Dynamic Plugin Loading Example

This example demonstrates how to create and use dynamically loaded collector plugins.

Overview

The monitoring system supports loading collector plugins from shared libraries at runtime. This allows:

• Third-party plugins without recompilation
• Plugin distribution as separate libraries
• On-demand plugin loading
• Plugin updates without rebuilding the main application

Files

• example_plugin.cpp - Sample plugin implementation
• plugin_loader_example.cpp - Example program that loads and uses the plugin
• CMakeLists.txt - Build configuration for the plugin

Building

Build the Plugin Library

cd examples/plugin_example
mkdir build
cd build
cmake ..
make

This creates:

• Linux: libexample_plugin.so
• macOS: libexample_plugin.dylib
• Windows: example_plugin.dll

Build the Example Program

From the project root:

mkdir build
cd build
cmake ..
make

Running

# Linux
./plugin_loader_example ./libexample_plugin.so
 
# macOS
./plugin_loader_example ./libexample_plugin.dylib
 
# Windows
plugin_loader_example.exe example_plugin.dll

Expected Output

=== Dynamic Plugin Loading Example ===
 
Loading plugin from: ./libexample_plugin.so
Plugin loaded successfully
 
Plugin Metadata:
  Name: example_plugin
  Description: Example dynamically loaded collector plugin
  Version: 1.0.0
  Available: yes
 
Initializing plugin...
Plugin initialized
 
Collecting metrics (5 iterations)...
 
Iteration 1:
  example.cpu_usage: 45.23 % [plugin=example, type=cpu]
  example.memory_usage: 512.67 MB [plugin=example, type=memory]
  example.request_count: 1 requests [plugin=example, type=counter]
 
Iteration 2:
  example.cpu_usage: 38.91 % [plugin=example, type=cpu]
  example.memory_usage: 487.32 MB [plugin=example, type=memory]
  example.request_count: 2 requests [plugin=example, type=counter]
 
...
 
Shutting down plugin...
Unloading plugin...
Plugin unloaded successfully
 
=== Example Complete ===

Creating Your Own Plugin

1. Implement the collector_plugin Interface

#include "kcenon/monitoring/plugins/collector_plugin.h"
#include "kcenon/monitoring/plugins/plugin_api.h"
 
class my_plugin : public kcenon::monitoring::collector_plugin {
public:
    auto name() const -> std::string_view override {
        return "my_plugin";
    }
 
    auto initialize(const config_map& config) -> bool override {
        // Initialize your plugin
        return true;
    }
 
    auto shutdown() -> void override {
        // Clean up resources
    }
 
    auto collect() -> std::vector<metric_data> override {
        // Collect and return metrics
        std::vector<metric_data> metrics;
        // ... add metrics ...
        return metrics;
    }
 
    auto is_available() const -> bool override {
        // Check if plugin is available on this platform
        return true;
    }
 
    auto get_metadata() const -> plugin_metadata_t override {
        return plugin_metadata_t{
            plugin_category::custom,
            plugin_type::collector,
            "My Plugin",
            "1.0.0",
            "Description"
        };
    }
};

2. Export the Plugin

Use the IMPLEMENT_PLUGIN macro at the end of your source file:

IMPLEMENT_PLUGIN(
    my_plugin,              // Plugin class name
    "my_plugin",           // Plugin name (must match name() method)
    "1.0.0",              // Version
    "My custom plugin",   // Description
    "Your Name",          // Author
    "custom"              // Category
)

3. Build as Shared Library

Create a CMakeLists.txt:

cmake_minimum_required(VERSION 3.20)
project(my_plugin VERSION 1.0.0 LANGUAGES CXX)
 
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
add_library(my_plugin SHARED my_plugin.cpp)
 
target_include_directories(my_plugin PRIVATE
    ${MONITORING_SYSTEM_INCLUDE_DIR}
)
 
set_target_properties(my_plugin PROPERTIES
    POSITION_INDEPENDENT_CODE ON
)

Build:

mkdir build
cd build
cmake ..
make

4. Load and Use

#include "kcenon/monitoring/plugins/collector_registry.h"
 
auto& registry = kcenon::monitoring::collector_registry::instance();
 
// Load plugin
if (!registry.load_plugin("/path/to/libmy_plugin.so")) {
    std::cerr << "Load failed: " << registry.get_plugin_loader_error() << "\n";
    return;
}
 
// Get and use plugin
auto* plugin = registry.get_plugin("my_plugin");
if (plugin) {
    plugin->initialize({});
    auto metrics = plugin->collect();
    // ... use metrics ...
}
 
// Unload when done
registry.unload_plugin("my_plugin");

Plugin API Version Compatibility

Plugins must be compiled with the same PLUGIN_API_VERSION as the monitoring system. If the versions don't match, the plugin will fail to load with an error message:

Incompatible API version: plugin=2, expected=1

To check the API version:

#include "kcenon/monitoring/plugins/plugin_api.h"
std::cout << "API Version: " << PLUGIN_API_VERSION << "\n";

Platform-Specific Notes

Linux

• Use .so extension
• Compile with -fPIC flag
• Link with -ldl for dynamic loading

macOS

• Use .dylib extension
• Compile with -fPIC flag
• May need to set DYLD_LIBRARY_PATH environment variable

Windows

• Use .dll extension
• Compile with /DEXPORT_PLUGIN or set WINDOWS_EXPORT_ALL_SYMBOLS
• Put DLL in same directory as executable or in PATH

Error Handling

Check for errors after loading:

if (!registry.load_plugin(path)) {
    std::string error = registry.get_plugin_loader_error();
    // Handle error...
}

Common errors:

• file_not_found - Plugin file doesn't exist
• library_load_failed - Failed to load shared library (missing dependencies)
• symbol_not_found - Required export function not found
• incompatible_api_version - Plugin compiled with different API version
• plugin_unavailable - Plugin's is_available() returned false
• already_loaded - Plugin with same name already loaded

Security Considerations

• Validate plugin paths before loading
• Only load plugins from trusted sources
• Check API version compatibility
• Consider implementing plugin signing/verification
• Be aware that plugins run with full application permissions

Performance

• Plugin loading incurs one-time cost for library loading
• Subsequent metric collection has same performance as built-in collectors
• Unloading plugins releases all associated resources