ffi: prevent premature GC of DynamicLibrary

Author: semimikoh

src/node_ffi.cc

@@ -194,6 +194,7 @@ void DynamicLibrary::CleanupFunctionInfo(
   FFIFunctionInfo* info = data.GetParameter();
   info->fn.reset();
   info->self.Reset();
+  info->library.Reset();
   delete info;
 }
 
@@ -313,6 +314,7 @@ MaybeLocal<Function> DynamicLibrary::CreateFunction(
   }
 
   info->self.Reset(isolate, ret);
+  info->library.Reset(isolate, object());
   info->self.SetWeak(info.release(),
                      DynamicLibrary::CleanupFunctionInfo,
                      WeakCallbackType::kParameter);

src/node_ffi.h

@@ -33,6 +33,8 @@ struct FFIFunctionInfo {
   std::shared_ptr<FFIFunction> fn;
   v8::Global<v8::Function> self;
   std::shared_ptr<v8::BackingStore> sb_backing;
+  // Keep the owning DynamicLibrary alive while the generated function is alive.
+  v8::Global<v8::Object> library;
 };
 
 struct FFICallback {

test/ffi/test-ffi-dynamic-library.js

@@ -1,7 +1,8 @@
-// Flags: --experimental-ffi
+// Flags: --experimental-ffi --expose-gc
 'use strict';
 const common = require('../common');
 common.skipIfFFIMissing();
+const { gcUntil } = require('../common/gc');
 const assert = require('node:assert');
 const { test } = require('node:test');
 const ffi = require('node:ffi');
@@ -117,6 +118,27 @@ test('getFunction caches signatures consistently', () => {
   }
 });
 
+test('FFI functions keep their owning library alive', async () => {
+  let lib = new ffi.DynamicLibrary(libraryPath);
+  const addI32 = lib.getFunction('add_i32', fixtureSymbols.add_i32);
+  const ref = new WeakRef(lib);
+
+  lib = null;
+
+  for (let i = 0; i < 5; i++) {
+    await gcUntil(
+      'FFI function keeps its owning library alive',
+      () => true,
+      1,
+    );
+    assert.ok(ref.deref() instanceof ffi.DynamicLibrary);
+    assert.strictEqual(addI32(20, 22), 42);
+  }
+
+  ref.deref().close();
+  assert.throws(() => addI32(20, 22), /Library is closed/);
+});
+
 test('closed libraries reject subsequent operations', () => {
   const { lib, functions } = ffi.dlopen(libraryPath, {
     add_i32: fixtureSymbols.add_i32,