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php 实现熔断

2026-01-29 16:03:38PHP

熔断机制简介

熔断是一种系统保护机制，当服务调用失败率达到阈值时，自动停止请求并快速失败，避免雪崩效应。常见实现方式包括计数器、滑动窗口等。

基于计数器的熔断实现

通过记录失败请求次数，当达到阈值时触发熔断：

class CircuitBreaker {
    private $failureThreshold = 3;
    private $failureCount = 0;
    private $state = 'CLOSED';

    public function callService(callable $service) {
        if ($this->state === 'OPEN') {
            throw new Exception("Service unavailable (Circuit Breaker Open)");
        }

        try {
            $result = $service();
            $this->reset();
            return $result;
        } catch (Exception $e) {
            $this->failureCount++;
            if ($this->failureCount >= $this->failureThreshold) {
                $this->state = 'OPEN';
                // 可添加定时器自动恢复
            }
            throw $e;
        }
    }

    private function reset() {
        $this->failureCount = 0;
        $this->state = 'CLOSED';
    }
}

基于时间窗口的熔断改进

记录最近N秒内的失败率，更精准判断熔断状态：

class TimeWindowBreaker {
    private $windowSize = 10; // 秒
    private $failureRateThreshold = 0.5;
    private $failures = [];
    private $state = 'CLOSED';

    public function callService(callable $service) {
        $this->cleanOldFailures();

        if ($this->state === 'OPEN') {
            throw new Exception("Service unavailable");
        }

        try {
            $result = $service();
            return $result;
        } catch (Exception $e) {
            $this->failures[] = time();
            $this->evaluateState();
            throw $e;
        }
    }

    private function cleanOldFailures() {
        $currentTime = time();
        $this->failures = array_filter(
            $this->failures,
            fn($t) => $currentTime - $t <= $this->windowSize
        );
    }

    private function evaluateState() {
        $totalCalls = count($this->failures) + 1; // +1 for current call
        $failureRate = count($this->failures) / $totalCalls;

        if ($failureRate >= $this->failureRateThreshold) {
            $this->state = 'OPEN';
            // 可设置延迟恢复逻辑
        }
    }
}

熔断状态恢复策略

自动恢复：通过定时器定期尝试重置状态
半开状态：允许部分请求通过测试稳定性

// 半开状态示例代码片段
if ($this->state === 'OPEN' && time() - $this->lastFailure > $this->cooldownPeriod) {
    $this->state = 'HALF_OPEN';
    try {
        $testResult = $service();
        $this->reset();
    } catch (Exception $e) {
        $this->lastFailure = time();
    }
}