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  • C# LINQ Where Predicate Type Arguments

    - by blu
    I have an XElement with values for mock data. I have an expression to query the xml: Expression<Func<XElement, bool>> simpleXmlFunction = b => int.Parse(b.Element("FooId").Value) == 12; used in: var simpleXml = xml.Elements("Foo").Where(simpleXmlFunction).First(); The design time error is: The type arguments for method 'System.Linq.Enumerable.Where(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly' The delegate supplied to Where should take in an XElement and return a bool, marking if the item matches the query, I am not sure how to add anything more to the delegate or the where clause to mark the type. Also, the parallel method for the real function against the Entity Framework does not have this issue. What is not correct with the LINQ-to-XML version?

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  • Efficiency of while(true) ServerSocket Listen

    - by Submerged
    I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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  • Detect aborted connection during ASIO request

    - by Tim Sylvester
    Is there an established way to determine whether the other end of a TCP connection is closed in the asio framework without sending any data? Using Boost.asio for a server process, if the client times out or otherwise disconnects before the server has responded to a request, the server doesn't find this out until it has finished the request and generated a response to send, when the send immediately generates a connection-aborted error. For some long-running requests, this can lead to clients canceling and retrying over and over, piling up many instances of the same request running in parallel, making them take even longer and "snowballing" into an avalanche that makes the server unusable. Essentially hitting F5 over and over is a denial-of-service attack. Unfortunately I can't start sending a response until the request is complete, so "streaming" the result out is not an option, I need to be able to check at key points during the request processing and stop that processing if the client has given up.

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  • Using device variable by multiple threads on CUDA

    - by ashagi
    I am playing around with cuda. At the moment I have a problem. I am testing a large array for particular responses, and when I get the response, I have to copy the data onto another array. For example, my test array of 5 elements looks like this: [ ][ ][v1][ ][ ][v2] Result must look like this: [v1][v2] The problem is how do I calculate the address of the second array to store the result? All elements of the first array are checked in parallel. I am thinking to declare a device variable int addr = 0. Every time I find a response, I will increment the addr. But I am not sure about that because it means that addr may be accessed by multiple threads at the same time. Will that cause problems? Or will the thread wait until another thread finishes using that variable?

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  • Porting Java app to Go - any advice?

    - by Devrim
    We want to rewrite kodingen.com backend with Go which currently is Java, running as daemon using jsvc. I have never touched any C in my life, am only experienced in Java so I don't know if this is something that I should even start. However, task is pretty simple read shell commands from mysql database queue and execute them in parallel save each shell output to the database that's it. So these simple requirements gives me hope that I can start using this wonderful language. What would you advise?

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  • Rolling back database changes

    - by justin
    Hi, I work in team which uses Work flow management tool. I was presented with a challenge where the user should be able to roll back the changes made anytime during the flow to a certain point in the past. Surely the toll can handle it but the additional database calls that may have made during these activities have to be manually rolled back. the challenge is that there are multiple parallel paths and there different permutations of external database calls. So is there a frame work or a way to keep track of these DB calls and rollback them?. thank you, Justin

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  • What's the coolest machine you've ever worked on?

    - by mxg
    What's the most exotic, coolest, unique, or interesting machine you've worked on? Most of us work on machines with x86 architectures using some Windows or Linux variant. I'm sure there are those of you out there who are working on or have worked on machines with experimental architecures, or operating systems. Maybe you worked on a machine that has some sigificance in the history of computing. I'd be interested to hear about it. I'm sure others reading SO will as well. EDIT: I appreciate all of you who took some time to talk about their experiences with interesting or unusual machines. I enjoyed reading your answers. Although it wasn't my intent to get nostalgic, I see that theme amongst the responses.

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  • Semantic stuff (RDF, OWL) on mobile phones - is it possible?

