flutter_isolate does not actually spawn isolates since 2.1.0

[srmncnk]

What it says in the title.

The problematic commit

While using FlutterEngineGroup is a great idea in terms of memory consumption and sharing complex objects, it actually does not run in separate threads. I checked this by running this via ffi:

int64_t get_thread_id() {
  return (int64_t)syscall(SYS_gettid);
}

And it returned the same number for all the isolates spawned by flutter_isolate. For version 2.0.4 (which did not use FlutterEngineGroup yet), every thread id is a different number.

This is a bug and it should be addressed this way - behaviour in heavy-lifting apps drastically changes when doing a seemingly harmless upgrade from 2.0.4 to 2.10.

[nmfisher]

Thanks @srmncnk - let me take a look at this next week.