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• OpenMP in Fortran

  - by user345293

  I very rarely use fortran, however I have been tasked with taking legacy code rewriting it to run in parallel. I'm using gfortran for my compiler choice. I found some excellent resources at https://computing.llnl.gov/tutorials/openMP/ as well as a few others. My problem is this, before I add any OpenMP directives, if I simply compile the legacy program: gfortran Example1.F90 -o Example1 everything works, but turning on the openmp compiler option even without adding directives: gfortran -openmp Example1.F90 -o Example1 ends up with a Segmentation fault when I run the legacy program. Using smaller test programs that I wrote, I've successfully compiled other programs with -openmp that run on multiple threads, but I'm rather at a loss why enabling the option alone and no directives is resulting in a seg fault. I apologize if my question is rather simple. I could post code but it is rather long. It faults as I assign initial values: REAL, DIMENSION(da,da) :: uconsold REAL, DIMENSION(da,da,dr,dk) :: uconsolde ... uconsold=0.0 uconsolde=0.0 The first assignment to "uconsold" works fine, the second seems to be the source of the fault as when I comment the line out the next several lines execute merrily until "uconsolde" is used again. Thank you for any help in this matter.

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• UnauthorizedAccessException when running desktop application from shared folder

  - by Atara

  I created a desktop application using VS 2008. When I run it locally, all works well. I shared my output folder (WITHOUT allowing network users to change my files) and ran my exe from another Vista computer on our intranet. When running the shared exe, I receive "System.UnauthorizedAccessException" when trying to read a file. How can I give permission to allow reading the file? Should I change the code? Should I grant permission to the application\folder on the Vista computer? how? Notes: I do not use ClickOnce. the application should be distributed using xcopy. My application target framework is ".Net Framework 2.0" On the Vista computer, "controlPanel | UninstallOrChangePrograms" it says it has "Microsoft .Net Framework 3.5 SP1" I also tried to map the folder drive, but got the same errors, only now the fileName is "T:\my.ocx" ' ---------------------------------------------------------------------- ' my code: Dim src As String = mcGlobals.cmcFiles.mcGetFileNameOcx() Dim ioStream As New System.IO.FileStream(src, IO.FileMode.Open) ' ---------------------------------------------------------------------- Public Shared Function mcGetFileNameOcx() As String ' ---------------------------------------------------------------------- Dim dirName As String = Application.StartupPath & "\" Dim sFiles() As String = System.IO.Directory.GetFiles(dirName, "*.ocx") Dim i As Integer For i = 0 To UBound(sFiles) Debug.WriteLine(System.IO.Path.GetFullPath(sFiles(i))) ' if found any - return the first: Return System.IO.Path.GetFullPath(sFiles(i)) Next Return "" End Function ' ---------------------------------------------------------------------- ' The Exception I receive: System.UnauthorizedAccessException: Access to the path '\\computerName\sharedFolderName\my.ocx' is denied. at System.IO._Error(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(...) at System.IO.FileStream..ctor(...) at System.IO.FileStream..ctor(String path, FileMode mode) ' ----------------------------------------------------------------------

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• hosting a high traffic facebook app (game)

  - by z3cko

  we are currently developing a high traffic facebook application. all the traffic will be within one month, where there are 500.000 to 1.000.000 expected users. after that month, the game is over and we have a winner - so the app will be archived. we are currently planning to develop the application with ruby on rails and searching for hosting options that can deal with the traffic. the problem is not so much the users, but the peak values: we will have around 500.000 requests coming daily within a short timeframe (lets say within 3 minutes in the worst case) we are expecting 500.000 to 1.000.000 users of the application, with peaks at 1:00pm (timezone GMT+1), where most (up to 80% of the users) will send most of the requests. the requests are from 11th of june to 11.july - after that, the app/game is closed/over. we are currently developing an aggressive caching mechanism - currently we are thinking about 2 or 3 small apps/webservices, that will handle the load. the load is distributed as follows: a) main application, cached data (11 screens, 200k each) b) voting: every day until 1:00pm (timezone GMT+1) - every user votes with about 10k data sent, high concurrent peak values! questions: is there any specific application setup that is recommendable? are there any hosting partners that can be recommended? thanks!

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• How to implement Administrator rights in Java Application?

