow going. Unfortunately, Wikipedia's articles on the subject are very cross-dependent and it's difficult to find an "in". The only thing I've been able to really find would seem to be a definition of the rough type of algorithm I need: "Exclusive Distance Clustering", one-dimensionally speaking. I did look at what seems to be the popularly referred-to algorithm on this site, the Bin Packing one, but I was unable to see exactly how it would work with my problem. Any help is appreciated. :)

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  • Parallel processing via multithreading in Java

    - by Robz
    There are certain algorithms whose running time can decrease significantly when one divides up a task and gets each part done in parallel. One of these algorithms is merge sort, where a list is divided into infinitesimally smaller parts and then recombined in a sorted order. I decided to do an experiment to test whether or not I could I increase the speed of this sort by using multiple threads. I am running the following functions in Java on a Quad-Core Dell with Windows Vista. One function (the control case) is simply recursive: // x is an array of N elements in random order public int[] mergeSort(int[] x) { if (x.length == 1) return x; // Dividing the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Sending them off to continue being divided mergeSort(a); mergeSort(b); // Recombining the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } return x; } The other is in the 'run' function of a class that extends thread, and recursively creates two new threads each time it is called: public class Merger extends Thread { int[] x; boolean finished; public Merger(int[] x) { this.x = x; } public void run() { if (x.length == 1) { finished = true; return; } // Divide the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Begin two threads to continue to divide the array Merger ma = new Merger(a); ma.run(); Merger mb = new Merger(b); mb.run(); // Wait for the two other threads to finish while(!ma.finished || !mb.finished) ; // Recombine the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } finished = true; } } It turns out that function that does not use multithreading actually runs faster. Why? Does the operating system and the java virtual machine not "communicate" effectively enough to place the different threads on different cores? Or am I missing something obvious?

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  • One letter game problem?

    - by Alex K
    Recently at a job interview I was given the following problem: Write a script capable of running on the command line as python It should take in two words on the command line (or optionally if you'd prefer it can query the user to supply the two words via the console). Given those two words: a. Ensure they are of equal length b. Ensure they are both words present in the dictionary of valid words in the English language that you downloaded. If so compute whether you can reach the second word from the first by a series of steps as follows a. You can change one letter at a time b. Each time you change a letter the resulting word must also exist in the dictionary c. You cannot add or remove letters If the two words are reachable, the script should print out the path which leads as a single, shortest path from one word to the other. You can /usr/share/dict/words for your dictionary of words. My solution consisted of using breadth first search to find a shortest path between two words. But apparently that wasn't good enough to get the job :( Would you guys know what I could have done wrong? Thank you so much. import collections import functools import re def time_func(func): import time def wrapper(*args, **kwargs): start = time.time() res = func(*args, **kwargs) timed = time.time() - start setattr(wrapper, 'time_taken', timed) return res functools.update_wrapper(wrapper, func) return wrapper class OneLetterGame: def __init__(self, dict_path): self.dict_path = dict_path self.words = set() def run(self, start_word, end_word): '''Runs the one letter game with the given start and end words. ''' assert len(start_word) == len(end_word), \ 'Start word and end word must of the same length.' self.read_dict(len(start_word)) path = self.shortest_path(start_word, end_word) if not path: print 'There is no path between %s and %s (took %.2f sec.)' % ( start_word, end_word, find_shortest_path.time_taken) else: print 'The shortest path (found in %.2f sec.) is:\n=> %s' % ( self.shortest_path.time_taken, ' -- '.join(path)) def _bfs(self, start): '''Implementation of breadth first search as a generator. The portion of the graph to explore is given on demand using get_neighboors. Care was taken so that a vertex / node is explored only once. ''' queue = collections.deque([(None, start)]) inqueue = set([start]) while queue: parent, node = queue.popleft() yield parent, node new = set(self.get_neighbours(node)) - inqueue inqueue = inqueue | new queue.extend([(node, child) for child in new]) @time_func def shortest_path(self, start, end): '''Returns the shortest path from start to end using bfs. ''' assert start in self.words, 'Start word not in dictionnary.' assert end in self.words, 'End word not in dictionnary.' paths = {None: []} for parent, child in self._bfs(start): paths[child] = paths[parent] + [child] if child == end: return paths[child] return None def get_neighbours(self, word): '''Gets every word one letter away from the a given word. We do not keep these words in memory because bfs accesses a given vertex only once. ''' neighbours = [] p_word = ['^' + word[0:i] + '\w' + word[i+1:] + '$' for i, w in enumerate(word)] p_word = '|'.join(p_word) for w in self.words: if w != word and re.match(p_word, w, re.I|re.U): neighbours += [w] return neighbours def read_dict(self, size): '''Loads every word of a specific size from the dictionnary into memory. ''' for l in open(self.dict_path): l = l.decode('latin-1').strip().lower() if len(l) == size: self.words.add(l) if __name__ == '__main__': import sys if len(sys.argv) not in [3, 4]: print 'Usage: python one_letter_game.py start_word end_word' else: g = OneLetterGame(dict_path = '/usr/share/dict/words') try: g.run(*sys.argv[1:]) except AssertionError, e: print e

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