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• Where to start when programming process synchronization algorithms like clone/fork, semaphores

  - by David

  I am writing a program that simulates process synchronization. I am trying to implement the fork and semaphore techniques in C++, but am having trouble starting off. Do I just create a process and send it to fork from the very beginning? Is the program just going to be one infinite loop that goes back and forth between parent/child processes? And how do you create the idea of 'shared memory' in C++, explicit memory address or just some global variable? I just need to get the overall structure/idea of the flow of the program. Any references would be appreciated.

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• Programmatic resource monitoring per process in Linux

  - by tuxx

  Hi, I want to know if there is an efficient solution to monitor a process resource consumption (cpu, memory, network bandwidth) in Linux. I want to write a daemon in C++ that does this monitoring for some given PIDs. From what I know, the classic solution is to periodically read the information from /proc, but this doesn't seem the most efficient way (it involves many system calls). For example to monitor the memory usage every second for 50 processes, I have to open, read and close 50 files (that means 150 system calls) every second from /proc. Not to mention the parsing involved when reading these files. Another problem is the network bandwidth consumption: this cannot be easily computed for each process I want to monitor. The solution adopted by NetHogs involves a pretty high overhead in my opinion: it captures and analyzes every packet using libpcap, then for each packet the local port is determined and searched in /proc to find the corresponding process. Do you know if there are more efficient alternatives to these methods presented or any libraries that deal with this problems?

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• http/html/ajax: show result before site is completely processed

  - by chris

  hi! I am looking for a way to show in a webapp in front of a task a wait-message and after it hide the message. The task is running a longer time. I dont know if it is possible at all. The problem is, so far I can see, that the site will be returned to the users browser AFTER the task is completed because the task is part of the site as a inline code replaces by the webserver interpreter (no matter if php, perl or whatever). The only solution I can imagine is to parallel the task with threads or processes and requery the state with ajax in the website. Any idea to do it less complex? Thanks for help! regards chris

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• Custom date time picker for Windows Forms that is locked to GMT time

  - by m3ntat

  Using Visual Studio 2008, c#, .net 2.0. I have a Windows Forms client application that contains a scheduling UI section, currently this is housed only in the London office with the standard datetime picker control, the selected time is saved in a UK database (GMT) and a London based server aapplication processes the schedules. There is a requirement to roll the client out to various global locations, Hong Kong, New York etc and allow them to setup schedules that run according to GMT time on the London server. I'll have a label on screen saying "note schedules are GMT" what I need is a good way to present a datetime picker that always shows and is in sync with the database server's GMT time regardless of where the client app is running globally. Suggestions on how to acheive this? thanks.

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• Parallelism in Python

  - by fmark

  What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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• Outlook Macro not executing

  - by Tim

  Hello all, we are using an an outlook macro for incoming emails to unzip the attachments, log them in sql server and copy them to a special working folder where a windows service processes them. The problems are: the user must be logged in at the server otherwise the macro wont run. I think there is no workaround for this. whenever a modal dialog pops up in outlook and waits for user input, the macro wont execute either (f.e. AutoArchive) I have stopped AutoArchiving all x-days in the options. Because its a productive environment, are there other possible windows preventing the macro to execute, which i must disable now? Our outlook-macro solution surely is not the best because of above problems. Are there better alternatives to read emails, unzip attachments and move them to a working folder? My language is VB.Net and server OS is windows 2008. Regards, Tim

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• What are your build and release steps? When to increment build numbers?

  - by Ed

  I am having trouble defining and automating my build process despite simple requirements: Every build should have a unique build number. Every tagged release should be reproducible What I have: A C++, Red Hat Enterprise Linux 5.x, Subversion development environment. A build machine ( actually a virtual machine ) A version.h file with #defines for major, minor, and buildnumber. A script for incrementing the version.h buildnumber. A rpmbuild spec file that exports the tagged Subversion source, builds, and makes the rpm installer packages. Questions: Assuming multiple developers per project, when should the build number be incremented and version.h file be checked-in? The build machine? Some sort of Subversion hook? Pre-build or post-build? Thanks in advance for those willing to take the time to share their experience with build processes. -Ed Linux newbie. Former Windows C++/.NET developer.

