BufferProvider: in preparation for a load test

To verify integration of this new engine-level facility,
it seems prudent to build a load test (without going into
extended stress- and performance testing).

For that we need
- random buffer demand
- a computational load that actually uses the buffer.

As part of the ''scheduler stress testing'', a self-calibrating
`ComputationalLoad` was developed, which even implements both a
merely computational load, but also a memory accessing computation.

This can be extended to optionally use an external buffer, instead
of allocating a precisely dimensioned memory block directly from heap.
Obviously this extension is ''dangerous'', since there is no way to
verify that the storage passed in can accommodated the storage required
based on the current calibration of the `ComputationalLoad`


As an aside: identified a timing check in `SchedulerService_test`
that showed the tendency to fail when invoked immediately after a build.

tests/vault/gear/scheduler-service-test.cpp

@@ -401,7 +401,7 @@ namespace test {
           CHECK (activity::PASS == res);                                    // instruction to check back once
           pullWork();
           CHECK (activity::WAIT == res);                                    // but next call will send this thread to sleep right away
-          CHECK (delay_us < 40);
+          CHECK (delay_us < 50);
           
           
           cout << "follow-up with some distance => follow-up delay"<<endl;

tests/vault/gear/scheduler-usage-test.cpp

@@ -87,7 +87,7 @@ namespace test {
   
   
   /** Register this test class... */
-  LAUNCHER (SchedulerUsage_test, "unit engine");
+  LAUNCHER (SchedulerUsage_test, "integration engine");
   
   
   

tests/vault/gear/test-chain-load.hpp

@@ -1324,6 +1324,7 @@ namespace test {
       microseconds timeBase = LOAD_DEFAULT_TIME;
       size_t       sizeBase = LOAD_DEFAULT_MEM_SIZE;
       bool useAllocation = false;
+      size_t* externalBuff{nullptr};
       
       /** cause a delay by computational load */
       double
@@ -1366,16 +1367,22 @@ namespace test {
           return computationSpeed(false) != LOAD_SPEED_BASELINE;
         }
       
+      size_t
+      requiredBuffSiz (uint scaleStep)  const
+        {
+          return useAllocation? allocNeeded(scaleStep).first : 0;
+        }
+      
     private:
       uint64_t
-      roundsNeeded (uint scaleStep)
+      roundsNeeded (uint scaleStep)  const
         {
           auto desiredMicros = scaleStep*timeBase.count();
           return uint64_t(desiredMicros*computationSpeed(useAllocation));
         }
       
-      auto
+      std::pair<size_t,size_t>
-      allocNeeded (uint scaleStep)
+      allocNeeded (uint scaleStep)  const
         {
           auto cnt = roundsNeeded(scaleStep);
           auto siz = max (scaleStep * sizeBase, 1u);
@@ -1401,13 +1408,15 @@ namespace test {
       causeMemProcessLoad (uint scaleStep)
         {
           auto [siz,round] = allocNeeded (scaleStep);
-          lib::UninitialisedDynBlock<size_t> memBlock{siz};
+          lib::UninitialisedDynBlock<size_t> memBlock;
+          size_t* mem = externalBuff? externalBuff
+                                    : memBlock.allocate (siz);
           Sink sink;
-          *memBlock.front() = sink+1;
+          *mem = sink+1;
           for ( ; 0 < round; --round)
-            for (size_t i=0; i<memBlock.size()-1; ++i)
+            for (size_t i=0; i<siz-1; ++i)
-              memBlock[i+1] += memBlock[i];
+              mem[i+1] += mem[i];
-          sink = *memBlock.back();
+          sink = mem[siz-1];
           sink = sink + 1;
         }