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  • How to detect pending system shutdown on Linux?

    - by Rajorshi
    Hi, I am working on an app where I need to detect system shutdown. However, I have not found any reliable way get a notification on this event. I know that on shutdown, my app will receive a SIGTERM signal followed by a SIGKILL. What I want to know is if there is someway to query if a SIGTERM is part of a shutdown sequence? Does any one know if there is a way to query that programmatically (C API)? As far as I know, the system does not provide any other method to query for an impending shutdowm. If it does, that would solve my problem as well. I have been trying out runlevels as well, but change in runlevels seem to be instantaneous and without any prior warnings.

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  • Issuing native system commands in Scala

    - by Tony
    I want to issue a native system command from a Scala program, and perhaps trap the output. ("ls" comes to mind. There may be other ways to get directory information without issuing the command, but that's beside the point of my question.) It would correspond to os.system(...) in Python. I've looked in "Programming in Scala". I've looked in O'Reilly's "Programming Scala". I've Googled several combinations of terms. No luck yet. Can someone out there give me an example, or point me at a resource where I can find an example?

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  • HOW TO understand the programmming of operation system..!!!

    - by piemesons
    Hello, I want to learn the operating system. How it works. I dont want to make my own operating system. I just want to learn how it works. As i can find out source code of any open source OS. But how to start. Like stating from the first elementary kernal(what ever it is). Some body suggested me try to implement linux from scratch.etc etc.Please guide me in a proper way. i want to know about the proper path to follow. I am ready to invest three four years just to understand the basics. I am having good fundamentals of c c++,php, Oops, compiler design

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  • Killing a script launched in a Process via os.system()

    - by L.J.
    I have a python script which launches several processes. Each process basically just calls a shell script: from multiprocessing import Process import os import logging def thread_method(n = 4): global logger command = "~/Scripts/run.sh " + str(n) + " >> /var/log/mylog.log" if (debug): logger.debug(command) os.system(command) I launch several of these threads, which are meant to run in the background. I want to have a timeout on these threads, such that if it exceeds the timeout, they are killed: t = [] for x in range(10): try: t.append(Process(target=thread_method, args=(x,) ) ) t[-1].start() except Exception as e: logger.error("Error: unable to start thread") logger.error("Error message: " + str(e)) logger.info("Waiting up to 60 seconds to allow threads to finish") t[0].join(60) for n in range(len(t)): if t[n].is_alive(): logger.info(str(n) + " is still alive after 60 seconds, forcibly terminating") t[n].terminate() The problem is that calling terminate() on the process threads isn't killing the launched run.sh script - it continues running in the background until I either force kill it from the command line, or it finishes internally. Is there a way to have terminate also kill the subshell created by os.system()?

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  • System.Net.WebClient Class in .Net CompactFramework 3.5 ?

    - by Leen15
    Hi at all! I need to comunicate with a Server that give me async answers (streamer connection). I find this: http://msdn.microsoft.com/en-en/library/ms144211%28v=VS.80%29.aspx that generate this event: http://msdn.microsoft.com/en-en/library/system.net.webclient.openreadcompleted%28v=VS.80%29.aspx I think this is what i need, but i don't have the WebClient class in my System.Net of CompactFramework 3.5. How can i do? Thanks. EDIT: I've done a more clear question: httpRequest, httpResponse, send GET through Stream and Receive the Result in C#

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  • pthreads recursively calling system command and segfault appears

    - by jess
    I have a code base where i am creating 8 threads and each thread just calls system command to display date in a continuous cycle, as shown below: void * system_thread(void *arg) { int cpu = (int)arg; printf("thread : start %d\n", cpu); for (;;) { // date ã³ãã³ãã®å®è¡ if (mode == 0) { system("date"); } else { f_hfp_nlc_Fsystem("date"); } } sleep(timerval); return NULL; } This application segfaults after running for 2-3 seconds, due to following 2 reasons: 1. read access, where the address is out of VM area 2. write acces, where it does not of write permission and its trying to modify some structure.

