benpm / cppmempool

very simple C++ heterogeneous memory pool with thread safety

💾 MemPool

A very simple (only ~150 lines) C++ thread safe heterogenous header-only memory pool class with smart pointer support. Use this if you want to eliminate frequent allocations for small, short-lived objects.

Features

• Heterogenous types: use any mix of any type in the pool
• Basic thread safety using std::mutex
• Support for directly creating smart pointers (that's actually all it can do rn... working on it)
• No dependencies! Not that that's surprising
• Configured through template arguments

Limitations

With the implementation being this simple, there are definitely some significant tradeoffs:

• Objects allocated cannot be larger than Chunk::size (default is 8192 bytes). You should get a compiler error if you try this
• Unused space in allocated chunks is not reused until the entire chunk is empty! So if some of your objects have long lifetimes, expect your memory usage to just continue growing as you make more allocations in the pool.
• Blocks are currently not deallocated when empty, but they are re-used
• Requires C++11

Usage

#include <iostream>
#include <mempool.hpp>

using namespace benpm;

struct Foo {
    std::string name;
    int hp;
    Foo(std::string name, int hp) : name(name), hp(hp) {}
};

struct Bar {
    float val;
    Bar(float val) : val(val) {}
};

int main(void) {
    MemPool pool;
    std::shared_ptr<Foo> fooA = pool.emplace<Foo>("foo A", 10);
    std::shared_ptr<Bar> barA = pool.emplace<Bar>(16.16);
    std::cout << fooA->name << std::endl;
    std::cout << barA->val << std::endl;
    ///TODO: put example for normal allocation and free
}

Check out benchmark.cpp for more

How it Works

todo

Benchmark

(This is a work in progress)

operation	time (pool)	time (no pool)
(raw) init insert	176ms	190ms
(raw) random removal	51ms	36ms
(raw) second insert	75ms	78ms
(raw) random access	817ms	898ms
(raw) sequential access	18ms	22ms
(raw) destruction	101ms	72ms
(shared) init insert	413ms	251ms
(shared) random removal	55ms	55ms
(shared) second insert	129ms	108ms
(shared) random access	974ms	930ms
(shared) sequential access	19ms	33ms
(shared) destruction	213ms	120ms

Contribution

I'm still a C++ baby so if you have some ideas for improvement, please feel free to make an issue or a PR!

Todo

• Support for non-smart pointer alloc
• std::unique_ptr support
• Benchmarks (with both insert after and insert before)
• More complex example
• Block alignment
• Explanation of how it works