fix: Preserve event delivery with gevent queues

[marandaneto]

💡 Motivation and Context

gevent 25.4.1 and later replaces queue.Queue when monkey.patch_all() runs. The replacement supports the public queue API but does not expose the synchronization attributes used by the PostHog consumer and flush paths. Consumer threads then stop with an AttributeError, flush fails, and captured events remain queued.

Fixes #865.

PostHog now checks whether the active queue exposes the synchronization interface required by its consumers. A working standard library queue is used without importing gevent. If gevent replaced the queue, PostHog retrieves the original queue through gevent.monkey.get_original().

If a lane cannot create a usable queue because gevent is unavailable or broken, the SDK logs the specific queue initialization or gevent recovery failure and disables asynchronous capture for that lane. Synchronous capture and queue-independent APIs such as feature flags remain available. A minimal private queue remains only so flush, shutdown, and fork cleanup stay safe on the unavailable lane.

The included example shows capture from gunicorn workers started with --worker-class gevent --preload.

💚 How did you test it?

• Reproduced the failure before the fix with gevent monkey-patching. The consumer stopped on a missing queue synchronization attribute, batch_post was not called, and the event remained queued.
• Added a subprocess regression test that applies gevent monkey-patching before importing the SDK. It verifies the client restores the original queue interface, sends the event, and drains the queue.
• Added fallback tests that verify a working queue does not import gevent and an unusable queue disables only asynchronous capture without raising. Synchronous capture and feature flag requests remain available.
• Ran the full test suite after addressing review feedback: 2063 passed, 15 skipped.
• Ran the focused client, consumer, fork, and gevent suites after the fallback change: 273 passed.
• Ran Ruff formatting and lint checks, mypy, the public API check, the warning-free import check, and the lockfile check.
• Ran the gunicorn gevent preload example against a local HTTP receiver and confirmed that both test requests were delivered.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented with Pi under human direction. We compared a copied CPython queue implementation with gevent's supported patch-state APIs. We chose capability detection with is_object_patched() and get_original() because it preserves the standard library queue type with a smaller maintenance surface. ReviewHog later identified that client-wide disabling would also suppress synchronous capture and feature flags; queue failures are now lane-local with regression coverage for those paths.

[github-actions]

posthog-python Compliance Report

Date: 2026-08-12 17:11:44 UTC
Duration: 256449ms

✅ All Tests Passed!

