Goroutines: Stack Growth, Scheduling Cost, and Preemption
Measure goroutine scheduling and stack memory, and test preemption with a negative control.
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What this chapter teaches
Goroutines are free. Spawn as many as you want — millions, one per request, one per item — it costs nothing.
a goroutine is a g struct plus a stack that starts at 2 KiB and grows by allocating a bigger stack and copying the old one. Creating one costs a few hundred nanoseconds; each live one holds its live stack memory (so 10k idle goroutines ≈ tens of MiB); and deep call chains can grow stacks, whose memory is accounted for separately from heap objects. Cheap enough to use freely, expensive enough that unbounded goroutine creation is a real resource leak — which is why runtime.NumGoroutine() belongs on your dashboards.
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