Information on TBB Scheduler and Task Stealing

Dmitriy Vyukov
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November 9, 2008 3:31 AM PST
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#4
Quoting - abhishek84

task* GenericScheduler::steal_task( UnpaddedArenaSlot& arena_slot, depth_type d ) {

...

TaskPool* tp = arena_slot.task_pool;
depth_type i = tp->prefix().steal_begin;
if( i<d )
i = d;
for(; i<=steal_end>>1; ++i ) {

if( result = tp->array[i] ) {

tp->array[i] = result->prefix().next;

#ifdef(MY_COUNTER)
counter--
#endif

...

}

It seems that you are working with not latest release. However be aware that in latest releases there is another issue - mailboxes. Single task can reside in thread's work-stealing deque AND in another thread's mailbox SIMULTANEOUSLY.

get_task() function copes with it internally. But steal_task() doesn't. I.e. steal_task() can return such task, and then the task will be discarded, because it's already consumed through get_task().

If you will be working with latest version you must account for this.

 

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