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.
- 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)
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
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 )
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.
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.
To trigger a graceful exit call appbase::app().quit() or send SIGTERM, SIGINT, or SIGPIPE to the process.
- c++14 or newer (clang or g++)
- Boost 1.60 or newer compiled with C++14 support
To compile boost with c++14 use:
./b2 ... cxxflags="-std=c++0x -stdlib=libc++" linkflags="-stdlib=libc++" ...
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