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• Memory allocation in Linux

  - by Goofy

  Hello! I have a multi threaded application where I allocate buffers with data, which then wait in queues to be send via sockets. All buffers are reproducible because I use only buffers of fixed size in whole program (1024, 2048, 2080 and 5248 bytes). I noticed, that my program usually use up to 10 buffers of each length type at the same moment. So far I always manually allocate new buffer and then free it (using malloc() and free ()) where it's not needed any more. I started wondering if Linux is enough smart to cache this memory for me, so next time I allocate new buffer system only quickly receive a buffer I have already used before and not perform heavy operation of allocating new memory block?

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• Overhead of serving pages - JSPs vs. PHP vs. ASPXs vs. C

  - by John Shedletsky

  I am interested in writing my own internet ad server. I want to serve billions of impressions with as little hardware possible. Which server-side technologies are best suited for this task? I am asking about the relative overhead of serving my ad pages as either pages rendered by PHP, or Java, or .net, or coding Http responses directly in C and writing some multi-socket IO monster to serve requests (I assume this one wins, but if my assumption is wrong, that would actually be most interesting). Obviously all the most efficient optimizations are done at the algorithm level, but I figure there has got to be some speed differences at the end of the day that makes one method of serving ads better than another. How much overhead does something like apache or IIS introduce? There's got to be a ton of extra junk in there I don't need. At some point I guess this is more a question of which platform/language combo is best suited - please excuse the in-adroitly posed question, hopefully you understand what I am trying to get at.

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• event vs thread programming on server side.

  - by AlxPeter

  We are planning to start a fairly complex web-portal which is expected to attract good local traffic and I've been told by my boss to consider/analyse node.js for the serve side. I think scalability and multi-core support can be handled with an Nginx or Cherokee up in the front. 1) Is this node.js ready for some serious/big business? 2) Does this 'event/asynchronous' paradigm on server side has the potential to support the heavy traffic and data operation ? considering the fact that 'everything' is being processed in a single thread and all the live connections would be lost if it got crashed (though its easy to restart). 3) What are the advantages of event based programming compared to thread based style ? or vice-versa. (I know of higher cost associated with thread switching but hardware can be squeezed with event model.) Following are interesting but contradicting (to some extent) papers:- 1) http://www.usenix.org/events/hotos03/tech/full_papers/vonbehren/vonbehren_html 2) http://pdos.csail.mit.edu/~rtm/papers/dabek:event.pdf

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• Have problem changing a value in an array

  - by aliov

  I have a multi-dimensional array with 4 entries in each value - (1st name, last name, email, password). I am trying to format the password value so I can insert it into a database. As you can see, my results are not what I need. Why is this the result and what should I do to get my intended result? Thanks php > $newlines[1][3] = "PASSWORD($newlines[1][3)]"; php > echo $newlines[1][3]; PASSWORD(Array[3)]

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• Loading Unmanaged C++ in C#. Error Attempted to read or write protected memory

  - by Thatoneguy

  I have a C++ function that looks like this __declspec(dllexport) int ___stdcall RegisterPerson(char const * const szName) { std::string copyName( szName ); // Assign name to a google protocol buffer object // Psuedo code follows.. Protobuf::Person person; person->set_name(copyName); // Error Occurs here... std::cerr << person->DebugString() << std::endl; } The corresponding C# code looks like this... [DllImport(@"MyLibrary.dll", SetLastError = true)] public static unsafe extern int RegisterPerson([MarshalAs(UnmanagedType.LPTStr)]string szName) Not sure why this is not working. My C++ library is compiled as Multi Threaded DLL with MultiByte encoding. Any help would be appreciated. I saw this is a common problem online but no answers lead me to a solution for my problem.

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• using APIs with oauth for single user

  - by Josh

  I'm trying to make use of various APIs including twitter, youtube, etc because we want to embed recent entries (tweets, videos) on our website. However, since I'm just retrieving my own data, I'm wondering how I can do this simpler than the multi-step process required by OAuth. Twitter provides me with my own access token I can use directly, so that kinda works, but I can't find any such token in the YouTube documentation. So how am I supposed to make use of the api if I just want to get a simple list of stuff? how exaclty am I supposed to authenticate my own website to use my own account? I think i might have things all wrong and if so please point me in the right direction. I tried using rss feeds but they don't give me as much control over what I retrieve as using the API directly... any insight or suggestions are appreciated!

