Why does std.concurrency.Mailbox use lists ?

[via Digitalmars-d]

On Monday, 8 September 2014 at 17:06:34 UTC, badlink wrote:
> Hello,
> I'm creating a real-time 3D app using std.concurrency for 
> exchanging messages between the renderer and a few mesher 
> threads.
> The app runs fine, but once in a while I get a consistent FPS 
> drop.
> Already aware that the cause is the GC (a call to GC.disable 
> eliminates the slowdowns) I timed all functions and found that 
> spawn() sometimes requires more than 50 ms to returns.
> I did a quick search through Phobos and found out that the 
> Mailbox implementation in std.concurency uses a private List 
> struct where every call to .put() needs to allocate a new node 
> :(
>
> Why is that ?
> I would have used for example a ring buffer which can do all 
> the things the Mailbox needs and faster in every way. The 
> growing time can be compensated by a right call to 
> setMaxMailboxSize() and any random removal can be a swap of the 
> last element with the one being removed.
>

AFAICS, the documentation doesn't write about any ordering 
guarantees of messages, but I can imagine that there are implicit 
expectations. In particular prioritySend() could break, if the 
implementation isn't done carefully.