wasmtime/runtime/vm/
gc.rs

1#[cfg(feature = "gc")]
2mod enabled;
3#[cfg(feature = "gc")]
4pub use enabled::*;
5
6#[cfg(not(feature = "gc"))]
7mod disabled;
8#[cfg(not(feature = "gc"))]
9pub use disabled::*;
10
11mod func_ref;
12mod gc_ref;
13mod gc_runtime;
14mod host_data;
15mod i31;
16
17pub use func_ref::*;
18pub use gc_ref::*;
19pub use gc_runtime::*;
20pub use host_data::*;
21pub use i31::*;
22
23use crate::prelude::*;
24use crate::runtime::vm::GcHeapAllocationIndex;
25use core::alloc::Layout;
26use core::any::Any;
27use core::mem::MaybeUninit;
28use wasmtime_environ::{GcArrayLayout, GcStructLayout, VMGcKind, VMSharedTypeIndex};
29
30/// GC-related data that is one-to-one with a `wasmtime::Store`.
31///
32/// Contains everything we need to do collections, invoke barriers, etc...
33///
34/// In general, exposes a very similar interface to `GcHeap`, but fills in some
35/// of the context arguments for callers (such as the `ExternRefHostDataTable`)
36/// since they are all stored together inside `GcStore`.
37pub struct GcStore {
38    /// This GC heap's allocation index (primarily used for integrating with the
39    /// pooling allocator).
40    pub allocation_index: GcHeapAllocationIndex,
41
42    /// The actual GC heap.
43    pub gc_heap: Box<dyn GcHeap>,
44
45    /// The `externref` host data table for this GC heap.
46    pub host_data_table: ExternRefHostDataTable,
47
48    /// The function-references table for this GC heap.
49    pub func_ref_table: FuncRefTable,
50}
51
52impl GcStore {
53    /// Create a new `GcStore`.
54    pub fn new(allocation_index: GcHeapAllocationIndex, gc_heap: Box<dyn GcHeap>) -> Self {
55        let host_data_table = ExternRefHostDataTable::default();
56        let func_ref_table = FuncRefTable::default();
57        Self {
58            allocation_index,
59            gc_heap,
60            host_data_table,
61            func_ref_table,
62        }
63    }
64
65    /// Perform garbage collection within this heap.
66    pub fn gc(&mut self, roots: GcRootsIter<'_>) {
67        let mut collection = self.gc_heap.gc(roots, &mut self.host_data_table);
68        collection.collect();
69    }
70
71    /// Asynchronously perform garbage collection within this heap.
72    #[cfg(feature = "async")]
73    pub async fn gc_async(&mut self, roots: GcRootsIter<'_>) {
74        let collection = self.gc_heap.gc(roots, &mut self.host_data_table);
75        collect_async(collection).await;
76    }
77
78    /// Get the kind of the given GC reference.
79    pub fn kind(&self, gc_ref: &VMGcRef) -> VMGcKind {
80        debug_assert!(!gc_ref.is_i31());
81        self.header(gc_ref).kind()
82    }
83
84    /// Get the header of the given GC reference.
85    pub fn header(&self, gc_ref: &VMGcRef) -> &VMGcHeader {
86        debug_assert!(!gc_ref.is_i31());
87        self.gc_heap.header(gc_ref)
88    }
89
90    /// Clone a GC reference, calling GC write barriers as necessary.
91    pub fn clone_gc_ref(&mut self, gc_ref: &VMGcRef) -> VMGcRef {
92        if gc_ref.is_i31() {
93            gc_ref.unchecked_copy()
94        } else {
95            self.gc_heap.clone_gc_ref(gc_ref)
96        }
97    }
98
99    /// Write the `source` GC reference into the uninitialized `destination`
100    /// slot, performing write barriers as necessary.
101    pub fn init_gc_ref(
102        &mut self,
103        destination: &mut MaybeUninit<Option<VMGcRef>>,
104        source: Option<&VMGcRef>,
105    ) {
106        // Initialize the destination to `None`, at which point the regular GC
107        // write barrier is safe to reuse.
108        let destination = destination.write(None);
109        self.write_gc_ref(destination, source);
110    }
111
112    /// Write the `source` GC reference into the `destination` slot, performing
113    /// write barriers as necessary.
114    pub fn write_gc_ref(&mut self, destination: &mut Option<VMGcRef>, source: Option<&VMGcRef>) {
115        // If neither the source nor destination actually point to a GC object
116        // (that is, they are both either null or `i31ref`s) then we can skip
117        // the GC barrier.
118        if destination.as_ref().map_or(true, |d| d.is_i31())
119            && source.as_ref().map_or(true, |s| s.is_i31())
120        {
121            *destination = source.map(|s| s.unchecked_copy());
122            return;
123        }
124
125        self.gc_heap
126            .write_gc_ref(&mut self.host_data_table, destination, source);
127    }
128
129    /// Drop the given GC reference, performing drop barriers as necessary.
130    pub fn drop_gc_ref(&mut self, gc_ref: VMGcRef) {
131        if !gc_ref.is_i31() {
132            self.gc_heap.drop_gc_ref(&mut self.host_data_table, gc_ref);
133        }
134    }
135
136    /// Hook to call whenever a GC reference is about to be exposed to Wasm.
137    ///
138    /// Returns the raw representation of this GC ref, ready to be passed to
139    /// Wasm.
