[AdityaSreevatsaK]

Summary

Fixes #1300.

Under concurrent HTTP/2 requests, a response can remain undelivered even after its events have been received and queued. Another stream may acquire the shared read lock and block on a subsequent network read, delaying an already-completed response.

Changes

• Introduce per-connection read-completion notifications, allowing waiting streams to process queued events without acquiring the read lock.
• Preserve single-reader coordination and recheck queued responses and flow-control availability before additional reads.
• Update both synchronous and asynchronous implementations.
• Add deterministic regression tests covering asyncio, Trio and readiness races.

Testing

Full test suite passed: Python 3.11–3.15.

• Ruff, mypy, packaging and documentation checks passed.
• 100% test coverage achieved.
• Generated synchronous/asynchronous code consistency verified.
• Security analysis passed.
• CodSpeed benchmarks executed, but results could not be uploaded because of fork-specific 401 authorisation.

CI: https://github.com/AdityaSreevatsaK/httpx2/actions/runs/43293561851

Security: https://github.com/AdityaSreevatsaK/httpx2/actions/runs/43293561652

Related work

PR #1298 refactors HTTP/2 stream ownership and modifies overlapping code. This change focuses specifically on coordinating network reads and waking streams with queued events.

The implementation has been prepared separately to allow review and integration with the ongoing HTTP/2 work.

Checklist

• Discussed the issue and proposed approach in HTTP/2: a received response waits until more data arrives on the connection #1300.
• Added regression tests for the fix.
• Verified the complete test suite and coverage.
• Kept the change focused without modifying public APIs.

Documentation was not changed because the fix corrects internal scheduling behaviour.

Prepared with AI assistance. The changes and test results have been reviewed.

[veria-ai]

PR overview

No security issues were found in this pull request.

Reviews

• d5e90b5 — No new issues
• f86b821 — No new issues

[codspeed]

Merging this PR will not alter performance

✅ 18 untouched benchmarks
⏩ 7 skipped benchmarks¹

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_{Comparing AdityaSreevatsaK:fix/http2-read-starvation-1300-ready (d5e90b5) with main (f4f65c1)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

1 issue found across 5 files

<sub>Reply with feedback, questions, or to request a fix.

View guided diff | Re-trigger cubic</sub>

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="tests/httpcore2/test_http2_read_dispatch.py">

<violation number="1" location="tests/httpcore2/test_http2_read_dispatch.py:53">
P3: This comment describes the old read-lock queueing, but waiting streams now block on the `_read_event` completion event, not `_read_lock`. Update it to match the mechanism the test relies on.</violation>
</file>