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Un grupo de subprocesos muy simple utilizando pthreads en C++

2010-08-24 19 views
13

Estoy tratando de comprender algunos de los conceptos básicos del uso de subprocesos POSIX. El tipo de cosas que necesito hacer (eventualmente) es paralelizar algunos cálculos, usando un modelo de grupo de subprocesos. En este momento quiero asegurarme de que tengo un sentido muy básico de cómo funciona el modelo POSIX pthread. Así que estoy tratando de crear el grupo de subprocesos más simple que sea lo suficientemente general como para hacer el tipo de cosas que quiero hacer. Habrá algo de memoria compartida, una cola de entrada y una cola de salida, y habrá mutexes que protegerán a cada uno. He escrito un código que hace precisamente eso, pero a la herramienta helgrind de valgrind no le gusta lo que hice. Sospecho que me estoy perdiendo algo básico. ¿Tiene ideas sobre mi código?Un grupo de subprocesos muy simple utilizando pthreads en C++

#include <stdlib.h> 
#include <string> 
#include <sstream> 
#include <list> 
#include <iostream> 

#include <pthread.h> 
#include <signal.h> 
#include <sys/select.h> 

// the muticies, protectors of the shared resources 
pthread_mutex_t coutLock; 
pthread_mutex_t inQueueLock; 
pthread_mutex_t outQueueLock; 
// the shared data 
std::list<std::string> inQueue; 
std::list<std::string> outQueue; 

struct thread_detail { // information to pass to worker threads 
unsigned long num; 
}; 

extern "C" { 
    void *workerThread(void *threadarg); 
} 

void *workerThread(void *threadarg) 
{ 
    struct thread_detail *my_data; 
    my_data = (thread_detail *) threadarg; 
    int taskid = my_data->num; 
    std::stringstream ss; ss<<taskid; std::string taskString(ss.str()); 

    bool somethingTodo=true; 
    while (somethingTodo) // keep on working until inQueue is empty 
    { 
     pthread_mutex_lock(&inQueueLock); 
     std::string workOnMe; 
     if (inQueue.size()==0) { somethingTodo=false; } 
     else 
     { 
     workOnMe = inQueue.front(); 
     inQueue.pop_front(); 
     } 
     pthread_mutex_unlock(&inQueueLock); 

     if (!somethingTodo) break; 
     workOnMe = "thread " + taskString + " worked on " + workOnMe; 
     // let's pretend this takes some time, add a delay to the computation 
     struct timeval timeout; 
     timeout.tv_sec = 0; timeout.tv_usec = 100000; // 0.1 second delay 
     select(0, NULL, NULL, NULL, & timeout); 

     pthread_mutex_lock(&outQueueLock); 
     outQueue.push_back(workOnMe); 
     pthread_mutex_unlock(&outQueueLock); 
    } 

    pthread_exit(NULL); 
} 


int main (int argc, char *argv[]) 
{ 
    unsigned long comp_DONE=0; 
    unsigned long comp_START=0; 
    // set-up the mutexes 
    pthread_mutex_init(&coutLock, NULL); 
    pthread_mutex_init(&inQueueLock, NULL); 
    pthread_mutex_init(&outQueueLock, NULL); 

    if (argc != 3) { std::cout<<"Program requires two arguments: (1) number of threads to use," 
          " and (2) tasks to accomplish.\n"; exit(1); } 
    unsigned long NUM_THREADS(atoi(argv[1])); 
    unsigned long comp_TODO(atoi(argv[2])); 
    std::cout<<"Program will have "<<NUM_THREADS<<" threads, working on "<<comp_TODO<<" things \n"; 
    for (unsigned long i=0; i<comp_TODO; i++) // fill inQueue will rubbish data since this isn't an actual computation... 
    { 
    std::stringstream ss; 
    ss<<"task "<<i; 
    inQueue.push_back(ss.str()); 
    } 

