feat(cli): configure the number of runtime worker threads - #111
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The worker count of the binary's async runtime, and so how many CPU cores the proxy keeps busy, could only be set through TOKIO_WORKER_THREADS. It is now `runtime.worker_threads` in the config file: - The binary loads the config synchronously, then builds a multi-thread runtime with the configured count, or tokio's default (the variable, else the available parallelism) when the key is unset, and runs the proxy on it. - The count must be a positive integer, and `runtime:` rejects unknown keys; either failure stops startup with an error naming the key. A bad TOKIO_WORKER_THREADS is refused by name instead of panicking in tokio. - The startup log states the count and where it came from. - The library lists `runtime` among its known top-level keys, so a file written for the binary loads without a warning; it does not read it. - README and packaging/config.yaml document the key. Closes #97
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📝 SummarySummary by CodeRabbit
WalkthroughThe standalone CLI now selects its Tokio worker count from configuration, the environment, or available parallelism. It builds and logs the runtime before serving. The shared configuration parser recognizes the ChangesStandalone runtime worker configuration
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant ConfigFile
participant CLI
participant RuntimeConfig
participant TokioRuntime
participant ProxyServer
ConfigFile->>CLI: YAML settings
CLI->>RuntimeConfig: Parse runtime section
RuntimeConfig->>TokioRuntime: Build with selected worker count
CLI->>ProxyServer: Load proxy configuration
CLI->>TokioRuntime: Run server.serve()
TokioRuntime->>ProxyServer: Execute server future
Merge Risk: 🔵 Low · up to The remaining risks are limited to a test failure when parallelism cannot be detected and an abnormal worker count that can terminate startup without a useful error. The PR is mergeable with those edge cases understood or corrected. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The new worker setting is controlled by the proxy's configuration or process environment, not by requests. Invalid values stop startup before the proxy serves traffic. A very large valid setting could still disrupt startup or exhaust resources; its impact depends on deployment limits. Retained concerns
Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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- An explicit `runtime.worker_threads: null` or empty value was taken for a left-out key, so a config mistake silently fell back to tokio's default. A present key must now hold a positive integer; only an absent one falls back. - The runtime tests set and removed TOKIO_WORKER_THREADS, a process-wide variable, so tests running in parallel in one process could read each other's value. The count is now computed by build_with from the variable's value, which build reads once; the tests pass values to it and leave the environment alone. With neither the key nor the variable the available parallelism is set explicitly, as tokio would. Regression test: an_invalid_worker_count_names_the_key (null, ~, empty) Part of #97
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Actionable comments posted: 2
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Inline comments:
In @cli/src/runtime.rs:
- Around line 115-118: In RuntimeConfig::build_with, reject worker counts
greater than usize::MAX minus Tokio’s default blocking-thread limit of 512
before constructing the multi-thread runtime. Include the selected source key in
the rejection error: runtime.worker_threads for YAML values or
TOKIO_WORKER_THREADS for environment values.
In @cli/src/runtime/tests.rs:
- Around line 33-34: Update the parallelism expectation in the runtime test to
handle `available_parallelism()` failure using the same one-worker fallback as
`build_with(None)`, rather than unwrapping the result. Keep the assertion
against `rt.metrics().num_workers()` so it checks the builder’s selected worker
count.
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README.mdcli/Cargo.tomlcli/src/main.rscli/src/runtime.rscli/src/runtime/tests.rscli/tests/cli.rspackaging/config.yamlsrc/config.rssrc/config/tests.rs
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tokio adds the blocking-thread limit to the worker count unchecked, so a count near usize::MAX from runtime.worker_threads or TOKIO_WORKER_THREADS panicked inside tokio's builder. The limit (tokio's default of 512) is now set explicitly and a count whose sum with it overflows is refused with the name of its source. A regression test covers both sources. The available-parallelism test expects the same one-worker fallback as the builder instead of unwrapping the query.
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Summary
The worker count of the standalone binary's async runtime, and so how many CPU cores the proxy keeps busy, is set in the config file:
TOKIO_WORKER_THREADSelse the available parallelism, when unset) and runs the proxy on it. The startup log states the count and its source.worker_threadsmust be a positive integer andruntime:rejects unknown keys; each failure stops startup with an error naming the key. An invalidTOKIO_WORKER_THREADS, or a worker count so large that tokio's thread limit (workers plus the 512 blocking threads, now set explicitly) would overflow, is refused by the name of its source rather than panicking inside tokio.runtimeas a known top-level key, so a file written for the binary loads throughProxyServer::from_yaml_strwithout a warning. It gains no runtime code and no dependency.packaging/config.yamldocument the key.Testing
fmt, clippy with
-D warnings, the test suite (including runtime tests that check the started worker count through the runtime metrics and CLI tests that run the built binary), doc tests andcargo publish --dry-run --workspacepass.Closes #97