concurrent-requests.md

Concurrent Requests Limiter

Overview

Limits the number of simultaneous active requests rather than rate per time window.

How It Works

1. Track count of active requests
2. Increment on request start
3. Decrement on request completion
4. Reject if at max concurrency

Implementation

export class ConcurrentRequestsLimiter {
  private maxConcurrent: number;
  private activeRequests: number = 0;

  constructor(maxConcurrent: number) {
    this.maxConcurrent = maxConcurrent;
  }

  allowRequest(): RateLimitResult {
    if (this.activeRequests < this.maxConcurrent) {
      this.activeRequests++;
      return { allowed: true, remaining: this.maxConcurrent - this.activeRequests };
    }
    return { allowed: false, remaining: 0 };
  }

  release(): void {
    this.activeRequests = Math.max(0, this.activeRequests - 1);
  }
}

Use Cases

• Database connection pools
• WebSocket connections
• Long-running operations
• Resource-limited services

Usage Pattern

const limiter = new ConcurrentRequestsLimiter(10);

async function handleRequest() {
  if (!limiter.allowRequest().allowed) {
    throw new Error('Too many concurrent requests');
  }

  try {
    await processRequest();
  } finally {
    limiter.release(); // Always release!
  }
}