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46 lines
1.6 KiB
Markdown
46 lines
1.6 KiB
Markdown
# Kata 10: The Worker Pool With Backpressure and Joined Errors
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**Target Idioms:** Worker Pools, Channel Ownership, `errors.Join`, Context Cancellation
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**Difficulty:** 🔴 Advanced
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## 🧠 The "Why"
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Many devs bring “thread pool” instincts and end up with:
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- goroutines that never exit,
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- unbounded queues,
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- “first error wins” even when you want a summary,
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- ad-hoc error channels without cleanup.
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This kata forces correctness: **bounded work**, **clean shutdown**, and **error aggregation**.
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## 🎯 The Scenario
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You process a stream of jobs (e.g., image resizing). You want:
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- fixed number of workers
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- bounded queue (backpressure)
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- either fail-fast OR collect all errors (configurable)
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## 🛠 The Challenge
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Implement:
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- `type Pool struct { ... }`
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- `Run(ctx context.Context, jobs <-chan Job) error`
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Where `Job` is `func(context.Context) error`.
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### 1. Functional Requirements
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- [ ] `N` workers process from `jobs`.
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- [ ] Optional `StopOnFirstError`.
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- [ ] If not fail-fast: return `errors.Join(errs...)` after draining.
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### 2. The "Idiomatic" Constraints (Pass/Fail Criteria)
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- [ ] **Must** use `errors.Join` for aggregation.
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- [ ] **Must** respect `ctx.Done()` (workers exit).
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- [ ] **Must** close internal channels from the sender side only.
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- [ ] **Must** guarantee no goroutine leak when `jobs` closes early or ctx cancels.
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## 🧪 Self-Correction (Test Yourself)
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- **If workers keep running after ctx cancel:** failed.
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- **If you can deadlock by closing channels from the wrong side:** failed.
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- **If you return before draining in non-fail-fast mode:** failed.
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## 📚 Resources
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- https://go.dev/doc/go1.20
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- https://go.dev/src/errors/join.go
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