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• how to make a program like fraps.

  - by blood

  i want to make a program that will capture video. what if the best way to captrue the video, i know c++ and im learning assembly and i found in my assembly book i can get data from the video card i think? would that be the best way? i know fraps hooks into programs but i want my program to take the full screen? so i want something fast low memory useage if i can and something i can use on other computers with them having the same hardware.

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• Does a static object within a function introduce a potential race condition?

  - by Jeremy Friesner

  I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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• "Can't Connect to Server" from 2nd virtual host on VPS

  - by chaoskreator

  I'm using Debian 7 Wheezy and Apache 2.2.22, and I'm setting up Virtual Hosts for a number of websites on my VPS. I've successfully configured the VirtualHost directives for one of the sites, but the second one continually gives "Problem Loading Page" in Firefox. I've run configtest and it has verified all my syntax is correct, and I've checked all the permissions. Everything on the 2nd domain is pretty much copy/pasted from the first, so I'm not sure what the issue is, as there are no entries into /var/log/apache2/error.log other than where I have reloaded the configurations: /# cat /var/log/apache2/error.log [Thu May 29 01:19:00 2014] [notice] Graceful restart requested, doing restart [Thu May 29 01:19:00 2014] [info] Init: Seeding PRNG with 656 bytes of entropy [Thu May 29 01:19:00 2014] [info] Init: Generating temporary RSA private keys (512/1024 bits) [Thu May 29 01:19:00 2014] [info] Init: Generating temporary DH parameters (512/1024 bits) [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(253): shmcb_init allocated 512000 bytes of shared memory [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(272): for 511920 bytes (512000 including header), recommending 32 subcaches, 133 indexes each [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(306): shmcb_init_memory choices follow [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(308): subcache_num = 32 [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(310): subcache_size = 15992 [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(312): subcache_data_offset = 3208 [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(314): subcache_data_size = 12784 [Thu May 29 01:19:00 2014] [debug] ssl_scache_shmcb.c(316): index_num = 133 [Thu May 29 01:19:00 2014] [info] Shared memory session cache initialised [Thu May 29 01:19:00 2014] [info] Init: Initializing (virtual) servers for SSL [Thu May 29 01:19:00 2014] [info] mod_ssl/2.2.22 compiled against Server: Apache/2.2.22, Library: OpenSSL/1.0.1e [Thu May 29 01:19:00 2014] [notice] Apache/2.2.22 (Debian) PHP/5.4.4-14+deb7u9 mod_ssl/2.2.22 OpenSSL/1.0.1e mod_perl/2.0.7 Perl/v5.14.2 configured -- resuming normal operations [Thu May 29 01:19:00 2014] [info] Server built: Mar 4 2013 22:05:16 [Thu May 29 01:19:00 2014] [debug] prefork.c(1023): AcceptMutex: sysvsem (default: sysvsem) I've ensured to enable each vhost with a2ensite {sitename.conf} with no errors there, either. Below are the contents of the configuration files... /etc/apache2/apache2.conf # Global configuration # LockFile ${APACHE_LOCK_DIR}/accept.lock PidFile ${APACHE_PID_FILE} Timeout 300 KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 5 ## ## Server-Pool Size Regulation (MPM specific) ## # prefork MPM # StartServers: number of server processes to start # MinSpareServers: minimum number of server processes which are kept spare # MaxSpareServers: maximum number of server processes which are kept spare # MaxClients: maximum number of server processes allowed to start # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # worker MPM # StartServers: initial number of server processes to start # MinSpareThreads: minimum number of worker threads which are kept spare # MaxSpareThreads: maximum number of worker threads which are kept spare # ThreadLimit: ThreadsPerChild can be changed