无法使用 QMutex 锁定变量

Question

我是多线程方面的新手。我有一个 PySide2 应用程序。它有 3 个不同的线程。第一个是运行 GUI 的主线程，后者负责相机流，第三个负责提供 API 从其他点访问 GUI 的 Flask。（根据文章从不同线程访问 GUI 不是一个好主意：https://realpython.com/python-pyqt-qthread/#reusing-threads-qrunnable-and-qthreadpool）。

当请求到达端点时，我想在 GUI 上获取一些值并 return 它们。我试图实现信号和槽机制来执行它。但是，在我从 GUI 获取变量之前，我的端点 returns 是变量的默认值。负责端点的线程不会等待 GUI 线程设置将被 returned 的值。我尝试以不同的方式使用 QMutex 锁定变量，首先通过 GUI 设置值，但我无法成功。如何在设置值后锁定变量和return？

在线程上运行的 Flask class：

from PySide2.QtCore import Signal, QObject, Slot, QMutex
from flask import Flask

from SharedData import SharedData

class API(QObject):
    signal_get_value = Signal()

    def __init__(self):
        super(API, self).__init__()
        self.app = Flask(__name__)
        self.app.add_url_rule('/get_value/', 'get_value', self.get_value)
        self.data = SharedData()


    def start(self):
        self.app.run()

    def get_value(self):
        self.signal_get_value.emit()
        measurement = self.data.get_measurement()
        data = {"measurement": measurement}

        return data

共享数据class:

class SharedData:
    __measurement = None

    @classmethod
    def get_measurement(cls):
        return cls.__measurement

    @classmethod
    def set_measurement(cls, measurement):
        cls.__measurement = measurement

我的GUI模块中修改值的方法：

mutex = QMutex()

    def read_measurement(self):
        self.mutex.lock()
        
        #some processes and the output assign to the 'result' variable
        
        self.api.data.set_measurement(result)
        self.mutex.unlock()

编辑

我正在添加一个代码来澄清它。您可以在其中找到 read_measurement 方法。其余代码相同。 @eyllanesc

import sys

from PySide2.QtCore import QThread, QMutex
from PySide2.QtGui import QPixmap
from PySide2.QtWidgets import QApplication, QVBoxLayout, QWidget, QPushButton, QHBoxLayout, QLabel

from API import API

class MainWindow(QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.init_UI()


    def init_UI(self):
        self.setFixedSize(690, 530)
        self.image_lbl = QLabel()

        self.image_lbl.setPixmap(QPixmap("img/im.jpg"))

        btn_cnt = QPushButton("Continue")
        btn_pa = QPushButton("Pause")

        hbox = QHBoxLayout()
        hbox.addWidget(btn_cnt)
        hbox.addWidget(btn_pa)

        vbox = QVBoxLayout()
        vbox.addWidget(self.image_lbl)
        vbox.addLayout(hbox)

        self.setLayout(vbox)

        self.start_api()
        self.show()


    def start_api(self):
        self.thread_API = QThread()
        self.api = API()
        self.api.moveToThread(self.thread_API)
        self.thread_API.started.connect(self.api.start)
        self.api.signal_get_value.connect(self.read_measurement)

        self.thread_API.start()

    dv = 0
    mutex = QMutex()

    def read_measurement(self):
        self.mutex.lock()

        measurement = None
        result = "measurement " + str(self.dv)
        self.dv += 1
        self.api.data.set_measurement(result)

        self.mutex.unlock()



if __name__ == '__main__':
    app = QApplication(sys.argv)
    main_form = MainWindow()
    sys.exit(app.exec_())

Answer 1

解决该问题的方法是暂停 API(worker) 线程。我仍然想知道我是否可以使用互斥量、信号量等。

添加了暂停线程的睡眠方法。

from time import sleep

from PySide2.QtCore import Signal, QObject, Slot, QMutex
from flask import Flask

from SharedData import SharedData

class API(QObject):
    signal_get_value = Signal()

    def __init__(self):
        super(API, self).__init__()
        self.__app = Flask(__name__)
        self.__app.add_url_rule('/get_value/', 'get_value', self.get_value)
        self.data = SharedData()
        self.pause = True


    def start(self):
        self.__app.run()

    def __sleep_thread(self):
        """method pauses the thread to enable other threads to get the request done 

        Returns
        -------
        None
        """

        while self.pause:
            sleep(0.05)

        self.pause = True


    def get_value(self):
        self.signal_get_value.emit()
        self.__sleep_thread()

        measurement = self.data.get_measurement()
        data = {"measurement": measurement}

        return data

GUI 模块。

import sys

from PySide2.QtCore import QThread, QMutex
from PySide2.QtGui import QPixmap
from PySide2.QtWidgets import QApplication, QVBoxLayout, QWidget, QPushButton, QHBoxLayout, QLabel

from API import API

class MainWindow(QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.init_UI()


    def init_UI(self):
        self.setFixedSize(690, 530)
        self.image_lbl = QLabel()

        self.image_lbl.setPixmap(QPixmap("img/im.jpg"))

        btn_cnt = QPushButton("Continue")
        btn_pa = QPushButton("Pause")

        hbox = QHBoxLayout()
        hbox.addWidget(btn_cnt)
        hbox.addWidget(btn_pa)

        vbox = QVBoxLayout()
        vbox.addWidget(self.image_lbl)
        vbox.addLayout(hbox)

        self.setLayout(vbox)

        self.start_api()
        self.show()


    def start_api(self):
        self.thread_API = QThread()
        self.api = API()
        self.api.moveToThread(self.thread_API)
        self.thread_API.started.connect(self.api.start)
        self.api.signal_get_value.connect(self.read_measurement)

        self.thread_API.start()
        # ToDo: Do I need the terminate thread when exited from the app?

    dv = 0
    def read_measurement(self):
        measurement = None
        result = "measurement " + str(self.dv)
        self.dv += 1
        self.api.data.set_measurement(result)
        self.api.pause = False



if __name__ == '__main__':
    app = QApplication(sys.argv)
    main_form = MainWindow()
    sys.exit(app.exec_())

无法使用 QMutex 锁定变量

Can't lock variable with QMutex

python

multithreading

pyside2