worker: use engine-provided deleter for SharedArrayBuffers

src/sharedarraybuffer_metadata.cc

@@ -89,8 +89,7 @@ SharedArrayBufferMetadata::ForSharedArrayBuffer(
   }
 
   SharedArrayBuffer::Contents contents = source->Externalize();
-  SharedArrayBufferMetadataReference r(new SharedArrayBufferMetadata(
-      contents.Data(), contents.ByteLength()));
+  SharedArrayBufferMetadataReference r(new SharedArrayBufferMetadata(contents));
   if (r->AssignToSharedArrayBuffer(env, context, source).IsNothing())
     return nullptr;
   return r;
@@ -111,17 +110,22 @@ Maybe<bool> SharedArrayBufferMetadata::AssignToSharedArrayBuffer(
                             obj);
 }
 
-SharedArrayBufferMetadata::SharedArrayBufferMetadata(void* data, size_t size)
-  : data(data), size(size) { }
+SharedArrayBufferMetadata::SharedArrayBufferMetadata(
+    const SharedArrayBuffer::Contents& contents)
+  : contents_(contents) { }
 
 SharedArrayBufferMetadata::~SharedArrayBufferMetadata() {
-  free(data);
+  contents_.Deleter()(contents_.Data(),
+                      contents_.ByteLength(),
+                      contents_.DeleterData());
 }
 
 MaybeLocal<SharedArrayBuffer> SharedArrayBufferMetadata::GetSharedArrayBuffer(
     Environment* env, Local<Context> context) {
   Local<SharedArrayBuffer> obj =
-      SharedArrayBuffer::New(env->isolate(), data, size);
+      SharedArrayBuffer::New(env->isolate(),
+                             contents_.Data(),
+                             contents_.ByteLength());
 
   if (AssignToSharedArrayBuffer(env, context, obj).IsNothing())
     return MaybeLocal<SharedArrayBuffer>();

src/sharedarraybuffer_metadata.h

@@ -46,16 +46,15 @@ class SharedArrayBufferMetadata
   SharedArrayBufferMetadata(const SharedArrayBufferMetadata&) = delete;
 
  private:
-  explicit SharedArrayBufferMetadata(void* data, size_t size);
+  explicit SharedArrayBufferMetadata(const v8::SharedArrayBuffer::Contents&);
 
   // Attach a lifetime tracker object with a reference count to `target`.
   v8::Maybe<bool> AssignToSharedArrayBuffer(
       Environment* env,
       v8::Local<v8::Context> context,
       v8::Local<v8::SharedArrayBuffer> target);
 
-  void* data = nullptr;
-  size_t size = 0;
+  v8::SharedArrayBuffer::Contents contents_;
 };
 
 }  // namespace worker

test/fixtures/wasm-threads-shared-memory.wat

@@ -0,0 +1,4 @@
+(module
+  (memory $mem 1 2 shared)
+  (export "memory" (memory $mem))
+)

test/parallel/test-worker-message-port-wasm-threads.js

@@ -0,0 +1,26 @@
+// Flags: --experimental-worker --experimental-wasm-threads
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { MessageChannel } = require('worker_threads');
+
+// Test that SharedArrayBuffer instances created from WASM are transferrable
+// through MessageChannels (without crashing).
+
+const fixtures = require('../common/fixtures');
+const wasmSource = fixtures.readSync('wasm-threads-shared-memory.wasm');
+const wasmModule = new WebAssembly.Module(wasmSource);
+const instance = new WebAssembly.Instance(wasmModule);
+
+const { buffer } = instance.exports.memory;
+assert(buffer instanceof SharedArrayBuffer);
+
+const { port1, port2 } = new MessageChannel();
+port1.postMessage(buffer);
+port2.once('message', common.mustCall((buffer2) => {
+  // Make sure serialized + deserialized buffer refer to the same memory.
+  const expected = 'Hello, world!';
+  const bytes = Buffer.from(buffer).write(expected);
+  const deserialized = Buffer.from(buffer2).toString('utf8', 0, bytes);
+  assert.deepStrictEqual(deserialized, expected);
+}));