worker: fix broadcast channel SharedArrayBuffer passing

Make sure that `SharedArrayBuffer`s can be deserialized on multiple
receiving ends. As a drive-by, also fix the condition of the
internal assertion that should occur if there are transferables
passed to multiple destinations.

PR-URL: #36501
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Gus Caplan <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: addaleax

src/node_messaging.cc

@@ -157,8 +157,7 @@ MaybeLocal<Value> Message::Deserialize(Environment* env,
   // Attach all transferred SharedArrayBuffers to their new Isolate.
   for (uint32_t i = 0; i < shared_array_buffers_.size(); ++i) {
     Local<SharedArrayBuffer> sab =
-        SharedArrayBuffer::New(env->isolate(),
-                               std::move(shared_array_buffers_[i]));
+        SharedArrayBuffer::New(env->isolate(), shared_array_buffers_[i]);
     shared_array_buffers.push_back(sab);
   }
 
@@ -1309,7 +1308,7 @@ Maybe<bool> SiblingGroup::Dispatch(
 
   // Transferables cannot be used when there is more
   // than a single destination.
-  if (size() > 2 && message->transferables().size()) {
+  if (size() > 2 && message->has_transferables()) {
     if (error != nullptr)
       *error = "Transferables cannot be used with multiple destinations.";
     return Nothing<bool>();

src/node_messaging.h

@@ -94,6 +94,9 @@ class Message : public MemoryRetainer {
   const std::vector<std::unique_ptr<TransferData>>& transferables() const {
     return transferables_;
   }
+  bool has_transferables() const {
+    return !transferables_.empty() || !array_buffers_.empty();
+  }
 
   void MemoryInfo(MemoryTracker* tracker) const override;
 

test/parallel/test-worker-broadcastchannel.js

@@ -111,12 +111,19 @@ assert.throws(() => new BroadcastChannel(), {
 {
   const bc1 = new BroadcastChannel('channel3');
   const bc2 = new BroadcastChannel('channel3');
-  bc2.postMessage(new SharedArrayBuffer(10));
-  bc1.addEventListener('message', common.mustCall(({ data }) => {
-    assert(data instanceof SharedArrayBuffer);
-    bc1.close();
-    bc2.close();
-  }));
+  const bc3 = new BroadcastChannel('channel3');
+  bc3.postMessage(new SharedArrayBuffer(10));
+  let received = 0;
+  for (const bc of [bc1, bc2]) {
+    bc.addEventListener('message', common.mustCall(({ data }) => {
+      assert(data instanceof SharedArrayBuffer);
+      if (++received === 2) {
+        bc1.close();
+        bc2.close();
+        bc3.close();
+      }
+    }));
+  }
 }
 
 {