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I did not care about compatibility, I threw out some of the old stuff, simplified other, so this is not a drop-in replacement for the original project and should not be used in production. It's just a tutorial in implementing memory allocators.

Skip to content. Star 2. Doug Lea's memory allocator 2 stars 2 forks. Branches Tags. Could not load branches. There are a lot of these bins This may look excessive, but works very well in practice. All procedures maintain the invariant that no consolidated chunk physically borders another one. Chunks in bins are kept in size order, with ties going to the approximately least recently used chunk.

The chunks in each bin are maintained in decreasing sorted order by size. This is irrelevant for the small bins, which all contain the same-sized chunks, but facilitates best-fit allocation for larger chunks. These lists are just sequential. Keeping them in order almost never requires enough traversal to warrant using fancier ordered data structures. Chunks of the same size are linked with the most recently freed at the front, and allocations are taken from the back. This results in LRU or FIFO allocation order, which tends to give each chunk an equal opportunity to be consolidated with adjacent freed chunks, resulting in larger free chunks and less fragmentation.

This bin is checked before other non-fitting chunks, so as to provide better locality for runs of sequentially allocated chunks. If supported, requests greater than a threshold are usually serviced via calls to mmap, and then later released via munmap. Larger bins are approximately logarithmically spaced. See the table below.

This makes no difference elsewhere. This is not to save space, but to simplify indexing, maintain locality, and avoid some initialization tests.

This is exploited in malloc. The bits are NOT always cleared as soon as all bins in a block are empty, but instead only when all are noticed to be empty during traversal in malloc. If any are not true, it's very likely that a user program has somehow trashed memory.

It's also possible that there is a coding error in malloc. In which case, please report it! Since more things can be checked with free chunks than inuse ones, if an inuse chunk borders them and debug is on, it's worth doing them.

Call these only with variables, not arbitrary expressions, as arguments. From there, the first successful of the following steps is taken: 1. The bin corresponding to the request size is scanned, and if a chunk of exactly the right size is found, it is taken.

Create a free Team What is Teams? Learn more. Ask Question. Asked 10 years, 3 months ago. Active 10 years, 3 months ago. Viewed 4k times. Improve this question. Dark Templar Dark Templar 6, 16 16 gold badges 44 44 silver badges 45 45 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Pubby Pubby 3, 1 1 gold badge 20 20 silver badges 26 26 bronze badges. I just have one quick question, though. Can dynamic memory ever "give memory back" to the system?

I know that sbrk is called whenever the heap needs to be extended when there are no suitable free blocks.