140    #[must_use]
141    pub fn expose_gc_ref_to_wasm(&mut self, gc_ref: VMGcRef) -> u32 {
142        let raw = gc_ref.as_raw_u32();
143        debug_assert_ne!(raw, 0);
144        if !gc_ref.is_i31() {
145            log::trace!("exposing GC ref to Wasm: {gc_ref:p}");
146            self.gc_heap.expose_gc_ref_to_wasm(gc_ref);
147        }
148        raw
149    }
150
151    /// Allocate a new `externref`.
152    ///
153    /// Returns:
154    ///
155    /// * `Ok(Ok(_))`: Successfully allocated the `externref`.
156    ///
157    /// * `Ok(Err(value))`: Failed to allocate the `externref`, but doing a GC
158    ///   and then trying again may succeed. Returns the given `value` as the
159    ///   error payload.
160    ///
161    /// * `Err(_)`: Unrecoverable allocation failure.
162    pub fn alloc_externref(
163        &mut self,
164        value: Box<dyn Any + Send + Sync>,
165    ) -> Result<Result<VMExternRef, Box<dyn Any + Send + Sync>>> {
166        let host_data_id = self.host_data_table.alloc(value);
167        match self.gc_heap.alloc_externref(host_data_id)? {
168            #[cfg_attr(not(feature = "gc"), allow(unreachable_patterns))]
169            Some(x) => Ok(Ok(x)),
170            None => Ok(Err(self.host_data_table.dealloc(host_data_id))),
171        }
172    }
173
174    /// Get a shared borrow of the given `externref`'s host data.
175    ///
176    /// Passing invalid `VMExternRef`s (eg garbage values or `externref`s
177    /// associated with a different heap is memory safe but will lead to general
178    /// incorrectness such as panics and wrong results.
179    pub fn externref_host_data(&self, externref: &VMExternRef) -> &(dyn Any + Send + Sync) {
180        let host_data_id = self.gc_heap.externref_host_data(externref);
181        self.host_data_table.get(host_data_id)
182    }
183
184    /// Get a mutable borrow of the given `externref`'s host data.
185    ///
186    /// Passing invalid `VMExternRef`s (eg garbage values or `externref`s
187    /// associated with a different heap is memory safe but will lead to general
188    /// incorrectness such as panics and wrong results.
189    pub fn externref_host_data_mut(
190        &mut self,
191        externref: &VMExternRef,
192    ) -> &mut (dyn Any + Send + Sync) {
193        let host_data_id = self.gc_heap.externref_host_data(externref);
194        self.host_data_table.get_mut(host_data_id)
195    }
196
197    /// Allocate a raw object with the given header and layout.
198    pub fn alloc_raw(&mut self, header: VMGcHeader, layout: Layout) -> Result<Option<VMGcRef>> {
199        self.gc_heap.alloc_raw(header, layout)
200    }
201
202    /// Allocate an uninitialized struct with the given type index and layout.
203    ///
204    /// This does NOT check that the index is currently allocated in the types
205    /// registry or that the layout matches the index's type. Failure to uphold
206    /// those invariants is memory safe, but will lead to general incorrectness
207    /// such as panics and wrong results.
208    pub fn alloc_uninit_struct(
209        &mut self,
210        ty: VMSharedTypeIndex,
211        layout: &GcStructLayout,
212    ) -> Result<Option<VMStructRef>> {
213        self.gc_heap.alloc_uninit_struct(ty, layout)
214    }
215
216    /// Deallocate an uninitialized struct.
217    pub fn dealloc_uninit_struct(&mut self, structref: VMStructRef) {
218        self.gc_heap.dealloc_uninit_struct(structref);
219    }
220
221    /// Get the data for the given object reference.
222    ///
223    /// Panics when the structref and its size is out of the GC heap bounds.
224    pub fn gc_object_data(&mut self, gc_ref: &VMGcRef) -> VMGcObjectDataMut<'_> {
225        self.gc_heap.gc_object_data(gc_ref)
226    }
227
228    /// Get the object datas for the given pair of object references.
229    ///
230    /// Panics if `a` and `b` are the same reference or either is out of bounds.
231    pub fn gc_object_data_pair(
232        &mut self,
233        a: &VMGcRef,
234        b: &VMGcRef,
235    ) -> (VMGcObjectDataMut<'_>, VMGcObjectDataMut<'_>) {
236        assert_ne!(a, b);
237        self.gc_heap.gc_object_data_pair(a, b)
238    }
239
240    /// Allocate an uninitialized array with the given type index.
241    ///
242    /// This does NOT check that the index is currently allocated in the types
243    /// registry or that the layout matches the index's type. Failure to uphold
244    /// those invariants is memory safe, but will lead to general incorrectness
245    /// such as panics and wrong results.
246    pub fn alloc_uninit_array(
247        &mut self,
248        ty: VMSharedTypeIndex,
249        len: u32,
250        layout: &GcArrayLayout,
251    ) -> Result<Option<VMArrayRef>> {
252        self.gc_heap.alloc_uninit_array(ty, len, layout)
253    }
254
255    /// Deallocate an uninitialized array.
256    pub fn dealloc_uninit_array(&mut self, arrayref: VMArrayRef) {
257        self.gc_heap.dealloc_uninit_array(arrayref);
258    }
259
260    /// Get the length of the given array.
261    pub fn array_len(&self, arrayref: &VMArrayRef) -> u32 {
262        self.gc_heap.array_len(arrayref)
263    }
264}
wasmtime/runtime/vm/gc.rs

wasmtime/runtime/vm/
gc.rs
