Go 1.24 Weak Pointer Concurrent Cache Eviction Standard | AgentRules.org

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backendcritical PriorityID: go-124-weak-pointer-concurrent-cache-standard

Go 1.24 Weak Pointer Concurrent Cache Eviction Standard

Enforces deterministic memory reclamation in high-cardinality in-memory Go caches using Go 1.24 weak pointers (`weak.Pointer`) paired with finalizers or cleanups (`runtime.AddCleanup`). This architecture delegates unreferenced object eviction directly to the runtime garbage collector, completely eliminating memory leaks and cache-induced out-of-memory crashes without requiring stop-the-world eviction loops.

Prohibited Anti-Pattern: Hard Reference Key/Value Map Caches Causing Silent OOM and Phantom Memory Retention

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---
description: Go 1.24 Weak Pointer Concurrent Cache Eviction Standard - Enforces deterministic memory reclamation in high-cardinality in-memory Go caches using Go 1.24 weak pointers (`weak.Pointer`) paired with finalizers or cleanups (`runtime.AddCleanup`). This architecture delegates unreferenced object eviction directly to the runtime garbage collector, completely eliminating memory leaks and cache-induced out-of-memory crashes without requiring stop-the-world eviction loops.
globs: **/*.go
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/go-124-weak-pointer-concurrent-cache-standard"
---

# Go 1.24 Weak Pointer Concurrent Cache Eviction Standard

> **Severity**: CRITICAL | **Category**: backend
> **Anti-Pattern Warning**: Hard Reference Key/Value Map Caches Causing Silent OOM and Phantom Memory Retention

## System Constraints
You are a Principal Engineer and Runtime Architect enforcing Go 1.24's standard library `weak` package patterns for high-throughput concurrent in-memory caches. You must reject any high-cardinality cache that retains strong pointers inside long-lived hash maps or sync.Maps without bounded memory controls. Mandate `weak.Make` and `weak.Pointer.Value()` semantics, paired with `runtime.AddCleanup` to eliminate dead hash table buckets and break circular reference cycles.

## Strict Guidelines
- Engineers MUST ALWAYS utilize Go 1.24+ `weak.Make[T](ptr)` to store references in cache indexes where retention must depend strictly on external caller lifecycles.
- Engineers MUST ALWAYS verify that `wp.Value()` does not return `nil` before dereferencing cached entities to prevent runtime panic on GC-collected objects.
- Engineers MUST pair weak-pointer cache insertions with `runtime.AddCleanup` to deterministically purge dead keys from internal sharded maps when target entities are collected.
- Engineers MUST NOT retain strong pointers (`*T`) within cache metadata structures, lock maps, or cleanup closures, which would inadvertently keep the underlying object alive.
- Services MUST execute concurrent cache reads using read locks (`sync.RWMutex.RLock`) or atomic operations while resolving weak references to preserve low-latency execution paths.
- Components NEVER use `runtime.SetFinalizer` for cache housekeeping; `runtime.AddCleanup` MUST be preferred as it does not delay collection by an entire GC cycle or create cyclic retention hazards.

## Bad vs Good Implementations
### Weak Reference Cache vs. Leaking Strong Reference Cache

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Storing direct *Entity pointers in a persistent map prevents the Go garbage collector from ever freeing the entity, even if no other active goroutine or caller holds a reference to it. This leads to unbounded memory growth and eventually crashes the container.
```go
package cache

import "sync"

type Entity struct {
	ID   string
	Data []byte
}

// BadCache retains strong references; items stay in memory indefinitely
// unless manually evicted, causing runaway memory expansion and OOM.
type BadCache struct {
	mu    sync.RWMutex
	items map[string]*Entity
}

func (c *BadCache) Get(id string) *Entity {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.items[id]
}

func (c *BadCache) Set(id string, e *Entity) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.items[id] = e
}
```