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  • DotNet Get User Operating System (HTTP_USER_AGENT)

    - by rockinthesixstring
    I'm looking at building an exhaustive function that returns a friendly name for the Users Operating System. I think I have most of the Windows stuff down, but I'm not sure about Linux, OSX, and others. Does anyone know where I can find an exhaustive list of HTTP_USER_AGENT's 'Gets the users operating system Public Shared Function GetUserOS() As String Dim strAgent As String = HttpContext.Current.Request.ServerVariables("HTTP_USER_AGENT") 'Windows OS's If InStr(strAgent, "Windows NT 6.1") Then : Return "Windows 7" ElseIf InStr(strAgent, "Windows NT 6.0") Then : Return "Windows Vista" ElseIf InStr(strAgent, "Windows NT 5.2") Then : Return "Windows Server 2003" ElseIf InStr(strAgent, "Windows NT 5.1") Then : Return "Windows XP" ElseIf InStr(strAgent, "Windows NT 5.0") Then : Return "Windows 2000" ElseIf InStr(strAgent, "Windows 98") Then : Return "Windows 98" ElseIf InStr(strAgent, "Windows 95") Then : Return "Windows 95" 'Mac OS's ElseIf InStr(strAgent, "Mac OS X") Then : Return "Mac OS X" 'Linux OS's ElseIf InStr(strAgent, "Linux") Then : Return "Linux" Else : Return "Unknown" End If End Function 'GetUserOS

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  • How to understand the programming of an operating system

    - by piemesons
    Hello, I want to learn the operating system. How it works. I don't want to make my own operating system. I just want to learn how it works. As I can find out source code of any open source OS. But how to start. Like starting from the first elementary kernel (whatever it is). Somebody suggested I try to implement Linux from scratch etc. Please guide me in a proper way. I want to know about the proper path to follow. I am ready to invest three to four years just to understand the basics. I have good fundamentals of C, C++, PHP, OOP and compiler design.

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  • Getting input in system() function (Mac)

    - by Alex
    #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

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  • Creating an email notification system based on polling database rows

    - by Ashish Sharma
    I have to design an email notification system based on the following requirements: The email notifications would be created based on polling rows in a Mysql 5.5 DB table when they are in a particular 'Completed' state. The email notification should be sent out in no more than 5 minutes from the time the row was created in the DB table (At the time of DB table row creation the state of the row might not be 'Completed'). Once 5 minutes for the DB table row expire in reaching the 'Completed' state, separate email notification need to be sent (basically telling the user that the original email notification would be delayed) and then sending the email notification as and when the row state reaches to being 'Completed'. The rest of the system requirements are : Adding relevant checks to monitor the whole system via MBeans interface. The system should be scalable so that if the rate of DB table rows creation increases so does the Email notification system be able to ramp up. So I request suggestions on following lines: What approach should I take in solving the problem described from a programming/Design pattern point of view? Suggestion for any third party plugin/software that can be used to solve the problem described? Points to take care regarding scalability and monitoring the health of the system? Java is the language of preference but I am open to using off the shelf components that can be interfaced with Java language or provide standard ports for communication. Currently I do have an in house grown system (written in Java) that is catering to the specified requirements, but it's now crumbling under increased load and now I want to give the problem a fresh look. thanks in advance Ashish

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  • Bootloader error Ubuntu 12.04, system goes to Grub-rescue instead of booting

    - by user83508
    I am trying to install ubuntu 12.04 on my system but it is constantly giving me bootloader install fail error. I have tried to lot to solve this issue but reading articles over the internet but still no gain. Firstly since the bootloader was not getting installed I tried to install it on all the alternative paths given in the installer, failing with I selected install ubuntu without bootloader. Then I tried to manually install bootloader via terminal at try ubuntu via grub-install, but I was not able to do that. Then I tried using boot-repair and it was also not able to install the bootloader because after it my system shows grub-rescue. I tried to use boot-repair and install bootloader on a seperate partition mounted to /boot and still my system is booting and it still shows grub-rescue. The error which my system shows during boot is: Error : no such device : 04ac0510-bd4f-43b8-b885-b885-11c4dec21db8 I am not dual booting and ubuntu is the only OS I am installing. I am using Raid 0 with two blue western digital hard drive so I am not sure whether it is right or not. The details given by boot-repair are in the below mentioned link; http://paste.ubuntu.com/1147208/ Afterwards, I made one more change I installed ubuntu again and this time I installed the bootloader at a different partition on /boot. After this the bootloader error has gone but I am still not able to boot to ubuntu as I get the same error I was getting before. I have not installed dmraid, I feel it is neccessary for Raid0, but I thought ubuntu already has Raid drivers. Moreover in the dmraid installation instructions for 12.04, I used the one for 10.04 and selected to install bootloader at the partitions from the dropdown. This time the installation finished normally without an error but still I am not able to boot my system as the same error shows during booting this time also. Now I am stucked and I have no clue on how I can boot my system. Please tell me how can I boot my system.

