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• c++ programming for clusters and HPC

  - by Abruzzo Forte e Gentile

  HI All I need to write a scientific application in C++ doing a lot of computations and using a lot of memory. I have part of the job but due to high requirements in terms of resources I was thinking to start moving to OpenMPI. Before doing that I have a simple curiosity: If I understood the principle of OpenMPI is the developer that has the task of splitting the jobs over different nodes calling SEND and RECEIVE based on node available at that time. Do you know if it does exist some library or OS or whatever that has this capability letting my code reamain as it is now? Basically something that connects all computers and let share as one their memory and CPU? I am a bit confused because of the high material available on the topic. Should I look at cloud computing? or Distributed Shared Memory? Can you help me or address me a bit? Thanks

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• prevent linux thread from being interrupted by scheduler

  - by johnnycrash

  How do you tell the thread scheduler in linux to not interrupt your thread for any reason? I am programming in user mode. Does simply locking a mutex acomplish this? I want to prevent other threads in my process from being scheduled when a certain function is executing. They would block and I would be wasting cpu cycles with context switches. I want any thread executing the function to be able to finish executing without interruption even if the threads' timeslice is exceeded.

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• save state of external running program

  - by SuitUp

  Hi, my goal is to save state of running process and later start from this point. This is not necessary need to be state from this exact moment, let's say save after 5 seconds is good too. Problem is, i can't alter in code of this external program, i am even don't aware of it's architecture. I have resources to save whole program to disk from memory, but i need some tips, where to start. I can't use any VM like Virtual Box to save state of whole operating system, and program can be written in c++ or c or c#...

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• Would this union work if char had stricter alignment requirements than int?

  - by paxdiablo

  Recently I came across the following snippet, which is an attempt to ensure all bytes of i (nad no more) are accessible as individual elements of c: union { int i; char c[sizeof(int)]; }; Now this seems a good idea, but I wonder if the standard allows for the case where the alignment requirements for char are more restrictive than that for int. In other words, is it possible to have a four-byte int which is required to be aligned on a four-byte boundary with a one-byte char (it is one byte, by definition, see below) required to be aligned on a sixteen-byte boundary? And would this stuff up the use of the union above? Two things to note. I'm talking specifically about what the standard allows here, not what a sane implementor/architecture would provide. I'm using the term "byte" in the ISO C sense, where it's the width of a char, not necessarily 8 bits.

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• Regex to find a word, then extract a line containing the first occurence of a different word immedia

  - by Hinchy

  World's most convuluted title I know, an example should explain it better. I have a large txt file in the below format, though details and amount of lines will change everytime: Username: john_joe Owner: John Joe Account: CLI: Default: LGICMD: Flags: Primary days: Secondary days: No access restrictions Expiration: Pwdlifetime: Last Login: Maxjobs: Maxacctjobs: Maxdetach: Prclm: Prio: Queprio: CPU: Authorized Privileges: BYPASS Default Privileges: SYSPRV This sequence is repeated a couple of thousand times for different users. I need to find every user (ideally the entire first line of the above) that has SYSPRV under "Default Permissions". I know I could write an application to do this, I was just hoping their might be a nice regex I could use. Cheers

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• Oracle: TABLE ACCESS FULL with Primary key?

  - by tim

  There is a table: CREATE TABLE temp ( IDR decimal(9) NOT NULL, IDS decimal(9) NOT NULL, DT date NOT NULL, VAL decimal(10) NOT NULL, AFFID decimal(9), CONSTRAINT PKtemp PRIMARY KEY (IDR,IDS,DT) ) ; SQL>explain plan for select * from temp; Explained. SQL> select plan_table_output from table(dbms_xplan.display('plan_table',null,'serial')); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- --------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| --------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 61 | 2 (0)| | 1 | TABLE ACCESS FULL| TEMP | 1 | 61 | 2 (0)| --------------------------------------------------------------- Note ----- - 'PLAN_TABLE' is old version 11 rows selected. SQL server 2008 shows in the same situation Clustered index scan. What is the reason?

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• How to implement low pass filter using java

  - by chai

  Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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• Is there a faster way to draw text?

