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  • Is it wrong to get feedback from Stack Overflow on a live system architecture?

    - by hal10001
    I am the technical director at a startup, and I will eventually be tasked with implementing a "real" system architecture when we hire more programmers. Right now our clients are small enough, and it is just me, so documented deployments, source control, unit tests and quality assurance servers are non-existent. Eventually I will need to devise a work-flow and architecture patterns for the majority of the work we will do (e-commerce). If I posted an architecture diagram, and asked for feedback, would that be a misuse of the Stack Overflow system? I don't want to get into that battle of "hey, don't ask us to do your job for you", but the reality is that any programmer who eventually moves into this realm will have to figure it out with feedback from other developers. HighScalability.com is what comes to mind when I think about this sorta thing in terms of the knowledge I need. So if this is not the right kind of forum for that, then any book recommendations or white papers you can recommend would be appreciated.

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  • Reading a child process's /proc/pid/mem file from the parent

    - by Amittai Aviram
    In the program below, I am trying to cause the following to happen: Process A assigns a value to a stack variable a. Process A (parent) creates process B (child) with PID child_pid. Process B calls function func1, passing a pointer to a. Process B changes the value of variable a through the pointer. Process B opens its /proc/self/mem file, seeks to the page containing a, and prints the new value of a. Process A (at the same time) opens /proc/child_pid/mem, seeks to the right page, and prints the new value of a. The problem is that, in step 6, the parent only sees the old value of a in /proc/child_pid/mem, while the child can indeed see the new value in its /proc/self/mem. Why is this the case? Is there any way that I can get the parent to to see the child's changes to its address space through the /proc filesystem? #include <fcntl.h> #include <stdbool.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/wait.h> #include <unistd.h> #define PAGE_SIZE 0x1000 #define LOG_PAGE_SIZE 0xc #define PAGE_ROUND_DOWN(v) ((v) & (~(PAGE_SIZE - 1))) #define PAGE_ROUND_UP(v) (((v) + PAGE_SIZE - 1) & (~(PAGE_SIZE - 1))) #define OFFSET_IN_PAGE(v) ((v) & (PAGE_SIZE - 1)) # if defined ARCH && ARCH == 32 #define BP "ebp" #define SP "esp" #else #define BP "rbp" #define SP "rsp" #endif typedef struct arg_t { int a; } arg_t; void func1(void * data) { arg_t * arg_ptr = (arg_t *)data; printf("func1: old value: %d\n", arg_ptr->a); arg_ptr->a = 53; printf("func1: address: %p\n", &arg_ptr->a); printf("func1: new value: %d\n", arg_ptr->a); } void expore_proc_mem(void (*fn)(void *), void * data) { off_t frame_pointer, stack_start; char buffer[PAGE_SIZE]; const char * path = "/proc/self/mem"; int child_pid, status; int parent_to_child[2]; int child_to_parent[2]; arg_t * arg_ptr; off_t child_offset; asm volatile ("mov %%"BP", %0" : "=m" (frame_pointer)); stack_start = PAGE_ROUND_DOWN(frame_pointer); printf("Stack_start: %lx\n", (unsigned long)stack_start); arg_ptr = (arg_t *)data; child_offset = OFFSET_IN_PAGE((off_t)&arg_ptr->a); printf("Address of arg_ptr->a: %p\n", &arg_ptr->a); pipe(parent_to_child); pipe(child_to_parent); bool msg; int child_mem_fd; char child_path[0x20]; child_pid = fork(); if (child_pid == -1) { perror("fork"); exit(EXIT_FAILURE); } if (!child_pid) { close(child_to_parent[0]); close(parent_to_child[1]); printf("CHILD (pid %d, parent pid %d).\n", getpid(), getppid()); fn(data); msg = true; write(child_to_parent[1], &msg, 1); child_mem_fd = open("/proc/self/mem", O_RDONLY); if (child_mem_fd == -1) { perror("open (child)"); exit(EXIT_FAILURE); } printf("CHILD: child_mem_fd: %d\n", child_mem_fd); if (lseek(child_mem_fd, stack_start, SEEK_SET) == (off_t)-1) { perror("lseek"); exit(EXIT_FAILURE); } if (read(child_mem_fd, buffer, sizeof(buffer)) != sizeof(buffer)) { perror("read"); exit(EXIT_FAILURE); } printf("CHILD: new value %d\n", *(int *)(buffer + child_offset)); read(parent_to_child[0], &msg, 1); exit(EXIT_SUCCESS); } else { printf("PARENT (pid %d, child pid %d)\n", getpid(), child_pid); printf("PARENT: child_offset: %lx\n", child_offset); read(child_to_parent[0], &msg, 1); printf("PARENT: message from child: %d\n", msg); snprintf(child_path, 0x20, "/proc/%d/mem", child_pid); printf("PARENT: child_path: %s\n", child_path); child_mem_fd = open(path, O_RDONLY); if (child_mem_fd == -1) { perror("open (child)"); exit(EXIT_FAILURE); } printf("PARENT: child_mem_fd: %d\n", child_mem_fd); if (lseek(child_mem_fd, stack_start, SEEK_SET) == (off_t)-1) { perror("lseek"); exit(EXIT_FAILURE); } if (read(child_mem_fd, buffer, sizeof(buffer)) != sizeof(buffer)) { perror("read"); exit(EXIT_FAILURE); } printf("PARENT: new value %d\n", *(int *)(buffer + child_offset)); close(child_mem_fd); printf("ENDING CHILD PROCESS.\n"); write(parent_to_child[1], &msg, 1); if (waitpid(child_pid, &status, 0) == -1) { perror("waitpid"); exit(EXIT_FAILURE); } } } int main(void) { arg_t arg; arg.a = 42; printf("In main: address of arg.a: %p\n", &arg.a); explore_proc_mem(&func1, &arg.a); return EXIT_SUCCESS; } This program produces the output below. Notice that the value of a (boldfaced) differs between parent's and child's reading of the /proc/child_pid/mem file. In main: address of arg.a: 0x7ffffe1964f0 Stack_start: 7ffffe196000 Address of arg_ptr-a: 0x7ffffe1964f0 PARENT (pid 20376, child pid 20377) PARENT: child_offset: 4f0 CHILD (pid 20377, parent pid 20376). func1: old value: 42 func1: address: 0x7ffffe1964f0 func1: new value: 53 PARENT: message from child: 1 CHILD: child_mem_fd: 4 PARENT: child_path: /proc/20377/mem CHILD: new value 53 PARENT: child_mem_fd: 7 PARENT: new value 42 ENDING CHILD PROCESS.

