Get finalizers working.

src/include/wren.h

@@ -167,6 +167,9 @@ WrenVM* wrenNewVM(WrenConfiguration* configuration);
 // call to [wrenNewVM].
 void wrenFreeVM(WrenVM* vm);
 
+// Immediately run the garbage collector to free unused memory.
+void wrenCollectGarbage(WrenVM* vm);
+
 // Runs [source], a string of Wren source code in a new fiber in [vm].
 //
 // [sourcePath] is a string describing where [source] was located, for use in

src/vm/wren_value.c

@@ -1089,7 +1089,7 @@ void wrenFreeObj(WrenVM* vm, Obj* obj)
     }
       
     case OBJ_FOREIGN:
-      // TODO: Call finalizer.
+      wrenFinalizeForeign(vm, (ObjForeign*)obj);
       break;
 
     case OBJ_LIST:

src/vm/wren_vm.c

@@ -125,7 +125,7 @@ void wrenSetCompiler(WrenVM* vm, Compiler* compiler)
   vm->compiler = compiler;
 }
 
-static void collectGarbage(WrenVM* vm)
+void wrenCollectGarbage(WrenVM* vm)
 {
 #if WREN_DEBUG_TRACE_MEMORY || WREN_DEBUG_TRACE_GC
   printf("-- gc --\n");
@@ -222,9 +222,9 @@ void* wrenReallocate(WrenVM* vm, void* memory, size_t oldSize, size_t newSize)
 #if WREN_DEBUG_GC_STRESS
   // Since collecting calls this function to free things, make sure we don't
   // recurse.
-  if (newSize > 0) collectGarbage(vm);
+  if (newSize > 0) wrenCollectGarbage(vm);
 #else
-  if (newSize > 0 && vm->bytesAllocated > vm->nextGC) collectGarbage(vm);
+  if (newSize > 0 && vm->bytesAllocated > vm->nextGC) wrenCollectGarbage(vm);
 #endif
 
   return vm->reallocate(memory, newSize);
@@ -615,10 +615,13 @@ static void bindForeignClass(WrenVM* vm, ObjClass* classObj, ObjModule* module)
   int symbol = wrenSymbolTableEnsure(vm, &vm->methodNames, "<allocate>", 10);
   wrenBindMethod(vm, classObj, symbol, method);
   
+  // Add the symbol even if there is no finalizer so we can ensure that the
+  // symbol itself is always in the symbol table.
+  symbol = wrenSymbolTableEnsure(vm, &vm->methodNames, "<finalize>", 10);
+  
   if (methods.finalize != NULL)
   {
     method.fn.foreign = methods.finalize;
-    symbol = wrenSymbolTableEnsure(vm, &vm->methodNames, "<finalize>", 10);
     wrenBindMethod(vm, classObj, symbol, method);
   }
 }
@@ -686,6 +689,32 @@ static void createForeign(WrenVM* vm, ObjFiber* fiber, Value* stack)
   // TODO: Check that allocateForeign was called.
 }
 
+void wrenFinalizeForeign(WrenVM* vm, ObjForeign* foreign)
+{
+  // TODO: Don't look up every time.
+  int symbol = wrenSymbolTableFind(&vm->methodNames, "<finalize>", 10);
+  ASSERT(symbol != -1, "Should have defined <finalize> symbol.");
+  
+  // If there are no finalizers, don't finalize it.
+  if (symbol == -1) return;
+  
+  // If the class doesn't have a finalizer, bail out.
+  ObjClass* classObj = foreign->obj.classObj;
+  if (symbol >= classObj->methods.count) return;
+  
+  Method* method = &classObj->methods.data[symbol];
+  if (method->type == METHOD_NONE) return;
+  
+  ASSERT(method->type == METHOD_FOREIGN, "Finalizer should be foreign.");
+  
+  // Pass the constructor arguments to the allocator as well.
+  Value slot = OBJ_VAL(foreign);
+  vm->foreignCallSlot = &slot;
+  vm->foreignCallNumArgs = 1;
+  
+  method->fn.foreign(vm);
+}
+
 // The main bytecode interpreter loop. This is where the magic happens. It is
 // also, as you can imagine, highly performance critical. Returns `true` if the
 // fiber completed without error.

