src: add consistency check to node_platform.cc

We use the `Isolate*` pointer as the sole identifier
for a V8 Isolate. In some environments (e.g. multi-threaded),
Isolates may be destroyed and new ones created; then, it
may happen that the memory that was previously used for
one `Isolate` can be re-used for another `Isolate`
after the first one has been disposed of.

This check is a little guard against accidentally
re-using the same per-Isolate platform data structure
in such cases, i.e. making sure (to the degree to which
that is possible) that the old `Isolate*` has been properly
unregistered before one at the same memory address is added.

(It’s not 100 % foolproof because the `uv_loop_t*`
pointer value could theoretically be the same as well.)

PR-URL: #21156
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/node_platform.cc

@@ -141,6 +141,7 @@ void NodePlatform::RegisterIsolate(IsolateData* isolate_data, uv_loop_t* loop) {
   Mutex::ScopedLock lock(per_isolate_mutex_);
   std::shared_ptr<PerIsolatePlatformData> existing = per_isolate_[isolate];
   if (existing) {
+    CHECK_EQ(loop, existing->event_loop());
     existing->ref();
   } else {
     per_isolate_[isolate] =

src/node_platform.h

@@ -72,6 +72,8 @@ class PerIsolatePlatformData :
   bool FlushForegroundTasksInternal();
   void CancelPendingDelayedTasks();
 
+  const uv_loop_t* event_loop() const { return loop_; }
+
  private:
   void DeleteFromScheduledTasks(DelayedTask* task);