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* arc(01KK7524KNGTPS4090QMF87FJN): implement (success) Arc-Run: 01KK7524KNGTPS4090QMF87FJN Arc-Completed: 2 Arc-Checkpoint: 1ff03c704805dfe8e7c37b37f97bd06dfa0e5dc5 * Fix: restore trailing newlines stripped by previous commit * arc(01KK7524KNGTPS4090QMF87FJN): simplify (success) Arc-Run: 01KK7524KNGTPS4090QMF87FJN Arc-Completed: 3 Arc-Checkpoint: 21771adfd26283a1d1e6b8a123a83a0c4277db48 --------- Co-authored-by: arc <arc@local> Co-authored-by: Arc Assistant <assistant@arc.dev> Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
119 lines
4.3 KiB
Text
119 lines
4.3 KiB
Text
---
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title: "Parallel Review"
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description: "Fan-out, fan-in, join policies, and merge nodes"
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---
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This tutorial runs three code review perspectives in parallel — security, architecture, and quality — then merges the results into a single report.
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## The workflow
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<Frame>
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<img src="/images/tutorial-parallel-review.svg" alt="Parallel Review workflow: Start → Fan Out → Security Audit, Architecture Review, Code Quality → Merge → Final Report → Exit" />
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</Frame>
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```dot title="parallel.dot"
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digraph Parallel {
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graph [goal="Perform a multi-perspective code review"]
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rankdir=LR
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start [shape=Mdiamond, label="Start"]
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exit [shape=Msquare, label="Exit"]
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fork [label="Fork Analysis", shape=component, join_policy="wait_all", error_policy="continue"]
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security [label="Security Audit", prompt="Examine the codebase for security concerns: hardcoded secrets, injection risks, unsafe dependencies. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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architecture [label="Architecture Review", prompt="Assess the codebase architecture: separation of concerns, dependency structure, modularity. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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quality [label="Code Quality", prompt="Check code quality: naming conventions, dead code, test coverage gaps, error handling. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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merge [label="Merge Findings", shape=tripleoctagon]
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report [label="Final Report", prompt="Synthesize the security, architecture, and code quality findings into a prioritized summary report with top 5 action items.", shape=tab]
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start -> fork
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fork -> security
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fork -> architecture
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fork -> quality
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security -> merge
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architecture -> merge
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quality -> merge
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merge -> report -> exit
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}
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```
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```bash
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arc run demo/06-parallel.dot
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```
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## Fan-out with the fork node
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The `fork` node has `shape=component`, making it a **parallel fan-out node**. Every outgoing edge becomes a concurrent branch:
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```dot
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fork [label="Fork Analysis", shape=component, join_policy="wait_all", error_policy="continue"]
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fork -> security
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fork -> architecture
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fork -> quality
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```
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All three branches start at the same time. Each gets an isolated copy of the run context, so branches can't interfere with each other.
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### Join policies
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The `join_policy` controls when execution can proceed past the merge:
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| Policy | Behavior |
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|---|---|
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| `wait_all` | Wait for every branch to finish (default) |
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| `first_success` | Proceed as soon as one branch succeeds |
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| `k_of_n(N)` | Proceed after N branches succeed |
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| `quorum(0.5)` | Proceed after a fraction of branches succeed |
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### Error policies
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The `error_policy` controls what happens when a branch fails:
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| Policy | Behavior |
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|---|---|
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| `continue` | Run all branches even if some fail (default) |
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| `fail_fast` | Cancel remaining branches as soon as one fails |
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| `ignore` | Treat all branch failures as successes |
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This workflow uses `error_policy="continue"` so that a failure in one review perspective doesn't cancel the others.
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## Fan-in with the merge node
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The `merge` node has `shape=tripleoctagon`, making it a **merge (fan-in) node**. It collects results from all branches into a single context:
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```dot
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merge [label="Merge Findings", shape=tripleoctagon]
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security -> merge
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architecture -> merge
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quality -> merge
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```
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The merged branch results are available to downstream nodes. The `report` node receives all three perspectives in its preamble and synthesizes them.
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## Concurrency control
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By default, Arc runs up to 4 parallel branches simultaneously. Control this with `max_parallel`:
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```dot
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fork [shape=component, max_parallel=2]
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```
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This is useful when branches are resource-intensive (e.g., each running a full agent session with tool calls) and you want to limit concurrency.
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## What you've learned
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- **Fan-out nodes** (`shape=component`) spawn concurrent branches
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- **Merge nodes** (`shape=tripleoctagon`) collect branch results
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- **Join policies** control when execution can proceed past the merge
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- **Error policies** control how branch failures are handled
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- Each branch gets an isolated copy of the context
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## Next
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<Card title="Multi-Model Routing" icon="arrow-right" href="/tutorials/multi-model">
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Assign different models to different workflow nodes using stylesheets.
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</Card>
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