extensionStreamHasListener top-level property
Whether the "Extension" stream currently has at least one listener.
A client of the VM service can register as a listener
on the extension stream using
The extension stream has a listener while at least one such
client has registered as a listener, and has not yet disconnected
Calling postEvent while the stream has listeners will attempt to deliver that event to all current listeners, although a listener can disconnect before the event is delivered. Calling postEvent when the stream has no listener means that no-one will receive the event, and the call is effectively a no-op.
@pragma("vm:recognized", "other") @pragma("vm:prefer-inline") external bool get extensionStreamHasListener;