Pyqt5 中的 QThreads：这是官方 QThread 文档的正确 C++ 到 Python 翻译吗？

关于如何实例化和使用的官方文档QThread可以在这里找到：http://doc.qt.io/qt-5/qthread.html http://doc.qt.io/qt-5/qthread.html

该文档描述了两种基本方法：(1) 工作对象方法和 (2)QThread子类方法。
我在几篇文章中读到第二种方法不好，所以让我们重点讨论第一种方法。

EDIT:
@ekhumoro 向我指出了以下有趣的文章：https://woboq.com/blog/qthread-you-were-not-doing-so-wrong.html https://woboq.com/blog/qthread-you-were-not-doing-so-wrong.html。显然，方法（1）和（2）各有其优点：

根据经验：

如果您确实不需要线程中的事件循环，则应该子类化。

如果您需要事件循环并处理线程内的信号和槽，则可能不需要子类化。

由于我确实需要 QApplication 线程和新 QThread 之间进行某种通信（并且我相信信号槽是一种很好的通信方式），因此我将使用工人-对象方法.

1. C++ 中的工作对象方法

我已经复制粘贴了 C++ 代码工人-对象方法（来自Qt5官方文档，参见http://doc.qt.io/qt-5/qthread.html http://doc.qt.io/qt-5/qthread.html):

class Worker : public QObject
{
    Q_OBJECT

public slots:
    void doWork(const QString &parameter) {
        QString result;
        /* ... here is the expensive or blocking operation ... */
        emit resultReady(result);
    }

signals:
    void resultReady(const QString &result);
};

class Controller : public QObject
{
    Q_OBJECT
    QThread workerThread;
public:
    Controller() {
        Worker *worker = new Worker;
        worker->moveToThread(&workerThread);
        connect(&workerThread, &QThread::finished, worker, &QObject::deleteLater);
        connect(this, &Controller::operate, worker, &Worker::doWork);
        connect(worker, &Worker::resultReady, this, &Controller::handleResults);
        workerThread.start();
    }
    ~Controller() {
        workerThread.quit();
        workerThread.wait();
    }
public slots:
    void handleResults(const QString &);
signals:
    void operate(const QString &);
};

2. Python 中的工作对象方法

我努力将给定的 C++ 代码翻译为 Python。如果您安装了 Python 3.6 和 PyQt5，您只需复制粘贴此代码并在您的计算机上运行即可。它应该有效。

import sys
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *

class Worker(QObject):

    resultReady = pyqtSignal(str)

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    @pyqtSlot(str)
    def doWork(self, param):
        result = "hello world"
        print("foo bar")
        # ...here is the expensive or blocking operation... #
        self.resultReady.emit(result)


class Controller(QObject):

    operate = pyqtSignal(str)

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        # 1. Create 'workerThread' and 'worker' objects
        # ----------------------------------------------
        self.workerThread = QThread()
        self.worker = Worker()          # <- SEE NOTE(1)
        self.worker.moveToThread(self.workerThread)

        # 2. Connect all relevant signals
        # --------------------------------
        self.workerThread.finished.connect(self.worker.deleteLater)
        self.workerThread.finished.connect(lambda: print("workerThread finished."))  # <- SEE NOTE(2)
        self.operate.connect(self.worker.doWork)
        self.worker.resultReady.connect(self.handleResults)

        # 3. Start the thread
        # --------------------
        self.workerThread.start()

    def __del__(self):
        self.workerThread.quit()
        self.workerThread.wait()

    @pyqtSlot(str)
    def handleResults(self, param):
        print(param)
        # One way to end application
        # ---------------------------
        # global app      # <- SEE
        # app.exit()      #     NOTE(3)

        # Another way to end application
        # -------------------------------
        self.workerThread.quit()   # <- SEE NOTE(4)
        self.thread().quit()


if __name__ == '__main__':
    app = QCoreApplication([])
    controller = Controller()
    controller.operate.emit("foo")      # <- SEE NOTE(5)
    sys.exit(app.exec_())

_{NOTE (1):
Initially I had implemented the worker variable as a local variable in the constructor. I was literally translating the C++ sample to Python, and this variable is also a local variable in the C++ sample.
As you can see in the comment of @pschill, this local variable was garbage collected, and therefore I couldn't get the thread running. After making the change, I get the expected output.}

_{NOTE (2):
I've added this line to know precisely when the workerThread finishes.}

_{NOTE (3):
Apparently I need to add these two codelines global app and app.exit() to the handleResults(..) slot. Thank you @Matic to point that out!}

_{NOTE (4):
I've discovered (through some documentations) this approach to end the application. The first codeline ends the workerThread (by killing its event-loop). The second codeline ends the mainThread (also by killing its event-loop).}

_{NOTE (5):
When running the code in a Windows console, nothing happened (it just hanged). On the advice of @pschill (see his comment below), I added this codeline to make sure that the doWork() function gets called.}

3.我的问题

1. 首先，我想知道我从 C++ 到 Python 的翻译是否正确。请告诉我我在哪里犯了错误（如果您发现任何错误）。

2. 添加代码行global app and app.exit() to the handleResults(..)插槽修复了悬挂问题。但背景到底发生了什么？这些代码线是否会杀死工作线程？还是 QApplication 主线程？

3. 有没有办法杀死工作线程而不杀死主 QApplication 线程？

4.一些答案

1.还是不确定..

 
2.我相信app.exit()杀死主线程，主线程又杀死工作线程，因为它是 deamon 类型。我发现工作线程是 deamon 类型，因为我插入了代码行print(threading.current_thread()) in the doWork(..)功能。它打印了<_DummyThread(Dummy-1, started daemon 9812)>。当程序退出时，所有守护线程都会自动终止。

 
3. 是的，我找到办法了！这QThread::quit()函数是你的朋友。官方文档对此是这么说的：

void QThread::quit()
Tells the thread's event loop to exit with return code 0 (success). Equivalent to calling QThread::exit(0).
This function does nothing if the thread does not have an event loop.
_{[http://doc.qt.io/qt-5/qthread.html#quit] http://doc.qt.io/qt-5/qthread.html#quit%5D}

所以我的功能handleResults(..)现在看起来像这样：

    @pyqtSlot(str)
    def handleResults(self, param):
        print(param)
        self.workerThread.quit()  # Kill the worker thread
        self.thread().quit()      # Kill the main thread

我通过在构造函数中插入这一行来检查工作线程的终止情况Controller(..):

    self.workerThread.finished.connect(lambda: print("workerThread finished."))

我确实按预期打印了该行。我还尝试以类似的方式检查主线程的终止：

    self.thread().finished.connect(lambda: print("mainThread finished."))

不幸的是这一行没有打印出来。为什么？

_{Hereby I provide my current system settings:
    >  Qt5 (QT_VERSION_STR = 5.10.1)
    >  PyQt5 (PYQT_VERSION_STR = 5.10.1)
    >  Python 3.6.3
    >  Windows 10, 64-bit}

您的 Python 示例应用程序需要以某种方式退出，否则它只会在Controller对象已初始化。

最简单的事情就是改变handleResults您的示例中的函数：

@pyqtSlot(str)
def handleResults(self, param):
    print(param)
    global app
    app.exit()

希望能帮助到你。