如何将ExecuteService与包含AutoCloseable资源的自定义线程一起使用

Question

I present here a simplification of the problem I am trying to solve. Summary of the classes I present:

• Processor: is a non thread-safe class, that can be created without any arguments and needs to be closed when you are done using it. Creating instances of this class is really expensive, so only one (per thread) should be created. It provides methods to do certain operations.
• ResultProvider: is a thread-safe class that manages requests that needs a Processor to be handled.

The current implementation is similar to the following:

class Processor implements AutoCloseable { (...) }

class ResultProvider implements AutoCloseable {

    private final Processor processor;

    public ResultProvider() {
        this.processor = Processor.createNewProcessor();
    }

    /*
     * The 'request' doesn't turn a Procesoor into a T, it rather uses a Processor
     * as a resource, to be able to compute a T
     */
    public synchronized <T> T handle(Function<Processor, T> request) {
        request.apply(processor);
    }

    public synchronized void close() {
        processor.close();
    }
}

Now I want to make ResultProvider able to use several CPU cores. Ideally I would like to be able to use an ExecutorService to do this. Note that each Thread needs to instanciate its own Processor at start, and needs to .close() it when the Thread is to be deleated. The 'ExecutorService' should probable use a ThreadFactory that creates a custom Thread subclass which instanciates and closes an internal Processor.

I think what I want would be something like this:

class ResultProvider implements AutoCloseable {

    private static class ProcessorThread extends Thread {
        final private Processor processor = Processor.createNewProcessor();

        public void run() {
            try {
                super.run();
            } finally {
                processor.close();
            }
        }
    }

    private final ExecutorService executor;
    /*
     * Not sure how to create one that uses my ProcessorThread and is able
     * to be submitted Function<Processor, T> to get T...
     */

    public ResultProvider() {
        // ...
    }

    /*
     * The 'request' doesn't turn a Procesoor into a T, it rather uses a Processor
     * as a resource, to be able to compute a T
     */
    public <T> T handle(Function<Processor, T> request) {
        return executor.submit?(request).get();
    }

    public synchronized void close() {
        executor.shutdown();
        executor.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
    }
}

Now, is the feasible? I don't know how to implement this using as much of the Java concurrent classes as possible. Any advice?

Answer 1

You don't need any custom thread. All you need is to create and submit a Callable that creates a processor, calls the function, and closes the processor:

public <T> T handle(Function<Processor, T> request) {
    Callable<T> callable = () -> {
        try(Processor processor = Processor.createNewProcessor()) {
            request.apply(processor);
        } 
    }
    return executor.submit(callable).get();
}

Note that synchronized is useless: the method doesn't use any mutable state.

If you really want a single processor per thread, rather than a processor per callable, then you can use a custom factory as your question shows, except the processor would be obtained from a ThreadLocal (both in the custom thread and in the task).