pub struct Store<T> { /* private fields */ }
Expand description
A Store
is a collection of WebAssembly instances and host-defined state.
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
.
A Store
is intended to be a short-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 the Store
itself is dropped.
This makes Store
unsuitable for creating an unbounded number of
instances in it because Store
will never release this memory. It’s
recommended to have a Store
correspond roughly to the lifetime of a “main
instance” that an embedding is interested in executing.
Type parameter T
Each Store
has a type parameter T
associated with it. This T
represents state defined by the host. This state will be accessible through
the Caller
type that host-defined functions get access
to. This T
is suitable for storing Store
-specific information which
imported functions may want access to.
The data T
can be accessed through methods like Store::data
and
Store::data_mut
.
Stores, contexts, oh my
Most methods in Wasmtime take something of the form
AsContext
or AsContextMut
as
the first argument. These two traits allow ergonomically passing in the
context you currently have to any method. The primary two sources of
contexts are:
Store<T>
Caller<'_, T>
corresponding to what you create and what you have access to in a host
function. You can also explicitly acquire a StoreContext
or
StoreContextMut
and pass that around as well.
Note that all methods on Store
are mirrored onto StoreContext
,
StoreContextMut
, and Caller
. This way no matter what
form of context you have you can call various methods, create objects, etc.
Stores and Default
You can create a store with default configuration settings using
Store::default()
. This will create a brand new Engine
with default
configuration (see Config
for more information).
Implementations
sourceimpl<T> Store<T>
impl<T> Store<T>
sourcepub fn new(engine: &Engine, data: T) -> Self
pub fn new(engine: &Engine, data: T) -> Self
Creates a new Store
to be associated with the given Engine
and
data
provided.
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. This can be overridden with the
Store::limiter
configuration method.
sourcepub fn into_data(self) -> T
pub fn into_data(self) -> T
Consumes this Store
, destroying it, and returns the underlying data.
sourcepub fn limiter(
&mut self,
limiter: impl FnMut(&mut T) -> &mut dyn ResourceLimiter + Send + Sync + 'static
)
pub fn limiter(
&mut self,
limiter: impl FnMut(&mut T) -> &mut dyn ResourceLimiter + Send + Sync + 'static
)
Configures the ResourceLimiter
used to limit resource creation
within this Store
.
Whenever resources such as linear memory, tables, or instances are
allocated the limiter
specified here is invoked with the store’s data
T
and the returned ResourceLimiter
is used to limit the operation
being allocated. The returned ResourceLimiter
is intended to live
within the T
itself, for example by storing a
StoreLimits
.
Note that this limiter is only used to limit the creation/growth of
resources in the future, this does not retroactively attempt to apply
limits to the Store
.
Examples
use wasmtime::*;
struct MyApplicationState {
my_state: u32,
limits: StoreLimits,
}
let engine = Engine::default();
let my_state = MyApplicationState {
my_state: 42,
limits: StoreLimitsBuilder::new()
.memory_size(1 << 20 /* 1 MB */)
.instances(2)
.build(),
};
let mut store = Store::new(&engine, my_state);
store.limiter(|state| &mut state.limits);
// Creation of smaller memories is allowed
Memory::new(&mut store, MemoryType::new(1, None)).unwrap();
// Creation of a larger memory, however, will exceed the 1MB limit we've
// configured
assert!(Memory::new(&mut store, MemoryType::new(1000, None)).is_err());
// The number of instances in this store is limited to 2, so the third
// instance here should fail.
let module = Module::new(&engine, "(module)").unwrap();
assert!(Instance::new(&mut store, &module, &[]).is_ok());
assert!(Instance::new(&mut store, &module, &[]).is_ok());
assert!(Instance::new(&mut store, &module, &[]).is_err());
sourcepub fn limiter_async(
&mut self,
limiter: impl FnMut(&mut T) -> &mut dyn ResourceLimiterAsync + Send + Sync + 'static
)
pub fn limiter_async(
&mut self,
limiter: impl FnMut(&mut T) -> &mut dyn ResourceLimiterAsync + Send + Sync + 'static
)
Configures the ResourceLimiterAsync
used to limit resource creation within this Store
.
This method is an asynchronous variant of the Store::limiter
method
where the embedder can block the wasm request for more resources with
host async
execution of futures.
