public void setLastLogIndex(final long lastLogIndex) {
        this.writeLock.lock();
        try {
            this.lastLogIndex = lastLogIndex;
        } finally {
            this.writeLock.unlock();
        }
    }
return true when this segment file is blank that we don't write any data into it.
@return
jraft-core/src/main/java/com/alipay/sofa/jraft/storage/log/SegmentFile.java