    // start the worker threads 
    std::list< pthread_t* > threadIdList; // just the thread ids 
    std::list<thread_detail> thread_table; // for keeping track of information on the various threads we'll create 
    for (unsigned long i=0; i<NUM_THREADS; i++) // start the threads 
    { 
    pthread_t *tId(new pthread_t); threadIdList.push_back(tId); 
    thread_detail Y; Y.num=i; thread_table.push_back(Y); 
    int rc(pthread_create(tId, NULL, workerThread, (void *)(&(thread_table.back())))); 
    if (rc) { std::cout<<"ERROR; return code from pthread_create() "<<comp_START<<"\n"; std::cout.flush(); 
       exit(-1); } 
    } 
    // now we wait for the threads to terminate, perhaps updating the screen with info as we go. 
    std::string stringOut; 
    while (comp_DONE != comp_TODO) 
    { 
     // poll the queue to get a status update on computation 
     pthread_mutex_lock(&inQueueLock); 
     comp_START = comp_TODO - inQueue.size(); 
     pthread_mutex_unlock(&inQueueLock); 
     pthread_mutex_lock(&outQueueLock); 
     comp_DONE = outQueue.size(); 
     pthread_mutex_unlock(&outQueueLock); 

     // update for users 
     pthread_mutex_lock(&coutLock); 
     for (unsigned long i=0; i<stringOut.length(); i++) std::cout<<"\b"; 
     std::stringstream ss; ss<<"started "<<comp_START<<" completed "<<comp_DONE<<" of "<<comp_TODO; 
     stringOut = ss.str(); std::cout<<stringOut; std::cout.flush(); 
     pthread_mutex_unlock(&coutLock); 

     // wait one second per update 
     struct timeval timeout; 
     timeout.tv_sec = 1; timeout.tv_usec = 0; 
     select(0, NULL, NULL, NULL, & timeout); 
     } // big while loop 

    // call join to kill all worker threads 
    std::list< pthread_t* >::iterator i(threadIdList.begin()); 
    while (i!=threadIdList.end()) 
    { 
    if (pthread_join(*(*i), NULL)!=0) { std::cout<<"Thread join error!\n"; exit(1); } 
    delete (*i); 
    threadIdList.erase(i++); 
    } 
    std::cout<<"\n"; 

    // let the user know what happened 
    for (std::list<std::string>::iterator i=outQueue.begin(); i!=outQueue.end(); i++) 
    { 
    std::cout<<(*i)<<"\n"; 
    } 
    // clean-up 
    pthread_mutex_destroy(&coutLock); 
    pthread_mutex_destroy(&inQueueLock); 
    pthread_mutex_destroy(&outQueueLock); 
    // pthread_exit(NULL); 
}

Aquí está la salida helgrind al pasar los argumentos 2 40 al programa compilado.