By using a ResourceLimiterAsync
with a Store
, you can no longer use
Memory::new
,
Memory::grow
,
Table::new
, and
Table::grow
. Instead, you must use their
async
variants: Memory::new_async
,
Memory::grow_async
,
Table::new_async
, and
Table::grow_async
.
Note that this limiter is only used to limit the creation/growth of
resources in the future, this does not retroactively attempt to apply
limits to the Store
. Additionally this must be used with an async
Store
configured via
Config::async_support
.
sourcepub fn call_hook_async(
&mut self,
hook: impl CallHookHandler<T> + Send + Sync + 'static
)
pub fn call_hook_async(
&mut self,
hook: impl CallHookHandler<T> + Send + Sync + 'static
)
Configures an async function that runs on calls and returns between
WebAssembly and host code. For the non-async equivalent of this method,
see Store::call_hook
.
The function is passed a CallHook
argument, which indicates which
state transition the VM is making.
This function’s future may return a Trap
. If a trap is returned
when an import was called, it is immediately raised as-if the host
import had returned the trap. If a trap is returned after wasm returns
to the host then the wasm function’s result is ignored and this trap is
returned instead.
After this function returns a trap, it may be called for subsequent returns to host or wasm code as the trap propagates to the root call.
sourcepub fn call_hook(
&mut self,
hook: impl FnMut(&mut T, CallHook) -> Result<(), Trap> + Send + Sync + 'static
)
pub fn call_hook(
&mut self,
hook: impl FnMut(&mut T, CallHook) -> Result<(), Trap> + Send + Sync + 'static
)
Configure a function that runs on calls and returns between WebAssembly and host code.
The function is passed a CallHook
argument, which indicates which
state transition the VM is making.
This function may return a Trap
. If a trap is returned when an
import was called, it is immediately raised as-if the host import had
returned the trap. If a trap is returned after wasm returns to the host
then the wasm function’s result is ignored and this trap is returned
instead.
After this function returns a trap, it may be called for subsequent returns to host or wasm code as the trap propagates to the root call.
sourcepub fn gc(&mut self)
pub fn gc(&mut self)
Perform garbage collection of ExternRef
s.
Note that it is not required to actively call this function. GC will automatically happen when internal buffers fill up. This is provided if fine-grained control over the GC is desired.
sourcepub fn fuel_consumed(&self) -> Option<u64>
pub fn fuel_consumed(&self) -> Option<u64>
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
.
sourcepub fn add_fuel(&mut self, fuel: u64) -> Result<()>
pub fn add_fuel(&mut self, fuel: u64) -> Result<()>
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.
Panics
This function will panic if the store’s Config
did
not have fuel consumption enabled.
sourcepub fn consume_fuel(&mut self, fuel: u64) -> Result<u64>
pub fn consume_fuel(&mut self, fuel: u64) -> Result<u64>
Synthetically consumes fuel from this Store
.
For this method to work fuel consumption must be enabled via
Config::consume_fuel
.
WebAssembly execution will automatically consume fuel but if so desired the embedder can also consume fuel manually to account for relative costs of host functions, for example.
This function will attempt to consume fuel
units of fuel from within
this store. If the remaining amount of fuel allows this then Ok(N)
is
returned where N
is the amount of remaining fuel. Otherwise an error
is returned and no fuel is consumed.
Errors
This function will return an either either if fuel consumption via
Config
is disabled or if fuel
exceeds the amount
of remaining fuel within this store.
sourcepub fn out_of_fuel_trap(&mut self)
pub fn out_of_fuel_trap(&mut self)
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.
sourcepub fn out_of_fuel_async_yield(
&mut self,
injection_count: u64,
fuel_to_inject: u64
)
pub fn out_of_fuel_async_yield(
&mut self,
injection_count: u64,
fuel_to_inject: u64
)
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.
Panics
This method will panic if it is not called on a store associated with an async config.
sourcepub fn set_epoch_deadline(&mut self, ticks_beyond_current: u64)
pub fn set_epoch_deadline(&mut self, ticks_beyond_current: u64)
Sets the epoch deadline to a certain number of ticks in the future.
When the Wasm guest code is compiled with epoch-interruption
instrumentation
(Config::epoch_interruption()
),
and when the Engine
’s epoch is incremented
(Engine::increment_epoch()
)
past a deadline, execution can be configured to either trap or
yield and then continue.
