父进程无法访问PyQt中的共享内存

1 投票
1 回答
1656 浏览
提问于 2025-04-16 12:37

我现在正在尝试使用 QSharedMemoryQProcess 在 PyQt 中做一些实验。所以我写了一个小程序来启动一个进程,这个进程会创建一个共享内存区域并往里面写数据。然后我的应用程序会在这个进程写数据时读取这些数据。

不过,当我的应用程序试图连接到这个共享内存区域时,出现了一个错误:QSharedMemory::handle: doesn't exist。看起来,父进程无法访问由子进程分配的共享内存区域,除非这个内存区域是由父进程自己分配的。

输出跟踪信息:

process state: Starting
process state: Running
process started
process output: Done writing to shared memory
Error accessing shared memory from parent process QSharedMemory::handle: doesn't exist 
Error accessing data
process state: Not running
process finished

我的应用程序代码:

from PyQt4 import QtGui, QtCore
import sys
import pickle

class Widget(QtGui.QWidget):
    def __init__(self):
        super(Widget,self).__init__()

        # create process
        self.p = QtCore.QProcess(self)    

        # Connect to process output 
        self.p.readyReadStandardOutput.connect( self.on_process_output )
        self.p.readyReadStandardError.connect( self.on_process_error_output )
        self.p.stateChanged.connect(self.on_process_state_change)                   
        self.p.finished.connect(self.on_process_finished)        
        self.p.started.connect(self.on_process_started)
        self.p.error.connect( self.on_process_error )

        self.key = 'share_mem_key'
        self.shmem = QtCore.QSharedMemory( self.key )

        self.p.start( 'python.exe shmem_process_test.py "%s"' % self.key )

    def on_process_output(self):        
        s_out = bytes.decode( bytes( self.sender().readAllStandardOutput() ) )        
        print 'process output: %s' % (s_out)

        if not self.shmem.isAttached() and not self.shmem.attach():
            print 'Error accessing shared memory from parent process: %s ' % self.shmem.errorString()

        self.shmem.lock()
        try:
            data = self.shmem.data()
            if data:                
                print pickle.loads(data.asstring())
        finally:
            print 'Error accessing data'
            self.shmem.unlock()

    def on_process_error_output(self):
        s_out = bytes.decode( bytes( self.sender().readAllStandardError() ) )                
        print 'process output: %s' % (s_out)

    def on_process_state_change(self,new_state):        
        states = ["Not running", "Starting", "Running"]        
        print 'process state: %s' % (states[new_state])

    def on_process_finished(self):
        print 'process finished'

    def on_process_started(self):
        print 'process started'

    def on_process_error(self):
        print 'process error'

# application loop    
app = QtGui.QApplication(sys.argv)
widget = Widget()

widget.show()
app.exec_()

我的进程代码:

from PyQt4 import QtCore
import ctypes
import ctypes.util
import pickle
import sys

CLIB = ctypes.cdll.LoadLibrary(ctypes.util.find_library('c'))

def main(argv):   
    key = argv[1]

    # write to shared memory      
    data = range(50)
    data_bytes = pickle.dumps( data, pickle.HIGHEST_PROTOCOL)
    data_len = len(data_bytes)      

    shmem = QtCore.QSharedMemory(key)

    if not shmem.create(data_len):
        sys.stderr.write( 'ERROR: shared memory creation' )
        sys.stderr.flush()        
        return

    if not shmem.isAttached() and not shmem.attach():
        sys.stderr.write( 'ERROR: shared memory access' )
        sys.stderr.flush()        
        return 

    shmem.lock()
    try:
        CLIB.memcpy(int(shmem.data()), data_bytes, data_len)
    finally:
        shmem.unlock()

    sys.stdout.write( "Done writing to shared memory" )
    sys.stdout.flush()

if __name__ == '__main__':
    main(sys.argv)

1 个回答

1

来自QSharedMemory文档的内容(我强调的部分):

警告:QSharedMemory以Qt特有的方式更改了键。因此,目前无法使用非Qt应用程序的共享内存与QSharedMemory一起使用。

不太确定你想做的事情(至少在可移植性方面)是否可行。

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