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  • How does operating system software maintains time clocks?

    - by Neeraj
    Hi everyone, This may sound a bit less relevant but I couldn't think of a better place to ask this question. Now consider this situation, you install an OS on your system, set the timezone and time, do some stuff and turn it off. (Note that there is no power going in to the computer). Now next time (say after some hours or days) you turn it on again, and you see the updated time. How is this possible even when my computer is not connected to the internet and was consuming no power during the period it was down.(Is there some kind of hardware hack?) please clarify!

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  • Returning the same type the function was passed

    - by Ken Bloom
    I have the following code implementation of Breadth-First search. trait State{ def successors:Seq[State] def isSuccess:Boolean = false def admissableHeuristic:Double } def breadthFirstSearch(initial:State):Option[List[State]] = { val open= new scala.collection.mutable.Queue[List[State]] val closed = new scala.collection.mutable.HashSet[State] open.enqueue(initial::Nil) while (!open.isEmpty){ val path:List[State]=open.dequeue() if(path.head.isSuccess) return Some(path.reverse) closed += path.head for (x <- path.head.successors) if (!closed.contains(x)) open.enqueue(x::path) } return None } If I define a subtype of State for my particular problem class CannibalsState extends State { //... } What's the best way to make breadthFirstSearch return the same subtype as it was passed? Supposing I change this so that there are 3 different state classes for my particular problem and they share a common supertype: abstract class CannibalsState extends State { //... } class LeftSideOfRiver extends CannibalsState { //... } class InTransit extends CannibalsState { //... } class RightSideOfRiver extends CannibalsState { //... } How can I make the types work out so that breadthFirstSearch infers that the correct return type is CannibalsState when it's passed an instance of LeftSideOfRiver? Can this be done with an abstract type member, or must it be done with generics?

