Initial merge of Networking TS compatibility.

Merged from chriskohlhoff/asio master branch as of commit
4a4d28b0d24c53236e229bd1b5f378c9964b1ebb.

example/cpp11/spawn/parallel_grep.cpp

@@ -0,0 +1,84 @@
+//
+// parallel_grep.cpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2017 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#include <boost/asio/dispatch.hpp>
+#include <boost/asio/post.hpp>
+#include <boost/asio/spawn.hpp>
+#include <boost/asio/strand.hpp>
+#include <boost/asio/thread_pool.hpp>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+using boost::asio::dispatch;
+using boost::asio::spawn;
+using boost::asio::strand;
+using boost::thread_pool;
+using boost::asio::yield_context;
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    if (argc < 2)
+    {
+      std::cerr << "Usage: parallel_grep <string> <files...>\n";
+      return 1;
+    }
+
+    // We use a fixed size pool of threads for reading the input files. The
+    // number of threads is automatically determined based on the number of
+    // CPUs available in the system.
+    thread_pool pool;
+
+    // To prevent the output from being garbled, we use a strand to synchronise
+    // printing.
+    strand<thread_pool::executor_type> output_strand(pool.get_executor());
+
+    // Spawn a new coroutine for each file specified on the command line.
+    std::string search_string = argv[1];
+    for (int argn = 2; argn < argc; ++argn)
+    {
+      std::string input_file = argv[argn];
+      spawn(pool,
+        [=](yield_context yield)
+        {
+          std::ifstream is(input_file.c_str());
+          std::string line;
+          std::size_t line_num = 0;
+          while (std::getline(is, line))
+          {
+            // If we find a match, send a message to the output.
+            if (line.find(search_string) != std::string::npos)
+            {
+              dispatch(output_strand,
+                  [=]
+                  {
+                    std::cout << input_file << ':' << line << std::endl;
+                  });
+            }
+
+            // Every so often we yield control to another coroutine.
+            if (++line_num % 10 == 0)
+              post(yield);
+          }
+        });
+    }
+
+    // Join the thread pool to wait for all the spawned tasks to complete.
+    pool.join();
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}