valgrind -v --tool=helgrind ./thread1 2 40 
==12394== Helgrind, a thread error detector 
==12394== Copyright (C) 2007-2009, and GNU GPL'd, by OpenWorks LLP et al. 
==12394== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info 
==12394== Command: ./thread1 2 40 
==12394== 
--12394-- Valgrind options: 
--12394-- --suppressions=/usr/lib/valgrind/debian-libc6-dbg.supp 
--12394-- -v 
--12394-- --tool=helgrind 
--12394-- Contents of /proc/version: 
--12394-- Linux version 2.6.32-24-generic ([email protected]) (gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5)) #38-Ubuntu SMP Mon Jul 5 09:20:59 UTC 2010 
--12394-- Arch and hwcaps: AMD64, amd64-sse3-cx16 
--12394-- Page sizes: currently 4096, max supported 4096 
--12394-- Valgrind library directory: /usr/lib/valgrind 
--12394-- Reading syms from /home/rybu/prog/regina/exercise/thread1 (0x400000) 
--12394-- Reading syms from /lib/ld-2.11.1.so (0x4000000) 
--12394-- Reading debug info from /lib/ld-2.11.1.so .. 
--12394-- .. CRC mismatch (computed 99d13f6f wanted 0962e544) 
--12394-- Reading debug info from /usr/lib/debug/lib/ld-2.11.1.so .. 
--12394-- Reading syms from /usr/lib/valgrind/helgrind-amd64-linux (0x38000000) 
--12394-- object doesn't have a dynamic symbol table 
--12394-- Reading suppressions file: /usr/lib/valgrind/debian-libc6-dbg.supp 
--12394-- Reading suppressions file: /usr/lib/valgrind/default.supp 
--12394-- Reading syms from /usr/lib/valgrind/vgpreload_core-amd64-linux.so (0x4a23000) 
--12394-- Reading syms from /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so (0x4c25000) 
--12394-- REDIR: 0x4018310 (index) redirected to 0x4c2be59 (index) 
--12394-- REDIR: 0x4018390 (strcmp) redirected to 0x4c2bf4b (strcmp) 
--12394-- REDIR: 0x40184a0 (strlen) redirected to 0x4c2bec5 (strlen) 
--12394-- Reading syms from /usr/lib/libregina-engine-4.6.1.so (0x4e31000) 
--12394-- Reading syms from /usr/lib/libgmp.so.3.5.2 (0x52f7000) 
--12394-- Reading debug info from /usr/lib/libgmp.so.3.5.2 .. 
--12394-- .. CRC mismatch (computed d65050b9 wanted 1e40f6c0) 
--12394-- object doesn't have a symbol table 
--12394-- Reading syms from /lib/libpthread-2.11.1.so (0x5557000) 
--12394-- Reading debug info from /lib/libpthread-2.11.1.so .. 
--12394-- .. CRC mismatch (computed 9da7e2f6 wanted 8161fac5) 
--12394-- Reading debug info from /usr/lib/debug/lib/libpthread-2.11.1.so .. 
--12394-- Reading syms from /lib/librt-2.11.1.so (0x5774000) 
--12394-- Reading debug info from /lib/librt-2.11.1.so .. 
--12394-- .. CRC mismatch (computed 0e4f4ece wanted 920c9bed) 
--12394-- Reading debug info from /usr/lib/debug/lib/librt-2.11.1.so .. 
--12394-- Reading syms from /lib/libz.so.1.2.3.3 (0x597c000) 
--12394-- Reading debug info from /lib/libz.so.1.2.3.3 .. 
--12394-- .. CRC mismatch (computed 86f1fa27 wanted 5f1ca823) 
--12394-- object doesn't have a symbol table 
--12394-- Reading syms from /usr/lib/libstdc++.so.6.0.13 (0x5b93000) 
--12394-- Reading debug info from /usr/lib/libstdc++.so.6.0.13 .. 
--12394-- .. CRC mismatch (computed 7b5bd5a5 wanted e2f63673) 
--12394-- object doesn't have a symbol table 
--12394-- Reading syms from /lib/libm-2.11.1.so (0x5ea7000) 
--12394-- Reading debug info from /lib/libm-2.11.1.so .. 
--12394-- .. CRC mismatch (computed 043548c3 wanted a081b93d) 
--12394-- Reading debug info from /usr/lib/debug/lib/libm-2.11.1.so .. 
--12394-- Reading syms from /lib/libgcc_s.so.1 (0x612a000) 
--12394-- Reading debug info from /lib/libgcc_s.so.1 .. 
--12394-- .. CRC mismatch (computed 7c01dfc9 wanted 9d78e511) 
--12394-- object doesn't have a symbol table 
--12394-- Reading syms from /lib/libc-2.11.1.so (0x6341000) 
--12394-- Reading debug info from /lib/libc-2.11.1.so .. 
--12394-- .. CRC mismatch (computed c73d5a83 wanted 02758e3e) 
--12394-- Reading debug info from /usr/lib/debug/lib/libc-2.11.1.so .. 
--12394-- Reading syms from /usr/lib/libxml2.so.2.7.6 (0x66c4000) 
--12394-- Reading debug info from /usr/lib/libxml2.so.2.7.6 .. 
