close method
void
close()
Close a mailbox.
If mailbox already contains a message then close will drop the message.
Implementation
void close() => _mutex.runLocked(() {
if (_mailbox.ref.state == _stateFull && _mailbox.ref.bufferLength > 0) {
malloc.free(_mailbox.ref.buffer);
}
_mailbox.ref.state = _stateClosed;
_mailbox.ref.buffer = nullptr;
_mailbox.ref.bufferLength = 0;
_condVar.notify();
});