Drain io_context after shutdown of plugins

README.md

@@ -94,20 +94,20 @@ Plugins can be registered by calling `appbase::application::register_plugin()`.
 ### Boost ASIO 
 
 AppBase maintains a singleton `application` instance which can be accessed via `appbase::app()`.  This 
-application owns a `boost::asio::io_service` which starts running when `appbase::exec()` is called. If 
+application owns a `boost::asio::io_context` which starts running when `appbase::exec()` is called. If 
 a plugin needs to perform IO or other asynchronous operations then it should dispatch it via `application`
-`io_service` which is setup to use an execution priority queue.
+`io_context` which is setup to use an execution priority queue.
 ```
 app().post( appbase::priority::low, lambda )
 ```
 OR
 ```
 delay_timer->async_wait( app().get_priority_queue().wrap( priority::low, lambda ) );
 ```
-Use of `get_io_service()` directly is not recommended as the priority queue will not be respected. 
+Use of `get_io_context()` directly is not recommended as the priority queue will not be respected. 
 
-Because the app calls `io_service::run()` from within `application::exec()` and does not spawn any threads
-all asynchronous operations posted to the io_service should be run in the same thread.  
+Because the app calls `io_context::run()` from within `application::exec()` and does not spawn any threads
+all asynchronous operations posted to the io_context should be run in the same thread.  
 
 ## Graceful Exit 
 

application_base.cpp

@@ -152,8 +152,8 @@ void application_base::wait_for_signal(std::shared_ptr<boost::asio::signal_set>
    });
 }
 
-void application_base::setup_signal_handling_on_ios(boost::asio::io_service& ios, bool startup) {
-   std::shared_ptr<boost::asio::signal_set> ss = std::make_shared<boost::asio::signal_set>(ios, SIGINT, SIGTERM);
+void application_base::setup_signal_handling_on_ios(boost::asio::io_context& io_ctx, bool startup) {
+   std::shared_ptr<boost::asio::signal_set> ss = std::make_shared<boost::asio::signal_set>(io_ctx, SIGINT, SIGTERM);
 #ifdef SIGPIPE
    ss->add(SIGPIPE);
 #endif
@@ -165,15 +165,15 @@ void application_base::setup_signal_handling_on_ios(boost::asio::io_service& ios
    wait_for_signal(ss);
 }
 
-void application_base::startup(boost::asio::io_service& io_serv) {
+void application_base::startup(boost::asio::io_context& io_ctx) {
    //during startup, run a second thread to catch SIGINT/SIGTERM/SIGPIPE/SIGHUP
-   boost::asio::io_service startup_thread_ios;
-   setup_signal_handling_on_ios(startup_thread_ios, true);
-   std::thread startup_thread([&startup_thread_ios]() {
-      startup_thread_ios.run();
+   boost::asio::io_context startup_thread_io_ctx;
+   setup_signal_handling_on_ios(startup_thread_io_ctx, true);
+   std::thread startup_thread([&startup_thread_io_ctx]() {
+      startup_thread_io_ctx.run();
    });
-   auto clean_up_signal_thread = [&startup_thread_ios, &startup_thread]() {
-      startup_thread_ios.stop();
+   auto clean_up_signal_thread = [&startup_thread_io_ctx, &startup_thread]() {
+      startup_thread_io_ctx.stop();
       startup_thread.join();
    };
 
@@ -185,16 +185,16 @@ void application_base::startup(boost::asio::io_service& io_serv) {
 
    } catch( ... ) {
       clean_up_signal_thread();
-      shutdown();
+      shutdown_plugins();
       throw;
    }
 
-   //after startup, shut down the signal handling thread and catch the signals back on main io_service
+   //after startup, shut down the signal handling thread and catch the signals back on main io_context
    clean_up_signal_thread();
-   setup_signal_handling_on_ios(io_serv, false);
+   setup_signal_handling_on_ios(io_ctx, false);
 
 #ifdef SIGHUP
-   std::shared_ptr<boost::asio::signal_set> sighup_set(new boost::asio::signal_set(io_serv, SIGHUP));
+   std::shared_ptr<boost::asio::signal_set> sighup_set(new boost::asio::signal_set(io_ctx, SIGHUP));
    start_sighup_handler( sighup_set );
 #endif
 }
@@ -441,7 +441,7 @@ void application_base::handle_exception(std::exception_ptr eptr, std::string_vie
    }
 }
 
