系統設計

1class FixedWindow {
2  private window = -1;
3  private count = 0;
4  constructor(private limit: number) {}
5 
6  allow(now: number): boolean {
7    const w = Math.floor(now);
8    if (w !== this.window) {
9      this.window = w;
10      this.count = 0;
11    }
12    if (this.count >= this.limit) return false;
13    this.count += 1;
14    return true;
15  }
16}
17 
18class SlidingWindowLog {
19  private log: number[] = [];                      // times allowed, oldest first
20  constructor(private limit: number) {}
21 
22  allow(now: number): boolean {
23    while (this.log.length > 0 && this.log[0] <= now - 1) this.log.shift();
24    if (this.log.length >= this.limit) return false;
25    this.log.push(now);
26    return true;
27  }
28}
29 
30class TokenBucket {
31  private tokens: number;
32  private last = 0;
33  constructor(private capacity: number, private ratePerSec: number) {
34    this.tokens = capacity;                        // starts full
35  }
36 
37  allow(now: number): boolean {
38    this.tokens = Math.min(this.capacity, this.tokens + (now - this.last) * this.ratePerSec);
39    this.last = now;
40    if (this.tokens < 1) return false;
41    this.tokens -= 1;
42    return true;
43  }
44}