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Subject: Re: [boost] Review Request: boost.lockfree
From: Tim Blechmann (tim_at_[hidden])
Date: 2009-12-14 09:54:26

hi christopher,

> I have been using this library for the past three weeks and have found
> it incredibly useful. Thank you for your excellent work, Tim!
> I have a pre-review question though. Is it possible to decouple
> container and the predefined wait lists so an user may use his own free
> list type? I have a use case which requires various container instances
> to share only one freelist instance, and I would like to implement this
> via an own free list type.

i reworked the freelist implementations, changing the api to:

template <typename T, bool fixed_size = false,
          typename Alloc = std::allocator<T> >
class internal_freelist;

the fixed_size template argument specifies, if `allocate' may hit the os
memory allocator, when the freelist is empty. if it is set to `true',
all memory needs to be allocated in the constructor, calling the default
constructor is impossible (raises a static assertion failure).

the fifo class has a freelist_t template argument for specifying the
freelist implementation:

template <typename T, typename freelist_t =
          internal_freelist<T, false, std::allocator<T> >
class fifo;

as a helper, a small wrapper class exists for supporting external (or
shared) freelists:

template <typename FreelistType>
class external_freelist;

with this api, you can use a shared freelist like:

typedef fifo<int>::freelist freelist; // freelist type
freelist fl(128); // shared
typedef external_freelist<freelist> freelist_wrapper;

// two fifos with, sharing the same freelist:
fifo<int, freelist_wrapper> f1(freelist_wrapper(fl));
fifo<int, freelist_wrapper> f2(freelist_wrapper(fl));

it is also possible to get a handle to the internal freelist of a fifo:

fifo<int> f(64);

typedef fifo<int>::freelist internal_freelist;
typedef external_freelist<internal_freelist> freelist_wrapper;

// use freelist of f for f2
internal_freelist & fl (f.get_freelist());
fifo<int, freelist_wrapper> f2(freelist_wrapper(fl));

the code is available from my git repository [1], branch
topic/freelist_tweaks. christopher (and others), what do you think about
this approach?

thanks, tim


The price an artist pays for doing what he wants is that he has to do
  William S. Burroughs

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