  - by Yatendra Goel

  I am developing a Data Modeling Software that is implemented in Java. This application converts the textual data (stored in a database) to graphical form so that users can interpret the data in a more efficient form. Now, this application will be accessed by 3 kinds of persons: 1. Managers (who can fill the database with data and they can also view the visual form of the data after entering the data into the database) 2. Viewers (who can only view the visual form of data that has been filled by managers) 3. Administrators (who can create and manage other administrators, managers and viewers) Now, how to implement 3 diff. views of the same application. Note: Managers, Viewers and Administrators can be located in any part of the world and should access the application through internet. One idea that came in my mind is as follows: Step1: Code all the business logic in EJBs so that it can be used in distributed environment (means which can be accessed by several users through internet) Step2: Code 3 Swing GUI Clients: One for administrators, one for managers and one for viewers. These 3 GUI clients can access business logic written in EJBs. Step3: Distribute the clients corresponding to their users. For instance, manager client to managers. =================================QUESTIONS======================================= Q1. Is the above approach is correct? Q2. This is very common functionality that various softwares have. So, Do they implement this kind of functionality through this way or any other way? Q3. If any other approach would be more better, then what is that approach?

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• Java: fastest way to do random reads on huge disk file(s)

  - by cocotwo

  I've got a moderately big set of data, about 800 MB or so, that is basically some big precomputed table that I need to speed some computation by several orders of magnitude (creating that file took several mutlicores computers days to produce using an optimized and multi-threaded algo... I do really need that file). Now that it has been computed once, that 800MB of data is read only. I cannot hold it in memory. As of now it is one big huge 800MB file but splitting in into smaller files ain't a problem if it can help. I need to read about 32 bits of data here and there in that file a lot of time. I don't know before hand where I'll need to read these data: the reads are uniformly distributed. What would be the fastest way in Java to do my random reads in such a file or files? Ideally I should be doing these reads from several unrelated threads (but I could queue the reads in a single thread if needed). Is Java NIO the way to go? I'm not familiar with 'memory mapped file': I think I don't want to map the 800 MB in memory. All I want is the fastest random reads I can get to access these 800MB of disk-based data. btw in case people wonder this is not at all the same as the question I asked not long ago: http://stackoverflow.com/questions/2346722/java-fast-disk-based-hash-set

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• Mutually beneficial IP/copyright clauses for contract-based freelance work

  - by Nathan de Vries

  I have a copyright section in the contract I give to my clients stating that I retain copyright on any works produced during my work for them as an independent contractor. This is most definitely not intended to place arbitrary restrictions on my clients, but rather to maintain my ability to decide on how the software I create is licensed and distributed. Almost every project I work on results in at least one part of it being released as open source. Every project I work on makes use of third-party software released in the same fashion, so returning the favour is something I would like to continue doing. Unfortunately, the contract is not so clear when it comes to defining the rights of the client in the use of said software. I mention that the code will be licensed to them, but do not mention specifics about exclusivity, ability to produce derivatives etc. As such, a client has raised concerns about the copyright section of my contract, and has suggested that I reword it such that all copyrights are transferred entirely to the client on final payment for the project. This will almost certainly reduce my ability to distribute the software I have created; I would much prefer to find a more mutually beneficial agreement where both our concerns are appeased. Are there any tried and true approaches to licensing software in this kind of situation? To summarise: I want to maintain the ability to license (parts of) the software under my own terms, independently of my relationship with the client; with some guarantee to the client that no trade-secrets or critical business logic will be shared; giving them the ability to re-use my code in their future projects; but not necessarily letting them sell it (I'm not sure about this, though...what happens if they sell their business and the software along with it?) I realise that everyone's feedback is going to be prefixed with "IANAL", however I appreciate any thoughts you might have on the matter.

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• The way cores, processes, and threads work exactly?

  - by unknownthreat

  I need a bit of an advice for understanding how this whole procedure work exactly. If I am incorrect in any part described below, please correct me. In a single core CPU, it runs each process in the OS, jumping around from one process to another to utilize the best of itself. A process can also have many threads, in which the CPU core runs through these threads when it is running on the respective process. Now, on a multiple core CPU, Do the cores run in every process together, or can the cores run separately in different processes at one particular point of time? For instance, you have program A running two threads, can a duo core CPU run both threads of this program? I think the answer should be yes if we are using something like OpenMP. But while the cores are running in this OpenMP-embedded process, can one of the core simply switch to other process? For programs that are created for single core, when running at 100%, why the CPU utilization of each core are distributed? (ex. A duo core CPU of 80% and 20%. The utilization percentage of all cores always add up to 100% for this case.) Do the cores try help each other run each thread of each process in some ways? Frankly, I'm not sure how this works exactly. Any advice is appreciated.

