n-api: adds function to adjust external memory

doc/api/n-api.md

@@ -3394,6 +3394,31 @@ support it:
 * If the function is not available, provide an alternate implementation
   that does not use the function.
 
+## Memory Management
+
+### napi_adjust_external_memory
+<!-- YAML
+added: REPLACEME
+-->
+```C
+NAPI_EXTERN napi_status napi_adjust_external_memory(napi_env env,
+                                                    int64_t change_in_bytes,
+                                                    int64_t* result);
+```
+
+- `[in] env`: The environment that the API is invoked under.
+- `[in] change_in_bytes`: The change in externally allocated memory that is
+kept alive by JavaScript objects.
+- `[out] result`: The adjusted value
+
+Returns `napi_ok` if the API succeeded.
+
+This function gives V8 an indication of the amount of externally allocated 
+memory that is kept alive by JavaScript objects (i.e. a JavaScript object
+that points to its own memory allocated by a native module). Registering 
+externally allocated memory will trigger global garbage collections more 
+often than it would otherwise.
+
 <!-- it's very convenient to have all the anchors indexed -->
 <!--lint disable no-unused-definitions remark-lint-->
 ## Promises

src/node_api.cc

@@ -3213,6 +3213,19 @@ napi_status napi_get_node_version(napi_env env,
   return napi_clear_last_error(env);
 }
 
+napi_status napi_adjust_external_memory(napi_env env,
+                                        int64_t change_in_bytes,
+                                        int64_t* adjusted_value) {
+  CHECK_ENV(env);
+  CHECK_ARG(env, &change_in_bytes);
+  CHECK_ARG(env, adjusted_value);
+
+  *adjusted_value = env->isolate->AdjustAmountOfExternalAllocatedMemory(
+      change_in_bytes);
+
+  return napi_clear_last_error(env);
+}
+
 namespace uvimpl {
 
 static napi_status ConvertUVErrorCode(int code) {

src/node_api.h

@@ -557,6 +557,11 @@ NAPI_EXTERN napi_status napi_is_promise(napi_env env,
                                         napi_value promise,
                                         bool* is_promise);
 
+// Memory management
+NAPI_EXTERN napi_status napi_adjust_external_memory(napi_env env,
+                                                    int64_t change_in_bytes,
+                                                    int64_t* adjusted_value);
+
 EXTERN_C_END
 
 #endif  // SRC_NODE_API_H_

test/addons-napi/test_general/test.js

@@ -91,3 +91,8 @@ z = null;
 global.gc();
 assert.strictEqual(test_general.finalizeWasCalled(), false,
                    'finalize callback was not called upon garbage collection');
+
+// test napi_adjust_external_memory
+const adjustedValue = test_general.testAdjustExternalMemory();
+assert.strictEqual(typeof adjustedValue, 'number');
+assert(adjustedValue > 0);

test/addons-napi/test_general/test_general.c

@@ -205,6 +205,16 @@ napi_value finalize_was_called(napi_env env, napi_callback_info info) {
   return it_was_called;
 }
 
+napi_value testAdjustExternalMemory(napi_env env, napi_callback_info info) {
+  napi_value result;
+  int64_t adjustedValue;
+
+  NAPI_CALL(env, napi_adjust_external_memory(env, 1, &adjustedValue));
+  NAPI_CALL(env, napi_create_double(env, adjustedValue, &result));
+
+  return result;
+}
+
 void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
   napi_property_descriptor descriptors[] = {
     DECLARE_NAPI_PROPERTY("testStrictEquals", testStrictEquals),
@@ -222,6 +232,7 @@ void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
     DECLARE_NAPI_PROPERTY("testFinalizeWrap", test_finalize_wrap),
     DECLARE_NAPI_PROPERTY("finalizeWasCalled", finalize_was_called),
     DECLARE_NAPI_PROPERTY("derefItemWasCalled", deref_item_was_called),
+    DECLARE_NAPI_PROPERTY("testAdjustExternalMemory", testAdjustExternalMemory)
   };
 
   NAPI_CALL_RETURN_VOID(env, napi_define_properties(