    - by Brian Schimmel
    I'm thinking about using semantic (web) technogies like RDF and OWL in an application on mobile devices. Currently I'm targeting android, but I'd also be interested in the possibilities on the iPhone and on J2ME. I would like to use a lib instead of implementing everything from scratch. I know that there are some libraries and frameworks like Jena, Redland, Protégé but they don't state on which platforms they are known to work. Having a dynamic object model and parsing from and to XML are must-haves for me. I'd also like to use reasoning, but I've been told it was rather computing-intensive, so that's only a nice-to-have. For all platforms mentioned, the question can be interpreted as Is it possible in theory (especially for J2ME I'm not sure) Are there libs that are known to work on those platforms? Is the performance on a mobile platform good enough for real world usage?

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  • Calculating 2D angles for 3D objects in perspective

    - by Will
    Imagine a photo, with the face of a building marked out. Its given that the face of the building is a rectangle, with 90 degree corners. However, because its a photo, perspective will be involved and the parallel edges of the face will converge on the horizon. With such a rectangle, is it possible to calculate the angle in 2D of the edges of a face that is 90 degrees to it? In the image below, the blue is the face marked on the photo, and I'm wondering how to calculate the 2D vector of the red lines of the other face:

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  • Performance optimization for SQL Server: decrease stored procedures execution time or unload the ser

    - by tim
    We have a web service which provides search over hotels. There is a problem with performance: a single request to the service takes around 5000 ms. Almost all of the time is spent in database by executing storing procedures. During the request our server (mssql2008) consumes ~90% of the processor time. When 2 requests are made in parallel the average time grows and is around 7000 ms. When number of request is increasing, the average time of response is increasing as well. We have 20-30 requests per minute. Which kind of optimization is the best in this case having in mind that the goal is to provide stable response time for the service: 1) Try to decrease the stored procedures execution time 2) Try to find the way how to unload the server It is interesting to hear from people who deal with booking sites.

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  • Perl, efficient parsing of csv file

    - by Mike
    I'm working on a project that involves parsing a large csv formatted file in Perl and am looking to make things more efficient. My approach has been to split() the file by lines first, and then split() each line again by commas to get the fields. But this suboptimal since at least two passes on the data are required. (once to split by lines, then once again for each line). This is a very large file, so cutting processing in half would be a significant improvement to the entire application. My question is, what is the most time efficient means of parsing a large CSV file using only built in tools? note: Each line has a varying number of tokens, so we can't just ignore lines and split by commas only. Also we can assume fields will contain only alphanumeric ascii data (no special characters or other tricks). Also, i don't want to get into parallel processing, although that might work effectively.

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  • iframe for ad loading good or bad?

    - by Cedar Jensen
    According to Yahoo's "Best Practices for Speeding Up your Site", the pros for using iframes: Helps with slow third-party content like badges and ads Download scripts in parallel but the cons are: Costly even if blank Blocks page onload I want to use an iframe to load ads using the technique mentioned on this site: http://meanderingpassage.com/2007/08/15/keeping-javascript-widgets-from-controlling-your-blog/ Does using this technique mean that as soon as the html contents requested by the iframe are returned to the client, it will load the ad script, potentially blocking the rest of the page's rendering and downloading? Or will the iframe request get processed concurrently while rest of the document is downloaded and rendered?

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  • Is there a decent vector / spline library for php?

    - by Brendan Heywood
    Does anyone know of the best way to render clean vectors into a php image and then serve it as a jpeg/png? Specifically I want to draw lines, polygons and splines which are anti-aliased and then serve them up as jpegs. Preferably also with an alpha option when rendering. What would be spectacular is a php library with a similar API to Raphael (without the animation) - not only because Raphael has a great API but also because I'm already using it on my website for the dynamic bits but also need to bake jpeg's in parallel for static consumption.

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  • Can SHA-1 algorithm be computed on a stream? With low memory footprint?

