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• Git as mercurial client? Why no git-hg?

  - by aapeli

  This is a question that's been bothering me for a while. I've done my homework and checked stackoverflow and found at least these two topics about my question: Git for Mercurial like git-svn and Git interoperability with a Mercurial repository I've done some serious googling to solve this issue, but so far with no luck. I've also read the Git Internals book, and the Mercurial Definitive Behind the Scenes to try to figure this out. I'm still a bit puzzled why I haven't been able to find any suitable git-hg type of a tool. From my perspective hg-svn is one of the main features, why I've chosen to use git over mercurial also at work. It allows me to use a workflow I like, and nobody else needs to bother, if they don't care. I just don't see the point in using the intermediate hg repo to convert back and forth, as suggested in one of the chains. So anyway, from what I've read hg and git seem very similar in conceptual design. There are differences under the hood, but none of those should prevent creating a git client for hg. As it seems to me, remote tracking branches and octopus merges make git even more powerful than hg is. So, the real question, is there any real reason why git-hg does not exist (or at least is very hard to find)? Is there some animosity from git users (and developers) towards their hg counterparts that has caused the lack of the git-hg tool? Do any of you have any plans to develop something like this, and go public with it? I could volunteer (although with very feeble C-skills) to participate to get this done. I just don't possess the full knowledge to start this up myself. Could this be the tool to end all DVCS wars for good?

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• What are the worst examples of moral failure in the history of software engineering?

  - by Amanda S

  Many computer science curricula include a class or at least a lecture on disasters caused by software bugs, such as the Therac-25 incidents or Ariane 5 Flight 501. Indeed, Wikipedia has a list of software bugs with serious consequences, and a question on StackOverflow addresses some of them too. We study the failures of the past so that we don't repeat them, and I believe that rather than ignoring them or excusing them, it's important to look at these failures squarely and remind ourselves exactly how the mistakes made by people in our profession cost real money and real lives. By studying failures caused by uncaught bugs and bad process, we learn certain lessons about rigorous testing and accountability, and we make sure that our innocent mistakes are caught before they cause major problems. There are kinds of less innocent failure in software engineering, however, and I think it's just as important to study the serious consequences caused by programmers motivated by malice, greed, or just plain amorality. Thus we can learn about the ethical questions that arise in our profession, and how to respond when we are faced with them ourselves. Unfortunately, it's much harder to find lists of these failures--the only one I can come up with is that apocryphal "DOS ain't done 'til Lotus won't run" story. What are the worst examples of moral failure in the history of software engineering?

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• How would i down-sample a .wav file then reconstruct it using nyquist? - in MATLAB

  - by Andrew

  This is all done in MATLAB 2010 My objective is to show the results of: undersampling, nyquist rate/ oversampling First i need to downsample the .wav file to get an incomplete/ or impartial data stream that i can then reconstuct. Heres the flow chart of what im going to be doing So the flow is analog signal - sampling analog filter - ADC - resample down - resample up - DAC - reconstruction analog filter what needs to be achieved: F= Frequency F(Hz=1/s) E.x. 100Hz = 1000 (Cyc/sec) F(s)= 1/(2f) Example problem: 1000 hz = Highest frequency 1/2(1000hz) = 1/2000 = 5x10(-3) sec/cyc or a sampling rate of 5ms This is my first signal processing project using matlab. what i have so far. % Fs = frequency sampled (44100hz or the sampling frequency of a cd) [test,fs]=wavread('test.wav'); % loads the .wav file left=test(:,1); % Plot of the .wav signal time vs. strength time=(1/44100)*length(left); t=linspace(0,time,length(left)); plot(t,left) xlabel('time (sec)'); ylabel('relative signal strength') **%this is were i would need to sample it at the different frequecys (both above and below and at) nyquist frequency.*I think.*** soundsc(left,fs) % shows the resaultant audio file , which is the same as original ( only at or above nyquist frequency however) Can anyone tell me how to make it better, and how to do the sampling at verious frequencies?

