系統設計

1class LockService {
2  holder: string | null = null;
3  expiresAt = 0;
4  private nextToken = 33;
5 
6  acquire(client: string, now: number, leaseMs: number) {
7    if (this.holder !== null && now >= this.expiresAt) {
8      this.holder = null;
9    }
10    if (this.holder !== null) return null;               // someone holds it
11    this.holder = client;
12    this.expiresAt = now + leaseMs;
13    this.nextToken += 1;
14    return { token: this.nextToken, expiresAt: this.expiresAt };
15  }
16 
17  renew(client: string, now: number, leaseMs: number): boolean {
18    if (this.holder !== client || now >= this.expiresAt) {
19      if (this.holder === client) this.holder = null;
20      return false;
21    }
22    this.expiresAt = now + leaseMs;
23    return true;
24  }
25}
26 
27class FencedStorage {
28  maxToken = 0;
29  value = "";
30 
31  write(token: number, value: string): boolean {
32    if (token < this.maxToken) return false;
33    this.maxToken = token;
34    this.value = value;
35    return true;
36  }
37}