为什么我们需要锁可以重入？(Why do we need a lock to be reentrant?)

 要做到这一点，你可能想要使用像knockout.js这样的库，它允许代码和标记之间的分离，从而使生活更容易。 以下是您正在寻找的淘汰示例实现： http ： //jsfiddle.net/pCc9w/4/ 
 
 HTML： 
 
<select data-bind="options:data, optionsText:'name', value:selectedLevel1"></select>

    <!--ko with: selectedLevel1 -->
        <select data-bind="options:subitems, optionsText:'name', value:$root.selectedLevel2"></select>
<!--/ko-->



    <!--ko with: selectedLevel2 -->
<select data-bind="options:subitems, optionsText:'name', value:$root.selectedLevel3"></select>
    <!--/ko-->    
 
 使用Javascript： 
 
var data = [
    {
        name:"level1",
        subitems:[
            {
                name:"level1.1",
                subitems:[
                    { name:"level1.1.1" },
                    { name:"level1.1.2" },
                    { name:"level1.1.3" }
                ]
            },
            {
                name:"level1.2",
                subitems:[
                    { name:"level1.2.1" },
                    { name:"level1.2.2" },
                    { name:"level1.2.3" }
                ]
            }]
    },
    {
        name:"level2",
        subitems:[
            {
                name:"level2.1",
                subitems:[
                    { name:"level2.1.1" },
                    { name:"level2.1.2" },
                    { name:"level2.1.3" }
                ]
            },
            {
                name:"level2.2",
                subitems:[
                    { name:"level2.2.1" },
                    { name:"level2.2.2" },
                    { name:"level2.2.3" }
                ]
            }]
    },    
]

    var dataViewModel = ko.mapping.fromJS(data);
    var mainViewModel = {
        data:dataViewModel,
        selectedLevel1:ko.observable(),
        selectedLevel2:ko.observable(),
        selectedLevel3:ko.observable()
    }



    ko.applyBindings(mainViewModel);    
 
 请记住，这只能解决问题的客户端部分。 在服务器端，您需要一些方法来获取数据阵列并将其发送到客户端。 可能你应该使用MVC框架。 一些例子是ruby on rails，django，asp.net MVC。 PHP也有很多MVC框架。 

To do this, you might want to use a library like knockout.js, which allows for separation between code and markup, thus making life much easier. Here is a knockout example implementation of what you are looking for: http://jsfiddle.net/pCc9w/4/
 
Html:
 
<select data-bind="options:data, optionsText:'name', value:selectedLevel1"></select>

    <!--ko with: selectedLevel1 -->
        <select data-bind="options:subitems, optionsText:'name', value:$root.selectedLevel2"></select>
<!--/ko-->



    <!--ko with: selectedLevel2 -->
<select data-bind="options:subitems, optionsText:'name', value:$root.selectedLevel3"></select>
    <!--/ko-->    
 
Javascript:
 
var data = [
    {
        name:"level1",
        subitems:[
            {
                name:"level1.1",
                subitems:[
                    { name:"level1.1.1" },
                    { name:"level1.1.2" },
                    { name:"level1.1.3" }
                ]
            },
            {
                name:"level1.2",
                subitems:[
                    { name:"level1.2.1" },
                    { name:"level1.2.2" },
                    { name:"level1.2.3" }
                ]
            }]
    },
    {
        name:"level2",
        subitems:[
            {
                name:"level2.1",
                subitems:[
                    { name:"level2.1.1" },
                    { name:"level2.1.2" },
                    { name:"level2.1.3" }
                ]
            },
            {
                name:"level2.2",
                subitems:[
                    { name:"level2.2.1" },
                    { name:"level2.2.2" },
                    { name:"level2.2.3" }
                ]
            }]
    },    
]

    var dataViewModel = ko.mapping.fromJS(data);
    var mainViewModel = {
        data:dataViewModel,
        selectedLevel1:ko.observable(),
        selectedLevel2:ko.observable(),
        selectedLevel3:ko.observable()
    }



    ko.applyBindings(mainViewModel);    
 
Keep in mind that this only solves the client-side part of the problem. On the server side, you need some way to obtain the data array and send it to the client. Probably you should use an MVC framework. Some examples are ruby on rails, django, asp.net MVC. PHP has lots of MVC frameworks too.