On 5/4/2020 3:26 PM, John Ladasky wrote:
Several years ago I built an application using multiprocessing. It only needed
to work in Linux. I got it working fine. At the time, concurrent.futures did
not exist.
My current project is an application which includes a PyQt5 GUI, and a live
video feed with some real-time image processing. Running all this in one
process resulted in unacceptable performance, so I'm trying to move all of the
heavy video work into its own process. I only need to define one child
process. I don't need a Pool. The child Process can run indefinitely, and it
will communicate multiple messages to the main process using a Pipe.
I built a working example in Linux, but it hangs in Windows. I built a minimum
example. My problem has nothing to do with PyQt. In Windows, my example hangs
when I try to create the child Process. Code:
import os
from multiprocessing import Pipe, Process
def child_app():
inlet.send("Child process id = {}".format(os.getpid()))
if __name__ == "__main__":
outlet, inlet = Pipe()
print("Parent process id =", os.getpid())
child_process = Process(target=child_app) # Windows hangs here
child_process.start()
print(outlet.recv())
child_process.join()
child_process.close()
print("Program complete.")
I'm working in Python 3.7.6 on Windows 10, and 3.7.5 on Ubuntu Linux 19.10.
Does the minimal example in the doc work for you?
(IE, do you only have a problem with Pipe?)
from multiprocessing import Process
def f(name):
print('hello', name)
if __name__ == '__main__':
p = Process(target=f, args=('bob',))
p.start()
p.join()
How about the Pipe example?
from multiprocessing import Process, Pipe
def f(conn):
conn.send([42, None, 'hello'])
conn.close()
if __name__ == '__main__':
parent_conn, child_conn = Pipe()
p = Process(target=f, args=(child_conn,))
p.start()
print(parent_conn.recv()) # prints "[42, None, 'hello']"
p.join()
If this does not work on Windows, the example or doc should be changed.
But I believe I tested it once. Note that unlike your code, the
child_conn is sent as argument. The relation between the module code
and child processes is different on Windows than *nix.
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