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• Cant we use a Set or collection as a return type in GAE?

  - by user273422

  In my code i have used Set<Employees> as a return type to my function addEmp(). So, i m gettin an Compilation error. The Error is: Compiling module com.employeedepartmentgae.Employeedepartmentgae Refreshing module from source Validating newly compiled units Removing units with errors [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 18: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 20: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java' [ERROR] Line 12: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 75: The method addEmp(String, String, String, AsyncCallback) from the type GreetingServiceAsync refers to the missing type Employee [ERROR] Line 75: The type new AsyncCallback(){} must implement the inherited abstract method AsyncCallback.onSuccess(Set) [ERROR] Line 75: Employee cannot be resolved to a type [ERROR] Line 94: The method onSuccess(Set) of type new AsyncCallback(){} must override or implement a supertype method [ERROR] Line 94: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 98: Employee cannot be resolved to a type Removing invalidated units [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/Employeedepartmentgae.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/DepartmentWidget.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java Computing all possible rebind results for 'com.employeedepartmentgae.client.Employeedepartmentgae' Rebinding com.employeedepartmentgae.client.Employeedepartmentgae Checking rule [ERROR] Unable to find type 'com.employeedepartmentgae.client.Employeedepartmentgae' [ERROR] Hint: Previous compiler errors may have made this type unavailable [ERROR] Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly So please help me.....

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• My kernel only works in block (0,0)

  - by ZeroDivide

  I am trying to write a simple matrixMultiplication application that multiplies two square matrices using CUDA. I am having a problem where my kernel is only computing correctly in block (0,0) of the grid. This is my invocation code: dim3 dimBlock(4,4,1); dim3 dimGrid(4,4,1); //Launch the kernel; MatrixMulKernel<<<dimGrid,dimBlock>>>(Md,Nd,Pd,Width); This is my Kernel function __global__ void MatrixMulKernel(int* Md, int* Nd, int* Pd, int Width) { const int tx = threadIdx.x; const int ty = threadIdx.y; const int bx = blockIdx.x; const int by = blockIdx.y; const int row = (by * blockDim.y + ty); const int col = (bx * blockDim.x + tx); //Pvalue stores the Pd element that is computed by the thread int Pvalue = 0; for (int k = 0; k < Width; k++) { Pvalue += Md[row * Width + k] * Nd[k * Width + col]; } __syncthreads(); //Write the matrix to device memory each thread writes one element Pd[row * Width + col] = Pvalue; } I think the problem may have something to do with memory but I'm a bit lost. What should I do to make this code work across several blocks?

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• A generic C++ library that provides QtConcurrent functionality?

  - by Lucas

  QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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• asp.net, wcf authentication and caching

  - by andrew

  I need to place my app business logic into a WCF service. The service shouldn't be dependent on ASP.NET and there is a lot of data regarding the authenticated user which is frequently used in the business logic hence it's supposed to be cached (probably using a distributed cache). As for authentication - I'm going to use two level authentication: Front-End - forms authentication back-end (WCF Service) - message username authentication. For both authentications the same custom membership provider is supposed to be used. To cache the authenticated user data, I'm going to implement two service methods: 1) Authenticate - will retrieve the needed data and place it into the cache(where username will be used as a key) 2) SignOut - will remove the data from the cache Question 1. Is correct to perform authentication that way (in two places) ? Question 2. Is this caching strategy worth using or should I look at using aspnet compatible service and asp.net session ? Maybe, these questions are too general. But, anyway I'd like to get any suggestions or recommendations. Any Idea

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• Why is there so much XML in Java these days?