--12394-- .. CRC mismatch (computed c2590bed wanted 7aaa27a0) 
--12394-- Reading debug info from /usr/lib/debug/usr/lib/libxml2.so.2.7.6 .. 
--12394-- Reading syms from /lib/libdl-2.11.1.so (0x6a14000) 
--12394-- Reading debug info from /lib/libdl-2.11.1.so .. 
--12394-- .. CRC mismatch (computed 4a29f474 wanted e0b8d72c) 
--12394-- Reading debug info from /usr/lib/debug/lib/libdl-2.11.1.so .. 
--12394-- REDIR: 0x55603c0 (pthread_mutex_lock) redirected to 0x4c299fb (pthread_mutex_lock) 
--12394-- REDIR: 0x5561a00 (pthread_mutex_unlock) redirected to 0x4c29e8c (pthread_mutex_unlock) 
--12394-- REDIR: 0x63bd520 (malloc) redirected to 0x4c28a06 (malloc) 
--12394-- REDIR: 0x63bf360 (calloc) redirected to 0x4c27cc9 (calloc) 
--12394-- REDIR: 0x5c5e380 (operator new[](unsigned long)) redirected to 0x4c28e97 (operator new[](unsigned long)) 
--12394-- REDIR: 0x5c5e250 (operator new(unsigned long)) redirected to 0x4c2921f (operator new(unsigned long)) 
--12394-- REDIR: 0x5c5c380 (operator delete(void*)) redirected to 0x4c28328 (operator delete(void*)) 
--12394-- REDIR: 0x5c5c3c0 (operator delete[](void*)) redirected to 0x4c27fa4 (operator delete[](void*)) 
--12394-- REDIR: 0x63c3fe0 (strlen) redirected to 0x4a235dc (_vgnU_ifunc_wrapper) 
--12394-- REDIR: 0x63c4010 (__GI_strlen) redirected to 0x4c2be91 (strlen) 
--12394-- REDIR: 0x63c7c60 (memcpy) redirected to 0x4c2bfdb (memcpy) 
Program will have 2 threads, working on 40 things 
--12394-- REDIR: 0x555dd60 ([email protected]@GLIBC_2.2.5) redirected to 0x4c2d4c7 ([email protected]*) 
==12394== Thread #2 was created 
==12394== at 0x64276BE: clone (clone.S:77) 
==12394== by 0x555E172: [email protected]@GLIBC_2.2.5 (createthread.c:75) 
==12394== by 0x4C2D42C: pthread_create_WRK (hg_intercepts.c:230) 
==12394== by 0x4C2D4CF: [email protected]* (hg_intercepts.c:257) 
==12394== by 0x401C22: main (in /home/rybu/prog/regina/exercise/thread1) 
==12394== 
==12394== Thread #1 is the program's root thread 
==12394== 
==12394== Possible data race during write of size 8 at 0x7fefffcf0 by thread #2 
==12394== at 0x4C2D54C: mythread_wrapper (hg_intercepts.c:200) 
==12394== This conflicts with a previous read of size 8 by thread #1 
==12394== at 0x4C2D440: pthread_create_WRK (hg_intercepts.c:235) 
==12394== by 0x4C2D4CF: [email protected]* (hg_intercepts.c:257) 
==12394== by 0x401C22: main (in /home/rybu/prog/regina/exercise/thread1) 
==12394== 
started 21 completed 19 of 40==12394== Thread #3 was created 
==12394== at 0x64276BE: clone (clone.S:77) 
==12394== by 0x555E172: [email protected]@GLIBC_2.2.5 (createthread.c:75) 
==12394== by 0x4C2D42C: pthread_create_WRK (hg_intercepts.c:230) 
==12394== by 0x4C2D4CF: [email protected]* (hg_intercepts.c:257) 
==12394== by 0x401C22: main (in /home/rybu/prog/regina/exercise/thread1) 
==12394== 
==12394== Possible data race during read of size 1 at 0x63401a7 by thread #3 
==12394== at 0x613A4D7: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A947: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x6138331: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
==12394== Possible data race during read of size 1 at 0x63401a6 by thread #3 
==12394== at 0x6139A12: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x6139AA8: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A724: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A982: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x613832A: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
==12394== Possible data race during read of size 1 at 0x63401b0 by thread #3 
==12394== at 0x6139AD7: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A724: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A982: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x6138370: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
--12394-- REDIR: 0x63bede0 (free) redirected to 0x4c28616 (free) 
started 40 completed 40 of 40--12394-- REDIR: 0x555ef30 (pthread_join) redirected to 0x4c29796 (pthread_join) 

