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• Is pthread_spin_trylock safe inside of sigsegv handler of multithreaded application?

  - by TWMouton

  I am trying to implement a handler that on SIGSEGV will collect some information such as process-id, thread-id and a backtrace and write this information to a file/pipe/socket. The problem lies in that there is the (probably pretty high) possibility that if one thread experienced a SIGSEGV that the others will shortly follow. If two threads happen to make it to the bit of code where they're writing their report out at the same time then they'll interleave their writing (to the same file). I know that I should only be using async-signal-safe functions as detailed in signal(7) I also have seen at least two cases here and video linked in top answer here where others have used pthread_spin_trylock to get around this problem. Is this a safe way to prevent the above problem?

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• Why use threading data race will occur, but will not use gevent

  - by onlytiancai

  My test code is as follows, using threading, count is not 5,000,000 , so there has been data race, but using gevent, count is 5,000,000, there was no data race . Is not gevent coroutine execution will atom "count + = 1", rather than split into a one CPU instruction to execute? # -*- coding: utf-8 -*- import threading use_gevent = True use_debug = False cycles_count = 100*10000 if use_gevent: from gevent import monkey monkey.patch_thread() count = 0 class Counter(threading.Thread): def __init__(self, name): self.thread_name = name super(Counter, self).__init__(name=name) def run(self): global count for i in xrange(cycles_count): if use_debug: print '%s:%s' % (self.thread_name, count) count = count + 1 counters = [Counter('thread:%s' % i) for i in range(5)] for counter in counters: counter.start() for counter in counters: counter.join() print 'count=%s' % count

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• Why might someone say R is *NOT* a programming language? [closed]

  - by Tal Galili

  I came by the following comment today on twitter "R is not a programming language, it's a statistics package with the GUI missing." And I am wondering - Why not? What is "missing" in R to make it a "programming language" ? Update: For the protocol, I am a big fan of R, use it daily, and support it's existence. I now changed the name of this thread from "Why is R NOT a programming language?" to "Why might someone say R is NOT a programming language?" Which better reflects my motivation for this thread (which is, to know if R has any programmatical disadvantages that I might have not heard about).

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• Fastest way for inserting very large number of records into a Table in SQL

  - by Irchi

  The problem is, we have a huge number of records (more than a million) to be inserted into a single table from a Java application. The records are created by the Java code, it's not a move from another table, so INSERT/SELECT won't help. Currently, my bottleneck is the INSERT statements. I'm using PreparedStatement to speed-up the process, but I can't get more than 50 recods per second on a normal server. The table is not complicated at all, and there are no indexes defined on it. The process takes too long, and the time it takes will make problems. What can I do to get the maximum speed (INSERT per second) possible? Database: MS SQL 2008. Application: Java-based, using Microsoft JDBC driver.

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• Is there a way to customise messages produced by statements in MS SQL Query Analyzer?

  - by Scott Leis

  If I run a simple query in SQL Query Analyzer, like: SELECT * FROM TableName the Messages pane always produces a message like: (30 row(s) affected) If I run a stored procedure with many statements, the messages are useless because there's no indication of what each one relates to. So firstly: Is there a way to customise the default messages on a per-query basis? E.g. I'd like a specific query to produce a message like: TableName query produced [numRowsAffected] results. replacing [numRowsAffected] with the number that would have appeared in the default message. Secondly, is there a way to suppress the default messages on a per-query basis? E.g. I have a local variable of type TABLE, used in several statements. I don't want any message to appear for statements where I'm just deleting data from that variable before re-using it. I'm seeking solutions that work in SQL Server 8.0.

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• Performing periodic audits and best practice

  - by DTown

  I'm doing a windows form and would like an audit task to happen every 30 seconds. This audit is essentially checking a series of services on remote computers and reporting back into a richtextbox the status. Current I have this running in an endless background thread and using an invoker to update the richtextbox in the main form. Is this best practice? If I made an endless loop in my main form that would prevent any of my buttons from working, correct? I'm just curious if every time I want to create a periodic audit check I have to create a new thread which checks the status or file or what have you?

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• Caching for database questions.

  - by SeanD

  When we say caching like using memcahe or Redis, is this a 1:1 caching between the user and the cache or can we cache 1 item and use it for all user? Some items like a Friend list will be 1:1 a that is unique per user. But if i want to cache the auto complete list for city lookups which can be used by any user, will it just store 1 list in the cache used by all users at same time or doe it need to store 1 list per user? Is it possible to cache the entire database, all the lookups, all the users, all their photos, etc using memache or redis? So from the above example: a friend list will be cleared from the cache when the user logs off. But something like city auto complete will stay in the cache 24-7-365, am i correct?