-void application_base::shutdown() {
+void application_base::shutdown_plugins() {
    std::exception_ptr eptr = nullptr;
 
    for(auto ritr = running_plugins.rbegin();
@@ -454,8 +454,17 @@ void application_base::shutdown() {
          handle_exception(std::current_exception(), (*ritr)->name());
       }
    }
-   for(auto ritr = running_plugins.rbegin();
-       ritr != running_plugins.rend(); ++ritr) {
+
+   // if we caught an exception while shutting down a plugin, rethrow it so that main()
+   // can catch it and report the error
+   if (eptr)
+      std::rethrow_exception(eptr);
+}
+
+void application_base::destroy_plugins() {
+   std::exception_ptr eptr = nullptr;
+
+   for(auto ritr = running_plugins.rbegin(); ritr != running_plugins.rend(); ++ritr) {
       try {
          plugins.erase((*ritr)->name());
       } catch(...) {
@@ -474,7 +483,6 @@ void application_base::shutdown() {
          eptr = std::current_exception();
       handle_exception(std::current_exception(), "plugin cleanup");
    }
-   quit();
 
    // if we caught an exception while shutting down a plugin, rethrow it so that main()
    // can catch it and report the error

examples/executor_example/application.hpp

@@ -18,11 +18,13 @@
 #include <appbase/application_base.hpp>
 #include <appbase/execution_priority_queue.hpp>
 
+#include <limits>
+
 class my_executor {
 public:
    template <typename Func>
    auto post( int priority, Func&& func ) {
-      return boost::asio::post(io_serv, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
+      return boost::asio::post(io_ctx, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
    }
 
    auto& get_priority_queue() { return pri_queue; }
@@ -31,11 +33,11 @@ class my_executor {
 
    void clear() { pri_queue.clear(); }
 
-   boost::asio::io_service& get_io_service() { return io_serv; }
+   boost::asio::io_context& get_io_context() { return io_ctx; }
 
 private:
    // members are ordered taking into account that the last one is destructed first
-   boost::asio::io_service  io_serv;
+   boost::asio::io_context io_ctx;
    appbase::execution_priority_queue pri_queue;
    std::size_t order = std::numeric_limits<size_t>::max(); // to maintain FIFO ordering in queue within priority
 };

include/appbase/application_base.hpp

@@ -114,8 +114,7 @@ class application_base {
       return initialize_impl(argc, argv, {find_plugin<Plugin>()...}, initialize_logging);
    }
 
-   void startup(boost::asio::io_service& io_serv);
-   void shutdown();
+   void startup(boost::asio::io_context& io_ctx);
 
    /**
     *  Wait until quit(), SIGINT or SIGTERM and then shutdown.
@@ -125,29 +124,51 @@ class application_base {
    void exec(Executor& exec) {
       std::exception_ptr eptr = nullptr;
       {
-         auto& io_serv{exec.get_io_service()};
-         boost::asio::io_service::work work(io_serv);
+         auto& io_ctx{exec.get_io_context()};
+         boost::asio::executor_work_guard<boost::asio::io_context::executor_type> work = boost::asio::make_work_guard(io_ctx);
          (void)work;
          bool more = true;
 
-         while (more || io_serv.run_one()) {
-            if (is_quiting())
-               break;
+         while (more || io_ctx.run_one()) {
             try {
-               io_serv.poll(); // queue up any ready; allowing high priority item to get into the queue
+               io_ctx.poll(); // queue up any ready; allowing high priority item to get into the queue
+               if (io_ctx.stopped())
+                  break;
                // execute the highest priority item
                more = exec.execute_highest();
             } catch (...) {
-               more = true; // so we exit the while loop without calling io_serv.run_one()
+               more = true; // so we exit the while loop without calling io_ctx.run_one()
                quit();
                eptr = std::current_exception();
                handle_exception(eptr, "application loop");
             }
          }
 
+         quit();
+
+         try {
+            shutdown_plugins();   // may rethrow exceptions
+         } catch (...) {
+            if (!eptr)
+               eptr = std::current_exception();
+         }
+
+         work.reset();
+
          try {
-            exec.clear(); // make sure the queue is empty
-            shutdown();   // may rethrow exceptions
+            // plugins shutdown down at this point,
+
+            // Drain the io_context of anything that could be referencing plugins.
+            // Note this does not call exec.execute_highest(), so only drains into the priority queue assuming nothing
+            // has hijacked the io_context for other purposes.
+            io_ctx.restart();
+            while (io_ctx.poll())
+               ;
+            // clear priority queue of anything pushed by poll()
+            exec.clear();
+
+            // destroy the plugins now that all lambda that reference them have been destroyed
+            destroy_plugins();
          } catch (...) {
             if (!eptr)
                eptr = std::current_exception();
@@ -290,6 +311,9 @@ class application_base {
    }
    ///@}
 
