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Programming with Mnesia</a></li> </ul> </li> <li id="no" title="Mnesia System Information" expanded="false">Mnesia System Information<ul> <li><a href="Mnesia_chap7.html"> Top of chapter </a></li> <li title="Database Configuration Data"><a href="Mnesia_chap7.html#id2276572">Database Configuration Data</a></li> <li title="Core Dumps"><a href="Mnesia_chap7.html#id2276614">Core Dumps</a></li> <li title="Dumping Tables"><a href="Mnesia_chap7.html#id2276638">Dumping Tables</a></li> <li title="Checkpoints"><a href="Mnesia_chap7.html#id2276678">Checkpoints</a></li> <li title="Files"><a href="Mnesia_chap7.html#id2276957">Files</a></li> <li title="Loading of Tables at Start-up"><a href="Mnesia_chap7.html#id2277368">Loading of Tables at Start-up</a></li> <li title="Recovery from Communication Failure"><a href="Mnesia_chap7.html#id2277560">Recovery from Communication Failure</a></li> <li title="Recovery of Transactions"><a href="Mnesia_chap7.html#id2277693">Recovery of Transactions</a></li> <li title="Backup, Fallback, and Disaster Recovery"><a href="Mnesia_chap7.html#id2277864">Backup, Fallback, and Disaster Recovery</a></li> </ul> </li> <li id="no" title="Combining Mnesia with SNMP" expanded="false">Combining Mnesia with SNMP<ul> <li><a href="Mnesia_chap8.html"> Top of chapter </a></li> <li title="Combining Mnesia and SNMP "><a href="Mnesia_chap8.html#id2278809">Combining Mnesia and SNMP </a></li> </ul> </li> <li id="no" title="Appendix A: Mnesia Error Messages" expanded="false">Appendix A: Mnesia Error Messages<ul> <li><a href="Mnesia_App_A.html"> Top of chapter </a></li> <li title="Errors in Mnesia"><a href="Mnesia_App_A.html#id2278969">Errors in Mnesia</a></li> </ul> </li> <li id="no" title="Appendix B: The Backup Call Back Interface" expanded="false">Appendix B: The Backup Call Back Interface<ul> <li><a href="Mnesia_App_B.html"> Top of chapter </a></li> <li title="mnesia_backup callback behavior"><a href="Mnesia_App_B.html#id2279207">mnesia_backup callback behavior</a></li> </ul> </li> <li id="loadscrollpos" title="Appendix C: The Activity Access Call Back Interface" expanded="true">Appendix C: The Activity Access Call Back Interface<ul> <li><a href="Mnesia_App_C.html"> Top of chapter </a></li> <li title="mnesia_access callback behavior"><a href="Mnesia_App_C.html#id2279378">mnesia_access callback behavior</a></li> </ul> </li> <li id="no" title="Appendix D: The Fragmented Table Hashing Call Back Interface" expanded="false">Appendix D: The Fragmented Table Hashing Call Back Interface<ul> <li><a href="Mnesia_App_D.html"> Top of chapter </a></li> <li title="mnesia_frag_hash callback behavior"><a href="Mnesia_App_D.html#id2279587">mnesia_frag_hash callback behavior</a></li> </ul> </li> </ul> </div></div> <div id="content"> <div class="innertube"> <h1>10 Appendix C: The Activity Access Call Back Interface</h1> <h3><a name="id2279378">10.1 mnesia_access callback behavior</a></h3> <p></p> <div class="example"><pre> -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 ]). </pre></div> <p></p> <div class="example"><pre> %% 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})); 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'. </pre></div> </div> <div class="footer"> <hr> <p>Copyright © 1997-2010 Ericsson AB. 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