  - by BD at Rivenhill

  This is really more of a philosophy/design issue. I did some work in Java back in the middle 90's and again in the early 2000's and now I'm coming back to it after spending a lot of time in C/C++ and it seems like there was an explosion of XML dependency while I was gone. Major build system tools like ant and maven depend on XML for their configuration, but I'm actually more concerned with all the frameworks, such as Spring, Hibernate, etc. My experience is that powerful supporting libraries like these are where a developer can really get leverage for building programs with lots of features without writing a lot of code, but it really seems like I'm getting one language for the price of two here. I write a bunch of Java classes, but then I also write a bunch of XML files to glue them together. The things that get done in the XML are things that I can see reasonable ways of doing in straight code without the middleman, and they don't really seem to be treated exactly like configuration files: they change rarely and they end up getting committed to source code control like the Java code itself, but they are distributed with the resulting application and need to be unpacked and installed in the classpath in order to get the application to work. I'm working with server applications that are not web-based, so maybe the domain is a bit different from what most people are doing, but I just can't help feeling that I must be doing something wrong here. Can someone point me to a good source of information for why these design choices were made and what problems they are meant to solve so that I can analyze my own experiences in this context?

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• Boost Include Files in VC++

  - by Dr. K

  For the last few years, I have been exclusively a C# developer. Previously, I developed in C++ and have a C++ application that I built about 3 years ago using VS2005. It made extensive use of the Boost libraries. I recently decided to brush off the old app and rebuild it in VS2008 with the latest version of Boost (the latest version with the "easy" installation program from BoostPro Computing), 1.39. Previously when I had the program running I was at 1.33. Also, the last time the program was running was at least 2 OS installations ago. The Boost installation is located on my machine at: "C:\Program Files\boost\boost_1_39". Anyway, I have done the following: Set the project's "Additional Include Directories" directory to "C:\Program Files\boost\boost_1_39" Added "C:\Program Files\boost\boost_1_39" to VS2008's Tools - Options - Projects and Solutions - VC++ Directories - Include Files I have a number of Boost includes in my stdafx.h file. The compiler fails upon attempting to open the first one - #include <boost/algorithm/string/string.hpp> I have confirmed that the above file is indeed located at "C:\Program Files\boost\boost_1_39\boost\algorithm\string\string.hpp" I continue to get: fatal error C1083: Cannot open include file: 'boost/algorithm/string/string.hpp': No such file or directory Any tips on what else to check would be greatly appreciated. Again, this is an application that compiled fine a few years ago, but the source has now been moved to a new machine/compiler.

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• How do software projects go over budget and under-deliver?

  - by Carlos

  I've come across this story quite a few times here in the UK: NHS Computer System Summary: We're spunking £12 Billion on some health software with barely anything working. I was sitting the office discussing this with my colleagues, and we had a little think about. From what I can see, all the NHS needs is a database + middle tier of drugs/hospitals/patients/prescriptions objects, and various GUIs for doctors and nurses to look at. You'd also need to think about security and scalability. And you'd need to sit around a hospital/pharmacy/GPs office for a bit to figure out what they need. But, all told, I'd say I could knock together something with that kind of structure in a couple of days, and maybe throw in a month or two to make it work in scale. If I had a few million quid, I could probably hire some really excellent designers to make a maintainable codebase, and also buy appropriate hardware to run the system on. I hate to trivialize something that seems to have caused to much trouble, but to me it looks like just a big distributed CRUD + UI system. So how on earth did this project bloat to £12B without producing much useful software? As I don't think the software sounds so complicated, I can only imagine that something about how it was organised caused this mess. Is it outsourcing that's the problem? Is it not getting the software designers to understand the medical business that caused it? What are your experiences with projects gone over budget, under delivered? What are best practices for large projects? Have you ever worked on such a project?

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• Many users, many cpus, no delays. Good for cloud?

