为什么在调用QThread.quit和随后的QThread.wait时出现竞赛？

编程问答 2022-08-12

问题描述

使用pyside2，我有一个运行后台事件循环的辅助线程。关闭应用程序后，我想quit()辅助线程并为其wait()完成其事件。

但是，一旦我调用wait()，我的应用就会出现死锁（或其他问题）。为了演示此问题，我创建了一个带有子类QThread的小型示例应用程序，该应用程序通过调用exec_()运行事件循环，然后使用一些模拟清理打印来模拟长时间退出。

import sys
import time

from pyside2.QtCore import QThread
from pyside2.QtWidgets import QApplication,QMainWindow


class AuxThread(QThread):

    def __init__(self):
        super().__init__()

    def run(self):
        print("Starting AuxThread")
        self.exec_()
        print("Stopping AuxThread")
        iteration = 0
        # Simulate a long time for thread finish
        while iteration < 100:
            iteration += 1
            print(f"{iteration} cleanup loops in {QThread.currentThread()}")


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.thread().setobjectName("main thread")

        self.aux_thread = AuxThread()
        self.aux_thread.setobjectName("aux thread")

        self.aux_thread.start()

    def closeEvent(self,event):
        print(f"Quitting aux_thread from {QThread.currentThread()}")
        self.aux_thread.quit()

        # Increasing this time allows the run() function to complete
        # If this time is too short,then execution hangs forever
        time.sleep(0.001)

        print(f"blocking thread {QThread.currentThread()}")
        self.aux_thread.wait()
        print(f"aux_thread is joined")


if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

此函数的输出如下所示，打印的迭代次数将根据时间而有所不同。

Starting AuxThread
Quitting aux_thread from <pyside2.QtCore.QThread(0x7fcc9cfd12b0,name = "main thread") at 0x11c4f1580>
Stopping AuxThread
1 cleanup loops in <__main__.AuxThread(0x7fcc9cfe5e40,name = "aux thread") at 0x11c4f15c0>
2 cleanup loops in <__main__.AuxThread(0x7fcc9cfe5e40,name = "aux thread") at 0x11c4f15c0>
... [output elided] ...
72 cleanup loops in <__main__.AuxThread(0x7fcc9cfe5e40,name = "aux thread") at 0x11c4f15c0>
73 cleanup loops in <__main__.AuxThread(0x7fcc9cfe5e40,name = "aux thread") at 0x11c4f15c0>
blocking thread <pyside2.QtCore.QThread(0x7fcc9cfd12b0,name = "main thread") at 0x11c4f1580>

docs说QThread.wait()“阻塞线程，直到QThread完成执行（即当它从run()返回时）”

有趣的是，他们没有提到这里阻塞了哪个线程，但是阻塞正在等待的QThread并没有任何意义。我认为aux_thread.wait()应该只阻塞主线程，为什么一旦调用wait()时就阻塞了aux线程中的执行？

我想念什么？

解决方法

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multithreadingpyside2pythonqtqthread