Introduce time warp safe replacement for safe_fixed option

The new time warp safe option is safe_fixed_monotonic_time which
gives erlang:monotonic_time().

The safe_fixed option was also slightly changed. It now gives
erlang:timestamp() instead of erlang:now(). This has however
not been documented, so it is considered a compatible change.

The above effects both ets, and dets.

This commit also include the bugfix OTP-13239 for
dets:info(Tab, safe_fixed). The timestamp in the result returned
by dets:info(Tab, safe_fixed) was unintentionally broken as a
result of the time API rewrites in OTP 18.0.

7 files changed, 145 insertions, 26 deletions

diff --git a/lib/stdlib/doc/src/dets.xml b/lib/stdlib/doc/src/dets.xml
index a0d3f95b6a..48400733d1 100644
--- a/lib/stdlib/doc/src/dets.xml
+++ b/lib/stdlib/doc/src/dets.xml
@@ -399,15 +399,40 @@
               kept in RAM.</p>
           </item>
           <item>
-            <p><c>{safe_fixed,</c> SafeFixed<c>}</c>. If the table
-              is fixed, SafeFixed is a tuple <c>{FixedAtTime, [{Pid,RefCount}]}</c>. <c>FixedAtTime</c> is the time when
+            <p><c>{safe_fixed_monotonic_time, SafeFixed}</c>. If the table
+              is fixed, <c>SafeFixed</c> is a tuple <c>{FixedAtTime, [{Pid,RefCount}]}</c>.
+	      <c>FixedAtTime</c> is the time when
               the table was first fixed, and <c>Pid</c> is the pid of
               the process that fixes the table <c>RefCount</c> times.
               There may be any number of processes in the list. If the
               table is not fixed, SafeFixed is the atom <c>false</c>.</p>
+	      <p><c>FixedAtTime</c> will correspond to the result
+	      returned by
+	      <seealso marker="erts:erlang#monotonic_time/0">erlang:monotonic_time/0</seealso>
+	      at the time of fixation. The usage of <c>safe_fixed_monotonic_time</c> is
+	      <seealso marker="erts:time_correction#Time_Warp_Safe_Code">time warp
+	      safe</seealso>.</p>
           </item>
           <item>
-            <p><c>{version, integer()</c>, the version of the format of
+            <p>
+	      <c>{safe_fixed, SafeFixed}</c>. The same as
+	      <c>{safe_fixed_monotonic_time, SafeFixed}</c> with the exception
+	      of the format and value of <c>FixedAtTime</c>.
+	    </p>
+	    <p>
+	      <c>FixedAtTime</c> will correspond to the result returned by
+	      <seealso marker="erts:erlang#timestamp/0">erlang:timestamp/0</seealso>
+	      at the time of fixation. Note that when the system is using
+	      single or multi
+	      <seealso marker="erts:time_correction#Time_Warp_Modes">time warp
+	      modes</seealso> this might produce strange results. This
+	      since the usage of <c>safe_fixed</c> is not
+	      <seealso marker="erts:time_correction#Time_Warp_Safe_Code">time warp
+	      safe</seealso>. Time warp safe code need to use
+	      <c>safe_fixed_monotonic_time</c> instead.</p>
+          </item>
+          <item>
+            <p><c>{version, integer()}</c>, the version of the format of
               the table.</p>
           </item>
         </list>
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml
index 7b01109ff8..447fe51130 100644
--- a/lib/stdlib/doc/src/ets.xml
+++ b/lib/stdlib/doc/src/ets.xml
@@ -488,14 +488,39 @@ Error: fun containing local Erlang function calls
           <item><c>Item=fixed, Value=boolean()</c>          <br></br>
 
