Intel Threading Building Blocks

Blocking Style with Children

Example 9-4 shows the recommended style for a recursive task of type T where each level spawns k children.

Example 9-4. Blocking style with children

task* T::execute() {
    if( not recursing any further ) {
        ...
    } else {
        set_ref_count(k+1);
        task& tk = new( allocate_child() ) T(...);  tk.spawn();
        task& tk-1= new( allocate_child() ) T(...); tk-1.spawn();
        ...
        task& t1 = new( allocate_child() ) T(...);  t1.spawn_and_wait(t1);
    }
    return NULL;
}

Child construction and spawning may be reordered if convenient, as long as a task is constructed before it is spawned.

The key points of the pattern are:

• The call to set_ref_count uses k+1 as its argument. The extra 1 is critical.

• Each task is allocated by allocate_child.