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The V8 platform currently creates the configured worker threads and a dedicated libuv loop for delayed tasks during Node.js bootstrap, then waits for those workers to become ready. Short-lived processes often never post background work, so this wastes startup time and RSS. Start workers as tasks are posted, up to the configured pool size, and create the delayed-task loop only when a delayed task is first scheduled. NumberOfWorkerThreads() now reports the configured size instead of the number of already-started threads (which previously included the scheduler thread). Assisted-by: Cursor Grok 4.6 Co-authored-by: Yagiz Nizipli <anonrig@users.noreply.github.com>
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Closing: A/B numbers show no startup, RSS, or thread-count win. V8 still starts the platform workers and delayed-task loop during isolate init. Will look for a change that actually moves those metrics. |
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This stops
NodePlatformfrom creating the V8 worker pool and the delayed-task libuv loop during bootstrap, then blocking until those workers are ready.Workers are started as tasks are posted, up to
--v8-pool-size. The delayed-task loop is started only when a delayed worker task is first scheduled.NumberOfWorkerThreads()now returns the configured pool size. It previously returnedstarted threads, which included the scheduler thread.V8 still posts compile and GC jobs during isolate initialization (
OptimizingCompileTaskExecutor, concurrent baseline/maglev, scavenger,MemoryPool::PostDelayedReleaseTask). A defaultnode -eprocess therefore still ends up with 4node-V8Workerthreads plusDelayedTaskSchedulerWorker. The libuv FS/DNS/crypto pool (UV_THREADPOOL_SIZE) is unchanged.Benchmarks
A/B on the same machine, same
configureflags (--ninja --without-intl --without-npm --without-node-snapshot --without-node-code-cache --v8-disable-temporal-support). Onlysrc/node_platform.{cc,h}differs. Snapshot-less startup is slower than a production build; the comparison is relative.benchmark/misc/startup-core.js(ops/sec, higher is better)empty.mjsmode=processn=30semicolon.jsmode=processn=30require-builtins.jsmode=processn=30Wall-clock spawn (n=40, warmup=5, lower is better)
benchmark/fixtures/empty.mjstest/fixtures/semicolon.jsnode -e ''Threads and RSS after user JS starts (
/proc/self/status)node-MainThread, 4×node-V8Worker,DelayedTaskSchedulerWorker,SignalInspectorStartup and RSS are within noise. Steady-state thread count is unchanged because V8 posts platform jobs during isolate init. The remaining effects are: no constructor barrier, on-demand creation for embedders that do not immediately initialize an isolate, and a correct worker-count for
CreateJob.Tests
cctest --gtest_filter=PlatformTest.Lazy*passedtest/parallel/test-v8-platform-lazy-workers.jspassedtest/parallel/test-v8-flag-pool-size-0.jspassed