erts: Add erlang:system_flag(system_logger,_)

This flag allows logger and other components to set the
process which log messages from ERTS are to be sent.

1 files changed, 69 insertions, 29 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index a42323b13d..7699f64c25 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -7539,7 +7539,39 @@ ok
     </func>
 
     <func>
-      <name name="system_flag" arity="2" clause_i="14" since=""/>
+      <name name="system_flag" arity="2" clause_i="14" since="OTP 21.3"/>
+      <fsummary>Set system logger process.</fsummary>
+      <desc>
+        <p>Sets the process that will receive the logging
+        messages generated by ERTS. If set to <c>undefined</c>,
+        all logging messages generated by ERTS will be dropped.
+        The messages will be in the format:</p>
+        <code>
+{log,Level,Format,ArgList,Metadata} where
+
+Level = atom(),
+Format = string(),
+ArgList = list(term()),
+Metadata = #{ pid => pid(),
+   group_leader => pid(),
+   time := logger:timestamp(),
+   error_logger := #{ emulator := true, tag := atom() }
+        </code>
+        <p>If the <c>system_logger</c> process dies,
+        this flag will be reset to <c>logger</c>.</p>
+        <p>The default is the process named <c>logger</c>.</p>
+        <p>Returns the old value of the flag.</p>
+        <note><p>This function is designed to be used by the
+        KERNEL <seealso marker="kernel:logger"><c>logger</c></seealso>.
+        Be careful if you change it to something else as
+        log messages may be lost. If you want to intercept
+        emulator log messages, do it by adding a specialized handler
+        to the KERNEL logger.</p></note>
+      </desc>
+    </func>
+
+    <func>
+      <name name="system_flag" arity="2" clause_i="15" since=""/>
       <fsummary>Set system flag trace_control_word.</fsummary>
       <desc>
         <p>Sets the value of the node trace control word to
@@ -7553,7 +7585,7 @@ ok
     </func>
 
