Memory Arena

General Usage Performance
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Please do not suggest any external libraries.

This suggests that you want to learn how to implement a simple arena allocator in julia. The short answer is “the obvious way, nothing julia specific here”.

Since you are asking the question anyway, I assume this is not obvious to you. Props to you for learning something new, don’t get annoyed when I write something that is in fact obvious to you.

julia> mutable struct Arena
       ptr::Ptr{Cvoid}
       len::Int
       cap::Int
       end
julia> function makeArena(cap::Int)
       cap == 0 && return Arena(Base.C_NULL, 0, 0)
       Arena(ccall(:malloc, Ptr{Cvoid}, (Csize_t,), cap), 0, cap)
       end
julia> function freeArena(a::Arena)
       ccall(:free, Cvoid, (Ptr{Cvoid},), a.ptr)
       a.ptr = C_NULL
       a.len = 0
       a.cap = 0
       nothing
       end
julia> function allocFromArena(a::Arena, size)
       a.len + size > a.cap && return C_NULL
       res = a.ptr + a.len
       a.len += size
       res
       end

And that’s it. You can make an arena, tear it down, and allocate memory from it. I even introduced some minor safety features to make double-free and use-after-free of the arena more benign.

From that, there are lots of ways you can go. Thread-safety via atomics. Convenience methods for using the arena as a stack. Methods to get aligned allocations. Avoid memory leaks by letting julia GC take over the freeing via finalizers. Whatever floats your boat.

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