首页 \ 问答 \ 使用动态密钥创建对象[重复](Creating object with dynamic key [duplicate])

使用动态密钥创建对象[重复](Creating object with dynamic key [duplicate])

 
  这个问题在这里已经有了答案：  
  
   用动态键创建对象[重复] 2个答案  
  
 
 我必须根据一些动态值创建一个对象键。 这里str的值将从用户到用户。 用户输入str的值。 我想使用用户输入的str值来创建Object。  
var str = $('#inputValue');

var obj = new Object();
obj.assignment = new Object();
obj.assignment.name= "assignmentName";
obj.assignment.str = new Object();

 
 This question already has an answer here: 
  
   Creating object with dynamic keys [duplicate]  2 answers   
  
 
I have to create a object key based on some dynamic value . Here the value of str will from user to user. The user enters the value of str. I want to use str value entered by user to create Object. 
var str = $('#inputValue');

var obj = new Object();
obj.assignment = new Object();
obj.assignment.name= "assignmentName";
obj.assignment.str = new Object();

原文：https://stackoverflow.com/questions/20519183

更新时间：2023-11-12 12:11

最满意答案

 要确切地确定实际需要多少个时钟周期是很难的。 相反，如果我们假设它是一个x86处理器（如注释中所述），我将尝试解释实际发生的情况，并且运行时库使用“锁定”指令实现atomic - 如果这些假设中的任何一个是假的，那么“所有的赌注都没有“俗话说：  
 执行atomic操作时，CPU将首先确保它具有对（可能）缓存值的“独占”访问权限。 这意味着向所有其他CPU发送消息说“我是这个变量的”。 然后，每个其他CPU必须刷新其副本（如果已修改）并将该值标记为“无效”，然后回复“我已完成”。  
 一旦所有处理器都说“我已经完成”，主处理器就可以继续。 此过程，尤其是在具有大量CPU（核心）的大型系统中，可能需要相当长的时间（数百或数千个周期）。  
 当然，CPU可以通过知道没有其他CPU读取此值，或者没有其他CPU为此值发出写入来优化这一点，在这种情况下，它可以非常快。  
 你也许可以通过编写一些代码来了解它在[在特定的机器上]有多糟糕，你可以在两个线程中循环，比如1秒，尝试更新和读取相同的原子变量，看看如何它是好还是坏。 然后尝试两个“更新”循环（这样你就可以在两个线程之间进行更新）。 

It's quite hard to determine exactly how many clockcycles it actually takes. I will, instead, try to explain what actually happens, if we assume it's an x86 processor (as stated in the comment), and the runtime library implements the atomic using "locked" instructions - if any of these assumptions are false, then "all bets are off" as the saying goes: 
When performing a atomic operation, the CPU will first ensure it has "exclusive" access to the (potentially) cached value. This means sending a message to all other CPU's saying "I'm it for this variable". Each of the other CPU's then has to flush its copy (if modified) and mark the value as "invalid", and then reply with "I'm done".  
Once all processors have said "I'm done", the main processor can continue. This process, especially in a large system with lots of CPU(cores) can take quite some time (hundreds or thousands of cycles).  
Of course, the CPU can optimise this by knowing that no other CPU has read this value, or that no other CPU has issued a write for this value, in which case, it can be really quick.  
You can perhaps get an idea of how bad this is [on a particular machine] by writing some code where you, in two threads, loop around for, say, 1 second, trying to update and read the same atomic variable, and see how good/bad it is. Then try two "update" loops (so you make updates between two threads).

使用动态密钥创建对象[重复](Creating object with dynamic key [duplicate])

最满意答案

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