How to check threads priority in a process using top or htop

I am trying to set priority of threads using poco threads and threadpool API. but when I try running program and try to see the set priority using htop it is always showing 20. Also the the OS min and MAX priority is being printed as 0 in terminal as as I have added couts to print the same. I am running program on ubuntu 16 based Linux. Any help or suggestion will be appreciated.

Essentially I want to increase the priority of few threads. I was using poco TaskManager but it is not providing the mechanism to set priority. so I am trying to use Poco threads to do the same but it is also not helping.

    #include <Poco/Runnable.h>
    #include <Poco/Thread.h>
    #include <Poco/ThreadPool.h>
    #include <Poco/ThreadTarget.h>
    #include <Poco/RunnableAdapter.h>

    #include <string>
    #include <iostream>

    class Foo : public Poco::Runnable
    {
    public:
        virtual void run()
        {
            std::cout << "  run() start" << std::endl;
            Poco::Thread *t = Poco::Thread::current();
            int pmax = t->getMaxOSPriority();
            int pmin = t->getMinOSPriority();
            cout << "T1 priority " << t->getOSPriority()  << " min " << pmin << " max " << pmax << endl;
            t->setOSPriority(pmax);
            cout << "T1 priority " << t->getOSPriority() << endl;
            cout << "T1 priority " << t->getPriority() << endl;
            Poco::Thread::sleep(200);
            std::cout << "  run() end" << std::endl;
        }


    };

    int main()
    {
        // setting priority Using threadpool 
        Poco::ThreadPool::defaultPool().addCapacity(16);

        Foo foo;
        Poco::ThreadPool::defaultPool().startWithPriority(Poco::Thread::Priority::PRIO_LOW, foo);
        Poco::ThreadPool::defaultPool().joinAll();

        // setting priority Using thread 
        Poco::Thread thread;
        thread.start(foo);
        thread.join();

        return 0;
    }