  - by Eric

  I wish to set up a CPU-intensive time-important query service for users on the internet. A usage scenario is described below. Is cloud computing the right way to go for such an implementation? If so, what cloud vendor(s) cater to this type of application? I ask specifically, in terms of: 1) pricing 2) latency resulting from: - slow CPUs, instance creations, JIT compiles, etc.. - internal management and communication of processes inside the cloud (e.g. a queuing process and a calculation process) - communication between cloud and end user 3) ease of deployment A usage scenario I am expecting is: - A typical user sends a query (XML of size around 1K) once every 30 seconds on average. - Each query requires a numerical computation of average time 0.2 sec and max time 1 sec on a 1 GHz Pentium. The computation requires no data other than the query itself and is performed by the same piece of code each time. - The delay a user experiences between sending a query and receiving a response should be on average no more than 2 seconds and in general no more than 5 seconds. - A background save to a DB of the response should occur (not time critical) - There can be up to 30000 simultaneous users - i.e., on average 1000 queries a second, each requiring an average 0.2 sec calculation, so that would necessitate around 200 CPUs. Currently I'm look at GAE Java (for quicker deployment and less IT hassle) and EC2 (Speed and price optimization) as options. Where can I learn more about the right way to set ups such a system? past threads, different blogs, books, etc.. BTW, if my terminology is wrong or confusing, please let me know. I'd greatly appreciate any help.

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• Are there any changes in the licensing of Visual Studio 2013 Express editions?

  - by Ramón García-Pérez

  As was going through reading the license.htm file provided as part of the VS2013_RTM_WebExp_ENU.iso offline installation media for the Visual Studio 2013 Express for Web, section 6 reads as follows: 6. PACKAGE MANAGER AND THIRD PARTY SOFTWARE INSTALLATION FEATURES. The software includes the following features (each a “Feature”), each of which enables you to obtain software applications or packages through the Internet from other sources: Extension Manager, New Project Dialog, Web Platform Installer, and Microsoft NuGet-Based Package Manager. Those software applications and packages are offered and distributed in some cases by third parties and in some cases by Microsoft, but each such application or package is under its own license terms. Microsoft is not developing, distributing or licensing any of the third-party applications or packages to you, but instead, as a convenience, enables you to use the Features to access or obtain those applications or packages directly from the third-party application or package providers. By using the Features, you acknowledge and agree that: you are obtaining the applications or packages from such third parties and under separate license terms applicable to each application or package (including, with respect to the package-manager Features, any terms applicable to software dependencies that may be included in the package); MICROSOFT MAKES NO REPRESENTATIONS, WARRANTIES OR GUARANTEES AS TO THE FEED OR GALLERY URL, ANY FEEDS OR GALLERIES FROM SUCH URL, THE INFORMATION CONTAINED THEREIN, OR ANY SOFTWARE APPLICATIONS OR PACKAGES REFERENCED IN OR ACCESSED BY YOU THROUGH SUCH FEEDS OR GALLERIES. MICROSOFT GRANTS YOU NO LICENSE RIGHTS FOR THIRD-PARTY SOFTWARE APPLICATIONS OR PACKAGES THAT ARE OBTAINED USING THE FEATURES. Are there any changes in the licensing of Visual Studio 2013 Express editions? If so, does this means that Visual Studio extensions installation in Express Editions is now allowed? PS: Previous versions of the Express editions did not allow the installation of extensions as per "EULA/TOS" discussed here: Limitations of Visual Studio 2012 Express Desktop

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• Web services or shared database for (game) server communication?

  - by jaaronfarr

  We have 2 server clusters: the first is made up of typical web applications backed by SQL databases. The second are highly optimized multiplayer game servers which keep all data in memory. Both clusters communicate with clients via HTTP (Ajax with JSON). There are a few cases in which we need to share data between the two server types, for example, reporting back and storing the results of a game (should ultimately end up in the database). We're considering several approaches for inter-server communication: Just share the MySQL databases between clusters (introduce SQL to the game servers) Sharing data in a distributed key-value store like Memcache, Redis, etc. Use an RPC technology like Google ProtoBufs or Apache Thrift Using RESTful web services (the game server would POST back to the web servers, for example) At the moment, we're leaning towards web services or just sharing the database. Sharing the database seems easy, but we're concerned this adds extra memory and a new dependency into the game servers. Web services provide good separation of concerns and fit with the existing Ajax we use, but add complexity, overhead and many more ways for communication to fail. Are there any other good reasons not to use one or the other approach? Which would be easier to scale?

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• In maven2, how do I assemble bits and pieces of different modules to create final distributions?