111/111 tests passed

---

Capture_V1 Tests

✅ 94/94 tests passed

View Details

Test	Status	Duration
Endpoint And Method.Targets V1 Endpoint	✅	517ms
Endpoint And Method.Does Not Use Legacy Endpoints	✅	511ms
Required Headers.Has Authorization Bearer Header	✅	511ms
Required Headers.Has Content Type Json	✅	510ms
Required Headers.Has Posthog Sdk Info Format	✅	511ms
Required Headers.Has Posthog Attempt Header	✅	510ms
Required Headers.Has Posthog Request Id	✅	511ms
Required Headers.Has Posthog Request Timestamp	✅	510ms
Required Headers.Has User Agent	✅	510ms
Body Format.Body Has Created At And Batch	✅	510ms
Body Format.No Api Key In Body	✅	511ms
Body Format.No Sent At In Body	✅	510ms
Event Format.Event Has Required Root Fields	✅	510ms
Event Format.Event Uuid Is Valid	✅	511ms
Event Format.Event Timestamp Is Rfc3339	✅	511ms
Event Format.Distinct Id Is String	✅	510ms
Event Format.Distinct Id At Root Not Properties	✅	511ms
Event Format.Custom Properties Preserved	✅	510ms
Event Format.Set Properties Preserved	✅	510ms
Event Format.Set Once Properties Preserved	✅	511ms
Event Format.Groups Properties Preserved	✅	510ms
Event Format.Sdk Generates Uuid If Not Provided	✅	511ms
Event Format.Event Has Required Root Fields Batch	✅	514ms
Event Format.Event Uuid Is Valid Batch	✅	514ms
Event Format.Event Timestamp Is Rfc3339 Batch	✅	514ms
Event Format.Distinct Id Is String Batch	✅	514ms
Event Format.Distinct Id At Root Not Properties Batch	✅	514ms
Event Format.Custom Properties Preserved Batch	✅	515ms
Event Format.Set Properties Preserved Batch	✅	515ms
Event Format.Set Once Properties Preserved Batch	✅	514ms
Event Format.Groups Properties Preserved Batch	✅	514ms
Event Format.Sdk Generates Uuid If Not Provided Batch	✅	514ms
Batch Behavior.Multiple Events In Single Batch	✅	518ms
Batch Behavior.Batch Envelope Smoke	✅	516ms
Batch Behavior.Flush With No Events Sends Nothing	✅	506ms
Batch Behavior.Flush At Triggers Batch	✅	1012ms
Batch Behavior.Created At Reflects Batch Creation Time	✅	511ms
Deduplication.Generates Unique Uuids	✅	518ms
Deduplication.Different Events Same Content Different Uuids	✅	512ms
Deduplication.Preserves Uuid On Retry	✅	6519ms
Deduplication.Preserves Timestamp On Retry	✅	6520ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	6519ms
Deduplication.No Duplicate Events In Batch	✅	519ms
Header Behavior On Retry.Attempt Header Starts At One	✅	511ms
Header Behavior On Retry.Attempt Header Increments On Retry	✅	13529ms
Header Behavior On Retry.Request Id Preserved On Retry	✅	6517ms
Header Behavior On Retry.Different Requests Have Different Request Ids	✅	3020ms
Header Behavior On Retry.Request Timestamp Changes On Retry	✅	6519ms
Response Format Validation.Success Response Has Uuid Keyed Results	✅	512ms
Response Format Validation.Success Response Has Ok For Each Event	✅	515ms
Response Format Validation.Success No Retry After When All Ok	✅	513ms
Response Format Validation.Success Retry After Present When Retry Events	✅	1516ms
Response Format Validation.Success No Retry After When Drop Only	✅	513ms
Response Format Validation.Response Echoes Request Id	✅	510ms
Retry Behavior.Retries On 408	✅	6515ms
Retry Behavior.Retries On 500	✅	6520ms
Retry Behavior.Retries On 503	✅	8524ms
Retry Behavior.Retries On 504	✅	6520ms
Retry Behavior.Retryable Errors Have Retry After	✅	3515ms
Retry Behavior.Respects Retry After On Retryable Error	✅	11523ms
Retry Behavior.Does Not Retry On 400	✅	2512ms
Retry Behavior.Does Not Retry On 401	✅	2514ms
Retry Behavior.Does Not Retry On 402	✅	2513ms
Retry Behavior.Does Not Retry On 413	✅	2514ms
Retry Behavior.Does Not Retry On 415	✅	2513ms
Retry Behavior.Non Retryable Errors Have No Retry After	✅	2514ms
Retry Behavior.Implements Backoff	✅	22526ms
Retry Behavior.Max Retries Respected	✅	22536ms
Partial Batch Handling.Handles 200 Full Success	✅	2514ms
Partial Batch Handling.Handles 200 With All Ok	✅	3516ms
Partial Batch Handling.Does Not Retry Dropped Events	✅	3516ms
Partial Batch Handling.Does Not Retry Limited Events	✅	3516ms
Partial Batch Handling.Prunes Ok Events On Partial Retry	✅	6522ms
Partial Batch Handling.Prunes Dropped Events On Partial Retry	✅	6518ms
Partial Batch Handling.Retries Only Retry Events From Partial	✅	6523ms
Partial Batch Handling.Partial Retry Preserves Uuids	✅	6522ms
Partial Batch Handling.Partial Retry Attempt Header Increments	✅	6517ms
Partial Batch Handling.Partial Retry Request Id Preserved	✅	6522ms
Partial Batch Handling.Respects Retry After On Partial	✅	8521ms
Partial Batch Handling.Unknown Result Treated As Terminal	✅	3517ms
Partial Batch Handling.Mixed Ok Drop Limited No Retry	✅	3517ms
Compression.Sends Gzip Content Encoding	✅	517ms
Compression.No Content Encoding When Disabled	✅	511ms
Compression.Compressed Body Is Decompressible	✅	510ms
Error Handling.Does Not Retry On Unknown 4Xx	✅	2513ms
Event Options.Cookieless Mode Override	✅	511ms
Event Options.Disable Skew Correction Override	✅	510ms
Event Options.Process Person Profile Override	✅	511ms
Event Options.Product Tour Id Override	✅	510ms
Event Options.Unset Options Omitted	✅	511ms
Event Options.Options Override In Batch	✅	513ms
Geoip And Historical Migration.Geoip Disable Injected Into Properties	✅	511ms
Geoip And Historical Migration.Historical Migration Set In Body	✅	510ms
Geoip And Historical Migration.Historical Migration Absent By Default	✅	510ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	12ms
Request Payload.Flags Request Uses V2 Query Param	✅	9ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	9ms
Request Payload.Flags Request Omits Authorization Header	✅	9ms
Request Payload.Token In Flags Body Matches Init	✅	10ms
Request Payload.Groups Round Trip	✅	10ms
Request Payload.Groups Default To Empty Object	✅	10ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	9ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	9ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	10ms
Request Lifecycle.No Flags Request On Init Alone	✅	3ms
Request Lifecycle.No Flags Request On Normal Capture	✅	510ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	14ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	9ms
Retry Behavior.Retries Flags On 502	✅	313ms
Retry Behavior.Retries Flags On 504	✅	313ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	512ms

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: preserve event delivery with gevent..." | Re-trigger Greptile}

[posthog]

🦔 ReviewHog reviewed this pull request

Found 1 must fix, 0 should fix, 0 consider.

Published 1 finding (view the review).

[posthog]

ReviewHog Alpha 🦔 If you find any issues helpful - please reply "valid", "invalid", etc., for evaluation purposes 🙏

[posthog]

ReviewHog Report

Changes

Issues: 1 issue

Files (5)

• .sampo/changesets/gevent-queue-compat.md
• examples/gevent_gunicorn.py
• posthog/_disabled_lane_queue.py
• posthog/client.py
• pyproject.toml