python - 通过日志记录更新 QTextEdit 时 PyQt5 程序崩溃

Question

我有一个需要很长时间的大型程序，需要充足的日志记录。我的前端有一个 GUI，其中包含自定义日志记录处理程序，定义如下:

class QHandler(logging.Handler, QTextEdit):
    def __init__(self, parent=None):
        QTextEdit.__init__(self, parent)
        logging.Handler.__init__(self)

        self.setLineWrapMode(QTextEdit.NoWrap)
        self.setReadOnly(True)

        self.emit_lock = Lock()

    def emit(self, record):
        with self.emit_lock:
            self.append(self.format(record))
            self.autoScroll()

    def format(self, record):
        if (record.levelno <= logging.INFO):
            bgcolor = WHITE
            fgcolor = BLACK
        if (record.levelno <= logging.WARNING):
            bgcolor = YELLOW
            fgcolor = BLACK
        if (record.levelno <= logging.ERROR):
            bgcolor = ORANGE
            fgcolor = BLACK
        if (record.levelno <= logging.CRITICAL):
            bgcolor = RED
            fgcolor = BLACK
        else:
            bgcolor = BLACK
            fgcolor = WHITE

        self.setTextBackgroundColor(bgcolor)
        self.setTextColor(fgcolor)
        self.setFont(DEFAULT_FONT)
        record = logging.Handler.format(self, record)
        return record

    def autoScroll(self):
        self.verticalScrollBar().setSliderPosition(self.verticalScrollBar().maximum())

我有主 gui (QMainWindow)，它通过以下方式添加此处理程序:

# inside __init__ of main GUI (QMainWindow):
self.status_handler = QHandler()
# Main gui is divided into tabs and the status handler box is added to the second tab
main_tabs.addTab(self.status_handler, 'Status') 

我有一个 Controller 函数，可以通过以下方式初始化日志处理程序:

# inside controller initializing function
gui = gui_class() # this is the main gui that initializes the handler among other things
logger = logging.getLogger()
gui.status_handler.setFormatter(file_formatter) # defined elsewhere
logger.addHandler(gui.status_handler)

一旦 GUI 启动并初始化日志记录，我将使用以下命令完成 python 执行:

app = QApplication.instance()
if (app is None):
    app = QApplication([])
    app.setStyle('Fusion')
app.exec_()

GUI 有几个连接到按钮信号的插槽，这些插槽会生成线程来执行实际处理。每个处理线程都有自己的日志记录调用，这似乎按预期工作。它们的定义如下:

class Subprocess_Thread(Thread):
    def __init__(self, <args>):
        Thread.__init__(self)
        self.logger = logging.getLogger(self.__class__.__name__)
        self.logger.info('Subprocess Thread Created')

    def run(self):
        # does a bunch of stuff
        self.logger.info('Running stuff')
        # iterates over other objects and calls on them to do stuff
        # where they also have a logger attached and called just like above

当我在没有 GUI 的情况下运行应用程序时，甚至在 GUI 最小化的情况下运行应用程序时，它每次都运行良好。我可以在控制台(命令提示符或 spyder)中看到我的日志消息。

如果我在没有最小化 GUI 的情况下运行相同的应用程序，我将在 GUI 中看到初始化的日志消息以及线程进程的一些第一部分，但随后它会在看似随机的时间挂起。没有错误消息，并且所使用的单核的 CPU 使用率似乎已达到最大值。我添加了一个锁，只是为了确保日志记录不会来自不同的线程，但这也没有帮助。

我尝试过使用 QPlainTextEdit 和 QListWidget 但每次都会遇到同样的问题。

有人知道为什么这个 GUI 元素会导致整个 Python 解释器在 View 中挂起并记录消息吗？

Answer 1

采样的QHandler不是线程安全的，因此如果从另一个线程调用它会产生问题，因为它是一个GUI，一个可能的解决方案是从辅助线程发送数据( def emit(self, record):) 通过 QMetaObject 发送到 GUI 线程，为此您必须使用 pyqtSlot:

class QHandler(logging.Handler, QtWidgets.QTextEdit):
    def __init__(self, parent=None):
        QtWidgets.QTextEdit.__init__(self, parent)
        logging.Handler.__init__(self)

        self.setLineWrapMode(QtWidgets.QTextEdit.NoWrap)
        self.setReadOnly(True)

        self.emit_lock = threading.Lock()

