wasmtime/runtime/store/async_.rs
1#[cfg(feature = "call-hook")]
2use crate::CallHook;
3use crate::fiber::{self};
4use crate::prelude::*;
5#[cfg(feature = "gc")]
6use crate::runtime::vm::VMStore;
7use crate::store::{Asyncness, ResourceLimiterInner, StoreInner, StoreOpaque};
8use crate::{Store, StoreContextMut, UpdateDeadline};
9
10/// An object that can take callbacks when the runtime enters or exits hostcalls.
11#[cfg(feature = "call-hook")]
12#[async_trait::async_trait]
13pub trait CallHookHandler<T>: Send {
14 /// A callback to run when wasmtime is about to enter a host call, or when about to
15 /// exit the hostcall.
16 async fn handle_call_event(&self, t: StoreContextMut<'_, T>, ch: CallHook) -> Result<()>;
17}
18
19impl<T> Store<T> {
20 /// Configures the [`ResourceLimiterAsync`](crate::ResourceLimiterAsync)
21 /// used to limit resource creation within this [`Store`].
22 ///
23 /// This method is an asynchronous variant of the [`Store::limiter`] method
24 /// where the embedder can block the wasm request for more resources with
25 /// host `async` execution of futures.
26 ///
27 /// By using a [`ResourceLimiterAsync`](`crate::ResourceLimiterAsync`)
28 /// with a [`Store`], you can no longer use
29 /// [`Memory::new`](`crate::Memory::new`),
30 /// [`Memory::grow`](`crate::Memory::grow`),
31 /// [`Table::new`](`crate::Table::new`), and
32 /// [`Table::grow`](`crate::Table::grow`). Instead, you must use their
33 /// `async` variants: [`Memory::new_async`](`crate::Memory::new_async`),
34 /// [`Memory::grow_async`](`crate::Memory::grow_async`),
35 /// [`Table::new_async`](`crate::Table::new_async`), and
36 /// [`Table::grow_async`](`crate::Table::grow_async`).
37 ///
38 /// Note that this limiter is only used to limit the creation/growth of
39 /// resources in the future, this does not retroactively attempt to apply
40 /// limits to the [`Store`].
41 ///
42 /// After configuring this method it's required that synchronous APIs in
43 /// Wasmtime are no longer used, such as [`Func::call`](crate::Func::call).
44 /// Instead APIs such as [`Func::call_async`](crate::Func::call_async) must
45 /// be used instead.
46 pub fn limiter_async(
47 &mut self,
48 mut limiter: impl (FnMut(&mut T) -> &mut dyn crate::ResourceLimiterAsync)
49 + Send
50 + Sync
51 + 'static,
52 ) {
53 // Apply the limits on instances, tables, and memory given by the limiter:
54 let inner = &mut self.inner;
55 let (instance_limit, table_limit, memory_limit) = {
56 let l = limiter(inner.data_mut());
57 (l.instances(), l.tables(), l.memories())
58 };
59 let innermost = &mut inner.inner;
60 innermost.instance_limit = instance_limit;
61 innermost.table_limit = table_limit;
62 innermost.memory_limit = memory_limit;
63
64 // Save the limiter accessor function:
65 inner.limiter = Some(ResourceLimiterInner::Async(Box::new(limiter)));
66 inner.set_async_required(Asyncness::Yes);
67 }
68
69 /// Configures an async function that runs on calls and returns between
70 /// WebAssembly and host code. For the non-async equivalent of this method,
71 /// see [`Store::call_hook`].
72 ///
73 /// The function is passed a [`CallHook`] argument, which indicates which
74 /// state transition the VM is making.
75 ///
76 /// This function's future may return a [`Trap`]. If a trap is returned
77 /// when an import was called, it is immediately raised as-if the host
78 /// import had returned the trap. If a trap is returned after wasm returns
79 /// to the host then the wasm function's result is ignored and this trap is
80 /// returned instead.
81 ///
82 /// After this function returns a trap, it may be called for subsequent
83 /// returns to host or wasm code as the trap propagates to the root call.
84 ///
85 /// [`Trap`]: crate::Trap
86 #[cfg(feature = "call-hook")]
87 pub fn call_hook_async(&mut self, hook: impl CallHookHandler<T> + Send + Sync + 'static) {
88 self.inner.call_hook = Some(crate::store::CallHookInner::Async(Box::new(hook)));
89 self.inner.set_async_required(Asyncness::Yes);
90 }
91
92 /// Perform garbage collection asynchronously.
93 ///
94 /// Note that it is not required to actively call this function. GC will
95 /// automatically happen according to various internal heuristics. This is
96 /// provided if fine-grained control over the GC is desired.
97 ///
98 /// This method is only available when the `gc` Cargo feature is enabled.