  - by mystify

  Shark complains about a big performance hit with this line, which takes like 80% of CPU time. I have a counter that is updated very frequently and performance seriously sucks. It's an custom UILabel subclass with -drawRect: implemented. Every time the counter value changes, this is used to draw the new text: [self.text drawInRect:textRect withFont:correctedFont lineBreakMode:self.lineBreakMode alignment:self.textAlignment]; When I comment this line out, performance rocks. Its smooth and fast. So Shark isn't wrong about this. But what could I do to improve this? Maybe go a level deeper? Does that make any sense? Probably drawing text is really so incredible heavy...?

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• How to find root cause for "too many connections" error in MySQL/PHP

  - by Nir

  I'm running a web service which runs algorithms that serve millions of calls daily and run some background processing as well. Every now and than I see "Too many connections" error in attempts to connect to the MySQL box" for a few seconds. However this is not necessarily attributed to high traffic times or anything I can put my finger on. I want to find the bottleneck causing it. Other than in the specific times this happens the server isn't too loaded in terms of CPU and Memory, and has 2-3 connections (threads) open and everything works smoothly. (I use Zabbix for monitoring) Any creative ideas on how to trace it?

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• varnish invalidate url REGEX from backend

  - by ooouuiii

  Say I have some highly-visited front-page, which displays number of some items by categories. When some item is added / deleted I need to invalidate this front-page/url and some 2 others. What is the best practice how to invalidate those urls from backend in Varnish (4.x)? From what I captured, I can: implement my HTTP PURGE handler in VCL configuration file, that "bans" urls matching received regex from backend to Varnish, send 3x HTTP PURGE requests for those 3 urls. But is this approach safe for this automatic usage? Basicly I need to invalidate some views everytime some related entity is inserted/updated/deleted. Can it lead to ban list cumulation and increasing CPU consumption? Is there any other approach? Thanks.

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• Is there any way to retrieve a float from a varargs function's parameters?

  - by Jared P

  If the function was defined with a prototype which explicitly stated the types of the parameters, eg. void somefunc(int arg1, float arg2); but is implemented as void somefunc(int arg1, ...) { ... } is it possible to use va_arg to retrieve a float? It's normally prevented from doing this because varargs functions have implicit type promotions, like float to double, so trying to retrieve an unpromoted type is unsupported, even though the function is being called with the unpromoted type do to the more specific function prototype. The reason for this is to retrieve arguments of different types at runtime, as part of an obj-c interpreter, where one function will be reused for all different types of methods. This would be best as architecture independent (so that if nothing else the same code works on simulator and on device), although if there is no way to do this then device specific fixes will be accepted.

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• How do I change the background image of my iPhone app?

  - by alJaree

  Hello I have looked around and found some code which so called chooses an image from an array of image objects, but cant find an explanation. I would like to make my app have a background image and the user can select next and previous buttons to scroll through some full screen images, setting them as the background image as they scroll. I know how to do this in java, but cant seem to do it for this app. How or what code is linked to a next button to grab the next image in the array and reverse for the back button? Then that needs to be displayed obviously. I have used a layered architecture with a MVC style approach but cant seem to put it together with Objective-C. Would the buttons call the appropriate methods of the so called delegates, which the delegates handle fetching and returning the Images? Would the buttons use the returned images and actually handle the redrawing? I would really appreciate the help. Regards Jarryd

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• How to find which method makes my iPhone app slow ?

  - by Stewart Hou

  Currently I am working on a production app. One function acts like the settings.app on iPhone. When the user click a cell of a tableView, as shown below http://www.penguintech.net/images/stackoverflow/1.png It will push another view, which includes a textfield to let user input something. However, on both simulator and device, after the app just loaded, the delay between clicking and showing the second view takes around 2 seconds. Then if user get back to previous view and click again, it will be no delay at all. To detect which method makes the delay, I put a NSLog() in every involved methods, but when I was inspecting the console while running the app, all NSLog() message showed in 0.1 seconds, and then still a delay on the app. Is there any other way to trace the performance footage of a app? The Instruments shows only CPU usage in Mac OS not in iPhone.

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• How big can a SQL Server row be before it's a problem?

