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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.


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