Trait wasmtime::MemoryCreator
source · [−]pub unsafe trait MemoryCreator: Send + Sync {
fn new_memory(
&self,
ty: MemoryType,
minimum: usize,
maximum: Option<usize>,
reserved_size_in_bytes: Option<usize>,
guard_size_in_bytes: usize
) -> Result<Box<dyn LinearMemory>, String>;
}
Expand description
A memory creator. Can be used to provide a memory creator to wasmtime which supplies host managed memory.
Safety
This trait is unsafe, as the memory safety depends on proper implementation of memory management. Memories created by the MemoryCreator should always be treated as owned by wasmtime instance, and any modification of them outside of wasmtime invoked routines is unsafe and may lead to corruption.
Note that this is a relatively new and experimental feature and it is recommended to be familiar with wasmtime runtime code to use it.
Required methods
fn new_memory(
&self,
ty: MemoryType,
minimum: usize,
maximum: Option<usize>,
reserved_size_in_bytes: Option<usize>,
guard_size_in_bytes: usize
) -> Result<Box<dyn LinearMemory>, String>
fn new_memory(
&self,
ty: MemoryType,
minimum: usize,
maximum: Option<usize>,
reserved_size_in_bytes: Option<usize>,
guard_size_in_bytes: usize
) -> Result<Box<dyn LinearMemory>, String>
Create a new LinearMemory
object from the specified parameters.
The type of memory being created is specified by ty
which indicates
both the minimum and maximum size, in wasm pages. The minimum and
maximum sizes, in bytes, are also specified as parameters to avoid
integer conversion if desired.
The reserved_size_in_bytes
value indicates the expected size of the
reservation that is to be made for this memory. If this value is None
than the implementation is free to allocate memory as it sees fit. If
the value is Some
, however, then the implementation is expected to
reserve that many bytes for the memory’s allocation, plus the guard
size at the end. Note that this reservation need only be a virtual
memory reservation, physical memory does not need to be allocated
immediately. In this case grow
should never move the base pointer and
the maximum size of ty
is guaranteed to fit within
reserved_size_in_bytes
.
The guard_size_in_bytes
parameter indicates how many bytes of space,
after the memory allocation, is expected to be unmapped. JIT code will
elide bounds checks based on the guard_size_in_bytes
provided, so for
JIT code to work correctly the memory returned will need to be properly
guarded with guard_size_in_bytes
bytes left unmapped after the base
allocation.
Note that the reserved_size_in_bytes
and guard_size_in_bytes
options
are tuned from the various Config
methods about
memory sizes/guards. Additionally these two values are guaranteed to be
multiples of the system page size.