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• C++ WIN32: Short multitasking example

  - by Con Current

  I searched for examples on how to create a simple multithreaded app that does something similar to this: #include <iostream> using namespace std; int myConcurrentFunction( ) { while( 1 ) { cout << "b" << endl; } } int main( ) { // Start a new thread for myConcurrentFunction while( 1 ) { cout << "a" << endl; } } How can I get the above to output a and b "randomly" by starting a new thread instead of just calling myConcurrentFunction normally? I mean: What is the minimal code for it? Is it really only one function I have to call? What files do I need to include? I use MSVC 2010, Win32

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• Setting the first day of the week with the wx.lib.calendar.Calendar control?

  - by Noah

  As per the title, is it possible to change the first day of the week (Monday instead of Sunday)?

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• Fast, cross-platform timer?

  - by dsimcha

  I'm looking to improve the D garbage collector by adding some heuristics to avoid garbage collection runs that are unlikely to result in significant freeing. One heuristic I'd like to add is that GC should not be run more than once per X amount of time (maybe once per second or so). To do this I need a timer with the following properties: It must be able to grab the correct time with minimal overhead. Calling core.stdc.time takes an amount of time roughly equivalent to a small memory allocation, so it's not a good option. Ideally, should be cross-platform (both OS and CPU), for maintenance simplicity. Super high resolution isn't terribly important. If the times are accurate to maybe 1/4 of a second, that's good enough. Must work in a multithreaded/multi-CPU context. The x86 rdtsc instruction won't work.

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• Image animation stops on minimizing and restoring

  - by lc

  I have a .NET WinForms application with an animated GIF in a PictureBox. It's a loading animation, shown while a BackgroundWorker does some processing in another thread. I load the image by setting the Image property and it animates on its own. All is fine until I minimize and restore the application. At which point, the image stops animating and just displays whatever frame it was last on. Note that: The background thread still runs fine and none of the "business" of the application is affected. Subsequently-displayed animated GIFs do work fine (unless the application is minimized again). Does anyone know what causes this problem? Any workarounds?

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• C#, Manage concurrency in database access

  - by Goul

  Hi there, I have written a while ago an application used by multiple users to handle trades creation. I haven't done development for some time now and can't remember how I managed the concurrency between the users and so would have liked your advices in term of design. The application was as follow: - One heavy client per user - A single database - Access to the database for each user to insert/update/delete trades - A grid in the application reflecting the trades table. That grid being updated each time someone changes a deal. My questions: 1- Do you confirm I shouldn't care about the connection to the database for each application. Considering that there is a singleton in each, I would expect on connexion per client with no issue. 2- How preventing the concurrency of the accesses? I guess I should lock when modifying the data, however don't remember how to. 3- How to have the grid automatically updated whenever the database is (by another user for example)? Thank you in advance for your help!

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• Which database should I use for best performance

  - by _simon_

  Hello, I am working in Visual Studio 2005, .NET 2.0. I need to write an application, which listens on COM port and saves incoming data to a database. Main feature: save incoming data (series of 13-digits numbers), if this number allready exists, then mark it as double. For example, there could be these records in database: 0000000000001 OK 0000000000002 OK 0000000000002 Double 0000000000003 OK 0000000000004 OK I could use SQL database, but I don't know if it is fast enough... Database should be able to store up to 10.000.000 records and write up to 100 records per minute (so it needs to check 100 times per minute if this record allready exists). Which database should I use? Maybe the whole database would need to be in RAM. Where could I learn more about this? Thanks

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• Custom SWT controls and layouts

  - by Alexey Romanov

  What custom controls and layouts for SWT/JFace do you use? Preferably, list one per answer.