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• Are compound command's second and subsequent lines not effected by HISTCONTROL in bash?

  - by UniMouS

  When consulting bash's man page, it read this sentence about bash history: The second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of the value of HISTCONTROL. But I have tried this: $ HISTCONTROL=ignorespace $ if [ -f /var/log/messages ] > then > echo "/var/log/message exists." > fi $ history | tail -2 18 HISTCONTROL=ignorespace 19 history | tail -2 Note that the if is leaded by a space. Why the second line of this if compound command still not appear in the history?

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• How to detect image orientation (text)

  - by Maciej

  My program is working with fax documents stored as separate bitmaps I wonder if there is a way to detect automatically page orientation (vertical or horizontal) to show image preview for user in right order (meant rotate if neccesary) Any advices much appreciated! EDIT: Clarification: When Faxmachine receives multi-page document it saves each page as separate TIFF file. My app has built-in viewer displaying those files. All files are scaled to A4 format and saved in TIFF (so there is no change to detect orientation by height/width parameters) My viewer displays images in portrait mode by default What I'd like to do is automagically detect situation when org document was printed in landscape mode (eg wide Excel tables) then I'd like to show rotated preview for end user to speed up preview process Obviously there are 4 possible fax orientation portrait / landscape x 2 kind of rotations. I'm even interested simplified solution detecting when org doc was landscape or portrait (I've noticed most of landscape docs needs to be rotated clockwise)

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• How do I extract info from a block of URLs in php?

  - by Jack

  I have a list of urls, which can come in any format. One per line, separated by commas, have random text in between them, etc. the URLs are all from 2 different sites, and have a similar structure For this example, lets say it looks like this Random Text - http://www.domain2.com/variable-value Random Text 2 - http://www.domain1.com/variable-value, http://www.domain1.com/variable-value, http://www.domain1.com/variable-value http://www.domain1.com/variable-value http://www.domain2.com/variable-value http://www.domain1.com/variable-value http://www.domain2.com/variable-value http://www.domain1.com/variable-value I need to extract 2 pieces of information. Check to see if its domain1 or domain2 and the value that follows "variable-" So it should create a multi-dimensional array, which would have 2 items: domain + value. Whats the best way of doing that?

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• How can I split the suckerfish Menu into two pieces so that I can put it in two frame?

  - by Kai

  I found a tutorial for developing multi-level drop down menu here.Its demo can be checked at www.kriesi.at/wp-content/extra_data/suckerfish_tutorial/step4.html#. I would like to enhance it to support cross-frames . It means, the horizontal part of the whole menu (html,css,javascript etc..in demo page) will exist in the upper frame and the rest will be put in the lower frame. Edit: There will be only one menu item in the horizontal part. It will be still ok if I can click that menu_item rather than mouse-hovering to show the lower part of the menu . Any idea will be appreciated. Thanks.

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• Using read in bash without empty fields collapsing

  - by Charles Duffy

  I'm trying to read a multi-line tab-separated file in bash. The format is such that empty fields are expected. Unfortunately, the shell is collapsing together field separators which are next to each other, as so: # IFS=$'\t' # read one two three <<<$'one\t\tthree' # printf '<%s> ' "$one" "$two" "$three"; printf '\n' <one> <three> <> ...as opposed to the desired output of <one> <> <three>. Can this be resolved without resorting to a separate language (such as awk)?

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• Take advantage of multiple cores executing SQL statements

  - by willvv

  I have a small application that reads XML files and inserts the information on a SQL DB. There are ~ 300 000 files to import, each one with ~ 1000 records. I started the application on 20% of the files and it has been running for 18 hours now, I hope I can improve this time for the rest of the files. I'm not using a multi-thread approach, but since the computer I'm running the process on has 4 cores I was thinking on doing it to get some improvement on the performance (although I guess the main problem is the I/O and not only the processing). I was thinking on using the BeginExecutingNonQuery() method on the SqlCommand object I create for each insertion, but I don't know if I should limit the max amount of simultaneous threads (nor I know how to do it). What's your advice to get the best CPU utilization? Thanks

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• Large strings: Text files or SQL DB?

