Swoole如何实现熔断机制？熔断如何触发？

<?php
// 假设你有一个CircuitBreaker类，其状态通过Swoole\Table来管理
class CircuitBreaker
{
    const STATE_CLOSED = 'closed';
    const STATE_OPEN = 'open';
    const STATE_HALF_OPEN = 'half_open';

    private $serviceName;
    private $table; // Swoole\Table实例，用于存储共享状态

    private $failureThreshold = 5; // 连续失败次数达到此值即熔断
    private $openTimeout = 5; // 熔断后开启状态持续时间（秒）
    private $halfOpenSuccessThreshold = 3; // 半开状态下连续成功次数达到此值即关闭

    public function __construct(string $serviceName, Swoole\Table $table)
    {
        $this->serviceName = $serviceName;
        $this->table = $table;
        // 初始化或获取服务状态
        if (!$this->table->exist($serviceName)) {
            $this->table->set($serviceName, [
                'state' => self::STATE_CLOSED,
                'failure_count' => 0,
                'last_failure_time' => 0,
                'success_count_half_open' => 0,
            ]);
        }
    }

    public function allowRequest(): bool
    {
        $data = $this->table->get($this->serviceName);
        $state = $data['state'];
        $lastFailureTime = $data['last_failure_time'];

        if ($state === self::STATE_OPEN) {
            if (time() - $lastFailureTime > $this->openTimeout) {
                // 超时，尝试进入半开状态
                $this->transition(self::STATE_HALF_OPEN);
                return true; // 允许一个请求通过进行试探
            }
            return false; // 仍然在熔断期，不允许请求
        } elseif ($state === self::STATE_HALF_OPEN) {
            // 半开状态只允许一个请求通过，或者按策略放行少量
            // 这里简化为每次判断都允许一个请求，直到成功或失败
            return true;
        }
        return true; // CLOSED 状态，允许所有请求
    }

    public function recordSuccess(): void
    {
        $data = $this->table->get($this->serviceName);
        $state = $data['state'];

        if ($state === self::STATE_HALF_OPEN) {
            $this->table->incr($this->serviceName, 'success_count_half_open');
            $data = $this->table->get($this->serviceName); // 重新获取更新后的数据
            if ($data['success_count_half_open'] >= $this->halfOpenSuccessThreshold) {
                $this->transition(self::STATE_CLOSED);
            }
        } elseif ($state === self::STATE_CLOSED) {
            // 成功时重置失败计数，保证即使之前有零星失败也不会轻易熔断
            $this->table->set($this->serviceName, ['failure_count' => 0]);
        }
        // OPEN 状态下不会调用此方法
    }

    public function recordFailure(): void
    {
        $data = $this->table->get($this->serviceName);
        $state = $data['state'];

        if ($state === self::STATE_CLOSED) {
            $this->table->incr($this->serviceName, 'failure_count');
            $data = $this->table->get($this->serviceName); // 重新获取更新后的数据
            if ($data['failure_count'] >= $this->failureThreshold) {
                $this->transition(self::STATE_OPEN);
            }
        } elseif ($state === self::STATE_HALF_OPEN) {
            // 半开状态下失败，立即重新进入 OPEN 状态
            $this->transition(self::STATE_OPEN);
        }
        // OPEN 状态下不会调用此方法，或者直接抛出熔断异常
    }

    private function transition(string $newState): void
    {
        $data = [
            'state' => $newState,
            'failure_count' => 0, // 切换状态时重置计数器
            'success_count_half_open' => 0, // 切换状态时重置半开成功计数
        ];
        if ($newState === self::STATE_OPEN) {
            $data['last_failure_time'] = time();
        }
        $this->table->set($this->serviceName, $data);
        echo "Service '{$this->serviceName}' transitioned to '{$newState}'\n";
    }
}

// 实际使用示例 (在协程中)
// $table = new Swoole\Table(1024);
// $table->column('state', Swoole\Table::TYPE_STRING, 10);
// $table->column('failure_count', Swoole\Table::TYPE_INT);
// $table->column('last_failure_time', Swoole\Table::TYPE_INT);
// $table->column('success_count_half_open', Swoole\Table::TYPE_INT);
// $table->create();

// $circuitBreaker = new CircuitBreaker('userService', $table);

// go(function () use ($circuitBreaker) {
//     try {
//         if ($circuitBreaker->allowRequest()) {
//             // 模拟调用外部服务
//             // $result = Co::httpGet('http://some-external-service/api/user');
//             if (rand(0, 10) < 3) { // 模拟30%失败率
//                 throw new Exception("Service call failed");
//             }
//             echo "Service call success!\n";
//             $circuitBreaker->recordSuccess();
//         } else {
//             echo "Circuit is OPEN for userService, request denied!\n";
//             // 可以在这里返回一个降级数据
//         }
//     } catch (Throwable $e) {
//         echo "Service call error: " . $e->getMessage() . "\n";
//         $circuitBreaker->recordFailure();
//     }
// });

CLOSED

OPEN

HALF_OPEN

CLOSED

OPEN