ed0301e2cf
* Address OTP24 warnings, ct and eunit paths * Reorg to add OTP 24 support * Update VOLUME.md * Correct broken refs * Update README.md * CI on all main branches Co-authored-by: Ulf Wiger <ulf@wiger.net>
126 lines
3.9 KiB
Erlang
126 lines
3.9 KiB
Erlang
%% -------- Utility Functions ---------
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%%
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%% Generally helpful funtions within leveled
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%%
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-module(leveled_util).
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-include("include/leveled.hrl").
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-include_lib("eunit/include/eunit.hrl").
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-export([generate_uuid/0,
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integer_now/0,
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integer_time/1,
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magic_hash/1,
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safe_rename/4]).
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-define(WRITE_OPS, [binary, raw, read, write]).
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-spec generate_uuid() -> list().
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%% @doc
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%% Generate a new globally unique ID as a string.
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%% Credit to
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%% https://github.com/afiskon/erlang-uuid-v4/blob/master/src/uuid.erl
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generate_uuid() ->
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<<A:32, B:16, C:16, D:16, E:48>> = leveled_rand:rand_bytes(16),
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L = io_lib:format("~8.16.0b-~4.16.0b-4~3.16.0b-~4.16.0b-~12.16.0b",
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[A, B, C band 16#0fff, D band 16#3fff bor 16#8000, E]),
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binary_to_list(list_to_binary(L)).
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-spec integer_now() -> non_neg_integer().
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%% @doc
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%% Return now in gregorian seconds
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integer_now() ->
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integer_time(os:timestamp()).
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-spec integer_time (erlang:timestamp()) -> non_neg_integer().
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%% @doc
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%% Return a given time in gergorian seconds
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integer_time(TS) ->
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DT = calendar:now_to_universal_time(TS),
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calendar:datetime_to_gregorian_seconds(DT).
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-spec magic_hash(any()) -> integer().
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%% @doc
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%% Use DJ Bernstein magic hash function. Note, this is more expensive than
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%% phash2 but provides a much more balanced result.
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%%
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%% Hash function contains mysterious constants, some explanation here as to
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%% what they are -
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%% http://stackoverflow.com/questions/10696223/reason-for-5381-number-in-djb-hash-function
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magic_hash({binary, BinaryKey}) ->
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H = 5381,
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hash1(H, BinaryKey) band 16#FFFFFFFF;
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magic_hash(AnyKey) ->
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BK = term_to_binary(AnyKey),
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magic_hash({binary, BK}).
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hash1(H, <<>>) ->
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H;
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hash1(H, <<B:8/integer, Rest/bytes>>) ->
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H1 = H * 33,
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H2 = H1 bxor B,
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hash1(H2, Rest).
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-spec safe_rename(string(), string(), binary(), boolean()) -> ok.
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%% @doc
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%% Write a file, sync it and rename it (and for super-safe mode read it back)
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%% An attempt to prevent crashes leaving files with empty or partially written
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%% values
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safe_rename(TempFN, RealFN, BinData, ReadCheck) ->
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{ok, TempFH} = file:open(TempFN, ?WRITE_OPS),
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ok = file:write(TempFH, BinData),
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ok = file:sync(TempFH),
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ok = file:close(TempFH),
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ok = file:rename(TempFN, RealFN),
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case ReadCheck of
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true ->
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{ok, ReadBack} = file:read_file(RealFN),
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true = (ReadBack == BinData),
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ok;
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false ->
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ok
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end.
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%%%============================================================================
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%%% Test
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%%%============================================================================
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-ifdef(TEST).
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-define(TEST_AREA, "test/test_area/util/").
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magichashperf_test() ->
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KeyFun =
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fun(X) ->
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K = {o, "Bucket", "Key" ++ integer_to_list(X), null},
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{K, X}
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end,
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KL = lists:map(KeyFun, lists:seq(1, 1000)),
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{TimeMH, HL1} = timer:tc(lists, map, [fun(K) -> magic_hash(K) end, KL]),
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io:format(user, "1000 keys magic hashed in ~w microseconds~n", [TimeMH]),
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{TimePH, _Hl2} = timer:tc(lists, map, [fun(K) -> erlang:phash2(K) end, KL]),
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io:format(user, "1000 keys phash2 hashed in ~w microseconds~n", [TimePH]),
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{TimeMH2, HL1} = timer:tc(lists, map, [fun(K) -> magic_hash(K) end, KL]),
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io:format(user, "1000 keys magic hashed in ~w microseconds~n", [TimeMH2]).
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safe_rename_test() ->
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ok = filelib:ensure_dir(?TEST_AREA),
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TempFN = filename:join(?TEST_AREA, "test_manifest0.pnd"),
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RealFN = filename:join(?TEST_AREA, "test_manifest0.man"),
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ok = safe_rename(TempFN, RealFN, <<1:128/integer>>, false),
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?assertMatch({ok, <<1:128/integer>>}, file:read_file(RealFN)),
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TempFN1 = filename:join(?TEST_AREA, "test_manifest1.pnd"),
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RealFN1 = filename:join(?TEST_AREA, "test_manifest1.man"),
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ok = safe_rename(TempFN1, RealFN1, <<2:128/integer>>, true),
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?assertMatch({ok, <<2:128/integer>>}, file:read_file(RealFN1)).
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-endif.
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