  - by Carcassi

  I have four maven project: client api jar web service war ui jar web interface war The service war will need to be packaged to include the client api jar, together with javadocs (so that each version is distributed with a matching client and documentation). The web interface war will need the ui jar and all the dependencies (webstart/applet deployment). So I need a 5th project that does all the packaging. How to do this with ant or a script is perfectly clear to me, but not in maven. I tried the following: having the javadocs included as part of the war packaging: this requires the execution of the javadocs goal in project 1 before execution of package in project 2. Haven't found a way to bind plugins/goals across different projects. Using the assembly plugin in project2 had the same problem. create a fifth project and use the assembly plugin. Still the same problems as before, with the problem that since I need different pieces from each sub-project I do not understand how this can be done using the assembly. Is this too hard to do in maven, and should I just give up? Or I am looking at it wrong, in which case, how should I be looking at it? Thanks! Upon further reflection, here is a partial answer: Each project should build all its artifacts. This is done by having the plugins configured to run as per the prepare-resources and package phases. So, in my case, I prepare all that needs to be generated (jar, javadocs, xsd documentation, ...) as different artifacts so that a single "package" goal execution creates all. So, it's not "how project 2 forces project 1 to run different goals", but it's "make project 1 create all of its artifact as part as the normal lifecycle). This seems to simplify things.

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• Fastest reliable way for Clojure (Java) and Ruby apps to communicate

  - by jkndrkn

  Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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• Behavior of Struts2 and convention-plugin when there is Index(extends ActionSupport)

  - by hanishi

  We have an Action class named 'Index' immediately under com.example.common.action and is annotated @ParentPackage('default') which is declared in package directive in struts.xml and has "/" for its namespace and extends "struts-default". It also declares @Result so that it responses with jsp files corresponding the string values returned by its execute() method. In our struts.xml, the following struts setting is configured along with other necessary configurations that are needed for convention-plugin. <constant name="struts.action.extension" value=","/> When accessing /my_context/none_existing_path, the request apparently hits this Index class and the contents of the jsp declared in the Index's @Result section gets returned. However, if we provide /my_context/, we receive the following error: HTTP Status 404-There is no Action mapped for namespace[/] and action name [] associated with context path [/my_context]. We want to know the reason why accessing /my_context/none_existing_path, where none_existing_path has no matching action, can fallback to Index class, but error is returned when when the URL requested is just /my_context/. Currently, our convention-plugin settings are declared as follows: <constant name="struts.convention.package.locators.basePackage" value="com.example"/> <constant name="struts.convention.package.locators" value="action"/> Strangely, if we changed the value of the struts.convention.package.locators.basePackage to om.example.common, in which the aforementioned Index file can be immediately found by narrowing the search scope, requesting /my_context/ displays the content of the jsps declared in @Result section of the Index class. However, as our action classes are distributed throughout the com.example.[a-z].action packages, where [a-z] represents the large volume of directories we have in our package structure, we cannot use this trick as a workaround. We have also tried placing index.jsp at the top level of the class path, and have the index.jsp redirect to /my_context/index, which worked but not what we want. Could this be a bug? We appreciate your responses. Thank you in advance. EDIT: JIRA registered, problem solved (from Struts 2.3.12 up)

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• Hadoop File Read

  - by user3684584

  Hadoop Distributed Cache Wordcount example in hadoop 2.2.0. Copied file into hdfs filesystem to be used inside setup of mapper class. protected void setup(Context context) throws IOException,InterruptedException { Path[] uris = DistributedCache.getLocalCacheFiles(context.getConfiguration()); cacheData=new HashMap(); for(Path urifile: uris) { try { BufferedReader readBuffer1 = new BufferedReader(new FileReader(urifile.toString())); String line; while ((line=readBuffer1.readLine())!=null) { System.out.println("**************"+line); cacheData.put(line,line); } readBuffer1.close(); } catch (Exception e) { System.out.println(e.toString()); } } } Inside Driver Main class Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs(); if (otherArgs.length != 3) { System.err.println("Usage: wordcount <in> <out>"); System.exit(2); } Job job = new Job(conf, "word_count"); job.setJarByClass(WordCount.class); job.setMapperClass(Map.class); job.setReducerClass(Reduce.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(otherArgs[0])); Path outputpath=new Path(otherArgs[1]); outputpath.getFileSystem(conf).delete(outputpath,true); FileOutputFormat.setOutputPath(job,outputpath); System.out.println("CachePath****************"+otherArgs[2]); DistributedCache.addCacheFile(new URI(otherArgs[2]),job.getConfiguration()); System.exit(job.waitForCompletion(true) ? 0 : 1); But getting exception java.io.FileNotFoundException: file:/home/user12/tmp/mapred/local/1408960542382/cache (No such file or directory) So Cache functionality not working properly. Any Idea ?