to this maximum value during a # graceful restart. ThreadLimit can only be changed by stopping # and starting Apache. # ThreadsPerChild: constant number of worker threads in each server process # MaxClients: maximum number of simultaneous client connections # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_worker_module> StartServers 2 MinSpareThreads 25 MaxSpareThreads 75 ThreadLimit 64 ThreadsPerChild 25 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # event MPM # StartServers: initial number of server processes to start # MinSpareThreads: minimum number of worker threads which are kept spare # MaxSpareThreads: maximum number of worker threads which are kept spare # ThreadsPerChild: constant number of worker threads in each server process # MaxClients: maximum number of simultaneous client connections # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_event_module> StartServers 2 MinSpareThreads 25 MaxSpareThreads 75 ThreadLimit 64 ThreadsPerChild 25 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # These need to be set in /etc/apache2/envvars User ${APACHE_RUN_USER} Group ${APACHE_RUN_GROUP} # # AccessFileName: The name of the file to look for in each directory # for additional configuration directives. See also the AllowOverride # directive. # AccessFileName .htaccess # # The following lines prevent .htaccess and .htpasswd files from being # viewed by Web clients. # <Files ~ "^\.ht"> Order allow,deny Deny from all Satisfy all </Files> DefaultType None HostnameLookups Off ErrorLog ${APACHE_LOG_DIR}/error.log LogLevel debug # Include module configuration: Include mods-enabled/*.load Include mods-enabled/*.conf # Include list of ports to listen on and which to use for name based vhosts Include ports.conf # # The following directives define some format nicknames for use with # a CustomLog directive (see below). # If you are behind a reverse proxy, you might want to change %h into %{X-Forwarded-For}i # # LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined LogFormat "%h %l %u %t \"%r\" %>s %O" common LogFormat "%{Referer}i -> %U" referer LogFormat "%{User-agent}i" agent <Directory "/var/www"> Order allow,deny Allow from all Require all granted </Directory> # Include generic snippets of statements Include conf.d/ # Include the virtual host configurations: Include sites-enabled/*.conf NameVirtualHost *:80 /etc/apache2/sites-available/site1.net.conf <VirtualHost *:80> ServerName site1.net ServerAlias site1.net *.site1.net DocumentRoot "/var/www/site1" ErrorLog "/var/www/site1/logs/error.log" CustomLog "/var/www/site1/logs/access.log" vhost_combined <Directory "/var/www/site1"> Options None AllowOverride All Order allow,deny Allow from all Satisfy Any </Directory> </VirtualHost> /etc/apache2/sites-available/site2.com.conf <VirtualHost *:80> ServerName site2.com ServerAlias site2.com *.site2.com DocumentRoot "/var/www/site2" ErrorLog "/var/www/site2/logs/error.log" CustomLog "/var/www/site2/logs/access.log" vhost_combined <Directory "/var/www/site2"> Options None AllowOverride All Order allow,deny Allow from all Satisfy Any </Directory> </VirtualHost> I've also tried setting NameVirtualHost like: Listen 80 NameVirtualHost 23.88.121.82:80 NameVirtualHost 127.0.0.1:80 and the VirtualHost Directives: <VirtualHost 23.88.121.82:80> ... </VirtualHost> for both sites, but that causes the first site to fail, as well. I'm wondering if I need to set up individual IPs for each site, possibly? I have 2 more IPv4 and 3 IPv6 addresses available, if that would make a difference. Also, in the grand scheme of things, I will need to enable SSL for the first site. I've been reading that I'll need to basically just mimic the directives for listening on port 80, only on port 443, and make sure mod_ssl is enabled? EDIT: I just ran apache2 -t to test the config files that way, and got the error: apache2: bad user name ${APACHE_RUN_USER}. However, apachectl configtest returns Syntax OK. There are no other mentions of errors with the mutex anywhere else, however. I was pretty sure if there was an error with the user apache was supposed to run under, the server wouldn't start at all... EDIT 2: Restarting apache fixed the bad user name error.