+   void shutdown_plugins();
+   void destroy_plugins();
+
    application_base(std::shared_ptr<void>&& e); ///< protected because application is a singleton that should be accessed via instance()
 
    /// !!! must be dtor'ed after plugins
@@ -318,7 +342,7 @@ class application_base {
    void print_default_config(std::ostream& os);
 
    void wait_for_signal(std::shared_ptr<boost::asio::signal_set> ss);
-   void setup_signal_handling_on_ios(boost::asio::io_service& ios, bool startup);
+   void setup_signal_handling_on_ios(boost::asio::io_context& io_ctx, bool startup);
 
    void handle_exception(std::exception_ptr eptr, std::string_view origin);
 };
@@ -343,12 +367,12 @@ class application_t : public application_base {
    }
 
    /**
-    * Post func to run on io_service with given priority.
+    * Post func to run on io_context with given priority.
     *
     * -- deprecated: use app().executor().post()
     *
     * @param priority can be appbase::priority::* constants or any int, larger ints run first
-    * @param func function to run on io_service
+    * @param func function to run on io_context
     * @return result of boost::asio::post
     */
    template <typename Func>
@@ -365,20 +389,36 @@ class application_t : public application_base {
    }
 
    /**
-    * Anything posted directly on this io_service is run at the highest of priority as it by-passes the
+    * Anything posted directly on this io_context is run at the highest of priority as it by-passes the
     * priority queue and is run immediately in exec(). Use with care and consider using app().executor().post() instead.
     * @return
     */
-   boost::asio::io_service& get_io_service() {
-      return executor().get_io_service();
+   boost::asio::io_context& get_io_context() {
+      return executor().get_io_context();
+   }
+
+   /**
+    * Create a timer with the main application io_context. Timer async_wait will execute on the main thread.
+    *
+    * Use with app().executor().wrap(priority::x, exec_queue::x, [](const boost::system::error_code& ec).
+    * For example:
+    *   _timer.async_wait(app().executor().wrap(priority::high, exec_queue::read_write,
+    *                                           [](const boost::system::error_code& ec) {
+    *                                              if (!ec)
+    *                                                 // do something
+    *                                           }));
+    */
+   template<typename Timer>
+   auto make_timer() {
+      return Timer{get_io_context()};
    }
 
    void startup() {
-      application_base::startup(get_io_service());
+      application_base::startup(get_io_context());
    }
 
    application_t() : application_base(std::make_shared<executor_t>()) {
-      set_stop_executor_cb([&]() { get_io_service().stop(); });
+      set_stop_executor_cb([&]() { get_io_context().stop(); });
       set_post_cb([&](int prio, std::function<void()> cb) { executor().post(prio, std::move(cb)); });
    }
 

include/appbase/default_executor.hpp

@@ -3,21 +3,23 @@
 #include <appbase/application_base.hpp>
 #include <appbase/execution_priority_queue.hpp>
 
+#include <limits>
+
 namespace appbase {
 
 class default_executor {
 public:
    template <typename Func>
    auto post(int priority, Func&& func) {
-      return boost::asio::post(io_serv, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
+      return boost::asio::post(io_ctx, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
    }
 
    /**
     * Provide access to execution priority queue so it can be used to wrap functions for
     * prioritized execution.
     *
     * Example:
-    *   boost::asio::steady_timer timer( app().get_io_service() );
+    *   boost::asio::steady_timer timer( app().get_io_context() );
     *   timer.async_wait( app().get_priority_queue().wrap(priority::low, [](){ do_something(); }) );
     */
    auto& get_priority_queue() {
@@ -33,16 +35,16 @@ class default_executor {
    }
 
    /**
-    * Do not run io_service in any other threads, as application assumes single-threaded execution in exec().
-    * @return io_serivice of application
+    * Do not run io_context in any other threads, as application assumes single-threaded execution in exec().
+    * @return io_context of application
     */
-   boost::asio::io_service& get_io_service() {
-      return io_serv;
+   boost::asio::io_context& get_io_context() {
+      return io_ctx;
    }
 
 private:
    // members are ordered taking into account that the last one is destructed first
-   boost::asio::io_service io_serv;
+   boost::asio::io_context  io_ctx;
    execution_priority_queue pri_queue;
    std::size_t order = std::numeric_limits<size_t>::max(); // to maintain FIFO ordering in queue within priority
 };