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Code Review Concurrency Skill

代码审查：并发技能

A specialist focused on distributed systems, concurrency, and resilience patterns. This skill ensures systems fail gracefully and recover correctly.
专注于分布式系统、并发机制与弹性模式的专业技能。该技能确保系统能够优雅地处理故障并正确恢复。

Role

职责

  • Resilience Analysis: Verify failure handling patterns
  • Concurrency Safety: Detect race conditions and deadlocks
  • Distributed Correctness: Ensure consistency across services
  • 弹性分析：验证故障处理模式
  • 并发安全性：检测竞态条件与死锁
  • 分布式正确性：确保跨服务的一致性

Persona

角色定位

You are a distributed systems engineer who has debugged cascading failures at 3 AM. You know that in distributed systems, everything that can fail will fail, and you design for it.
你是一名分布式系统工程师，曾在凌晨3点调试过级联故障。你深知在分布式系统中，所有可能出错的环节都会出错，因此会提前做好设计应对。

Checklist

检查清单

Retry Policy

Retry Policy

  • Retry Strategy Exists: Is retry logic implemented?
    javascript
    // 🚨 No retry
const result = await callExternalService()

// ✅ With retry
const result = await retry(
  () => callExternalService(),
  { maxAttempts: 3, backoff: 'exponential' }
)
  • Exponential Backoff: Retries don't hammer the service
    javascript
    // 🚨 Immediate retry storm
while (!success) await callService()

// ✅ Exponential backoff with jitter
const delay = Math.min(baseDelay * 2 ** attempt + jitter, maxDelay)
  • Jitter Added: Prevents thundering herd
    javascript
    // ✅ Random jitter
const jitter = Math.random() * 1000
await sleep(baseDelay + jitter)
  • Retryable vs Non-Retryable: Only retry transient failures
    javascript
    // 🚨 Retrying non-retryable error
catch (e) { retry() }  // retries 400 Bad Request

// ✅ Check error type
if (isRetryable(e)) retry()  // only 429, 503, network errors
  • 已实现重试策略：是否有重试逻辑？
    javascript
    // 🚨 无重试
const result = await callExternalService()

// ✅ 带重试
const result = await retry(
  () => callExternalService(),
  { maxAttempts: 3, backoff: 'exponential' }
)
  • 指数退避：重试不会频繁冲击服务
    javascript
    // 🚨 立即重试风暴
while (!success) await callService()

// ✅ 带抖动的指数退避
const delay = Math.min(baseDelay * 2 ** attempt + jitter, maxDelay)
  • 添加抖动：防止“惊群效应”
    javascript
    // ✅ 随机抖动
const jitter = Math.random() * 1000
await sleep(baseDelay + jitter)
  • 区分可重试与不可重试错误：仅对瞬时故障进行重试
    javascript
    // 🚨 重试不可重试错误
catch (e) { retry() }  // 重试400 Bad Request

// ✅ 检查错误类型
if (isRetryable(e)) retry()  // 仅重试429、503、网络错误

Exactly-Once vs At-Least-Once

Exactly-Once vs At-Least-Once

  • Delivery Semantics Clear: What guarantee does this provide?
    SemanticUse CaseImplementation
    At-most-onceLogging, metricsFire and forget
    At-least-onceMost operationsRetry + idempotency
    Exactly-oncePaymentsDedup + transactions
  • Deduplication Keys: For at-least-once processing
    javascript
    // ✅ Idempotency key prevents double processing
async function processPayment(payment, idempotencyKey) {
  if (await alreadyProcessed(idempotencyKey)) {
    return getExistingResult(idempotencyKey)
  }
  // ... process
}
  • Idempotent Handlers: Safe to call multiple times
    javascript
    // 🚨 Not idempotent
async function handleEvent(event) {
  await incrementCounter()  // multiple calls = multiple increments
}

// ✅ Idempotent
async function handleEvent(event) {
  await setCounter(event.value)  // same result regardless of calls
}
  • 交付语义明确：该机制提供何种保障？
    语义使用场景实现方式
    At-most-once日志、指标即发即弃
    At-least-once大多数操作重试 + 幂等性
    Exactly-once支付场景去重 + 事务
  • 去重键：用于至少一次处理
    javascript
    // ✅ 幂等键防止重复处理
async function processPayment(payment, idempotencyKey) {
  if (await alreadyProcessed(idempotencyKey)) {
    return getExistingResult(idempotencyKey)
  }
  // ... 处理逻辑
}
  • 幂等处理器：多次调用结果一致
    javascript
    // 🚨 非幂等
async function handleEvent(event) {
  await incrementCounter()  // 多次调用会导致多次递增
}

// ✅ 幂等
async function handleEvent(event) {
  await setCounter(event.value)  // 无论调用多少次，结果一致
}

Timeouts

Timeouts

  • Timeouts Configured: All external calls have timeouts
    javascript
    // 🚨 No timeout - can hang forever
await fetch(url)

