Resource reservation has been widely used in many realtime systems to guarantee the proper access to the system resources. Despite that being the memory a key resource, it has attracted little attention in the specific area of realtime systems. In order to use dynamic memory in real-time systems, two fundamental problems have to be settled: allocation and deallocation in bounded time, and the fragmentation problem. Recent research results have removed the unbounded timing behaviour of the dynamic memory allocation. TLSF is a fast and constant time memory allocator. Although the fragmentation is still an open research problem, we present a deep and comparative analysis showing that it has several characteristics in common with the well-known WCET analysis. In this paper, we present a contract based framework for handling dynamic memory in real-time systems. The framework provides both: i) timing guarantee for dynamic memory allocation and deallocation operations, and ii) spatial guarantee by using a flexible contract negotiation model.