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• Web development: Haskell or Scheme

  - by Robert E. Lester

  I would like to to choose one of these languages for building web applications. I'm not interested in framework per say, but have the following needs: Rapid development. Easy to scale. Strong community for the web. Quick and easy to deploy. I'm very familiar with Haskell, and have some familiarity with scheme (in particular PLT). Scheme appeals to me as good candidate for web development due to it's simple syntax which is homogenous across libraries. I state this despite my subjective opinion that Haskell is a 'cleaner' language. Haskell web apps seem to require learning and building a patchwork of different combinator libraries. On the plus side, I realise this can be quite expressive, although I'd prefer to eliminate impedance mismatches where possible. While scheme-plt looks to be a good fit, I can find but one example of it being used in the "real world". Haskell doesn't seem to fair too much better here, but there seems to be a bigger community behind the web side. Please help me make up my mind. For the most part I'm interested in real-world use cases.

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• Using CURL within a loop to download a file, 1st one works, 2nd one times out

  - by kitenski

  Morning all, I am using CURL to download an image file within a loop. The first time it runs fine and I see the image appear in the directory. The second time it fails with a timeout, despite it being a valid URL. Can anyone suggest why it always fails on the 2nd time and how to fix it? The snippet of code is: // download image $extension = "gif"; $ch = curl_init(); curl_setopt($ch, CURLOPT_TIMEOUT, 90); curl_setopt($ch, CURLOPT_URL, $imgurl); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); echo $imgurl . " attempting to open URL "; $i = curl_exec($ch); if ( $i==false ) { echo curl_errno($ch).' '.curl_error($ch); } $image_name=time().'.'.$extension; $f = fopen('/fulldirectorypath/' . $image_name ,'w+'); fwrite($f,$i); fclose($f); I have put an echo in there to display the $IMGURL, to check it is valid, and upped the timeout to 90 secs, but it still fails. This is what I see on screen: http://images.eu-xmedia.de/thumbnails/34555861/5676051/pt=pic,lang=2,origfile=yes/image.gif attempting to open URL 28 Operation timed out after 90 seconds with 0 bytes received an empty file is created in my directory. thanks alot, Greg

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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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• Javascript: How to test JSONP on localhost

  - by hqt

  Here is the way I test JSONP: I run XAMPP, and in folder htdocs I create a javascript folder . I create json1.json file contain some data to process. After that, I run this html file locally, and it will call a function in "other machine" (in this case is localhost) Here is my code : <head> <script> function updateSales(sales) { alert('test jsonp'); // real code here } </script> </head> <body> <h1>JSONP Example</h1> <script src="http://localhost:85/javascript/json1.json?callback=updateSales"></script> </body> But when I run, nothing happen. But if change to other real json on the internet, it will work. It means change line : <script src="http://localhost:85/javascript/json1.json?callback=updateSales"></script> to line: <script src="http://gumball.wickedlysmart.com/?callback=updateSales"></script> It will work smoothly. So, I don't know how to test JSONP by using localhost, please help me. Thanks :)

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• Moving inserted container element if possible

  - by doublep

  I'm trying to achieve the following optimization in my container library: when inserting an lvalue-referenced element, copy it to internal storage; but when inserting rvalue-referenced element, move it if supported. The optimization is supposed to be useful e.g. if contained element type is something like std::vector, where moving if possible would give substantial speedup. However, so far I was unable to devise any working scheme for this. My container is quite complicated, so I can't just duplicate insert() code several times: it is large. I want to keep all "real" code in some inner helper, say do_insert() (may be templated) and various insert()-like functions would just call that with different arguments. My best bet code for this (a prototype, of course, without doing anything real): #include <iostream> #include <utility> struct element { element () { }; element (element&&) { std::cerr << "moving\n"; } }; struct container { void insert (const element& value) { do_insert (value); } void insert (element&& value) { do_insert (std::move (value)); } private: template <typename Arg> void do_insert (Arg arg) { element x (arg); } }; int main () { { // Shouldn't move. container c; element x; c.insert (x); } { // Should move. container c; c.insert (element ()); } } However, this doesn't work at least with GCC 4.4 and 4.5: it never prints "moving" on stderr. Or is what I want impossible to achieve and that's why emplace()-like functions exist in the first place?

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• SQL Server performance issue.

