Question

I want to get a thread-pool behavior using TBB. But whenever I read documents about TBB they always talk about parallel-for, parallel-dowhile etc. In contrast what I need is a main thread to assign tasks to a thread pool so those tasks will be executed ‘on their own’ – execute tasks asynchronously. Tasks here can be event handling for a GUI.

Is the TBB task scheduler appropriate for such behavior? The impression I got from task scheduler is that it’s only beneficial if I have tasks that can be broken down and executed in parallel to each other.

Answer 1

Starting from version 3.0, TBB has support for asynchronous execution of tasks. For that, a special work offering method tbb::task::enqueue() was added. Unlike tbb::task::spawn(), this method guarantees that the enqueued task will be executed even if the originating thread never enters a task dispatch method such as wait_for_all().

A short usage example for task::enqueue():

class MyTask : public tbb::task {
    /*override*/ tbb::task* execute() {
        // Do the job
        return NULL; // or a pointer to a new task to be executed immediately
    }
};

MyTask* t = new (tbb::task::allocate_root()) MyTask();
tbb::task::enqueue(*t);
// Do other job; the task will be executed asynchronously

As @JimMishell mentioned in the comment, an example how to use it for handling of GUI events can be found in “Design Patterns”; and the formal description of the method is available in the Reference manual (see TBB documentation for both).