PHP实现熔断降级功能

class CircuitBreaker {  
    private $failureThreshold;  
    private $failureCount;  
    private $state; // 可选值：'closed', 'open', 'half-open'  
    private $resetTimeout;  
    private $lastFailureTime;  
    private $defaultFallback;  
    public function __construct($failureThreshold = 5, $resetTimeout = 60, $defaultFallback = null) {  
        $this->failureThreshold = $failureThreshold;  
        $this->state = 'closed';  
        $this->resetTimeout = $resetTimeout;  
        $this->defaultFallback = $defaultFallback;  
        $this->failureCount = 0;  
    }  
    public function execute($serviceCall, $fallback = null) {  
        if ($this->state === 'closed') {  
            try {  
                return $serviceCall();  
            } catch (Exception $e) {  
                $this->failureCount++;  
                if ($this->failureCount >= $this->failureThreshold) {  
                    $this->state = 'open';  
                    $this->lastFailureTime = time();  
                }  
                return $fallback ?: $this->defaultFallback;  
            }  
        } elseif ($this->state === 'open') {  
            if (time() - $this->lastFailureTime > $this->resetTimeout) {  
                $this->state = 'half-open';  
            } else {  
                return $fallback ?: $this->defaultFallback;  
            }  
        }  
        // half-open state  
        try {  
            $result = $serviceCall();  
            $this->state = 'closed';  
            $this->failureCount = 0;  
            return $result;  
        } catch (Exception $e) {  
            $this->state = 'open';  
            $this->lastFailureTime = time();  
            return $fallback ?: $this->defaultFallback;  
        }  
    }  
}

$breaker = new CircuitBreaker(3, 60, 'Sorry, service temporarily unavailable.');  
$result = $breaker->execute(function() {  
    // 模拟服务调用，可能会抛出异常  
    if (rand(0, 1) === 0) {  
        throw new Exception('Service failed.');  
    } else {  
        return 'Service succeeded.';  
    }  
}, 'Fallback data.'); // 提供可选的降级数据或逻辑  
echo $result; // 输出服务调用结果或降级信息

// 1. Fail Silent —— 静默返回默认值（适合埋点、推荐位、非核心日志）
$chain->fallback(fn($e) => []);
// 2. Cache Fallback —— 缓存兜底（适合商品详情、配置）
$chain->fallback(function ($e) use ($redis, $key) {
    $v = $redis->get($key);
    if ($v === false) throw $e;
    return json_decode($v, true);
});
// 3. Failover —— 切换备用服务（适合多机房、主备数据源）
$chain->fallback(fn($e) => $backupClient->query($params));
// 4. Fail Fast —— 快速失败，交给上游（适合支付、扣款等不能假的场景）
//    不注册任何 fallback，直接抛异常
// 5. 限流降级 —— 被限流时返回排队页/静态页
if ($limiter->tooMany()) {
    return response('当前访问人数较多，请稍后重试', 503);
}