Java根据参数进行同步(名为互斥/锁) [英] Java synchronizing based on a parameter (named mutex/lock)

问题描述

我正在寻找一种基于接收到的参数来同步方法的方法，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
}

我希望基于这样的name参数同步方法doSomething:

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将在不同步的情况下执行代码，但是线程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Tudor的解释，我认为我面临着另一个问题: 这是新代码的示例:

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);
}

之所以不填充锁映射，是因为name可以具有任何值.

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

基于上面的示例，由于HashMap不是线程安全的，因此在多个线程同时从哈希映射中添加/删除值时，可能会出现问题.

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，如果我将HashMap设置为线程安全的ConcurrentHashMap，则同步块将阻止其他线程访问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

使用映射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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