异步JavaScript的循环处理 [英] Javascript async loop processing
本文介绍了异步JavaScript的循环处理的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有一个JavaScript循环，需要一些时间来处理。我希望我可以苗条下来，但它必须处理大量的数据。虽然它运行的浏览器不响应，当然。我读过来处理这个在JavaScript中使用某种类型的异步循环的最佳方式。这种方式的鼠标点击等，可以继续在循环处理之间进行处理。有没有，会为这项工作做得很好任何标准异步框架？或有人可以提供如何，这可能是codeD一个简单的例子？谢谢！
I have a javascript loop that takes some time to process. I wish I could slim it down but it has to process a large amount of data. While it's running the browser becomes unresponsive of course. I've read the best way to handle this in javascript is using an asynchronous loop of some sort. This way mouse clicks, etc, can continue to be processed in between loop processing. Is there any standard async frameworks that will work well for this? Or can someone provide a simple example of how this might be coded? Thanks!
推荐答案
可悲的是WebWorkers都尚未公布每个人的浏览器。我一直在使用的setTimeout（Func键，0）;诱骗大约一年。下面是最近的一些研究，我写了解释如何加快步伐一点。如果你只是想要的答案，请跳到第4步。1 2和3解释推理和力学;
Sadly WebWorkers are not available yet on everyone's browser. I have been using the "setTimeout(Func,0);" trick for about year. Here is some recent research i wrote up to explain how to speed it up a bit. If you just want the answer, skip to Step 4. Step 1 2 and 3 explain the reasoning and mechanics;
// In Depth Analysis of the setTimeout(Func,0) trick.
//////// setTimeout(Func,0) Step 1 ////////////
// setTimeout and setInterval impose a minimum
// time limit of about 2 to 10 milliseconds.
console.log("start");
var workCounter=0;
var WorkHard = function()
{
if(workCounter>=2000) {console.log("done"); return;}
workCounter++;
setTimeout(WorkHard,0);
};
// this take about 9 seconds
// that works out to be about 4.5ms per iteration
// Now there is a subtle rule here that you can tweak
// This minimum is counted from the time the setTimeout was executed.
// THEREFORE:
console.log("start");
var workCounter=0;
var WorkHard = function()
{
if(workCounter>=2000) {console.log("done"); return;}
setTimeout(WorkHard,0);
workCounter++;
};
// This code is slightly faster because we register the setTimeout
// a line of code earlier. Actually, the speed difference is immesurable
// in this case, but the concept is true. Step 2 shows a measurable example.
///////////////////////////////////////////////
//////// setTimeout(Func,0) Step 2 ////////////
// Here is a measurable example of the concept covered in Step 1.
var StartWork = function()
{
console.log("start");
var startTime = new Date();
var workCounter=0;
var sum=0;
var WorkHard = function()
{
if(workCounter>=2000)
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: sum=" + sum + " time=" + ms + "ms");
return;
}
for(var i=0; i<1500000; i++) {sum++;}
workCounter++;
setTimeout(WorkHard,0);
};
WorkHard();
};
// This adds some difficulty to the work instead of just incrementing a number
// This prints "done: sum=3000000000 time=18809ms".
// So it took 18.8 seconds.
var StartWork = function()
{
console.log("start");
var startTime = new Date();
var workCounter=0;
var sum=0;
var WorkHard = function()
{
if(workCounter>=2000)
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: sum=" + sum + " time=" + ms + "ms");
return;
}
setTimeout(WorkHard,0);
for(var i=0; i<1500000; i++) {sum++;}
workCounter++;
};
WorkHard();
};
// Now, as we planned, we move the setTimeout to before the difficult part
// This prints: "done: sum=3000000000 time=12680ms"
// So it took 12.6 seconds. With a little math, (18.8-12.6)/2000 = 3.1ms
// We have effectively shaved off 3.1ms of the original 4.5ms of dead time.
// Assuming some of that time may be attributed to function calls and variable
// instantiations, we have eliminated the wait time imposed by setTimeout.
// LESSON LEARNED: If you want to use the setTimeout(Func,0) trick with high
// performance in mind, make sure your function takes more than 4.5ms, and set
// the next timeout at the start of your function, instead of the end.
///////////////////////////////////////////////
//////// setTimeout(Func,0) Step 3 ////////////
// The results of Step 2 are very educational, but it doesn't really tell us how to apply the
// concept to the real world. Step 2 says "make sure your function takes more than 4.5ms".
// No one makes functions that take 4.5ms. Functions either take a few microseconds,
// or several seconds, or several minutes. This magic 4.5ms is unattainable.
// To solve the problem, we introduce the concept of "Burn Time".
// Lets assume that you can break up your difficult function into pieces that take
// a few milliseconds or less to complete. Then the concept of Burn Time says,
// "crunch several of the individual pieces until we reach 4.5ms, then exit"
// Step 1 shows a function that is asyncronous, but takes 9 seconds to run. In reality
// we could have easilly incremented workCounter 2000 times in under a millisecond.
// So, duh, that should not be made asyncronous, its horrible. But what if you don't know
// how many times you need to increment the number, maybe you need to run the loop 20 times,
// maybe you need to run the loop 2 billion times.
console.log("start");
var startTime = new Date();
var workCounter=0;
for(var i=0; i<2000000000; i++) // 2 billion
{
workCounter++;
}
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
// prints: "done: workCounter=2000000000 time=7214ms"
// So it took 7.2 seconds. Can we break this up into smaller pieces? Yes.
