如何从不同的进程向GUI中的插槽发出信号？

Question

上下文:在Python语言中，主线程产生第二个进程(使用多处理模块)，然后启动图形用户界面(使用PyQt4)。此时，主线程会阻塞，直到GUI关闭。第二个进程总是在处理，理想情况下应该以异步方式向GUI中的特定插槽发出信号。

问:在Python和PyQt4中有哪些方法/工具可以实现这一点?如何实现？优选地以软中断方式而不是轮询方式。

抽象地说，我能想到的解决方案是在主线程中实例化的“工具/处理程序”，它从GUI实例获取可用的插槽，并与从第二个进程获取的信号连接，假设我为该工具提供了一些预期或硬编码的信息。这可以实例化到第三个进程/线程。

Answer 1

这是一个示例Qt应用程序，演示从子进程向母进程中的插槽发送信号。我不确定这是不是正确的方法，但它是有效的。

我将进程区分为母进程和子进程，因为在Qt上下文中已经使用了父这个词。

母进程有两个线程。母进程的主线程通过multiprocessing.Queue向子进程发送数据。子进程将处理后的数据和信号签名通过multiprocessing.Pipe发送给母进程的第二个线程。母进程的第二个线程实际发出信号。

Python2.x，PyQt4：

from multiprocessing import Process, Queue, Pipe
from threading import Thread
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *

class Emitter(QObject, Thread):

    def __init__(self, transport, parent=None):
        QObject.__init__(self,parent)
        Thread.__init__(self)
        self.transport = transport

    def _emit(self, signature, args=None):
        if args:
            self.emit(SIGNAL(signature), args)
        else:
            self.emit(SIGNAL(signature))

    def run(self):
        while True:
            try:
                signature = self.transport.recv()
            except EOFError:
                break
            else:
                self._emit(*signature)

class Form(QDialog):

    def __init__(self, queue, emitter, parent=None):
        super(Form,self).__init__(parent)
        self.data_to_child = queue
        self.emitter = emitter
        self.emitter.daemon = True
        self.emitter.start()
        self.browser = QTextBrowser()
        self.lineedit = QLineEdit('Type text and press <Enter>')
        self.lineedit.selectAll()
        layout = QVBoxLayout()
        layout.addWidget(self.browser)
        layout.addWidget(self.lineedit)
        self.setLayout(layout)
        self.lineedit.setFocus()
        self.setWindowTitle('Upper')
        self.connect(self.lineedit,SIGNAL('returnPressed()'),self.to_child)
        self.connect(self.emitter,SIGNAL('data(PyQt_PyObject)'), self.updateUI)

    def to_child(self):
        self.data_to_child.put(unicode(self.lineedit.text()))
        self.lineedit.clear()

    def updateUI(self, text):
        text = text[0]
        self.browser.append(text)

class ChildProc(Process):

    def __init__(self, transport, queue, daemon=True):
        Process.__init__(self)
        self.daemon = daemon
        self.transport = transport
        self.data_from_mother = queue

    def emit_to_mother(self, signature, args=None):
        signature = (signature, )
        if args:
            signature += (args, )
        self.transport.send(signature)

    def run(self):
        while True:
            text = self.data_from_mother.get()
            self.emit_to_mother('data(PyQt_PyObject)', (text.upper(),))

if __name__ == '__main__':

    app = QApplication(sys.argv)
    mother_pipe, child_pipe = Pipe()
    queue = Queue()
    emitter = Emitter(mother_pipe)
    form = Form(queue, emitter)
    ChildProc(child_pipe, queue).start()
    form.show()
    app.exec_()