  - by Jit

  Hi Friends, I have been trying to analyze performance issue with SQL Server 2005. We have 30 jobs, one for each databases (30 databases, one per each client). The jobs run at early morning at an interval of 5 minutes. When I run the job individually for testing, for most of the databases it finishes in 7 to 9 minutes. But when these jobs run at early morning, I see few jobs taking 2 to 3 hours to finish and the same takes few minutes as mentioned above if ran independently. We dont have any other job scheduled during that time, other than these 30 jobs. If we restart the server then for 2 or so days all the jobs finishes in few minutes, but over the period of time (from 3rd day suddenly), few jobs start taking hours to finish. What could be the possible reason of performance degradation over the period of time? I verified all the SPs and we uses temp tables and I made sure none of the temp table is left without dropping at the end of SP. Let me know what are the possible reasons for such behavior. Appreciate your time and help. Thanks

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• How do I make a web interface for a socket server

  - by mgroat

  I've got a socket server running (it's something that's basically like a chat server). Users can telnet into it, but I'd like to make a web interface. This is the first time I've ever done something like this, so I'm not really sure where to start. A few thoughts I've had: Have some server-side Python (or PHP) on my webserver, which accesses the socket server. I think I know enough about sockets to have Python interact with the server, but how do I go about getting the website that the user sees to update in real time? Should I just have the website refresh few seconds? I would prefer to do things this way if I can figure out how. Write a Java applet that interacts with the socket server, and embed the applet in the website. I would have to re-learn a language that I haven't touched in years, but my main goal here is learning -- so that wouldn't be such a bad thing. The main problem I have with this is that it requires end users to have Java installed on their computers, which I'd rather not do. Is one of these two solutions the right way to go? Anybody know where I can find a good tutorial to get started? Edit: There's no real security concerns with exposing the server to the internet.

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• How to benchmark on multi-core processors

  - by Pascal Cuoq

  I am looking for ways to perform micro-benchmarks on multi-core processors. Context: At about the same time desktop processors introduced out-of-order execution that made performance hard to predict, they, perhaps not coincidentally, also introduced special instructions to get very precise timings. Example of these instructions are rdtsc on x86 and rftb on PowerPC. These instructions gave timings that were more precise than could ever be allowed by a system call, allowed programmers to micro-benchmark their hearts out, for better or for worse. On a yet more modern processor with several cores, some of which sleep some of the time, the counters are not synchronized between cores. We are told that rdtsc is no longer safe to use for benchmarking, but I must have been dozing off when we were explained the alternative solutions. Question: Some systems may save and restore the performance counter and provide an API call to read the proper sum. If you know what this call is for any operating system, please let us know in an answer. Some systems may allow to turn off cores, leaving only one running. I know Mac OS X Leopard does when the right Preference Pane is installed from the Developers Tools. Do you think that this make rdtsc safe to use again? More context: Please assume I know what I am doing when trying to do a micro-benchmark. If you are of the opinion that if an optimization's gains cannot be measured by timing the whole application, it's not worth optimizing, I agree with you, but I cannot time the whole application until the alternative data structure is finished, which will take a long time. In fact, if the micro-benchmark were not promising, I could decide to give up on the implementation now; I need figures to provide in a publication whose deadline I have no control over.

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• UIDatePicker date method is picking wrong date: iPhone Dev

  - by prd

  Hi, I am getting very strange behaviour on UIDatePicker. I have a view with date picker declared in .h file as IBOutlet UIDatePicker *datePicker; with property nonatomic and retain. datePicker is properly linked in IB file. In the code I am setting the minimum, maximum, initial date and action to call for UICOntrolEventValueChanged using following code If (!currentDate) { initialDate = [NSDate date]; } else { initialDate = currentdate; } [datePicker setMinimumDate:[NSDate date]]; [datePicker setMaximumDate:[[NSDate date] addTimeInterval:5 * 365.25 * 24 * 60 * 60]]; // to get upto 5 years [datePicker setDate:initialDate animated:YES]; [datePicker addTarget:self action:@selector(getDatePickerValue:) forControlEvents:UIControlEventValueChanged]; In getDatePickerValue, I get the new date using datePicker.date. When the view is closed (using a done button), I get the current value of the date using datePicker.date. Now if the view is called with no 'currentDate', the picker returns 'todays date'. This is what happens the 'first' time my pickerView is called. Each subsequent call to the view, with no 'current date' gives me a different and later date from today. So, first time I get today's date say 9 Jun 2010 second time datePicker.date returns 10 Jun 2010 third time 11 Jun 2010 and so on. Though its not always incremental, but mostly it is. I have put NSLogs, and verified the initial date is set correctly. The problem is only on the device (on OS 3.0), the issue is not replicated on simulator. I can't find what I have done wrong. I hope somebody else has come across similar problem and can help me resolve this.

