can _sync_val_compare_and_swap return anything other than int?

Question

I am trying to implement a lock free list. For this project I need and atomic compare and swap instruction that can compare a 32 bit pointer to my 'node' struct.

The node struct is as follows:

 typedef struct node
 {
    int data;
    struct node * next;
    struct node * backlink;
 }node_lf;

I am using _sync_val_compare_and_swap() to perform compare and swap operation. My question is, can this function return a value other than int? This is what I am trying to do:

node_lf cs(node_lf * address, cs_arg *old_val, cs_arg *new_val)
{
    node_lf ptr;
    ptr = (node_lf)__sync_val_compare_and_swap ((int *)address, old_val->node, new_val->node);  
    return (ptr);
}

where cs_arg is another struct to hold the node pointer and other bookkeeping information.

If there are any other methods to implement atomic compare and swap, please suggest.

David Wohlferd David Wohlferd · Accepted Answer · 2016-06-16T01:50:09

My question is, can this function return a value other than int?

The answer is yes, __sync_val_compare_and_swap can work with types other than int, including char, short, long long and __int128 (on x64).

Note that you may need to cast non-integer types to an appropriately-sized integer for __sync_val_compare_and_swap to work with them.

can _sync_val_compare_and_swap return anything other than int?

1 Answers