Port overload when running multiple instances leads to timeout

[mk-french]

Describe the bug
When executing multiple instances of a script, wexpect overloads on the same port and will typically timeout on the first use of expect(). In some cases, I've observed a race condition where the ConsoleReader of the second process connects to the port of the first and things get a little mixed up...

To Reproduce
Call this script from two seperate terminals without specifying a port. The second instance will time-out on expect('>').
Then call them again but specify unique ports. All is well.

import wexpect
import os
import sys

pid = os.getpid()
if len(sys.argv) > 1:
    port = sys.argv[1]
else:
    port = None

print(f'Started process {pid}, using port {port}')

if not port:
    child = wexpect.host.SpawnSocket(f'cmd.exe', interact=True)
else:
    child = wexpect.host.SpawnSocket(f'cmd.exe', interact=True, port=int(port))

child.expect('>')
print("Prompt detected...")

string = f'echo Hello From {pid}'

child.sendline(string)
child.expect(string)

print(child.match)

wait = input("Press Enter to close.")

An obvious workaround is to specify a unique port to the constructor but it took me a while to work out what was going on...

Expected behavior
If a port is not specified, I would expect the default port to be a random free port.
Or at a minimum, maybe this behaviour could be documented?

Screenshots
N/A

Environment:

• Windows 10.0.19044.2132
• Python 3.7.0
• wexpect 4.0.0

Additional context
N/A