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• Representing complex scheduled reoccurance in a database

  - by David Pfeffer

  I have the interesting problem of representing complex schedule data in a database. As a guideline, I need to be able to represent the entirety of what the iCalendar -- ics -- format can represent, but in a database. I'm not actually implementing anything relating to ics, but it gives a good scope of the type of rules I need to be able to model. I need to allow allow representation of a single event or a reoccurring event based on multiple times per day, days of the week, week of a month, month, year, or some combination of those. For example, the third Thursday in November annually, or the 25th of December annually, or every two weeks starting November 2 and continuing until September 8 the following year. I don't care about insertion efficiency but query efficiency is critical. The operation I will be doing most often is providing either a single date/time or a date/time range, and trying to determine if the defined schedule matches any part of the date/time range. Other operations can be slower. For example, given January 15, 2010 at 10:00 AM through January 15, 2010 at 11:00 AM, find all schedules that match at least part of that time. (i.e. a schedule that covers 10:30 - 11:00 still matches.) Any suggestions? I looked at http://stackoverflow.com/questions/1016170/how-would-one-represent-scheduled-events-in-an-rdbms but it doesn't cover the scope of the type of reoccurance rules I'd like to model.

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• how to know application is going to destroy/remove?

  - by Bhavesh Jethani

  My requirement is, i want to cancel my alarm manager or services when application going to destroy/closed. if i am in activity A by clicking on button started activity B suddenly user is going to press home button. ---- if application is running in background then don't cancel service. but when he going to remove from recent list of application at that time cancel service. Service/Alarm manager will work even when user has sent application in background by pressing home screen. No of way application can destroy or removed. 1) by clicking back button multiple times if stack have multiple activities. 2) by pressing home button and then remove from recent list. i am facing issue with (2)second option. in that when user press home button at that time service or alarm manager should be work. But when user will be going to remove application from recent list at that time i want to cancel service/alarm manager. Second issue. my service is called at fix interval of time. if i will write code on onCreate(), onDestroy() in each activity. then timer will start from beginning. Is there any listners who talk me application is going to closed?

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• Visual Studio 2010: very slow web applications debugging!

  - by micha12

  I recently installed Visual Studio 2010 (Ultimate edition, final version released in April), and found that debugging a web application became very slow (2-3 times slower than in Visual Studio 2008)! I took the same web application and checked the speed of loading of one of its pages in VS 2008 and VS 2010, and compared the time it takes to load the page. I tested it using 2 approaches: 1) debugging under ASP.NET Development Server (by pressing the "Start" button) and 2) using ASP.NET Development Server without debugging (by using the "View in Browser" menu command). And I got the following results for Visual Studio 2008 and 2010. 1) ASP.NET Development Server withoud debugging ("View in Browser"): the speed of page loading is the same in VS 2008 and 2010. 2) Debugging under ASP.NET Development Server ("Start" button): in VS 2010 the page takes more time to load than in VS 2008 - VS 2010 debugging is 2-3 times slower than in VS 2008! 3) At the same time, when debugging a web application in VS 2008, it takes the same time to load the page compared to when using only the "View in Browser" command. That is, VS 2008 debugging does not introduce any overhead to page loading in the web browser! I wanted to make sure that other people have the same problem with slow debugging of web applications in VS 2010. Can this issue be solved by any means? BTW, I am using Windows XP SP3. Thank you.

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• How can I track the last location of a shipment effeciently using latest date of reporting?

