[takeokunn]

Relation to the HTTP/2 scheduler in PR #13

PR #13 adds an HTTP/2 connection mutex around stream setup and elects one caller to pump inbound frames. The native HTTP/3 scheduler uses a single-owner pump as well: the first request caller becomes the owner, and other callers enqueue and wait. QUIC assigns HTTP/3 stream IDs, so this scheduler does not reserve stream IDs under the HTTP/2 connection mutex.

The owner runs the connection loop synchronously until its request is complete and both the pending queue and active-stream table are empty. It opens pending streams, polls QUIC, services critical control and QPACK streams, and advances active request streams round-robin while respecting pending writes. Body and response callbacks run inline on the owner. A request submitted reentrantly from a callback is rejected.

The owner loop serializes scheduler-owned request QPACK preparation, HEADERS writing, and encoder commit. make-http3-client's :serialize callback defaults to invoking its thunk directly without a lock. Callers that mutate public QPACK state concurrently outside the owner loop must supply a :serialize callback that provides their synchronization.

Native scheduler callbacks and close behavior

Native scheduler operation requires poll-function, try-read-stream, and stream-write-pending-p together. try-write-stream is optional: when present, the scheduler uses it to submit request frames without waiting; when absent, it falls back to write-stream. Other synchronous operations continue to use write-stream.

close-http3-client closes HTTP/3 streams and stops the HTTP/3 scheduler, but leaves the underlying QUIC connection open. close-http3-quic-adapter closes HTTP/3 streams and then closes QUIC. Both return true after successful or already-completed close; a reentrant close by the close owner returns nil. If both HTTP/3 cleanup and QUIC close fail, close-http3-quic-adapter raises the HTTP/3 cleanup error and warns about the QUIC error. If only HTTP/3 cleanup fails and QUIC close succeeds, it raises the cleanup error. If only QUIC close fails, it raises the QUIC error.

Dependency pins

The root pins cl-crypto-kit at 761e9592 as a flake input so the updated cl-quic-kit input can follow the root crypto dependency. The cl-quic-kit pin advances to 46bfeacc for its public client-receive-frames(client, level, packet-number, frames) API, which lets tests supply frame batches at a selected packet number.

Scheduler test coverage

Scheduler tests exercise concurrent progress while one request streams a large upload; ownership handoff after the owner caller's deadline, unwind, interruption, and request error; QPACK-blocked request resumption; close waking all waiters with one condition; QUIC close failure preservation; and discovery of peer control and QPACK streams that arrive after setup. The late-stream test uses the optional accept-peer-unidirectional-stream callback supplied to make-http3-client.

Protocol-boundary tests verify that a response stream is not read while its QPACK section is blocked, duplicate control streams close QUIC while request-stream errors remain isolated, peer stream-count and prefix-byte limits apply before retention, and the public scheduler emits the dynamic-QPACK field section and encoder instructions.

The response-preservation test injects STOP_SENDING(H3_NO_ERROR) during a streaming request and verifies that the complete response is returned and further request writes stop.

Scheduler portability

The scheduler mutex and condition variable are available only under SBCL. Non-SBCL builds use no-op lock and wait wrappers, so concurrent callers are not serialized there. Scheduler concurrency tests use SBCL threads.