Merge branch 'nthreads' into 'develop'

Environment variable BA_NTHREADS provides default number of threads

See merge request !556

Resample/Options/SimulationOptions.cpp

@@ -14,11 +14,21 @@
 
 #include "Resample/Options/SimulationOptions.h"
 #include "Base/Util/Assert.h"
+#include <cstdlib>
+#include <iostream>
+#include <string>
 #include <thread>
 
 SimulationOptions::SimulationOptions()
     : m_mc_integration(false), m_include_specular(false), m_use_avg_materials(false), m_mc_points(1)
 {
+    if (const char* env_p = std::getenv("BA_NTHREADS")) {
+        std::cout << "Got number of threads from environment variable BA_NTHREADS = "
+                  << env_p << std::endl;
+        m_thread_info.n_threads = std::stoi(env_p);
+        if (m_thread_info.n_threads>0)
+            return;
+    }
     m_thread_info.n_threads = getHardwareConcurrency();
 }