     <func>
-      <name name="system_flag" arity="2" clause_i="15"
+      <name name="system_flag" arity="2" clause_i="16"
 	    anchor="system_flag_time_offset" since="?"/>
       <fsummary>Finalize the time offset.</fsummary>
       <desc>
@@ -7703,8 +7735,9 @@ ok
               <seealso marker="#system_info_nif_version"><c>nif_version</c></seealso>,
               <seealso marker="#system_info_otp_release"><c>otp_release</c></seealso>,
               <seealso marker="#system_info_port_parallelism"><c>port_parallelism</c></seealso>,
-              <seealso marker="#system_info_system_version"><c>system_version</c></seealso>,
               <seealso marker="#system_info_system_architecture"><c>system_architecture</c></seealso>,
+              <seealso marker="#system_info_system_logger"><c>system_logger</c></seealso>,
+              <seealso marker="#system_info_system_version"><c>system_version</c></seealso>,
               <seealso marker="#system_info_trace_control_word"><c>trace_control_word</c></seealso>,
               <seealso marker="#system_info_version"><c>version</c></seealso>,
               <seealso marker="#system_info_wordsize"><c>wordsize</c></seealso>
@@ -7876,7 +7909,7 @@ ok
 	    anchor="system_info_cpu_topology" since=""/>           <!-- cpu_topology -->
       <name name="system_info" arity="1" clause_i="13" since=""/>  <!-- {cpu_topology, _} -->
       <name name="system_info" arity="1" clause_i="38" since=""/>  <!-- logical_processors -->
-      <name name="system_info" arity="1" clause_i="73" since="?"/>  <!-- update_cpu_info -->
+      <name name="system_info" arity="1" clause_i="74" since="?"/>  <!-- update_cpu_info -->
       <fsummary>Information about the CPU topology of the system.</fsummary>
       <type name="cpu_topology"/>
       <type name="level_entry"/>
@@ -8231,10 +8264,10 @@ ok
       <name name="system_info" arity="1" clause_i="50" since="OTP 18.0"/>  <!-- os_monotonic_time_source -->
       <name name="system_info" arity="1" clause_i="51" since="OTP 18.0"/>  <!-- os_system_time_source -->
       <name name="system_info" arity="1" clause_i="63" since="OTP 18.0"/>  <!-- start_time -->
-      <name name="system_info" arity="1" clause_i="68" since="OTP 18.0"/>  <!-- time_correction -->
-      <name name="system_info" arity="1" clause_i="69" since="OTP 18.0"/>  <!-- time_offset -->
-      <name name="system_info" arity="1" clause_i="70" since="OTP 18.0"/>  <!-- time_warp_mode -->
-      <name name="system_info" arity="1" clause_i="71" since="?"/>  <!-- tolerant_timeofday -->
+      <name name="system_info" arity="1" clause_i="69" since="OTP 18.0"/>  <!-- time_correction -->
+      <name name="system_info" arity="1" clause_i="70" since="OTP 18.0"/>  <!-- time_offset -->
+      <name name="system_info" arity="1" clause_i="71" since="OTP 18.0"/>  <!-- time_warp_mode -->
+      <name name="system_info" arity="1" clause_i="72" since="?"/>  <!-- tolerant_timeofday -->
       <fsummary>Information about system time.</fsummary>
       <desc>
         <marker id="system_info_time_tags"/>
@@ -8466,8 +8499,8 @@ ok
       <name name="system_info" arity="1" clause_i="60" since=""/>  <!-- scheduler_id -->
       <name name="system_info" arity="1" clause_i="61" since=""/>  <!-- schedulers -->
       <name name="system_info" arity="1" clause_i="62" since=""/>  <!-- smp_support -->
-      <name name="system_info" arity="1" clause_i="66" since=""/>  <!-- threads -->
-      <name name="system_info" arity="1" clause_i="67" since=""/>  <!-- thread_pool_size -->
+      <name name="system_info" arity="1" clause_i="67" since=""/>  <!-- threads -->
+      <name name="system_info" arity="1" clause_i="68" since=""/>  <!-- thread_pool_size -->
       <fsummary>Information about system schedulers.</fsummary>
       <desc>
         <marker id="system_info_scheduler_tags"/>
@@ -8889,19 +8922,20 @@ ok
       <!-- <name name="system_info" arity="1" clause_i="61"/>  schedulers -->
       <!-- <name name="system_info" arity="1" clause_i="62"/>  smp_support -->
       <!-- <name name="system_info" arity="1" clause_i="63"/>  start_time -->
-      <name name="system_info" arity="1" clause_i="64" since=""/>  <!-- system_version -->
-      <name name="system_info" arity="1" clause_i="65" since=""/>  <!-- system_architecture -->
-      <!-- <name name="system_info" arity="1" clause_i="66"/>  threads -->
-      <!-- <name name="system_info" arity="1" clause_i="67"/>  thread_pool_size -->
-      <!-- <name name="system_info" arity="1" clause_i="68"/>  time_correction -->
-      <!-- <name name="system_info" arity="1" clause_i="69"/>  time_offset -->
-      <!-- <name name="system_info" arity="1" clause_i="70"/>  time_warp_mode -->
-      <!-- <name name="system_info" arity="1" clause_i="71"/>  tolerant_timeofday -->
-      <name name="system_info" arity="1" clause_i="72" since=""/>  <!-- trace_control_word -->
-      <!-- <name name="system_info" arity="1" clause_i="73"/>  update_cpu_info -->
-      <name name="system_info" arity="1" clause_i="74" since=""/>  <!-- version -->
-      <name name="system_info" arity="1" clause_i="75" since=""/>  <!-- wordsize -->
-      <!-- <name name="system_info" arity="1" clause_i="76"/>  overview -->
+      <name name="system_info" arity="1" clause_i="64" since=""/>  <!-- system_architecture -->
+      <name name="system_info" arity="1" clause_i="65" since="OTP 21.3"/>  <!-- system_logger -->
+      <name name="system_info" arity="1" clause_i="66" since=""/>  <!-- system_version -->
+      <!-- <name name="system_info" arity="1" clause_i="67"/>  threads -->
+      <!-- <name name="system_info" arity="1" clause_i="68"/>  thread_pool_size -->
+      <!-- <name name="system_info" arity="1" clause_i="69"/>  time_correction -->
+      <!-- <name name="system_info" arity="1" clause_i="70"/>  time_offset -->
+      <!-- <name name="system_info" arity="1" clause_i="71"/>  time_warp_mode -->
+      <!-- <name name="system_info" arity="1" clause_i="72"/>  tolerant_timeofday -->
+      <name name="system_info" arity="1" clause_i="73" since=""/>  <!-- trace_control_word -->
+      <!-- <name name="system_info" arity="1" clause_i="74"/>  update_cpu_info -->
+      <name name="system_info" arity="1" clause_i="75" since=""/>  <!-- version -->
+      <name name="system_info" arity="1" clause_i="76" since=""/>  <!-- wordsize -->
+      <!-- <name name="system_info" arity="1" clause_i="77"/>  overview -->
       <fsummary>Information about the system.</fsummary>
       <desc>
         <marker id="system_info_misc_tags"/>
@@ -9057,18 +9091,24 @@ ok
               <seealso marker="erl#+spp"><c>+spp</c></seealso>
               in <c>erl(1)</c>.</p>
           </item>
-          <tag><marker id="system_info_system_version"/>
-            <c>system_version</c></tag>
-          <item>
-            <p>Returns a string containing version number and
-              some important properties, such as the number of schedulers.</p>
-          </item>
           <tag><marker id="system_info_system_architecture"/>
             <c>system_architecture</c></tag>
           <item>
             <p>Returns a string containing the processor and OS
               architecture the emulator is built for.</p>
           </item>
+          <tag><marker id="system_info_system_logger"/>
+            <c>system_logger</c></tag>
+          <item>
+            <p>Returns the current <c>system_logger</c> as set by
+            <seealso marker="#system_flag/2"><c>erlang:system_flag(system_logger, _)</c></seealso>.</p>
+          </item>
+          <tag><marker id="system_info_system_version"/>
+            <c>system_version</c></tag>
+          <item>
+            <p>Returns a string containing version number and
+              some important properties, such as the number of schedulers.</p>
+          </item>
           <tag><marker id="system_info_trace_control_word"/>
             <c>trace_control_word</c></tag>
           <item>