pyqt5 python 3.8 中的多处理共享内存

Question

I'm a little confused why the following isn't updating the numpy array across processes? There are no errors thrown in this, but the main process doesn't reflect the child's update to the shared array sample . I'm unsure why this isn't working. The example on the shared_memory page works fine on my machine. The shared events work fine as well. Is this is a Qt-related issue perhaps?

import time
from PyQt5.QtCore import QTimer
from PyQt5.QtWidgets import QWidget, QVBoxLayout, QProgressBar, QPushButton
import multiprocessing
from multiprocessing import shared_memory
import numpy as np

DATA_SIZE = 1
DTYPE = np.int64


class DataPuller(multiprocessing.get_context("spawn").Process):
    def __init__(
            self,
            event,
            shared_mem_name,
    ):
        super().__init__()
        self.event = event
        self.shm = shared_memory.SharedMemory(name=shared_mem_name)
        self.sample = np.ndarray(
            shape=(DATA_SIZE, 1), dtype=DTYPE, buffer=self.shm.buf)
        self.counter = 0

    def run(self):
        print("child process started")
        while not self.event.is_set():
            time.sleep(0.1)
            self.sample[:, 0] = self.counter
            print("child: ", self.sample[0, 0])
            self.counter += 1
            if self.counter >= 1000:
                self.counter = 0
        self.shm.close()
        print("child process finished")


class Window(QWidget):
    def __init__(self, *args, **kwargs):
        super(Window, self).__init__(*args, **kwargs)
        layout = QVBoxLayout(self)
        self.progressBar = QProgressBar(self)
        self.timer = QTimer(self)
        self.timer.timeout.connect(self.onTimer)
        self.progressBar.setRange(0, 1000)
        layout.addWidget(self.progressBar)
        layout.addWidget(QPushButton('开启线程', self, clicked=self.onStart))

        self.counter = 0
        self.shared_mem_name = "data"
        self.base_array = np.zeros((DATA_SIZE, 1), dtype=DTYPE)
        self.shm = shared_memory.SharedMemory(
            create=True,
            size=self.base_array.nbytes,
            name=self.shared_mem_name)
        self.sample = np.ndarray(
            shape=self.base_array.shape,
            dtype=self.base_array.dtype,
            buffer=self.shm.buf)
        self.event = multiprocessing.Event()
        self._process = DataPuller(self.event, self.shared_mem_name)

    def onStart(self):
        if not self._process.is_alive():
            print("main starting process")
            self._process.start()
            self.timer.start(500)
        else:
            pass

    def onTimer(self):
        print("main: ", self.sample[0, 0])
        self.progressBar.setValue(self.sample[0, 0])

    def closeEvent(self, event):
        if self._process.is_alive():
            self.event.set()
            self._process.join()
        self.shm.close()
        self.shm.unlink()
        self.close()
        print("main process finished")


if __name__ == '__main__':
    import sys
    from PyQt5.QtWidgets import QApplication
    app = QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())

Answer 1

The problem is that the Event does not belong to the DataPuller context so it will never enter the while. The solution is to create the Event using the context.

The problem is that the __init__ method of DataPuller is executed in the initial process where shared memory is created so it is not available for the secondary DataPuller process. The solution in this case is to create the shared memory in the run method.

import time
from PyQt5.QtCore import QTimer
from PyQt5.QtWidgets import QWidget, QVBoxLayout, QProgressBar, QPushButton
import multiprocessing
from multiprocessing import shared_memory
import numpy as np

DATA_SIZE = 1
DTYPE = np.int64

context = multiprocessing.get_context("spawn")


class DataPuller(context.Process):
    def __init__(
        self, event, shared_mem_name,
    ):
        super().__init__()
        self.event = event
        self.shared_mem_name = shared_mem_name

    def run(self):
        self.shm = shared_memory.SharedMemory(name=self.shared_mem_name)
        self.sample = np.ndarray(shape=(DATA_SIZE, 1), dtype=DTYPE, buffer=self.shm.buf)
        self.counter = 0

        while not self.event.is_set():
            time.sleep(0.1)
            self.sample[:, 0] = self.counter
            print("child: ", self.sample[0, 0])
            self.counter += 1
            if self.counter >= 1000:
                self.counter = 0
        self.shm.close()
        print("child process finished")


class Window(QWidget):
    def __init__(self, *args, **kwargs):
        super(Window, self).__init__(*args, **kwargs)
        layout = QVBoxLayout(self)
        self.progressBar = QProgressBar()
        self.timer = QTimer(self)
        self.timer.timeout.connect(self.onTimer)
        self.progressBar.setRange(0, 1000)
        layout.addWidget(self.progressBar)
        layout.addWidget(QPushButton("开启线程", clicked=self.onStart))

        self.counter = 0
        self.shared_mem_name = "data"
        self.base_array = np.zeros((DATA_SIZE, 1), dtype=DTYPE)
        self.shm = shared_memory.SharedMemory(
            create=True, size=self.base_array.nbytes, name=self.shared_mem_name
        )
        self.sample = np.ndarray(
            shape=self.base_array.shape,
            dtype=self.base_array.dtype,
            buffer=self.shm.buf,
        )
        self.event = context.Event()
        print(self.event.is_set())
        self._process = DataPuller(self.event, self.shared_mem_name)

    def onStart(self):
        if not self._process.is_alive():
            print("main starting process")
            self._process.start()
            self.timer.start(500)
        else:
            pass

    def onTimer(self):
        print("main: ", self.sample[0, 0])
        self.progressBar.setValue(self.sample[0, 0])

    def closeEvent(self, event):
        if self._process.is_alive():
            self.event.set()
            self._process.join()
        self.shm.close()
        self.shm.unlink()
        self.close()
        print("main process finished")


if __name__ == "__main__":
    import sys
    from PyQt5.QtWidgets import QApplication

    app = QApplication(sys.argv)
    w = Window()
    w.show()
    sys.exit(app.exec_())