Helgrindで誤検知を避けるには？

Question

私のスレッドの同期 "スタイル"は、helgrindをオフにしているようです。問題を再現するシンプルなプログラムを次に示します。

#include <thread> 
#include <atomic> 
#include <iostream> 

int main() 
{ 
    std::atomic<bool> isReady(false); 

    int i = 1; 

    std::thread t([&isReady, &i]() 
    { 
     i = 2; 
     isReady = true; 
    }); 

    while (!isReady) 
     std::this_thread::yield(); 

    i = 3; 

    t.join(); 

    std::cout << i; 

    return 0; 
} 

私の知る限り、上記は完全に整形式のプログラムです。しかし、私は次のコマンドを使用してhelgrind実行したときに、私はエラーを取得：

valgrind --tool=helgrind ./a.out 

これの出力は次のとおりです。

==6247== Helgrind, a thread error detector 
==6247== Copyright (C) 2007-2015, and GNU GPL'd, by OpenWorks LLP et al. 
==6247== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info 
==6247== Command: ./a.out 
==6247== 
==6247== ---Thread-Announcement------------------------------------------ 
==6247== 
==6247== Thread #1 is the program's root thread 
==6247== 
==6247== ---Thread-Announcement------------------------------------------ 
==6247== 
==6247== Thread #2 was created 
==6247== at 0x56FBB1E: clone (clone.S:74) 
==6247== by 0x4E46189: create_thread (createthread.c:102) 
==6247== by 0x4E47EC3: pthread_create@@GLIBC_2.2.5 (pthread_create.c:679) 
==6247== by 0x4C34BB7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==6247== by 0x5115DC2: std::thread::_M_start_thread(std::shared_ptr<std::thread::_Impl_base>, void (*)()) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21) 
==6247== by 0x4010EF: std::thread::thread<main::{lambda()#1}>(main::{lambda()#1}&&) (in /home/arman/a.out) 
==6247== by 0x400F93: main (in /home/arman/a.out) 
==6247== 
==6247== ---------------------------------------------------------------- 
==6247== 
==6247== Possible data race during read of size 1 at 0xFFF00035B by thread #1 
==6247== Locks held: none 
==6247== at 0x4022C3: std::atomic<bool>::operator bool() const (in /home/arman/a.out) 
==6247== by 0x400F9F: main (in /home/arman/a.out) 
==6247== 
==6247== This conflicts with a previous write of size 1 by thread #2 
==6247== Locks held: none 
==6247== at 0x40233D: std::__atomic_base<bool>::operator=(bool) (in /home/arman/a.out) 
==6247== by 0x40228E: std::atomic<bool>::operator=(bool) (in /home/arman/a.out) 
==6247== by 0x400F4A: main::{lambda()#1}::operator()() const (in /home/arman/a.out) 
==6247== by 0x40204D: void std::_Bind_simple<main::{lambda()#1}()>::_M_invoke<>(std::_Index_tuple<>) (in /home/arman/a.out) 
==6247== by 0x401FA3: std::_Bind_simple<main::{lambda()#1}()>::operator()() (in /home/arman/a.out) 
==6247== by 0x401F33: std::thread::_Impl<std::_Bind_simple<main::{lambda()#1}()> >::_M_run() (in /home/arman/a.out) 
==6247== by 0x5115C7F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21) 
==6247== by 0x4C34DB6: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==6247== Address 0xfff00035b is on thread #1's stack 
==6247== in frame #1, created by main (???:) 
==6247== 
==6247== ---------------------------------------------------------------- 
==6247== 
==6247== Possible data race during write of size 4 at 0xFFF00035C by thread #1 
==6247== Locks held: none 
==6247== at 0x400FAE: main (in /home/arman/a.out) 
==6247== 
==6247== This conflicts with a previous write of size 4 by thread #2 
==6247== Locks held: none 
==6247== at 0x400F35: main::{lambda()#1}::operator()() const (in /home/arman/a.out) 
==6247== by 0x40204D: void std::_Bind_simple<main::{lambda()#1}()>::_M_invoke<>(std::_Index_tuple<>) (in /home/arman/a.out) 
==6247== by 0x401FA3: std::_Bind_simple<main::{lambda()#1}()>::operator()() (in /home/arman/a.out) 
==6247== by 0x401F33: std::thread::_Impl<std::_Bind_simple<main::{lambda()#1}()> >::_M_run() (in /home/arman/a.out) 
==6247== by 0x5115C7F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21) 
==6247== by 0x4C34DB6: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==6247== by 0x4E476F9: start_thread (pthread_create.c:333) 
==6247== by 0x56FBB5C: clone (clone.S:109) 
==6247== Address 0xfff00035c is on thread #1's stack 
==6247== in frame #0, created by main (???:) 
==6247== 
3==6247== 
==6247== For counts of detected and suppressed errors, rerun with: -v 
==6247== Use --history-level=approx or =none to gain increased speed, at 
==6247== the cost of reduced accuracy of conflicting-access information 
==6247== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0) 

Helgrindは競合状態として私whileループを拾っているようです。偽陽性を投げ捨てるのを避けるために、私はどのようにこのプログラムを作りますか？

Answer 1

問題は、HelgrindがGCCの組み込み組み込み関数を理解していないため、レースフリーであり、プログラムに命令を課すことを認識していないということです。

http://valgrind.org/docs/manual/hg-manual.html#hg-manual.effective-useを参照するためにコードに注釈を付ける方法があります（しかし、私はここでそれらをどのように使用するのかは分かりませんが、すでにsbabbiが示していることを試してみました。