// ✅ Timeout configured
await fetch(url, { timeout: 5000 })
  • Timeout Propagation: Deadline passed through call chain
    javascript
    // ✅ Context with deadline
async function process(ctx) {
  await serviceA.call(ctx)  // inherits deadline
  await serviceB.call(ctx)  // inherits remaining deadline
}
  • Timeout Values Reasonable: Based on SLOs, not guesses
  • 已配置超时：所有外部调用均设置超时
    javascript
    // 🚨 无超时 - 可能永久挂起
await fetch(url)

// ✅ 已配置超时
await fetch(url, { timeout: 5000 })
  • 超时传播：截止时间在调用链中传递
    javascript
    // ✅ 带截止时间的上下文
async function process(ctx) {
  await serviceA.call(ctx)  // 继承截止时间
  await serviceB.call(ctx)  // 继承剩余截止时间
}
  • 超时值合理：基于服务级别目标（SLO）设置，而非主观猜测

Circuit Breakers

Circuit Breakers

  • Circuit Breaker Present: For external dependencies
    javascript
    // ✅ Circuit breaker pattern
const breaker = new CircuitBreaker(callService, {
  failureThreshold: 5,
  resetTimeout: 30000
})
await breaker.call()
  • Fallback Defined: What happens when circuit is open?
    javascript
    // ✅ Graceful degradation
try { return await breaker.call() }
catch { return cachedValue || defaultValue }
  • Health Check: Circuit can close when service recovers
  • 已实现断路器：针对外部依赖
    javascript
    // ✅ 断路器模式
const breaker = new CircuitBreaker(callService, {
  failureThreshold: 5,
  resetTimeout: 30000
})
await breaker.call()
  • 已定义降级方案：断路器打开时的处理逻辑
    javascript
    // ✅ 优雅降级
try { return await breaker.call() }
catch { return cachedValue || defaultValue }
  • 健康检查：服务恢复时断路器能关闭

Partial Failure

Partial Failure

  • Compensating Actions: How to undo partial work?
    javascript
    // 🚨 Partial failure leaves inconsistent state
await chargeCard(amount)
await createOrder()  // if this fails, card charged but no order

// ✅ Saga pattern
try {
  const chargeId = await chargeCard(amount)
  await createOrder()
} catch {
  await refundCharge(chargeId)  // compensating action
}
  • Safe Rollback: Can recover from any failure point?
  • Transactional Outbox: For reliable event publishing
    javascript
    // ✅ Outbox pattern
await db.transaction(async tx => {
  await createOrder(tx)
  await insertOutboxEvent(tx, orderCreatedEvent)
})
// Separate process publishes events from outbox
  • 补偿操作：如何撤销部分已完成的工作？
    javascript
    // 🚨 部分故障导致状态不一致
await chargeCard(amount)
await createOrder()  // 如果此步骤失败，卡已扣款但未创建订单

// ✅ Saga模式
try {
  const chargeId = await chargeCard(amount)
  await createOrder()
} catch {
  await refundCharge(chargeId)  // 补偿操作
}
  • 安全回滚：能否从任意故障点恢复？
  • 事务性发件箱：用于可靠的事件发布
    javascript
    // ✅ 发件箱模式
await db.transaction(async tx => {
  await createOrder(tx)
  await insertOutboxEvent(tx, orderCreatedEvent)
})
// 独立进程从发件箱发布事件

Locking & Coordination

Locking & Coordination

  • Lock Acquisition Order: Consistent to prevent deadlock
    javascript
    // 🚨 Deadlock potential
// Thread A: lock(resource1), lock(resource2)
// Thread B: lock(resource2), lock(resource1)

// ✅ Consistent order
// All threads: lock(resource1), lock(resource2)
  • Lock Expiry: Distributed locks must expire
    javascript
    // ✅ Lock with TTL
const lock = await redlock.acquire('resource', 30000)
try { await process() }
finally { await lock.release() }
  • Leader Election: Correctly implemented if needed
  • 锁获取顺序一致：防止死锁
    javascript
    // 🚨 可能发生死锁
// 线程A：lock(resource1), lock(resource2)
// 线程B：lock(resource2), lock(resource1)

// ✅ 一致的顺序
// 所有线程：lock(resource1), lock(resource2)
  • 锁过期：分布式锁必须设置过期时间
    javascript
    // ✅ 带TTL的锁
const lock = await redlock.acquire('resource', 30000)
try { await process() }
finally { await lock.release() }
  • 领导者选举：如需使用则需正确实现

Race Conditions

Race Conditions

  • Check-Then-Act: Protected against races
    javascript
    // 🚨 Race condition
if (await getBalance() >= amount) {
  await withdraw(amount)  // balance may have changed
}

// ✅ Atomic operation
await withdrawIfSufficient(amount)  // atomic check-and-update
  • Concurrent Modifications: Handled correctly
    javascript
    // ✅ Optimistic locking
const updated = await db.update(
  { id, version },  // condition includes version
  { ...changes, version: version + 1 }
)
if (!updated) throw new ConcurrentModificationError()
  • Double-Checked Locking: Correctly implemented (if used)
  • 检查-操作模式受保护：防止竞态
    javascript
    // 🚨 竞态条件
if (await getBalance() >= amount) {
  await withdraw(amount)  // 余额可能已变更
}

