Java synchronized块与Collections.synchronizedMap [英] Java synchronized block vs. Collections.synchronizedMap

问题描述

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);
      }
    }
  }
}

来自我的理解，我需要 addToMap（）中的synchronized块，以防止另一个线程调用 remove（）或 containsKey（）在我通过调用 put（）之前，但我不需要<$ c $中的同步块c> doWork（）因为在 remove（） addToMap（）中的synchronized块c $ c>返回，因为我最初使用 Collections.synchronizedMap（）创建了Map。那是对的吗？有没有更好的方法呢？

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（）保证您要在地图上运行的每个原子操作都将被同步。

Collections.synchronizedMap() guarantees that each atomic operation you want to run on the map will be synchronized.

然而，必须在地图上同步运行两个（或更多）操作块。
是的 - 您正在正确同步。

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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