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• [c#] SoundPlayer.PlaySync stopping prematurely

  - by JeffE

  I want to play a wav file synchronously on the gui thread, but my call to PlaySync is returning early (and prematurely stopping playback). The wav file is 2-3 minutes. Here's what my code looks like: //in gui code (event handler) //play first audio file JE_SP.playSound("example1.wav"); //do a few other statements doSomethingUnrelated(); //play another audio file JE_SP.playSound("example2.wav"); //library method written by me, called in gui code, but located in another assembly public static int playSound(string wavFile, bool synchronous = true, bool debug = true, string logFile = "", int loadTimeout = FIVE_MINUTES_IN_MS) { SoundPlayer sp = new SoundPlayer(); sp.LoadTimeout = loadTimeout; sp.SoundLocation = wavFile; sp.Load(); switch (synchronous) { case true: sp.PlaySync(); break; case false: sp.Play(); break; } if (debug) { string writeMe = "JE_SP: \r\n\tSoundLocation = " + sp.SoundLocation + "\r\n\t" + "Synchronous = " + synchronous.ToString(); JE_Log.logMessage(writeMe); } sp.Dispose(); sp = null; return 0; } Some things I've thought of are the load timeout, and playing the audio on another thread and then manually 'freeze' the gui by forcing the gui thread to wait for the duration of the sound file. I tried lengthening the load timeout, but that did nothing. I'm not quite sure what the best way to get the duration of a wav file is without using code written by somebody who isn't me/Microsoft. I suppose this can be calculated since I know the file size, and all of the encoding properties (bitrate, sample rate, sample size, etc) are consistent across all files I intend to play. Can somebody elaborate on how to calculate the duration of a wav file using this info? That is, if nobody has an idea about why PlaySync is returning early. Of Note: I encountered a similar problem in VB 6 a while ago, but that was caused by a timeout, which I don't suspect to be a problem here. Shorter (< 1min) files seem to play fine, so I might decide to manually edit the longer files down, then play them separately with multiple calls.

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• sigwait in Linux (Fedora 13) vs OS X

  - by Silas

  So I'm trying to create a signal handler using pthreads which works on both OS X and Linux. The code below works on OS X but doesn't work on Fedora 13. The application is fairly simple. It spawns a pthread, registers SIGHUP and waits for a signal. After spawning the signal handler I block SIGHUP in the main thread so the signal should only be sent to the signal_handler thread. On OS X this works fine, if I compile, run and send SIGHUP to the process it prints "Got SIGHUP". On Linux it just kills the process (and prints Hangup). If I comment out the signal_handler pthread_create the application doesn't die. I know the application gets to the sigwait and blocks but instead of return the signal code it just kills the application. I ran the test using the following commands: g++ test.cc -lpthread -o test ./test & PID="$!" sleep 1 kill -1 "$PID" test.cc #include <pthread.h> #include <signal.h> #include <iostream> using namespace std; void *signal_handler(void *arg) { int sig; sigset_t set; sigemptyset(&set); sigaddset(&set, SIGHUP); while (true) { cout << "Wait for signal" << endl; sigwait(&set, &sig); if (sig == SIGHUP) { cout << "Got SIGHUP" << endl; } } } int main() { pthread_t handler; sigset_t set; // Create signal handler pthread_create(&handler, NULL, signal_handler, NULL); // Ignore SIGHUP in main thread sigfillset(&set); sigaddset(&set, SIGHUP); pthread_sigmask(SIG_BLOCK, &set, NULL); for (int i = 1; i < 5; i++) { cout << "Sleeping..." << endl; sleep(1); } pthread_join(handler, NULL); return 0; }

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• Is it possible to make an online registration process for a course in Google Docs with a cap on registrations?

  - by user61551

  I am trying to build an online registration form for an institute I intern at that is running a training programme with multiple courses and hundreds of applicants. I've done registration forms with Google Docs Forms before, but the tricky spot this time round is that I'm trying to put a registration cap on each of the courses. Every person needs to register for one course in every timeslot, and there are seven or so timeslots. However, as seating space in every venue is limited, we would like to cap registrations per course (venue) to 200 per course, after which either a) the applicant will be informed that they need to register for another course in that timeslot if they apply to a full course, or b) ideal case scenario, the option will be greyed out. Is this possible using Google Docs Forms at all? If not, is there a free alternative that might do the job properly?

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• Compressing digitalized document images

  - by Adabada

  Hello, We are now required by law to digitalize all the financial documents in our company and submit them to evaluations every 3 months. Since this is sensitive data we decided to take matters into our own hands and build some sort of digital data archiver. The tool works perfectly, but after 7 months of usage we are begining to worry about the disk space used by these images. Here some info on the amount of documents digitalized: 15K documents scanned and archived per day, with final PNG size of +- 860KB: 15 000 * 860 kilobits = 1.53779984 gigabytes 30 days of work per month: 1.53779984 gigabytes * 30 = 46.1339952 gigabytes Expectation of disk space usage after 1 year: 46.1339952 gigabytes * 12 = 553.607942 gigabytes So far we're at 424 gigabytes of disk space used, without counting backup. We're using PNG as image format, but I would like to know if anyone have any advice on a better compression algorithm for images or alternative strategies for compressing the PNG's even more or even better ways to archive images as to save disk space. Any help would be appreciated, thanks.

