python multiprocessing - 将子进程日志发送到在父进程中运行的 GUI

Question

我正在编写的一些分析代码之上构建一个界面，该代码执行一些 SQL 并处理查询结果。 在我想向用户公开的这个分析代码中，有许多事件的日志记录。 因为分析代码运行时间相当长，而且我不希望 UI 被阻塞，所以到目前为止我是通过将分析函数放入自己的线程来完成的。

我现在拥有的简化示例（完整脚本）：

import sys
import time
import logging
from PySide2 import QtCore, QtWidgets

def long_task():
    logging.info('Starting long task')
    time.sleep(3) # this would be replaced with a real task
    logging.info('Long task complete')

class LogEmitter(QtCore.QObject):
    sigLog = QtCore.Signal(str)

class LogHandler(logging.Handler):
    def __init__(self):
        super().__init__()
        self.emitter = LogEmitter()
    def emit(self, record):
        msg = self.format(record)
        self.emitter.sigLog.emit(msg)

class LogDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super().__init__(parent)
        log_txt = QtWidgets.QPlainTextEdit(self)
        log_txt.setReadOnly(True)
        layout = QtWidgets.QHBoxLayout(self)
        layout.addWidget(log_txt)
        self.setWindowTitle('Event Log')
        handler = LogHandler()
        handler.emitter.sigLog.connect(log_txt.appendPlainText)
        logger = logging.getLogger()
        logger.addHandler(handler)
        logger.setLevel(logging.INFO)

class Worker(QtCore.QThread):
    results = QtCore.Signal(object)

    def __init__(self, func, *args, **kwargs):
        super().__init__()
        self.func = func
        self.args = args
        self.kwargs = kwargs

    def run(self):
        results = self.func(*self.args, **self.kwargs)
        self.results.emit(results)

class MainWindow(QtWidgets.QMainWindow):

    def __init__(self):
        super().__init__()
        widget = QtWidgets.QWidget()
        layout = QtWidgets.QHBoxLayout(widget)
        start_btn = QtWidgets.QPushButton('Start')
        start_btn.clicked.connect(self.start)
        layout.addWidget(start_btn)
        self.setCentralWidget(widget)

        self.log_dialog = LogDialog()
        self.worker = None

    def start(self):
        if not self.worker:
            self.log_dialog.show()
            logging.info('Run Starting')
            self.worker = Worker(long_task)
            self.worker.results.connect(self.handle_result)
            self.worker.start()

    def handle_result(self, result=None):
        logging.info('Result received')
        self.worker = None

if __name__ == '__main__':
    app = QtWidgets.QApplication()
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())

这工作正常，除了我需要能够允许用户停止执行分析代码。 我读过的所有内容都表明无法很好地中断线程，因此使用multiprocessing库似乎是要走的路（无法重新编写分析代码以允许定期轮询，因为大部分时间只是等待查询返回结果）。 通过使用multiprocessing.Pool和apply_async以不阻塞 UI 的方式执行分析代码，获得相同的功能是很容易的。

例如从上面替换MainWindow为：

class MainWindow(QtWidgets.QMainWindow):

    def __init__(self):
        super().__init__()
        widget = QtWidgets.QWidget()
        layout = QtWidgets.QHBoxLayout(widget)
        start_btn = QtWidgets.QPushButton('Start')
        start_btn.clicked.connect(self.start)
        layout.addWidget(start_btn)
        self.setCentralWidget(widget)

        self.log_dialog = LogDialog()
        self.pool = multiprocessing.Pool()
        self.running = False

    def start(self):
        if not self.running:
            self.log_dialog.show()
            logging.info('Run Starting')
            self.pool.apply_async(long_task, callback=self.handle_result)

    def handle_result(self, result=None):
        logging.info('Result received')
        self.running = False

但我似乎无法弄清楚如何从子进程检索日志输出并将其传递给父进程以更新日志对话框。 我已经阅读了几乎所有关于此的 SO 问题以及如何处理从多个进程写入单个日志文件的食谱示例，但我无法围绕如何使这些想法适应我​​的想法我想在这里做。

