Make realtime sideband startup async#20715
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This was referenced May 2, 2026
Move the WebRTC sideband websocket connect out of the start critical path. The call-create request still returns the SDP answer synchronously, while the sideband input task connects in the background and uses the existing input channels to queue text, handoff output, and audio until the websocket is ready. Add coverage that a delayed sideband accepts queued text after the SDP answer has already been emitted. Co-authored-by: Codex <noreply@openai.com>
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kmeelu-oai
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May 4, 2026
| .await | ||
| .map_err(map_api_error)?; | ||
| (connection, Some(call.sdp)) | ||
| let task = spawn_webrtc_sideband_input_task(RealtimeWebrtcSidebandInputTask { |
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This now also runs run_realtime_input_task, as you'll see below. We can alternatively make that clearer by running a spawn_webrtc_sideband_and_realtime_input_tasks and chain them (we could even put that logic here, if desired).
kmeelu-oai
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May 4, 2026
| event_parser, | ||
| } = input; | ||
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| tokio::spawn(async move { |
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big diff hides the fact that we're just putting this within spawn_realtime_input_task, which calls tokio::spawn.
kmeelu-oai
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May 4, 2026
| } | ||
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| let connection = match client | ||
| .connect_webrtc_sideband( |
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fyi: defaults to 4 retries.
Wait for the sideband outbound request before asserting on the recorded handshake so async sideband startup cannot race the test on musl. Co-authored-by: Codex <noreply@openai.com>
aibrahim-oai
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May 4, 2026
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Summary
Moves the WebRTC realtime sideband websocket join out of the voice start critical path. Call creation still posts the SDP offer and session config synchronously so the client gets the SDP answer, but the sideband websocket now connects in the input task async and doesn't block conversation state installation.
This lets the normal realtime input channels buffer text, handoff output, and audio while the WebRTC sideband websocket is connecting. If the sideband join fails while the conversation is still active, the task sends a RealtimeEvent::Error through the existing events_tx / fanout path.
To rephrase this:
Validation
env CODEX_SKIP_VENDORED_BWRAP=1 cargo test --manifest-path codex-rs/Cargo.toml -p codex-core --test all conversation_webrtc_start_posts_generated_sessionCODEX_SKIP_VENDORED_BWRAP=1is needed in this local environment becauselibcap.pcis not installed for the vendored bubblewrap build.Testing
I tested this locally by running
cargo run -p codex-cli --bin codex -- --enable realtime_conversationand invoking/realtime. Then, we get logs emitted in~/.codex/log/codex-tui.log.Before the Change
Logging commit (c0299e6)
After the Change
Logging commit (c8b00ac)
Conclusion
Here we see that we saved about a half a second in conversation startup (1532ms -> 969ms). This also checks out with my sanity tests; I was seeing at most a second of saving.