PyQt:在使用QApplication.witt时偶尔出现分段错误

Question

注意：我也在PyQt邮件列表上发布了这篇文章——如果有好的答案，我会在这里回答我自己的问题

我在执行时偶尔会遇到segfault问题QApplication.quit()，可能与libQt5Network.so和/或QtWebkit。

首先，我使用的3个测试系统：

• Arch Linux，PyQt 5.2，Qt 5.2.0，Python 3.3.3
• 虚拟机中的Ubuntu 13.10、PyQt 5.0.1、Qt 5.0.2、Python 3.3.2
• Windows 7、PyQt 5.2、Qt 5.2.0、Python 3.3.3

到目前为止，这些崩溃对我来说从未在Arch上发生过，而且经常发生在Ubuntu，以及不时在Windows中运行。(尽管Windows只是我猜，我只是得到这个python.exe不再工作foo。)

原始崩溃

我第一次注意到这个问题是在一个大型(ger)项目qutebrowser中，当我在Ubuntu上输入:quit时，它给了我这个堆栈竞争：

#0  0xb5c296fc in QMutex::lock() () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#1  0xb3bdd97d in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#2  0xb3bdf0d0 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#3  0xb3bd4418 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#4  0xb3bd8b1e in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#5  0xb5dedf10 in QMetaObject::activate(QObject*, int, int, void**) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#6  0xb5dee48b in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#7  0xb5e59155 in QIODevice::readyRead() ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#8  0xb3bb1f14 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#9  0xb3ba4d99 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#10 0xb3bc03bb in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#11 0xb6483a54 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Widgets.so.5
#12 0xb6488e66 in QApplication::notify(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Widgets.so.5
#13 0xb6bb7e80 in sipQApplication::notify(QObject*, QEvent*) ()
from /usr/lib/python3/dist-packages/PyQt5/QtWidgets.cpython-33m-i386-linux-gnu.so
#14 0xb5dc737a in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#15 0xb5e11f67 in ?? () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#16 0xb5aaf83e in g_main_context_dispatch ()
from /lib/i386-linux-gnu/libglib-2.0.so.0
#17 0xb5aafbe8 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#18 0xb5aafca8 in g_main_context_iteration ()
from /lib/i386-linux-gnu/libglib-2.0.so.0
#19 0xb5e1138f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#20 0xb5dc5c06 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#21 0xb5dc6014 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#22 0xb5c2b90b in QThread::exec() ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#23 0xb5c2b99b in QThread::run() () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#24 0xb5c2fa08 in ?? () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#25 0xb7774d78 in start_thread (arg=0xa5314b40) at pthread_create.c:311
#26 0xb76ac01e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:131

此处为核心转储(15MB，gzip)。

最小示例

然后我用一个最小的例子再试了一次用QTimer在一秒钟后自动进行。我不得不循环运行在它发生之前大约一分钟左右：

from PyQt5.QtCore import QUrl, QTimer
from PyQt5.QtWidgets import QApplication
from PyQt5.QtWebKitWidgets import QWebView
app = QApplication([])
wv = QWebView()
wv.load(QUrl("http://www.heise.de/"))
t = QTimer()
t.timeout.connect(QApplication.quit)
t.start(1000)
wv.show()
app.exec_()

这给了我一个非常相似的stacktrace(在Ubuntu上)：

#0  0xb6cfd8d2 in QCoreApplication::postEvent(QObject*, QEvent*, int) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#1  0xb6d21c83 in QMetaObject::activate(QObject*, int, int, void**) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#2  0xb6d2248b in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#3  0xb3e47935 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#4  0xb3dcf687 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#5  0xb3e483b3 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#6  0xb6d21f10 in QMetaObject::activate(QObject*, int, int, void**) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#7  0xb6d2248b in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#8  0xb3e43fe5 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#9  0xb3d93b1e in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#10 0xb3d94630 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#11 0xb3d9471b in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#12 0xb6d21f10 in QMetaObject::activate(QObject*, int, int, void**) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#13 0xb6d2248b in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#14 0xb6d8d155 in QIODevice::readyRead() ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#15 0xb3e09f14 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#16 0xb3dfcd99 in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#17 0xb3e183bb in ?? () from /usr/lib/i386-linux-gnu/libQt5Network.so.5
#18 0xb492ba54 in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Widgets.so.5
#19 0xb4930e66 in QApplication::notify(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Widgets.so.5
#20 0xb505fe80 in sipQApplication::notify(QObject*, QEvent*) ()
from /usr/lib/python3/dist-packages/PyQt5/QtWidgets.cpython-33m-i386-linux-gnu.so
#21 0xb6cfb37a in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#22 0xb6d45f67 in ?? () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#23 0xb65f483e in g_main_context_dispatch ()
from /lib/i386-linux-gnu/libglib-2.0.so.0
#24 0xb65f4be8 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#25 0xb65f4ca8 in g_main_context_iteration ()
from /lib/i386-linux-gnu/libglib-2.0.so.0
#26 0xb6d4536d in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#27 0xb6cf9c06 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#28 0xb6cfa014 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#29 0xb6b5f90b in QThread::exec() ()
from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#30 0xb6b5f99b in QThread::run() () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#31 0xb6b63a08 in ?? () from /usr/lib/i386-linux-gnu/libQt5Core.so.5
#32 0xb7798d78 in start_thread (arg=0xa7812b40) at pthread_create.c:311
#33 0xb76d001e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:131

此处为核心转储(15MB，gzip)。

有人知道那里出了什么问题吗？一些神奇的东西垃圾收集方式不对？我也试了一些PyQt4上类似症状的变通方法，但没有也可以帮忙。

*在描述的位置找不到StackOverflow答案--基本上将QtWidgets.qApp设置为之前的QApplication实例运行exec_()并且随后到None。

Answer 1

我在PyQt/PySide中捕获segfault已经有一段时间了。基本上，我发现大多数segfault都可以归咎于库的异步性质(因此也归咎于我们)。

对于您的确切示例，您已经将timeout信号连接到quit方法。这里可能发生的情况是，在超时的情况下，调用quit，并且当进程终止时，突然对应用程序对象的所有引用都无效。但是，当该操作发生时，QT的事件循环仍在运行，它试图访问它的QNetworkAccessManager以调度另一个信号，但对该内存位置的引用已经无效，因此发生了segfault。

在这些情况下，需要执行的是实现一种关闭方法，该方法将确保停止所有操作，以正确的顺序删除您正在使用的QT组件，然后，就在这时，调用allow exiting。

我在这里详细介绍了这个主题，包括QtWebKit应用程序的安全关闭方法：https://github.com/integricho/path-of-a-pyqter/tree/master/qttut08