[Boost-users] Priority task queues using Boost.Asio and Boost.Thread

Subject: [Boost-users] Priority task queues using Boost.Asio and Boost.Thread
From: Kelvin Chung (kelvSYC_at_[hidden])
Date: 2011-12-08 11:30:08

Suppose I have this abstract class Task like so:

struct Task {
        virtual int doStuff() = 0;
};

I then also have this:

class CompositeTask : public Task {
        std::vector<Task> tasks;
public:
        int doStuff() {
                for (std::vector<Task>::const_iterator it = tasks.begin(); it != 
tasks.end(); ++it) {
                        it->do_stuff();
                }
        }
};

Now suppose that there is a point where I have a list of Tasks and I 
want to have them executed concurrently.  To do so, I've leveraged 
Boost.Asio to create a thread pool task queue construct (via 
boost::asio::io_service).  The next step beyond that is that I want to 
evaluate each of the tasks in CompositeTasks in parallel.  I have a few 
questions about this:

* One idea is to make a separate task thread for each CompositeTask.  
I'm under the impression that there is an absolute limit to the number 
of threads that I can make, which is determined by 
boost::thread::hardware_concurrency().  Is this true?  If so, if the 
main Task queue has that many threads, would making a second task queue 
fail because it can't get more?
* If I keep to one task queue (ie. throw all the Tasks in the 
CompositeTask to the main Task queue), then the possiblity exists of 
some kind of starvation (eg. the queue is full of CompositeTasks, and 
they are all blocking due to dependencies on Tasks in the queue).  Is 
there a way to prioritize Tasks in the queue so that this doesn't 
happen?