void try_reclaim(node* old_head)
{
if (threads_in_pop == 1) {
// claim list of to-be-deleted nodes
node* nodes_to_delete = to_be_deleted.exchange(nullptr);
// are you the only thread in pop()?
if (!--threads_in_pop) {
// on other thread can be accessing this list of pending nodes.
// There may be new pending nodes, but you're not bothered
// about them for now, as long as it's safe to reclaim your
// list.
delete_nodes(nodes_to_delete);
}
else if (nodes_to_delete) {
// not safe to reclaim the nodes, so if there are any,
// you must chain them back onto the list of nodes
// pending deletion.
// This can happen if there are multiple threads accessing the
// data structure concurrently. Other threads might have
// called pop() in between the first tet of thread_in_pop and
// the "claiming" of the list, potentially adding new nodes to
// the list that are still being accesed by one or more of
// those other threads.
chain_pending_nodes(nodes_to_delete);
}
delete old_head;
}
else {
// not safe to delete any nodes, add the node to the pending list
chain_pending_node(old_head);
--threads_in_pop;
}
}
void lock_free_stack<T>::try_reclaim(Node* old_head)
{
if (threads_in_pop == 1) //единственный в pop() => попытка удалить
{
//можно безопасно удалять только что исключенный из списка old_head
delete old_head;
//Пытаемся удалить накопившиеся исключенные узлы
Node* nodes_to_delete = to_be_deleted.exchange(nullptr); //захватить список на удаление
if (!--threads_in_pop)//точно единственный?
{
//удаляем узлы, накопившиеся в списке nodes_to_delete
while(nodes_to_delete)
{
Node* next = nodes_to_delete->next;
delete nodes_to_delete;
nodes_to_delete = next;
}
}
else if(nodes_to_delete)
{
chain_pending_nodes(nodes_to_delete);
} //если в захваченном списке что-то было, вернуть это в общий список узлов на удаление
}
else
{ //удалять old_head сейчас нельзя => добавим в список для удаления (удалим как-нибудь потом)
chain_pending_node(old_head);
--threads_in_pop;
}
}
void try_reclaim(node* old_head) {
if (1 == threads_in_pop) {
node* nodes_to_delete =
to_be_deleted.exchange(nullptr);
if (!--threads_in_pop) {
delete_nodes(nodes_to_delete);
}
else if(nodes_to_delete) {
chain_pending_nodes(nodes_to_delete);
}
delete old_head;
}
else {
chain_pending_node(old_head);
--threads_in_pop;
}
}
