为什么Worker线程会损害GUI响应能力

Question

我试图理解为什么这个Worker线程故意使用相当大的处理量(尤其是对这些字典的排序(，导致GUI线程变得没有响应。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都没有明显的响应：按钮不会获取它们的"；悬停在"；颜色(浅蓝色(并且似乎不能被点击(尽管点击"停止"确实会在许多秒后导致停止(。可怕的旋转器不时出现(W10操作系统中的蓝色圆圈(。

大约12%之后，就可以正常使用按钮了。

我做错了什么？

Answer 1

一个非常简单的解决方案是"睡眠；使用基本time.sleep的线程：即使间隔很小，也会给主线程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。}

Answer 2

Python不能运行多个CPU密集型线程。其原因是GIL。基本上，Python线程不适合做任何事情，只适合等待I/O。

如果您想要CPU密集型部件，请尝试使用Cython重写密集型部件或使用multiprocessing，但来回发送数据的时间可能会很长。

Answer 3

无法复制，即使资源有限，ui也能保持响应。你试过在没有调试器的情况下运行它吗？

正如@9000所暗示的那样，GIL可能是个问题。

或者可能是充满progress信号的事件循环，尝试为每个序列发出少于一个信号。

顺便说一句：若每次使用dict_reorder都不丢弃排序结果，那个么程序的工作速度会更快。尝试替换

dict_reorder(Sequence.simple_sequence_map)

带有

Sequence.simple_sequence_map = dict_reorder(Sequence.simple_sequence_map)

和

dict_reorder(Sequence.sequence_to_sequence_map)

带有

Sequence.sequence_to_sequence_map = dict_reorder(Sequence.sequence_to_sequence_map)