private void pushContext() {
        final Context contextToPush;
        // Do note: Never put this.context in the cache. It would be totally
        // meaningless, since it's a final.
        if (nextIndex() == entryIndex) {
            contextToPush = context.shallowCopy();
        } else {
            contextToPush = context.copyIfChanged(contextCache[nextIndex() - 1]);
        }
        contextCache[nextIndex()] = contextToPush;
    }
Calls ping on the next search in this chain. If there is no next, a Pong is created and returned.
container-search/src/main/java/com/yahoo/search/searchchain/Execution.java