编辑

所以试图弄清楚为什么我看到的行为与我添加的@eyllanesc 不同：

logger = logging.getLogger()
print(f'In Func: {logger} at {id(logger)}')

和

logger = logging.getLogger()
print(f'In Main: {logger} at {id(logger)}')

分别到long_task和Mainwindow.start 。 当我运行main.py我得到：

In Main: <RootLogger root (INFO)> at 2716746681984
In Func: <RootLogger root (WARNING)> at 1918342302352

这似乎是this SO question中描述的内容

这种使用Queue和QueueHandler作为解决方案的想法似乎类似于@eyllanesc 的原始解决方案

Answer 1

信号不会在进程之间传输数据，因此对于这种情况，必须使用管道然后发出信号：

# other imports
import threading
# ...

class LogHandler(logging.Handler):
    def __init__(self):
        super().__init__()
        self.r, self.w = multiprocessing.Pipe()
        self.emitter = LogEmitter()
        threading.Thread(target=self.listen, daemon=True).start()

    def emit(self, record):
        msg = self.format(record)
        self.w.send(msg)

    def listen(self):
        while True:
            try:
                msg = self.r.recv()
                self.emitter.sigLog.emit(msg)
            except EOFError:
                break

# ...

Answer 2

万一有人在路上徘徊，使用QueueHandler和QueueListener会导致解决方案也适用于 Windows。 从这个回答中大量借用了一个类似问题：

import logging
import sys
import time
import multiprocessing
from logging.handlers import QueueHandler, QueueListener
from PySide2 import QtWidgets, QtCore

def long_task():
    logging.info('Starting long task')
    time.sleep(3) # this would be replaced with a real task
    logging.info('Long task complete')

def worker_init(q):
    qh = QueueHandler(q)
    logger = logging.getLogger()
    logger.setLevel(logging.INFO)
    logger.addHandler(qh)

class LogEmitter(QtCore.QObject):
    sigLog = QtCore.Signal(str)

class LogHandler(logging.Handler):
    def __init__(self):
        super().__init__()
        self.emitter = LogEmitter()
    def emit(self, record):
        msg = self.format(record)
        self.emitter.sigLog.emit(msg)

class LogDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.log_txt = QtWidgets.QPlainTextEdit(self)
        self.log_txt.setReadOnly(True)
        layout = QtWidgets.QHBoxLayout(self)
        layout.addWidget(self.log_txt)
        self.setWindowTitle('Event Log')

class MainWindow(QtWidgets.QMainWindow):

    def __init__(self):
        super().__init__()
        widget = QtWidgets.QWidget()
        layout = QtWidgets.QHBoxLayout(widget)
        start_btn = QtWidgets.QPushButton('Start')
        start_btn.clicked.connect(self.start)
        layout.addWidget(start_btn)
        self.setCentralWidget(widget)

        self.log_dialog = LogDialog()
        self.running = False

        # sets up handler that will be used by QueueListener
        # which will update the LogDialoag
        handler = LogHandler()
        handler.emitter.sigLog.connect(self.log_dialog.log_txt.appendPlainText)

        self.q = multiprocessing.Queue()
        self.ql = QueueListener(self.q, handler)
        self.ql.start()

        # main process should also log to a QueueHandler
        self.main_log = logging.getLogger('main')
        self.main_log.propagate = False
        self.main_log.setLevel(logging.INFO)
        self.main_log.addHandler(QueueHandler(self.q))

        self.pool = multiprocessing.Pool(1, worker_init, [self.q])

    def start(self):
        if not self.running:
            self.log_dialog.show()
            self.main_log.info('Run Starting')
            self.pool.apply_async(long_task, callback=self.handle_result)

    def handle_result(self, result=None):
        time.sleep(2)
        self.main_log.info('Result received')
        self.running = False

    def closeEvent(self, _):
        self.ql.stop()

if __name__ == '__main__':
    app = QtWidgets.QApplication()
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())