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  • System testing - making sure the system conforms to specification. Validation?

    - by user970696
    After weeks of research I have nearly completed my thesis, yet I am unable to clear up my confusion contained in all previous threads here (and in many books): During system testing, we check the system function against system analysis (functional system design) - but that would fit to a definition of verification according to many books. But I follow ISO12207, which considers all testing as validation (making sure work product meets requirement for intended use). How can I justify that unit testing or system testing is validation, even though when I check it against specification? Which fullfils the definiton of verification? When testing that e.g. "Save button" works, is it validation? This picture shows my understanding of V&V, so different from many other sources, including ISTQB etc. Essential problem I have is that a book using the same picture also states on another place that: test activities in the area of validation are usability, alpha and beta testing. For verification, testable system requirements are defined whose correct implementation can be tested through system tests. Isn't that the opposite of what the picture says? Most books present the following picture, where validation is just making sure that customer needs are satisfied. Mind you that according to ISO, validation activity is testing.

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  • Web migration of a VB6 system with VWG

    - by Webgui
    Brinks Bolivia eSAC System (Customer Service) allows to register all different kinds of contacts for a customer; addition to maintaining an updated status of each service or customer request, to have accurate information and perform the appropriate procedures for all applications. The system was originally developed in VB6 and since web access was essential it was offered via Citrix. Since the application's performance was a critical issue as well as the need to offer the system without specific installations the company looked for a solution that would solve those drawbacks of using Citrix. Searching for a solution that would allow it to offer the eSAC system over the web without the need for specific client installations and provide sufficient performance levels even when there is limited bandwidth lead Brinks to a decision to migrate their VB6 Customer Service system to to Visual WebGui. "Developing on Visual WebGui we were able to migrate the system to web environment and even add new features in less time which allows us to offer it over a standard web browser with better performance and no installations as was required with Citrix," concluded Alexander Cuellar. The full article and screenshots of the system are available here.

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  • Can't start system due to mdadm failing

    - by user101212
    I used to have a 5-disk RAID5 partition, all working very well. I have then decided to add 3 more disks on it, totaling 8 equal disks. I've opened Webmin and just asked to add the disks. Then I've realized the three disks had NTFS partitions, wich mdadm didn't complain, so I tried to stop the growing to remove the Windows partitions. I've tried to remove a disk using the same Webmin, but (as you might guess and call me fool...), the system became unstable. By restarting the system, I've started receiving these messages: "udev[126]: timeout: killing '/sbin/mdadm --incremental /dev/sdh1' [311]" "udev[124]: timeout: killing '/sbin/mdadm --detail --export /dev/md0' [316]" I've formated the system disk, hoping to get a system up and running. I did that with all RAID disks disconected, so everything was fine. I then reconnected the disks, wich was also ok. And finally installed mdadm using apt-get. By reboot, the system has found the mdadm intention of growing the system, so the same messages appear again. I other words: I can't even reach a command prompt to do something. Any ideas of what to do? I believe I could turn off the system, disconnect the disks and look for the mdadm.conf file. Would that be a good idead? I'm no Linux expert, so I'm really lost here.

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  • How to train yourself to avoid writing “clever” code?

    - by Dan Abramov
    Do you know that feeling when you just need to show off that new trick with Expressions or generalize three different procedures? This does not have to be on Architecture Astronaut scale and in fact may be helpful but I can't help but notice someone else would implement the same class or package in a more clear, straightforward (and sometimes boring) manner. I noticed I often design programs by oversolving the problem, sometimes deliberately and sometimes out of boredom. In either case, I usually honestly believe my solution is crystal clear and elegant, until I see evidence to the contrary but it's usually too late. There is also a part of me that prefers undocumented assumptions to code duplication, and cleverness to simplicity. What can I do to resist the urge to write “cleverish” code and when should the bell ring that I am Doing It Wrong? The problem is getting even more pushing as I'm now working with a team of experienced developers, and sometimes my attempts at writing smart code seem foolish even to myself after time dispels the illusion of elegance.

