Redis hack to get notified when a key expire

db.c

// Change propagateExpire function in db.c as follows:

void propagateExpire(redisDb *db, robj *key) {

    /*     HORRIBLE HACK STARTS HERE  */
    /* robj *argv[2]; */
    robj *argv[3];
    /*     HORRIBLE HACK ENDS HERE  */

    argv[0] = shared.del;
    argv[1] = key;
    incrRefCount(argv[0]);
    incrRefCount(argv[1]);

    if (server.aof_state != REDIS_AOF_OFF)
        feedAppendOnlyFile(server.delCommand,db->id,argv,2);
    if (listLength(server.slaves))
        replicationFeedSlaves(server.slaves,db->id,argv,2);

    decrRefCount(argv[0]);
    decrRefCount(argv[1]);

    /*    HORRIBLE HACK STARTS HERE  */
    if ( ((char *)(key->ptr))[0] == '@' )
    {
      static redisClient *c = NULL;
      if ( !c )
         c = createClient(-1);
      
      argv[0] = createStringObject("LPUSH",5);
      argv[1] = createStringObject("#expired",8);
      argv[2] = key;
      incrRefCount(argv[2]);
      
      c->argv = argv;
      c->argc = 3;
      c->cmd = lookupCommand(argv[0]->ptr);
      selectDb(c,db->id);
      call(c,REDIS_CALL_SLOWLOG | REDIS_CALL_STATS);

      c->bufpos = 0;
      while(listLength(c->reply))
        listDelNode(c->reply,listFirst(c->reply));

      decrRefCount(argv[0]);
      decrRefCount(argv[1]);
      decrRefCount(argv[2]);
    }                      
    /*    HORRIBLE HACK ENDS HERE  */
}