Better OS system time implementation

2 files changed, 65 insertions, 4 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 7cb417ac92..bd5efb712c 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -6031,6 +6031,8 @@ ok
       <name name="system_info" arity="1" clause_i="62"/>
       <name name="system_info" arity="1" clause_i="63"/>
       <name name="system_info" arity="1" clause_i="64"/>
+      <name name="system_info" arity="1" clause_i="65"/>
+      <name name="system_info" arity="1" clause_i="66"/>
       <fsummary>Information about the system</fsummary>
       <desc>
         <p>Returns various information about the current system
@@ -6482,6 +6484,59 @@ ok
 	      <seealso marker="#type_time_unit">time unit</seealso>.</p></item>
 	    </taglist>
           </item>
+          <tag><marker id="system_info_os_system_time_source"><c>os_system_time_source</c></marker></tag>
+          <item>
+            <p>Returns a list containing information about the source of
+	    <seealso marker="erts:time_correction#OS_System_Time">OS
+	    system time</seealso> that is used by the runtime system.</p>
+	    <p>The list contains two-tuples with <c>Key</c>s
+	    as first element, and <c>Value</c>s as second element. The
+	    order if these tuples is undefined. Currently the following
+	    tuples may be part of the list, but more tuples may be
+	    introduced in the future:</p>
+	    <taglist>
+	      <tag><c>{function, Function}</c></tag>
+	      <item><p><c>Function</c> is the name of the funcion
+	      used.</p></item>
+
+	      <tag><c>{clock_id, ClockId}</c></tag>
+	      <item><p>This tuple only exist if <c>Function</c>
+	      can be used with different clocks. <c>ClockId</c>
+	      corresponds to the clock identifer used when calling
+	      <c>Function</c>.</p></item>
+
+	      <tag><c>{resolution, OsSystemTimeResolution}</c></tag>
+	      <item><p>Highest possible
+	      <seealso marker="time_correction#Time_Resolution">resolution</seealso>
+	      of current OS system time source as parts per
+	      second. If no resolution information can be retreived
+	      from the OS, <c>OsSystemTimeResolution</c> will be
+	      set to the resolution of the time unit of
+	      <c>Function</c>s return value. That is, the actual
+	      resolution may be lower than
+	      <c>OsSystemTimeResolution</c>. Also note that
+	      the resolution does not say anything about the
+	      <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>,
+	      and that the
+	      <seealso marker="time_correction#Time_Precision">precision</seealso>
+	      might not align with the resolution. You do,
+	      however, know that the precision won't be
+	      better than
+	      <c>OsSystemTimeResolution</c>.</p></item>
+
+	      <tag><c>{parallel, Parallel}</c></tag>
+	      <item><p><c>Parallel</c> equals <c>yes</c> if
+	      <c>Function</c> is called in parallel from multiple
+	      threads. If it is not called in parallel, because
+	      calls needs to be serialized, <c>Parallel</c> equals
+	      <c>no</c>.</p></item>
+
+	      <tag><c>{time, OsSystemTime}</c></tag>
+	      <item><p><c>OsSystemTime</c> equals current OS
+	      system time in <c>native</c>
+	      <seealso marker="#type_time_unit">time unit</seealso>.</p></item>
+	    </taglist>
+          </item>
 	  <tag><marker id="system_info_port_parallelism"><c>port_parallelism</c></marker></tag>
 	  <item><p>Returns the default port parallelism scheduling hint used.
 	  For more information see the
diff --git a/erts/doc/src/time_correction.xml b/erts/doc/src/time_correction.xml
index ed658ff58c..979a37d7ff 100644
--- a/erts/doc/src/time_correction.xml
+++ b/erts/doc/src/time_correction.xml
@@ -147,7 +147,9 @@
       This may or may not be an accurate view of POSIX time. This time
       may typically be adjusted both backwards and forwards without
       limitation. That is, huge leaps both backwards and forwards in time
-      may be observed.</p>
+      may be observed. You can get information about the Erlang runtime
+      system's source of OS system time by calling
+      <seealso marker="erlang#system_info_os_system_time_source"><c>erlang:system_info(os_system_time_source)</c></seealso>.</p>
     </section>
 
     <marker id="OS_Monotonic_Time"/>
@@ -161,7 +163,9 @@
       point in time that is not connected to
       <seealso marker="#OS_System_Time">OS system time</seealso>. Note that
       this type of time is not necessarily provided by all operating
-      systems.</p>
+      systems. You can get information about the Erlang runtime
+      system's source of OS monotonic time by calling
+      <seealso marker="erlang#system_info_os_monotonic_time_source"><c>erlang:system_info(os_monotonic_time_source)</c></seealso>.</p>
     </section>
 
     <marker id="Erlang_System_Time"/>
@@ -597,6 +601,7 @@
       <item><p><seealso marker="erlang#monitor/2"><c>erlang:monitor(time_offset, clock_service)</c></seealso></p></item>
       <item><p><seealso marker="erlang#system_flag_time_offset"><c>erlang:system_flag(time_offset, finalize)</c></seealso></p></item>
       <item><p><seealso marker="erlang#system_info_os_monotonic_time_source"><c>erlang:system_info(os_monotonic_time_source)</c></seealso></p></item>
+      <item><p><seealso marker="erlang#system_info_os_system_time_source"><c>erlang:system_info(os_system_time_source)</c></seealso></p></item>
       <item><p><seealso marker="erlang#system_info_time_offset"><c>erlang:system_info(time_offset)</c></seealso></p></item>
       <item><p><seealso marker="erlang#system_info_time_warp_mode"><c>erlang:system_info(time_warp_mode)</c></seealso></p></item>
       <item><p><seealso marker="erlang#system_info_time_correction"><c>erlang:system_info(time_correction)</c></seealso></p></item>
@@ -852,8 +857,9 @@ EventTag = {Time, UMI}</code>
     when it is not available. Fortunately almost all of the new
     API can easily be implemented using existing primitives
     (except for
-    <seealso marker="erlang#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso>, and
-    <seealso marker="erlang#system_info_os_monotonic_time_source"><c>erlang:system_info(os_monotonic_time_source)</c></seealso>).
+    <seealso marker="erlang#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso>,
+    <seealso marker="erlang#system_info_os_monotonic_time_source"><c>erlang:system_info(os_monotonic_time_source)</c></seealso>, and
+    <seealso marker="erlang#system_info_os_system_time_source"><c>erlang:system_info(os_system_time_source)</c></seealso>).
     By wrapping the API with functions that fall back on
     <c>erlang:now/0</c> when the new API is not available,
     and using these wrappers instead of using the API directly