public synchronized Service threadPool(int maxThreads, int minThreads, int idleTimeoutMillis) {
        if (initialized) {
            throwBeforeRouteMappingException();
        }

        this.maxThreads = maxThreads;
        this.minThreads = minThreads;
        this.threadIdleTimeoutMillis = idleTimeoutMillis;

        return this;
    }
Configures the embedded web server's thread pool.

@param maxThreads        max nbr of threads.
@param minThreads        min nbr of threads.
@param idleTimeoutMillis thread idle timeout (ms).
@return the object with the embedded web server's thread pool configured
src/main/java/spark/Service.java