Method get_task

benchmarks/tbb/scheduler.cpp:855–907

#endif /* __TBB_TASK_PRIORITY */

inline task* generic_scheduler::get_task() {
    __TBB_ASSERT( in_arena(), NULL );
    task* result = NULL;
    size_t T = __TBB_load_relaxed(my_arena_slot->tail); // mirror
retry:
    __TBB_store_relaxed(my_arena_slot->tail, --T);
    atomic_fence();
    if ( (intptr_t)__TBB_load_relaxed(my_arena_slot->head) > (intptr_t)T ) {
        acquire_task_pool();
        size_t H = __TBB_load_relaxed(my_arena_slot->head); // mirror
        if ( (intptr_t)H <= (intptr_t)T ) {
            // The thief backed off - grab the task
            result = my_arena_slot->task_pool_ptr[T];
            __TBB_ASSERT( !is_poisoned(result), NULL );
            poison_pointer( my_arena_slot->task_pool_ptr[T] );
        }
        else {
            __TBB_ASSERT ( H == __TBB_load_relaxed(my_arena_slot->head)
                        && T == __TBB_load_relaxed(my_arena_slot->tail)
                        && H == T + 1, "victim/thief arbitration algorithm failure" );
        }
        if ( (intptr_t)H < (intptr_t)T )
            release_task_pool();
        else
            reset_deque_and_leave_arena( /*locked=*/true );
    }
    else {
        __TBB_control_consistency_helper(); // on my_arena_slot->head
        result = my_arena_slot->task_pool_ptr[T];
        __TBB_ASSERT( !is_poisoned(result), NULL );
        poison_pointer( my_arena_slot->task_pool_ptr[T] );
    }
    if( result && is_proxy(*result) ) {
        task_proxy &tp = *(task_proxy*)result;
        result = tp.extract_task<task_proxy::pool_bit>();
        if( !result ) {
            // Proxy was empty, so it's our responsibility to free it
            free_task<small_task>(tp);
            if ( in_arena() )
                goto retry;
            __TBB_ASSERT( is_quiescent_local_task_pool_reset(), NULL );
            return NULL;
        }
        GATHER_STATISTIC( ++my_counters.proxies_executed );
        // Following assertion should be true because TBB 2.0 tasks never specify affinity, and hence are not proxied.
        __TBB_ASSERT( is_version_3_task(*result), "backwards compatibility with TBB 2.0 broken" );
        // Task affinity has changed.
        my_innermost_running_task = result;
        result->note_affinity(my_affinity_id);
    }
    __TBB_ASSERT( result || is_quiescent_local_task_pool_reset(), NULL );
    return result;
} // generic_scheduler::get_task

task* generic_scheduler::steal_task( arena_slot& victim_slot ) {
    task** victim_pool = lock_task_pool( &victim_slot );