Google App Engine Java程序并发

Question

In order to improve the execution speed of a Java program running in Google App Engine, can I create additional Java threads during the runtime to make use of idle machines in the data center?

I've found conflicting data thus far.

Answer 1

If your primary concern is to improve the execution time, take a look at Memcache and Tasks. They can be used to reduce or avoid the latency of reading from or writing to the Datastore or other storage options, fetching URLs, sending emails, etc. If you do a lot of difficult computations that can run in parallel, look at MapReduce API.

Once you remove all the delays from your program, there will be no reason to use multiple threads within a single request.

Note that App Engine instances can use multithreading to execute multiple requests at the same time, so they tend to use allocated resources efficiently. To enable it, see:

https://developers.google.com/appengine/docs/java/config/appconfig#Java_appengine_web_xml_Using_concurrent_requests

Answer 2

If you have a problem that calls for a multithreaded solution, you can use threads (as described on the link that you included in your question).

However, based on your reasoning ("to make use of idle machines in the datacenter"), it seems like you're misguided. You should not use threads for that reason. You use the machines hours that you pay for and not more. The only time you will have an idle machine is if you tell App Engine to keep around an extra idle machine so that it doesn't have to start up an extra machine your app gets a big usage spike.

Most of the time, unless you are truly doing parallel computation, you won't need to use multiple threads in App Engine. For instance, the datastore has an asynchronous API so that you can do multiple datastore operations in parallel without having to deal with threads yourself.

Does that make sense?