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Copy path9-pool.js
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79 lines (64 loc) · 1.55 KB
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'use strict';
const timers = require('node:timers/promises');
class Connection {
#id = undefined;
constructor(id) {
this.#id = id;
}
async query(sql) {
console.log(`Connection ${this.#id}: ${sql}`);
await timers.setTimeout(20);
}
}
class Lease {
#resource = null;
#release = null;
constructor(resource, release) {
this.#resource = resource;
this.#release = release;
}
query(sql) {
if (!this.#resource) throw new ReferenceError('Lease expired');
return this.#resource.query(sql);
}
[Symbol.dispose]() {
if (!this.#resource) return;
const resource = this.#resource;
this.#resource = null;
this.#release(resource);
}
}
class Pool {
#available;
#waiters = [];
constructor(size) {
this.#available = Array.from(
{ length: size },
(_, index) => new Connection(index + 1),
);
}
#release(resource) {
const resolve = this.#waiters.shift();
if (resolve) {
resolve(new Lease(resource, (item) => this.#release(item)));
return;
}
this.#available.push(resource);
}
async acquire() {
const resource = this.#available.shift();
if (resource) return new Lease(resource, (item) => this.#release(item));
return new Promise((resolve) => {
this.#waiters.push(resolve);
});
}
}
const client = async (pool, id) => {
using connection = await pool.acquire();
await connection.query(`select ${id}`);
};
const main = async () => {
const pool = new Pool(2);
await Promise.all([client(pool, 1), client(pool, 2), client(pool, 3)]);
};
main();