QThread：最も単純なコードの競合条件

アプリのデバッグ私は明らかに私たちのコードに起因しないいくつかの奇妙な競合状態を発見しました。次のコードでテストを行うHelgrindは、5000秒を超える潜在的な競合状態を数秒で報告します。ここでQThread：最も単純なコードの競合条件

コード：

#include <QApplication> 
#include <QThread> 

int main(int argc, char *argv[]) { 
    QApplication app(argc, argv); 

    QThread thread; 
    thread.start(); 

    return app.exec(); 
}

ここhellgrind報告書の最初の部分：

==9856== Helgrind, a thread error detector 
==9856== Copyright (C) 2007-2015, and GNU GPL'd, by OpenWorks LLP et al. 
==9856== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info 
==9856== Command: /home/gianks/NetBeansProjects/ThreadTest/dist/Debug/GNU-Linux/ThreadTest 
==9856== 
==9856== ---Thread-Announcement------------------------------------------ 
==9856== 
==9856== Thread #1 is the program's root thread 
==9856== 
==9856== ---Thread-Announcement------------------------------------------ 
==9856== 
==9856== Thread #2 was created 
==9856== at 0x6041B1E: clone (clone.S:74) 
==9856== by 0x6852189: create_thread (createthread.c:102) 
==9856== by 0x6853EC3: [email protected]@GLIBC_2.2.5 (pthread_create.c:679) 
==9856== by 0x4C34BB7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5571DB7: QThread::start(QThread::Priority) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F9778: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5E3: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0003: QGuiApplicationPrivate::createPlatformIntegration() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0F0C: QGuiApplicationPrivate::createEventDispatcher() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== 
==9856== ---------------------------------------------------------------- 
==9856== 
==9856== Possible data race during read of size 4 at 0x599E9B0 by thread #1 
==9856== Locks held: none 
==9856== at 0x556AD30: QBasicMutex::unlockInternal() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C344E7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5571D23: QThread::start(QThread::Priority) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F9778: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5E3: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0003: QGuiApplicationPrivate::createPlatformIntegration() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0F0C: QGuiApplicationPrivate::createEventDispatcher() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x5757A85: QCoreApplication::init() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x5757AF5: QCoreApplication::QCoreApplication(QCoreApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== 
==9856== This conflicts with a previous write of size 4 by thread #2 
==9856== Locks held: none 
==9856== at 0x556A977: QBasicMutex::lockInternal() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34377: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5572754: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34DB6: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x68536F9: start_thread (pthread_create.c:333) 
==9856== by 0x6041B5C: clone (clone.S:109) 
==9856== Address 0x599e9b0 is in the Data segment of /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1 
==9856== 
==9856== ---------------------------------------------------------------- 
==9856== 
==9856== Possible data race during write of size 8 at 0xBF41830 by thread #1 
==9856== Locks held: none 
==9856== at 0x556AD3A: QBasicMutex::unlockInternal() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C344E7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5571D23: QThread::start(QThread::Priority) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F9778: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5E3: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0003: QGuiApplicationPrivate::createPlatformIntegration() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0F0C: QGuiApplicationPrivate::createEventDispatcher() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x5757A85: QCoreApplication::init() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x5757AF5: QCoreApplication::QCoreApplication(QCoreApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== 
==9856== This conflicts with a previous read of size 8 by thread #2 
==9856== Locks held: none 
==9856== at 0x556A9A5: QMutex::lock() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34377: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5572754: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34DB6: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x68536F9: start_thread (pthread_create.c:333) 
==9856== by 0x6041B5C: clone (clone.S:109) 
==9856== Address 0xbf41830 is 112 bytes inside a block of size 168 alloc'd 
==9856== at 0x4C2F50F: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x556D793: QThread::QThread(QObject*) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F96B2: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5D4: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0003: QGuiApplicationPrivate::createPlatformIntegration() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0F0C: QGuiApplicationPrivate::createEventDispatcher() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x5757A85: QCoreApplication::init() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x5757AF5: QCoreApplication::QCoreApplication(QCoreApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x63F2D08: QGuiApplication::QGuiApplication(QGuiApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== Block was alloc'd by thread #1 
==9856== 
==9856== ---------------------------------------------------------------- 
==9856== 
==9856== Possible data race during read of size 8 at 0xBF41830 by thread #2 
==9856== Locks held: none 
==9856== at 0x556A92D: QBasicMutex::lockInternal() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34377: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5572754: ??? (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C34DB6: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x68536F9: start_thread (pthread_create.c:333) 
==9856== by 0x6041B5C: clone (clone.S:109) 
==9856== 
==9856== This conflicts with a previous write of size 8 by thread #1 
==9856== Locks held: none 
==9856== at 0x556AD3A: QBasicMutex::unlockInternal() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x4C344E7: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x5571D23: QThread::start(QThread::Priority) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F9778: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5E3: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== Address 0xbf41830 is 112 bytes inside a block of size 168 alloc'd 
==9856== at 0x4C2F50F: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so) 
==9856== by 0x556D793: QThread::QThread(QObject*) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x40F96B2: ??? (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40FF5D4: QXcbConnection::QXcbConnection(QXcbNativeInterface*, bool, unsigned int, char const*) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x41029EC: QXcbIntegration::QXcbIntegration(QStringList const&, int&, char**) (in /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.5.1) 
==9856== by 0x40293AC: ??? (in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so) 
==9856== by 0x63E3DD1: QPlatformIntegrationFactory::create(QString const&, QStringList const&, int&, char**, QString const&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0003: QGuiApplicationPrivate::createPlatformIntegration() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x63F0F0C: QGuiApplicationPrivate::createEventDispatcher() (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== by 0x5757A85: QCoreApplication::init() (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x5757AF5: QCoreApplication::QCoreApplication(QCoreApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.5.1) 
==9856== by 0x63F2D08: QGuiApplication::QGuiApplication(QGuiApplicationPrivate&) (in /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.5.1) 
==9856== Block was alloc'd by thread #1

