Introduce a new time API

The old time API is based on erlang:now/0. The major issue with
erlang:now/0 is that it was intended to be used for so many
unrelated things. This tied these unrelated operations together
and unnecessarily caused performance, scalability as well as
accuracy, and precision issues for operations that do not need
to have such issues. The new API spreads different functionality
over multiple functions in order to improve on this.

The new API consists of a number of new BIFs:
- erlang:convert_time_unit/3
- erlang:monotonic_time/0
- erlang:monotonic_time/1
- erlang:system_time/0
- erlang:system_time/1
- erlang:time_offset/0
- erlang:time_offset/1
- erlang:timestamp/0
- erlang:unique_integer/0
- erlang:unique_integer/1
- os:system_time/0
- os:system_time/1

and a number of extensions of existing BIFs:
- erlang:monitor(time_offset, clock_service)
- erlang:system_flag(time_offset, finalize)
- erlang:system_info(os_monotonic_time_source)
- erlang:system_info(time_offset)
- erlang:system_info(time_warp_mode)
- erlang:system_info(time_correction)
- erlang:system_info(start_time)

See the "Time and Time Correction in Erlang" chapter of the
ERTS User's Guide for more information.

2 files changed, 303 insertions, 1 deletions

diff --git a/erts/example/Makefile b/erts/example/Makefile
index 6e1a88b4da..b637bee033 100644
--- a/erts/example/Makefile
+++ b/erts/example/Makefile
@@ -30,7 +30,7 @@ CFLAGS += $(OUR_C_FLAGS)
 CXXFLAGS += $(OUR_C_FLAGS)
 
 TARGETS = pg_sync.beam pg_async.beam pg_sync.so pg_async.so \
-next_perm.so next_perm.beam
+next_perm.so next_perm.beam time_compat.beam
 
 all: $(TARGETS)
 
