TBB task allocation assertion

foxcub · ‎11-02-2011

I'm trying to traverse a tree via TBB tasks and continuations. The code is below. When I run the code it keeps aborting (frequently, although not always) with the following error:

Assertion t_next->state()==task::allocated failed on line 334 of file ../../src/tbb/custom_scheduler.h Detailed description: if task::execute() returns task, it must be marked as allocated

What can be causing this problem?

template
void
traverse_tree(NodeVisitor& nv)
{
  TreeTraversal& tt = *(new(task::allocate_root()) TreeTraversal(nv));
  task::spawn_root_and_wait(tt);
}

template
class TreeTraversal: public task
{
  public:
    struct Continuation;

  public:
          TreeTraversal(NodeVisitor nv_):
            nv(nv_)                   {}

    task*    execute()
    {
      nv.pre();

      Continuation* c = new(allocate_continuation()) Continuation(nv);
      c->set_ref_count(nv.size());
      for (size_t i = 0; i < nv.size(); ++i)
      {
        TreeTraversal& tt = *(new(c->allocate_child()) TreeTraversal(nv.child(i)));
        spawn(tt);
      }

      if (!nv.size())
        return c;

      return NULL;
    }

  private:
    NodeVisitor   nv;
};

template
class TreeTraversal::Continuation: public task
{
  public:
            Continuation(NodeVisitor& nv_):
              nv(nv_)               {}
    task*      execute()                { nv.post(); return NULL; }

  private:
    NodeVisitor   nv;
};

foxcub · ‎11-02-2011

Alexey Kukanov has solved the problem on StackOverflow.