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• Linux - preventing an application from failing due to lack of disk space [migrated]

  - by Jernej

  Due to an unpredicted scenario I am currently in need of finding a solution to the fact that an application (which I do not wish to kill) is slowly hogging the entire disk space. To give more context I have an application in Python that uses multiprocessing.Pool to start 5 threads. Each thread writes some data to its own file. The program is running on Linux and I do not have root access to the machine. The program is CPU intensive and has been running for months. It still has a few days to write all the data. 40% of the data in the files is redundant and can be removed after a quick test. The system on which the program is running only has 30GB of remaining disk space and at the current rate of work it will surely be hogged before the program finishes. Given the above points I see the following solutions with respective problems Given that the process number i is writing to file_i, is it safe to move file_i to an external location? Will the OS simply create a new instance of file_i and write to it? I assume moving the file would remove it and the process would end up writing to a "dead" file? Is there a "command line" way to stop 4 of the 5 spawned workers and wait until one of them finishes and then resume their work? (I am sure one single worker thread would avoid hogging the disk) Suppose I use CTRL+Z to freeze the main process. Will this stop all the other processes spawned by multiprocessing.Pool? If yes, can I then safely edit the files as to remove the redundant lines? Given the three options that I see, would any of them work in this context? If not, is there a better way to handle this problem? I would really like to avoid the scenario in which the program crashes just few days before its finish.

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• .NET multithreading, volatile and memory model

  - by fedor-serdukov

  Assume that we have the following code: class Program { static volatile bool flag1; static volatile bool flag2; static volatile int val; static void Main(string[] args) { for (int i = 0; i < 10000 * 10000; i++) { if (i % 500000 == 0) { Console.WriteLine("{0:#,0}",i); } flag1 = false; flag2 = false; val = 0; Parallel.Invoke(A1, A2); if (val == 0) throw new Exception(string.Format("{0:#,0}: {1}, {2}", i, flag1, flag2)); } } static void A1() { flag2 = true; if (flag1) val = 1; } static void A2() { flag1 = true; if (flag2) val = 2; } } } It's fault! The main quastion is Why... I suppose that CPU reorder operations with flag1 = true; and if(flag2) statement, but variables flag1 and flag2 marked as volatile fields...

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• Coredump in Multithreading Application in RHEL-5(Help Required)

  - by Chinnu

  I am working on multi-threading application it is dumping frequently.I could not able to analyaze the core.The core is showing like this Core was generated by `thread-process '. Program terminated with signal 6, Aborted. 0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 (gdb) where 0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 1 0x00000038f4e31ae0 in abort () from /lib64/libc.so.6 2 0x00000038f4e681bb in __libc_message () from /lib64/libc.so.6 3 0x00000038f4e72b96 in free () from /lib64/libc.so.6 4 0x000000000046a137 in std::string::substr () 5 0x000000000042c549 in std::operator<< , std::allocator () 6 0x000000000042cc1d in std::operator<< , std::allocator () 7 0x000000000046b069 in std::string::substr () 8 0x000000000046c866 in std::string::substr () 9 0x0000000000431062 in std::operator<< , std::allocator () 10 0x00000038f5a062e7 in start_thread () from /lib64/libpthread.so.0 11 0x00000038f4ece3bd in clone () from /lib64/libc.so.6

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• Sockets and multithreading

  - by V0idExp

  Hi to all! I have an interesting (to me) problem... There are two threads, one for capturing data from std input and sending it through socket to server, and another one which receives data from blocking socket. So, when there's no reply from server, recv() call waits indefenitely, right? But instead of blocking only its calling thread, it blocks the overall process! Why this thing occurs?

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• c++ volatile multithreading variables

  - by anon

  I'm writing a C++ app. I have a class variable that more than one thread is writing to. In C++, anything that can be modified without the compiler "realizing" that it's being changed needs to be marked volatile right? So if my code is multi threaded, and one thread may write to a var while another reads from it, do I need to mark the var volaltile? [I don't have a race condition since I'm relying on writes to ints being atomic] Thanks!