99 #[cfg(feature = "gc")]
100 pub async fn gc_async(&mut self, why: Option<&crate::GcHeapOutOfMemory<()>>)
101 where
102 T: Send,
103 {
104 StoreContextMut(&mut self.inner).gc_async(why).await
105 }
106
107 /// Configures epoch-deadline expiration to yield to the async
108 /// caller and the update the deadline.
109 ///
110 /// When epoch-interruption-instrumented code is executed on this
111 /// store and the epoch deadline is reached before completion,
112 /// with the store configured in this way, execution will yield
113 /// (the future will return `Pending` but re-awake itself for
114 /// later execution) and, upon resuming, the store will be
115 /// configured with an epoch deadline equal to the current epoch
116 /// plus `delta` ticks.
117 ///
118 /// This setting is intended to allow for cooperative timeslicing
119 /// of multiple CPU-bound Wasm guests in different stores, all
120 /// executing under the control of an async executor. To drive
121 /// this, stores should be configured to "yield and update"
122 /// automatically with this function, and some external driver (a
123 /// thread that wakes up periodically, or a timer
124 /// signal/interrupt) should call
125 /// [`Engine::increment_epoch()`](crate::Engine::increment_epoch).
126 ///
127 /// See documentation on
128 /// [`Config::epoch_interruption()`](crate::Config::epoch_interruption)
129 /// for an introduction to epoch-based interruption.
130 #[cfg(target_has_atomic = "64")]
131 pub fn epoch_deadline_async_yield_and_update(&mut self, delta: u64) {
132 self.inner.epoch_deadline_async_yield_and_update(delta);
133 }
134}
135
136impl<'a, T> StoreContextMut<'a, T> {
137 /// Perform garbage collection of `ExternRef`s.
138 ///
139 /// Same as [`Store::gc`].
140 ///
141 /// This method is only available when the `gc` Cargo feature is enabled.
142 #[cfg(feature = "gc")]
143 pub async fn gc_async(&mut self, why: Option<&crate::GcHeapOutOfMemory<()>>)
144 where
145 T: Send + 'static,
146 {
147 let (mut limiter, store) = self.0.resource_limiter_and_store_opaque();
148 store
149 .gc(
150 limiter.as_mut(),
151 None,
152 why.map(|e| e.bytes_needed()),
153 crate::store::Asyncness::Yes,
154 )
155 .await;
156 }
157
158 /// Configures epoch-deadline expiration to yield to the async
159 /// caller and the update the deadline.
160 ///
161 /// For more information see
162 /// [`Store::epoch_deadline_async_yield_and_update`].
163 #[cfg(target_has_atomic = "64")]
164 pub fn epoch_deadline_async_yield_and_update(&mut self, delta: u64) {
165 self.0.epoch_deadline_async_yield_and_update(delta);
166 }
167}
168
169impl<T> StoreInner<T> {
170 #[cfg(target_has_atomic = "64")]
171 fn epoch_deadline_async_yield_and_update(&mut self, delta: u64) {
172 // All future entrypoints must be async to handle the case that an epoch
173 // changes and a yield is required.
174 self.set_async_required(Asyncness::Yes);
175
176 self.epoch_deadline_behavior =
177 Some(Box::new(move |_store| Ok(UpdateDeadline::Yield(delta))));
178 }
179}
180
181#[doc(hidden)]
182impl StoreOpaque {
183 pub(crate) fn allocate_fiber_stack(&mut self) -> Result<wasmtime_fiber::FiberStack> {
184 if let Some(stack) = self.async_state.last_fiber_stack().take() {
185 return Ok(stack);
186 }
187 self.engine().allocator().allocate_fiber_stack()
188 }
189
190 pub(crate) fn deallocate_fiber_stack(&mut self, stack: wasmtime_fiber::FiberStack) {
191 self.flush_fiber_stack();
192 *self.async_state.last_fiber_stack() = Some(stack);
193 }
194
195 /// Releases the last fiber stack to the underlying instance allocator, if
196 /// present.
197 pub fn flush_fiber_stack(&mut self) {
198 if let Some(stack) = self.async_state.last_fiber_stack().take() {
199 unsafe {
200 self.engine.allocator().deallocate_fiber_stack(stack);
201 }
202 }
203 }
204}
205
206impl<T> StoreContextMut<'_, T> {
207 /// Executes a synchronous computation `func` asynchronously on a new fiber.
208 pub(crate) async fn on_fiber<R: Send + Sync>(
209 &mut self,
210 func: impl FnOnce(&mut StoreContextMut<'_, T>) -> R + Send + Sync,
211 ) -> Result<R> {
212 fiber::on_fiber(self.0, |me| func(&mut StoreContextMut(me))).await
213 }
214}