Locust / pypy fails with "AttributeError: module 'gc' has no attribute 'freeze'" error.

[jimoleary]

Prerequisites

• I am using the latest version of Locust
• I am reporting a bug, not asking a question

Description

Running a locust workload with --processes fails on pypy.

This is due to this change and it results in an AttributeError: module 'gc' has no attribute 'freeze'. The root cause is due to the fact that pypy doesn't have a freeze function.

See the following:

$ docker run --mount type=bind,source=.,target=/mnt/locust pypy:3.10 bash -c "pip3 install -q locust && locust -f /mnt/locust/examples/basic.py --processes=-1 --headless -t 5"

WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv

[notice] A new release of pip is available: 23.0.1 -> 24.1.2
[notice] To update, run: pip install --upgrade pip
Traceback (most recent call last):
  File "/opt/pypy/bin/locust", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/opt/pypy/lib/pypy3.10/site-packages/locust/main.py", line 214, in main
    gc.freeze()  # move all objects to perm gen so ref counts dont get updated
    ^^^^^^^^^^^
AttributeError: module 'gc' has no attribute 'freeze'

The following patch fixes the issue:

From 90c0a525940dbbae8da22eded4e52ff143a68436 Mon Sep 17 00:00:00 2001
From: "jim.oleary" <jim.oleary@gmail.com>
Date: Wed, 24 Jul 2024 18:20:31 +0100
Subject: [PATCH] fix: gc.freeze() is not currently available on pypy.

---
 locust/main.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/locust/main.py b/locust/main.py
index 16446164..c1885802 100644
--- a/locust/main.py
+++ b/locust/main.py
@@ -211,7 +211,8 @@ def main():
             sys.exit(1)
         # Optimize copy-on-write-behavior to save some memory (aprx 26MB -> 15MB rss) in child processes
         gc.collect()  # avoid freezing garbage
-        gc.freeze()  # move all objects to perm gen so ref counts dont get updated
+        if hasattr(gc, "freeze"):
+            gc.freeze()  # move all objects to perm gen so ref counts dont get updated
         for _ in range(options.processes):
             if child_pid := gevent.fork():
                 children.append(child_pid)
-- 
2.34.1

With the patch applied and installed, the workloads runs:

make dist
docker run --mount type=bind,source=.,target=/mnt/locust pypy:3.10 bash -c "pip3 install -q /mnt/locust/dist/locust-2.29.2.dev1-py3-none-any.whl && locust -f /mnt/locust/examples/basic.py --processes=-1 --headless -t 5 "     
WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv

[notice] A new release of pip is available: 23.0.1 -> 24.1.2
[notice] To update, run: pip install --upgrade pip
[2024-07-27 14:19:49,636] e46c755e6b11/INFO/root: Waiting for workers to be ready, 0 of 12 connected
[2024-07-27 14:19:49,642] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_91f431ad9c8c452db2d43d8b0b942617 (index 0) reported as ready. 1 workers connected.
Type     Name                                                                          # reqs      # fails |    Avg     Min     Max    Med |   req/s  failures/s
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
--------|----------------------------------------------------------------------------|-------|-------------|-------|-------|-------|-------|--------|-----------
         Aggregated                                                                         0     0(0.00%) |      0       0       0      0 |    0.00        0.00

[2024-07-27 14:19:49,644] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,775] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_1af9327b13d845dfa024cb4a1ba80152 (index 1) reported as ready. 2 workers connected.
[2024-07-27 14:19:49,777] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,778] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_7f7a7ff8f7aa4f649e4870a1e8f91acd (index 2) reported as ready. 3 workers connected.
[2024-07-27 14:19:49,780] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,780] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_1339140c19e94d64bab8e6f60d3379be (index 3) reported as ready. 4 workers connected.
[2024-07-27 14:19:49,782] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,783] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_b55f14d4b8594903b37d2e4419ed82a1 (index 4) reported as ready. 5 workers connected.
[2024-07-27 14:19:49,785] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,786] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_dbcc5bbf1913440d9305d05afad406b0 (index 5) reported as ready. 6 workers connected.
[2024-07-27 14:19:49,789] e46c755e6b11/INFO/locust.main: Starting Locust 2.29.2.dev1
[2024-07-27 14:19:49,792] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_bd31f951b61b46fc94cda4c1190aff82 (index 6) reported as ready. 7 workers connected.
[2024-07-27 14:19:49,794] e46c755e6b11/INFO/locust.runners: Worker e46c755e6b11_4e8bebbb8f6a43c9ba4d9f4205e2690d (index 7) reported as ready. 8 workers connected.

Using locust<=2.20.1 or manually launching worker processes maybe a workaround for now, but I'd like to be able to use newer versions and --processes=-1 is too convenient not to use:

docker run --mount type=bind,source=.,target=/mnt/locust pypy:3.10 bash -c "pip3 install -q 'locust<=2.20.1' && locust -f /mnt/locust/examples/basic.py --processes=-1 --headless -t 5"

Command line

docker run --mount type=bind,source=.,target=/mnt/locust pypy:3.10 bash -c "pip3 install -q locust && locust -f /mnt/locust/examples/basic.py --processes=-1 --headless -t 5"

Locustfile contents

# The locust file doesn't matter as the call fails in main.py

Python version

any pypy version

Locust version

= 2.21.0

Operating system

any

[cyberw]

Interesting, I didnt know anyone used pypy to run Locust :) Whats the performance like for you?

[jimoleary]

We have been evaluating testing with a mix of versions, python 3.9, python 3.12 and pypy 3.10 (v7.3.13).

For our read tests (which are lower latency):

• 3.12 is ~50% faster than 3.9
• pypy is ~100% faster than 3.9

There isn't a huge difference for our higher latency tests.

We haven't tried 3.13 pre release / free-threaded versions yet that sounds too scary for now!

[cyberw]

Cool, thanks for sharing!

We might want to look at supporting pypy properly then... we're doing a lot of work on our CI (github actions + poetry + tox) right now, but if you would come back in a couple of weeks after things settle down with a PR to add pypy to the build I'd be very happy :)

[jimoleary]

TYVM, I will add it to my calendar!