@Override
    public void stop() {
        if (scheduler != null) {
            scheduler.stop();
        }
    }
Gets all the end timestamps of previous sessions.

@param state
@return map with the values of each previous session's end timestamp and with the key as the sesssio key
modules/siddhi-core/src/main/java/io/siddhi/core/query/processor/stream/window/SessionWindowProcessor.java