    - by raoulsson
    I am looking for a way to compute SHA-1 checksums of very large files without having to fully load them into memory at once. I don't know the details of the SHA-1 implementation and therefore would like to know if it is even possible to do that. If you know the SAX XML parser, then what I look for would be something similar: Computing the SHA-1 checksum by only always loading a small part into memory at a time. All the examples I found, at least in Java, always depend on fully loading the file/byte array/string into memory. If you even know implementations (any language), then please let me know!

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  • Strategy for developing namespaced and non-namespaced versions of same PHP code

    - by porneL
    I'm maintaining library written for PHP 5.2 and I'd like to create PHP 5.3-namespaced version of it. However, I'd also keep non-namespaced version up to date until PHP 5.3 becomes so old, that even Debian stable ships it ;) I've got rather clean code, about 80 classes following Project_Directory_Filename naming scheme (I'd change them to \Project\Directory\Filename of course) and only few functions and constants (also prefixed with project name). Question is: what's the best way to develop namespaced and non-namespaced versions in parallel? Should I just create fork in repository and keep merging changes between branches? Are there cases where backslash-sprinkled code becomes hard to merge? Should I write script that converts 5.2 version to 5.3 or vice-versa? Should I use PHP tokenizer? sed? C preprocessor? Is there a better way to use namespaces where available and keep backwards compatibility with older PHP?

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  • How to leverage Spring Integration in a real-world JMS distributed architecture?

    - by ngeek
    For the following scenario I am looking for your advices and tips on best practices: In a distributed (mainly Java-based) system with: many (different) client applications (web-app, command-line tools, REST API) a central JMS message broker (currently in favor of using ActiveMQ) multiple stand-alone processing nodes (running on multiple remote machines, computing expensive operations of different types as specified by the JMS message payload) How would one best apply the JMS support provided by the Spring Integration framework to decouple the clients from the worker nodes? When reading through the reference documentation and some very first experiments it looks like the configuration of an JMS inbound adapter inherently require to use a subscriber, which in a decoupled scenario does not exist. Small side note: communication should happen via JMS text messages (using a JSON data structure for future extensibility).

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  • Can you dynamically resize a java.util.concurrent.ThreadPoolExecutor while it still has tasks waitin

    - by Edward Shtern
    I'm working with a java.util.concurrent.ThreadPoolExecutor to process a number of items in parallel. Although the threading itself works fine, at times we've run into other resource constraints due to actions happening in the threads, which made us want to dial down the number of Threads in the pool. I'd like to know if there's a way to dial down the number of the threads while the threads area actually working. I know that you can call setMaximumPoolSize() and/or setCorePoolSize(), but these only resize the pool once threads become idle, but they don't become idle until there are no tasks waiting in the queue.

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  • Avoid copying of data between user and kernel space and vice-versa

    - by bala1486
    Hello, I am developing a active messaging protocol for parallel computation that replaces TCP/IP. My goal is to decrease the latency of a packet. Since the environment is a LAN, i can replace TCP/IP with simpler protocol to reduce the packet latency. I am not writing any device driver and i am just trying to replace the TCP/IP stack with something simpler. Now I wanted to avoid copying of a packet's data from user space to kernel space and vice-versa. I heard of the mmap(). Is it the best way to do this? If yes, it will be nice if you can give links to some examples. I am a linux newbie and i really appreciate your help.. Thank you... Thanks, Bala

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  • Storing dates as UTC in database

    - by James
    I am storing date/times in the database as UTC and computing them inside my application back to local time based on the specific timezone. Say for example I have the following date/time: 01/01/2010 00:00 Say it is for a country e.g. UK which observes DST (Daylight Savings Time) and at this particular time we are in daylight savings. When I convert this date to UTC and store it in the database it is actually stored as: 31/12/2009 23:00 As the date would be adjusted -1 hours for DST. This works fine when your observing DST. However, what happens when the clock is adjusted back? When I pull that date from the database and convert it to local time that particular datetime would be seen as 31/12/2009 23:00 when in reality it was processed as 01/01/2010 00:00. Correct me if I am wrong but isn't this a bit of a flaw when storing times as UTC?

