A Wait-Free Dynamic Storage Allocator by Adopting the Helping Queue Pattern

P. Stellwag, J. Krainz, and W. Schröder-Preikschat (Germany)


Storage Allocator, Malloc, Wait-Free, Real-Time Systems


Most of the real-time applicable dynamic storage allocators rely on conventional locking strategies for protecting globally accessible data. But it is common that lock compositions do not scale well under high allocation and deallocation rates in parallel scenarios, as they lead to convoy effects. Furthermore, lock compositions lead to jitter, which is often a critical factor in real-time systems. Additionally, it is often desirable to guarantee progress of threads in order to be able to determine the worst-case execution time. This led us designing a wait-free dynamic storage allocator (DSA), which can guarantee progress of threads and does not influence other threads to make progress. Our DSA implementation relies on a kind of buddy strategy with approximate best-fit. Hence, it ensures for this kind of allocation strategy typical memory wastage as a result of internal fragmentation. Preliminary tests show that we can outperform established DSA implementations in terms of predictability, like the famous TLSF memory allocator. To the best of our knowledge, our DSA is the first known approach using a scalable and bounded nonblocking synchronization strategy. Our approach towards a wait-free DSA algorithm is applicable in real-time applications where adequate a priori knowledge about the memory requirements is available because it uses a statically allocated heap. We think that most real-time systems — especially ones with hard timing constraints — fulfill this precondition.

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