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速率限制可以用来限制物理或逻辑资源的访问速率，例如，为了防止资源被有意或无意过度使用。

限制使用

假设您不想每秒运行超过两个任务

use util\invoke\RateLimiting;

$rateLimiter= new RateLimiting(2);
foreach ($tasks as $task) {
  $rateLimiter->acquire();    // will wait if necessary
  $task->run();
}

限制带宽

您可以通过为每个字节获取许可来实现带宽节流

use util\invoke\{RateLimiting, Rate, Per};

$rateLimiter= new RateLimiting(new Rate(1000000, Per::$MINUTE));
while ($bytes= $source->read()) {
  $rateLimiter->acquire(strlen($bytes));
  $target->write($bytes);
}

限制用户速率

实现以下类似的过滤器

use web\{Filter, Error};
use util\invoke\{RateLimiting, Rate, Per};

class RateLimitingFilter implements Filter {
  private $rates, $rate, $timeout;

  public function __construct(KeyValueStorage $rates) {
    $this->rates= $rates;
    $this->rate= new Rate(5000, Per::$HOUR);
    $this->timeout= 0.2;
  }

  public function filter($request, $response, $invocation) {
    $remote= $request->header('Remote-Addr');

    $limits= $this->rates->get($remote) ?: new RateLimiting($this->rate);
    $permitted= $limits->tryAcquiring(1, $this->timeout);
    $this->rates->put($remote, $limits);

    $response->header('X-RateLimit-Limit', $limits->rate()->value());
    $response->header('X-RateLimit-Remaining', $limits->remaining());
    $response->header('X-RateLimit-Reset', $limits->resetTime());

    if (!$permitted) {
      throw new Error(429, 'Rate limit exceeded');
    }

    return $invocation->proceed($request, $response);
  }
}

进一步阅读

• RateLimiter - 发现Google Guava by Tomasz Nurkiewicz
• Guava的RateLimiter类 - 该项目就是受其启发。