Re: [Boost-users] multi_index reserve but allocate

Hi Joaquin, My goal is not to be fast but to avoid allocation as I am in a high priority thread and I want to avoid possible allocation lock. I tried the allocator solution following a thread on stackoverflow (where you answered as well) https://stackoverflow.com/questions/37095641/how-to-use-boostobject-pool-as-... using something like that  boost::pool_allocator>; My issue with this solution is that the pool is actually shared across all object using a boost::pool_allocator that requires a mutex as there are multiple thread in my app. One solution could be to tag the allocator but this seems to be not possible anymore unless I am mistaken https://stackoverflow.com/questions/26188586/tag-template-parameter-in-boost... Is there a way otherwise to get a pool for each instances of my multi_index ? Thanks ! Le 19/03/2019 à 21:49, Joaquin M López Muñoz via Boost-users a écrit :

El 19/03/2019 a las 18:14, Olivier Tristan via Boost-users escribió:

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Hi,

Hi Olivier,

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Looks like that even if I call reserve on a multi_index, it stills allocate memory while I am still below the reserve size.

Is this the intended behavior ?

Yes it is. multi_index_container is node based, and, like std node-based containers (std::list, std::set, std::unordered_set, etc.), will allocate memory for its nodes as needed.

Hashed and random-access indices provide reserve() member functions (with non-equivalent semantics) that control the size of internal contiguous memory chunks maintained by these indices additionally to the nodes. So, reserve() (when available) does not (nor is designed to) guarantee that no additional memory will be allocated on further insertions.

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If so, what is the best way to avoid allocation in a fixed sized multi_index

You can write your own allocator that allocates the memory beforehand and then serves it piece by piece on allocate(). I suspect, however, that this is not going to be faster than using the default std::allocator.

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Thanks !

Best,

Joaquín M López Muñoz

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