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• Limit a process's relative (not absolute) processor consumption in Linux

  - by BobBanana

  What is the standard way in Linux to enforce a system policy to limit the relative CPU use of a single process? That is, on a quad-core machine, I never want a process to use more than 2 CPUs at once, even if the process creates more threads. I do not want an absolute time limit, just a relative limit so that one task cannot dominate the machine. This is also different than renice, which allows a process to use all the resources but just politely step aside if others need them too. ulimit is the usual resource limiting tool, but it does not allow such CPU restrictions.. it can limit the number of processes per user, or absolute CPU time, not restrict the maximum number of active threads of a single process. I've found a couple of user-level tools, like CPUlimit, but not a system level tool or setting. Does such a standard resource controller exist in Linux (Red Hat Enterprise, if it matters.) If there is such a limit imposed, how would a user identify it?

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• perl multithreading issue for autoincrement

  - by user3446683

  I'm writing a multi threaded perl script and storing the output in a csv file. I'm trying to insert a field called sl.no. in the csv file for each row entered but as I'm using threads, the sl. no. overlaps in most. Below is an idea of my code snippet. for ( my $count = 1 ; $count <= 10 ; $count++ ) { my $t = threads->new( \&sub1, $count ); push( @threads, $t ); } foreach (@threads) { my $num = $_->join; } sub sub1 { my $num = shift; my $start = '...'; #distributing data based on an internal logic my $end = '...'; #distributing data based on an internal logic my $next; for ( my $x = $start ; $x <= $end ; $x++ ) { my $count = $x + 1; #part of code from which I get @data which has name and age my $j = 0; if ( $x != 0 ) { $count = $next; } foreach (@data) { #j is required here for some extra code flock( OUTPUT, LOCK_EX ); print OUTPUT $count . "," . $name . "," . $age . "\n"; flock( OUTPUT, LOCK_UN ); $j++; $count++; } $next = $count; } return $num; } I need the count to be incremented which is the serial number for the rows that would be inserted in the csv file. Any help would be appreciated.

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• redmine multitheaded

  - by Alex

  Our redmine server is not responding due to connecting it to a large repository. It has not crashed but it's just busy until it checks it out, or whatever redmine does when you set a new repo for a project. What is surprisning is that this operation is not running int the background but blocking the server. Is there any way to have redmine to this in the background next time we connect a large repo? Thanks

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• How does Apache process several requests at a time?

  - by Vicenç Gascó

  In a short question: If 10 requests hit Apache, does it process them one by one, so when R3 finishes, then it starts to run R4, or does it fire 10 processes/threads/whatever and are resolved simultaneously? Now some background: I have a PHP script that takes up to two minutes to do some processes. My question is: while a client is waiting for this 2 minutes, all the other clients requests are being processed? Or also waiting for this one to end? By the way, if there are simultaneous request, how can I handle them? Let's say put a limit on them. Or a limit on resources consumed. For instance I want the server to use its 80% performance on serving the webapp, and just a 20% for those long operations ... because I have no hurry to end them. Doesn't know if it cares but is all in PHP. Thanks in advance!!

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• Is there a way to ‘join’ (block) in POSIX threads, without exiting the joinee?

  - by elliottcable

  I’m buried in multithreading / parallelism documents, trying to figure out how to implement a threading implementation in a programming language I’ve been designing. I’m trying to map a mental model to the pthreads.h library, but I’m having trouble with one thing: I need my interpreter instances to continue to exist after they complete interpretation of a routine (the language’s closure/function data type), because I want to later assign other routines to them for interpretation, thus saving me the thread and interpreter setup/teardown time. This would be fine, except that pthread_join(3) requires that I call pthread_exit(3) to ‘unblock’ the original thread. How can I block the original thread (when it needs the result of executing the routine), and then unblock it when interpretation of the child routine is complete?

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• [newbie]Webservice - Threads - close if no active threads, if any activen, then wait till its compl

  - by Raj

  Hi I have an ASP.Net webservice running. When the system date changes, i want to close all the threads and restart them again, if the thread/s aren't doing any work. If any of the thread/s is in the process of doing some work(active threads), then i need to wait till the current thread/s complete its process and then close. This will prevent from aborting any current process. Any ideas on how i can perform such a task? Thanks PS:I am new to ASP.NET and Multithreading.

