blocks|key|1142569|text|只要你在当前时间上多加一些秒，你就会好起来。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1142570|用这种方式尝试time+%2B=+newtime;，而不是做time+=+newtime;，你不会失去你担心的那一秒。|offset|length|style|CODE|1142571|不过，在最坏的情况下，你只会损失一秒。|1142572|entityMap^0|0|7|G|S|F|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]|$D|P|E|Q|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|K|$]]

As long as you add some more seconds to you current time you should be fine.

Instead of doing <code>time = newtime;</code> try <code>time += newtime;</code> This way you will not lose the second you're worried about.

Still, you are only losing a second at worst.

blocks|key|1357627|text|这个问题需要一些信号量。我在前一个完成后发送ajax做了很多这样的事情。你的情况有点相似;)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1357628|试试这样的东西。它应该忽略与ajax回调冲突所有减少时间的尝试。|1357629|window.TimeKeeper+=+new+function(){
this.time=0;+//initial+value,+whatever
this.isopen=true;

this.decrement+=+function(){+
+if(this.isopen){
++this.time--;
++redisplay(this.time);
++}
+}
this.set+=+function(val){
+if(this.isopen){
++this.isopen=false;
++this.time=val;
++this.isopen=true;
++}+else+{
++//another+AJAX+callback+is+modifying+time.+
+++//You+can+enqueue+current+value+and+put+it+later
++}
+}

}

function+tick()+{
++++TimeKeeper.decrement();

};
function+update(newtime)+{
++++TimeKeeper.set(newtime);
};|code-block|syntax|javascript|1357630|还有一件事-+setTimeout的工作方式就像一个新的线程，我希望浏览器会同步内存访问，所以在减少之前检查一下这个值是否没有增长就足够了。但上述解决方案更加灵活和安全。|1357631|还有一个小技巧-避免太频繁地使用AJAX查询-这可能会导致额外的问题-比如请求返回的顺序与发送的顺序不同，以及firefox内存使用量在一分钟内因ajax太多而积累了很多;)|1357632|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The problem needs some semaphores. I do that a lot for sending ajax after previous one finishes. Your case is a bit alike ;)

Try something like that. It should ignore all attempts to decrement time that collide with ajax callback.

<pre><code>window.TimeKeeper = new function(){
this.time=0; //initial value, whatever
this.isopen=true;

this.decrement = function(){ 
 if(this.isopen){
 this.time--;
 redisplay(this.time);
 }
 }
this.set = function(val){
 if(this.isopen){
 this.isopen=false;
 this.time=val;
 this.isopen=true;
 } else {
 //another AJAX callback is modifying time. 
 //You can enqueue current value and put it later
 }
 }

}

function tick() {
 TimeKeeper.decrement();

};
function update(newtime) {
 TimeKeeper.set(newtime);
};
</code></pre>

One more thing - the setTimeout works like a new thread and I would expect that browsers do the synchronising mem access, so It might be enough to check if the value didn't grow before decrementing. But the above solution is more flexible and safe.

And one little tip - avoid querying with AJAX too often - it may cause extra problems - like requests coming back in different order than sent, and firefox memory usage building up a lot on too much ajax a minute ;)

blocks|key|1357752|text|Javascript是单线程的。没有竞争条件。在javascript中，time+=+newtime;和time+-=+1;这两行代码不可能在执行过程中重叠。事实上，这两个功能可以保证不会重叠。它们中的一个将运行，然后另一个将运行。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1357753|entityMap^0|10|F|1G|A|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

Javascript is single threaded. There is no race condition. There's no way in javascript for the two lines <code>time = newtime;</code> and <code>time -= 1;</code> to overlap during execution. In fact, the two functions are guaranteed not to overlap. One of them will run and then the other will run.

blocks|key|1142801|text|您没有竞争条件，因为Javascript不会并发执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1142802|每次从异步操作(AJAX、setTimeout等)触发回调时，必须先完成该回调的执行，然后才能调用另一个异步操作的另一个回调。因此，如果update()正在运行，则没有其他Javascript在运行。一旦update()完成，就可以触发来自异步操作的其他回调(例如，tick())。有趣的是，这也是为什么setTimeout和它的同类不能保证在到达超时的精确时刻执行的原因:一些其他的javascript可能会阻塞回调的执行。|offset|length|style|CODE|1142803|请查看http://ejohn.org/blog/how-javascript-timers-work/，了解有关这一切如何工作的一些好信息。|1142804|entityMap|0|LINK|mutability|MUTABLE|url|http://ejohn.org/blog/how-javascript-timers-work/^0|0|D|A|1W|8|2U|8|3P|6|48|A|0|3|1D|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@$D|T|E|U|F|G]|$D|V|E|W|F|G]|$D|X|E|Y|F|G]|$D|Z|E|10|F|G]|$D|11|E|12|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@$D|14|E|15|1|16]]|A|$]]|$1|J|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

You don't have a race condition, because Javascript doesn't execute concurrently.

Every time a callback is fired from an async operation (AJAX, <code>setTimeout</code>, etc), that callback must finish executing before another callback from another async operation can be called. So if <code>update()</code> is running, no other Javascript is. Once <code>update()</code> finishes, other callbacks from async operations can be fired (for example, <code>tick()</code>). Interestingly enough, this is also why <code>setTimeout</code> and its ilk aren't guaranteed to execute at the precise moment the timeout is reached: some other javascript could be blocking the callback's execution.

Check out <a href="http://ejohn.org/blog/how-javascript-timers-work/" rel="noreferrer">http://ejohn.org/blog/how-javascript-timers-work/</a> for some good information on how all this works.

I have a web application where there is a timer that is constantly counting down. Meanwhile, the client frequently checks with the server to see if more time has been added to the timer. The code looks something like this:

<pre><code>function tick() {
 // This function is called once every second
 time -= 1;
 redisplay(time);
};
function update(newtime) {
 // This function is called whenever the ajax request
 // to the server yields a new time
 time = newtime;
};
</code></pre>

It is, of course, a bit more complex than that, but you can see the inherent race condition. What if the update and the tick function are both trying to modify <code>time</code> at the same time?

Frankly, I don't know nearly enough javascript to understand how to deal with this sort of concurrency issue: is there an easy way to do this, or if not, can somebody point me towards resources where I can learn more?

Thank you.

Ajax concurrency

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个web应用程序，其中有一个不断倒计时的计时器。同时，客户端频繁地与服务器进行检查，以查看是否向计时器添加了更多时间。代码看起来像这样：function tick() {    // This function is called once every second    time -= 1;    redisp...

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