Re: [boost] [lockfree::fifo] Review

Subject: Re: [boost] [lockfree::fifo] Review
From: Helge Bahmann (hcb_at_[hidden])
Date: 2009-12-21 09:58:26

On Mon, 21 Dec 2009, Chris M. Thomasson wrote:
>       object = m_buffer[i].exchange(object, memory_order_release);
>
>       if (object)
>       {
>           atomic_thread_fence(memory_order_acquire);
>       }
>
>       return object;

[...]

>   T* pop()
>   {
>       T* object = m_buffer[m_tail].exchange(NULL, memory_order_acquire);
>
>       if (object)
>       {
>           m_tail = (m_tail == T_depth - 1) ? 0 : (m_tail + 1);
>       }
>
>       return object;

you generally do not need "memory_order_acquire" when dereferencing an 
"atomically published" pointer -- "memory_order_consume" suffices to 
provide the proper ordering for all operations that are data-dependent on 
the pointer value (and any dereference obviously needs the value to 
compute the memory address to access).

This is faster on any non-x86 and non-alpha by a fair amount.

Regards,
Helge