Method bind_to

benchmarks/tbb/task_group_context.cpp:260–318

}

void task_group_context::bind_to ( generic_scheduler *local_sched ) {
    __TBB_ASSERT ( __TBB_load_relaxed(my_kind) == binding_required, "Already bound or isolated?" );
    __TBB_ASSERT ( !my_parent, "Parent is set before initial binding" );
    my_parent = local_sched->my_innermost_running_task->prefix().context;
#if __TBB_FP_CONTEXT
    // Inherit FPU settings only if the context has not captured FPU settings yet.
    if ( !(my_version_and_traits & fp_settings) )
        copy_fp_settings(*my_parent);
#endif

    // Condition below prevents unnecessary thrashing parent context's cache line
    if ( !(my_parent->my_state & may_have_children) )
        my_parent->my_state |= may_have_children; // full fence is below
    if ( my_parent->my_parent ) {
        // Even if this context were made accessible for state change propagation
        // (by placing __TBB_store_with_release(s->my_context_list_head.my_next, &my_node)
        // above), it still could be missed if state propagation from a grand-ancestor
        // was underway concurrently with binding.
        // Speculative propagation from the parent together with epoch counters
        // detecting possibility of such a race allow to avoid taking locks when
        // there is no contention.

        // Acquire fence is necessary to prevent reordering subsequent speculative
        // loads of parent state data out of the scope where epoch counters comparison
        // can reliably validate it.
        uintptr_t local_count_snapshot = __TBB_load_with_acquire( my_parent->my_owner->my_context_state_propagation_epoch );
        // Speculative propagation of parent's state. The speculation will be
        // validated by the epoch counters check further on.
        my_cancellation_requested = my_parent->my_cancellation_requested;
#if __TBB_TASK_PRIORITY
        my_priority = my_parent->my_priority;
#endif /* __TBB_TASK_PRIORITY */
        register_with( local_sched ); // Issues full fence

        // If no state propagation was detected by the following condition, the above
        // full fence guarantees that the parent had correct state during speculative
        // propagation before the fence. Otherwise the propagation from parent is
        // repeated under the lock.
        if ( local_count_snapshot != the_context_state_propagation_epoch ) {
            // Another thread may be propagating state change right now. So resort to lock.
            context_state_propagation_mutex_type::scoped_lock lock(the_context_state_propagation_mutex);
            my_cancellation_requested = my_parent->my_cancellation_requested;
#if __TBB_TASK_PRIORITY
            my_priority = my_parent->my_priority;
#endif /* __TBB_TASK_PRIORITY */
        }
    }
    else {
        register_with( local_sched ); // Issues full fence
        // As we do not have grand-ancestors, concurrent state propagation (if any)
        // may originate only from the parent context, and thus it is safe to directly
        // copy the state from it.
        my_cancellation_requested = my_parent->my_cancellation_requested;
#if __TBB_TASK_PRIORITY
        my_priority = my_parent->my_priority;
#endif /* __TBB_TASK_PRIORITY */
    }
    __TBB_store_relaxed(my_kind, binding_completed);