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• How are a session identifiers generated?

  - by Asaf R

  Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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• preg replace h2 tags with spaces [closed]

  - by fire

  Possible Duplicate: PHP Regular express to remove <h1> tags (and their content) I have some HTML that looks like this: <h2> Fund Management</h2> <p> The majority of property investments are now made via our Funds.</p> Trying to use a regular expression to strip h2 tags but doesn't work because of the space between the opening and closing h2 tags. preg_replace('/<h2>(.+?)<\/h2>/', '', $content); Any ideas on how to make this work? Also I would ideally like it to replace h1-h6 tags so maybe it needs [1-6] or something?

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• Need help understanding .net ThreadPool

  - by Meredith

  I am trying to understand what ThreadPool does, I have this .NET example: class Program { static void Main() { int c = 2; // Use AutoResetEvent for thread management AutoResetEvent[] arr = new AutoResetEvent[50]; for (int i = 0; i < arr.Length; ++i) { arr[i] = new AutoResetEvent(false); } // Set the number of minimum threads ThreadPool.SetMinThreads(c, 4); // Enqueue 50 work items that run the code in this delegate function for (int i = 0; i < arr.Length; i++) { ThreadPool.QueueUserWorkItem(delegate(object o) { Thread.Sleep(100); arr[(int)o].Set(); // Signals completion }, i); } // Wait for all tasks to complete WaitHandle.WaitAll(arr); } } Does this run 50 "tasks", in groups of 2 (int c) until they all finish? Or I am not understanding what it really does.

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• MySQL Cluster data nodes - slow SELECTs

  - by Boyan Georgiev

  Hi to all. First off, I'm new to MySQL Cluster. This is my pain: I've managed to setup a MySQL Cluster with two data nodes, two SQL nodes and one management server. Everything works pretty well, except the following: my data nodes are spread across an intranet link which incurs latency into communications between the data nodes. Apparently, due to MySQL Cluster's internal partitioning schemes, when my PHP application pulls data from the cluster via SELECT queries, parts of the data are pulled from both data nodes. This makes the page appear onscreen REALLY slowly. If I bring one data node offline, the data can only be pulled from that single remaining data node, and thus, the final result (HTML output) appears on the screen in a very timely fashion. So, my question is this: can the data nodes/cluster be told to pull data from partitions stored only on a particular data node?

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• Garbage Collection Java

  - by simion

  On the slides i am revising from it says the following; Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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• running Hadoop software on office computers (when they are idle)

  - by Shahbaz

  Is there a project which helps setup a Hadoop cluster on office desktops, when they are idle? I'd like to experiment with Hadoop/MR/hbase but don't have acces to 5-10 computers. The computers at work are idle after hours and are connected to each other through a very high speed connection. What's more, data on these computers stays within our network so there is no privacy issue. In order for this to work I need a fairly light weight monitor running on each machine. When the computer has been idle for X hours, it will join the cluster. If the user logs on, it has to drop out of the cluster and return all CPU/memory back. Does something like this exist?

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• In C, as free() knows an array size, why isn't there a function that gets the array size? [closed]

  - by user354959

  Possible Duplicate: If free() knows the length of my array, why can’t I ask for it in my own code? Searching around (including here at stackoverflow), I got that malloc() allocates an array and also creates a header to control the array info. In this header, there's also the array size. free() use such information to know how to deallocate that array. So, if the array size info is "there" (somewhere in the memory), why there isn't a function that returns an array size, looking for this at the array header? Or am I missing something?

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• Quick way to do data lookup in PHP

  - by Ghostrider

  I have a data table with 600,000 records that is around 25 megabytes large. It is indexed by a 4 byte key. Is there a way to find a row in such dataset quickly with PHP without resorting to MySQL? The website in question is mostly static with minor PHP code and no database dependencies and therefore fast. I would like to add this data without having to use MySQL if possible. In C++ I would memory map the file and do a binary search in it. Is there a way to do something similar in PHP?

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• Detect movie being played (Windows)

  - by modosansreves

  Watching a movie is quite a different user activity. User doesn't touch neither mouse nor keyboard. Yet he 'actively' uses the computer. Thus, screensaver shouldn't run, indexing should be performed with care etc. On the other side, playing video requires either using direct write to video memory, or DirectShow, or some other API. This may be the key to the answer. What is the Dead Simple Way to determine that a video is being played?