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• SoundPlayer causing Memory Leaks?

  - by Nick Udell

  I'm writing a basic writing app in C# and I wanted to have the program make typewriter sounds as you typed. I've hooked the KeyPress event on my RichTextBox to a function that uses a SoundPlayer to play a short wav file every time a key is pressed, however I've noticed after a while my computer slows to a crawl and checking my processes, audiodlg.exe was using 5 GIGABYTES of RAM. The code I'm using is as follows: I initialise the SoundPlayer as a global variable on program start with SoundPlayer sp = new SoundPlayer("typewriter.wav") Then on the KeyPress event I simply call sp.Play(); Does anybody know what's causing the heavy memory usage? The file is less than a second long, so it shouldn't be clogging the thing up too much.

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• rails wiki site - article edit highlighting/strikethrough with htmldiff maxes cpu

  - by mark

  Hi I'm implementing a wiki style site and want to highlight changes made to articles between successive versions. Using htmldiff to highlight changes works great, except it is rather cpu intensive. I'm using the awesome vestal_versions plugin for versioning. So how best to handle this? I considered having an on_create callback on version creation create a delayed job that processes and then stores the htmldiff processed article (in the version table row). If this is a good approach, how can I extend vestal_versions without touching the gem? Or maybe there would be a better approach. Any advice is much appreciated. :)

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• Android Image Problem and threshold

  - by Danny_E

  Hey Guys, Long time reader never posted until now. Im having some trouble with Android, im implementing a library called JJIL its an open source imaging library. My problem is this i need to run some analysis on an image and to do so i need to have it in jjil.core.image format and once those processes are complete i need to convert the changed image from jjil.core.image to java.awt.image. I cant seem to find a method of doing this does anyone have any ideas or have any experience with this? I would be grateful of any help. Danny

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• What is application and process?

  - by Lu Lu

  An application consists of one or more processes. A process, in the simplest terms, is an executing program. One or more threads run in the context of the process. A thread is the basic unit to which the operating system allocates processor time. A thread can execute any part of the process code, including parts currently being executed by another thread. Source: http://msdn.microsoft.com/en-us/library/ms684841%28VS.85%29.aspx I understand about thread, but I can't distinguish between application & process. What is application? What is process? How do an application have more than 1 process? And please give me an example in C#. Thanks.

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• Python subprocess: callback when cmd exits

  - by Anon

  Hi, I'm currently launching a programme using subprocess.Popen(cmd, shell=TRUE) I'm fairly new to Python, but it 'feels' like there ought to be some api that lets me do something similar to: subprocess.Popen(cmd, shell=TRUE, postexec_fn=function_to_call_on_exit) I am doing this so that function_to_call_on_exit can do something based on knowing that the cmd has exited (for example keeping count of the number of external processes currently running) I assume that I could fairly trivially wrap subprocess in a class that combined threading with the Popen.wait() method, but as I've not done threading in Python yet and it seems like this might be common enough for an API to exist, I thought I'd try and find one first. Thanks in advance :)

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• How to write async background workers that work on WPF flowdocument

  - by iBe

  I'm trying to write a background worker that processes a flowdocument. I can't access the properties of flowdocument objects because of the thread verification. I tried to serialize the document and loaded it on the worker thread which actually solved the thread verfication issue. However, once the processing is complete I also need to use things like TextPointer objects. Those objects now point to a objects in the copy not the original. Can anyone suggest the best way to approach such background processing in WPF?

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• Threading Practice with Polling.

  - by Stacey

  I have a C# application that has to constantly read from a program; sometimes there is a chance it will not find what it needs, which will throw an exception. This is a limitation of the program it has to read from. This frequently causes the program to lock up as it tries to poll. So I solved it by spawning the 'polling' off into a separate thread. However watching the debugger, the thread is created and destroyed each time. I am uncertain if this is typical or not; but my question is, is this good practice, or am I using the threading for the wrong purpose? ProgramReader { static Thread oThread; public static void Read( Program program ) { // check to see if the program exists if ( false ) oThread = new ThreadStart(program.Poll); if(oThread != null || !oThread.IsAlive ) oThread.Start(); } } This is my general pseudocode. It runs every 10 seconds or so. Is this a huge hit to performance? The operation it performs is relatively small and lightweight; just repetitive.