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• Singleton again, but with multi-thread and Objective-C

  - by Tonny Xu

  I know Singleton pattern has been discussed so much. But because I'm not fully understand the memory management mechanism in Objective-C, so when I combined Singleton implementation with multithreading, I got a big error and cost me a whole day to resolve it. I had a singleton object, let's call it ObjectX. I declared an object inside ObjectX that will detach a new thread, let's call that object objectWillSpawnNewThread, when I called [[ObjectX sharedInstance].objectWillSpawnNewThread startNewThread]; The new thread could not be executed correctly, and finally I found out that I should not declare the object objectWillSpawnNewThread inside the singleton class. Here are my questions: How does Objective-C allocate static object in the memory? Where does Objective-C allocate them(Main thread stack or somewhere else)? Why would it be failed if we spawn a new thread inside the singleton object? I had searched the Objective-C language [ObjC.pdf] and Objective-C memory management document, maybe I missed something, but I currently I could not find any helpful information.

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• How to deal with OpenMP thread pool contention

  - by dpe82

  I'm working on an application that uses both coarse and fine grained multi-threading. That is, we manage scheduling of large work units on a pool of threads manually, and then within those work units certain functions utilize OpenMP for finer grain multithreading. We have realized gains by selectively using OpenMP in our costliest loops, but are concerned about creating contention for the OpenMP worker pool as we add OpenMP blocks to cheaper loops. Is there a way to signal to OpenMP that a block of code should use the pool if it is available, and if not it should process the loop serially?

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• In a multithreaded app, would a multi-core or multiprocessor arrangement be better?

  - by Michael

  I've read a lot on this topic already both here (e.g., stackoverflow.com/questions/1713554/threads-processes-vs-multithreading-multi-core-multiprocessor-how-they-are or http://stackoverflow.com/questions/680684/multi-cpu-multi-core-and-hyper-thread) and elsewhere (e.g., ixbtlabs.com/articles2/cpu/rmmt-l2-cache.html or software.intel.com/en-us/articles/multi-core-introduction/), but I still am not sure about a couple things that seem very straightforward. So I thought I'd just ask. (1) Is a multi-core processor in which each core has dedicated cache effectively the same as a multiprocessor system (balanced of course for processor speed, cache size, and so on)? (2) Let's say I have some images to analyze (i.e., computer vision), and I have these images loaded into RAM. My app spawns a thread for each image that needs to be analyzed. Will this app on a shared cache multi-core processor run slower than on a dedicated cache multi-core processor, and would the latter run at the same speed as on an equivalent single-core multiprocessor machine? Thank you for the help!

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• WinForms equivalent of performSelectorOnMainThread in Objective-C

  - by jamone

  I haven't done much multithreading before and now find the need to do some background work and keep the UI responsive. I have the following code. data.ImportProgressChanged += new DataAccess.ImportDelegate(data_ImportProgressChanged); Thread importThread = new Thread( new ThreadStart(data.ImportPeopleFromFAD)); importThread.IsBackground = true; importThread.Start(); void data_ImportProgressChanged(int progress) { toolStripProgressBar.Value = progress; } //In my data object I have public void ImportPeopleFromFAD() { ImportProgressChanged(someInt); } But the UI doesn't get updated since the ImportProgressChanged() call is made on the background thread. In objective C I know you can use performSelectorOnMainThread and pass it a method to call using the main thread. What is the equivalent way of calling ImportProgressChanged() from the main thread?

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• Threading in C#

  - by Lalit Dhake

  Hi, I have console application. In that i have some process that fetch the data from database through different layers ( business and Data access). and generate outputs. This process will execute many times say 10 times. Ok? I want to run simultaneously this process. not one will start, it will finish and then second will start. I want after starting 1'st process, just 2'nd , 3rd....10'th must be start. Means it should be multithreading. how can i achieve this ? is that will give me error while connection with data base open and close ?