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  • php mysql database users connection handling

    - by aviv
    What is the best way to handle mysql database users connection in PHP? I have a web server running a PHP application on MySQL. I have created a database user for the application: dbuser1 with limited access - only for query, insert and update tables. No alter table. Now the question is, should i use the same dbuser1 widely in my scripts, so if there are 100 current people using my system and hence 100 scripts running parallel they all connect to the database with the same dbuser1? or should i create a few users and assign each script a different user or load-balance between the dbusers ?

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  • Mahout Recommendations on Binary data

    - by Pranay Kumar
    Hi, I'm a newbie to mahout.My aim is to produce recommendations on binary user purchased data.So i applied item-item similarity model in computing top N recommendations for movie lens data assuming 1-3 ratings as a 0 and 4-5 ratings as a 1.Then i tried evaluating my recommendations with the ratings in the test-data but hardly there have been two or three matches from my top 20 recommendations to the top rated items in test data and no match for most users. So are my recommendations totally bad by nature or do i need to go for a different measure for evaluating my recommendations ? Please help me ! Thanks in advance. Pranay, 2nd yr ,UG student.

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  • Restart Delphi Application Programmatically

    - by Smasher
    It should not be possible to run multiple instances of my application. Therefore the project source contains: CreateMutex (nil, False, PChar (ID)); if (GetLastError = ERROR_ALREADY_EXISTS) then Halt; Now I want to restart my application programmatically. The usual way would be: AppName := PChar(Application.ExeName) ; ShellExecute(Handle,'open', AppName, nil, nil, SW_SHOWNORMAL) ; Application.Terminate; But this won't work in my case because of the mutex. Even if I release the mutex before starting the second instace it won't work because shutdown takes some time and two instance cannot run in parallel (because of common resources and other effects). Is there a way to restart an application with such characteristics? (If possible without an additional executable) Thanks in advance.

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  • starting 64 Bit Windows Application Development

    - by user173438
    I intend to start writing a 64 Bit Scientific Computing Application (signal processing) for Windows using Microsoft Visual Studio 2008. What should I have ready as far as a development platform is concerned? How would it be different from 32 Bit development? What could be the porting issues for a 32 Bit version that I already have (ok - this might too early to ask.. even before I start compiling)? As you might have guessed, I am looking for general directions. All pointers would be much appreciated! :) Thanks in advance..

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  • Is Work Stealing always the most appropriate user-level thread scheduling algorithm?

    - by Il-Bhima
    I've been investigating different scheduling algorithms for a thread pool I am implementing. Due to the nature of the problem I am solving I can assume that the tasks being run in parallel are independent and do not spawn any new tasks. The tasks can be of varying sizes. I went immediately for the most popular scheduling algorithm "work stealing" using lock-free deques for the local job queues, and I am relatively happy with this approach. However I'm wondering whether there are any common cases where work-stealing is not the best approach. For this particular problem I have a good estimate of the size of each individual task. Work-stealing does not make use of this information and I'm wondering if there is any scheduler which will give better load-balancing than work-stealing with this information (obviously with the same efficiency). NB. This question ties up with a previous question.

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  • Where are the static methods in gcc's dump file.c.135r.jump

    - by Customizer
    When I run gcc with the parameter -fdump-rtl-jump, I get a dump file with the name file.c.135r.jump, where I can read some information about the intermediate representation of the methods in my C or C++ file. I just recently discovered, that the static methods of a project are missing in this dump file. Do you know, why they are missing in that representation and if there is a possibility to include the static methods in this file, too. Update (some additional information): The test program, I'm using here, is the Hybrid OpenMP MPI Benchmark. Update2: I just reproduced the problem with a serial application, so it has nothing to do with parallel sections.

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