Struct MemoryImage 

pub struct MemoryImage { /* private fields */ }

Available on crate feature runtime only.

A copy-on-write image of the initial contents of a linear memory.

When Config::memory_init_cow is enabled Wasmtime prepares, where possible, an image of a module’s data segments for each of its linear memories that can be mapped into memory copy-on-write instead of being copied byte-by-byte. Such images are handed to LinearMemory::init_from_image for the specific memory implementation to map into its underlying representation.

An image covers len() bytes of the linear memory starting at linear_memory_offset(). Both values are multiples of the host page size, and the image always lies within the minimum size of the memory it was created for. All other bytes are expected to be zero.

Cloning a MemoryImage is cheap and keeps the underlying image alive.

Implementations

impl MemoryImage

pub fn linear_memory_offset(&self) -> usize

Returns the offset, in bytes, within linear memory where this image starts.

This is guaranteed to be a multiple of the host page size.

pub fn len(&self) -> usize

Returns the length, in bytes, of this image.

This is guaranteed to be a multiple of the host page size.

pub fn is_empty(&self) -> bool

Returns whether this image is empty (length equal to zero).

pub fn data(&self) -> &[u8]

Returns the bytes of this image.

The returned slice is len() bytes long and holds the initial contents of linear memory starting at linear_memory_offset(). All bytes of the memory outside of that range are initially zero.

pub unsafe fn map_at(&self, base: *mut u8) -> Result<()>

Maps this image copy-on-write into the linear memory starting at base.

The bytes base + linear_memory_offset() up to base + linear_memory_offset() + len() are replaced with a private, readable and writable copy-on-write mapping of the image. Nothing outside of that range is modified.

Returns an error if base is not aligned to the host page size or if the underlying mapping operation fails.

Safety

The caller must exclusively own the virtual memory range being mapped over, nothing may hold references into it, and it must be valid for its pages to be replaced by a new mapping (for example by mmap with MAP_FIXED on Unix). Any previous contents and memory protections of that range are lost. The mapping lives until the range is unmapped or mapped over again by its owner. In particular, the runtime does not unmap the image by itself. The owner of the virtual memory range must clean it up after usage.

The typical usage is owning a memory-mapped region and requesting the image to be mapped into a subrange of that mapping. Unmapping the entire region at the end of the memory’s lifetime takes care of the cleanup.

Trait Implementations

impl Clone for MemoryImage

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MemoryImage

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

Formats the value using the given formatter.

impl Eq for MemoryImage

impl Hash for MemoryImage

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for MemoryImage

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.