shcache.dot

digraph G {
    compound=true;

    cache_load              [ label = "cache load\n\nshdict:get(key)" ];
    cache_load_stale        [ label = "cache load stale\n\ndata, flags = shdict:get_stale(key)" ];

    cache_load_2            [ label = "cache load 2\n\nshdict:get(key)" ];

    cache_save_positive     [ label = "cache save positive\n\nshdict:set(key, data,\npositive_ttl, positive_flag)" ];
    cache_save_negative     [ label = "cache save negative\n\nshdict:set(key, _EMPTY_,\nnegative_ttl, negative_flag)" ];

    cache_save_actualize    [ label = "cache save actualize\n(only positive gets actualized)\n\nshdict:set(key, stale_data,\nactualize_ttl, stale_flag)" ];

    lock_key                [ label = "lock(key)" ];

    process_hit             [ label = "process cache hit" ];

    { node [ style = filled ];
        start;
        ret_data_from_cache     [ label = "return data, from_cache = true" ];
        ret_nil_from_cache      [ label = "return nil, from_cache = true" ];
        ret_data_not_cache      [ label = "return data, from_cache = false" ];
        ret_nil_not_cache      [ label = "return nil, from_cache = false" ];
    }

    { node [ shape = box, style = filled, color = lightblue ]
        lookup                  [ label = "external lookup\n(kt / dns / ...)" ];
        encode_data             [ label = "serialize data" ];
        decode_data             [ label = "de-serialize data" ];
    }

    start -> cache_load;

    cache_load  -> lock_key                 [ label = "miss" ];
    cache_load  -> process_hit              [ label = "hit", style = bold, color = green ];

    # fail at locking
    lock_key            -> error                    [ label = "fail", style=bold, color=red ];
    error               -> lookup                   [ label = "still lookup, unlock will fail"];

    # locked (immediate)
    lock_key            -> cache_load_2             [ label = "immediate\n(elapsed == 0)" ];

    # locked (waited)
    lock_key            -> cache_load_2             [ label = "locked\n(elapsed > 0)", style = bold, color = blue ];


    cache_load_2 ->  lookup                         [ label = "miss" ];
    cache_load_2 ->  unlock                         [ label = "hit2", style = bold, color = green ];


    lookup              -> cache_load_stale         [ label = "fail", style = bold, color = red ];
    lookup              -> encode_data -> cache_save_positive      [ label = "succ" ];

    cache_load_stale    -> cache_save_negative      [ label = "miss", style = bold, color = red ];
    cache_load_stale    -> stale_process            [ label = "hit_stale", style = bold, color = orange ];

    stale_process       -> cache_save_actualize     [ label = "flags == positive_flag", style = bold, color = orange ]
    stale_process       -> cache_save_negative      [ label = "flags != positive_flag", style = bold, color = red ];

    cache_save_actualize -> unlock -> process_hit   [ label = "hit_stale", style = bold, color = orange ];

    cache_save_negative -> unlock   -> ret_nil_not_cache                [ label = "no_data", style = bold, color = red ];

    cache_save_positive -> unlock -> ret_data_not_cache                 [ label = "valid data", style = bold, color = blue];

    unlock -> process_hit                           [ label = "hit2", style = bold, color = green ];

    process_hit -> ret_nil_from_cache               [ label = "data == _EMPTY_ AND\nflags == negative_flag" ];

    process_hit -> decode_data -> ret_data_from_cache                [ label = "valid data" ];

}