#### Production Standard (Correct)
> **Standard**: Go 1.24's `weak.Make(e)` allows the GC to reclaim `e` as soon as external strong references vanish. `runtime.AddCleanup` takes `id` by value, avoiding closure capture of `e`, which safely removes dead map keys without blocking memory reclamation across GC cycles.
```go
package cache

import (
	"runtime"
	"sync"
	"weak"
)

type Entity struct {
	ID   string
	Data []byte
}

// GoodCache holds weak pointers; when outside references drop to zero,
// the runtime GC reclaims the entity and triggers automatic map key eviction.
type GoodCache struct {
	mu    sync.RWMutex
	items map[string]weak.Pointer[Entity]
}

func NewGoodCache() *GoodCache {
	return &GoodCache{
		items: make(map[string]weak.Pointer[Entity]),
	}
}

func (c *GoodCache) Get(id string) (*Entity, bool) {
	c.mu.RLock()
	wp, exists := c.items[id]
	c.mu.RUnlock()
	if !exists {
		return nil, false
	}

	val := wp.Value()
	if val == nil {
		// Object was collected; lazily clean up key
		c.mu.Lock()
		delete(c.items, id)
		c.mu.Unlock()
		return nil, false
	}
	return val, true
}

func (c *GoodCache) Set(id string, e *Entity) {
	c.mu.Lock()
	c.items[id] = weak.Make(e)
	c.mu.Unlock()

	// Register runtime cleanup without capturing *Entity inside the closure
	runtime.AddCleanup(e, func(cacheKey string) {
		c.mu.Lock()
		// Only delete if the pointer in the map is indeed stale/nil
		if wp, ok := c.items[cacheKey]; ok && wp.Value() == nil {
			delete(c.items, cacheKey)
		}
		c.mu.Unlock()
	}, id)
}
```

Recommended MCP Servers (mcp-serverlist.com)

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

Validates git revision history and branch diffs for Go version compatibility checks.

Recommended Agent Skills (askills.dev)

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

Go Vet and Static Analysis

Runs official Go toolchain static analyzers to identify incorrect lock handling and weak pointer usage.

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Go 1.24 Weak Pointer Concurrent Cache Eviction Standard

Go 1.24 Weak Pointer Concurrent Cache Eviction Standard defines an industrial-grade behavioral standard for backend engineering. Enforces deterministic memory reclamation in high-cardinality in-memory Go caches using Go 1.24 weak pointers (`weak.Pointer`) paired with finalizers or cleanups (`runtime.AddCleanup`). This architecture delegates unreferenced object eviction directly to the runtime garbage collector, completely eliminating memory leaks and cache-induced out-of-memory crashes without requiring stop-the-world eviction loops. 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: Hard Reference Key/Value Map Caches Causing Silent OOM and Phantom Memory Retention 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	Hard Reference Key/Value Map Caches Causing Silent OOM and Phantom Memory Retention	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 utilize Go 1.24+ `weak.Make[T](ptr)` to store references in cache indexes where retention must depend strictly on external caller lifecycles.

Engineers MUST ALWAYS utilize Go 1.24+ `weak.Make[T](ptr)` to store references in cache indexes where retention must depend strictly on external caller lifecycles.

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 ALWAYS verify that `wp.Value()` does not return `nil` before dereferencing cached entities to prevent runtime panic on GC-collected objects.

Engineers MUST ALWAYS verify that `wp.Value()` does not return `nil` before dereferencing cached entities to prevent runtime panic on GC-collected objects.

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

Engineers MUST pair weak-pointer cache insertions with `runtime.AddCleanup` to deterministically purge dead keys from internal sharded maps when target entities are collected.

Engineers MUST pair weak-pointer cache insertions with `runtime.AddCleanup` to deterministically purge dead keys from internal sharded maps when target entities are collected.

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

Engineers MUST NOT retain strong pointers (`*T`) within cache metadata structures, lock maps, or cleanup closures, which would inadvertently keep the underlying object alive.

Engineers MUST NOT retain strong pointers (`*T`) within cache metadata structures, lock maps, or cleanup closures, which would inadvertently keep the underlying object alive.

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

Services MUST execute concurrent cache reads using read locks (`sync.RWMutex.RLock`) or atomic operations while resolving weak references to preserve low-latency execution paths.

Services MUST execute concurrent cache reads using read locks (`sync.RWMutex.RLock`) or atomic operations while resolving weak references to preserve low-latency execution paths.

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.

6

Components NEVER use `runtime.SetFinalizer` for cache housekeeping

Components NEVER use `runtime.SetFinalizer` for cache housekeeping; `runtime.AddCleanup` MUST be preferred as it does not delay collection by an entire GC cycle or create cyclic retention hazards.

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 Weak Pointer Concurrent Cache Eviction Standard critical for AI coding assistants?

Enforces deterministic memory reclamation in high-cardinality in-memory Go caches using Go 1.24 weak pointers (`weak.Pointer`) paired with finalizers or cleanups (`runtime.AddCleanup`). This architecture delegates unreferenced object eviction directly to the runtime garbage collector, completely eliminating memory leaks and cache-induced out-of-memory crashes without requiring stop-the-world eviction loops. 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 (Hard Reference Key/Value Map Caches Causing Silent OOM and Phantom Memory Retention) 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.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

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