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node-api: force env shutdown deferring behavior · nodejs/node@b5b1ad3 · GitHub

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node-api: force env shutdown deferring behavior
The finalizer normally never gets called while a reference is strong. However, during environment shutdown all finalizers must get called. In order to unify the deferring behavior with that of a regular finalization, we must force the reference to be weak when we call its finalizer during environment shutdown. Fixes: #37236 Co-authored-by: Chengzhong Wu <legendecas@gmail.com> PR-URL: #37303 Backport-PR-URL: #37802 Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Michael Dawson <midawson@redhat.com>
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‎src/js_native_api_v8.cc‎

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@@ -270,8 +270,17 @@ class RefBase : protected Finalizer, RefTracker {
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protected:
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inline void Finalize(bool is_env_teardown = false) override {
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// During environment teardown we have to convert a strong reference to
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// a weak reference to force the deferring behavior if the user's finalizer
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// happens to delete this reference so that the code in this function that
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// follows the call to the user's finalizer may safely access variables from
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// this instance.
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if (is_env_teardown && RefCount() > 0) _refcount = 0;
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if (_finalize_callback != nullptr) {
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_env->CallFinalizer(_finalize_callback, _finalize_data, _finalize_hint);
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// This ensures that we never call the finalizer twice.
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_finalize_callback = nullptr;
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}
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// this is safe because if a request to delete the reference

‎test/js-native-api/test_reference_double_free/binding.gyp‎

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{
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"targets": [
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{
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"target_name": "test_reference_double_free",
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"sources": [
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"../entry_point.c",
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"test_reference_double_free.c"
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]
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}
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]
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}

‎test/js-native-api/test_reference_double_free/test.js‎

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'use strict';
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// This test makes no assertions. It tests a fix without which it will crash
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// with a double free.
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const { buildType } = require('../../common');
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const addon = require(`./build/${buildType}/test_reference_double_free`);
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{ new addon.MyObject(true); }
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{ new addon.MyObject(false); }

‎test/js-native-api/test_reference_double_free/test_reference_double_free.c‎

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#include <stdlib.h>
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#include <js_native_api.h>
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#include "../common.h"
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static size_t g_call_count = 0;
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static void Destructor(napi_env env, void* data, void* nothing) {
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napi_ref* ref = data;
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NAPI_CALL_RETURN_VOID(env, napi_delete_reference(env, *ref));
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free(ref);
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}
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static void NoDeleteDestructor(napi_env env, void* data, void* hint) {
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napi_ref* ref = data;
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size_t* call_count = hint;
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// This destructor must be called exactly once.
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if ((*call_count) > 0) abort();
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*call_count = ((*call_count) + 1);
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free(ref);
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}
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static napi_value New(napi_env env, napi_callback_info info) {
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size_t argc = 1;
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napi_value js_this, js_delete;
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bool delete;
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napi_ref* ref = malloc(sizeof(*ref));
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NAPI_CALL(env,
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napi_get_cb_info(env, info, &argc, &js_delete, &js_this, NULL));
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NAPI_CALL(env, napi_get_value_bool(env, js_delete, &delete));
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if (delete) {
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NAPI_CALL(env,
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napi_wrap(env, js_this, ref, Destructor, NULL, ref));
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} else {
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NAPI_CALL(env,
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napi_wrap(env, js_this, ref, NoDeleteDestructor, &g_call_count, ref));
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}
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NAPI_CALL(env, napi_reference_ref(env, *ref, NULL));
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return js_this;
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}
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EXTERN_C_START
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napi_value Init(napi_env env, napi_value exports) {
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napi_value myobj_ctor;
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NAPI_CALL(env,
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napi_define_class(
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env, "MyObject", NAPI_AUTO_LENGTH, New, NULL, 0, NULL, &myobj_ctor));
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NAPI_CALL(env,
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napi_set_named_property(env, exports, "MyObject", myobj_ctor));
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return exports;
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}
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EXTERN_C_END

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