node-api: add napi_create_external_sharedarraybuffer

Creates a SharedArrayBuffer from externally managed memory.

Fixes: https://github.com/nodejs/node/issues/62259
PR-URL: https://github.com/nodejs/node/pull/62623
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Vladimir Morozov <vmorozov@microsoft.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>

test/node-api/test_buffer/binding.gyp

@@ -3,7 +3,8 @@
     {
       "target_name": "test_buffer",
       "defines": [
-        'NAPI_VERSION=10'
+        "NAPI_EXPERIMENTAL",
+        "NODE_API_EXPERIMENTAL_NO_WARNING"
       ],
       "sources": [ "test_buffer.c" ]
     },

test/node-api/test_buffer/test.js

@@ -4,7 +4,8 @@
 const common = require('../../common');
 const binding = require(`./build/${common.buildType}/test_buffer`);
 const assert = require('assert');
-const tick = require('util').promisify(require('../../common/tick'));
+const util = require('util');
+const tick = util.promisify(require('../../common/tick'));
 
 (async function() {
   assert.strictEqual(binding.newBuffer().toString(), binding.theText);
@@ -26,6 +27,17 @@ const tick = require('util').promisify(require('../../common/tick'));
   console.log('gc2');
   assert.strictEqual(binding.getDeleterCallCount(), 2);
 
+  // Caveat emptor: it's indeterminate when the SharedArrayBuffer's backing
+  // store is reclaimed; at least some of the time it happens even before
+  // calling gc().
+  let sab = binding.newExternalSharedArrayBuffer();
+  assert(util.types.isSharedArrayBuffer(sab));
+  sab = null;
+  global.gc();
+  await tick(10);
+  console.log('gc3');
+  assert.strictEqual(binding.getDeleterCallCount(), 3);
+
   // To test this doesn't crash
   binding.invalidObjectAsBuffer({});
 

test/node-api/test_buffer/test_buffer.c

@@ -58,6 +58,30 @@ static napi_value newExternalBuffer(napi_env env, napi_callback_info info) {
   return theBuffer;
 }
 
+static char externalSharedArrayBufferData[1];
+
+static void freeExternalSharedArrayBuffer(void* data, void* hint) {
+  (void)hint;
+  NODE_API_BASIC_ASSERT_RETURN_VOID(
+      data == (void*)externalSharedArrayBufferData,
+      "SharedArrayBuffer points to wrong data");
+  deleterCallCount++;
+}
+
+static napi_value newExternalSharedArrayBuffer(napi_env env,
+                                               napi_callback_info info) {
+  napi_value sab;
+  NODE_API_CALL(
+      env,
+      node_api_create_external_sharedarraybuffer(env,
+                                                 externalSharedArrayBufferData,
+                                                 1,
+                                                 freeExternalSharedArrayBuffer,
+                                                 NULL,
+                                                 &sab));
+  return sab;
+}
+
 static napi_value getDeleterCallCount(napi_env env, napi_callback_info info) {
   napi_value callCount;
   NODE_API_CALL(env, napi_create_int32(env, deleterCallCount, &callCount));
@@ -171,6 +195,8 @@ static napi_value Init(napi_env env, napi_value exports) {
   napi_property_descriptor methods[] = {
       DECLARE_NODE_API_PROPERTY("newBuffer", newBuffer),
       DECLARE_NODE_API_PROPERTY("newExternalBuffer", newExternalBuffer),
+      DECLARE_NODE_API_PROPERTY("newExternalSharedArrayBuffer",
+                                newExternalSharedArrayBuffer),
       DECLARE_NODE_API_PROPERTY("getDeleterCallCount", getDeleterCallCount),
       DECLARE_NODE_API_PROPERTY("copyBuffer", copyBuffer),
       DECLARE_NODE_API_PROPERTY("bufferHasInstance", bufferHasInstance),