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• when to use Hibernate vs. Simple ResultSets for small application

  - by luke

  I just started working on upgrading a small component in a distributed java application. The main application is a rather complicated applet/servlet combo running on JBoss and it extensively uses Hibernate for its DataAccess. The component i am working on however is very a very straightforward data importing service. Basically the workflow is Listen for a network event Parse the data packet, extract a set of identifiers Map the identifier set to a primary key in our database Parse the rest of the packet and insert items in a related table using the foreign key found in step 3 Repeat in the previous version of this component it used a hibernate based DAL, that is no longer usable for a variety of reasons (in particular it is EOL), so I am in charge of replacing the Data Access layer for this component. So on the one hand I think i should use Hibernate because that's what the rest of the application does, but on the other i think i should just use regular java.sql.* classes because my requirements are really straightforward and aren't expected to change any time soon. So my question is (and i understand it is subjective) at what point do you think that the added complexity of using an ORM tool (in terms of configuration, dependencies...) is worth it? UPDATE due to the way the DataAccesLayer for the main application was written (weird dependencies) i cannot easily use it, i would have to implement it myself.

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• Creating multiple instances of a generic database

  - by sagekilla

  Hi all, currently I'm trying to have a setup where a generic database is distributed to students. They would develop an application using this database (Say a shopping cart application), submit their project onto our server, and then it would be graded automatically. These databases are being run in Microsoft SQL Server 2005. We're using user instances to instantiate each database, and multiple requests could be serviced at once. But, the problem is when more than one student submitted a project to be graded, the first database to be instantiated would be the only one and would overwrite all other copies that were currently open. So if stu1 modified his database and stu2 and stu3 had their projects being graded concurrently, at the end of the grading stu1, stu2, and stu3 would have identical DB's at the end. Is there any way I can have multiple independent copies of a generic database, each of which I can load concurrently and modify without having any changes made to any one affecting the others? I did a little reading, and thought it might be possible to do something along the lines of: Student submits project Attach the database with unique db name (specified by student) Do all necessary operations Detach the database I'm unsure if this would fix our problem or be possible, so any help would be much appreciated!

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• Mysql - wondering about scaling a twitter-like application ?

  - by user246114

  Hi, I'm developing an app that is vaguely similar to twitter, in that it allows users to follow one another. I wanted to do this using google app engine, for its scalability promises, but it's proving kind of difficult to get running for a few different reasons. I'd basically like to have a _users table, and a _followers table. Users go into the users table, follower relationships go into _followers. The problem is that each row in the users table will probably have like 100 corresponding records in the _followers table as users start following one another. So the number of rows is going to explode quickly. Using app engine, the volume [shouldn't] be a problem. If I go with mysql, and I do actually start to get some traction, how do I scale this up? Am I going to just end up moving to a distributed database in the end anyway? Should I fight it out with google app engine? I read that Twitter was using mysql, and they've run into this problem, and are now switching to cassandra. Thanks

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• Parallel programming, are we not learning from history again?

  - by mezmo

  I started programming because I was a hardware guy that got bored, I thought the problems being solved in the software side of things were much more interesting than those in hardware. At that time, most of the electrical buses I dealt with were serial, some moving data as fast as 1.5 megabit!! ;) Over the years these evolved into parallel buses in order to speed communication up, after all, transferring 8/16/32/64, whatever bits at a time incredibly speeds up the transfer. Well, our ability to create and detect state changes got faster and faster, to the point where we could push data so fast that interference between parallel traces or cable wires made cleaning the signal too expensive to continue, and we still got reasonable performance from serial interfaces, heck some graphics interfaces are even happening over USB for a while now. I think I'm seeing a like trend in software now, our processors were getting faster and faster, so we got good at building "serial" software. Now we've hit a speed bump in raw processor speed, so we're adding cores, or "traces" to the mix, and spending a lot of time and effort on learning how to properly use those. But I'm also seeing what I feel are advances in things like optical switching and even quantum computing that could take us far more quickly that I was expecting back to the point where "serial programming" again makes the most sense. What are your thoughts?

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