为什么 GUI 响应能力会受到工作线程的影响？

Question

我试图理解为什么这个 Worker 线程故意使用相当大量的处理（特别是对这些词典的排序）导致 GUI 线程变得无响应。这是一个 MRE：

from PyQt5 import QtCore, QtWidgets
import sys, time, datetime, random

def time_print(msg):
    ms_now = datetime.datetime.now().isoformat(sep=' ', timespec='milliseconds')
    thread = QtCore.QThread.currentThread()
    print(f'{thread}, {ms_now}: {msg}')
    
def dict_reorder(dictionary):
    return {k: v for k, v in sorted(dictionary.items())}
    
class Sequence(object):
    n_sequence = 0
    simple_sequence_map = {}
    sequence_to_sequence_map = {}
    prev_seq = None
    
    def __init__(self):
        Sequence.n_sequence += 1 
        if Sequence.n_sequence % 1000 == 0:
            print(f'created sequence {Sequence.n_sequence}')
        rand_int = random.randrange(100000)
        self.text = str(rand_int)
        Sequence.simple_sequence_map[self] = rand_int
        if Worker.stop_ordered:
            time_print(f'init() A: stop ordered... stopping now')
            return
        dict_reorder(Sequence.simple_sequence_map)
        if Sequence.prev_seq:
            Sequence.sequence_to_sequence_map[self] = Sequence.prev_seq
            if Worker.stop_ordered:
                time_print(f'init() B: stop ordered... stopping now')
                return
            dict_reorder(Sequence.sequence_to_sequence_map)
        Sequence.prev_seq = self

    def __lt__(self, other):
        return self.text < other.text    
        
class WorkerSignals(QtCore.QObject):
    progress = QtCore.pyqtSignal(int)
    stop_me = QtCore.pyqtSignal()

class Worker(QtCore.QRunnable):
    def __init__(self, *args, **kwargs):
        super().__init__()
        self.signals = WorkerSignals()
        
    def stop_me_slot(self):
        time_print('stop me slot')    
        Worker.stop_ordered = True
    
    @QtCore.pyqtSlot()
    def run(self):
        total_n = 30000
        Worker.stop_ordered = False
        for n in range(total_n):
            progress_pc = int(100 * float(n+1)/total_n)
            self.signals.progress.emit(progress_pc)
            Sequence()
            if Worker.stop_ordered:
                time_print(f'run(): stop ordered... stopping now, n {n}')
                return

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        
        layout = QtWidgets.QVBoxLayout()
        self.progress = QtWidgets.QProgressBar()
        layout.addWidget(self.progress)
        
        start_button = QtWidgets.QPushButton('Start')
        start_button.pressed.connect(self.execute)
        layout.addWidget(start_button)
        
        self.stop_button = QtWidgets.QPushButton('Stop')
        layout.addWidget(self.stop_button)
        
        w = QtWidgets.QWidget()
        w.setLayout(layout)
        self.setCentralWidget(w)
        self.show()
        self.threadpool = QtCore.QThreadPool()
        self.resize(800, 600)

    def execute(self):
        self.worker = Worker()
        self.worker.signals.progress.connect(self.update_progress)
        self.stop_button.pressed.connect(self.worker.stop_me_slot)
        self.threadpool.start(self.worker)
        
    def update_progress(self, progress):
        self.progress.setValue(progress)        
              
app = QtWidgets.QApplication(sys.argv)
window = MainWindow()
app.exec_()

在我的机器上，直到大约 12%，GUI 明显没有响应：按钮没有获得它们的“悬停”颜色（浅蓝色）并且似乎无法点击（虽然点击“停止”确实会在许多秒后导致停止）。间歇性地出现可怕的微调器（W10 OS 中的蓝色圆圈）。

12%左右后就可以正常使用按钮了。

我做错了什么？

Answer 1

Python 不能运行超过一个 CPU 密集线程。原因是GIL。基本上 Python 线程除了等待 I/O.

什么都做不了

如果你想要 CPU 密集部分，请尝试重写密集部分 using Cython，或使用 multiprocessing，但这样来回发送数据的时间可能会意义重大。

Answer 2

无法重现，ui 即使资源有限也能保持响应。你试过运行它没有调试器吗？

GIL 可能是@9000 所建议的问题。

或者 eventloop 可能充斥着 progress 信号，尝试为每个序列发出少于一个信号。

作为旁注：如果您不每次都使用 dict_reorder 丢弃排序结果，程序会运行得更快。尝试替换

dict_reorder(Sequence.simple_sequence_map)

和

Sequence.simple_sequence_map = dict_reorder(Sequence.simple_sequence_map)

和

dict_reorder(Sequence.sequence_to_sequence_map)

和

Sequence.sequence_to_sequence_map = dict_reorder(Sequence.sequence_to_sequence_map)

Answer 3

一个非常简单的解决方案是使用基本 time.sleep 使线程“休眠”：即使间隔非常小，它也会为主线程提供足够的时间来处理其事件队列，避免 UI 锁定：

    def run(self):
        total_n = 30000
        Worker.stop_ordered = False
        for n in range(total_n):
            progress_pc = int(100 * float(n+1)/total_n)
            self.signals.progress.emit(progress_pc)
            Sequence()
            if Worker.stop_ordered:
                time_print(f'run(): stop ordered... stopping now, n {n}')
                return
            time.sleep(.0001)

^{注意：pyqtSlot 装饰器是无用的，因为它只适用于 QObject 子类（QRunnable 不是）；你可以删除它。}

为什么 GUI 响应能力会受到工作线程的影响？

Why is GUI responsiveness impaired by a Worker thread?

python

pyqt5

python-multithreading

qthread

qrunnable