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• Homemade fstat to get file size, always return 0 length.

  - by Fred

  Hello, I am trying to use my own function to get the file size from a file. I'll use this to allocate memory for a data structure to hold the information on the file. The file size function looks like this: long fileSize(FILE *fp){ long start; fflush(fp); rewind(fp); start = ftell(fp); return (fseek(fp, 0L, SEEK_END) - start); } Any ideas what I'm doing wrong here?

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• Which external DSLs do you like to use?

  - by Max Toro

  The reason I'm asking is because right now there seems to be tendency to make DSLs internal. One example is LINQ in C# and VB. You can use it against in-memory objects, or you can use it as a replacement of SQL or other external DSL. Another example is HTML5 vs XHTML2. XHTML2 supported decentralized extensibility through namespaces, in other words you embed external DSL code (XForms, SVG, MathML, etc.) in your XHTML code. Sadly HTML5 doesn't seem to have such mechanism, instead new features are internal (e.g. <canvas> instead of SVG). I'd like to know what other developers think about this. Do you like using external DSLs ? Which ones ? If not, why ?

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• whats wrong with this peace of code for saving contacts

  - by Shadow

  Hi, i am using the latest Nokia Qt SDK. i have tried to add the contacts, its not getting added.. what is missing here.. // Construct contact manager for default contact backend QContactManager* cm = new QContactManager("simulator"); // QContactManager* cm = new QContactManager("memory"); // i tried this, its also not working // Create example contact QContact example; // Add contact name QContactName name; name.setFirstName("John"); name.setLastName("Doe"); example.saveDetail(&name); // Add contact email address //QContactEmailAddress email; // email.setContexts(QContactDetail::ContextHome); //email.setEmailAddress(“[email protected]”); // example.saveDetail(&email); // Finally, save the contact details cm->saveContact(&example); delete cm; Thanks

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• Connect two daemons in python

  - by Simon

  What is the best way to connect two daemons in Python? I have daemon A and B. I'd like to receive data generated by B in A's module (maybe bidirectional). Both daemons support plugins, so I'd like to shut communication in plugins. What's the best and cross-platform way to do that? I know few mechanisms from low-level solutions - shared memory (C/C++), linux pipe, sockets (TCP/UDP), etc. and few high-level - queue (JMS, Rabbit), RPC. Both daemons should run on the same host, but obviously better approach is to abstract from connection type. What are typical solutions/libraries in python? I'm looking for an elegant and lightweight solution. I don't need external server, just two processes talking with each other. What should I use in python to do that?

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• Writing a PHP web crawler using cron

  - by Horse

  Hi all I have written myself a web crawler using simplehtmldom, and have got the crawl process working quite nicely. It crawls the start page, adds all links into a database table, sets a session pointer, and meta refreshes the page to carry onto the next page. That keeps going until it runs out of links That works fine however obviously the crawl time for larger websites is pretty tedious. I wanted to be able to speed things up a bit though, and possibly make it a cron job. Any ideas on making it as quick and efficient as possible other than setting the memory limit / execution time higher?

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• Is there a version of postActionEvent for KeyEvent (specifically for a JTextArea)?

  - by Brian Pelc

  I'm writing a program that contains multiple JTextFields and 2 JTextAreas within an input panel. I have a submit button on the bottom. I have it set up so when a user types something into each field (including the JTextAreas) and hits the Enter key, it updates a text file, and when they press the submit button it updates the file then outputs a new version of it in the local directory. If the user presses Enter in any of the fields, it validates their input, however, I want to re-validate all fields when they press the submit button. Each field (again, JTextAreas included) has it's own validation check within its ActionListener or KeyListener (for the JTextAreas). It's easy enough to use postActionEvent() for the JTextFields, but is there a similar method for the JTextAreas to force fire a KeyEvent? I don't want to duplicate code and consume memory by re-writing the validation for those 2 Components inside the ActionEvent for the JButton. Unfortunately, I can't provide a sample because I'm writing the program on a classified machine (PC).

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• Double indirection and structures passed into a function

  - by ZPS

  I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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• [Ruby] How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: (0..9).sort_by{rand}.map{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle could be used to increase efficiency, but this code is sufficient for many purposes. My problem is that sort_by will transform the range into an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do?

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• UInt32 to IntPtr

  - by ffenix

  I have the following problem: public class ListenThread : SocketInvoke { [DllImport("Ws2_32", CharSet = CharSet.Auto)] public unsafe static extern UInt32 WSAWaitForMultipleEvents(UInt32 cEvents, IntPtr hEventObject, UInt32 fWaitAll, UInt32 dwTimeout, Boolean fAlertable); public void ListenConnections(NetSharedData data) { while (true) { unsafe { if (WSAWaitForMultipleEvents((UInt32)1, data.signal, (UInt32)0, (UInt32)100, false) != WSA_WAIT_TIMEOUT) { } } } } data.signal is a UInt32 how i can cast it to IntPtr?, i try: IntPtr signal = (IntPtr)data.signal; but it doesn't work because i need a pointer to data.signal (UInt32) type and not the int value as an pointer, that will make a memory exception. An C++ example of what i need: int signal = 0; int* psignal = &signal;

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• Implications of Fulltext Search over many columns

  - by Alex

  Hello, I have a really wide table which includes separate columns for billing address, shipping address, primary address, names, aliases etc. (I can't normalize this table further, and that's not the question here anyways). I'm implementing SQL Server fulltext search, and I'm wondering whether I should limit the search ability to just the primary fields (primary address and names for example), or if I can extend the search ability across all columns without occurring too much of a performance or memory penalty. I've done some basic testing with 10,000 sample rows and it's quite fast but I don't have much experience with fulltext indexing, especially its dictionary internals, so I don't know if the index is going to grow over time, or if there is anything else to consider. Thoughts?

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• Is it possible to give a python dict an initial capacity (and is it usefull)

  - by Peter Smit

  I am filling a python dict with around 10,000,000 items. My understanding of dict (or hashtables) is that when too much elements get in them, the need to resize, an operation that cost quite some time. Is there a way to say to a python dict that you will be storing at least n items in it, so that it can allocate memory from the start? Or will this optimization not do any good to my running speed? (And no, I have not checked that the slowness of my small script is because of this, I actually wouldn't now how to do that. This is however something I would do in Java, set the initial capacity of the HashSet right)

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• Memcachedb Versus MongoDB Versus CouchDB in terms of file based caching solution?

