From 5b913ca7e6bf13310a2ae4362867d3247943084a Mon Sep 17 00:00:00 2001
From: Matthias Hochsteger <matthias.hochsteger@tuwien.ac.at>
Date: Tue, 16 Jul 2019 11:56:09 +0200
Subject: [PATCH] Atomic utility functions

---
 libsrc/core/utils.hpp      | 36 ++++++++++++++++++++
 tests/catch/CMakeLists.txt |  1 +
 tests/catch/utils.cpp      | 67 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 104 insertions(+)
 create mode 100644 tests/catch/utils.cpp

diff --git a/libsrc/core/utils.hpp b/libsrc/core/utils.hpp
index 3645ea18..e1da760c 100644
--- a/libsrc/core/utils.hpp
+++ b/libsrc/core/utils.hpp
@@ -1,6 +1,7 @@
 #ifndef NETGEN_CORE_UTILS_HPP
 #define NETGEN_CORE_UTILS_HPP
 
+#include <atomic>
 #include <chrono>
 #include <map>
 #include <ostream>
@@ -119,6 +120,41 @@ namespace ngcore
     return std::equal(end.rbegin(), end.rend(), str.rbegin());
   }
 
+  template<typename T>
+  NETGEN_INLINE std::atomic<T> & AsAtomic (T & d)
+  {
+    return reinterpret_cast<std::atomic<T>&> (d);
+  }
+
+  NETGEN_INLINE double AtomicAdd( double & sum, double val )
+  {
+      std::atomic<double> & asum = AsAtomic(sum);
+      double current = asum.load();
+      while (!asum.compare_exchange_weak(current, current + val))
+          ;
+      return current;
+  }
+
+  template<typename T>
+  NETGEN_INLINE T AtomicMin( T & minval, T val )
+  {
+      std::atomic<T> & aminval = AsAtomic(minval);
+      T current = aminval.load();
+      while (!aminval.compare_exchange_weak(current, std::min(current, val)))
+          ;
+      return current;
+  }
+
+  template<typename T>
+  NETGEN_INLINE T AtomicMax( T & maxval, T val )
+  {
+      std::atomic<T> & amaxval = AsAtomic(maxval);
+      T current = amaxval.load();
+      while (!amaxval.compare_exchange_weak(current, std::max(current, val)))
+          ;
+      return current;
+  }
+
 } // namespace ngcore
 
 #endif // NETGEN_CORE_UTILS_HPP
diff --git a/tests/catch/CMakeLists.txt b/tests/catch/CMakeLists.txt
index 1dc6dd10..3b727af8 100644
--- a/tests/catch/CMakeLists.txt
+++ b/tests/catch/CMakeLists.txt
@@ -27,6 +27,7 @@ endmacro()
 
 add_unit_test(archive archive.cpp)
 add_unit_test(symboltable symboltable.cpp)
+add_unit_test(utils utils.cpp)
 add_unit_test(version version.cpp)
 
 endif(ENABLE_UNIT_TESTS)
diff --git a/tests/catch/utils.cpp b/tests/catch/utils.cpp
new file mode 100644
index 00000000..4258b5b9
--- /dev/null
+++ b/tests/catch/utils.cpp
@@ -0,0 +1,67 @@
+
+#include "catch.hpp"
+#include <core/ngcore.hpp>
+using namespace ngcore;
+using namespace std;
+
+
+long shuffle(long N, long i) {
+    // Shuffle the numbers using multiplication with a prime number to force many updates of min, max
+    constexpr long P = 101;
+    return (N/2 + i*P) % N;
+}
+
+void testThreading(int n_threads)
+{
+  TaskManager::SetNumThreads(n_threads);
+  n_threads = EnterTaskManager();
+
+  constexpr long N = 100000;
+
+
+  SECTION( "atomic operations" ) {
+      long i_min = 2*N;
+      long i_max = 0;
+      long i_sum = 0;
+
+      double d_min = 1e100;
+      double d_max = 0.0;
+      double d_sum = 0.0;
+
+      ParallelFor( Range(N), [&] (long i) {
+          AtomicMin(i_min, shuffle(N,i));
+      });
+      REQUIRE( i_min==0 );
+
+      ParallelFor( Range(N), [&] (long i) {
+          AtomicMax(i_max, shuffle(N,i));
+      });
+      REQUIRE( i_max==N-1 );
+
+      ParallelFor( Range(N), [&] (long i) {
+          AsAtomic(i_sum) += i;
+      });
+      REQUIRE( i_sum==N*(N-1)/2 );
+
+      ParallelFor( Range(N), [&] (double i) {
+          AtomicMin(d_min, static_cast<double>(shuffle(N,i)));
+      });
+      REQUIRE( d_min==0 );
+
+      ParallelFor( Range(N), [&] (double i) {
+          AtomicMax(d_max, static_cast<double>(shuffle(N,i)));
+      });
+      REQUIRE( d_max==N-1 );
+
+      ParallelFor( Range(N), [&] (double i) {
+          AtomicAdd(d_sum, i);
+      });
+      REQUIRE( d_sum==N*(N-1)/2 );
+
+  }
+  ExitTaskManager(n_threads);
+}
+
+TEST_CASE("Threading - 1 Thread") { testThreading(1); }
+TEST_CASE("Threading - 2 Thread") { testThreading(2); }
+TEST_CASE("Threading - 8 Thread") { testThreading(8); }