PCSafeDeque

import java.io.*;
import java.util.Arrays;
import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.function.Function;

final class Main {

    private static final class ThreadPool<T> implements Closeable {
        private final Thread[] actionThreads;
        private final Queue<T> taskQueue = new LinkedBlockingQueue<>();
        private volatile boolean working = false;

        public ThreadPool(
                final int threadsAmount,
                final Function<T, Void> action
        ) {
            actionThreads = new Thread[threadsAmount];

            for (int i = 0; i < threadsAmount; i++)
                actionThreads[i] = new Thread(() -> {
                    while (working || !taskQueue.isEmpty()) {
                        final var v = taskQueue.poll();
                        if (v != null) action.apply(v);
                    }
                });
        }

        public final void start() {
            working = true;
            Arrays.stream(actionThreads).forEach(Thread::start);
        }

        public final void push(final T elem) {
            taskQueue.offer(elem);
        }

        @Override
        public void close() {
            working = false;
        }
    }

    private static final int fib(final int number) {
        if (number < 3)
            return 1;

        var f = 1;
        var s = 1;

        for (int i = 3; i <= number; i++) {
            final var mem = s;
            s += f;
            f = mem;
        }

        return s;
    }

    public static final void main(final String[] args) throws IOException {
        final var out = System.out;

        try (final var reader = new BufferedReader(new InputStreamReader(System.in))) {
            out.print("Threads amount: ");

            try  (final var pool = new ThreadPool<Integer>(
                    Integer.parseInt(reader.readLine()),
                    (num) -> {
                        out.println(fib(num));
                        return null;
                    }
            )) {
                try (final var fileReader = new BufferedReader(new FileReader("file.txt"))) {
                    pool.start();
                    fileReader.lines().forEach((x) -> pool.push(Integer.parseInt(x)));
                }
            }
        }
    }
}