  - by Scott Faisal

  We need a caching solution that essentially caches data (text files) anywhere from 3 days up to a week based on user preferences and criteria. In this case memory based caching does not make sense to us. We were referred to MemcacheDB however I also thought of some NO SQL solutions. Our current application uses RDMS (MYSQL) and I guess it makes sense to use MemcacheDB however NOSQL does appeal as it is something more on the horizon. However we have not deployed a production level application under NOSQL and the beta stuff does not settle well with management/investors. Any how what are your thoughts and how would you address it? Thank You

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• RSA encrypted data block size

  - by calccrypto

  how do you store an rsa encrypted data block? the output might be significantly greater than the original input data block size, and i dont think people waste memory by padding bucket loads of 0s in front of each data block. besides, how would they be removed? or is each block stored on new lines within the file? if that is the case, how would you tell the difference between legitimate new line and a '\n' char written into the file? what am i missing? im writing the "write to file" part in python, so maybe its one of the differences between: open(file,'w') open(file,'w+b') open(file,'wb') that i dont know. or is it something else?

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• NSArray vs. SQLite for Complex Queries on iPhone

  - by GingerBreadMane

  Developing for iPhone, I have a collection of points that I need to make complex queries on. For example: "How many points have a y-coordinate of 10" and "Return all points with an X-coordinate between 3 and 5 and a y-coordinate of 7". Currently, I am just cycling through each element of an NSArray and checking to see if each element matches my query. It's a pain to write the queries though. SQLite would be much nicer. I'm not sure which would be more efficient though since a SQLite database resides on disk and not in memory (to my understanding). Would SQLite be as efficient or more efficient here? Or is there a better way to do it other than these methods that I haven't thought of? I would need to perform the multiple queries with multiple sets of points thousands of times, so the best performance is important.

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• How to create a NSAutoreleasePool without Objective-C?

  - by fbafelipe

  I have multiplatform game written in C++. In the mac version, even though I do not have any obj-c code, one of the libraries I use seems to be auto-releasing stuff, and I get memory leaks for that, since I did not create a NSAutoreleasePool. What I want is to be able to create (and destroy) a NSAutoreleasePool without using obj-c code, so I don't need to create a .m file, and change my build scripts just for that. Is that possible? How can that be done? OBS: Tagged C and C++, because a solution in any of those languages will do.

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• C Programming: calling free() on error?

  - by kouei

  Hi all, This a follow up on my previous question. link here. My question is: Let's say I have the following code.. char* buf = (char*) malloc(1024); ... for(; i<20; i++) { if(read(fd, buf, 1024) == -1) { // read off a file and store in buffer perror("read failed"); return 1; } ... } free(buf); what i'm trying to get at is that - what if an error occurs at read()? does that mean my allocated memory never gets freed? If that's the case, how do I handle this? Should I be calling free() as part of error handling? Once again, I apologize for the bad English. ^^; Many thanks, K.

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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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• Is there any significant benefit to reading string directly from control instead of moving it into a

  - by Kevin

  sqlInsertFrame.Parameters.AddWithValue("@UserName", txtUserName.txt); Given the code above...if I don't have any need to move the textbox data into a string variable, is it best to read the data directly from the control? In terms of performance, it would seem smartest to not create any unnecessary variables which use up memory if its not needed. Or is this a situation where its technically true but doesn't yield any real world results due to the size of the data in question. Forgive me, I know this is a very basic question.

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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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• how to read httpWebRequest's request stream in c#, i got error" the stream is not readable" ?

  - by sam

  hi i want to read request stream from a custom httpWebRequest class that inherits from httpWebRequest and i have tried to read the request stream in different stages but sitll not sure how to archieve that in the class,thanks very much for any help. This custom httpWebRequest is used to serilize soap message and i want to know what request has been sent in string format. I also implemented custom HttpRequestCreator,HttpWebResponse but till cant find a place/stage i can read the request stream. If i output everything in a memory stream then copy the content to request stream, anyone knows which stage i can do it in the constructor, BeginGetRequestStream,EndGetRequestStream or GetRequestStream?

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• Repository Design Pattern Guidance

  - by thefactor

  Let's say you have an MVVM CRM application. You have a number of customer objects in memory, through a repository. What would be the appropriate place to handle tasks that aren't associated with traditional MVVM tasks from a GUI? For example, let's say every few minutes you want to check to see if their address is valid and pop up a notification if it is not. Or you want to send out an hourly e-mail update. Or you want a window to pop up to remind you to call a customer at a specific time. Where does this logic go? It's not GUI/action-oriented, and it's not logic that would be appropriate for a repository, I think.

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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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