Plugin Practice and Notice

This article outlines some practices and considerations when developing BifroMQ plugins.

Remote Debugging with BifroMQ

BifroMQ supports remote debugging, which can be activated through the JVM_DEBUG environment variable. Additionally, the remote debugging port can be specified through the JAVA_DEBUG_PORT environment variable. If not specified, the default port is 8008. Before starting the BifroMQ process, specify these environment variables using shell:

export JVM_DEBUG=true
export JAVA_DEBUG_PORT=8008
export DEBUG_SUSPEND_FLAG=n

Ensure the debugging port is correctly configured to avoid port conflicts. Remote debugging can be performed using an IDE (for example, IntelliJ or Eclipse). Setting DEBUG_SUSPEND_FLAG=y can assist in debugging the plugin's initialization process.

Pay Attention to Java ClassLoading

BifroMQ uses separate ClassLoaders for each plugin to load classes from the plugin's classpath. Therefore, ensure your plugin's packaging includes all dependencies used (except those provided by BifroMQ). Some third-party libraries might load classes in other ways, leading to class loading failures. Most situations can be resolved by swapping the Thread ContextLoader:

class MyPlugin {
    public void pluginMethod() {
        ClassLoader originalLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(this.getClass().getClassLoader());
            // Initialize dependencies here  
            dependenciesInit();
        } finally {
            Thread.currentThread().setContextClassLoader(originalLoader);
        }
    }
}

Properly Organize the Plugin Directory

When developing plugins, ensure there are no unrelated jar files in the plugin directory. pf4j recursively checks jar files in the plugin directory, and unrelated jars may lead to PF4J validation errors. Keeping the plugin directory clean and containing only necessary jar files ensures smooth plugin loading and prevents conflicts or validation issues.

Metrics and Logging

• Plugin developers are encouraged to utilize the BifroMQ logging framework for plugin logging, making use of the same logback.xml for logger configuration.
• BifroMQ captures and records metrics during invocations of plugin methods, offering useful insights for debugging and performance optimization.