[SimplestFibTest] Run Runtime destructor and allow worker count reduction

tests/SimplestFibTest.cpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
-// Copyright © 2020 Florian Schmaus
+// Copyright © 2020-2022 Florian Schmaus
+#include <algorithm>
 #include <cstdlib>	 // for abort, exit, EXIT_SUCCESS
 #include <iostream>	 // for operator<<, basic_ostream::o...
 
@@ -74,15 +75,17 @@ static void fibKickoff() {
 	sem.wait();
 
 	std::cout << "fib(" << fibNum << ") = " << result << std::endl;
-	exit(EXIT_SUCCESS);
+	Runtime::getRuntime()->initiateTermination();
 }
 
 auto main(UNUSED_ARG int argc, UNUSED_ARG char* argv[]) -> int {
-	// const unsigned nthreads = std::thread::hardware_concurrency();
-	const unsigned nthreads = 2;
+	const workerid_t defaultWorkerCount = Runtime::getDefaultWorkerCount();
+	const workerid_t maxWorkerCount = 2;
+	const workerid_t nthreads = std::min(maxWorkerCount, defaultWorkerCount);
 
 	std::cout << "Number of threads: " << nthreads << std::endl;
 
+	{
 		Runtime runtime(nthreads);
 
 		Fiber* fibFiber = Fiber::from(&fibKickoff);
@@ -92,6 +95,7 @@ auto main(UNUSED_ARG int argc, UNUSED_ARG char* argv[]) -> int {
 		runtime.scheduleFromAnywhere(*fibFiber);
 
 		runtime.waitUntilFinished();
+	}
 
 	return 0;
 }