如何从QThread和Queue运行的函数返回值

Question

请解释我们如何从Queue管理的线程发送/接收数据....

首先,我子类"的QThread"定义其run()时启动方法QThread的.start()调用:

class SimpleThread(QtCore.QThread):
    def __init__(self, queue, parent=None):
        QtCore.QThread.__init__(self, parent)      
        self.queue=queue        
    def run(self):
        while True:
            arg=self.queue.get() 
            self.fun(arg)    
            self.queue.task_done()
    def fun(self, arg):
        for i in range (3):
            print 'fun: %s'%i
            self.sleep(1)
        return arg+1

然后我声明两个Thread实例(因此只占用两个CPU核心)将self.queue实例作为参数发送.

self.queue=queue.Queue()
for i in range(2):
    thread=SimpleThread(self.queue)
    thread.start()

现在如果我理解正确thread.start()就没有开始.真正的"开始"只有在我打电话时才会发生queue.put():

for arg in [1,2,3]: self.queue.put(arg)

最后一行是进行"真实"通话的原因.除了创建和启动Queue项 之外,还put()允许将任意值保存到每个Queue项..put()同时做几件事:它创建,启动,它通过队列移动处理,它允许在队列项的"内部"放置一个变量(以后可以从函数处理器内部检索:使用队列项目'.get()`方法).

但是如何从fun()函数返回值.一个"正常" fun()的 return resultValue不正常工作.而且我不能使用self.queue.put()方法,因为这个方法除了存储数据"创建"一个新的队列项...

稍后编辑:

这里是稍微调整过的代码(从另一篇文章中复制/粘贴),显示了如何从已完成的Thread返回值的方法.我不确定这里使用的方法是否适用于QThread ...如果我错了,请纠正我:

import os, sys
import threading
import Queue

def callMe(incomingFun, daemon=False):
    def execute(_queue, *args, **kwargs):
        result=incomingFun(*args, **kwargs)
        _queue.put(result)

    def wrap(*args, **kwargs):
        _queue=Queue.Queue()
        _thread=threading.Thread(target=execute, args=(_queue,)+args, kwargs=kwargs)
        _thread.daemon=daemon
        _thread.start()
        _thread.result_queue=_queue        
        return _thread

    return wrap

@callMe
def localFunc(x):
    import time
    x = x + 5
    time.sleep(5)
    return x

thread=localFunc(10)

# this blocks, waiting for the result
result = thread.result_queue.get()
print result

Answer 1

在正常情况下,您将使用结果队列返回结果,然后运行其他一些等待结果的线程:

class SimpleThread(QtCore.QThread):
    def __init__(self, queue, result_queue, parent=None):
        QtCore.QThread.__init__(self, parent)      
        self.queue=queue
        self.result_queue = result_queue

    def run(self):
        while True:
            arg=self.queue.get() 
            self.fun(arg)    
            self.queue.task_done()

    def fun(self, arg):
        for i in range (3):
            print 'fun: %s'%i
            self.sleep(1)
        self.result_queue.put(arg+1)

def handle_results(result_queue):
   while True:
       result = result_queue.get()
       print("Got result {}".format(result))

主线程:

self.queue=queue.Queue()
self.result_queue = queue.Queue()

result_handler = threading.Thread(target=handle_results, self.result_queue)
for i in range(2):
    thread=SimpleThread(self.queue, self.result_queue)
    thread.start()

这样做可以防止在等待结果时阻止GUI的事件循环.这是等效的样子multiprocessing.pool.ThreadPool:

from multiprocessing.pool import ThreadPool
import time


def fun(arg):
    for i in range (3):
        print 'fun: %s'%i
        time.sleep(1)
    return arg+1

def handle_result(result):
   print("got result {}".format(result))

pool = ThreadPool(2)
pool.map_async(fun, [1,2,3], callback=handle_result)

哪个更简单.它在内部创建一个结果处理线程,它将handle_result在fun完成时自动为您调用.

也就是说,您正在使用QThread,并且您希望结果更新GUI小部件,因此您确实希望将结果发送回主线程,而不是结果处理线程.在这种情况下,使用Qt的信号系统是有意义的,这样您就可以在收到结果时安全地更新GUI:

from PyQt4 import QtCore, QtGui
import sys
import Queue as queue

class ResultObj(QtCore.QObject):
    def __init__(self, val):
        self.val = val

class SimpleThread(QtCore.QThread):
    finished = QtCore.pyqtSignal(object)

    def __init__(self, queue, callback, parent=None):
        QtCore.QThread.__init__(self, parent)      
        self.queue = queue
        self.finished.connect(callback)

    def run(self):
        while True:
            arg = self.queue.get() 
            if arg is None: # None means exit
                print("Shutting down")
                return
            self.fun(arg)    

    def fun(self, arg):
        for i in range(3):
            print 'fun: %s' % i
            self.sleep(1)
        self.finished.emit(ResultObj(arg+1))


class AppWindow(QtGui.QMainWindow):
    def __init__(self):
        super(AppWindow, self).__init__()
        mainWidget = QtGui.QWidget()
        self.setCentralWidget(mainWidget)
        mainLayout = QtGui.QVBoxLayout()
        mainWidget.setLayout(mainLayout)  
        button = QtGui.QPushButton('Process')
        button.clicked.connect(self.process)
        mainLayout.addWidget(button)

    def handle_result(self, result):
        val = result.val
        print("got val {}".format(val))
        # You can update the UI from here.

    def process(self):
        MAX_CORES=2
        self.queue = queue.Queue()
        self.threads = []
        for i in range(MAX_CORES):
            thread = SimpleThread(self.queue, self.handle_result)
            self.threads.append(thread)
            thread.start()  

        for arg in [1,2,3]:
            self.queue.put(arg)

        for _ in range(MAX_CORES): # Tell the workers to shut down
            self.queue.put(None)

app = QtGui.QApplication([])
window = AppWindow()
window.show()
sys.exit(app.exec_())

按下按钮时输出:

fun: 0
 fun: 0
fun: 1
 fun: 1
fun: 2
 fun: 2
fun: 0
got val 2
got val 3
Shutting down
fun: 1
fun: 2
Shutting down
got val 4