I'm trying to create a multithreaded application in Java using ExecutorService thread pools. The application basically queries a third party service for data about a given keyword. Since I have many keywords and each request takes some time to generate, I would like to query the service in parallel. The requests are made through a ServiceHandler object which takes care of authentication and parsing the results out.
In my initial implementation, I create a new Callable for each keyword and creates a new ServiceHandler object to query the service. For some reason, this runs faster than sharing a singleton ServiceHandler object across all Callable. However, with large input data sets, I'm running into memory issues because it is creating new objects for each input keyword.
Is there a way to still use ExecutorService but only create a distinct instance of ServiceHandler for each worker thread? For example, if I have 1000 keywords and a fixed pool of 20 threads, I want to only create one ServiceHandler for each thread (20 total) while still having one Callable for each keyword(1000 total).
I tried adding a static ThreadLocal object to each Callable objects that returns a new ServiceHandler in its initialValue() , but it seems like only one ServiceHandler is being created? I can post my code for this, but I'm not even sure if this is the right approach.
Yes, there is a way to create only one instance of object per thread, you should use ThreadLocal<ServiceHandler> and declare it as a static field. This would create only one instance of object per thread.
You can check http://docs.oracle.com/javase/6/docs/api/java/lang/ThreadLocal.html this for official documentation.