MongoClient hangs for 0.5 seconds on script exit

Hello,

• On script exit, MongoClient() hangs for ~0.5 seconds for no apparent reason.
  • Even without any active connection or any operation done.

How to reproduce }}{{:{{}}

docker run -it --rm debian bash

#

apt update

apt install -y python3-pip

pip3 install pymongo

#

cat /etc/debian_version

  -> 9.9

python3 -c "import sys; print(sys.version)"

  -> 3.5.3 (default, Sep 27 2018, 17:25:39)

  -> [GCC 6.3.0 20170516]

python3 -c "import pymongo; print(pymongo.version); print(pymongo.has_c())"

  -> 3.8.0

  -> True

#  

echo '''

import sys

import pymongo

if len(sys.argv) > 1:

    print("MongoClient")

    pymongo.MongoClient(connect=False)

else:

    print("nothing")

print("end")

''' > test.py

#

time python3 test.py

  nothing

  end

  -> real    0m0.120s

time python3 test.py foo

  MongoClient

  end

  -> real    0m0.633s

• on the 1st run (without foo arg), their is not lag between the "end" and the time command output.
• but, on the 2nd run (with foo arg to trigger MongoClient) their is a distinct lag between the "end" and the time command output.
• this is the simplest example to reproduce the bug, but :
  • a explicit ".close()" on MongoClient does NOT help.
  • a "connect=True" does NOT help.
  • doing real CRUD operations on a real authenticated mongod/replicaset/mongos does NOT help.

• When your applicative processing - including mongo auth and CRUD - takes about 200ms, a +500ms is a huge performance loss.
• I tried to reproduce this bug in php and nodejs but could not :
  • php : 21ms -> 29ms => no loss.
  • nodejs : 48ms -> 107ms => +50ms loss (still huge, but acceptable).

Any help would be greatly appreciated.