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• Webcrawler, feedback?

  - by Jan Kuboschek

  Hey folks, every once in a while I have the need to automate data collection tasks from websites. Sometimes I need a bunch of URLs from a directory, sometimes I need an XML sitemap (yes, I know there is lots of software for that and online services). Anyways, as follow up to my previous question I've written a little webcrawler that can visit websites. Basic crawler class to easily and quickly interact with one website. Override "doAction(String URL, String content)" to process the content further (e.g. store it, parse it). Concept allows for multi-threading of crawlers. All class instances share processed and queued lists of links. Instead of keeping track of processed links and queued links within the object, a JDBC connection could be established to store links in a database. Currently limited to one website at a time, however, could be expanded upon by adding an externalLinks stack and adding to it as appropriate. JCrawler is intended to be used to quickly generate XML sitemaps or parse websites for your desired information. It's lightweight. Is this a good/decent way to write the crawler, provided the limitations above? http://pastebin.com/VtgC4qVE - Main.java http://pastebin.com/gF4sLHEW - JCrawler.java http://pastebin.com/VJ1grArt - HTMLUtils.java Thanks for your feedback in advance! :)

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• User control always crashes Visual Studio

  - by NickAldwin

  I'm trying to open a user control in one of our projects. It was created, I believe, in VS 2003, and the project has been converted to VS2008. I can view the code fine, but when I try to load the designer view, VS stops responding and I have to close it with the task manager. I have tried leaving it running for several minutes, but it does not do anything. I ran "devenv /log" but didn't see anything unusual in the log. I can't find a specific error message anywhere. Any idea what the problem might be? Is there a lightweight editing mode I might be able to use or something? The reason I need to have a look at the visual representation of this control is to decide where to insert some new components. I've tried googling it and searching SO, but either I don't know what to search or there is nothing out there about this. Any help is appreciated. (The strangest thing is that the user control seems to load fine in another project which references, but VS crashes as soon as I even so much as click on it in that project.)

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• file upload in existing site with jquery and codeigniter

  - by Sam

  I am a new bee to ajax world. I am working on a site which uses jquery and codeigniter which processes big files like 2GB. It basically parses file and stores some extracted data from it, it uses ajax to show how far the files have been processed etc. Now I want to change the way we process files. I want to first store the file on server side and then start the processing. I evaluated upload class of codeigniter but looks like I cannot use it for this purpose as this class works with field_name and I could not find a way to make an ajax call to the upload class. My questions is : What would be suitable for my problem? Thanks in advance, Sam

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• MPI and C structs

  - by hanno

  I have to admit, I was quite shocked to see how many lines of code are required to transfer one C struct with MPI. Under what circumstances will it work to simply transmit a struct using the predefined dataype MPI_CHAR? Consider the following example: struct particle { double x; double y; long i; }; struct particle p; MPI_Isend(&p, sizeof(particle), MPI_CHAR, tag, MPI_COMM_WORLD, &sendr); In my case, all processes run on the same architecture. Is padding the only issue?

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• nginx-tornado-django request timeout

  - by Xie

  We are using nginx-tornado-django to provide web services. That is, no web page frontend. The nginx server serves as a load-balancer. The server has 8 cores, so we launched 8 tornado-django processes on every server. Memcached is also deployed to gain better performance. The requests per day is about 1 million per server. We use MySQL as backend DB. The code is tested and correct. Our profiling shows that normally every request are processed within 100ms. The problem is, we find that about 10 percent of the requests suffers from time-out issue. Many requests didn't even reach tornado. I really don't have much experience on tuning of nginx/tornado/MySQL. Right now I don't have a clue on what is going wrong. Any advise is appreiciated.

