python - 如何在 PyQt 中的另一个线程中暂停线程中的循环

Question

我正在尝试编写一个使用两个工作人员的简单 PyQt 小部件。第一个工人（工人 1）立即开始其循环，而第二个工人（工人 2）睡眠 2 秒然后开始。我想得到以下信息：

1. Worker 2 暂停 Worker 1 的执行
2. Worker 2 启动并完成循环
3. Worker 2 完成并让 Worker 1 完成自己的循环。

我试图通过为工人类实现以下代码来实现这一点：

class Worker(QObject):
    """
    Create worker class
    """
    worker_finished = pyqtSignal()
    ask_to_work = pyqtSignal()
    glob_lock = QMutex()

    def __init__(self, name, sleep_time = 0.5, loops = 10, sleep_at_start=False):
        super().__init__()
        self._name = name
        self.sleep_time = sleep_time
        self.loops = loops
        self._sleep_at_start = sleep_at_start
        self.worker_finished.connect(self.at_finish)
        self.ask_to_work.connect(self.pause_execution)

    @pyqtSlot()
    def run(self):
        #This is to make the worker sleep 2 seconds, then ask to run its loop
        if self._sleep_at_start:
            print("{:s} is sleeping.".format(self._name))
            sleep(2)
            print("{:s} has awaken.".format(self._name))
            self.ask_to_work.emit()

        #This acquires the lock and starts the worker loop
        self.glob_lock.lock()
        print("Lock acquired by {:s}".format(self._name))
        for ii in range(self.loops):
            print("I am {:s} and I am at step {:d}".format(self._name, ii))
            sleep(self.sleep_time)
        self.worker_finished.emit()

    #Function to attempt the interruption of the worker loop
    @pyqtSlot()
    def pause_execution(self):
        try:
            print("Request lock")
            self.glob_lock.unlock()
            print("Request succeded")
        except:
            print("No lock to release")

    @pyqtSlot()
    def at_finish(self):
        try:
            self.glob_lock.unlock()
            print("Successfully released lock at finish.")
        except:
            print("Releasing the lock at finish went wrong.")

而小部件和执行是：

class MainApp(QWidget):
    """
    Make the widget
    """
    def __init__(self):
        super().__init__()
        #Set the widget layout
        layout = QHBoxLayout(self)

        self.button_run = QPushButton("Run workers")
        layout.addWidget(self.button_run)

        self._threads = []
        self._workers = []

        #Initialize the workers
        worker = Worker("Worker 1", loops=10)
        self._workers.append(worker)

        worker = Worker("Worker 2", sleep_time=1,
                        loops=1, sleep_at_start=True)
        self._workers.append(worker)

        #Connect workers' run methods to the widget button and put the workers into separate threads
        self.activate_and_connect_workers()

    def activate_and_connect_workers(self):
        for worker in self._workers:
            self.button_run.clicked.connect(worker.run)
            a_thread = QThread()
            self._threads.append(a_thread)
            worker.moveToThread(a_thread)
            a_thread.start()

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = MainApp()
    window.show()
    sys.exit(app.exec_())

我想在终端看到的是：

Lock acquired by Worker 1
Worker 2 is sleeping
I am Worker 1 and I am at step 0
I am Worker 1 and I am at step 1
#...Some lines of Worker 1
Worker 2 has awaken.
Request lock
Request succeded
Lock acquired by Worker 2
I am Worker 2 and I am at step 0
#...Some lines of Worker 2
Worker 2 uccessfully released lock at finish.
Lock acquired by Worker 1
#...More lines of Worker 1
Worker 1 uccessfully released lock at finish.

这不会发生，因为 Worker 2 发出了“对自己”释放锁的信号，并且无法将其发送给 Worker 1。这意味着两个进程不同步。最重要的是，程序在 Worker 1 循环结束时崩溃（可能是因为在 Worker 1 重新启动时锁已经被释放）。

我应该怎么做才能使代码以所需的方式工作？

标签： pythonmultithreadingpyqtsignalsmutex

Answer 1

该文件指出：

当您在一个线程中调用 lock() 时，其他尝试在同一位置调用 lock() 的线程将阻塞，直到获得锁的线程调用 unlock()。

因此，唯一允许解锁的线程是 Worker1 的线程。

根据您对要实现的目标的描述，我认为 lock() 是错误的方法。锁定“保护”一段代码，因此一次只有一个线程可以访问它。

如果您仍然想使用这种阻塞机制，我建议使用以下模式：

添加一个“is_blocking”标志，确定工作人员是否应该在其生命周期内获得锁。如果工作人员没有阻塞，它会定期尝试锁定和解锁。如果阻塞的 Worker 处于活动状态，则会导致阻塞行为。

这是一个粗略的演示，基于您的示例：

import sys
from PyQt5.QtCore import QObject, pyqtSignal, QMutex, pyqtSlot, QThread, Qt
from PyQt5.QtWidgets import QWidget, QHBoxLayout, QPushButton, QApplication
from time import sleep

glob_lock = QMutex()

class Worker(QObject):
    worker_finished = pyqtSignal()

    def __init__(self, name, sleep_time = 0.5, loops = 10, sleep_at_start=False, is_blocking=False):
        super().__init__()
        self._name = name
        self.sleep_time = sleep_time
        self.loops = loops
        self._sleep_at_start = sleep_at_start
        self.worker_finished.connect(self.at_finish)
        self.is_blocking = is_blocking

    @pyqtSlot()
    def run(self):
        if self._sleep_at_start:
            print("{:s} is sleeping.".format(self._name))
            sleep(2)
            print("{:s} has awaken.".format(self._name))
        if self.is_blocking:
            glob_lock.lock()
            print("Lock acquired by {:s}".format(self._name))
        for ii in range(self.loops):
            if not self.is_blocking:
                glob_lock.lock()
                glob_lock.unlock()
            print("I am {:s} and I am at step {:d}".format(self._name, ii))
            sleep(self.sleep_time)
        self.worker_finished.emit()


    @pyqtSlot()
    def at_finish(self):
        if self.is_blocking:
            glob_lock.unlock()
            print("Successfully released lock at finish.")
        else:
            print("Successfully finished.")

class MainApp(QWidget):
    def __init__(self):
        super().__init__()
        layout = QHBoxLayout(self)
        self.button_run = QPushButton("Run workers")
        layout.addWidget(self.button_run)

        self._threads = []
        self._workers = []

        worker = Worker("Worker 1", loops=10)
        self._workers.append(worker)
        worker = Worker("Worker 2", sleep_time=1, loops=5, sleep_at_start=True, is_blocking=True)
        self._workers.append(worker)
        self.activate_and_connect_workers()

    def activate_and_connect_workers(self):
        for worker in self._workers:
            self.button_run.clicked.connect(worker.run)
            a_thread = QThread()
            self._threads.append(a_thread)
            worker.moveToThread(a_thread)
            a_thread.start()

if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = MainApp()
    window.show()
    sys.exit(app.exec_())