ConfigReloadOnHup.java

package org.esigate.extension;

import java.io.File;
import java.util.Properties;

import org.esigate.Driver;
import org.esigate.DriverFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import sun.misc.Signal;
import sun.misc.SignalHandler;

/**
 * This extension reloads configuration when signal HUP is received. On POSIX systems, this signal is sent using :
 * <code>
 * kill -1 <esigatepid>
 * </code>
 * <p>
 * This only works on configuration defined using "esigate.config" system property.
 * <p>
 * This class relies on the sun.misc package and may not work on all JVM.
 * 
 * @author Nicolas Richeton
 * 
 */
@SuppressWarnings("restriction")
public class ConfigReloadOnHup implements Extension {
    private static final Logger LOG = LoggerFactory.getLogger(ConfigReloadOnHup.class);
    private static final String SIGNAL_NAME = "HUP";

    @Override
    public void init(Driver driver, Properties properties) {
        // Initialization is done is static block.
    }

    private static final SignalHandler SH = new SignalHandler() {
        @Override
        public void handle(Signal signal) {
            if (SIGNAL_NAME.equals(signal.getName())) {
                LOG.warn("Signal " + SIGNAL_NAME + " received. Reloading configuration.");
                DriverFactory.configure();
            }

        }
    };

    // Static block to ensure signal handler is added only once.
    static {
        String envPath = System.getProperty("esigate.config");
        if (envPath != null) {
            File configuration = new File(envPath);

            // Register for signal
            Signal signal = new Signal(SIGNAL_NAME);
            Signal.handle(signal, SH);

            LOG.info("Will reload configuration from {} on signal {}", configuration.getAbsoluteFile(),
                    signal.getNumber());
        } else {
            // Do nothing if configuration is loaded from the classpath
            LOG.warn("Cannot reload configuration from classpath. Please use -Desigate.config");
        }
    }
}