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• Boost Shared Pointer: Simultaneous Read Access Across Multiple Threads

  - by Nikhil

  I have a thread A which allocates memory and assigns it to a shared pointer. Then this thread spawns 3 other threads X, Y and Z and passes a copy of the shared pointer to each. When X, Y and Z go out of scope, the memory is freed. But is there a possibility that 2 threads X, Y go out of scope at the exact same point in time and there is a race condition on reference count so instead of decrementing it by 2, it only gets decremented once. So, now the reference count newer drops to 0, so there is a memory leak. Note that, X, Y and Z are only reading the memory. Not writing or resetting the shared pointer. To cut a long story short, can there be a race condition on the reference count and can that lead to memory leaks?

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• Comparing 2 linq applications: Unexpected result

  - by lukesky

  I drafted 2 ASP.NET applications using LINQ. One connects to MS SQL Server, another to some proprietary memory structure. Both applications work with tables of 3 int fields, having 500 000 records (the memory structure is identical to SQL Server table). The controls used are regular: GridView and ObjectDataSource. In the applications I calculate the average time needed for each paging click processing. LINQ + MS SQL application demands 0.1 sec per page change. LINQ + Memory Structure demands 0.8 sec per page change. This Is shocking result. Why the application handling data in memory works 8 times slower than the application using hard drive? Can anybody tell me why that happens?

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• Match a word with similar words using Solr?

  - by fayer

  I want to search for threads in my mysql database with Solr. But i want it to not just search the thread words, but for similar words. Eg. if a thread title is "dog for sale" and if the user searches for dogs the title will be in the result. and also if a user searches for "mac os x" the word "snow leopard" will appear. and the ability to link words the application thinks is related eg. house and apartment. how is this kind of logic done? i know that you can with solr look up words in a dictionary file you create/add, so solr will look for dogs and see what related words there are (eg. dog). but where do you find such a dictionary? i have no idea about this kind of implementation. please point me into right direction. thanks

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• Should i use lock.lock(): in this method?

  - by user962800

  I wrote this method whose purpose is to give notice of the fact that a thread is leaving a specific block of code A thread stands for a car which is leaving a bridge so other cars can traverse it . The bridge is accessible to a given number of cars (limited capacity) and it's one way only. public void getout(int diection){ // release the lock semaphore.release(); try{ lock.lock(); //access to shared data if(direction == Car.NORTH) nNordTraversing--; //decreasing traversing threads else nSudTraversing--; bridgeCond.signal(); }finally{ lock.unlock(); } } My question is: should I use lock.lock(); or it's just nonsense? thanks in advance

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• Create a PHP cache system in MySQL database?

  - by Zach Smith

  I'm creating a web service that often scrapes data from remote web pages. After scraping this data, I have a simple multidimensional array of information to use. The scraping process is fairly taxing on my server, and the page load takes a while. I was considering adding a simple cache system using a MySQL database, where I create one row per remote web page with a the array of information pulled from it stored as a JSON encoded string. Is this a good enough system? Or would something like a text file per web page be a better idea?

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• Is it possible to get collection of some ejb`s instances from container?

  - by kislo_metal

  Hi! Scenario: I have some @Statefull bean for user session (not an http session, it is web services session). And I need to manage user`s session per user. Goal: I need to have possibility to get collection of @Statefull UserSession`s instances and control maximum number of session`s per user, and session`s life time. Q: Is it possible to get Collection of ejb`s instances from ejb container, instead of storing them in some collection, map etc. ? I am using glassfish v3 , ejb 3.1, jax-ws. Thank You!

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• Improve disk read performance (multiple files) with threading

  - by pablo

  I need to find a method to read a big number of small files (about 300k files) as fast as possible. Reading them sequentially using FileStream and reading the entire file in a single call takes between 170 and 208 seconds (you know, you re-run, disk cache plays its role and time varies). Then I tried using PInvoke with CreateFile/ReadFile and using FILE_FLAG_SEQUENTIAL_SCAN, but I didn't appreciate any changes. I tried with several threads (divide the big set in chunks and have every thread reading its part) and this way I was able to improve speed just a little bit (not even a 5% with every new thread up to 4). Any ideas on how to find the most effective way to do this?

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