// I know, this is a retarded example, bear with me.
console.log("start");
var startTime = new Date();
var workCounter=0;
var each = function()
{
workCounter++;
};
for(var i=0; i<20000000; i++) // 20 million
{
each();
}
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
// The easiest way is to break it up into 2 billion smaller pieces, each of which take
// only several picoseconds to run. Ok, actually, I am reducing the number from 2 billion
// to 20 million (100x less). Just adding a function call increases the complexity of the loop
// 100 fold. Good lesson for some other topic.
// prints: "done: workCounter=20000000 time=7648ms"
// So it took 7.6 seconds, thats a good starting point.
// Now, lets sprinkle in the async part with the burn concept
console.log("start");
var startTime = new Date();
var workCounter=0;
var index=0;
var end = 20000000;
var each = function()
{
workCounter++;
};
var Work = function()
{
var burnTimeout = new Date();
burnTimeout.setTime(burnTimeout.getTime() + 4.5); // burnTimeout set to 4.5ms in the future
while((new Date()) < burnTimeout)
{
if(index>=end)
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
return;
}
each();
index++;
}
setTimeout(Work,0);
};
// prints "done: workCounter=20000000 time=107119ms"
// Sweet Jesus, I increased my 7.6 second function to 107.1 seconds.
// But it does prevent the browser from locking up, So i guess thats a plus.
// Again, the actual objective here is just to increment workCounter, so the overhead of all
// the async garbage is huge in comparison.
// Anyway, Lets start by taking advice from Step 2 and move the setTimeout above the hard part.
console.log("start");
var startTime = new Date();
var workCounter=0;
var index=0;
var end = 20000000;
var each = function()
{
workCounter++;
};
var Work = function()
{
if(index>=end) {return;}
setTimeout(Work,0);
var burnTimeout = new Date();
burnTimeout.setTime(burnTimeout.getTime() + 4.5); // burnTimeout set to 4.5ms in the future
while((new Date()) < burnTimeout)
{
if(index>=end)
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
return;
}
each();
index++;
}
};
// This means we also have to check index right away because the last iteration will have nothing to do
// prints "done: workCounter=20000000 time=52892ms"
// So, it took 52.8 seconds. Improvement, but way slower than the native 7.6 seconds.
// The Burn Time is the number you tweak to get a nice balance between native loop speed
// and browser responsiveness. Lets change it from 4.5ms to 50ms, because we don't really need faster
// than 50ms gui response.
console.log("start");
var startTime = new Date();
var workCounter=0;
var index=0;
var end = 20000000;
var each = function()
{
workCounter++;
};
var Work = function()
{
if(index>=end) {return;}
setTimeout(Work,0);
var burnTimeout = new Date();
burnTimeout.setTime(burnTimeout.getTime() + 50); // burnTimeout set to 50ms in the future
while((new Date()) < burnTimeout)
{
if(index>=end)
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
return;
}
each();
index++;
}
};
// prints "done: workCounter=20000000 time=52272ms"
// So it took 52.2 seconds. No real improvement here which proves that the imposed limits of setTimeout
// have been eliminated as long as the burn time is anything over 4.5ms
///////////////////////////////////////////////
//////// setTimeout(Func,0) Step 4 ////////////
// The performance numbers from Step 3 seem pretty grim, but GUI responsiveness is often worth it.
// Here is a short library that embodies these concepts and gives a descent interface.
var WilkesAsyncBurn = function()
{
var Now = function() {return (new Date());};
var CreateFutureDate = function(milliseconds)
{
var t = Now();
t.setTime(t.getTime() + milliseconds);
return t;
};
var For = function(start, end, eachCallback, finalCallback, msBurnTime)
{
var i = start;
var Each = function()
{
if(i==-1) {return;} //always does one last each with nothing to do
setTimeout(Each,0);
var burnTimeout = CreateFutureDate(msBurnTime);
while(Now() < burnTimeout)
{
if(i>=end) {i=-1; finalCallback(); return;}
eachCallback(i);
i++;
}
};
Each();
};
var ForEach = function(array, eachCallback, finalCallback, msBurnTime)
{
var i = 0;
var len = array.length;
var Each = function()
{
if(i==-1) {return;}
setTimeout(Each,0);
var burnTimeout = CreateFutureDate(msBurnTime);
while(Now() < burnTimeout)
{
if(i>=len) {i=-1; finalCallback(array); return;}
eachCallback(i, array[i]);
i++;
}
};
Each();
};
var pub = {};
pub.For = For; //eachCallback(index); finalCallback();
pub.ForEach = ForEach; //eachCallback(index,value); finalCallback(array);
WilkesAsyncBurn = pub;
};
///////////////////////////////////////////////
//////// setTimeout(Func,0) Step 5 ////////////
// Here is an examples of how to use the library from Step 4.
WilkesAsyncBurn(); // Init the library
console.log("start");
var startTime = new Date();
var workCounter=0;
var FuncEach = function()
{
if(workCounter%1000==0)
{
var s = "<div></div>";
var div = jQuery("*[class~=r1]");
div.append(s);
}
workCounter++;
};
var FuncFinal = function()
{
var ms = (new Date()).getTime() - startTime.getTime();
console.log("done: workCounter=" + workCounter + " time=" + ms + "ms");
};
WilkesAsyncBurn.For(0,2000000,FuncEach,FuncFinal,50);
// prints: "done: workCounter=20000000 time=149303ms"
// Also appends a few thousand divs to the html page, about 20 at a time.
// The browser is responsive the entire time, mission accomplished
// LESSON LEARNED: If your code pieces are super tiny, like incrementing a number, or walking through
// an array summing the numbers, then just putting it in an "each" function is going to kill you.
// You can still use the concept here, but your "each" function should also have a for loop in it
// where you burn a few hundred items manually.
///////////////////////////////////////////////
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