This deadline is always set relative to the current epoch:
delta_beyond_current
ticks in the future. The deadline can
be set explicitly via this method, or refilled automatically
on a yield if configured via
epoch_deadline_async_yield_and_update()
. After
this method is invoked, the deadline is reached when
Engine::increment_epoch()
has been invoked at least
ticks_beyond_current
times.
By default a store will trap immediately with an epoch deadline of 0 (which has always “elapsed”). This method is required to be configured for stores with epochs enabled to some future epoch deadline.
See documentation on
Config::epoch_interruption()
for an introduction to epoch-based interruption.
sourcepub fn epoch_deadline_trap(&mut self)
pub fn epoch_deadline_trap(&mut self)
Configures epoch-deadline expiration to trap.
When epoch-interruption-instrumented code is executed on this store and the epoch deadline is reached before completion, with the store configured in this way, execution will terminate with a trap as soon as an epoch check in the instrumented code is reached.
This behavior is the default if the store is not otherwise
configured via
epoch_deadline_trap()
,
epoch_deadline_callback()
or
epoch_deadline_async_yield_and_update()
.
This setting is intended to allow for coarse-grained interruption, but not a deterministic deadline of a fixed, finite interval. For deterministic interruption, see the “fuel” mechanism instead.
Note that when this is used it’s required to call
Store::set_epoch_deadline
or otherwise wasm will always immediately
trap.
See documentation on
Config::epoch_interruption()
for an introduction to epoch-based interruption.
sourcepub fn epoch_deadline_callback(
&mut self,
callback: impl FnMut(&mut T) -> Result<u64> + Send + Sync + 'static
)
pub fn epoch_deadline_callback(
&mut self,
callback: impl FnMut(&mut T) -> Result<u64> + Send + Sync + 'static
)
Configures epoch-deadline expiration to invoke a custom callback function.
When epoch-interruption-instrumented code is executed on this store and the epoch deadline is reached before completion, the provided callback function is invoked.
This function should return a positive delta
, which is used to
update the new epoch, setting it to the current epoch plus
delta
ticks. Alternatively, the callback may return an error,
which will terminate execution.
This setting is intended to allow for coarse-grained interruption, but not a deterministic deadline of a fixed, finite interval. For deterministic interruption, see the “fuel” mechanism instead.
See documentation on
Config::epoch_interruption()
for an introduction to epoch-based interruption.
sourcepub fn epoch_deadline_async_yield_and_update(&mut self, delta: u64)
pub fn epoch_deadline_async_yield_and_update(&mut self, delta: u64)
Configures epoch-deadline expiration to yield to the async caller and the update the deadline.
When epoch-interruption-instrumented code is executed on this
store and the epoch deadline is reached before completion,
with the store configured in this way, execution will yield
(the future will return Pending
but re-awake itself for
later execution) and, upon resuming, the store will be
configured with an epoch deadline equal to the current epoch
plus delta
ticks.
This setting is intended to allow for cooperative timeslicing
of multiple CPU-bound Wasm guests in different stores, all
executing under the control of an async executor. To drive
this, stores should be configured to “yield and update”
automatically with this function, and some external driver (a
thread that wakes up periodically, or a timer
signal/interrupt) should call
Engine::increment_epoch()
.
See documentation on
Config::epoch_interruption()
for an introduction to epoch-based interruption.
Trait Implementations
sourceimpl<T> AsContext for Store<T>
impl<T> AsContext for Store<T>
sourcefn as_context(&self) -> StoreContext<'_, T>
fn as_context(&self) -> StoreContext<'_, T>
Returns the store context that this type provides access to.
sourceimpl<T> AsContextMut for Store<T>
impl<T> AsContextMut for Store<T>
sourcefn as_context_mut(&mut self) -> StoreContextMut<'_, T>
fn as_context_mut(&mut self) -> StoreContextMut<'_, T>
Returns the store context that this type provides access to.
Auto Trait Implementations
impl<T> !RefUnwindSafe for Store<T>
impl<T> Send for Store<T> where
T: Send,
impl<T> Sync for Store<T> where
T: Sync,
impl<T> Unpin for Store<T>
impl<T> !UnwindSafe for Store<T>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more