appbase: A C++ repository from conr2d

AppBase

The AppBase library provides a basic framework for building applications from a set of plugins. AppBase manages the plugin life-cycle and ensures that all plugins are configured, initialized, started, and shutdown in the proper order.

Key Features

Dynamically Specify Plugins to Load
Automatically Load Dependent Plugins in Order
Plugins can specify commandline arguments and configuration file options
Program gracefully exits from SIGINT, SIGTERM, and SIGPIPE
Minimal Dependencies (Boost 1.60, c++14)

Defining a Plugin

A simple example of a 2-plugin application can be found in the /examples directory. Each plugin has a simple life cycle:

Initialize - parse configuration file options
Startup - start executing, using configuration file options
Shutdown - stop everything and free all resources

All plugins complete the Initialize step before any plugin enters the Startup step. Any dependent plugin specified by APPBASE_PLUGIN_REQUIRES will be Initialized or Started prior to the plugin being Initialized or Started.

Shutdown is called in the reverse order of Startup.

class net_plugin : public appbase::plugin<net_plugin>
{
   public:
     net_plugin(){};
     ~net_plugin(){};

     APPBASE_PLUGIN_REQUIRES( (chain_plugin) );

     virtual void set_program_options( options_description& cli, options_description& cfg ) override
     {
        cfg.add_options()
              ("listen-endpoint", bpo::value<string>()->default_value( "127.0.0.1:9876" ), "The local IP address and port to listen for incoming connections.")
              ("remote-endpoint", bpo::value< vector<string> >()->composing(), "The IP address and port of a remote peer to sync with.")
              ("public-endpoint", bpo::value<string>()->default_value( "0.0.0.0:9876" ), "The public IP address and port that should be advertized to peers.")
              ;
     }

     void plugin_initialize( const variables_map& options ) { std::cout << "initialize net plugin\n"; }
     void plugin_startup()  { std::cout << "starting net plugin \n"; }
     void plugin_shutdown() { std::cout << "shutdown net plugin \n"; }

};

int main( int argc, char** argv ) {
   try {
      appbase::app().register_plugin<net_plugin>(); // implict registration of chain_plugin dependency
      if( !appbase::app().initialize( argc, argv ) )
         return -1;
      appbase::app().startup();
      appbase::app().exec();
   } catch ( const boost::exception& e ) {
      std::cerr << boost::diagnostic_information(e) << "\n";
   } catch ( const std::exception& e ) {
      std::cerr << e.what() << "\n";
   } catch ( ... ) {
      std::cerr << "unknown exception\n";
   }
   std::cout << "exited cleanly\n";
   return 0;
}

This example can be used like follows:

./examples/appbase_example --plugin net_plugin
initialize chain plugin
initialize net plugin
starting chain plugin
starting net plugin
^C
shutdown net plugin
shutdown chain plugin
exited cleanly

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 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.

app().post( appbase::priority::low, lambda )

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.

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.

Graceful Exit

To trigger a graceful exit call appbase::app().quit() or send SIGTERM, SIGINT, or SIGPIPE to the process.

Dependencies

c++14 or newer (clang or g++)
Boost 1.60 or newer compiled with C++14 support

To compile boost with c++14 use: