我有一个变量can_run,可以是1或0,然后我有一个函数队列,一旦变量从0切换到1(但一次只有1个这样的函数),应该运行.
现在,我做的是
var can_run=1;
function wait_until_can_run(callback) {
if (can_run==1) {
callback();
} else {
window.setTimeout(function(){wait_until_can_run(callback)},100);
}
}
//...somewhere else...
wait_until_can_run( function(){
can_run=0;
//start running something
});
//..somewhere else,as a reaction to the task finishing..
can_run=1;
然而,它起作用并不会让我持续运行大约100次超时非常有效.像信号量这样的东西在这里会很方便;但一般来说,JavaScript中并不真正需要信号量.
那么,在这里使用什么？
编辑：我写过“功能队列”但是如此处所见,我并不关心订单.
解决方法
这是一个很好的Queue类,您可以在不使用超时的情况下使用它：
var Queue = (function () {
Queue.prototype.autorun = true;
Queue.prototype.running = false;
Queue.prototype.queue = [];
function Queue(autorun) {
if (typeof autorun !== "undefined") {
this.autorun = autorun;
}
this.queue = []; //initialize the queue
};
Queue.prototype.add = function (callback) {
var _this = this;
//add callback to the queue
this.queue.push(function () {
var finished = callback();
if (typeof finished === "undefined" || finished) {
// if callback returns `false`,then you have to
// call `next` somewhere in the callback
_this.dequeue();
}
});
if (this.autorun && !this.running) {
// if nothing is running,then start the engines!
this.dequeue();
}
return this; // for chaining fun!
};
Queue.prototype.dequeue = function () {
this.running = false;
//get the first element off the queue
var shift = this.queue.shift();
if (shift) {
this.running = true;
shift();
}
return shift;
};
Queue.prototype.next = Queue.prototype.dequeue;
return Queue;
})();
它可以像这样使用：
// passing false into the constructor makes it so
// the queue does not start till we tell it to
var q = new Queue(false).add(function () {
//start running something
}).add(function () {
//start running something 2
}).add(function () {
//start running something 3
});
setTimeout(function () {
// start the queue
q.next();
},2000);
小提琴演示：http://jsfiddle.net/maniator/dUVGX/
更新为使用es6和新es6 Promises：
class Queue {
constructor(autorun = true,queue = []) {
this.running = false;
this.autorun = autorun;
this.queue = queue;
this.prevIoUsValue = undefined;
}
add(cb) {
this.queue.push((value) => {
const finished = new Promise((resolve,reject) => {
const callbackResponse = cb(value);
if (callbackResponse !== false) {
resolve(callbackResponse);
} else {
reject(callbackResponse);
}
});
finished.then(this.dequeue.bind(this),(() => {}));
});
if (this.autorun && !this.running) {
this.dequeue();
}
return this;
}
dequeue(value) {
this.running = this.queue.shift();
if (this.running) {
this.running(value);
}
return this.running;
}
get next() {
return this.dequeue;
}
}
它可以以相同的方式使用：
const q = new Queue(false).add(() => {
console.log('this is a test');
return {'banana': 42};
}).add((obj) => {
console.log('test 2',obj);
return obj.banana;
}).add((number) => {
console.log('THIS IS A NUMBER',number)
});
// start the sequence
setTimeout(() => q.next(),2000);
