Why does std.concurrency.Mailbox use lists ?

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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.

If I haven't overlooked something, I'd like to fill a performance 
bug on Bugzilla.