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perf(windows): remove the dedicated PTY input forwarding thread - #4850
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📝 WalkthroughWalkthroughThe Windows PTY input forwarder now runs as a Tokio task. It awaits writer acknowledgements and uses a Tokio timer between text and Enter writes. Shutdown waits for pending Enter completion before disabling input and sending the shutdown command. Tests cover asynchronous sequencing, shutdown waiting, and failure or disconnection cases. Suggested reviewers: Priority: ➖ Normal Merge Risk: 🟡 Moderate · up to If a child stops reading PTY input, closing its pane can hang. Provide a way to unblock the writer while preserving committed Enter handling before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The inspected changes preserve existing input controls and do not establish a new security weakness. Behavior during runtime interruption and prolonged Windows I/O stalls is not fully demonstrated. Retained concerns Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
Resilience and Maintainability Implications
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @src/pty/actor.rs:
- Around line 187-197: Update shutdown so it takes enter_completion and sets
accepting.accepting to false while holding the acceptance mutex, then releases
the mutex before waiting. Add a bounded cancellation path that unblocks
run_writer and resolves the taken completion before waiting on it; do not rely
on recv_timeout alone. Preserve the completion wait before sending
PtyIoControlCommand::Shutdown.
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src/pty/actor.rs
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@coderabbitai review |
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Windows keeps a dedicated input-forwarding OS thread for every PTY actor. Move input receive, writer acknowledgement, and submission delay onto the existing Tokio runtime, removing one OS thread per live actor.
Preserve text → Enter → subsequent input ordering, completion after flush, terminal-response interleaving, expired queued-submission rejection, and committed Enter after caller timeout/disconnection. Shutdown still waits synchronously for an already queued Enter to finish flushing or fail before the pane terminates its child.
Before/after performance
Three paired runs at each actor count, fixed 80×24 geometry, system ConPTY and owned
cmd.exe /d /qchildren. Process measurements cover the isolated actor harness and exclude child processes. OS thread additions are relative to the harness before actors start; private memory is total harness private memory. Each idle CPU sample lasts five seconds.Memory and CPU values are medians of three runs. The primary improvement is one fewer OS thread per actor. No measurable idle CPU gain was demonstrated. The measured memory difference applies to this isolated harness; production savings have not been measured.
Input latency measures queueing zero-delay text + Enter through writer flush acknowledgement. Each row covers three runs × 300 submissions (900 samples). Reported median and p99 are medians of the three per-run values. Contention uses two Tokio workers with 16 cooperative tasks doing bounded 100µs work slices before yielding; ordinary runs use the same two workers without contenders.
Contended median latency increased by 0.119ms / 0.241ms. Measured tail stalls stayed comparable, but baseline runs were noisy and async forwarding now depends on Tokio scheduling. These samples support the footprint change; they do not establish a production throughput or CPU improvement. The harness excludes rendering, detection, the pane child waiter, and the agent prompt's normal 300ms delay. The user's running server and configuration were untouched.
Residual limitation: shutdown still waits for committed blocking Enter I/O to return. The base already enforced this by holding the acceptance mutex through the writer acknowledgement. This change preserves that boundary; bounded native-writer cancellation requires separate design and validation.
Validation
just test-one 'pty::actor::windows::tests': all seven actor tests passed.just check: formatting/clippy, 3,338 Rust tests, 150 maintenance tests, architecture/integration/docs suites, and debug build passed; commitjust linthook passed.--mode fast,rvw_9c55ac62: both reviewers returned no findings; local review green.a6b045fda63bdd0d2df9817a973dae3dffa24de0. Shutdown findings were verified against the base and resolved; CodeRabbit withdrew its finding. Review Suite validation is complete.