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  • Data validation best practices: how can I better construct user feedback?

    - by Cory Larson
    Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. I've migrated this question from StackOverflow where I originally asked it with little response. Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interested in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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  • What "bad practice" do you do, and why?

    - by coppro
    Well, "good practice" and "bad practice" are tossed around a lot these days - "Disable assertions in release builds", "Don't disable assertions in release builds", "Don't use goto.", we've got all sorts of guidelines above and beyond simply making your program work. So I ask of you, what coding practices do you violate all the time, and more importantly, why? Do you disagree with the establishment? Do you just not care? Why should everyone else do the same? cross links: What's your favorite abandoned rule? Rule you know you should follow but don't

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  • Which software development methodologies can be seen as foundations

    - by Bas
    I'm writing a small research paper which involves software development methodologiess. I was looking into all the available methodology's and I was wondering, from all methodologies, are there any that have provided the foundations for the others? For an example, looking at the following methodologies: Agile, Prototyping, Cleanroom, Iterative, RAD, RUP, Spiral, Waterfall, XP, Lean, Scrum, V-Model, TDD. Can we say that: Prototyping, Iterative, Spiral and Waterfall are the "foundation" for the others? Or is there no such thing as "foundations" and does each methodology has it's own unique history? I would ofcourse like to describe all the methodology's in my research paper, but I simply don't have the time to do so and that is why I would like to know which methodologies can be seen as representatives.

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  • Where can I find video resources of people programming?

    - by Corey
    This might be a strange question. I'm looking for videos of people actively coding something while explaining it. However, I don't want is a beginner video that delves into what variables and objects are. Nick Gravelyn's tile engine tutorial is a great example of what I'm looking for. (He actually used to host the full, unbroken video files in his site's archive, but I guess he took them down...) I tend to learn best by "action" examples; it's difficult for me to learn by reading through documentation and text tutorials, but if I see somebody actively doing a task, I can immediately register it and apply it myself. I'm hard-of-hearing, so I would really prefer that if the video has a lot of talking, it have captioning or subtitling of some sort, or at the very least, a transcript. The tile engine videos did not have captions, but the code he was writing was very self-documenting, so I understood it for the most part. I've gone through most of the relevant GoogleDevelopers and GoogleTechTalks videos on Youtube, so those need not apply. Are there any resources out there, or even websites dedicated to this kind of thing?

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  • Why are invariants important in Computer Science

    - by Antony Thomas
    I understand 'invariant' in its literal sense. I also recognize them when I type code. But I don't think I understand the importance of this term in the context of computer science. Whenever I read conversations\white papers about language design from famous programmers\computer scientists, the term 'invariant' keeps popping up as a jargon; and that is the part I don't understand. What is so special about it?

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  • Is there a better term than "smoothness" or "granularity" to describe this language feature?

    - by Chris Stevens
    One of the best things about programming is the abundance of different languages. There are general purpose languages like C++ and Java, as well as little languages like XSLT and AWK. When comparing languages, people often use things like speed, power, expressiveness, and portability as the important distinguishing features. There is one characteristic of languages I consider to be important that, so far, I haven't heard [or been able to come up with] a good term for: how well a language scales from writing tiny programs to writing huge programs. Some languages make it easy and painless to write programs that only require a few lines of code, e.g. task automation. But those languages often don't have enough power to solve large problems, e.g. GUI programming. Conversely, languages that are powerful enough for big problems often require far too much overhead for small problems. This characteristic is important because problems that look small at first frequently grow in scope in unexpected ways. If a programmer chooses a language appropriate only for small tasks, scope changes can require rewriting code from scratch in a new language. And if the programmer chooses a language with lots of overhead and friction to solve a problem that stays small, it will be harder for other people to use and understand than necessary. Rewriting code that works fine is the single most wasteful thing a programmer can do with their time, but using a bazooka to kill a mosquito instead of a flyswatter isn't good either. Here are some of the ways this characteristic presents itself. Can be used interactively - there is some environment where programmers can enter commands one by one Requires no more than one file - neither project files nor makefiles are required for running in batch mode Can easily split code across multiple files - files can refeence each other, or there is some support for modules Has good support for data structures - supports structures like arrays, lists, and especially classes Supports a wide variety of features - features like networking, serialization, XML, and database connectivity are supported by standard libraries Here's my take on how C#, Python, and shell scripting measure up. Python scores highest. Feature C# Python shell scripting --------------- --------- --------- --------------- Interactive poor strong strong One file poor strong strong Multiple files strong strong moderate Data structures strong strong poor Features strong strong strong Is there a term that captures this idea? If not, what term should I use? Here are some candidates. Scalability - already used to decribe language performance, so it's not a good idea to overload it in the context of language syntax Granularity - expresses the idea of being good just for big tasks versus being good for big and small tasks, but doesn't express anything about data structures Smoothness - expresses the idea of low friction, but doesn't express anything about strength of data structures or features Note: Some of these properties are more correctly described as belonging to a compiler or IDE than the language itself. Please consider these tools collectively as the language environment. My question is about how easy or difficult languages are to use, which depends on the environment as well as the language.