  - by John Leidegren

  Occasionally I run into this limitation using SQL Server 2000 that a row size can not exceed 8K bytes. SQL Server 2000 isn't really state of the art, but it's still in production code and because some tables are denormalized that's a problem. However, this seems to be a non issue with SQL Server 2005. At least, it won't complain that row sizes are bigger than 8K, but what happens instead and why was this a problem in SQL Server 2000? Do I need to care about my rows growing? Should I try and avoid large rows? Are varchar(max) and varbinary(max) a solution or expensive, in terms of size in database and/or CPU time? Why do I care at all about specifying the length of a particular column, when it seems like it's just a matter of time before someones going to hit that upper limit?

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• Query about the service or technology behind gmail service

  - by user1726908

  I am a final year computer science student. I am studying in hyderabad, andhra pradesh, india. I have come to know that the gmail is a cloud service. I am very much interested in learning more about cloud computing. This technology has been puzzling,tickling,increasing my curiosity and i just want to learn as much as i can about it. And through experience, i have learnt that practically doing can improve our knowledge and thirst to learn more. Thus, I would like to know "what are the security measures which you have taken to keep the cloud service like gmail secure and authentic? What is the architecture of the service? What are the technologies used in building it? What are the different levels of security applied in general for building a private cloud?"

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• Zend DB inserting relational data

  - by Wimbjorno

  I'm using the Zend Framework database relationships for a couple of weeks now. My first impression is pretty good, but I do have a question related to inserting related data into multiple tables. For a little test application I've related two tables with each other by using a fuse table. +---------------+ +---------------+ +---------------+ | Pages | | Fuse | | Prints | +---------------+ +---------------+ +---------------+ | pageid | | fuseid | | printid | | page_active | | fuse_page | | print_title | | page_author | | fuse_print | | print_content | | page_created | | fuse_locale | | ... | | ... | | ... | +---------------+ +---------------+ +---------------+ Above is an example of my DB architecture Now, my problem is how to insert related data to two separate tables and insert the two newly created ID's into the fuse table at the same time. If someone could could maybe explain or give me a topic related tutorial. I would appreciate it!

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• How can I write faster JavaScript?

  - by a paid nerd

  I'm writing an HTML5 canvas visualization. According to the Chrome Developer Tools profiler, 90% of the work is being done in (program), which I assume is the V8 interpreter at work calling functions and switching contexts and whatnot. Other than logic optimizations (e.g., only redrawing parts of the visualization that have changed), what can I do to optimize the CPU usage of my JavaScript? I'm willing to sacrifice some amount of readability and extensibility for performance. Is there a big list I'm missing because my Google skills suck? I have some ideas but I'm not sure if they're worth it: Limit function calls When possible, use arrays instead of objects and properties Use variables for math operation results as much as possible Cache common math operations such as Math.PI / 180 Use sin and cos approximation functions instead of Math.sin() and Math.cos() Reuse objects when passing around data instead of creating new ones Replace Math.abs() with ~~ Study jsperf.com until my eyes bleed Use a preprocessor on my JavaScript to do some of the above operations

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• extension file "curl" is must be loaded

  - by Sharvan

  Using XAMPP 1.6.7 I installed the community version of Magento. But there seems to be a problem. I am getting the error message 'extension file "curl" is must be loaded'. In another computer, everything seems fine. (the other computer) intel(R) Pentium(R) Dual CPU, E2140 @ 1.60Hz, 1.60 GHz. 504 MB of RAM and XP professional 2002 sp2 My computer is less powerful (Inet Pentium 4 1.6 GHz. with sp2.) Please help me, thanks.

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• why it is up to the compiler to decide what value to assign when assigning an out-of-range value to

  - by Allopen

  in C++ Primer 4th edition 2.1.1, it says "when assigning an out-of-range value to a signed type, it is up to the compiler to decide what value to assign". I can't understand it. I mean, if you have code like "char 5 = 299", certainly the compiler will generate asm code like "mov BYTE PTR _sc$[ebp], 43"(VC) or "movb $43, -2(%ebp)"(gcc+mingw), it IS decided by the compiler. but what if we assign a value that is given by the user input? like, via command line? and the asm code generated will be "movb %al, -1(%ebp)"(gcc+mingw) and " mov cl, BYTE PTR _i$[ebp] mov BYTE PTR _sc$[ebp], cl "(VC), so now how can compiler decide what will happen? I think now it is decided by the CPU. Can you give me a clear explanation?