  - by hash

  I need to find the latest location of each cargo item in a consignment. We mostly do this by looking at the route selected for a consignment and then finding the latest (max) time entered against nodes of this route. For example if a route has 5 nodes and we have entered timings against first 3 nodes, then the latest timing (max time) will tell us its location among the 3 nodes. I am really stuck on this query regarding performance issues. Even on few hundred rows, it takes more than 2 minutes. Please suggest how can I improve this query or any alternative approach I should acquire? Note: ATA= Actual Time of Arrival and ATD = Actual Time of Departure SELECT DISTINCT(c.id) as cid,c.ref as cons_ref , c.Name, c.CustRef FROM consignments c INNER JOIN routes r ON c.Route = r.ID INNER JOIN routes_nodes rn ON rn.Route = r.ID INNER JOIN cargo_timing ct ON c.ID=ct.ConsignmentID INNER JOIN (SELECT t.ConsignmentID, Max(t.firstata) as MaxDate FROM cargo_timing t GROUP BY t.ConsignmentID ) as TMax ON TMax.MaxDate=ct.firstata AND TMax.ConsignmentID=c.ID INNER JOIN nodes an ON ct.routenodeid = an.ID INNER JOIN contract cor ON cor.ID = c.Contract WHERE c.Type = 'Road' AND ( c.ATD = 0 AND c.ATA != 0 ) AND (cor.contract_reference in ('Generic','BP001','020-543-912')) ORDER BY c.ref ASC

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• Website Live Chat Script - Interface With Windows Live Messenger?

  - by Sootah

  Hello again fellow StackOverflow users! What I am looking for currently is your opinions on the what the best live chat script would be for my website. I'd be using this on both my local computer repair (which I've not really set up yet) company's site, as well as my other technical support site that is geared more towards showing people how to fix whatever problem they have themselves. It'll be a little bit before I launch it on either site, as I need to find a good design for my local computer repair company's site, as well as redesign TweaksForGeeks.com's layout so that it's more magazine like. (If you have any suggestions on good Wordpress templates for these, that'd also be swell. :) ) Features I'd like for the live chat script to have: (if possible) Real-time posting of messages (or as close to real time as possible) Integration into my Windows Live Messenger account - By this I mean it'd be handy if instead of me having to man a separate open browser window and constantly check it for new messages, it'd be much more convenient if it would instead just allow me to receive and respond to messages via my Windows Live account the same way I'd chat with any other person on my contact list. Sound notification of new messages when the chat isn't the focused window - In the event that using Windows Messenger isn't possible then I'd need it to notify me upon receipt of a new message. Recording of chat transcripts - This is a MUST HAVE Easy customization - I'll likely want to modify how it looks and whatnot, in addition to the fact that I'm going to set it up so that the chat transcripts can be posted to my site easily in order to be useful to my other visitors later on. With all that in mind, what is available out there? I've not really researched this at all yet; aside from doing a cursory search just before I decided to ask my StackOverflow brothers. As always, thank you! -Sootah

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• Cache data in SQL CE database

  - by user93422

  Background I have an SQL CE database, that is constantly updated (every second). I have a (web) application that allows a user to look at the data in real-time. At some point a user can click "take a snapshot" button, and it will open the snapshot in a different window. And then on that form, there is "print" and "download" buttons that will either generate a page for printing, or will stream the data as CSV file - but same data snapshot has to be used, i.e. I can't go to the DB to get latest data for that. Details SQL CE dabatase is exposed through WCF web service. Snapshot consists of up to 500 records, 10 columns each. Expiration time on the snapshot of 2 hours is sufficient. It is a low-traffic application, so I don't expect more than few (5) connections at the same time. Loosing snapshot is not a big deal, user can simply generate new one. database is accessed by self-hosted WCF web service using Linq-to-SQL. Web site is ASP.NET MVC hosted on UltiDev Cassini. database, and web site are most likely be on the same box, when deployed. The entire app is intranet bound. Problem I need to cache the snapshot of the data at the moment user pressed "take a snapshot" button, so that I can use same data to generate print page, or generate a file for download. Solution 1: Each time there is a need to generate a snapshot, I will create a table in the database. Since there are no temp tables in SQL CE, I will need to clean it up myself. Solution 2: Cache the snapshot in-memory on either DB server, or web server. Question: Is there anything wrong with proposed solutions? Any different solution suggestions?

