Google App Engine（java）服务类是线程安全的吗？ [英] Are Google App Engine (java) service classes Thread-Safe?

问题描述

是否可以从工厂获得对服务的引用，并将其用于处理多个请求？使用以下伪代码可以很好地解释servlet：

  SomeServlet ... {
 MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService（）; 
 UserService userService = UserServiceFactory.getUserService（）; 
 DatastoreService datastoreService = DatastoreServiceFactory.getDatastoreService（）; 
 
 doGet（...）{
 userService.doSomething（...）; 
} 
 ... 
} 
  

可能是不成熟的优化，但我只是想知道为每个请求获得服务的成本是多少。请分享您的洞察力。

解决方案

在google group thread http://groups.google.com/group/google-appengine-java/browse_thread/thread/d3f1536084f59c22 ，Ikai Lan （来自Google的GAE团队）表示MemcacheService是线程安全的，但缓存它并不有用，因为每次从工厂获得服务时都只有一个对象分配。

由于所有服务都是以类似的方式获得的，我认为我们可以假设它们都遵循相同的设计并且都是线程安全的。但是由于在每个查询中获取新实例并不昂贵，我不会缓存它们。

Is it okay to obtain a reference to a service from factory once and use it for handling multiple requests? It can be best explained using following pseudo-code for a servlet:

SomeServlet...{
  MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();
  UserService userService = UserServiceFactory.getUserService();
  DatastoreService datastoreService = DatastoreServiceFactory.getDatastoreService();

  doGet(...){
    userService.doSomething(...);
  }
...
}

It may be a premature optimization but i am just curious to know what is the cost of obtaining service for each request. Please share your insight.

解决方案

In the google group thread http://groups.google.com/group/google-appengine-java/browse_thread/thread/d3f1536084f59c22, Ikai Lan (from the GAE team at Google) says MemcacheService is thread-safe, but that caching it is not useful, because there is just one object allocation each time you get the service from the factory.

Since all the services are obtained in a similar way, I think we could assume that they all follow the same design and are all thread-safe. But since it isn't costly to get a new instance at each query, I wouldn't cache them.

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