src/vm/wren_vm.h

@@ -89,17 +89,17 @@ struct WrenVM
   Obj* tempRoots[WREN_MAX_TEMP_ROOTS];
 
   int numTempRoots;
-
+  
+  // Pointer to the first node in the linked list of active value handles or
+  // NULL if there are no handles.
+  WrenValue* valueHandles;
+  
   // Foreign function data:
 
   // During a foreign function call, this will point to the first argument (the
   // receiver) of the call on the fiber's stack.
   Value* foreignCallSlot;
 
-  // Pointer to the first node in the linked list of active value handles or
-  // NULL if there are no handles.
-  WrenValue* valueHandles;
-
   // During a foreign function call, this will contain the number of arguments
   // to the function.
   int foreignCallNumArgs;
@@ -143,6 +143,9 @@ struct WrenVM
 //   [oldSize] will be zero. It should return NULL.
 void* wrenReallocate(WrenVM* vm, void* memory, size_t oldSize, size_t newSize);
 
+// Invoke the finalizer for the foreign object referenced by [foreign].
+void wrenFinalizeForeign(WrenVM* vm, ObjForeign* foreign);
+
 // Creates a new [WrenValue] for [value].
 WrenValue* wrenCaptureValue(WrenVM* vm, Value value);
 

test/api/foreign_class.c

@@ -3,6 +3,18 @@
 
 #include "foreign_class.h"
 
+static int finalized = 0;
+
+static void apiGC(WrenVM* vm)
+{
+  wrenCollectGarbage(vm);
+}
+
+static void apiFinalized(WrenVM* vm)
+{
+  wrenReturnDouble(vm, finalized);
+}
+
 static void counterAllocate(WrenVM* vm)
 {
   double* value = (double*)wrenAllocateForeign(vm, sizeof(double));
@@ -60,8 +72,20 @@ static void pointToString(WrenVM* vm)
   wrenReturnString(vm, result, (int)strlen(result));
 }
 
+static void resourceAllocate(WrenVM* vm)
+{
+  wrenAllocateForeign(vm, 0);
+}
+
+static void resourceFinalize(WrenVM* vm)
+{
+  finalized++;
+}
+
 WrenForeignMethodFn foreignClassBindMethod(const char* signature)
 {
+  if (strcmp(signature, "static Api.gc()") == 0) return apiGC;
+  if (strcmp(signature, "static Api.finalized") == 0) return apiFinalized;
   if (strcmp(signature, "Counter.increment(_)") == 0) return counterIncrement;
   if (strcmp(signature, "Counter.value") == 0) return counterValue;
   if (strcmp(signature, "Point.translate(_,_,_)") == 0) return pointTranslate;
@@ -84,4 +108,11 @@ void foreignClassBindClass(
     methods->allocate = pointAllocate;
     return;
   }
+
+  if (strcmp(className, "Resource") == 0)
+  {
+    methods->allocate = resourceAllocate;
+    methods->finalize = resourceFinalize;
+    return;
+  }
 }

test/api/foreign_class.wren

@@ -1,3 +1,8 @@
+class Api {
+  foreign static gc()
+  foreign static finalized
+}
+
 // Class with a default constructor.
 foreign class Counter {
   foreign increment(amount)
@@ -46,3 +51,25 @@ var error = Fiber.new {
   class Subclass is Point {}
 }.try()
 IO.print(error) // expect: Class 'Subclass' cannot inherit from foreign class 'Point'.
+
+// Class with a finalizer.
+foreign class Resource {}
+
+var resources = [
+  Resource.new(),
+  Resource.new(),
+  Resource.new()
+]
+
+Api.gc()
+IO.print(Api.finalized) // expect: 0
+
+resources.removeAt(-1)
+
+Api.gc()
+IO.print(Api.finalized) // expect: 1
+
+resources.clear()
+
+Api.gc()
+IO.print(Api.finalized) // expect: 3