2024年9月20日 02:58，Boqun Feng <boqun.feng@xxxxxxxxx> wrote：
>
> On Thu, Sep 19, 2024 at 09:57:12PM +0800, Alan Huang wrote:
> [...]
>>>
>>> I think you're right. (Although the node will be eventually deleted at
>>> cleanup_hazptr_context(), however there could be a long-live
>>> hazptr_context). It should be:
>>>
>>> hazptr_t val = smp_load_acquire(&hzcp->slots[i]);
>>> struct hazptr_slot_snap *snap = &hzcp->snaps[i];
>>>
>>> if (val != snap->slot) { // val changed, need to update the tree node.
>>> // Already in the tree, need to remove first.
>>> if (!is_null_or_unused(snap->slot)) {
>>> reader_del(tree, snap);
>>> }
>>>
>>> // use the latest snapshot.
>>> snap->slot = val;
>>>
>>> // Add it into tree if there is a reader
>>> if (!is_null_or_unused(val))
>>> reader_add(tree, snap);
>>> }
>>
>> It seems like that two different hazptr_context can’t be used to protect the same pointer?
>>
>> Otherwise the following can happen?
>>
>> thread1 thread2 thread3(worker) thread4
>> hazptr_tryprotect(hzp1, ptr1) hazptr_tryprotect(hzp2, ptr1)
>> add ptr1 to tree
>
> Note that we have snapshot rb_node for each hazard pointer slot, so here
> thread3 actually would add two rb_nodes with ->slot == ptr1 here.
Ok, good to know the rbtree can have multiple nodes with the same key.
Thanks for the explanation!
>
>> hazptr_clear(hzp1)
>> hazptr_tryprotect(hzp1, ptr2)
>> delete ptr1 from tree unpub ptr1
>
> Therefore, there is still one rb_node with ->slot == ptr1 in the tree
> after the deletion, so updaters won't invoke ptr1's callback.
>
> Regards,
> Boqun
>
>> call_hazptr(ptr1)
>> oops: invoke ptr1's callback
>> Or am I missing something?
>>
>>>
>>> Regards,
>>> Boqun
>>>
>>>> I'm not so sure...
>>>>
>>>> Thanks
>>>> Lai