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• Java Web App: Passing form parameters across multiple pages

  - by digiarnie

  Hi, what is the best practice or best way of passing form parameters from page to page in a flow? If I have a flow where a user enters data in a form and hits next and repeats this process until they get to an approval page, what ways could I approach this problem to make the retention of data as simple as possible over the flow? I guess you could put all the information as you go in the session but could you get into memory issues if a lot of people are using your app and going through the flow at the same time?

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• Application disappears after starting - C++ linking managed code dll

  - by Axarydax

  Hello, we have a problem with our applications. We have recently upgraded our toolchain to Visual Studio 2010 and friends, it all works fine on Windows Vista + Windows 7 developer machines and Windows 7 customer machines. (all x86) Today we did a first installation to a client PC running Windows XP SP3 x86, and all applications linking managed code dll do not work. After starting the .exe seemingly nothing happens, no window pops up, no memory gets eaten, no task shows in task manager, nothing, nada. Event log is empty, everything is just as if the application returned to the OS right after the start. I am at loss about this, I really don't know how should I start even debugging this problem. I don't want to install VS2010 and everything onto a Windows XP box, I'd like to try something less time intensive first. This all is happening just to native C++ apps that link managed c++ DLL. Pure managed C# apps do work. Pure native C++ apps do work.

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• Objective-C: Initializing char with char at index of string.

  - by Mr. McPepperNuts

  unichar myChar = [myString characterAtIndex:0]; [myNSMutableArray addObject:myChar]; I am trying to insert the first char of a string into an array, to create an array of chars. the first line does not give me an error. The second line however, provides the following error: warning: passing argument 1 of 'addObject:' makes pointer from integer without a cast This also crashes the application with a "bad address" error. I thought this error was due to a problem with memory allocation. Can someone shed some light on this.

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• How do I write Push and Pop in Scheme?

  - by kunjaan

  Right now I have (define (push x a-list) (set! a-list (cons a-list x))) (define (pop a-list) (let ((result (first a-list))) (set! a-list (rest a-list)) result)) But I get this result: Welcome to DrScheme, version 4.2 [3m]. Language: Module; memory limit: 256 megabytes. > (define my-list (list 1 2 3)) > (push 4 my-list) > my-list (1 2 3) > (pop my-list) 1 > my-list (1 2 3) What am I doing wrong? Is there a better way to write push so that the element is added at the end and pop so that the element gets deleted from the first?

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• How to create a new IDA project based on an existing one with different offsets?

  - by tbergelt

  I have an existing IDA Pro project for a C166 processor embedded application. This project already has many functions, variables, etc defined. There are different versions of the embedded application I am looking at. The different versions of the application are 99% the same, but with slight variations in code and data that cause functions and variables to be at different memory offsets. I want to create a new IDA project for a different version of the application. I would like to somehow import all of my function and variable definitions from my existing IDA project. I would like IDA to recognize the signatures of the existing function definitions and define them at there new location in the new project. How can I do this? Are there certain plugins for IDA I can chain together?

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• c, pass awk syntax as argument to execl

  - by Skuja

  I want to run following command in c to read systems cpu and memory usage: ps aux|awk 'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}' I am trying to pass it to execl command and after that read its output: execl("/bin/ps", "/bin/ps", "aux|awk", "'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}'",(char *) 0); but in terminal i am getting following error: ERROR: Unsupported option (BSD syntax) I would like to know how to properly pass awk as argument to execl?

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• Is it faster to use a complicated boolean to limit a ResultSet at the MySQL end or at the Java end?

  - by javanix

  Lets say I have a really big table filled with lots of data (say, enough not to fit comfortably in memory), and I want to analyze a subset of the rows. Is it generally faster to do: SELECT (column1, column2, ... , columnN) FROM table WHERE (some complicated boolean clause); and then use the ResultSet, or is it faster to do: SELECT (column1, column2, ... , columnN) FROM table; and then iterate over the ResultSet, accepting different rows based on a java version of your boolean condition? I think it comes down to whether the Java iterator/boolean evaluator is faster than the MySQL boolean evaluator.

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• Is it possible to find out what FlashBuilder is doing during compilation?

