问题
It seems that a successful test of the existence of a windows named pipe by using os.path.exists()
prevents the pipe from working. Why would this be?
Here is successfully working windows named-pipe code:
import time
import multiprocessing as mp
import win32pipe, win32file
PIPENAME = r'\\.\pipe\Foo'
def producer(pipe_name: str):
print('producer')
# if not os.path.exists(pipe_name):
# print(f'No pipe {pipe_name}')
# return
pipe = win32file.CreateFile(pipe_name,
win32file.GENERIC_READ | win32file.GENERIC_WRITE, # dwDesiredAccess
0, # dwShareMode
None, # lpSecurityAttributes
win32file.OPEN_EXISTING, # dwCreationDisposition
0, # dwFlagsAndAttributes
None
)
win32pipe.SetNamedPipeHandleState(pipe, win32pipe.PIPE_READMODE_MESSAGE, None, None)
win32file.WriteFile(pipe, b'foobar')
def receiver(pipe_name: str):
print('receiver')
pipe = win32pipe.CreateNamedPipe(pipe_name,
win32pipe.PIPE_ACCESS_DUPLEX,
win32pipe.PIPE_TYPE_MESSAGE | win32pipe.PIPE_READMODE_MESSAGE | win32pipe.PIPE_WAIT,
1, # nMaxInstances
65536, # nOutBufferSize
65536, # nInBufferSize
0, # 50ms timeout (the default)
None) # securityAttributes
win32pipe.ConnectNamedPipe(pipe)
msg = win32file.ReadFile(pipe, 65536)
print(f'msg: {msg}')
if __name__ == '__main__':
recv_p = mp.Process(target=receiver, args=(PIPENAME,))
prod_p = mp.Process(target=producer, args=(PIPENAME,))
recv_p.start()
time.sleep(0.1)
prod_p.start()
prod_p.join()
recv_p.join()enter code here
This works as expected, with the receiver printing the received message.
But if the three commented-out lines in the producer are uncommented, the os.path.exists(pipe_name)
call somehow breaks the pipe so the output becomes:
receiver
producer
Process Process-2:
Process Process-1:
Traceback (most recent call last):
File "C:\Users\redacted\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
self.run()
File "C:\Users\redacted\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
self._target(*self._args, **self._kwargs)
File "C:\git\redacted\named_pipe_mqtt_test.py", line 18, in producer
None
pywintypes.error: (231, 'CreateFile', 'All pipe instances are busy.')
Traceback (most recent call last):
File "C:\Users\redacted\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 297, in _bootstrap
self.run()
File "C:\Users\redacted\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py", line 99, in run
self._target(*self._args, **self._kwargs)
File "C:\git\redacted\named_pipe_mqtt_test.py", line 35, in receiver
msg = win32file.ReadFile(pipe, 65536)
pywintypes.error: (109, 'ReadFile', 'The pipe has been ended.')
Why would os.path.exists
break windows named pipes?
I've ruled out the python multiprocessing library. I've tried a delay after os.path.exists
.
This is not a blocking problem for me, but I am curious.
来源:https://stackoverflow.com/questions/51255352/why-does-os-path-exists-stop-windows-named-pipes-from-connecting