async function getSomething() {}

let global_something
let fetching = false

const callbacks = []

function updateSomething() {
  return new Promise<void>((resolve) => {
    if (fetching) {
      callbacks.push(() => resolve())
      return
    }
    fetching = true

    getSomething()
      .then((data) => {
        global_something = data
      })
      .finally(() => {
        fetching = false
        resolve()
        callbacks.forEach((callback) => callback())
        callbacks.length = 0
      })
  })
}

适用于：

• 多个地方同时请求同一个全局资源
• 需要避免并发重复请求
• 第一次请求未完成时，其它 await 都要挂起等待
• 请求完成后所有等待者都要 resolve