[Feature request] ServiceFactory 应该缓存创建 client 的 promise

[pilaoda]

The feature, motivation（功能、动机）

midway/packages/core/src/common/serviceFactory.ts

Lines 47 to 57 in 7c45ca2

	public async createInstance(config, clientName?): Promise<T | undefined> {
	// options.default will be merge in to options.clients[id]
	config = extend(true, {}, this.options['default'], config);
	const client = await this.createClient(config, clientName);
	if (client) {
	if (clientName) {
	this.clients.set(clientName, client);
	}
	return client;
	}
	}

如果用户需要根据请求动态创建 client，先判断 has，再创建，这一步有可能多个并发创建同一个 id 的 client

Alternatives（替代方案）

public async createInstance(config, clientName?): Promise<T | undefined> {
    // options.default will be merge in to options.clients[id]
    config = extend(true, {}, this.options['default'], config);

    if (this.clientPromises.get(clientName)) {
        return this.clientPromises.get(clientName);
    }

    const clientPromise = this.createClient(config, clientName);
    this.clientPromises.set(clientName, clientPromise);

    const client = await clientPromise;
    if (client) {
      if (clientName) {
        this.clients.set(clientName, client);
      }
      return client;
    }
  }

Additional context（其他上下文）

No response

[czy88840616]

理论上是可以的，这个跟 dataSource 创建一样，在 v4 调整一下好了