            Indicates if the table is fixed by any process or not.</item>
-          <item>
-            <p><c>Item=safe_fixed, Value={FirstFixed,Info}|false</c>              <br></br>
+          <item><marker id="info_2_safe_fixed_monotonic_time"/>
+            <p><c>Item=safe_fixed|safe_fixed_monotonic_time, Value={FixationTime,Info}|false</c>              <br></br>
 </p>
-            <p>If the table has been fixed using <c>safe_fixtable/2</c>,
-              the call returns a tuple where <c>FirstFixed</c> is the
+            <p>If the table has been fixed using
+	    <seealso marker="#safe_fixtable/2"><c>safe_fixtable/2</c></seealso>,
+              the call returns a tuple where <c>FixationTime</c> is the
               time when the table was first fixed by a process, which
               may or may not be one of the processes it is fixed by
               right now.</p>
+	    <p>The format and value of <c>FixationTime</c> depends on
+	    <c>Item</c>:</p>
+	    <taglist>
+	      <tag><c>safe_fixed</c></tag>
+	      <item><p><c>FixationTime</c> will correspond to the result
+	      returned by
+	      <seealso marker="erts:erlang#timestamp/0">erlang:timestamp/0</seealso>
+	      at the time of fixation. Note that when the system is using
+	      single or multi
+	      <seealso marker="erts:time_correction#Time_Warp_Modes">time warp
+	      modes</seealso> this might produce strange results. This
+	      since the usage of <c>safe_fixed</c> is not
+	      <seealso marker="erts:time_correction#Time_Warp_Safe_Code">time warp
+	      safe</seealso>. Time warp safe code need to use
+	      <c>safe_fixed_monotonic_time</c> instead.</p></item>
+
+	      <tag><c>safe_fixed_monotonic_time</c></tag>
+	      <item><p><c>FixationTime</c> will correspond to the result
+	      returned by
+	      <seealso marker="erts:erlang#monotonic_time/0">erlang:monotonic_time/0</seealso>
+	      at the time of fixation. The usage of <c>safe_fixed_monotonic_time</c> is
+	      <seealso marker="erts:time_correction#Time_Warp_Safe_Code">time warp
+	      safe</seealso>.</p></item>
+	    </taglist>
             <p><c>Info</c> is a possibly empty lists of tuples
               <c>{Pid,RefCount}</c>, one tuple for every process the
               table is fixed by right now. <c>RefCount</c> is the value
@@ -1135,9 +1160,11 @@ clean_all_with_value(Tab,X,Key) ->
           table but never releases it, the memory used by the deleted
           objects will never be freed. The performance of operations on
           the table will also degrade significantly.</p>
-        <p>Use <c>info/2</c> to retrieve information about which
-          processes have fixed which tables. A system with a lot of
-          processes fixing tables may need a monitor which sends alarms
+        <p>Use
+	<seealso marker="#info_2_safe_fixed_monotonic_time"><c>info(Tab,
+	safe_fixed_monotonic_time)</c></seealso> to retrieve information
+	about which processes have fixed which tables. A system with a lot
+	of processes fixing tables may need a monitor which sends alarms
           when tables have been fixed for too long.</p>
         <p>Note that for tables of the <c>ordered_set</c> type,
           <c>safe_fixtable/2</c> is not necessary as calls to
diff --git a/lib/stdlib/src/dets.erl b/lib/stdlib/src/dets.erl
index 6d07f4018a..2d037ff795 100644
--- a/lib/stdlib/src/dets.erl
+++ b/lib/stdlib/src/dets.erl
@@ -372,7 +372,7 @@ info(Tab) ->
       Item :: 'access' | 'auto_save' | 'bchunk_format'
             | 'hash' | 'file_size' | 'filename' | 'keypos' | 'memory'
             | 'no_keys' | 'no_objects' | 'no_slots' | 'owner' | 'ram_file'
-            | 'safe_fixed' | 'size' | 'type' | 'version',
+            | 'safe_fixed' | 'safe_fixed_monotonic_time' | 'size' | 'type' | 'version',
       Value :: term().
 
 info(Tab, owner) ->
@@ -1964,7 +1964,9 @@ do_safe_fixtable(Head, Pid, true) ->
     case Head#head.fixed of 
 	false -> 
 	    link(Pid),
-	    Fixed = {utime_now(), [{Pid, 1}]},
+	    MonTime = erlang:monotonic_time(),
+	    TimeOffset = erlang:time_offset(),
+	    Fixed = {{MonTime, TimeOffset}, [{Pid, 1}]},
 	    Ftab = dets_utils:get_freelists(Head),
 	    Head#head{fixed = Fixed, freelists = {Ftab, Ftab}};
 	{TimeStamp, Counters} ->
@@ -2091,7 +2093,22 @@ finfo(H, no_keys) ->
 finfo(H, no_slots) -> {H, (H#head.mod):no_slots(H)};
 finfo(H, pid) -> {H, self()};
 finfo(H, ram_file) -> {H, H#head.ram_file};
-finfo(H, safe_fixed) -> {H, H#head.fixed};
+finfo(H, safe_fixed) ->
+    {H,
+     case H#head.fixed of
+	 false ->
+	     false;
+	 {{FixMonTime, TimeOffset}, RefList} ->
+	     {make_timestamp(FixMonTime, TimeOffset), RefList}
+     end};
+finfo(H, safe_fixed_monotonic_time) ->
+    {H,
+     case H#head.fixed of
+	 false ->
+	     false;
+	 {{FixMonTime, _TimeOffset}, RefList} ->
+	     {FixMonTime, RefList}
+     end};
 finfo(H, size) -> 
     case catch write_cache(H) of
 	{H2, []} ->
@@ -3275,11 +3292,14 @@ err(Error) ->
 time_now() ->
     erlang:monotonic_time(1000000).
 
