protected void markFutureDoneAndOffer(SyncFuture future, long txid, Throwable t) {
    future.done(txid, t);
    syncFutureCache.offer(future);
  }
Helper that marks the future as DONE and offers it back to the cache.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java