Update taskflow to 3.6.0 (#93)

Fixed potential data-race issues induced by incorrect memory order.

Co-authored-by: Alex A. Yermoshenko <ermoshenko@devoler.com>

lib/taskflow/algorithm/critical.hpp

@@ -0,0 +1,78 @@
+#pragma once
+
+#include "../core/task.hpp"
+
+/**
+@file critical.hpp
+@brief critical include file
+*/
+
+namespace tf {
+
+// ----------------------------------------------------------------------------
+// CriticalSection
+// ----------------------------------------------------------------------------
+
+/**
+@class CriticalSection
+
+@brief class to create a critical region of limited workers to run tasks
+
+tf::CriticalSection is a warpper over tf::Semaphore and is specialized for
+limiting the maximum concurrency over a set of tasks.
+A critical section starts with an initial count representing that limit.
+When a task is added to the critical section,
+the task acquires and releases the semaphore internal to the critical section.
+This design avoids explicit call of tf::Task::acquire and tf::Task::release.
+The following example creates a critical section of one worker and adds
+the five tasks to the critical section.
+
+@code{.cpp}
+tf::Executor executor(8);   // create an executor of 8 workers
+tf::Taskflow taskflow;
+
+// create a critical section of 1 worker
+tf::CriticalSection critical_section(1);
+
+tf::Task A = taskflow.emplace([](){ std::cout << "A" << std::endl; });
+tf::Task B = taskflow.emplace([](){ std::cout << "B" << std::endl; });
+tf::Task C = taskflow.emplace([](){ std::cout << "C" << std::endl; });
+tf::Task D = taskflow.emplace([](){ std::cout << "D" << std::endl; });
+tf::Task E = taskflow.emplace([](){ std::cout << "E" << std::endl; });
+
+critical_section.add(A, B, C, D, E);
+
+executor.run(taskflow).wait();
+@endcode
+
+*/
+class CriticalSection : public Semaphore {
+
+  public:
+
+    /**
+    @brief constructs a critical region of a limited number of workers
+    */
+    explicit CriticalSection(size_t max_workers = 1);
+
+    /**
+    @brief adds a task into the critical region
+    */
+    template <typename... Tasks>
+    void add(Tasks...tasks);
+};
+
+inline CriticalSection::CriticalSection(size_t max_workers) :
+  Semaphore {max_workers} {
+}
+
+template <typename... Tasks>
+void CriticalSection::add(Tasks... tasks) {
+  (tasks.acquire(*this), ...);
+  (tasks.release(*this), ...);
+}
+
+
+}  // end of namespace tf. ---------------------------------------------------
+
+