Re: [boost] [fiber] new version in vault

Subject: Re: [boost] [fiber] new version in vault
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2009-12-01 11:02:03

Helge Bahmann wrote:
(I'm not going to reply to most of this because I've now forgotten most 
of what I learnt when I looked into it...)

>> - An inline spin lock is the only thing that doesn't involve a function call, 
>> so leaf functions remain leaf functions and are themselves more likely to be 
>> inlined or otherwise optimised.  On systems with small caches or small flash 
>> chips where code size is important, this is a significant benefit.
>
> I'm not sure I'm following here -- for small cache sizes, inlining is 
> *not* preferrable, right?

Many C++ leaf functions are so trivial that they are smaller when 
inlined than when out-of-line, when you allow for the 
register-shuffling needed to get the arguments in the right places for 
the function call.

> A home-grown futex-based implementation is of course valid and useful, but 
> on most architectures it will not be faster, and when it is not, I fail to 
> see why it would not be preferrable to fix the problems at the libc level 
> instead.

I think that the main problem with pthread_mutex is that it has several 
features that unavoidably require extra space in the struct.  This 
can't be fixed in libc without making it no longer a pthread_mutex.

Phil.