Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail | AgentRules.org

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backendcritical PriorityID: go124-iter-pull-resource-disposal

Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail

Go 1.24 pull iterators (iter.Pull and iter.Pull2) allocate underlying coroutine runtime machinery to transform push iterators into stateful pull closures. Failure to invoke the returned stop function when execution terminates before sequence exhaustion permanently leaks the runtime goroutine and pinned stack allocations. All pull iterators must enforce an immediate defer-stop contract across all error, early exit, and panic paths.

Prohibited Anti-Pattern: Dangling iter.Pull Coroutines Leaking Background Goroutines on Early Exit

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---
description: Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail - Go 1.24 pull iterators (iter.Pull and iter.Pull2) allocate underlying coroutine runtime machinery to transform push iterators into stateful pull closures. Failure to invoke the returned stop function when execution terminates before sequence exhaustion permanently leaks the runtime goroutine and pinned stack allocations. All pull iterators must enforce an immediate defer-stop contract across all error, early exit, and panic paths.
globs: **/*.go
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/go124-iter-pull-resource-disposal"
---

# Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail

> **Severity**: CRITICAL | **Category**: backend
> **Anti-Pattern Warning**: Dangling iter.Pull Coroutines Leaking Background Goroutines on Early Exit

## System Constraints
You are a Principal Go Systems Architect enforcing strict concurrency boundaries and memory safety for Go 1.24 iterators. Mandate explicit defer-stop contracts on iter.Pull and iter.Pull2 conversions to eliminate coroutine goroutine leaks across concurrent data stream boundaries. Reject any code where iter.Pull or iter.Pull2 is called without an immediate defer stop() or strictly owned lifecycle manager.

## Strict Guidelines
- Engineers MUST ALWAYS invoke `defer stop()` immediately following the assignment of `(next, stop)` closures from `iter.Pull` or `iter.Pull2`.
- Engineers MUST NOT rely on iterator exhaustion (`ok == false`) as the sole resource cleanup mechanism, as early returns, context cancellations, or panics bypass exhaustion and leak the coroutine.
- Code SHOULD encapsulate pull iterator consumption within a dedicated lexical function scope whenever deferring `stop()` within a long-lived parent loop would delay resource reclamation.
- Services MUST NOT share `next` closures across concurrent goroutines; pull iterators are non-reentrant and statefully bound to a single calling sequence.
- Components NEVER discard the `stop` closure returned by `iter.Pull` using the blank identifier (`_`).

## Bad vs Good Implementations
### Streaming Log Processor with iter.Pull Resource Guard

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: iter.Pull constructs a coroutine backed by a runtime goroutine. Discarding `stop` and returning early when `val > threshold` leaves that goroutine permanently blocked waiting for the next pull, leaking stack memory and runtime resources.
```go
package stream

import (
	"context"
	"errors"
	"iter"
)

// Bad: Omitting defer stop() leaks the coroutine goroutine if an early error occurs
// or if the loop terminates before the stream finishes.
func MatchFirstThreshold(ctx context.Context, seq iter.Seq[int], threshold int) (int, error) {
	next, _ := iter.Pull(seq) // VIOLATION: Discarding stop closure causes permanent goroutine leak

	for {
		val, ok := next()
		if !ok {
			return 0, errors.New("not found")
		}
		if val > threshold {
			// Goroutine created by iter.Pull is now leaked forever
			return val, nil
		}
	}
}
```

#### Production Standard (Correct)
> **Standard**: Invoking `defer stop()` ensures that when `val > threshold` triggers an early return or when `ctx.Done()` cancels execution, the coroutine is cleanly interrupted and destroyed by the Go runtime, preventing goroutine leaks.
```go
package stream

import (
	"context"
	"errors"
	"iter"
)

// Good: Immediate defer stop() enforces deterministic cleanup across all control flows.
func MatchFirstThreshold(ctx context.Context, seq iter.Seq[int], threshold int) (int, error) {
	next, stop := iter.Pull(seq)
	defer stop() // INVARIANT: Guaranteed coroutine termination regardless of early exit or panic

	for {
		select {
		case <-ctx.Done():
			return 0, ctx.Err()
		default:
		}

		val, ok := next()
		if !ok {
			return 0, errors.New("not found")
		}
		if val > threshold {
			return val, nil
		}
	}
}
```

Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

GolangCI-Lint MCP Server

Executes static analysis and custom Go AST linters to detect unhandled iter.Pull return values.

Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

Go Language Server CLI

Performs diagnostic checks, type validation, and symbol lifecycle tracing for Go 1.24 iterators.

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail

Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail defines an industrial-grade behavioral standard for backend engineering. Go 1.24 pull iterators (iter.Pull and iter.Pull2) allocate underlying coroutine runtime machinery to transform push iterators into stateful pull closures. Failure to invoke the returned stop function when execution terminates before sequence exhaustion permanently leaks the runtime goroutine and pinned stack allocations. All pull iterators must enforce an immediate defer-stop contract across all error, early exit, and panic paths. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Dangling iter.Pull Coroutines Leaking Background Goroutines on Early Exit Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Dangling iter.Pull Coroutines Leaking Background Goroutines on Early Exit	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS invoke `defer stop()` immediately following the assignment of `(next, stop)` closures from `iter.Pull` or `iter.Pull2`.

Engineers MUST ALWAYS invoke `defer stop()` immediately following the assignment of `(next, stop)` closures from `iter.Pull` or `iter.Pull2`.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

2

Engineers MUST NOT rely on iterator exhaustion (`ok == false`) as the sole resource cleanup mechanism, as early returns, context cancellations, or panics bypass exhaustion and leak the coroutine.

Engineers MUST NOT rely on iterator exhaustion (`ok == false`) as the sole resource cleanup mechanism, as early returns, context cancellations, or panics bypass exhaustion and leak the coroutine.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

3

Code SHOULD encapsulate pull iterator consumption within a dedicated lexical function scope whenever deferring `stop()` within a long-lived parent loop would delay resource reclamation.

Code SHOULD encapsulate pull iterator consumption within a dedicated lexical function scope whenever deferring `stop()` within a long-lived parent loop would delay resource reclamation.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

4

Services MUST NOT share `next` closures across concurrent goroutines

Services MUST NOT share `next` closures across concurrent goroutines; pull iterators are non-reentrant and statefully bound to a single calling sequence.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

5

Components NEVER discard the `stop` closure returned by `iter.Pull` using the blank identifier (`_`).

Components NEVER discard the `stop` closure returned by `iter.Pull` using the blank identifier (`_`).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.

Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.

Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Go 1.24 iter.Pull Explicit Defer-Stop Coroutine Lifecycle Guardrail critical for AI coding assistants?

Go 1.24 pull iterators (iter.Pull and iter.Pull2) allocate underlying coroutine runtime machinery to transform push iterators into stateful pull closures. Failure to invoke the returned stop function when execution terminates before sequence exhaustion permanently leaks the runtime goroutine and pinned stack allocations. All pull iterators must enforce an immediate defer-stop contract across all error, early exit, and panic paths. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Dangling iter.Pull Coroutines Leaking Background Goroutines on Early Exit) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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