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• Helpful advice on developing a professional MS Word add-on

  - by Dan Tao

  A few months back I put together a simple proof-of-concept piece of software for a small firm with an idea for a document editing tool. The company wanted this tool to be integrated into Microsoft Word, understandably, to maximize its accessibility to the average user. I essentially wrote the underlying library with all of the core functionality as a C# project, and then used VSTO to get it running inside of Word. It felt like a bit of a duct tape solution, really; but then, I have (practically) zero experience developing tools for integration with MS Office, and it was only a proof of concept anyway. Well, the firm was quite pleased with my work overall, and they're looking to move from "proof of concept" to the real deal. Fortunately, as I said, the core functionality is all there and will only need to be somewhat tweaked and enhanced. My main concern is figuring out how to put together an application that will integrate with MS Word in a clean and polished way, and which can be deployed easily in accordance with a regular user's expectations (i.e., simply running an install program and voila, it's there in Word). I seem to remember reading somewhere that nobody uses VSTO for real professional projects. Is this true? False? What are the alternatives? And what are the tips and gotchas that I should be aware of before getting started on this issue of MS Word integration?

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• Career Choice in JEE, are EJBs standard?

  - by John Baker

  I have chosen to go the JEE route for a career path but I have been having a hard time determining which core technologies that I need to be most familiar with. I'm at the point I can write web apps without a problem with JSP's and regular servlets using JDBC or some basic Hibernate stuff (I know, HTML, CSS and have used MVC extensively on a number of different platforms). What I'm trying to find out is if there is some standard as far as J2EE technologies go. When I look at most of the Job listings, occasionally you will see someone mention Struts or Spring but rarely do I see any mention of EJB's. So my question is really, are EJB's basically required by most JEE employers? Or are most of them working with POJO's? Is it a mix? I have a hard time figuring out if I should put the majority of my time into Struts, Spring/Hibernate, EJB's, etc. And if I do need to master EJB's what version should I learn? 2.1 or 3.0. 3.0 has some obviously better features but I figure a lot of companies probably chose to write their apps in 2.1 just because it was the standard of the time and now migrating would be a big deal. Any advice on this is greatly appreciated.

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• parsing the output of the 'w' command?

  - by Blackbinary

  I'm writing a program which requires knowledge of the current load on the system, and the activity of any users (it's a load balancer). This is a university assignment, and I am required to use the w command. I'm having a hard time parsing this command because it is very verbose. Any suggestions on what I can do would be appreciated. This is a small part of the program, and I am free to use whatever method i like. The most condensed version of w which still has the information I require is `w -u -s -f' which produces this: 10:13:43 up 9:57, 2 users, load average: 0.00, 0.00, 0.00 USER TTY IDLE WHAT fsm tty7 22:44m x-session-manager fsm pts/0 0.00s w -u -s -f So out of that, I am interested in the first number after load average and the smallest idle time (so i will need to parse them all). My background process will call w, so the fact that w is the lowest idle time will not matter (all i will see is the tty time). Do you have any ideas? Thanks (I am allowed to use alternative unix commands, like grep, if that helps).

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• java GC periodically enters into several full GC cycles