thread 0 worked on task 0 
thread 1 worked on task 1 
thread 0 worked on task 2 
thread 1 worked on task 3 
thread 0 worked on task 4 
thread 1 worked on task 5 
thread 0 worked on task 6 
thread 1 worked on task 7 
thread 0 worked on task 8 
thread 1 worked on task 9 
thread 0 worked on task 10 
thread 1 worked on task 11 
thread 0 worked on task 12 
thread 1 worked on task 13 
thread 0 worked on task 14 
thread 1 worked on task 15 
thread 0 worked on task 16 
thread 1 worked on task 17 
thread 0 worked on task 18 
thread 1 worked on task 19 
thread 0 worked on task 20 
thread 1 worked on task 21 
thread 0 worked on task 22 
thread 1 worked on task 23 
thread 0 worked on task 24 
thread 1 worked on task 25 
thread 0 worked on task 26 
thread 1 worked on task 27 
thread 0 worked on task 28 
thread 1 worked on task 29 
thread 0 worked on task 30 
thread 1 worked on task 31 
thread 0 worked on task 32 
thread 1 worked on task 33 
thread 0 worked on task 34 
thread 1 worked on task 35 
thread 0 worked on task 36 
thread 1 worked on task 37 
thread 0 worked on task 38 
thread 1 worked on task 39 
==12394== 
==12394== ERROR SUMMARY: 7 errors from 4 contexts (suppressed: 804 from 64) 
==12394== 
==12394== 1 errors in context 1 of 4: 
==12394== Possible data race during read of size 1 at 0x63401a7 by thread #3 
==12394== at 0x613A4D7: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A947: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x6138331: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
==12394== 
==12394== 2 errors in context 2 of 4: 
==12394== Possible data race during read of size 1 at 0x63401b0 by thread #3 
==12394== at 0x6139AD7: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A724: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A982: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x6138370: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
==12394== 
==12394== 2 errors in context 3 of 4: 
==12394== Possible data race during read of size 1 at 0x63401a6 by thread #3 
==12394== at 0x6139A12: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x6139AA8: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A724: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A982: _Unwind_Resume (in /lib/libgcc_s.so.1) 
==12394== by 0x4019C9: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== by 0x555D9C9: start_thread (pthread_create.c:300) 
==12394== by 0x64276FC: clone (clone.S:112) 
==12394== This conflicts with a previous write of size 1 by thread #2 
==12394== at 0x613832A: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x5563F42: pthread_once (pthread_once.S:104) 
==12394== by 0x613A4C9: ??? (in /lib/libgcc_s.so.1) 
==12394== by 0x613A7B6: _Unwind_ForcedUnwind (in /lib/libgcc_s.so.1) 
==12394== by 0x556508F: __pthread_unwind (unwind.c:130) 
==12394== by 0x555EEB4: pthread_exit (pthreadP.h:265) 
==12394== by 0x40198E: workerThread(void*) (in /home/rybu/prog/regina/exercise/thread1) 
==12394== by 0x4C2D558: mythread_wrapper (hg_intercepts.c:202) 
==12394== 
==12394== 
==12394== 2 errors in context 4 of 4: 
==12394== Possible data race during write of size 8 at 0x7fefffcf0 by thread #2 
==12394== at 0x4C2D54C: mythread_wrapper (hg_intercepts.c:200) 
==12394== This conflicts with a previous read of size 8 by thread #1 
==12394== at 0x4C2D440: pthread_create_WRK (hg_intercepts.c:235) 
==12394== by 0x4C2D4CF: [email protected]* (hg_intercepts.c:257) 
==12394== by 0x401C22: main (in /home/rybu/prog/regina/exercise/thread1) 
==12394== 
--12394-- 
--12394-- used_suppression: 610 helgrind-glibc2X-101 
--12394-- used_suppression: 192 helgrind---...-*Unwind*-*pthread_unwind* 
--12394-- used_suppression:  2 helgrind-glibc2X-112 
==12394== 
==12394== ERROR SUMMARY: 7 errors from 4 contexts (suppressed: 804 from 64)