  - by Tommo

  I am coding a forum system using PHP. I am currently storing a threads ID, title, author, views and other attributes in an SQL database and then storing the thread body (the HTML and BBcode) in text files inside a folder named after the thread ID. In practise it's really simple to grab the database values then just grab the thread body from the text file, but I was wondering if this is the 'proper way'? I have personally no problems doing this but if it turns out it is massively inefficient and I should instead store both the thread body HTML and BBcode in the database instead then I will change. However, to me it seems wrong to store such a (very possibly) huge string of multi-line text along with lots of different characters in a database - I was taught that databases are more for short field 'values' rather than website content. I would just like a definitive answer to this because it's been bugging me for ages as to wherever I’ve been doing it properly. Does anyone know how popular forum systems store threads?

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• callin' c from lua crashes while reallocating

  - by mkind

  hi folks, i got a crazy error within that for-loop matr=realloc(matr, newmax*sizeof(matr*)); for (i=0; i<newmax; i++){ matr[i]=realloc(matr[i], newmax*sizeof(int)); } matr is a multi-dimension array: int **matr. i need to resize column and row. first line resizes column and the for-loop resizes every row. it worked fine in c. now im working on a library for lua and it crashs here. compilin' works fine as well. but calling from lua crashs with lua: malloc.c:3552: mremap_chunk: Assertion `((size + offset) & (mp_.pagesize-1)) == 0' failed. i have no damn idea since it's working fine using it in c.

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• Thread processing in EMS connection

  - by aladine

  I am setting up a client and exchange project and both are connecting to a remote server. Exchange will connect to the server by EMS connection. While client will connect by FIX. For the aim of building of black box testing, both client and exchange engine will be given some predefined testcases to send and receive to the server. I design the client engine with multithread processing to manipulate many testcases. Actually it is able to run succesfully. For exchange engine, I wonder that multi thread is applicable in the context that the exchange engine just need to publish a message when it received msg from subscribed topic on server. Flow of messages transmission: Client--SERVER--Exchange FIX EMS Exchange--SERVER--Client EMS FIX Thanks if you can help me on this issue.

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• Scrolling through list element causes text elements to scroll as well

  - by DMK

  I'm using a list element with variableRowHeight and word-wrap set to true like in the example below: http://blog.flexexamples.com/2007/10/27/creating-multi-line-list-rows-with-variable-row-heights/ When I scroll through the list with a mouse scrollwheel the text in the listItems also scroll. I know that this is to do with the height of the textField... but I am unsure how to best resolve this issue. Any thoughts are appreciated! The issue that I am experiencing also occurs in the example above.

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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• What technologies to use for a particle system with enormous calculation demand?

  - by Amir Rezaei

  I have a particle system with X particles. Each particle tests for collision with other particles. This gives X*X = X^2 collision tests per frame. For 60f/s, this corresponds to 60*X^2 collision detection per second. What is the best technological approach for these intensive calculations? Should I use F#, C, C++ or C#, or something else? The following are constraints The code is written in C# with the latest XNA Multi-threaded may be considered No special algorithm that tests the collision with the nearest neighbors or that reduces the problem The last constraint may be strange, so let me explain. Regardless constraint 3, given a problem with enormous computational requirement what would be the best approach to solve the problem. An algorithm reduces the problem; still the same algorithm may behave different depending on technology. Consider pros and cons of CLR vs native C.

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• Why isn't it possible to update an ObservableCollection from a different thread?

  - by MainMa

  In a multi-threaded WPF application, it is not possible to update an ObservableCollection from a thread other than WPF window thread. I know there are workarounds, so my question is not how to avoid the "This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread" exception. My question is, why there is such an exception? Why wasn't it possible to allow collection updates from any thread? Personally, I don't see any reason to block UI update when ObservableCollection is changed from other threads. If two threads (including parallel ones) are accessing the same object, one listening for changes of object properties through events, the other one doing changes, it will always work, at least if locks are used properly. So, what are the reasons?

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• How can I use multithreading in a Windows Forms application to update a progress bar?