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• MS DOS function like ipconfig to get system performance specs?

  - by JustADude

  I am aware of MSINFO32, but I'm wondering if there is a MS DOS command similar to ipconfig in order to get system specifications? I would like for the system specifications to be displayed in the MS DOS prompt. I would like to see at least: CPU RAM BUS speed Thanks for any insights. Edit: I am unable to install any other software, so just have to use existing DOS programming commands to extract this information. Thank you again. 2nd Edit: Whoops. Using Windows XP and Windows Vista.

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• How do I get MSBuild Task to generate XML Documents when building a solution?

  - by toba303

  I have a solution with lots of projects. Each project is configured to generate the XML documentation file when building in Debug-Mode (which is default). That works when I build in Visual Studio 2008. In my build script on my integration server I advise MSBuild to build the whole solution, but it won't generate the documentation files. What can I do? I already tried to explicitly give the Debug-Condition to the build process, but it makes no difference. <Target Name="BuilSolution"> <MSBuild Projects="C:\Path\To\MySolution.sln" targets="Build" Properties="SolutionConfigurationPlatforms='Debug|Any CPU'"/> </Target> There seem to be some ideas to solve this problem when building single projects, but I can't afford to do this, so I need a hint for doing it this way. Thanks in advance!

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• How to read system information in C++ on Windows and Linux?

  - by f4

  I need to read system information like CPU/RAM/disks usage in C++. Maybe swap, network and process too but that's less important. It has probably been done thousand of times before so I first tried to search for a library. Someone here suggested SIGAR, which seems to fit my needs but it has a GPL license and it is for inclusion in a proprietary product. So it's not an option here. I feel like it's something not that easy to implement, as it'll need testing on several platforms. So a library would be welcome. If you don't know of any library, could you point me in the right direction for both platforms?

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• MPI_Bsend and MPI_Isend. How do they work ?

  - by GBBL

  Hi, using buffered send and non blocking send I was wondering how and if they implement a new level of parallelism in my application eventually generating a thread. Imagine that a slave process generates a large amount of data and want to send it to the master. My idea was to start a buffered or non blocking send then immediately begin to compute the next result. Just when I would have to send the new data I wold check if I can reuse the buffer. This would introduce a new level of parallelism in my application between CPU and communication. Does anybody knows how this is done in MPI ? Does MPI generate a new thread to handle the Bsend or Isend ? Thanks.

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• How to optimize indexing of large number of DB records using Zend_Lucene and Zend_Paginator

  - by jdichev

  So I have this cron script that is deployed and ran using Cron on a host and indexes all the records in a database table - the index is later used both for the front end of the site and the backed operations as well. After the operation, the index is about 3-4 MB. The problem is it takes a lot of resources (CPU: 30+ and a good chunk of memory) and slows the machine down. My question is about how to optimize the operation described below: First there is a select query built using the Zend Framework API, this query is then passed to a Paginator factory that returns a paginator which I am using to balance the current number of items being indexed and not iterate over too much items. The script is iterating over the current items in the paginator object using a foreach loop until reaching the end and then it starts from the beginning after getting items for the next page. I am suspecting this overhead is caused by the Zend_Lucene but no idea how this could be improved.

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• Grid computing projects similar to NGrid (thread based)

  - by DivdeAndConquer

  Hello there, first time poster. This is a great place for reading about programming problems. I've been looking at some grid computing projects for .Net/Mono and stumbled upon NGrid. NGrid seems really appealing for grid computing because you simply pass threads to it and there is very little modification you have to make to your code. However, I see that NGrid (http://ngrid.sourceforge.net/?page=overview) is still at version 0.7 and hasn't been updated since May 2008. So, I'm wondering if there are any other grid computing projects that use a similar thread-passing architecture and if anyone has had success using NGrid.

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