Question

Problem

I have a UDPlistener application that I need to write a unit test for. This listener continuously listens on a port and is meant to always be running on the product. We use the poco libraries for frameworks not in the standard library.

Now I need to add it to the unit test application.

Curent Solution

I thought it would be easiest to implement Poco::Runnable in a class RunApp that runs the application. Then I can create a new Poco::Thread in my unit test to run the RunApp class.

This works; my listener is running and I can send test messages in the unit test body after the thread is spawned. BUT, I need to stop the listener so other unit tests can run. I added a UDP message that tells the listener to kill itself but this is only used by the unit test and a potential security problem.

Question

Is there a way to force a Poco::Thread to stop? Or I structuring this unit test wrong? I don’t want the listener to run during all the other unit tests.

Answer 1

If instead of using a Poco::Thread you use a Poco::Task, you get a thread that can be cancelled. The following sample code (ready to run as-is) should give you an idea:

#include <Poco/Task.h>
#include <Poco/TaskManager.h>
#include <Poco/Thread.h>

#include <string>
#include <iostream>
using namespace std;

class UdpListenerTask : public Poco::Task {
public:
    UdpListenerTask(const string& name) : Task(name) { }

    void runTask() {
        cout << name() << ": starting" << endl;
        while (! isCancelled()) {
            // Do some work. Cannot block indefinitely, otherwise it
            // will never test the isCancelled() condition.
            doSomeWork();
        }
        cout << endl << name() << ": cancelled " << endl;
    }
private:
    int doSomeWork() {
        cout << "*" << flush;
        // Simulate some time spent doing work
        int i;
        for (i = 0; i < INT32_MAX/1000; i++) { }
        return i;
    }
};

void runUdpProbe() {
    // Simulate some time spent running the probe.
    Poco::Thread::sleep(1000);
}

int main() {
    Poco::TaskManager tm;
    UdpListenerTask* st = new UdpListenerTask("task1");
    tm.start(st); // tm takes ownership

    // Run test 1.
    runUdpProbe();
    // Test 1 done. Cancel the UDP listener
    st->cancel();

    // Run all the other tests

    // cleanup
    tm.joinAll();
    return 0;
}

The POCO slides Multithreading give examples of usage of both Poco::Thread and Poco::Task.

As an aside, a unit test should bypass the UDP communication via abstract classes and mock objects; I think this test should be called feature test 🙂