Add new execution framework

Inspired by std::execution

src/libslic3r/Execution/ExecutionTBB.hpp

@@ -0,0 +1,77 @@
+#ifndef EXECUTIONTBB_HPP
+#define EXECUTIONTBB_HPP
+
+#include <tbb/spin_mutex.h>
+#include <tbb/mutex.h>
+#include <tbb/parallel_for.h>
+#include <tbb/parallel_reduce.h>
+#include <tbb/task_arena.h>
+
+#include "Execution.hpp"
+
+namespace Slic3r {
+
+struct ExecutionTBB {};
+template<> struct IsExecutionPolicy_<ExecutionTBB> : public std::true_type {};
+
+// Execution policy using Intel TBB library under the hood.
+static constexpr ExecutionTBB ex_tbb = {};
+
+template<> struct execution::Traits<ExecutionTBB> {
+private:
+
+    template<class Fn, class It>
+    static IteratorOnly<It, void> loop_(const tbb::blocked_range<It> &range, Fn &&fn)
+    {
+        for (auto &el : range) fn(el);
+    }
+
+    template<class Fn, class I>
+    static IntegerOnly<I, void> loop_(const tbb::blocked_range<I> &range, Fn &&fn)
+    {
+        for (I i = range.begin(); i < range.end(); ++i) fn(i);
+    }
+
+public:
+    using SpinningMutex = tbb::spin_mutex;
+    using BlockingMutex = tbb::mutex;
+
+    template<class It, class Fn>
+    static void for_each(const ExecutionTBB &,
+                         It from, It to, Fn &&fn, size_t granularity)
+    {
+        tbb::parallel_for(tbb::blocked_range{from, to, granularity},
+                          [&fn](const auto &range) {
+            loop_(range, std::forward<Fn>(fn));
+        });
+    }
+
+    template<class I, class MergeFn, class T, class AccessFn>
+    static T reduce(const ExecutionTBB &,
+                    I          from,
+                    I          to,
+                    const T   &init,
+                    MergeFn  &&mergefn,
+                    AccessFn &&access,
+                    size_t     granularity = 1
+                    )
+    {
+        return tbb::parallel_reduce(
+            tbb::blocked_range{from, to, granularity}, init,
+            [&](const auto &range, T subinit) {
+                T acc = subinit;
+                loop_(range, [&](auto &i) { acc = mergefn(acc, access(i)); });
+                return acc;
+            },
+            std::forward<MergeFn>(mergefn));
+    }
+
+    static size_t max_concurrency(const ExecutionTBB &)
+    {
+        return tbb::this_task_arena::max_concurrency();
+    }
+};
+
+}
+
+#endif // EXECUTIONTBB_HPP