  - by Peter

  Environment: sun JDK 1.6.0_16 vm settings: -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -Xms1024 -Xmx1024M -XX:MaxNewSize=448m -XX:NewSize=448m -XX:SurvivorRatio=4(6 also checked) -XX:MaxPermSize=128M OS: windows server 2003 processor: 4 cores of INTEL XEON 5130, 2000 Hz my application description: high intensity of concurrent(java 5 concurrency used) operations completed each time by commit to oracle. it's about 20-30 threads run non stop, doing tasks. application runs in JBOSS web container. My GC starts work normally, I see a lot of small GCs and all that time CPU shows good load, like all 4 cores loaded to 40-50%, CPU graph is stable. Then , after 1 min of good work, CPU starts drop to 0% on 2 cores from 4, it's graph becomes unstable, goes up and down("teeth"). I see, that my threads work slower(I have monitoring), I see that GC starts produce a lot of FULL GC during that time and next 4-5 minutes this situation remains as is, then for short period of time, like 1 minute, it gets back to normal situation, but shortly after that all bad thing repeats. Question: Why I have so frequent full GC??? How to prevent that? I played with SurvivorRatio - does not help. I noticed, that application behaves normally until first FULL GC occurs, while I have enough memory. Then it runs badly. my GC LOG: starts good then long period of FULL GCs(many of them) 1027.861: [GC 942200K-623526K(991232K), 0.0887588 secs] 1029.333: [GC 803279K(991232K), 0.0927470 secs] 1030.551: [GC 967485K-625549K(991232K), 0.0823024 secs] 1030.634: [GC 625957K(991232K), 0.0763656 secs] 1033.126: [GC 969613K-632963K(991232K), 0.0850611 secs] 1033.281: [GC 649899K(991232K), 0.0378358 secs] 1035.910: [GC 813948K(991232K), 0.3540375 secs] 1037.994: [GC 967729K-637198K(991232K), 0.0826042 secs] 1038.435: [GC 710309K(991232K), 0.1370703 secs] 1039.665: [GC 980494K-972462K(991232K), 0.6398589 secs] 1040.306: [Full GC 972462K-619643K(991232K), 3.7780597 secs] 1044.093: [GC 620103K(991232K), 0.0695221 secs] 1047.870: [Full GC 991231K-626514K(991232K), 3.8732457 secs] 1053.739: [GC 942140K(991232K), 0.5410483 secs] 1056.343: [Full GC 991232K-634157K(991232K), 3.9071443 secs] 1061.257: [GC 786274K(991232K), 0.3106603 secs] 1065.229: [Full GC 991232K-641617K(991232K), 3.9565638 secs] 1071.192: [GC 945999K(991232K), 0.5401515 secs] 1073.793: [Full GC 991231K-648045K(991232K), 3.9627814 secs] 1079.754: [GC 936641K(991232K), 0.5321197 secs]

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• Expand chaining hashtable. Errors on code.

  - by FILIaS

  Expanding a hashtable with linked lists there are some errors and warnings. I wanna make sure that the following code is right (expand method) and find out what happens that raise these warnings/errors typedef struct { int length; struct List *head; struct List *tail; } HashTable; //resolving collisions using linked lists - chaining typedef struct { char *number; char *name; int time; struct List *next; }List; //on the insert method i wanna check hashtable's size, //if it seems appropriate there is the following code: //Note: hashtable variable is: Hashtable * ...... hashtable = expand(hashtable,number,name,time); /**WARNING**:assignment makes pointer from integer without a cast*/ HashTable* expand( HashTable* h ,char number[10],char* name,int time) /**error**: conflicting types for ‘expand’ previous implicit declaration of ‘expand’ was here*/ { HashTable* new; int n; clientsList *node,*next; PrimesIndex++; int new_size= primes[PrimesIndex]; /* double the size,odd length */ if (!(new=malloc((sizeof( List*))*new_size))) return NULL; for(n=0; n< h->length; ++n) { for(node=h[n].head; node; node=next) { add (&new, node->number, node->name,node->time); next=node->next;//// free(node); } } free(h); return new; }

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• Cross-Platform Camera API

  - by Karim

  Hi, I'm now building a video transforming filter that have to transform video frames in real-time. One of the key requirements of the filter is to have high performance to minimize the number of dropped frames during the transform. Another requirement that is of lower priority but also nice to have is to make it cross-platform (both PC's and Mobile devices). The application is built in C++. Now my question is: is there any API that is more portable and has a similar or better performance characteristics than DirectShow? as DirectShow's portability is only limited to Windows-based devices (PCs and Windows Mobile&CE platforms). Also I've notices that for example using HTC's custom camera API has far better performance than what DirectShow offers. If you want to check this, try to build a filter in DirectShow that will multiply each color by 2 and render that in real-time from camera on the screen. Then do the same with HTC's API. There is almost 4-5x performance boost with vendor's specific API. So it'd be very nice if the library used the device-specific implementation of the driver, as performance is critical when doing this transforms on a mobile device (which is about ~500 MHz).

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