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• Is there a way to formerly define a time interval for configuring a process?

  - by gshauger

  Horrible worded question...I know. I'm working on an application that processes data for the previous day. The problem is that I know the customer is going to eventually ask to it for every hour or some other arbitrary time interval. I know that languages such as Java or SQL have masks for defining dates. Well what about a way to define a time interval? Let me ask it this way. If someone asked you to create a configurable piece of software how would you allow the user to specify the time intervals?

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• Elegant setup of Python logging in Django

  - by Parand

  I have yet to find a way of setting up Python logging with Django that I'm happy with. My requirements are fairly simple: Different log handlers for different events - that is, I want to be able to log to different files Easy access to loggers in my modules. The module should be able to find its logger with little effort. Should be easily applicable to command-line modules. Parts of the system are stand-alone command line or daemon processes. Logging should be easily usable with these modules. My current setup is to use a logging.conf file and setup logging in each module I log from. It doesn't feel right. Do you have a logging setup that you like? Please detail it: how do you setup the configuration (do you use logging.conf or set it up in code), where/when do you initiate the loggers, and how do you get access to them in your modules, etc.

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• The Utilization of Software Engineering Development Principles

  - by Chance

  Being a CS student I've had to take a course in basic software engineering. I was a little curious to find such elaborate "software development processes", like the spiral model, the waterfall model, et cetera. Some of these methodologies seem a little antiquated to me and, after speaking with several employed developers, I can't seem to find anyone who actually adheres to these models. Does anyone here have experience working under the guidance of these models? Were they useful to you and your team during the development of your product? Or are these models just some way to communicate a sense of progression to interested parties outside of the development team?

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• How to get a service to listen on port 80 on Windows Server 2003

  - by Miky D

  I've coded a custom windows service that listens on TCP port 80 but when I try to install it on a Windows Server 2003 machine it fails to start because some other service is already listening on that port. So far I've disabled the IIS Admin service and the HTTP SSL service but no luck. When I run netstat -a -n -o | findstr 0.0:80 it gives me the process id 4 as the culprit, but when I look at the running processes that process id points to the "System" process. What can I do to get the System process to stop listening on port 80 and get my service to listen instead? P.S. I should point out that the service runs fine if I install it on my Windows XP or Windows 7 development boxes. Also, I should specify that this has nothing to do with it being a service. I've tried starting a regular application that attempts to bing to port 80 on the Windows Server 2003 with the same outcome - it fails because another application is already bound to that port.

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• ptrace'ing of parent process

  - by osgx

  Hello Can child process use the ptrace system call to trace its parent? Os is linux 2.6 Thanks. upd1: I want to trace process1 from "itself". It is impossible, so I do fork and try to do ptrace(process1_pid, PTRACE_ATTACH) from child process. But I can't, there is a strange error, like kernel prohibits child from tracing their parent processes UPD2: such tracing can be prohibited by security policies. Which polices do this? Where is the checking code in the kernel? UPD3: on my embedded linux I have no errors with PEEKDATA, but not with GETREGS: child: getregs parent: -1 errno is 1, strerror is Operation not permitted errno = EPERM

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• Different return XML in a WCF Operation

  - by Sean Hederman

  I am writing a service to a international HTTP standard, and there is one method that can return three different XML results, call them Single, Multiple and Error. Now I've written an IXmlSerializable class that can consume each of these results and generate them. However, WCF seems to insist that I can only have a single return XML root name. I have to choose an XmlRoot for my custom object of either Single, Multiple or Error. How can I set up WCF so that I can choose at runtime what the root will be? This is what I have currently. /// <summary> /// A collection of items. /// </summary> [XmlRoot("Multiple", Namespace = "DAV:")] public sealed class ItemCollection : IEnumerable<Item>, IXmlSerializable /// <summary> /// Processes and returns the items. /// </summary> [WebInvoke(Method = "POST", UriTemplate = "{*path}", BodyStyle = WebMessageBodyStyle.Bare)] [OperationContract] [XmlSerializerFormat] ItemCollection Process(string path);

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