    def emit(self, record):
        with self.emit_lock:
            QtCore.QMetaObject.invokeMethod(self, 
                "append",  
                QtCore.Qt.QueuedConnection,
                QtCore.Q_ARG(str, self.format(record)))
            QtCore.QMetaObject.invokeMethod(self, 
                "autoScroll",
                QtCore.Qt.QueuedConnection)

    def format(self, record):
        if record.levelno == logging.INFO:
            bgcolor = WHITE
            fgcolor = BLACK
        elif record.levelno == logging.WARNING:
            bgcolor = YELLOW
            fgcolor = BLACK
        elif record.levelno == logging.ERROR:
            bgcolor = ORANGE
            fgcolor = BLACK
        elif record.levelno == logging.CRITICAL:
            bgcolor = RED
            fgcolor = BLACK
        else:
            bgcolor = BLACK
            fgcolor = WHITE

        self.setTextBackgroundColor(bgcolor)
        self.setTextColor(fgcolor)
        self.setFont(DEFAULT_FONT)
        record = logging.Handler.format(self, record)
        return record

    @QtCore.pyqtSlot()
    def autoScroll(self):
        self.verticalScrollBar().setSliderPosition(self.verticalScrollBar().maximum())

示例:

import random
import logging
import threading
from PyQt5 import QtCore, QtGui, QtWidgets

WHITE, BLACK, YELLOW, ORANGE, RED = QtGui.QColor("white"), QtGui.QColor("black"), QtGui.QColor("yellow"), QtGui.QColor("orange"), QtGui.QColor("red")
DEFAULT_FONT = QtGui.QFont()

class QHandler(logging.Handler, QtWidgets.QTextEdit):
    def __init__(self, parent=None):
        QtWidgets.QTextEdit.__init__(self, parent)
        logging.Handler.__init__(self)

        self.setLineWrapMode(QtWidgets.QTextEdit.NoWrap)
        self.setReadOnly(True)

        self.emit_lock = threading.Lock()

    def emit(self, record):
        with self.emit_lock:
            QtCore.QMetaObject.invokeMethod(self, 
                "append",  
                QtCore.Qt.QueuedConnection,
                QtCore.Q_ARG(str, self.format(record)))
            QtCore.QMetaObject.invokeMethod(self, 
                "autoScroll",
                QtCore.Qt.QueuedConnection)

    def format(self, record):
        if record.levelno == logging.INFO:
            bgcolor = WHITE
            fgcolor = BLACK
        elif record.levelno == logging.WARNING:
            bgcolor = YELLOW
            fgcolor = BLACK
        elif record.levelno == logging.ERROR:
            bgcolor = ORANGE
            fgcolor = BLACK
        elif record.levelno == logging.CRITICAL:
            bgcolor = RED
            fgcolor = BLACK
        else:
            bgcolor = BLACK
            fgcolor = WHITE

        self.setTextBackgroundColor(bgcolor)
        self.setTextColor(fgcolor)
        self.setFont(DEFAULT_FONT)
        record = logging.Handler.format(self, record)
        return record

    @QtCore.pyqtSlot()
    def autoScroll(self):
        self.verticalScrollBar().setSliderPosition(self.verticalScrollBar().maximum())


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.status_handler = QHandler()
        self.setCentralWidget(self.status_handler)

        logging.getLogger().addHandler(self.status_handler)
        self.status_handler.setFormatter(logging.Formatter('%(asctime)s - %(levelname)s - %(message)s'))
        logging.getLogger().setLevel(logging.DEBUG)
        timer = QtCore.QTimer(self, interval=1000, timeout=self.on_timeout)
        timer.start()

    def on_timeout(self):
        logging.info('From Gui Thread {}'.format(QtCore.QDateTime.currentDateTime().toString()))


class Subprocess_Thread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.logger = logging.getLogger(self.__class__.__name__)
        self.logger.info('Subprocess Thread Created')

    def run(self):
        while True:
            t = random.choice(["info", "warning", "error", "critical"])
            msg = "Type: {}, thread: {}".format(t, threading.currentThread())
            getattr(self.logger, t)(msg)
            QtCore.QThread.sleep(1)

if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication.instance()
    if app is None:
        app = QtWidgets.QApplication(sys.argv)
        app.setStyle('Fusion')
    w = MainWindow()
    w.show()
    th = Subprocess_Thread()
    th.daemon = True
    th.start()
    sys.exit(app.exec_())