Closes this.
If the stream has not been canceled yet, adds a close-event to the event queue and discards any further incoming messages.
If the stream has already been canceled this method has no effect.
Source
/**
* Closes `this`.
*
* If the stream has not been canceled yet, adds a close-event to the event
* queue and discards any further incoming messages.
*
* If the stream has already been canceled this method has no effect.
*/
void close();