10 Appendix B: Activity Access Callback Interface
10.1 mnesia_access Callback Behavior
-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, first/3, next/4, prev/4, last/3, clear_table/4 ]).
%% Callback functions which provides transparent %% access of fragmented tables from any activity %% access context. lock(ActivityId, Opaque, {table , Tab}, LockKind) -> case frag_names(Tab) of [Tab] -> mnesia:lock(ActivityId, Opaque, {table, Tab}, LockKind); Frags -> DeepNs = [mnesia:lock(ActivityId, Opaque, {table, F}, LockKind) || F <- Frags], mnesia_lib:uniq(lists:append(DeepNs)) end; lock(ActivityId, Opaque, LockItem, LockKind) -> mnesia:lock(ActivityId, Opaque, LockItem, LockKind). write(ActivityId, Opaque, Tab, Rec, LockKind) -> Frag = record_to_frag_name(Tab, Rec), mnesia:write(ActivityId, Opaque, Frag, Rec, LockKind). delete(ActivityId, Opaque, Tab, Key, LockKind) -> Frag = key_to_frag_name(Tab, Key), mnesia:delete(ActivityId, Opaque, Frag, Key, LockKind). delete_object(ActivityId, Opaque, Tab, Rec, LockKind) -> Frag = record_to_frag_name(Tab, Rec), mnesia:delete_object(ActivityId, Opaque, Frag, Rec, LockKind). read(ActivityId, Opaque, Tab, Key, LockKind) -> Frag = key_to_frag_name(Tab, Key), mnesia:read(ActivityId, Opaque, Frag, Key, LockKind). match_object(ActivityId, Opaque, Tab, HeadPat, LockKind) -> MatchSpec = [{HeadPat, [], ['$_']}], select(ActivityId, Opaque, Tab, MatchSpec, LockKind). select(ActivityId, Opaque, Tab, MatchSpec, LockKind) -> do_select(ActivityId, Opaque, Tab, MatchSpec, LockKind). select(ActivityId, Opaque, Tab, MatchSpec, Limit, LockKind) -> init_select(ActivityId, Opaque, Tab, MatchSpec, Limit, LockKind). all_keys(ActivityId, Opaque, Tab, LockKind) -> Match = [mnesia:all_keys(ActivityId, Opaque, Frag, LockKind) || Frag <- frag_names(Tab)], lists:append(Match). clear_table(ActivityId, Opaque, Tab, Obj) -> [mnesia:clear_table(ActivityId, Opaque, Frag, Obj) || Frag <- frag_names(Tab)], ok. index_match_object(ActivityId, Opaque, Tab, Pat, Attr, LockKind) -> Match = [mnesia:index_match_object(ActivityId, Opaque, Frag, Pat, Attr, LockKind) || Frag <- frag_names(Tab)], lists:append(Match). index_read(ActivityId, Opaque, Tab, Key, Attr, LockKind) -> Match = [mnesia:index_read(ActivityId, Opaque, Frag, Key, Attr, LockKind) || Frag <- frag_names(Tab)], lists:append(Match). foldl(ActivityId, Opaque, Fun, Acc, Tab, LockKind) -> Fun2 = fun(Frag, A) -> mnesia:foldl(ActivityId, Opaque, Fun, A, Frag, LockKind) end, lists:foldl(Fun2, Acc, frag_names(Tab)). foldr(ActivityId, Opaque, Fun, Acc, Tab, LockKind) -> Fun2 = fun(Frag, A) -> mnesia:foldr(ActivityId, Opaque, Fun, A, Frag, LockKind) end, lists:foldr(Fun2, Acc, frag_names(Tab)). table_info(ActivityId, Opaque, {Tab, Key}, Item) -> Frag = key_to_frag_name(Tab, Key), table_info2(ActivityId, Opaque, Tab, Frag, Item); table_info(ActivityId, Opaque, Tab, Item) -> table_info2(ActivityId, Opaque, Tab, Tab, Item). table_info2(ActivityId, Opaque, Tab, Frag, Item) -> case Item of size -> SumFun = fun({_, Size}, Acc) -> Acc + Size end, lists:foldl(SumFun, 0, frag_size(ActivityId, Opaque, Tab)); memory -> SumFun = fun({_, Size}, Acc) -> Acc + Size end, lists:foldl(SumFun, 0, frag_memory(ActivityId, Opaque, Tab)); base_table -> lookup_prop(Tab, base_table); node_pool -> lookup_prop(Tab, node_pool); n_fragments -> FH = lookup_frag_hash(Tab), FH#frag_state.n_fragments; foreign_key -> FH = lookup_frag_hash(Tab), FH#frag_state.foreign_key; foreigners -> lookup_foreigners(Tab); n_ram_copies -> length(val({Tab, ram_copies})); n_disc_copies -> length(val({Tab, disc_copies})); n_disc_only_copies -> length(val({Tab, disc_only_copies})); n_external_copies -> length(val({Tab, external_copies})); frag_names -> frag_names(Tab); frag_dist -> frag_dist(Tab); frag_size -> frag_size(ActivityId, Opaque, Tab); frag_memory -> frag_memory(ActivityId, Opaque, Tab); _ -> mnesia:table_info(ActivityId, Opaque, Frag, Item) end. first(ActivityId, Opaque, Tab) -> case ?catch_val({Tab, frag_hash}) of {'EXIT', _} -> mnesia:first(ActivityId, Opaque, Tab); FH -> FirstFrag = Tab, case mnesia:first(ActivityId, Opaque, FirstFrag) of '$end_of_table' -> search_first(ActivityId, Opaque, Tab, 1, FH); Next -> Next end end. search_first(ActivityId, Opaque, Tab, N, FH) when N < FH#frag_state.n_fragments -> NextN = N + 1, NextFrag = n_to_frag_name(Tab, NextN), case mnesia:first(ActivityId, Opaque, NextFrag) of '$end_of_table' -> search_first(ActivityId, Opaque, Tab, NextN, FH); Next -> Next end; search_first(_ActivityId, _Opaque, _Tab, _N, _FH) -> '$end_of_table'. last(ActivityId, Opaque, Tab) -> case ?catch_val({Tab, frag_hash}) of {'EXIT', _} -> mnesia:last(ActivityId, Opaque, Tab); FH -> LastN = FH#frag_state.n_fragments, search_last(ActivityId, Opaque, Tab, LastN, FH) end. search_last(ActivityId, Opaque, Tab, N, FH) when N >= 1 -> Frag = n_to_frag_name(Tab, N), case mnesia:last(ActivityId, Opaque, Frag) of '$end_of_table' -> PrevN = N - 1, search_last(ActivityId, Opaque, Tab, PrevN, FH); Prev -> Prev end; search_last(_ActivityId, _Opaque, _Tab, _N, _FH) -> '$end_of_table'. prev(ActivityId, Opaque, Tab, Key) -> case ?catch_val({Tab, frag_hash}) of {'EXIT', _} -> mnesia:prev(ActivityId, Opaque, Tab, Key); FH -> N = key_to_n(FH, Key), Frag = n_to_frag_name(Tab, N), case mnesia:prev(ActivityId, Opaque, Frag, Key) of '$end_of_table' -> search_prev(ActivityId, Opaque, Tab, N); Prev -> Prev end end. search_prev(ActivityId, Opaque, Tab, N) when N > 1 -> PrevN = N - 1, PrevFrag = n_to_frag_name(Tab, PrevN), case mnesia:last(ActivityId, Opaque, PrevFrag) of '$end_of_table' -> search_prev(ActivityId, Opaque, Tab, PrevN); Prev -> Prev end; search_prev(_ActivityId, _Opaque, _Tab, _N) -> '$end_of_table'. next(ActivityId, Opaque, Tab, Key) -> case ?catch_val({Tab, frag_hash}) of {'EXIT', _} -> mnesia:next(ActivityId, Opaque, Tab, Key); FH -> N = key_to_n(FH, Key), Frag = n_to_frag_name(Tab, N), case mnesia:next(ActivityId, Opaque, Frag, Key) of '$end_of_table' -> search_next(ActivityId, Opaque, Tab, N, FH); Prev -> Prev end end. search_next(ActivityId, Opaque, Tab, N, FH) when N < FH#frag_state.n_fragments -> NextN = N + 1, NextFrag = n_to_frag_name(Tab, NextN), case mnesia:first(ActivityId, Opaque, NextFrag) of '$end_of_table' -> search_next(ActivityId, Opaque, Tab, NextN, FH); Next -> Next end; search_next(_ActivityId, _Opaque, _Tab, _N, _FH) -> '$end_of_table'.
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