Allocators

Lifetimes Hierarchy

• Permanent Allocation :

  • Memory that is never freed until the end of the program. This memory is persistent during the program lifetime.

• Transient Allocation :

  • Memory that has a cycle-based lifetime. This memory only persists for the “cycle” and is freed at the end of this cycle. An example of a cycle could be a frame within a graphical program (e.g. a game) or an update loop.

• Scratch/Temporary Allocation :

  • Short-lived, quick memory that you just want to allocate and forget about. A common case for this is when generating a string and outputting it to a log.

Types of Allocators

• Odin#Memory: Allocators .

  • There's a lot of things there.

• C#malloc .

Where to allocate

Algorithms for searching for free blocks

• First Fit.

• Next Fit.

  • Optimization from First Fit, but increases fragmentation, apparently.

• Best Fit.

Coalescing ("Growing together, fusing")

• When we have two free blocks next to each other, merge them together into one large block.

Strategies

• On free: coalesce.

  • Coalesce only above and below, once on free.

  • This is preferred as it has a more predictable performance.

• Coalesce once in a while.

  • This can take a little while, but removes the need to do it every operation.

• Free List, Where to allocate a block, Coalescing - Chris Kanich .

• Exploring a heap allocated memory with gdb , showing free lists, etc - Chris Kanich .