diff --git a/erts/example/time_compat.erl b/erts/example/time_compat.erl
new file mode 100644
index 0000000000..d582117ceb
--- /dev/null
+++ b/erts/example/time_compat.erl
@@ -0,0 +1,302 @@
+%%
+%% %CopyrightBegin%
+%% 
+%% Copyright Ericsson AB 2014. All Rights Reserved.
+%% 
+%% The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%% 
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%% 
+%% %CopyrightEnd%
+%%
+
+%%
+%% If your code need to be able to execute on ERTS versions both
+%% earlier and later than 7.0, the best approach is to use the new
+%% time API introduced in ERTS 7.0 and implement a fallback
+%% solution using the old primitives to be used on old ERTS
+%% versions. This way your code can automatically take advantage
+%% of the improvements in the API when available. This is an
+%% example of how to implement such an API, but it can be used
+%% as is if you want to. Just add this module to your project,
+%% and call the API via this module instead of calling the
+%% BIFs directly.
+%%
+
+-module(time_compat).
+
+%% We don't want warnings about the use of erlang:now/0 in
+%% this module.
+-compile(nowarn_deprecated_function).
+%%
+%% We don't use
+%%   -compile({nowarn_deprecated_function, [{erlang, now, 0}]}).
+%% since this will produce warnings when compiled on systems
+%% where it has not yet been deprecated.
+%%
+
+-export([monotonic_time/0,
+	 monotonic_time/1,
+	 erlang_system_time/0,
+	 erlang_system_time/1,
+	 os_system_time/0,
+	 os_system_time/1,
+	 time_offset/0,
+	 time_offset/1,
+	 convert_time_unit/3,
+	 timestamp/0,
+	 unique_integer/0,
+	 unique_integer/1,
+	 monitor/2,
+	 system_info/1,
+	 system_flag/2]).
+
+monotonic_time() ->
+    try
+	erlang:monotonic_time()
+    catch
+	error:undef ->
+	    %% Use Erlang system time as monotonic time
+	    erlang_system_time_fallback()
+    end.
+
+monotonic_time(Unit) ->
+    try
+	erlang:monotonic_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    %% Use Erlang system time as monotonic time
+	    STime = erlang_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+erlang_system_time() ->
+    try
+	erlang:system_time()
+    catch
+	error:undef ->
+	    erlang_system_time_fallback()
+    end.
+
+erlang_system_time(Unit) ->
+    try
+	erlang:system_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    STime = erlang_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+os_system_time() ->
+    try
+	os:system_time()
+    catch
+	error:undef ->
+	    os_system_time_fallback()
+    end.
+
+os_system_time(Unit) ->
+    try
+	os:system_time(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    STime = os_system_time_fallback(),
+	    try
+		convert_time_unit_fallback(STime, native, Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end
+    end.
+
+time_offset() ->
+    try
+	erlang:time_offset()
+    catch
+	error:undef ->
+	    %% Erlang system time and Erlang monotonic
+	    %% time are always aligned
+	    0
+    end.
+
+time_offset(Unit) ->
+    try
+	erlang:time_offset(Unit)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Unit]);
+	error:undef ->
+	    try
+		_ = integer_time_unit(Unit)
+	    catch
+		error:bad_time_unit -> erlang:error(badarg, [Unit])
+	    end,
+	    %% Erlang system time and Erlang monotonic
+	    %% time are always aligned
+	    0
+    end.
+
+convert_time_unit(Time, FromUnit, ToUnit) ->
+    try
+	erlang:convert_time_unit(Time, FromUnit, ToUnit)
+    catch
+	error:undef ->
+	    try
+		convert_time_unit_fallback(Time, FromUnit, ToUnit)
+	    catch
+		_:_ ->
+		    erlang:error(badarg, [Time, FromUnit, ToUnit])
+	    end;
+	error:Error ->
+	    erlang:error(Error, [Time, FromUnit, ToUnit])
+    end.
+
+timestamp() ->
+    try
+	erlang:timestamp()
+    catch
+	error:undef ->
+	    erlang:now()
+    end.
+
+unique_integer() ->
+    try
+	erlang:unique_integer()
+    catch
+	error:undef ->
+	    {MS, S, US} = erlang:now(),
+	    (MS*1000000+S)*1000000+US
+    end.
+
+unique_integer(Modifiers) ->
+    try
+	erlang:unique_integer(Modifiers)
+    catch
+	error:badarg ->
+	    erlang:error(badarg, [Modifiers]);
+	error:undef ->
+	    case is_valid_modifier_list(Modifiers) of
+		true ->
+		    %% now() converted to an integer
+		    %% fullfill the requirements of
+		    %% all modifiers: unique, positive,
+		    %% and monotonic...
+		    {MS, S, US} = erlang:now(),
+		    (MS*1000000+S)*1000000+US;
+		false ->
+		    erlang:error(badarg, [Modifiers])
+	    end
+    end.
+
+monitor(Type, Item) ->
+    try
+	erlang:monitor(Type, Item)
+    catch
+	error:Error ->
+	    case {Error, Type, Item} of
+		{badarg, time_offset, clock_service} ->
+		    %% Time offset is final and will never change.
+		    %% Return a dummy reference, there will never
+		    %% be any need for 'CHANGE' messages...
+		    make_ref();
+		_ ->
+		    erlang:error(Error, [Type, Item])
+	    end
+    end.
+
+system_info(Item) ->
+    try
+	erlang:system_info(Item)
+    catch
+	error:badarg ->
+	    case Item of
+		time_correction ->
+		    case erlang:system_info(tolerant_timeofday) of
+			enabled -> true;
+			disabled -> false
+		    end;
+		time_warp_mode ->
+		    no_time_warp;
+		time_offset ->
+		    final;
+		NotSupArg when NotSupArg == os_monotonic_time_source;
+			       NotSupArg == start_time ->
+		    %% Cannot emulate this...
+		    erlang:error(notsup, [NotSupArg]);
+		_ ->
+		    erlang:error(badarg, [Item])
+	    end;
+	error:Error ->
+	    erlang:error(Error, [Item])
+    end.
+
+system_flag(Flag, Value) ->
+    try
+	erlang:system_flag(Flag, Value)
+    catch
+	error:Error ->
+	    case {Error, Flag, Value} of
+		{badarg, time_offset, finalize} ->
+		    %% Time offset is final
+		    final;
+		_ ->
+		    erlang:error(Error, [Flag, Value])
+	    end
+    end.
+
+%%
+%% Internal functions
+%%
+
+integer_time_unit(native) -> 1000*1000;
+integer_time_unit(nano_seconds) -> 1000*1000*1000;
+integer_time_unit(micro_seconds) -> 1000*1000;
+integer_time_unit(milli_seconds) -> 1000;
+integer_time_unit(seconds) -> 1;
+integer_time_unit(I) when is_integer(I), I > 0 -> I;
+integer_time_unit(BadRes) -> erlang:error(bad_time_unit, [BadRes]).
+
+erlang_system_time_fallback() ->
+    {MS, S, US} = erlang:now(),
+    (MS*1000000+S)*1000000+US.
+
+os_system_time_fallback() ->
+    {MS, S, US} = os:timestamp(),
+    (MS*1000000+S)*1000000+US.
+
+convert_time_unit_fallback(Time, FromUnit, ToUnit) ->
+    FU = integer_time_unit(FromUnit),
+    TU = integer_time_unit(ToUnit),
+    case Time < 0 of
+	true -> TU*Time - (FU - 1);
+	false -> TU*Time
+    end div FU.
+
+is_valid_modifier_list([positive|Ms]) ->
+    is_valid_modifier_list(Ms);
+is_valid_modifier_list([monotonic|Ms]) ->
+    is_valid_modifier_list(Ms);
+is_valid_modifier_list([]) ->
+    true;
+is_valid_modifier_list(_) ->
+    false.