Hazard pointers needed with GC ?

[deadalnix]

Le 07/12/2011 18:02, Martin Nowak a écrit :
> I implemented a lock-free doubly linked list some time ago.
> I omitted the use of hazard lists because flagging the lowest
> bit would still make a valid pointer into the list node.
> Afterwards I found that
> http://www.d-programming-language.org/garbage.html explicitly states:
> p = cast(void*)(cast(int)p | 1); // error: undefined behavior
>
> Is this really needed? Guess the current GC would work properly.
>
> Also if a list node were
> Node(T)
> {
> ubyte[2] data;
> T t;
> }
> Than both a pointer to data[0] as well as one to data[1] are valid
> and effectively hold the node.
>
> martin

When doing so, you should anyway have a local pointer to that data. So 
it will not be collected until you release that local pointer, when the 
flagged one is already removed.

Flagged pointer is a temporary state. It is usefull because falgging can 
be done as an atomic operation. But the flagged pointer is not here to 
stay. It is here to mention to others thread that an ongoing operation 
is concurently running.