QThread:用最简单的代码竞态条件
QThread: race condition with the simplest code
调试我正在工作的应用程序，我发现了一些奇怪的竞争条件显然不是由我们的代码引起的。Helgrind在几秒钟内报告了5000多个潜在的竞争条件。
代码如下:
#include <QApplication>
#include <QThread>
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
QThread thread;
thread.start();
return app.exec();
}
下面是hellgrind报告的开头部分:
==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: pthread_create@@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
真的有bug吗?
一个注意:我也试过调用开始与排队连接，相同的效果，所以开始事件循环之前的其他线程不是一个解决方案。
谢谢
helgrind不理解Qt内部使用的原子。您需要抑制该警告(并忽略它)。获取:
https://github.com/KDE/kde-dev-scripts/blob/master/kde.supp并将--suppressions=/path/to/kde.supp添加到helgrind命令行。
有关在Qt应用程序中使用helgrind的更多信息，请查看这篇博客文章。
(旁注:破坏一个仍在运行的QThread会使你的程序崩溃，所以一定要在从main返回之前加入它)
您没有以正确的方式使用QThread，按照Qt文档http://doc.qt.io/qt-5/qthread.html
您需要创建QThread的子类并重新实现run()，或者您可以使用QObject::moveToThread()将worker对象移动到线程中。
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