Drain the io_context instead of destroying it

examples/executor_example/application.hpp

@@ -19,13 +19,12 @@
 #include <appbase/execution_priority_queue.hpp>
 
 #include <limits>
-#include <optional>
 
 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_serv, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
    }
 
    auto& get_priority_queue() { return pri_queue; }
@@ -34,13 +33,11 @@ class my_executor {
 
    void clear() { pri_queue.clear(); }
 
-   void reset() { io_serv.emplace(); }
-
-   boost::asio::io_service& get_io_service() { return *io_serv; }
+   boost::asio::io_service& get_io_service() { return io_serv; }
 
 private:
    // members are ordered taking into account that the last one is destructed first
-   std::optional<boost::asio::io_service> io_serv{std::in_place};
+   boost::asio::io_context io_serv;
    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

@@ -155,10 +155,17 @@ class application_base {
 
          try {
             // plugins shutdown down at this point,
-            exec.clear(); // make sure the queue is empty
-            // Recreate the io_context since it doesn't provide a clear and we want the destructors of all the
-            // lambdas posted to the io_context to execute before destroying the plugins
-            exec.reset();
+
+            // Drain the io_service 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_service for other purposes.
+            io_serv.restart();
+            while (io_serv.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)

include/appbase/default_executor.hpp

@@ -4,15 +4,14 @@
 #include <appbase/execution_priority_queue.hpp>
 
 #include <limits>
-#include <optional>
 
 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_serv, pri_queue.wrap(priority, --order, std::forward<Func>(func)));
    }
 
    /**
@@ -35,21 +34,17 @@ class default_executor {
       pri_queue.clear();
    }
 
-   void reset() {
-      io_serv.emplace();
-   }
-
    /**
     * Do not run io_service in any other threads, as application assumes single-threaded execution in exec().
     * @return io_serivice of application
     */
    boost::asio::io_service& get_io_service() {
-      return *io_serv;
+      return io_serv;
    }
 
 private:
    // members are ordered taking into account that the last one is destructed first
-   std::optional<boost::asio::io_service> io_serv{std::in_place};
+   boost::asio::io_context  io_serv;
    execution_priority_queue pri_queue;
    std::size_t order = std::numeric_limits<size_t>::max(); // to maintain FIFO ordering in queue within priority
 };