私はとにかくビジーなループで降伏しないようにしていますが、それは同期の悪い形です。それはそうのような条件変数で行うことができます。

#include <thread> 
#include <atomic> 
#include <iostream> 
#include <condition_variable> 

int main() 
{ 
    bool isReady(false); 
    std::mutex mx; 
    std::condition_variable cv; 

    int i = 1; 

    std::thread t([&isReady, &i, &mx, &cv]() 
    { 
     i = 2; 
     std::unique_lock<std::mutex> lock(mx); 
     isReady = true; 
     cv.notify_one(); 
    }); 

    { 
     std::unique_lock<std::mutex> lock(mx); 
     cv.wait(lock, [&] { return isReady; }); 
    } 

    i = 3; 

    t.join(); 

    std::cout << i; 

    return 0; 
} 

Answer 2

Valgrindのは（店舗および負荷の暗黙のmemory_order_releaseとmemory_order_consume旗と一緒に）while (!isReady)ループは、声明i = 2が注文依存性があることを意味していることを知ることができません前にi = 3。あなたが明示的にvalgrindのANNOTATE_HAPPENS_BEFOREとANNOTATE_HAPPENS_AFTERマクロを使用して、この不変を述べる必要はあり

：

#include <valgrind/drd.h> 

#include <thread> 
#include <atomic> 
#include <iostream> 

int main() 
{ 
    std::atomic<bool> isReady(false); 

    int i = 1; 

    std::thread t([&isReady, &i]() 
    { 
     i = 2; 
     ANNOTATE_HAPPENS_BEFORE(&isReady); 
     isReady = true; 
    }); 

    while (!isReady) 
     std::this_thread::yield(); 

    ANNOTATE_HAPPENS_AFTER(&isReady); 
    i = 3; 

    t.join(); 

    std::cout << i; 

    return 0; 
} 

ここでは、ANNOTATE_HAPPENS_BEFOREのラインは常にANNOTATE_HAPPENS_AFTERのラインの前に起こることを言っている、私たちは原因の検査をすることをを知っていますプログラムのロジックが、valgrindはあなたのためにそれを証明することはできません。

このプログラムが生成します。

valgrind --tool=helgrind ./a.out 
==714== Helgrind, a thread error detector 
==714== Copyright (C) 2007-2015, and GNU GPL'd, by OpenWorks LLP et al. 
==714== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info 
==714== Command: ./val 
==714== 
==714== ---Thread-Announcement------------------------------------------ 
==714== 
==714== Thread #1 is the program's root thread 
==714== 
==714== ---Thread-Announcement------------------------------------------ 
==714== 
==714== Thread #2 was created 
==714== at 0x59E169E: clone (in /usr/lib/libc-2.23.so) 
==714== by 0x4E421D9: create_thread (in /usr/lib/libpthread-2.23.so) 
==714== by 0x4E43C42: pthread_create@@GLIBC_2.2.5 (in /usr/lib/libpthread-2.23.so) 
==714== by 0x4C316F3: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==714== by 0x4C327D7: pthread_create@* (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==714== by 0x5113DB4: __gthread_create (gthr-default.h:662) 
==714== by 0x5113DB4: std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)()) (thread.cc:163) 
==714== by 0x40109C: std::thread::thread<main::{lambda()#1}>(main::{lambda()#1}&&) (in /home/ennio/val) 
==714== by 0x400F55: main (in /home/ennio/val) 
==714== 
==714== ---------------------------------------------------------------- 
==714== 
==714== Possible data race during read of size 1 at 0xFFF00061F by thread #1 
==714== Locks held: none 
==714== at 0x401585: std::atomic<bool>::operator bool() const (in /home/ennio/val) 
==714== by 0x400F61: main (in /home/ennio/val) 
==714== 
==714== This conflicts with a previous write of size 1 by thread #2 
==714== Locks held: none 
==714== at 0x4015D5: std::__atomic_base<bool>::operator=(bool) (in /home/ennio/val) 
==714== by 0x401550: std::atomic<bool>::operator=(bool) (in /home/ennio/val) 
==714== by 0x400F1B: main::{lambda()#1}::operator()() const (in /home/ennio/val) 
==714== by 0x40146F: void std::_Bind_simple<main::{lambda()#1}()>::_M_invoke<>(std::_Index_tuple<>) (in /home/ennio/val) 
==714== by 0x40140C: std::_Bind_simple<main::{lambda()#1}()>::operator()() (in /home/ennio/val) 
==714== by 0x4013EB: std::thread::_State_impl<std::_Bind_simple<main::{lambda()#1}()> >::_M_run() (in /home/ennio/val) 
==714== by 0x5113A9E: execute_native_thread_routine (thread.cc:83) 
==714== by 0x4C318E7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==714== Address 0xfff00061f is on thread #1's stack 
==714== in frame #1, created by main (???:) 
==714== 
3==714== 
==714== For counts of detected and suppressed errors, rerun with: -v 
==714== Use --history-level=approx or =none to gain increased speed, at 
==714== the cost of reduced accuracy of conflicting-access information 
==714== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) 

isReady自体にエラーを削除するには、私は__atomic_base<bool>::operator=の抑制ファイルが十分であると仮定します。