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  • Is there any functional difference between immutable value types and immutable reference types?

    - by Kendall Frey
    Value types are types which do not have an identity. When one variable is modified, other instances are not. Using Javascript syntax as an example, here is how a value type works. var foo = { a: 42 }; var bar = foo; bar.a = 0; // foo.a is still 42 Reference types are types which do have an identity. When one variable is modified, other instances are as well. Here is how a reference type works. var foo = { a: 42 }; var bar = foo; bar.a = 0; // foo.a is now 0 Note how the example uses mutatable objects to show the difference. If the objects were immutable, you couldn't do that, so that kind of testing for value/reference types doesn't work. Is there any functional difference between immutable value types and immutable reference types? Is there any algorithm that can tell the difference between a reference type and a value type if they are immutable? Reflection is cheating. I'm wondering this mostly out of curiosity.

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  • Game Components, Game Managers and Object Properties

    - by George Duckett
    I'm trying to get my head around component based entity design. My first step was to create various components that could be added to an object. For every component type i had a manager, which would call every component's update function, passing in things like keyboard state etc. as required. The next thing i did was remove the object, and just have each component with an Id. So an object is defined by components having the same Ids. Now, i'm thinking that i don't need a manager for all my components, for example i have a SizeComponent, which just has a Size property). As a result the SizeComponent doesn't have an update method, and the manager's update method does nothing. My first thought was to have an ObjectProperty class which components could query, instead of having them as properties of components. So an object would have a number of ObjectProperty and ObjectComponent. Components would have update logic that queries the object for properties. The manager would manage calling the component's update method. This seems like over-engineering to me, but i don't think i can get rid of the components, because i need a way for the managers to know what objects need what component logic to run (otherwise i'd just remove the component completely and push its update logic into the manager). Is this (having ObjectProperty, ObjectComponent and ComponentManager classes) over-engineering? What would be a good alternative?

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  • Do you think natively compiled languages have reached their EOL?

    - by Yuval A
    If we look at the major programming languages in use today it is pretty noticeable that the vast majority of them are, in fact, interpreted. Looking at the largest piece of the pie we have Java and C# which are both enterprise-ready, heavy-duty, serious programming languages which are basically compiled to byte-code only to be interpreted by their respective VMs (the JVM and the CLR). If we look at scripting languages, we have Perl, Python, Ruby and Lua which are all interpreted (either from code or from bytecode - and yes, it should be noted that they are absolutely not the same). Looking at compiled languages we have C which is nowadays used in embedded and low-level, real-time environments, and C++ which is still alive and kicking, when you want to get down to serious programming as close to the hardware as you can, but still have some nice abstractions to help you with day to day tasks. Basically, there is no real runner-up compiled language in the distance. Do you feel that languages which are natively compiled to executable, binary code are a thing of the past, taken over by interpreted languages which are much more portable and compatible? Does C++ mark an end of an era? Why don't we see any new compiled languages anymore? I think I should clarify: I do not want this to turn into a "which language is better" discussion, because that is not the issue at hand. The languages I gave as example are only examples. Please focus on the question I raised, and if you disagree with my statement that compiled languages are less frequent these days, that is totally fine, I am more than happy to be proved mistaken.

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