使用java ConcurrentHashMap实现缓存 [英] Implementing a cache using a java ConcurrentHashMap

问题描述

我想在web java应用程序中实现对重量级对象的简单缓存。但我无法弄清楚如何正确地做。

I'd like to implement a simple caching of heavyweight objects in a web java application. But I can't figure out how to do it properly.

我缺少一些东西或ConcurrentHashMap方法（putIfAbsent，...）是不够的，需要额外的同步？

Am I missing something or ConcurrentHashMap methods (putIfAbsent, ...) are not enough and additional synchronization is needed ?

有没有更好的简单API（在内存存储，没有外部配置）？

Is there a better simple API (In memory storage, no external config) to do this ?

P。

推荐答案

如果可以安全地暂时拥有多个要缓存的内容的实例，如下所示执行无锁高速缓存：

If it is safe to temporarily have more than one instance for the thing you're trying to cache, you can do a "lock-free" cache like this:

public Heavy instance(Object key) {
  Heavy info = infoMap.get(key);
  if ( info == null ) {
    // It's OK to construct a Heavy that ends up not being used
    info = new Heavy(key);
    Heavy putByOtherThreadJustNow = infoMap.putIfAbsent(key, info);
    if ( putByOtherThreadJustNow != null ) {
      // Some other thread "won"
      info = putByOtherThreadJustNow;
    }
    else {
      // This thread was the winner
    }
  }
  return info;
}

多个线程可以竞相创建和添加项的项，但只有一个人应该赢得。

Multiple threads can "race" to create and add an item for the key, but only one should "win".

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