在以下情况下建议使用Thread.sleep（）

Question

I have a webservice which calls this method

public void process(Incoming incoming) {
   // code to persist data
   ...
   Thread.sleep(20000);
   // check persisted data and if status != CANCELLED then process
}

Requirement is that I have to wait 20 seconds (as business has high probability to send cancel request within 20 seconds in which case we should not process).

I understand that Thread.sleep() doesn't even bother the cpu until time's up.

• But concern is, since it is being called from a webservice, these Threads might be from a pool of some sort and might exhaust if lot of requests come?
• Or do new servlet containers automatically create extra threads if exhausted and we can write this kind of code without worrying about these things?
• Does scheduling an asynchronous task which runs after 20 seconds a better option? Here also, we have to have a Thread pool to execute these tasks anyways.

Answer 1

Does scheduling an asynchronous task which runs after 20 seconds a better option? Here also, we have to have a Thread pool to execute these tasks anyways.

If your end user/application does not need any outcome from the webservice call, then its a better idea not to hold the thread. You should go asynch way.

Answer 2

Does scheduling an asynchronous task which runs after 20 seconds a better option? Here also, we have to have a Thread pool to execute these tasks anyway.

Yes, it is a better option, because with Thread.sleep(20000); you are blocking one thread per each request. With scheduled thread pool, you are adding tasks to some kind of queue, and later they are executed using the constant number of threads - so there is no possibility of exhausting all available threads.

Answer 3

Or do new servlet containers automatically create extra threads if exhausted and we can write this kind of code without worrying about these things?

To customise the size of this thread pool you should specify a non-zero value for the server.tomcat.max-threads property in your application.properties or application.xml file.