为了方便起见，还有Python3.x，PySide：

from multiprocessing import Process, Queue, Pipe
from threading import Thread

from PySide import QtGui, QtCore

class Emitter(QtCore.QObject, Thread):

    def __init__(self, transport, parent=None):
        QtCore.QObject.__init__(self, parent)
        Thread.__init__(self)
        self.transport = transport

    def _emit(self, signature, args=None):
        if args:
            self.emit(QtCore.SIGNAL(signature), args)
        else:
            self.emit(QtCore.SIGNAL(signature))

    def run(self):
        while True:
            try:
                signature = self.transport.recv()
            except EOFError:
                break
            else:
                self._emit(*signature)

class Form(QtGui.QDialog):

    def __init__(self, queue, emitter, parent=None):
        super().__init__(parent)
        self.data_to_child = queue
        self.emitter = emitter
        self.emitter.daemon = True
        self.emitter.start()
        self.browser = QtGui.QTextBrowser()
        self.lineedit = QtGui.QLineEdit('Type text and press <Enter>')
        self.lineedit.selectAll()
        layout = QtGui.QVBoxLayout()
        layout.addWidget(self.browser)
        layout.addWidget(self.lineedit)
        self.setLayout(layout)
        self.lineedit.setFocus()
        self.setWindowTitle('Upper')
        self.lineedit.returnPressed.connect(self.to_child)
        self.connect(self.emitter, QtCore.SIGNAL('data(PyObject)'), self.updateUI)

    def to_child(self):
        self.data_to_child.put(self.lineedit.text())
        self.lineedit.clear()

    def updateUI(self, text):
        self.browser.append(text[0])

class ChildProc(Process):

    def __init__(self, transport, queue, daemon=True):
        Process.__init__(self)
        self.daemon = daemon
        self.transport = transport
        self.data_from_mother = queue

    def emit_to_mother(self, signature, args=None):
        signature = (signature, )
        if args:
            signature += (args, )
        self.transport.send(signature)

    def run(self):
        while True:
            text = self.data_from_mother.get()
            self.emit_to_mother('data(PyQt_PyObject)', (text.upper(),))

if __name__ == '__main__':

    app = QApplication(sys.argv)
    mother_pipe, child_pipe = Pipe()
    queue = Queue()
    emitter = Emitter(mother_pipe)
    form = Form(queue, emitter)
    ChildProc(child_pipe, queue).start()
    form.show()
    app.exec_()

Answer 2

大家好，

我希望这不会被认为是一场死亡转储，但我认为更新尼扎姆的答案会很好，方法是将更新他的示例添加到PyQt5中，添加一些注释，删除一些python2语法，最重要的是使用PyQt中提供的新样式的信号。希望有人觉得它有用。

"""
Demo to show how to use PyQt5 and qt signals in combination with threads and
processes.

Description:
Text is entered in the main dialog, this is send over a queue to a process that 
performs a "computation" (i.e. capitalization) on the data. Next the process sends 
the data over a pipe to the Emitter which will emit a signal that will trigger 
the UI to update.

Note:
At first glance it seems more logical to have the process emit the signal that 
the UI can be updated. I tried this but ran into the error 
"TypeError: can't pickle ChildProc objects" which I am unable to fix.
"""

import sys
from multiprocessing import Process, Queue, Pipe

from PyQt5.QtCore import pyqtSignal, QThread
from PyQt5.QtWidgets import QApplication, QLineEdit, QTextBrowser, QVBoxLayout, QDialog


class Emitter(QThread):
    """ Emitter waits for data from the capitalization process and emits a signal for the UI to update its text. """
    ui_data_available = pyqtSignal(str)  # Signal indicating new UI data is available.

    def __init__(self, from_process: Pipe):
        super().__init__()
        self.data_from_process = from_process

    def run(self):
        while True:
            try:
                text = self.data_from_process.recv()
            except EOFError:
                break
            else:
                self.ui_data_available.emit(text.decode('utf-8'))


class ChildProc(Process):
    """ Process to capitalize a received string and return this over the pipe. """

    def __init__(self, to_emitter: Pipe, from_mother: Queue, daemon=True):
        super().__init__()
        self.daemon = daemon
        self.to_emitter = to_emitter
        self.data_from_mother = from_mother

    def run(self):
        """ Wait for a ui_data_available on the queue and send a capitalized version of the received string to the pipe. """
        while True:
            text = self.data_from_mother.get()
            self.to_emitter.send(text.upper())


class Form(QDialog):
    def __init__(self, child_process_queue: Queue, emitter: Emitter):
        super().__init__()
        self.process_queue = child_process_queue
        self.emitter = emitter
        self.emitter.daemon = True
        self.emitter.start()