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• C# equlivent of performSelectorOnMainThread

  - by jamone

  I haven't done much multithreading before and now find the need to do some background work and keep the UI responsive. I have the following code. data.ImportProgressChanged += new DataAccess.ImportDelegate(data_ImportProgressChanged); Thread importThread = new Thread( new ThreadStart(data.ImportPeopleFromFAD)); importThread.IsBackground = true; importThread.Start(); void data_ImportProgressChanged(int progress) { toolStripProgressBar.Value = progress; } //In my data object I have public void ImportPeopleFromFAD() { ImportProgressChanged(someInt); } But the UI doesn't get updated since the ImportProgressChanged() call is made on the background thread. In objective C I know you can use performSelectorOnMainThread and pass it a method to call using the main thread. What is the equivalent way of calling ImportProgressChanged() from the main thread?

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• Could Grand Central Dispatch (`libdispatch`) ever be made available on Windows?

  - by elliottcable

  I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage? Edit: Some things I already know, to get the discussion started: We need a blocks-compatible compiler that will compile on Windows, no? Will PLBlocks handle that? Can we use the LLVM blocks runtime? Can’t we replace all the pthread.h dependencies in userspace libdispatch with APR calls, for portability? Or, alternatively, use pthreads-win32 I suppose…

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• Could Grand Central Dispatch (`libdispatch`) ever be available on Windows?

  - by elliottcable

  I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage?

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• C# Importing Large Volume of Data from CSV to Database

  - by guazz

  What's the most efficient method to load large volumes of data from CSV (3 million + rows) to a database. The data needs to be formatted(e.g. name column needs to be split into first name and last name, etc.) I need to do this in a efficiently as possible i.e. time constraints I am siding with the option of reading, transforming and loading the data using a C# application row-by-row? Is this ideal, if not, what are my options? Should I use multithreading?

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• Buffering db inserts in multithreaded program

  - by Winter

  I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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• Do I need to syncronize thread access to an int

  - by Martin Harris

  I've just written a method that is called by multiple threads simultaneously and I need to keep track of when all the threads have completed, the code uses this pattern: private void RunReport() { _reportsRunning++; try { //code to run the report } finally { _reportsRunning--; } } This is the only place within the code that _reportsRunning's value is changed, and the method takes about a second to run. Occasionally when I have more than six or so threads running reports together the final result for _reportsRunning can get down to -1, if I wrap the calls to _runningReports++ and _runningReports-- in a lock then the behaviour appears to be correct and consistant. So, to the question: When I was learning multithreading in C++ I was taught that you didn't need to synchronize calls to increment and decrement operations because they were always one assembly instruction and therefore it was impossible for the thread to be switched out mid-call. Was I taught correctly, and if so how come that doesn't hold true for C#?

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• iphone dev - loading table content asynchronously

  - by Brian

  My app has a navigation controller which push and pop a series of views. One of the tableViews loads .xml file from URL and it takes 4-5 seconds. If I click the back button on the navigation bar, it will only respond after the content of the table finish loading. Is there an easy way to load the content asynchronously so that the app will still respond to my gesture on the navigation bar? p.s. I search this on the Internet and people are talking about multithreading. I don't know a lot about threads so please be more specific. Thanks in advanced =)

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• C# regularly return values from a different thread

  - by sdds

  Hello, I'm very new to multithreading and lack experience. I need to compute some data in a different thread so the UI doesn't hang up, and then send the data as it is processed to a table on the main form. So, basically, the user can work with the data that is already computed, while other data is still being processed. What is the best way to achieve this? I would also be very grateful for any examples. Thanks in advance.

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• c++ simple start a function with its own thread

  - by user1397417

  i had once had a very simple one or two line code that would start a function with its own thread and continue running until application closed, c++ console app. lost the project it was in, and remember it was hard to find. cant find it online now. most example account for complicated multithreading situations. but i just need to open this one function in its own thread. hopefully someone knows what im talking about, or a similar solution. eg. start void abc in its own thread, no parameters

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