Python 通过 win32com 运行 MessageQueue.Peek，如何获得超时？

Question

For starters, I would like to say if anyone can help here, you are incredible.

General Question

My Python program needs to interact with MSMQ. Basically, I want to peek at a queue, specifying a timeout if there's nothing in the queue.

However, despite my best efforts, I cannot get Peek() to wait out the timeout interval, when there's no value previously in the queue. Can you please point out what is missing from this code?

---

My Current Code

Here is my code right now:

from socket import gethostname

import win32com.client
import pythoncom

import clr
clr.AddReference("System")
clr.AddReference("System.Messaging")
from System import TimeSpan
from System.Messaging import MessageQueue


# Source: [1]
# [1] https://docs.microsoft.com/en-us/previous-versions/windows/desktop/msmq/ms707027%28v%3dvs.85%29
MQ_DENY_NONE = 0x0
MQ_PEEK_ACCESS = 0x1
MQ_SEND_ACCESS = 0x2


# Set up queue
pythoncom.CoInitialize()
qinfo = win32com.client.Dispatch("MSMQ.MSMQQueueInfo")
qinfo.FormatName = f"direct=os:{gethostname()}\\PRIVATE$\\MyQueue"
queue = qinfo.Open(MQ_PEEK_ACCESS, MQ_DENY_NONE)

# Receive a value
timeout_sec = 1.0
timespan = TimeSpan.FromSeconds(timeout_sec)
label, body = "", ""
# TODO: timeout value does not appear working. It never waits when
#  there's no message
if queue.Peek(pythoncom.Empty, pythoncom.Empty, timespan):
    msg = queue.Receive() . # Blocking receive --> remove msg from the queue
    if msg is not None:
        label = msg.Label
        body = msg.Body

I run: inspect.getfullargspec(queue.Peek) and get:

FullArgSpec(args=['self', 'WantDestinationQueue', 'WantBody', 'ReceiveTimeout', 'WantConnectorType'], varargs=None, varkw=None, defaults=(<PyOleMissing object at 0x00000147F5D43BD0>, <PyOleMissing object at 0x00000147F5D43BD0>, <PyOleMissing object at 0x00000147F5D43BD0>, <PyOleMissing object at 0x00000147F5D43BD0>), kwonlyargs=[], kwonlydefaults=None, annotations={})

---

Things I've Tried

This question : saying ReceiveTimeout=timespan doesn't seem to solve my problem.

Replacing pythoncom.Empty with pythoncom.Missing doesn't seem to work

This unanswered question seems very similar to mine

Answer 1

I found this article sending-msmq-messages-python

The article shows you how to send and receive a message using msmq. I don't understand why you can't just standard socket connection syntax to say if I haven't received a packet/connection then close connection

import select
mysocket.setblocking(0)
ready = select.select([mysocket], [], [], timeout_in_seconds)
if ready[0]:
    data = mysocket.recv(4096)

So something like that shouldn't be too difficult. Worst case scenario create a thread that checks every timeout_time if a variable is zero or not. If it's zero close queue nothing received if it's >0 set to zero and wait for more messages. I also found a GitHub about asynchronous msmq for python logging. asynchronous msmq This one just said receive while True dlopes7 msmq

import time
t_end = time.time() + 60 * 15
messages=0
while time.time() < t_end or messages>0:
    msg = queue.Receive()
    messages+=1
    if(time.time() > t_end and messages>0):
        messages=0
        t_end = time.time() + 60 * 15
    print(f'Got Message from {queue_name}: {msg.Label} - {msg.Body}')

Not the answer you wanted but one that will work.

Answer 2

In the original question's comments, @PeterBrittain suggested to try just using:

an integer (in milliseconds) for their timeout

I got around to trying that out, and actually, it worked! I found float values to work as well. Here is some sample Python code:

timeout_sec = 1.0
queue.Peek(pythoncom.Empty, pythoncom.Empty, timeout_sec * 1000):

Thank you @PeterBrittain!