--compile({inline, [utime_now/0]}).
-utime_now() ->
-    Time = time_now(),
-    UniqueCounter = erlang:unique_integer([monotonic]),
-    {Time, UniqueCounter}.
+make_timestamp(MonTime, TimeOffset) ->
+    ErlangSystemTime = erlang:convert_time_unit(MonTime+TimeOffset,
+						native,
+						micro_seconds),
+    MegaSecs = ErlangSystemTime div 1000000000000,
+    Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000,
+    MicroSecs = ErlangSystemTime rem 1000000,
+    {MegaSecs, Secs, MicroSecs}.
 
 %%%%%%%%%%%%%%%%%  DEBUG functions %%%%%%%%%%%%%%%%
 
diff --git a/lib/stdlib/src/ets.erl b/lib/stdlib/src/ets.erl
index 847def2fd8..1fca3624dc 100644
--- a/lib/stdlib/src/ets.erl
+++ b/lib/stdlib/src/ets.erl
@@ -146,7 +146,7 @@ info(_) ->
       Tab :: tab(),
       Item :: compressed | fixed | heir | keypos | memory
             | name | named_table | node | owner | protection
-            | safe_fixed | size | stats | type
+            | safe_fixed | safe_fixed_monotonic_time | size | stats | type
 	    | write_concurrency | read_concurrency,
       Value :: term().
 
diff --git a/lib/stdlib/src/stdlib.app.src b/lib/stdlib/src/stdlib.app.src
index 7f9bbbf649..b8a7973cf2 100644
--- a/lib/stdlib/src/stdlib.app.src
+++ b/lib/stdlib/src/stdlib.app.src
@@ -105,7 +105,7 @@
                dets]},
   {applications, [kernel]},
   {env, []},
-  {runtime_dependencies, ["sasl-2.6","kernel-4.1","erts-7.0","crypto-3.3",
+  {runtime_dependencies, ["sasl-2.6","kernel-4.1","erts-7.3","crypto-3.3",
 			  "compiler-5.0"]}
 ]}.
 
diff --git a/lib/stdlib/test/dets_SUITE.erl b/lib/stdlib/test/dets_SUITE.erl
index 7f5e06524a..35e587afcc 100644
--- a/lib/stdlib/test/dets_SUITE.erl
+++ b/lib/stdlib/test/dets_SUITE.erl
@@ -1876,9 +1876,33 @@ fixtable(Config, Version) when is_list(Config) ->
     {ok, _} = dets:open_file(T, [{type, duplicate_bag} | Args]),
     %% In a fixed table, delete and re-insert an object.
     ok = dets:insert(T, {1, a, b}),
+    SysBefore = erlang:timestamp(),
+    MonBefore = erlang:monotonic_time(),
     dets:safe_fixtable(T, true),
+    MonAfter = erlang:monotonic_time(),
+    SysAfter = erlang:timestamp(),
+    Self = self(),
+    {FixMonTime,[{Self,1}]} = dets:info(T,safe_fixed_monotonic_time),
+    {FixSysTime,[{Self,1}]} = dets:info(T,safe_fixed),
+    true = is_integer(FixMonTime),
+    true = MonBefore =< FixMonTime,
+    true = FixMonTime =< MonAfter,
+    {FstMs,FstS,FstUs} = FixSysTime,
+    true = is_integer(FstMs),
+    true = is_integer(FstS),
+    true = is_integer(FstUs),
+    case erlang:system_info(time_warp_mode) of
+	no_time_warp ->
+	    true = timer:now_diff(FixSysTime, SysBefore) >= 0,
+	    true = timer:now_diff(SysAfter, FixSysTime) >= 0;
+	_ ->
+	    %% ets:info(Tab,safe_fixed) not timewarp safe...
+	    ignore
+    end,
     ok = dets:match_delete(T, {1, a, b}),
     ok = dets:insert(T, {1, a, b}),
+    {FixMonTime,[{Self,1}]} = dets:info(T,safe_fixed_monotonic_time),
+    {FixSysTime,[{Self,1}]} = dets:info(T,safe_fixed),
     dets:safe_fixtable(T, false),
     1 = length(dets:match_object(T, '_')),
 