  - by Steve Syfuhs

  There are two objects. The Windows Form with a button and a progress bar, and another object that handles an algorithm. In the algorithm object there is an event, and a property. The event is ProgressChanged, and the property is Progress (which is an int). In the calling window, the button starts off a set of steps in the algorithm object. As each step (or substeps) occurs, the ProgressChanged event fires, and in the window there is an event handler that essentially increments the progress bar relative to the Progress property. The problem I am running into is that because the algorithm has a possibility (and high liklihood) of running a relatively long time, I need to move it into it's own background thread and push the event back up to the window. My issue is that I'm not completely sure what I'm doing when it comes to multi-threading. I've looked at Control.Invoke and I'm a little lost. Can someone point me in the right direction?

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• C# Spawn Multiple Threads for work then wait until all finished

  - by pharoc

  just want some advice on "best practice" regarding multi-threading tasks. as an example, we have a C# application that upon startup reads data from various "type" table in our database and stores the information in a collection which we pass around the application. this prevents us from hitting the database each time this information is required. at the moment the application is reading data from 10 tables synchronously. i would really like to have the application read from each table in a different thread all running in parallel. the application would wait for all the threads to complete before continuing with the startup of the application. i have looked into BackGroundWorker but just want some advice on accomplishing the above. Does the method sound logical in order to speed up the startup time of our application How can we best handle all the threads keeping in mind that each thread's work is independent of one another, we just need to wait for all the threads to complete before continuing. i look forward to some answers

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• Java Authenticator on a per connection basis?

  - by Martijn Laarman

  I'm building an Eclipse plugin that talks to a REST interface which uses Basic Authentication. When the authentication fails I would like to popup my plugin's settings dialog and retry. Normally I could use the static Authenticator.setDefault() to setup an authenticator for all HttpURLConnection's for this, but since I am writing a plugin I don't want to overwrite Eclipse's default Authenticator (org.eclipse.ui.internal.net.auth); I thought of setting my custom Authenticator before loading and putting Eclipse's default back afterwards, but I imagine this will cause all sorts of race issues with multithreading so I quickly lost that notion. Google searches yield all sorts of results basically telling me it's not possible: The Java URLConnection API should have a setAuthenticator(Authenticator) method for making it easier to use this class in multi-threaded context where authentication is required. Source If applications contains few third party plugins and each plugin use its own Authenticator what we should do? Each invocation of "Authenticator.setDefault()" method rewrite previously defined Authenticator... Source Are there any different approaches that might help me overcome this issue?

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• Portable Socket programming in C/C++ possible?

  - by questions

  I am thinking of creating a multi-platform portable C++ server-client application. Is it even possible while using only standard libraries? If no, what other libraries are there? Are there any improvements in this direction in C++11x? Like for threads, now we have std::threads. To make it more clear.. I want something like boost::thread, which provides multiplatform portable multithreading, for networking. And why C++ doesn't have libraries(standard) for such basic things like networking?

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• How does lock(syncRoot) make sense on a static method?

  - by Rising Star

  The following code is excerpted from the (Windows Identity Foundation SDK) template that MS uses to create a new Security Token Service Web Site. public static CustomSecurityTokenServiceConfiguration Current { get { HttpApplicationState httpAppState = HttpContext.Current.Application; CustomSecurityTokenServiceConfiguration customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { lock ( syncRoot ) { customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { customConfiguration = new CustomSecurityTokenServiceConfiguration(); httpAppState.Add( CustomSecurityTokenServiceConfigurationKey, customConfiguration ); } } } return customConfiguration; } } I'm relatively new to multi-threaded programming. I assume that the reason for the lock statement is to make this code thread-safe in the event that two web requests arrive at the web site at the same time. However, I would have thought that using lock (syncRoot) would not make sense because syncRoot refers to the current instance that this method is operating on... but this is a static method? How does this make sense?

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• DTOs Collections mapping Problem

  - by the_knight5000

  I'm working now on a multi-tier project which has layers as following : DAL BLL GUI Layer and Shared DTOs between BLL and GUI layers. I'm facing a problem in mapping the Objects from DAO To DTO, No problem in the simple objects. The problem is in the Objects who have child collections of another objects. ex: Author Category --Categories --Authors the execution goes in an infinite loop of mapping and it get more complex when I want model Self-join tables ex: Safe Safe --TransferSafe(Collection<Safe>) --TransferSafe(Collection<Safe>) the execution goes in an infinite loop of mapping any suggestions about a good solution or a practical mapping pattern?

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