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  • How to manipulate *huge* amounts of data

    - by Alejandro
    Hi there! I'm having the following problem. I need to store huge amounts of information (~32 GB) and be able to manipulate it as fast as possible. I'm wondering what's the best way to do it (combinations of programming language + OS + whatever you think its important). The structure of the information I'm using is a 4D array (NxNxNxN) of double-precission floats (8 bytes). Right now my solution is to slice the 4D array into 2D arrays and store them in separate files in the HDD of my computer. This is really slow and the manipulation of the data is unbearable, so this is no solution at all! I'm thinking on moving into a Supercomputing facility in my country and store all the information in the RAM, but I'm not sure how to implement an application to take advantage of it (I'm not a professional programmer, so any book/reference will help me a lot). An alternative solution I'm thinking on is to buy a dedicated server with lots of RAM, but I don't know for sure if that will solve the problem. So right now my ignorance doesn't let me choose the best way to proceed. What would you do if you were in this situation? I'm open to any idea. Thanks in advance!

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  • Are there any languages that are dynamically typed but do not allow weak typing?

    - by Maulrus
    For example, adding a (previously undeclared) int and a string in pseudocode: x = 1; y = "2"; x + y = z; I've seen strongly typed languages that would not allow adding the two types, but those are also statically typed, so it's impossible to have a situation like above. On the other hand, I've seen weakly typed languages that allow the above and are statically typed. Are there any languages that are dynamically typed but are also strongly typed as well, so that the piece of code above would not be valid?

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  • open source gossip-based membership protocol?

    - by Aaron
    I am looking for a library which I can plug into a distributed application which implements any gossip-based membership protocol. Such a library would allow me to send/receive membership lists, merge received membership lists, etc... Even better would be if the library implemented a protocol with performance O(logn) performance guarantees. Does anyone know of any open source library like this? It doesn't need to meet all of the aforementioned requirements; even something partially implemented would be helpful.

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  • Extending the .NET type system so the compiler enforces semantic meaning of primitive values in cert

    - by Drew Noakes
    I'm working with geometry a bit at the moment and am converting a lot between degrees and radians. Unfortunately, both of these are represented by double, so there's compile time warning/error if I try to pass a value in degrees where radians are expected. I believe F# has a compile-time solution for this (called units of measure.) I'd like to do something similar in C#. As another example, imagine a SQL library that accepts various query parameters as strings. It'd be good to have a way of enforcing that only clean strings were allowed to be passed in at runtime, and the only way to get a clean string was to pass through some SQL injection attack preventing logic. The obvious solution is to wrap the double/string/whatever in a new type to give it the type information the compiler needs. I'm curious if anyone has an alternative solution. If you do think wrapping is the only/best way, then please go into some of the downsides of the pattern (and any upsides I haven't mentioned too.) I'm especially concerned about the performance of abstracted primitive numeric types on my calculations at runtime.

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  • Ubuntu Linux main utilities

    - by Harry
    I've never used Ubuntu Linux before, but I am researching about the main system tools that are included, e.g. Windows has Disk Cleanup, Disk Defrag... but what does Ubuntu Linux have. I need to know what the main five utilities that are included on Ubuntu Linux and what do they do.

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  • Bash PATH: How long is too long?

    - by ajwood
    Hi, I'm currently designing a software quarantine pattern to use on Ubuntu. I'm not sure how standard "quarantine" is in this context, so here is what I hope to accomplish... Inside a particular quarantine is all of the stuff one needs to run an application (bin, share, lib, etc.). Ideally, the quarantine has no leaks, which means it's not relying on any code outside of itself on the system. A quarantine can be defined as a set of executables (and some environment settings needed to make them run). I think it will be beneficial to separate the built packages enough such that upgrading to a newer version of the quarantine won't require rebuilding the whole thing. I'll be able to update just a few packages, and then the new quarantine can use some of old parts and some of the new parts. One issue I'm wondering about is the environment variables I'll be setting up to use a particular quarantines. Is there a hard limit on how big PATH can be? (either in number of characters, or in the number of directories it contains) Might a path be so long that it affects performance? Thanks very much, Andrew p.s. Any other wisdom that might help my design would be greatly appreciated :)

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  • How to use a class's type as the type argument for an inherited collection property in C#

    - by Edelweiss Peimann
    I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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  • How to receive packets on the MCU's serial port?

