see #2: revision of parallelism and concurrency

code/7/7.4.futures.cpp

@@ -0,0 +1,31 @@
+//
+// 7.2.critical.section.a.cpp
+// chapter 7 parallelism and concurrency
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <iostream>
+#include <thread>
+#include <iostream>
+#include <future>
+#include <thread>
+
+void foo() {
+
+}
+
+int main() {
+    // pack a lambda expression that returns 7 into a std::packaged_task
+    std::packaged_task<int()> task([](){return 7;});
+    // get the future of task
+    std::future<int> result = task.get_future();    // run task in a thread
+    std::thread(std::move(task)).detach();
+    std::cout << "waiting...";
+    result.wait(); // block until future has arrived
+    // output result
+    std::cout << "done!" << std:: endl << "future result is " << result.get() << std::endl;
+    return 0;
+}