为并发调用返回false的简单锁- javascript
为并发调用返回false的简单锁- javascript
提问于 2020-04-09 10:47:56
我想锁定一个异步函数，使其不能同时执行。函数只能由一个调用者执行，它应该在执行后作为输出得到true，而其他调用者在没有执行函数的逻辑内容的情况下得到false作为返回。其他人不应该等待当前调用者完成。
这就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
}
}但看起来它并没有像预期的那样工作。有人能帮我改进一下吗？
回答 1
Stack Overflow用户
回答已采纳
发布于 2020-04-13 08:29:17
Promise的执行并不总是保证在解决或拒绝之后立即停止；在检查锁并退出或相应地继续promise之后，您必须返回一个布尔值。
运行下面的代码片段；它是一个包含3个按钮的示例，这些按钮具有相同的承诺和3秒的延迟。当一个按钮正在运行时，所有其他按钮都不能执行。
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>
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/61113167
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