Java 同步块与 Collections.synchronizedMap
以下代码是否设置为正确同步 synchronizedMap
上的调用?
Is the following code set up to correctly synchronize the calls on synchronizedMap
?
public class MyClass {
private static Map<String, List<String>> synchronizedMap = Collections.synchronizedMap(new HashMap<String, List<String>>());
public void doWork(String key) {
List<String> values = null;
while ((values = synchronizedMap.remove(key)) != null) {
//do something with values
}
}
public static void addToMap(String key, String value) {
synchronized (synchronizedMap) {
if (synchronizedMap.containsKey(key)) {
synchronizedMap.get(key).add(value);
}
else {
List<String> valuesList = new ArrayList<String>();
valuesList.add(value);
synchronizedMap.put(key, valuesList);
}
}
}
}
据我了解,我需要 addToMap()
中的同步块来防止另一个线程调用 remove()
或 containsKey()
在我完成对 put()
的调用之前,但我不需要 doWork()
中的同步块,因为另一个线程无法进入 addToMap()
在 remove()
返回之前,因为我最初使用 Collections.synchronizedMap()
创建了地图.那是对的吗?有没有更好的方法来做到这一点?
From my understanding, I need the synchronized block in addToMap()
to prevent another thread from calling remove()
or containsKey()
before I get through the call to put()
but I do not need a synchronized block in doWork()
because another thread cannot enter the synchronized block in addToMap()
before remove()
returns because I created the Map originally with Collections.synchronizedMap()
. Is that correct? Is there a better way to do this?
推荐答案
Collections.synchronizedMap()
保证你想在地图上运行的每个原子操作都会被同步.
Collections.synchronizedMap()
guarantees that each atomic operation you want to run on the map will be synchronized.
但是,在地图上运行两个(或更多)操作必须在一个块中同步.所以是的 - 你正在正确同步.
Running two (or more) operations on the map however, must be synchronized in a block. So yes - you are synchronizing correctly.
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