diff --git a/lib/stdlib/test/ets_SUITE.erl b/lib/stdlib/test/ets_SUITE.erl
index ae431d66d9..30a158d9e1 100644
--- a/lib/stdlib/test/ets_SUITE.erl
+++ b/lib/stdlib/test/ets_SUITE.erl
@@ -3989,15 +3989,37 @@ safe_fixtable_do(Opts) ->
     ?line true = ets:safe_fixtable(Tab, true),
     ?line receive after 1 -> ok end,
     ?line true = ets:safe_fixtable(Tab, false),
-    ?line false = ets:info(Tab,safe_fixed),
-    ?line true = ets:safe_fixtable(Tab, true),
+    false = ets:info(Tab,safe_fixed_monotonic_time),
+    false = ets:info(Tab,safe_fixed),
+    SysBefore = erlang:timestamp(),
+    MonBefore = erlang:monotonic_time(),
+    true = ets:safe_fixtable(Tab, true),
+    MonAfter = erlang:monotonic_time(),
+    SysAfter = erlang:timestamp(),
     Self = self(),
-    ?line {{_,_,_},[{Self,1}]} = ets:info(Tab,safe_fixed),
+    {FixMonTime,[{Self,1}]} = ets:info(Tab,safe_fixed_monotonic_time),
+    {FixSysTime,[{Self,1}]} = ets:info(Tab,safe_fixed),
+    true = is_integer(FixMonTime),
+    true = MonBefore =< FixMonTime,
+    true = FixMonTime =< MonAfter,
+    {FstMs,FstS,FstUs} = FixSysTime,
+    true = is_integer(FstMs),
+    true = is_integer(FstS),
+    true = is_integer(FstUs),
+    case erlang:system_info(time_warp_mode) of
+	no_time_warp ->
+	    true = timer:now_diff(FixSysTime, SysBefore) >= 0,
+	    true = timer:now_diff(SysAfter, FixSysTime) >= 0;
+	_ ->
+	    %% ets:info(Tab,safe_fixed) not timewarp safe...
+	    ignore
+    end,
     %% Test that an unjustified 'unfix' is a no-op.
     {Pid,MRef} = my_spawn_monitor(fun() -> true = ets:safe_fixtable(Tab,false) end),
     {'DOWN', MRef, process, Pid, normal} = receive M -> M end,
-    ?line true = ets:info(Tab,fixed),
-    ?line {{_,_,_},[{Self,1}]} = ets:info(Tab,safe_fixed),
+    true = ets:info(Tab,fixed),
+    {FixMonTime,[{Self,1}]} = ets:info(Tab,safe_fixed_monotonic_time),
+    {FixSysTime,[{Self,1}]} = ets:info(Tab,safe_fixed),
     %% badarg's
     ?line {'EXIT', {badarg, _}} = (catch ets:safe_fixtable(Tab, foobar)),
     ?line true = ets:info(Tab,fixed),
@@ -4043,6 +4065,7 @@ info_do(Opts) ->
     ?line undefined = ets:info(non_existing_table_xxyy,type),
     ?line undefined = ets:info(non_existing_table_xxyy,node),
     ?line undefined = ets:info(non_existing_table_xxyy,named_table),
+    ?line undefined = ets:info(non_existing_table_xxyy,safe_fixed_monotonic_time),
     ?line undefined = ets:info(non_existing_table_xxyy,safe_fixed),
     ?line verify_etsmem(EtsMem).
 
@@ -5532,7 +5555,7 @@ otp_8166_zombie_creator(T,Deleted) ->
 						  [{'=<','$1', Deleted}],
 						  [true]}]),
 	    Pid ! zombies_created,
-	    repeat_while(fun() -> case ets:info(T,safe_fixed) of
+	    repeat_while(fun() -> case ets:info(T,safe_fixed_monotonic_time) of
 				      {_,[_P1,_P2]} ->
 					  false;
 				      _ ->