Library: investigate drawing random numbers concurrently

''In theory,'' the random number generators are in no way threadsafe,
neither the old `rand()`, nor the mersenne twister of the C++ standard.

However, since all we want is some arbitrarily diffused numbers,
chances are that this issue can be safely ignored; because a random
number computation broken by concurrency will most likely generate --
well, a garbled number or "randomly" corrupted internal state.

Validating this reasoning by an empiric investigation seems advisable though.

tests/16calculation.tests

@@ -15,3 +15,8 @@ END
 TEST "Random numbers and Seed" Random_test << END
 return: 0
 END
+
+
+TEST "Concurrent PRNG access" RandomConcurrent_test << END
+return: 0
+END

tests/library/random-concurrent-test.cpp

@@ -0,0 +1,110 @@
+/*
+  RandomConcurrent(Test)  -  investigate concurrent random number generation
+
+  Copyright (C)         Lumiera.org
+    2024,               Hermann Vosseler <Ichthyostega@web.de>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of
+  the License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+* *****************************************************/
+
+/** @file random-concurrent-test.cpp
+ ** unit test \ref RandomConcurrent_test
+ */
+
+
+
+#include "lib/test/run.hpp"
+#include "lib/sync-barrier.hpp"
+#include "lib/random.hpp"
+#include "lib/thread.hpp"
+#include "lib/sync.hpp"
+#include "lib/util.hpp"
+#include "lib/scoped-collection.hpp"
+#include "lib/test/microbenchmark.hpp"
+#include "lib/test/diagnostic-output.hpp"
+
+#include <deque>
+//using util::isLimited;
+
+namespace lib {
+namespace test {
+  
+  namespace {
+    const uint NUM_THREADS = 8;
+    
+    const uint NUM_INVOKE = 1'000'000;
+    
+    
+  }
+  
+  /******************************************************************//**
+   * @test demonstrate simple access to random number generation,
+   *       as well as the setup of controlled random number sequences.
+   * @see  random.hpp
+   */
+  class RandomConcurrent_test : public Test
+    {
+      
+      virtual void
+      run (Arg)
+        {
+          seedRand();
+          investigate_concurrentAccess();
+        }
+      
+      
+      /** @test examine behaviour of PRNG under concurrency stress */
+      void
+      investigate_concurrentAccess()
+        {
+          struct Results
+            : std::deque<double>
+            , Sync<>
+            {
+              void
+              post (double val)
+                {
+                  Lock sync(this);
+                  push_back (val);
+                }
+            };
+            
+            Results results;
+          
+          const uint N = NUM_INVOKE;
+          auto expect = RAND_MAX / 2;
+          
+          auto drawRandom = [&]()
+                              {
+                                double avg{0.0};
+                                for (uint i=0; i<N; ++i)
+                                  avg += 1.0/N * rani();
+                                auto error = avg/expect - 1;
+                                results.post (error);
+                              };
+          
+          auto [dur,sum] = threadBenchmark<NUM_THREADS> (drawRandom, 1);
+          for (auto res : results)
+            SHOW_EXPR(res);
+          SHOW_EXPR(sum)
+          SHOW_EXPR(dur/NUM_INVOKE)
+        }
+    };
+  
+  LAUNCHER (RandomConcurrent_test, "unit common");
+  
+  
+}} // namespace lib::test

tests/library/thread-wrapper-join-test.cpp

@@ -132,9 +132,9 @@ namespace test {
       
       
       void
-      joinOnceOnly ()
+      joinOnceOnly()
         {
-          ThreadJoinable theThread{"joining-4"
+          ThreadJoinable theThread{"test join-4"
                                   ,[]{ sleep_for (10ms); }};
           theThread.join();
           