    - by itisravi
    Hello, Consider this code running on my microcontroller unit(MCU): while(1){ do_stuff; if(packet_from_PC) send_data_via_gpio(new_packet); //send via general purpose i/o pins else send_data_via_gpio(default_packet); do_other_stuff; } The MCU is also interfaced to a PC via a UART.Whenever the PC sends data to the MCU, the *new_packet* is sent, otherwise the *default_packet* is sent.Each packet can be 5 or more bytes with a pre defined packet structure. My question is: 1.Should i receive the entire packet from PC using inside the UART interrut service routine (ISR)? In this case, i have to implement a state machine inside the ISR to assemble the packet (which can be lengthy with if-else or switch-case blocks). 2.Detect a REQUEST command (one byte)from the PC in my ISR set a flag, diable UART interrupt alone and form the packet in my while(1) loop by polling the UART?

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  • Benefits and features of different requirements-management systems and tools available?

    - by Gnark
    I am looking for a good comparision of different available professionial requirement managment tools. I am especially interested in the the features available within the different software solutions. Additionally to the "obvious" features I am looking for a proffesional Requirement Management System that supports for: multi-lingual customizable generation of documentation & history (graphs) search features (e.g. fulltext for comments), ordering, priorities version history bi-directional traceability of changes, artefacts, requirements, changes in requirements, etc. Any kind of integration of V-Model XT would be a really-nice-to-have-feature... Besides, I'd like to hear any personal motivated recommendations and/or experiences with different requirement management systems. Any input is highly appreciated. content consulted : similar question reqm tool with v-model nice, but too old paper (pdf) Tools Journal

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  • Benefits and features of different requirements-management systems and tools available?

    - by DevDevDave
    I am looking for a good comparision of different available professional requirement management tools. I am especially interested in the the features available within the different software solutions. Additionally to the "obvious" features I am looking for a proffesional Requirement Management System that supports for: multi-lingual customizable generation of documentation & history (graphs) search features (e.g. fulltext for comments), ordering, priorities version history bi-directional traceability of changes, artefacts, requirements, changes in requirements, etc. Any kind of integration of V-Model XT would be a really-nice-to-have-feature. Besides, I'd like to hear any personal motivated recommendations and/or experiences with different requirement management systems. Any input is highly appreciated. Content consulted: similar question reqm tool with v-model ToolsJournal.com nice, but too old paper (pdf)

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  • Which of the following relational database management systems would a company adopt (for migration), if any, MS Access, MS SQL Server or MySQL?

    - by Hassan Hagi
    Dear programmers, as part of my final year university project, I am conducting research into relational database management systems such as Microsoft Office Access 2007, Microsoft SQL Server 2008 and MySQL 5.1. The description does not need to be detailed however; I am trying to find empirical evidence and professional opinion/fact to determine which of the three databases are best suited for the required size of company (stated or unstated). OS: Microsoft windows (XP or newer) Please consider the following, but full details are not necessary: Memory management Migration Design constraints Integrity (data and others) Triggers User constraints Ease of use Performance Crash Recovery (not the operating system) Total Cost of Ownership (TCO) Also any info on Open source (to do with the three RDBMS) Thank you for your time and help. Hassan Hagi

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  • what are the best concert-ticket systems? comercial and open source

    - by helle
    can anybody recommend (of developers-opinion) such systems, where you can book tickets for concerts, conferences, etc. one should be able to book a seat as well, and it shell do the debitcard stuff, and has a good interface for accounting. I am looking for an open source solution, but I am also interested in commercial ones, to have a comparison of features and prices, etc. thanks for everybodys suggestions - pros and cons to it are very wellcome ;) well, it shouldn't has a flash component multi languages :) would be great an extra mobile-view is preferred the extra extra bonus for such a system would be a very good wordpress compatibility p.s. sorry for my english well ... I already googled a lot. But I found so very many, that I hope you could help me to find a good choice, to have a base from where I can do a further lookup. and for sure :) What are the things you I have to have in mind. What brings troubles, what brings costs?