  - by justkevin

  I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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• Forcing a templated object to construct from a pointer

  - by SalamiArmi

  I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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• Excel workbooks produced by POI don't work when linked

  - by Eric Nicolas

  Here is what I'm doing : Create a workbook in memory (book = new HSSFWorkbook(), ...) Save it to disk (book.write(...)) Open in Excel (ok) Create another workbook in Excel, which links to the first one (=PoiWorkbook?xls!A1) Close Excel Then everytime I open the second workbook again, all the links are #N/A, unless I also open the POI-generated workbook at the same time. I never saw this behaviour with standard workbooks created in Excel. Anyone has seen this and found a workaround ? Thanks.

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• Easiest way to combine a dataset and other data in a single file?

  - by Tim Gradwell

  I have a dataset in C# which I can serialise using dataset.WriteXml(filename); but I want the file to contain other data as well (essentially some meta data about the dataset). I could add another table to the dataset which contained the metadata, but I'd prefer to keep it separate, if at all possible. Essentially I think I want to create a 'combination of files' file, that looks something like this: size_of_file1 file1 size_of_file2 file2 ... etc Then, I'd like to load the file into memory, and split the file into separate streams, so that I can feed the dataset into dataset.ReadXml(stream); and the metadata into something else. Sound possible? Can anyone tell me how I can do it? Thanks Tim

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• Unit testing with serialization mock objects in C++

  - by lhumongous

  Greetings, I'm fairly new to TDD and ran across a unit test that I'm not entirely sure how to address. Basically, I'm testing a couple of legacy class methods which read/write a binary stream to a file. The class functions take a serializable object as a parameter, which handles the actual reading/writing to the file. For testing this, I was thinking that I would need a serialization mock object that I would pass to this function. My initial thought was to have the mock object hold onto a (char*) which would dynamically allocate memory and memcpy the data. However, it seems like the mock object might be doing too much work, and might be beyond the scope of this particular test. Is my initial approach correct, or can anyone think of another way of correctly testing this? Thanks!

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• OpenGL texture not showing up on some computers, problem with auxDIBImageLoad?

  - by CptanPanic

  I have a simple openGL GUI that has uses a bmp as a texture. The problem is on some computers the texture doesn't show up. But on ones with newer OpenGL drivers it works. How can I make it more compatible. I think the problem may be with auxDIBImageLoad. When I inspect the result, I see the x,y correct, but the data pointer points to memory bank with all zeros. What could be wrong?

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• Why hasn't anybody started a hosted continuous integration service?

  - by Teflon Ted

  There's a dozen services that provide hosted version control, hosted ticket tracking, hosted project management, and combinations of all of the above, there's even hosted web-based IDEs. But nobody's yet offered a hosted continuous integration service; at least that I can find. The concept seems simple enough: I register and provide the URL to my source code repository, it grabs my code and builds it via ant/rake/whatever, then runs the suite of tests and some metrics (code coverage, performance, etc.). Is there some prohibitive barrier to entry I'm not considering?

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• What would you use for auto completion in Rails app?

  - by Andrei

  I want to use auto-completion in a number of fields (5-7) in my forms. There is a screencast on auto-completion with Prototype library by Ryan Bates ( http://railscasts.com/episodes/102-auto-complete-association). On the other hand, I have noticed that quite many guys suggest jQuery for this task ( http://jquery.bassistance.de/autocomplete/demo/). And I guess, there was probably some development last year(s), so I ask you - what would you use nowadays to auto-complete your form fields and why? BTW, I still have an open question on auto completion for HABTM association: http://stackoverflow.com/questions/1510935/how-to-do-habtm-management-with-auto-completion-in-rails

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• usage of 2 charectors in single qoutes in c

  - by user1632141

  #include<stdio.h> int main() { char ch = 'A'; printf("%d\n",'ag'); printf("%d\n",'a'); printf("%d, %d, %d, %d", sizeof(ch), sizeof('a'), sizeof('Ag'), sizeof(3.14f)); return 0; } I used to have many doubts on the output of this question while running on g++ and gcc. But I have cleared almost all the doubts by referring these links: Single and double quotes in C/C++ Single quotes vs. double quotes in C I still need to understand one thing about the output of this question. Can someone please explain the output of printf("%d\n",'ag'); mentioned above in the program. How is it actually stored in the memory? The output for the program on the Linux/GCC platform is: 24935 97 1, 4, 4, 4

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