        # ------------------------------------------------------------------------------------------------------------
        # Create the UI
        # -------------------------------------------------------------------------------------------------------------
        self.browser = QTextBrowser()
        self.lineedit = QLineEdit('Type text and press <Enter>')
        self.lineedit.selectAll()
        layout = QVBoxLayout()
        layout.addWidget(self.browser)
        layout.addWidget(self.lineedit)
        self.setLayout(layout)
        self.lineedit.setFocus()
        self.setWindowTitle('Upper')

        # -------------------------------------------------------------------------------------------------------------
        # Connect signals
        # -------------------------------------------------------------------------------------------------------------
        # When enter is pressed on the lineedit call self.to_child
        self.lineedit.returnPressed.connect(self.to_child)

        # When the emitter has data available for the UI call the updateUI function
        self.emitter.ui_data_available.connect(self.updateUI)

    def to_child(self):
        """ Send the text of the lineedit to the process and clear the lineedit box. """
        self.process_queue.put(self.lineedit.text().encode('utf-8'))
        self.lineedit.clear()

    def updateUI(self, text):
        """ Add text to the lineedit box. """
        self.browser.append(text)


if __name__ == '__main__':
    # Some setup for qt
    app = QApplication(sys.argv)

    # Create the communication lines.
    mother_pipe, child_pipe = Pipe()
    queue = Queue()

    # Instantiate (i.e. create instances of) our classes.
    emitter = Emitter(mother_pipe)
    child_process = ChildProc(child_pipe, queue)
    form = Form(queue, emitter)

    # Start our process.
    child_process.start()

    # Show the qt GUI and wait for it to exit.
    form.show()
    app.exec_()

Answer 3

首先应该看看信号/插槽在一个Python进程中是如何工作的：

如果只有一个正在运行的QThread，它们就直接调用插槽。

如果信号是在不同的线程上发出的，它必须找到该信号的目标线程，并将消息/ post事件放入该线程的线程队列中。然后，此线程将在适当的时候处理消息/事件并调用信号。

因此，内部总是涉及到某种类型的轮询，重要的是轮询是非阻塞的。

由multiprocessing创建的进程可以通过管道进行通信，这为每一端提供了两个connections。

Connection的poll函数是非阻塞的，因此我会定期使用QTimer轮询它，然后相应地发出信号。

另一种解决方案可能是让来自线程模块(或QThread)的Thread专门等待来自具有队列的get函数的Queue的新消息。有关详细信息，请参阅multiprocessing的管道和队列部分。

下面是一个在另一个Process中启动Qt的示例，以及一个监听Connection的Thread，并在收到特定消息时关闭GUI，然后该GUI终止该进程。

from multiprocessing import Process, Pipe
from threading import Thread
import time
from PySide import QtGui

class MyProcess(Process):

    def __init__(self, child_conn):
        super().__init__()
        self.child_conn = child_conn

    def run(self):
        # start a qt application
        app = QtGui.QApplication([])
        window = QtGui.QWidget()
        layout = QtGui.QVBoxLayout(window)
        button = QtGui.QPushButton('Test')
        button.clicked.connect(self.print_something)
        layout.addWidget(button)
        window.show()

        # start thread which listens on the child_connection
        t = Thread(target=self.listen, args = (app,))
        t.start()

        app.exec_() # this will block this process until somebody calls app.quit

    def listen(self, app):
        while True:
            message = self.child_conn.recv()
            if message == 'stop now':
                app.quit()
                return

    def print_something(self):
        print("button pressed")

if __name__ == '__main__':
    parent_conn, child_conn = Pipe()
    s = MyProcess(child_conn)
    s.start()
    time.sleep(5)
    parent_conn.send('stop now')
    s.join()