How to use mmap to allocate a memory in heap?

Question

Just the question stated, how can I use mmap() to allocate a memory in heap? This is my only option because malloc() is not a reentrant function.

Answer 1

Make a simple slab allocator

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Although allocating memory in a signal handler¹ does seem like something best avoided, it certainly can be done.

No, you can't directly use malloc(). If you want it to be in the heap then mmap won't work either.

My suggestion is that you make a special-purpose slab allocator based on malloc.

Decide exactly what size of object you want and preallocate some number of them. Allocate them initially with malloc() and save them for concurrent use later. There are intrinsically reentrant queue-and-un-queue functions that you can use to obtain and release these blocks. If they only need to be managed from the signal handler then even that isn't necessary.

Problem solved!

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^{1. And if you are not doing that then it seems like you have an embedded system or could just use malloc().}