Struct wasmtime::Store

pub struct Store { /* private fields */ }

A Store is a collection of WebAssembly instances and host-defined items.

All WebAssembly instances and items will be attached to and refer to a Store. For example instances, functions, globals, and tables are all attached to a Store. Instances are created by instantiating a Module within a Store.

Store is not thread-safe and cannot be sent to other threads. All items which refer to a Store additionally are not threadsafe and can only be used on the original thread that they were created on.

A Store is not intended to be a long-lived object in a program. No form of GC is implemented at this time so once an instance is created within a Store it will not be deallocated until all references to the Store have gone away (this includes all references to items in the store). This makes Store unsuitable for creating an unbounded number of instances in it because Store will never release this memory. It’s instead recommended to have a long-lived Engine and instead create a Store for a more scoped portion of your application.

Stores and Clone

Using clone on a Store is a cheap operation. It will not create an entirely new store, but rather just a new reference to the existing object. In other words it’s a shallow copy, not a deep copy.

Stores and Default

You can create a store with default configuration settings using Store::default(). This will create a brand new Engine with default ocnfiguration (see Config for more information).

Implementations

impl Store

pub fn new(engine: &Engine) -> Store

Creates a new store to be associated with the given Engine.

pub fn engine(&self) -> &Engine

Returns the Engine that this store is associated with.

pub fn same(a: &Store, b: &Store) -> bool

Returns whether the stores a and b refer to the same underlying Store.

Because the Store type is reference counted multiple clones may point to the same underlying storage, and this method can be used to determine whether two stores are indeed the same.

pub fn interrupt_handle(&self) -> Result<InterruptHandle>

Creates an InterruptHandle which can be used to interrupt the execution of instances within this Store.

An InterruptHandle handle is a mechanism of ensuring that guest code doesn’t execute for too long. For example it’s used to prevent wasm programs for executing infinitely in infinite loops or recursive call chains.

The InterruptHandle type is sendable to other threads so you can interact with it even while the thread with this Store is executing wasm code.

There’s one method on an interrupt handle: InterruptHandle::interrupt. This method is used to generate an interrupt and cause wasm code to exit “soon”.

When are interrupts delivered?

The term “interrupt” here refers to one of two different behaviors that are interrupted in wasm:

• The head of every loop in wasm has a check to see if it’s interrupted.
• The prologue of every function has a check to see if it’s interrupted.

This interrupt mechanism makes no attempt to signal interrupts to native code. For example if a host function is blocked, then sending an interrupt will not interrupt that operation.

Interrupts are consumed as soon as possible when wasm itself starts executing. This means that if you interrupt wasm code then it basically guarantees that the next time wasm is executing on the target thread it will return quickly (either normally if it were already in the process of returning or with a trap from the interrupt). Once an interrupt trap is generated then an interrupt is consumed, and further execution will not be interrupted (unless another interrupt is set).

When implementing interrupts you’ll want to ensure that the delivery of interrupts into wasm code is also handled in your host imports and functionality. Host functions need to either execute for bounded amounts of time or you’ll need to arrange for them to be interrupted as well.

Return Value

This function returns a Result since interrupts are not always enabled. Interrupts are enabled via the Config::interruptable method, and if this store’s Config hasn’t been configured to enable interrupts then an error is returned.

Examples

// Enable interruptable code via `Config` and then create an interrupt
// handle which we'll use later to interrupt running code.
let engine = Engine::new(Config::new().interruptable(true));
let store = Store::new(&engine);
let interrupt_handle = store.interrupt_handle()?;

// Compile and instantiate a small example with an infinite loop.
let module = Module::new(&engine, r#"
    (func (export "run") (loop br 0))
"#)?;
let instance = Instance::new(&store, &module, &[])?;
let run = instance
    .get_func("run")
    .ok_or(anyhow::format_err!("failed to find `run` function export"))?
    .get0::<()>()?;

// Spin up a thread to send us an interrupt in a second
std::thread::spawn(move || {
    std::thread::sleep(std::time::Duration::from_secs(1));
    interrupt_handle.interrupt();
});

let trap = run().unwrap_err();
assert!(trap.to_string().contains("wasm trap: interrupt"));

pub fn gc(&self)

Perform garbage collection of ExternRefs.

Trait Implementations

impl Clone for Store

fn clone(&self) -> Store

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Store

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

Formats the value using the given formatter.

impl Default for Store

fn default() -> Store

Returns the “default value” for a type.

impl StoreExt for Store

unsafe fn set_signal_handler<H>(&self, handler: H) where
    H: 'static + Fn(c_int, *const siginfo_t, *const c_void) -> bool, 

The signal handler must be async-signal-safe.

impl TrapInfo for Store

fn as_any(&self) -> &dyn Any

Converts this object into an Any to dynamically check its type.

fn is_wasm_code(&self, addr: usize) -> bool

Returns whether the given program counter lies within wasm code, indicating whether we should handle a trap or not.

fn custom_signal_handler(
    &self,
    call: &dyn Fn(&SignalHandler<'_>) -> bool
) -> bool

Uses call to call a custom signal handler, if one is specified.

fn max_wasm_stack(&self) -> usize

Returns the maximum size, in bytes, the wasm native stack is allowed to grow to.