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  • Web Platform Installer issues deploying Azure SDK 1.4 on refreshed systems.

    - by Enrique Lima
    Recently I have been doing quite a bit of testing on different means to deploy the Azure SDKs and such. After a very successful couple of systems, I started running into issues last night. Here is the problem, if I go to the Windows Azure Website, and go to Develop, then click on the SDK and Tools, then Get Tools & SDK, it launches the Web Platform Installer.  All seems well at that point, except it will go through the initial process, will find the SDK files for 1.4, but since the tools for Visual Studio are still 1.3, the location throws back a 404, which causes the Installer to fail.  NOTE:If you already had SDK 1.3 and the tools in place, it will go through. The fix is to go directly to the Microsoft Download Center location and download the files.  Here is the link … http://www.microsoft.com/downloads/en/details.aspx?FamilyID=7a1089b6-4050-4307-86c4-9dadaa5ed018

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  • Is installing Rational Developer for Power Systems on Ubuntu recommended?

    - by ZS6JCE
    I am interested in installing Rational Developer for Power 8.0.3 (RDPi) on Ubuntu 12.04. I would like to know if other Ubuntu users have run into issues? Is it recommended or should I just stick to using RDPi in Windows 7 in VirtualBox? I have done some research, but could not divine a solution. From IBM's Developerworks website: Ubuntu clients are obviously missing from the list. While not officially supported, we have had some success in running ... on Ubuntu 10.04 LTS and later. Detailed installation instructions for the supported operation systems can be found here.

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  • best approach to learning for an undergrad operating systems course?

    - by rrazd
    what is the best approach to learning for an undergrad operating systems course in order to understand the concepts and get a good grade in the exam? I know that some courses can be mastered through diligently reading the textbook or attending lectures while for others the concepts can only be understood by doing hands on projects. Is there a general studying approach that should be adopted for this type of a course? I know this may be subjective but I am looking for personal experiences/study methods by those who have taken similar courses to see if there is one particular method that worked well for the majority.

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  • Result of the "How long do you wait before Solaris 11 gets on your prod systems?"

    - by nospam(at)example.com (Joerg Moellenkamp)
    I just removed the poll at 10:52, so this is the final result: My conclusions out of it: While the removal of UltraSPARC I to VI+ support in Solaris 11 may hit some of the people voting in the categories "Wait?" to "6 month", most of the users keep Solaris 10 running on their existing system anyway or migrate that late that even the newest system have reached their end-of-service-live or are near of it, so a migration doesn't sound that feasible. So i assume Product Management was right with their decision to remove the support in order to make the feature i can't talk of possible, as i don't think that many of the early migrators are still using the system in question, as most systems have reached EOSL. Didn't thought that there would be people waiting three years and more ...

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  • Poll: How long will you wait before using Solaris 11 on production systems?

    - by nospam(at)example.com (Joerg Moellenkamp)
    When Sun released Solaris 10, it was my first migration phase to a new Solaris major release while being part of Sun. At that time i heard a lot of comments between "Oh, we will install it on new systems on day 1" to "oh ... not that fast ... we will wait ... we are not that fast ... we will do it in a year". I would like to get some additional insight and so i set up the poll plugin for s9y to get the answer to the question "How long will you wait before using Solaris 11 on production system?". Thank you for your participation!

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  • How to change the coordinate origin in Flash's stage with Actionscript?

    - by Petruza
    I think I did this before but can't find the code. Flash as many other graphical frameworks use the top-left corner as the coordinate origin (0,0) because it's how the underlying memory model is by convention. But it would be really simpler for my calculations if the origin was in the center of the stage, because all the game revolves around the center and uses a lot of trigonometry, angles, etc. Is there some built-in method like Stage::setOrigin( uint, uint ); or something like that?

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  • Identifying Swing component at a particular screen coordinate? (And manually dispatching MouseEvents

    - by DVA
    I'm doing some work making a Java app compatible with alternative input devices. Unfortunately, the device in question has a Java API that's barely into the alpha stages right now, so it's pretty poor. What I need to do is essentially set up a replacement structure for the dispatch of MouseEvents. Does anyone know if there's a way in Swing to take a screen coordinate and find out what Swing component is displayed on top at that screen point?

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