No tengo tanta confianza cuando se trata de interpretar la salida de helgrind.

Gracias por cualquier idea.

Fuente

2010-08-24 Ryan Budney

+2

+1 por darnos no solo el código sino también la descripción de los mensajes de error. – wheaties

+2

No veo nada mal. ¿Tal vez falsos positivos de Helgrind? – Starkey

+0

Bien, después de jugar lo suficiente con suficiente código escrito por otras personas que usan pthreads con éxito, parece que el problema es helgrind simplemente dando demasiados falsos positivos. –

Respuesta

1

Varios de sus errores provienen de libgcc_s.so. Algunos de ellos aparecen durante la inicialización del hilo, incluso antes de que se llame a su función.

Intente compilar con gcc -pthread para asegurarse de que el compilador sepa lo que está sucediendo.

Fuente

2010-08-24 22:56:23 Potatoswatter

+0

Eso es lo que estoy haciendo. ¿No tienes los mismos problemas si ejecutas helgrind en el ejecutable? –

+0

He notado que la aplicación "pbzip2" usa un grupo de subprocesos, también está escrito en un estilo C/C++ como mi código. Helgrind solo tiene una queja cuando se ejecuta pbzip2, es lo mismo que la queja más alta en mi salida de helgrind. Entonces esa queja quizás no es tan importante, pero los demás no sé lo que significan. –

+0

@Ryan: los otros errores mencionan 'pthread_once', que se usa para inicializar variables estáticas. Además, sabemos que ocurren antes del ciclo en los trabajadores. Como lo único interesante es la creación de un 'stringstream' y algunos' string's, intente construir un dummy 'stringstream' y hacer algo similar en' main' antes de 'pthread_create', solo para inicializar los globales. Además, podría valer la pena probar diferentes versiones del compilador. – Potatoswatter

2

me falta un extern "C" {} bloque para su función del hilo al menos, desde una biblioteca C esperaría un C ABI. Aparte de eso, no puedo ver nada obvio.

E.g. crear un prototipo como:

extern "C" { 
    void *workerThread(void *threadarg); 
}

Fuente

2010-08-24 21:25:49 Maister

6

Está utilizando un bucle ocupado:

if (inQueue.size()==0) { somethingTodo=false; } 
    else 
    { 
    workOnMe = inQueue.front(); 
    inQueue.pop_front(); 
    } 
    pthread_mutex_unlock(&inQueueLock); 

    if (!somethingTodo) continue;

mirar hacia arriba variable de condición.
De esta manera su hilo no está consumiendo recursos esperando a que el trabajo aparezca en la cola.
See this question

Marcó la pregunta C++ pero está utilizando moldes de estilo C.
También tenga en cuenta que en C++ no necesita agregar struct aquí.

my_data = (struct thread_detail *) threadarg;

Técnicamente se debe declarar la función de devolución de llamada para utilizar el C ABI (ya que esto es una biblioteca C.

extern "C" void *workerThread(void *threadarg);

La elección personal mover el * junto al tipo (pero eso es sólo mi pref personales).

no está utilizando RAII. Así que su bloqueo/desbloqueo senarios no están a salvo excepción.

pthread_mutex_lock(&inQueueLock); 

    // Stuff that could throw. 

    pthread_mutex_unlock(&inQueueLock);

Incluso si las cosas en el medio no pueden lanzar ahora. Estás asumiendo que alguien no agregará un código que no arroje en el futuro. Hazlo seguro creando un objeto de bloqueo.

Fuente

2010-08-24 21:33:49

+0

El usuario llamado "Dima" etiquetó la pregunta como C++, no como yo. En cuanto al comentario de "bucle ocupado", solo se llama al hilo de trabajo si la cola no está vacía y, una vez que está vacía, finaliza el hilo de trabajo. Por lo tanto, nunca desperdicia recursos en una cola vacía. Creo que tal vez estás pensando que mi código es más sofisticado de lo que es. El grupo de subprocesos de trabajo solo se inicia cuando hay un trabajo que hacer, y luego se destruye. Esto no parece abordar la salida helgrind. A juzgar por los comentarios de la gente hasta ahora, parece que Helgrind no brinda información confiable, incluso sobre el "buen" código pthread? –

+0

En relación con su último comentario sobre las llamadas de bloqueo/desbloqueo de mutex, por ahora solo quiero asegurarme de que este experimento independiente se ejecute correctamente. Este no es un código que alguien más va a tocar. Soy un programador aficionado. Estoy bien, no estoy cumpliendo con RAII. Esto es solo acerca de mí entendiendo pthreads por ahora. –

+1

@Ryan: Sería más claro decir 'if (! SomethingToDo) break;' en lugar de 'continue', ya que' continue' lleva inmediatamente a una salida de bucle. – Potatoswatter

1

Eso en realidad depende de su compilador. Tanto en gnu como en clang no necesitas el c externo alrededor de la llamada a la función. Aunque he escuchado en algunos compiladores, sí.

Fuente

2014-03-05 20:17:39

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