Struct wasmtime::Store[][src]

pub struct Store { /* fields omitted */ }

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).


impl Store[src]

pub fn new(engine: &Engine) -> Self[src]

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

The created Store will place no additional limits on the size of linear memories or tables at runtime. Linear memories and tables will be allowed to grow to any upper limit specified in their definitions.

The store will limit the number of instances, linear memories, and tables created to 10,000.

Use Store::new_with_limits with a StoreLimitsBuilder to specify different limits for the store.

pub fn new_with_limits(
    engine: &Engine,
    limiter: impl ResourceLimiter + 'static
) -> Self

Creates a new Store to be associated with the given Engine and using the supplied resource limiter.

A ResourceLimiter can be implemented by hosts to control the size of WebAssembly linear memories and tables when a request is made to grow them.

StoreLimitsBuilder can be used to create a StoreLimits that implements ResourceLimiter using static limit values.


// Place a limit on linear memories so they cannot grow beyond 1 MiB
let engine = Engine::default();
let store = Store::new_with_limits(&engine, StoreLimitsBuilder::new().memory_pages(16).build());

pub fn get_host_func(&self, module: &str, name: &str) -> Option<Func>[src]

Gets a host function from the Config associated with this Store.

Returns None if the given host function is not defined.

pub fn engine(&self) -> &Engine[src]

Returns the Engine that this store is associated with.

pub fn get<T: Any>(&self) -> Option<&T>[src]

Gets a context value from the store.

Returns a reference to the context value if present.

pub fn set<T: Any>(&self, value: T) -> Result<(), T>[src]

Sets a context value into the store.

Returns the given value as an error if an existing value is already set.

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

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>[src]

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.


// 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_typed_func::<(), ()>("run")?;

// Spin up a thread to send us an interrupt in a second
std::thread::spawn(move || {

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

pub fn gc(&self)[src]

Perform garbage collection of ExternRefs.

pub fn fuel_consumed(&self) -> Option<u64>[src]

Returns the amount of fuel consumed by this store’s execution so far.

If fuel consumption is not enabled via Config::consume_fuel then this function will return None. Also note that fuel, if enabled, must be originally configured via Store::add_fuel.

pub fn add_fuel(&self, fuel: u64) -> Result<()>[src]

Adds fuel to this Store for wasm to consume while executing.

For this method to work fuel consumption must be enabled via Config::consume_fuel. By default a Store starts with 0 fuel for wasm to execute with (meaning it will immediately trap). This function must be called for the store to have some fuel to allow WebAssembly to execute.

Most WebAssembly instructions consume 1 unit of fuel. Some instructions, such as nop, drop, block, and loop, consume 0 units, as any execution cost associated with them involves other instructions which do consume fuel.

Note that at this time when fuel is entirely consumed it will cause wasm to trap. More usages of fuel are planned for the future.


This function will panic if the store’s Config did not have fuel consumption enabled.

pub fn out_of_fuel_trap(&self)[src]

Configures a Store to generate a Trap whenever it runs out of fuel.

When a Store is configured to consume fuel with Config::consume_fuel this method will configure what happens when fuel runs out. Specifically a WebAssembly trap will be raised and the current execution of WebAssembly will be aborted.

This is the default behavior for running out of fuel.

pub fn out_of_fuel_async_yield(&self, injection_count: u32, fuel_to_inject: u64)[src]

Configures a Store to yield execution of async WebAssembly code periodically.

When a Store is configured to consume fuel with Config::consume_fuel this method will configure what happens when fuel runs out. Specifically executing WebAssembly will be suspended and control will be yielded back to the caller. This is only suitable with use of a store associated with an async config because only then are futures used and yields are possible.

The purpose of this behavior is to ensure that futures which represent execution of WebAssembly do not execute too long inside their Future::poll method. This allows for some form of cooperative multitasking where WebAssembly will voluntarily yield control periodically (based on fuel consumption) back to the running thread.

Note that futures returned by this crate will automatically flag themselves to get re-polled if a yield happens. This means that WebAssembly will continue to execute, just after giving the host an opportunity to do something else.

The fuel_to_inject parameter indicates how much fuel should be automatically re-injected after fuel runs out. This is how much fuel will be consumed between yields of an async future.

The injection_count parameter indicates how many times this fuel will be injected. Multiplying the two parameters is the total amount of fuel this store is allowed before wasm traps.


This method will panic if it is not called on a store associated with an async config.

Trait Implementations

impl Clone for Store[src]

impl Debug for Store[src]

impl Default for Store[src]

impl StoreExt for Store[src]

impl TrapInfo for Store[src]

Auto Trait Implementations

impl !RefUnwindSafe for Store

impl !Send for Store

impl !Sync for Store

impl Unpin for Store

impl !UnwindSafe for Store

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T> Pointable for T

type Init = T

The type for initializers.

impl<T> Same<T> for T

type Output = T

Should always be Self

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<V, T> VZip<V> for T where
    V: MultiLane<T>,