PublisherClient creation isn't thread safe and hangs if called by concurrent threads

[matt-mcallister]

Environment details

• OS type and version: Linux - docker container using python:3.10.13-bookworm as the base image
• Python version: 3.10.13
• pip version: 23.0.1
• google-cloud-pubsub version: 2.19.7

Steps to reproduce

Calling PublisherClient.from_service_account_info() from multiple concurrent threads causes the program to hang.

Code example

import concurrent.futures
from google.cloud.pubsub_v1 import PublisherClient

creds = {
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "client_email": "",
    "client_id": "",
    "client_x509_cert_url": "",
    "private_key_id": "",
    "project_id": "",
    "token_uri": "https://oauth2.googleapis.com/token",
    "type": "service_account",
    "private_key": ""
}

def run(publisher_number):
    PublisherClient.from_service_account_info(creds)
    print(f'Created publisher {publisher_number}')

with concurrent.futures.ThreadPoolExecutor(max_workers=2) as executor:
    total_publishers = 10
    futures = []
    for i in range(0, total_publishers):
        futures.append(executor.submit(run, i))

    print(f"Submitted all {total_publishers} to thread executor")
    for f in futures:
        f.result()

Output

$ python test.py
Submitted all 10 to thread executor
^C^\Quit (core dumped)

Stack trace

The program hangs so there is no stack trace, but this is the core dump

$ pystack core core.72129
Using executable found in the core file: /home/temp/bin/python

Core file information:
state: R zombie: True niceness: 0
pid: 72129 ppid: 71086 sid: 71086
uid: 10001 gid: 30001 pgrp: 72129
executable: python arguments: python test.py

The process died due receiving signal SIGQUIT
Traceback for thread 72131 [Has the GIL] (most recent call last):
    (Python) File "/usr/local/lib/python3.10/threading.py", line 973, in _bootstrap
        self._bootstrap_inner()
    (Python) File "/usr/local/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
        self.run()
    (Python) File "/usr/local/lib/python3.10/threading.py", line 953, in run
        self._target(*self._args, **self._kwargs)
    (Python) File "/usr/local/lib/python3.10/concurrent/futures/thread.py", line 83, in _worker
        work_item.run()
    (Python) File "/usr/local/lib/python3.10/concurrent/futures/thread.py", line 58, in run
        result = self.fn(*self.args, **self.kwargs)
    (Python) File "/home/test.py", line 48, in run
        PublisherClient.from_service_account_info(creds)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/client.py", line 172, in from_service_account_info
        return cls(*args, **kwargs)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/cloud/pubsub_v1/publisher/client.py", line 139, in __init__
        super().__init__(**kwargs)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/client.py", line 712, in __init__
        self._transport = Transport(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/transports/grpc.py", line 165, in __init__
        self._grpc_channel = type(self).create_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/transports/grpc.py", line 222, in create_channel
        return grpc_helpers.create_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/api_core/grpc_helpers.py", line 386, in create_channel
        return grpc.secure_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/grpc/__init__.py", line 2119, in secure_channel
        return _channel.Channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/grpc/_channel.py", line 2046, in __init__
        self._channel = cygrpc.Channel(

Traceback for thread 72130 [] (most recent call last):
    (Python) File "/usr/local/lib/python3.10/threading.py", line 973, in _bootstrap
        self._bootstrap_inner()
    (Python) File "/usr/local/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
        self.run()
    (Python) File "/usr/local/lib/python3.10/threading.py", line 953, in run
        self._target(*self._args, **self._kwargs)
    (Python) File "/usr/local/lib/python3.10/concurrent/futures/thread.py", line 83, in _worker
        work_item.run()
    (Python) File "/usr/local/lib/python3.10/concurrent/futures/thread.py", line 58, in run
        result = self.fn(*self.args, **self.kwargs)
    (Python) File "/home/test.py", line 48, in run
        PublisherClient.from_service_account_info(creds)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/client.py", line 172, in from_service_account_info
        return cls(*args, **kwargs)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/cloud/pubsub_v1/publisher/client.py", line 139, in __init__
        super().__init__(**kwargs)
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/client.py", line 712, in __init__
        self._transport = Transport(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/transports/grpc.py", line 165, in __init__
        self._grpc_channel = type(self).create_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/pubsub_v1/services/publisher/transports/grpc.py", line 222, in create_channel
        return grpc_helpers.create_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/google/api_core/grpc_helpers.py", line 386, in create_channel
        return grpc.secure_channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/grpc/__init__.py", line 2119, in secure_channel
        return _channel.Channel(
    (Python) File "/home/temp/lib/python3.10/site-packages/grpc/_channel.py", line 2046, in __init__
        self._channel = cygrpc.Channel(
    (Python) File "/usr/local/lib/python3.10/pkgutil.py", line 639, in get_data
        return loader.get_data(resource_name)
    (Python) File "<frozen importlib._bootstrap_external>", line 1073, in get_data

Traceback for thread 72129 [] (most recent call last):
    (Python) File "/home/test.py", line 60, in <module>
        f.result()
    (Python) File "/usr/local/lib/python3.10/concurrent/futures/_base.py", line 453, in result
        self._condition.wait(timeout)
    (Python) File "/usr/local/lib/python3.10/threading.py", line 320, in wait
        waiter.acquire()

[pedrorjbr]

I suppose that I am suffering from the same problem.
https://stackoverflow.com/questions/78337450/publishing-message-to-gcp-pubsub-from-a-fastapi-app
is there any workaround?

As I am using the PublisherClient from CloudRun, I can´t find way to reuse the same PublisherClient.
It seems a so basic use case.

[florianorpeliere]

Hello,

I have exactly the same problem. I use the PublisherClient in an Apache Beam (Dataflow) job and I noticed mutual blocking problems.

I have a fairly simple way to reproduce it:

import threading
from google.cloud import pubsub_v1

def pubsub():
    for i in [1, 2, 3, 4, 5]:
        print(i)
        pubsub_v1.PublisherClient()


t1 = threading.Thread(target=pubsub)
t2 = threading.Thread(target=pubsub)
t1.start()
t2.start()
t1.join()
t2.join()

Producing:

$ python block.py
1
1
^C^C^C^C
[1]    63732 terminated  python3 block.py

OS: macOS 14.4.1 (23E224) - M2 Pro
Python: Python 3.12.1
google-cloud-pubsub: 2.21.1

I hope this will help you.
If there is a need to open another issue, no problem.

Thank you in advance for your help.