使用 concurrent.futures.ThreadPoolExecutor 时用户界面冻结

Question

我认为在这里使用 concurrent.futures.ThreadPoolExecutor 时用户界面不应该被冻结，但它不符合我的期望，任何人都可以解释为什么？这里还有其他不让用户界面冻结的解决方案吗？

import sys   
from PyQt4.QtGui import *
from PyQt4.QtCore import *
import time

import concurrent.futures
import urllib.request

URLS = ['http://www.tmall.com/',
        'http://www.cnn.com/',
        'http://huawei.com/',
        'http://www.bbc.co.uk/',
        'http://jd.com/', 
        'http://weibo.com/?c=spr_web_360_hao360_weibo_t001', 
        'http://www.sina.com.cn/', 
        'http://taobao.com',
        'http://www.amazon.cn/?tag=360daohang-23', 
        'http://www.baidu.com/', 
        'http://www.pconline.com.cn/?ad=6347&360hot_site']

# Retrieve a single page and report the url and contents
def load_url(url, timeout):
    conn = urllib.request.urlopen(url, timeout=timeout)
    return conn.readall()




class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        QTimer.singleShot(3000, self.speedCalculate)

#        self.timerC = QTimer();
#        self.timerC.timeout.connect(self.speedCalculate)
#        self.timerC.start(1000)




    def speedCalculate(self):#compare with for loop
        t1=time.clock()
        # We can use a with statement to ensure threads are cleaned up promptly
        with concurrent.futures.ThreadPoolExecutor(max_workers=len(URLS)) as executor:
            # Start the load operations and mark each future with its URL
            future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}
            for future in concurrent.futures.as_completed(future_to_url):
                url = future_to_url[future]
                try:
                    data = future.result()
                except Exception as exc:
                    print('%r generated an exception: %s' % (url, exc))
                else:
                    print('%r page is %d bytes' % (url, len(data)))

        t2=time.clock()
        print('t2-t1-------------', t2-t1)
#        
#        for url in URLS:
#            data=load_url(url, 60)
#            print(url, len(data))
#        
#        t3=time.clock()
#        print('t3-t2-------------', t3-t2)
    #    
if __name__ == '__main__':                         
    app =QApplication(sys.argv)      
    splitter =MainWindow()   
    splitter.show()      
    app.exec_()

Answer 1

这里有两件事你需要知道：

1. Slots 在对象的线程中被调用，这意味着在这种情况下speedCalculate 在主线程中被调用。
2. concurrent.futures.as_completed 在已完成的期货上返回一个迭代器，这意味着在所有期货都完成之前，对此的 for 循环不会完成。

因此，您的 speedCalculate 方法仅在所有下载完成后才会返回，从而阻塞您的应用程序事件循环。

您应该做的是以不同的方法完成您当前在 speedCalculate 中所做的所有工作，例如 _speedCalculate 并在 speedCalculate 插槽内的新线程中调用它。

类似：

def speedCalculate(self):
    threading.Thread(target=self._speedCalculate).start()

def _speedCalculate(self):#compare with for loop
    t1=time.clock()
    # We can use a with statement to ensure threads are cleaned up promptly
    with concurrent.futures.ThreadPoolExecutor(max_workers=len(URLS)) as executor:
        # Start the load operations and mark each future with its URL
        future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}
        for future in concurrent.futures.as_completed(future_to_url):
            url = future_to_url[future]
            try:
                data = future.result()
            except Exception as exc:
                print('%r generated an exception: %s' % (url, exc))
            else:
                print('%r page is %d bytes' % (url, len(data)))

    t2=time.clock()
    print('t2-t1-------------', t2-t1)