Task seemingly dropped

pedro_p_3 · ‎09-24-2015

Hi there,

I am using TBB 4.1 in production and I have recently came across a problem that *seems* to indicate that on occasion tasks can be dropped without every being executed. I am using the following call to spawn a task:

      auto &task = *new(tbb::task::allocate_root()) DrainMailbox(*me, this);
      LOG << "Spawning " << &task;
      tbb::task::spawn(task);

And inside the task I log as follows:

struct TBBMailbox::DrainMailbox : public tbb::task 
{   
   DrainMailbox (TBBMailbox::PImpl &me, TBBMailbox const *ptr)
      : me (me), mbox_ptr (ptr)
   {}
   
   tbb::task* execute () 
   {
      LOG  << " task: " << this << " executing";

...

On occasion I see the "spawn" log entry but not the corresponding "executing" log entry (other tasks are still being spawned and executed - so I know TBB has enough non blocked threads to work with).

Any ideas on what could be going wrong? This is in on Linux x64, 3.13.

Thanks in advance

RafSchietekat · ‎09-24-2015

If you want to "fire and forget" a task, use enqueue() rather than spawn(). Otherwise you could explicitly spawn_root_and_wait().