Add a GC function to the C API

crates/c-api/include/wasmtime.h

@@ -299,6 +299,17 @@ WASM_API_EXTERN own wasmtime_error_t* wasmtime_wat2wasm(
     own wasm_byte_vec_t *ret
 );
 
+/**
+ * \brief Perform garbage collection within the given store.
+ *
+ * Garbage collects `externref`s that are used within this store. Any
+ * `externref`s that are discovered to be unreachable by other code or objects
+ * will have their finalizers run.
+ *
+ * The `store` argument must not be NULL.
+ */
+WASM_API_EXTERN void wasmtime_store_gc(wasm_store_t* store);
+
 /**
  * \typedef wasmtime_linker_t
  * \brief Convenience alias for #wasmtime_linker_t

crates/c-api/src/store.rs

@@ -17,6 +17,11 @@ pub extern "C" fn wasm_store_new(engine: &wasm_engine_t) -> Box<wasm_store_t> {
     })
 }
 
+#[no_mangle]
+pub extern "C" fn wasmtime_store_gc(store: &wasm_store_t) {
+    store.store.gc();
+}
+
 #[repr(C)]
 pub struct wasmtime_interrupt_handle_t {
     handle: InterruptHandle,

examples/externref.c

@@ -82,6 +82,9 @@ int main() {
   printf("Creating new `externref`...\n");
 
   // Create a new `externref` value.
+  //
+  // Note that if you need clean up for after the externref is reclaimed, you
+  // can use `wasmtime_externref_new_with_finalizer`.
   wasm_val_t externref;
   wasmtime_externref_new("Hello, World!", &externref);
   assert(externref.kind == WASM_ANYREF);
@@ -148,6 +151,11 @@ int main() {
   assert(results[0].kind == WASM_ANYREF);
   assert(wasm_ref_same(results[0].of.ref, externref.of.ref));
 
+  // We can GC any now-unused references to our externref that the store is
+  // holding.
+  printf("GCing within the store...\n");
+  wasmtime_store_gc(store);
+
   // Clean up after ourselves at this point
   printf("All finished!\n");
   ret = 0;

examples/externref.rs

@@ -46,6 +46,9 @@ fn main() -> Result<()> {
     assert!(ret.is_some());
     assert!(ret.unwrap().ptr_eq(&externref));
 
+    println!("GCing within the store...");
+    store.gc();
+
     println!("Done.");
     Ok(())
 }