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  <TITLE>Appendix C: The Activity Access Call Back Interface</TITLE>
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<H2>10 Appendix C: The Activity Access Call Back Interface</H2>
<A NAME="10.1"><!-- Empty --></A>
<H3>10.1 mnesia_access callback behavior</H3>

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-module(mnesia_frag).

%% Callback functions when accessed within an activity
-export([
         lock/4,
         write/5, delete/5, delete_object/5,
         read/5, match_object/5, all_keys/4,
         select/5,select/6,select_cont/3,
         index_match_object/6, index_read/6,
         foldl/6, foldr/6,
         table_info/4
       ]).


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%% Callback functions which provides transparent
%% access of fragmented tables from any activity
%% access context.

lock(ActivityId, Opaque, {table , Tab}, LockKind) -&#62;
    case frag_names(Tab) of
        [Tab] -&#62;
            mnesia:lock(ActivityId, Opaque, {table, Tab}, LockKind);        
        Frags -&#62;
            DeepNs = [mnesia:lock(ActivityId, Opaque, {table, F}, LockKind) ||
                         F &#60;- Frags],
            mnesia_lib:uniq(lists:append(DeepNs))
    end;

lock(ActivityId, Opaque, LockItem, LockKind) -&#62;
    mnesia:lock(ActivityId, Opaque, LockItem, LockKind).

write(ActivityId, Opaque, Tab, Rec, LockKind) -&#62;
    Frag = record_to_frag_name(Tab, Rec),
    mnesia:write(ActivityId, Opaque, Frag, Rec, LockKind).

delete(ActivityId, Opaque, Tab, Key, LockKind) -&#62;
    Frag = key_to_frag_name(Tab, Key),
    mnesia:delete(ActivityId, Opaque, Frag, Key, LockKind).

delete_object(ActivityId, Opaque, Tab, Rec, LockKind) -&#62;
    Frag = record_to_frag_name(Tab, Rec),
    mnesia:delete_object(ActivityId, Opaque, Frag, Rec, LockKind).

read(ActivityId, Opaque, Tab, Key, LockKind) -&#62;
    Frag = key_to_frag_name(Tab, Key),
    mnesia:read(ActivityId, Opaque, Frag, Key, LockKind).

match_object(ActivityId, Opaque, Tab, HeadPat, LockKind) -&#62;
    MatchSpec = [{HeadPat, [], ['$_']}],
    select(ActivityId, Opaque, Tab, MatchSpec, LockKind).

select(ActivityId, Opaque, Tab, MatchSpec, LockKind) -&#62;
    do_select(ActivityId, Opaque, Tab, MatchSpec, LockKind).


select(ActivityId, Opaque, Tab, MatchSpec, Limit, LockKind) -&#62;
    init_select(ActivityId, Opaque, Tab, MatchSpec, Limit, LockKind).


all_keys(ActivityId, Opaque, Tab, LockKind) -&#62;
    Match = [mnesia:all_keys(ActivityId, Opaque, Frag, LockKind)
             || Frag &#60;- frag_names(Tab)],
    lists:append(Match).

index_match_object(ActivityId, Opaque, Tab, Pat, Attr, LockKind) -&#62;
    Match =
        [mnesia:index_match_object(ActivityId, Opaque, Frag, Pat, Attr, LockKind)
         || Frag &#60;- frag_names(Tab)],
    lists:append(Match).

index_read(ActivityId, Opaque, Tab, Key, Attr, LockKind) -&#62;
    Match =
        [mnesia:index_read(ActivityId, Opaque, Frag, Key, Attr, LockKind)
             || Frag &#60;- frag_names(Tab)],
    lists:append(Match).

foldl(ActivityId, Opaque, Fun, Acc, Tab, LockKind) -&#62;
    Fun2 = fun(Frag, A) -&#62;
                   mnesia:foldl(ActivityId, Opaque, Fun, A, Frag, LockKind)
           end,
    lists:foldl(Fun2, Acc, frag_names(Tab)).

foldr(ActivityId, Opaque, Fun, Acc, Tab, LockKind) -&#62;
    Fun2 = fun(Frag, A) -&#62;
                   mnesia:foldr(ActivityId, Opaque, Fun, A, Frag, LockKind)
           end,
    lists:foldr(Fun2, Acc, frag_names(Tab)).

table_info(ActivityId, Opaque, {Tab, Key}, Item) -&#62;
    Frag = key_to_frag_name(Tab, Key),
    table_info2(ActivityId, Opaque, Tab, Frag, Item);
table_info(ActivityId, Opaque, Tab, Item) -&#62;
    table_info2(ActivityId, Opaque, Tab, Tab, Item).

table_info2(ActivityId, Opaque, Tab, Frag, Item) -&#62;
    case Item of
        size -&#62;
            SumFun = fun({_, Size}, Acc) -&#62; Acc + Size end,
            lists:foldl(SumFun, 0, frag_size(ActivityId, Opaque, Tab));
        memory -&#62;
            SumFun = fun({_, Size}, Acc) -&#62; Acc + Size end,
            lists:foldl(SumFun, 0, frag_memory(ActivityId, Opaque, Tab));
        base_table -&#62;
            lookup_prop(Tab, base_table);
        node_pool -&#62;
            lookup_prop(Tab, node_pool);
        n_fragments -&#62;
            FH = lookup_frag_hash(Tab),
            FH#frag_state.n_fragments;
        foreign_key -&#62;
            FH = lookup_frag_hash(Tab),
            FH#frag_state.foreign_key;
        foreigners -&#62;
            lookup_foreigners(Tab);
        n_ram_copies -&#62;
            length(val({Tab, ram_copies}));
        n_disc_copies -&#62;
            length(val({Tab, disc_copies}));
        n_disc_only_copies -&#62;
            length(val({Tab, disc_only_copies}));

        frag_names -&#62;
            frag_names(Tab);
        frag_dist -&#62;
            frag_dist(Tab);
        frag_size -&#62;
            frag_size(ActivityId, Opaque, Tab);
        frag_memory -&#62;
            frag_memory(ActivityId, Opaque, Tab);
        _ -&#62;
            mnesia:table_info(ActivityId, Opaque, Frag, Item)
    end.

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