が実際にバグはありますか？

注：私はまた、キューイングされた接続、同じエフェクトでstartを呼び出そうとしました。そのため、他のスレッドが解決策ではない前にイベントループを開始します。

おかげ

出典

2016-09-24 Gianks

あなたはQThreadのサブクラスを作成し、（実行を再実装するか必要があるQtのドキュメントhttp://doc.qt.io/qt-5/qthread.html

ごとにあなたが）、正しい方法でQThreadを使用していない、またはあなたがそれらを移動することにより、労働者のオブジェクトを使用することができますスレッドはQObject :: moveToThread（）を使用しています。

出典

2016-09-24 19:57:25 HazemGomaa

それはちょうど（起動に完全に合法だ）、プレーンQThreadインスタンス。 – peppe

@peppe参考にしてください。 – HazemGomaa

QThreadの[スタート]ドキュメント（https://doc.qt.io/qt-5/qthread.html#start）によると、次のようになります：* run（）*を呼び出してスレッドの実行を開始します。 [run]（https://doc.qt.io/qt-5/qthread.html#run）のドキュメントには次のように書かれています：* [...]デフォルトの実装は単純にexec（）*を呼び出します。言い換えれば、それは完全に正当なものであり、行動は明確に定義されています。 – peppe

helgrindはQt自体で使用されるアトミックを理解していません。あなたはその警告を抑制し（そして無視する）必要があります。このフェッチ：

https://github.com/KDE/kde-dev-scripts/blob/master/kde.supp

そしてhelgrindコマンドラインに--suppressions=/path/to/kde.suppを追加します。

Qtアプリケーションでhelgrindを使用する方法の詳細については、this blog postを参照してください。

（サイドノート：。QThreadを破壊し、まだ実行されているので、メインから復帰する前に、それに参加するようにしてください、あなたのプログラムがクラッシュします）

出典

2016-09-24 21:09:28 peppe

返信いただきありがとうございます、私はすでにあなたが示唆した運が見つかりませんでした。数時間後に結果を投稿する別の試してみましょう、ありがとう！ – Gianks

Qtのデバッグビルドを使用していますか？（リリースビルドがアトミックをインラインにして、ヘルグリンドを混乱させると思っている） – peppe

QThread：最も単純なコードの競合条件

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