Function main

examples/thread_pool_ex.cpp:99–181

// ----------------------------------------------------------------------------------------

int main() try
{
    // tell the logger to print out everything
    dlog.set_level(LALL);


    dlog << LINFO << "schedule a few tasks";

    test taskobj;
    // Schedule the thread pool to call taskobj.mytask().  Note that all forms of
    // add_task() pass in the task object by reference.  This means you must make sure,
    // in this case, that taskobj isn't destructed until after the task has finished
    // executing.
    tp.add_task(taskobj, &test::mytask);

    // This behavior of add_task() enables it to guarantee that no memory allocations
    // occur after the thread_pool has been constructed, so long as the user doesn't
    // call any of the add_task_by_value() routines.  The future object also doesn't
    // perform any memory allocations or contain any system resources such as mutex
    // objects.  If you don't care about memory allocations then you will likely find
    // the add_task_by_value() interface more convenient to use, which is shown below.



    // If we call add_task_by_value() we pass task objects to a thread pool by value.
    // So in this case we don't have to worry about keeping our own instance of the
    // task.  Here we create a lambda function and pass it right in and everything
    // works like it should.
    dlib::future<int> num = 3;
    tp.add_task_by_value([](int& val){val += 7;}, num);  // adds 7 to num
    int result = num.get();
    dlog << LINFO << "result = " << result;   // prints result = 10


    // dlib also contains dlib::async(), which is essentially identical to std::async()
    // except that it launches tasks to a dlib::thread_pool (using add_task_by_value)
    // rather than starting an unbounded number of threads.  As an example, here we
    // make 10 different tasks, each assigns a different value into the elements of the
    // vector vect.
    std::vector<std::future<unsigned long>> vect(10);
    for (unsigned long i = 0; i < vect.size(); ++i)
        vect[i] = dlib::async(tp, [i]() { return i*i; });
    // Print the results
    for (unsigned long i = 0; i < vect.size(); ++i)
        dlog << LINFO << "vect["<<i<<"]: " << vect[i].get();


    // Finally, it's usually a good idea to wait for all your tasks to complete.
    // Moreover, if any of your tasks threw an exception then waiting for the tasks
    // will rethrow the exception in the calling context, allowing you to handle it in
    // your local thread.  Also, if you don't wait for the tasks and there is an
    // exception and you allow the thread pool to be destructed your program will be
    // terminated.  So don't ignore exceptions :)
    tp.wait_for_all_tasks();


    /* A possible run of this program might produce the following output (the first
       column is the time the log message occurred and the value in [] is the thread