Struct wasmtime_runtime::MemoryImageSlot

pub struct MemoryImageSlot { /* private fields */ }

A single slot handled by the copy-on-write memory initialization mechanism.

The mmap scheme is:

base ==> (points here)

• (image.offset bytes) anonymous zero memory, pre-image
• (image.len bytes) CoW mapping of memory image
• (up to static_size) anonymous zero memory, post-image

The ordering of mmaps to set this up is:

• once, when pooling allocator is created:

  • one large mmap to create 8GiB * instances * memories slots

• per instantiation of new image in a slot:

  • mmap of anonymous zero memory, from 0 to max heap size (static_size)
  • mmap of CoW’d image, from image.offset to image.offset + image.len. This overwrites part of the anonymous zero memory, potentially splitting it into a pre- and post-region.
  • mprotect(PROT_NONE) on the part of the heap beyond the initial heap size; we re-mprotect it with R+W bits when the heap is grown.

Trait Implementations

impl Debug for MemoryImageSlot

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Drop for MemoryImageSlot

fn drop(&mut self)

Executes the destructor for this type.