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 &lt;esigatepid&gt;
   * </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");
          }
      }
  }