feat: daemon accept loop honours --max-connections admission cap#4042
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Wire `ConnectionCounter::active()` (previously `#[allow(dead_code)]`) into the accept loop. When `--max-connections N` is set and N worker guards are live, the next accepted socket is refused with `@ERROR: max connections (N) reached -- try again later\n` and dropped without spawning a thread, while the accept loop continues. upstream: clientserver.c:744-756 - `claim_connection()` emits the same wording for per-module caps via `io_printf(f_out, ...)`. Closes the daemon-scalability admission gap surfaced by the thread-per-connection audit at `docs/audits/daemon-thread-per-connection-1673.md`.
oferchen
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May 18, 2026
Wire `ConnectionCounter::active()` (previously `#[allow(dead_code)]`) into the accept loop. When `--max-connections N` is set and N worker guards are live, the next accepted socket is refused with `@ERROR: max connections (N) reached -- try again later\n` and dropped without spawning a thread, while the accept loop continues. upstream: clientserver.c:744-756 - `claim_connection()` emits the same wording for per-module caps via `io_printf(f_out, ...)`. Closes the daemon-scalability admission gap surfaced by the thread-per-connection audit at `docs/audits/daemon-thread-per-connection-1673.md`.
oferchen
added a commit
that referenced
this pull request
May 18, 2026
Wire `ConnectionCounter::active()` (previously `#[allow(dead_code)]`) into the accept loop. When `--max-connections N` is set and N worker guards are live, the next accepted socket is refused with `@ERROR: max connections (N) reached -- try again later\n` and dropped without spawning a thread, while the accept loop continues. upstream: clientserver.c:744-756 - `claim_connection()` emits the same wording for per-module caps via `io_printf(f_out, ...)`. Closes the daemon-scalability admission gap surfaced by the thread-per-connection audit at `docs/audits/daemon-thread-per-connection-1673.md`.
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Summary
ConnectionCounter::active()into the daemon accept loop so a configurable concurrent-connection ceiling is actually enforced; the helper previously carried#[allow(dead_code)]and was never consulted.--max-connections Nto the daemon CLI parser, with duplicate detection mirroring--max-sessions.@ERROR: max connections (N) reached -- try again later\n(matching upstreamclientserver.c:744-756byte for byte), the socket is dropped, no worker thread is spawned, and the accept loop continues serving future connections.--max-connectionsthe daemon behaves exactly as before.This implements task D1 from the daemon-scalability audit added in #4023 (
docs/audits/daemon-thread-per-connection-1673.md). Under high concurrency (10k+ conns) the daemon previously panicked withclone3: EAGAIN; with this change it gracefully refuses excess clients instead.Test plan
cargo fmt --allcrates/daemon/src/daemon/sections/server_runtime/tests.rs:accept_loop_refuses_when_at_capacity- two guards held, third connect receives the exact upstream wording and the counter is left at 2.accept_loop_recovers_after_disconnect- same setup, dropping one guard re-admits the next connect.refuse_if_at_capacity_admits_when_no_cap_configured- guard count is irrelevant when the cap is unset.crates/daemon/src/daemon/runtime_options/tests.rscover the option, zero/non-numeric rejection, and duplicate detection.--max-connectionsis unset).