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0.2.3 Apr 13, 2019
0.2.2 Apr 13, 2019
0.1.7 Apr 12, 2019

#291 in Memory management

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Used in context-coroutine

MIT license

4.5K SLoC


This provides allocators suitable for a number of use cases.

All of these allocators implement the traits ::std::alloc::GlobalAlloc and ::std::alloc::Alloc, as we as a common base trait, Allocator.

The most useful is a global allocator which allows switching between thread, coroutine and global (and thuse lockable) memory allocators, using the macro global_thread_and_coroutine_switchable_allocator().

Allocators provided include:-

  • BumpAllocator, a never-freeing bump allocator with slight optimization for reallocating the last allocation.
  • BitSetAllocator, an allocator that uses a bit set of free blocks; uses 64-bit chunks to optimize searches.
  • MultipleBinarySearchTreeAllocator, an efficient allocator which minimizes fragmentation by using multiple red-black trees of free blocks which are aggresively defragmented.
  • ContextAllocator, a choice of either BumpAllocator, BitSetAllocator or MultipleBinarySearchTreeAllocator.
  • MemoryMapAllocator, a NUMA-aware mmap allocator with support for NUMA policies.
  • GlobalThreadAndCoroutineSwitchableAllocator, suitable for replacing the global allocator and provides switchable allocators for global, thread local and context (coroutine) local needs; must b created using the macro global_thread_and_coroutine_switchable_allocator.

Allocators use a MemorySource to obtain and release memory. Memory sources provided include:-

  • MemoryMapSource, useful for thread-local allocators as it can obtain memory from NUMA-local memory.
  • ArenaMemorySource, an arena of fixed blocks which is itself backed by a memory source; this is useful as a source for the BumpAllocator and BitSetAllocator when used for contexts.

Additionally a number of adaptors are provided:-

  • AllocatorAdaptor, an adaptor of Allocator to GlobalAlloc and Alloc; use it by calling Allocator.adapt()
  • GlobalAllocToAllocatorAdaptor, an adaptor of GlobalAlloc to Allocator, useful for assigning a global allocator to GlobalThreadAndCoroutineSwitchableAllocator.
  • AllocToAllocatorAdaptor, an adaptor of Alloc to Allocator.

When using GlobalThreadAndCoroutineSwitchableAllocator, it is possible to save and restore the allocator state for the currently running context (coroutine). It is also possible to create a lockless, fast thread-local allocator which make use of NUMA memory, unlike a conventional malloc.


  • Investigate wrapping Rampant Pixel's Memory Allocator.
  • Investigate using DPDK's allocator.
  • Investigate a B-tree backed allocator.
  • Investigate a design that uses multiple doubly-linked 'free' lists of blocks; blocks can be variable in size but the free list is sorted
    • Iteration over a particular free-list range may encountered blocks too small, or blocks so large they can be split up.
    • This design is similar to that used by DPDK.
    • To make the allocator multi-threaded, DPDK takes a spin lock on a particular 'heap', which is a set of free lists.
  • Investigate a fall-back over-size allocator for a thread-local allocator, which could use the NumaMemoryMapSource underneath.
  • Investigate supporting over-size allocations in MultipleBinarySearchTreeAllocator by scanning the largest binary search tree for contiguous blocks.
  • Investigate a persistent-memory backed allocator.
  • Properly support excess allocations and Alloc's grow_in_place functions, but only if these are used by downstream collections.
  • Investigate the use of the BMI1 intrinsics _blsi_u64 (extract lowest set bit), _blsmsk_u64 and _blsr_u64.


The license for this project is MIT.