java同步基于参数 [英] java synchronizing based on a parameter

问题描述

我正在寻找一种基于它接收的参数同步方法的方法，如下所示：

I'm looking for a way to synchronize a method based on the parameter it receives, something like this:

public synchronized void doSomething(name){
//some code
}

I希望方法 doSomething 基于 name 参数进行同步，如下所示：

I want the method doSomething to be synchronized based on the name parameter like this:

线程1：doSomething（a）;

Thread 1: doSomething("a");

线程2：doSomething（b）;

Thread 2: doSomething("b");

线程3：doSomething（c）;

Thread 3: doSomething("c");

线程4：doSomething（a）;

Thread 4: doSomething("a");

线程1，线程2和线程3将执行代码而不进行同步，但线程4将等待，直到线程1完成代码，因为它具有相同的a值。

Thread 1 , Thread 2 and Thread 3 will execute the code without being synchronized , but Thread 4 will wait until Thread 1 has finished the code because it has the same "a" value.

谢谢

更新

基于都铎解释我认为我面临另一个问题：
这里是新代码的示例：

Based on Tudor explanation I think I'm facing another problem: here is a sample of the new code:

private HashMap locks=new HashMap();
public void doSomething(String name){
    locks.put(name,new Object());
    synchronized(locks.get(name)) {
        // ...
    }
    locks.remove(name);
}

我没有填充锁定地图的原因是因为名称可以有任何值。

The reason why I don't populate the locks map is because name can have any value.

根据上面的示例，在同一时间由多个线程添加/删除hashmap中的值时会出现问题，因为HashMap不是线程 - 安全。

Based on the sample above , the problem can appear when adding / deleting values from the hashmap by multiple threads in the same time, since HashMap is not thread-safe.

所以我的问题是如果我使 HashMap a ConcurrentHashMap 哪个是线程安全的，同步块会阻止其他线程访问locks.get（name）??

So my question is if I make the HashMap a ConcurrentHashMap which is thread safe, will the synchronized block stop other threads from accessing locks.get(name) ??

推荐答案

使用地图将字符串与锁定对象相关联：

Use a map to associate strings with lock objects:

Map<String, Object> locks = new HashMap<String, Object>();
locks.put("a", new Object());
locks.put("b", new Object());
// etc.

然后：

public void doSomething(String name){
    synchronized(locks.get(name)) {
        // ...
    }
}

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