javascript - 对并发调用返回 false 的简单锁 - javascript

Question

我想锁定异步函数以防止同时执行。该函数只能由一个调用者执行，并且它应该在执行后得到 true 作为输出，而其他人得到 false 作为返回而不执行函数的逻辑内容。其他人不应等待当前调用者完成。

这是我到目前为止所尝试的：

class Lock {
    constructor() {
        this.locked = false;
    }
    lock(resolve) {
        if (this.locked) {
            resolve(false)
        }
        this.locked = true
        return
    }
    release(resolve) {
        this.locked = false;
        resolve(true)
    }


}

let lock = new Lock();

function myFunction() {
    return new Promise(resolve => {
        lock.lock(resolve);
        //do something - this takes time includes some api calls and db operations
        lock.release(resolve);
    })
}

async function callSite() {
    const executed = await myFunction();
    if(executed){
        //do something
    }
    else{
        //do another thing
    }
}

但似乎它没有按预期工作。任何人都可以帮助我改善这一点吗？

标签： javascriptasync-awaitlockinges6-promise

Answer 1

承诺执行并不总是保证在解决或拒绝后立即停止；在检查锁并退出或相应地继续承诺后，您必须返回一个布尔值。

运行以下代码段；这是一个具有 3 个具有相同承诺和 3 秒延迟的按钮的示例。当一个按钮运行时，所有其他按钮都无法执行。

class Lock {
  constructor() {
    this.locked = false;
  }

  lock(resolve) {
    if (this.locked) {
      resolve(false);
      return false;
    }
    this.locked = true
    return true;
  }

  release(resolve) {
    this.locked = false;
      resolve(true)
  }
}

let lock = new Lock();

function myFunction({ resultEl }) {
  resultEl.textContent = "Is running";
    
  return new Promise(resolve => {
    // Check if it's locked
    if (!lock.lock(resolve)) {
      // If it is, return and exit the function even if the promise is already resolved
      return;
    }

    // do something - this takes time includes some api calls and db operations
    // just wait 3 seconds for demontration
    setTimeout(() => {
      lock.release(resolve);
    }, 3000);
  })
}

async function callSite() {
  this.disabled = true;

  const executed = await myFunction({ resultEl : this.nextSibling });
    
  this.disabled = false;

  if (executed) {
    this.nextSibling.textContent = `Finished at ${(new Date).getTime()}`;
  }
  else {
    this.nextSibling.textContent = `Was NOT executed at ${(new Date).getTime()}`;
  }
}

document.getElementById('a-button').addEventListener('click', callSite);
document.getElementById('b-button').addEventListener('click', callSite);
document.getElementById('c-button').addEventListener('click', callSite);

div {
  margin-bottom: 10px;
}

button {
  margin-right: 5px;
}

<div>
  <button id="a-button">Run A</button><span></span>
</div>

<div>
  <button id="b-button">Run B</button><span></span>
</div>

<div>
  <button id="c-button">Run C</button><span></span>
</div>