wiki/thinkPad.ichthyo.mm

@@ -57622,8 +57622,8 @@
 <node CREATED="1731710016247" ID="ID_1116003187" MODIFIED="1731710023256" TEXT="nochmal im Einzelnen analysiert"/>
 <node CREATED="1731710023964" ID="ID_778217189" MODIFIED="1731710032544" TEXT="jede denkbare L&#xf6;sung ist nicht-trivial"/>
 <node COLOR="#435e98" CREATED="1731710053533" ID="ID_722076886" MODIFIED="1731713106542" TEXT="denkbar w&#xe4;re zumindest ein Refactoring">
-<linktarget COLOR="#23b91f" DESTINATION="ID_722076886" ENDARROW="Default" ENDINCLINATION="1530;2127;" ID="Arrow_ID_1785760257" SOURCE="ID_872583288" STARTARROW="None" STARTINCLINATION="-1253;43;"/>
 <linktarget COLOR="#7298c6" DESTINATION="ID_722076886" ENDARROW="Default" ENDINCLINATION="-173;13;" ID="Arrow_ID_1252004977" SOURCE="ID_778660910" STARTARROW="None" STARTINCLINATION="411;21;"/>
+<linktarget COLOR="#23b91f" DESTINATION="ID_722076886" ENDARROW="Default" ENDINCLINATION="1530;2127;" ID="Arrow_ID_1785760257" SOURCE="ID_872583288" STARTARROW="None" STARTINCLINATION="-1253;43;"/>
 <icon BUILTIN="idea"/>
 <node COLOR="#338800" CREATED="1731710077230" ID="ID_1009222978" MODIFIED="1731712876022" TEXT="man k&#xf6;nnte die Erkennung dieser Situation in eine Methode auf Layer-1 extrahieren">
 <icon BUILTIN="button_ok"/>
@@ -57714,8 +57714,7 @@
       Hier wird zun&#228;chst &#187;auf dem Trockenen&#171; demonstriert, wie aus der Kapazit&#228;tsrechnung eine zu erwartende effektive concurrent-run-time abgeleitet wird. Am Ende wird ein tats&#228;chlicher Scheduler-Lauf mit diesem (relativ locker dimensionierten) Schedule gestartet&#160;&#160;&#8212; und <b>hier</b>&#160;&#252;berschreiten wir den <b>Timeout von 5 Sekunden</b>, was bedeutet, da&#223; das Schedule komplett aus dem Ruder gelaufen sein mu&#223; (m&#246;glicherweise wurden sogar Job-Deadlines &#252;berfahren, in welchem Fall das Scheduler unvollst&#228;ndig h&#228;ngen bleibt)
     </p>
   </body>
-</html>
+</html></richcontent>
-</richcontent>
 </node>
 </node>
 </node>
@@ -58021,6 +58020,7 @@
 </node>
 <node BACKGROUND_COLOR="#fdfdcf" COLOR="#ff0000" CREATED="1731455444796" ID="ID_784243083" MODIFIED="1731455723202" TEXT="Concurrent Tests umstellen">
 <icon BUILTIN="bell"/>
+<node CREATED="1731728363475" ID="ID_1473702684" MODIFIED="1731728367146" TEXT="problematisch">
 <node CREATED="1731455475587" ID="ID_1622000187" MODIFIED="1731455475587" TEXT="CallQueue_test"/>
 <node CREATED="1731455716786" ID="ID_943344715" MODIFIED="1731455716786" TEXT="DiagnosticContext_test"/>
 <node CREATED="1731458234804" ID="ID_1185469440" MODIFIED="1731458234804" TEXT="SessionCommandFunction_test"/>
@@ -58047,7 +58047,22 @@
 <node CREATED="1731464903922" ID="ID_349618800" MODIFIED="1731464903922" TEXT="ThreadWrapperJoin_test"/>
 </node>
 </node>
-<node CREATED="1731465663005" MODIFIED="1731465663005" TEXT="BusTerm_test"/>
+<node CREATED="1731465663005" ID="ID_444907234" MODIFIED="1731465663005" TEXT="BusTerm_test"/>
+</node>
+<node BACKGROUND_COLOR="#f0d5c5" COLOR="#990033" CREATED="1731728379707" ID="ID_38959317" MODIFIED="1731728399492" TEXT="gibt es &#xfc;berhaupt ein Problem hier?">
+<icon BUILTIN="help"/>
+<node CREATED="1731728402020" ID="ID_216802866" MODIFIED="1731728433241" TEXT="theoretisch ist PRNG nicht thread-safe"/>
+<node CREATED="1731728433837" ID="ID_975708385" MODIFIED="1731728441330" TEXT="aber ... was kann schon passieren??"/>
+<node CREATED="1731728442361" ID="ID_444376696" MODIFIED="1731728582512" TEXT="schlimmstenfalls eine &quot;zuf&#xe4;llig&quot; kaputte Zahl au&#xdf;erhalb des Definitionsbereichs..."/>
+<node BACKGROUND_COLOR="#eef0c5" COLOR="#990000" CREATED="1731728584572" ID="ID_1568853077" MODIFIED="1731728594906" TEXT="empirisch untersuchen">
+<icon BUILTIN="yes"/>
+<icon BUILTIN="pencil"/>
+<node CREATED="1731728599474" ID="ID_1952720762" MODIFIED="1731728615563" TEXT="mit allen Cores parallel Zufallszahlen ziehen"/>
+<node CREATED="1731728616535" ID="ID_59784960" MODIFIED="1731728640632" TEXT="einzelne Zahlen pr&#xfc;fen"/>
+<node CREATED="1731728641175" ID="ID_177314578" MODIFIED="1731728668212" TEXT="MIttelwert pr&#xfc;fen (bias)"/>
+<node CREATED="1731728672328" ID="ID_132879815" MODIFIED="1731728703703" TEXT="1. Test : 1 Million Aufrufe &#x27f9; sieht gut aus"/>
+</node>
+</node>
 </node>
 </node>
 </node>