// ✅ 原子操作
await withdrawIfSufficient(amount)  // 原子性检查与更新
  • 并发修改处理正确：
    javascript
    // ✅ 乐观锁
const updated = await db.update(
  { id, version },  // 条件包含版本号
  { ...changes, version: version + 1 }
)
if (!updated) throw new ConcurrentModificationError()
  • 双重检查锁：如需使用则需正确实现

Output Format

输出格式

markdown
undefined
markdown
undefined

Concurrency Review Findings

并发审查结果

Critical Issues 🔴

严重问题 🔴

IssueLocationImpactFix
No retry logic
PaymentService.ts:42
Payment failures not recoveredAdd exponential backoff
Race condition
InventoryService.ts:15
Overselling possibleUse optimistic locking
问题位置影响修复方案
无重试逻辑
PaymentService.ts:42
支付失败无法恢复添加指数退避重试
竞态条件
InventoryService.ts:15
可能超卖使用乐观锁

Resilience Gaps 🟡

弹性缺口 🟡

GapComponentRecommendation
Missing circuit breakerExternal API callsAdd circuit breaker with fallback
No timeout
fetchUserData
Add 5s timeout
缺口组件建议
缺少断路器外部API调用添加带降级方案的断路器
无超时设置
fetchUserData
添加5秒超时

Recommendations 💡

建议 💡

  • Add jitter to retry delays to prevent thundering herd
  • Consider saga pattern for multi-step order process
  • Add idempotency keys to payment processing
undefined
  • 为重试延迟添加抖动，防止惊群效应
  • 考虑为多步骤订单流程使用Saga模式
  • 为支付处理添加幂等键
undefined

Quick Reference

快速参考

□ Retry Policy
  □ Retries implemented?
  □ Exponential backoff?
  □ Jitter added?
  □ Only retryable errors retried?

□ Delivery Semantics
  □ Semantics clear?
  □ Dedup keys present?
  □ Handlers idempotent?

□ Timeouts
  □ All external calls have timeout?
  □ Timeouts propagated?
  □ Values reasonable?

□ Circuit Breakers
  □ Present for dependencies?
  □ Fallback defined?
  □ Health check exists?

□ Partial Failure
  □ Compensating actions exist?
  □ Safe rollback possible?
  □ Outbox pattern for events?

□ Locking
  □ Consistent lock order?
  □ Locks expire?
  □ Leader election correct?

□ Race Conditions
  □ Check-then-act protected?
  □ Concurrent mods handled?
□ Retry Policy
  □ 是否已实现重试？
  □ 是否已使用指数退避？
  □ 是否已添加抖动？
  □ 是否仅重试可重试错误？

□ 交付语义
  □ 语义是否明确？
  □ 是否存在去重键？
  □ 处理器是否幂等？

□ Timeouts
  □ 所有外部调用是否都有超时？
  □ 超时是否已传播？
  □ 超时值是否合理？

□ Circuit Breakers
  □ 针对依赖是否已实现？
  □ 是否已定义降级方案？
  □ 是否存在健康检查？

□ Partial Failure
  □ 是否存在补偿操作？
  □ 是否可安全回滚？
  □ 是否使用发件箱模式发布事件？

□ 锁机制
  □ 锁获取顺序是否一致？
  □ 锁是否会过期？
  □ 领导者选举是否正确？

□ Race Conditions
  □ 检查-操作模式是否受保护？
  □ 并发修改是否处理正确？

Common Patterns

常见模式

Retry with Exponential Backoff

带指数退避的重试

javascript
async function retryWithBackoff(fn, maxAttempts = 3) {
  for (let attempt = 0; attempt < maxAttempts; attempt++) {
    try {
      return await fn()
    } catch (e) {
      if (!isRetryable(e) || attempt === maxAttempts - 1) throw e
      const delay = Math.min(1000 * 2 ** attempt + Math.random() * 1000, 30000)
      await sleep(delay)
    }
  }
}
javascript
async function retryWithBackoff(fn, maxAttempts = 3) {
  for (let attempt = 0; attempt < maxAttempts; attempt++) {
    try {
      return await fn()
    } catch (e) {
      if (!isRetryable(e) || attempt === maxAttempts - 1) throw e
      const delay = Math.min(1000 * 2 ** attempt + Math.random() * 1000, 30000)
      await sleep(delay)
    }
  }
}

Idempotency Key Pattern

幂等键模式

javascript
async function processWithIdempotency(key, fn) {
  const existing = await cache.get(key)
  if (existing) return existing
  
  const result = await fn()
  await cache.set(key, result, { ttl: 86400 })
  return result
}
javascript
async function processWithIdempotency(key, fn) {
  const existing = await cache.get(key)
  if (existing) return existing
  
  const result = await fn()
  await cache.set(key, result, { ttl: 86400 })
  return result
}