Package com.sun.akuma

Class Daemon

  • Direct Known Subclasses:
    Daemon.WithoutChdir, NetworkServer
    public class Daemon
extends java.lang.Object
    Forks a copy of the current process into the background.

    Because of the fork/exec involved in doing this, your code has to call Daemonizer in a certain sequence. Specifically, from your main method: 

     public static void main(String[] args) {
     Daemon d = new Daemon();
     if(d.isDaemonized()) {
         // perform initialization as a daemon
         // this involves in closing file descriptors, recording PIDs, etc.
         d.init();
     } else {
         // if you are already daemonized, no point in daemonizing yourself again,
         // so do this only when you aren't daemonizing.
         if(you decide to launch a copy into background) {
             d.daemonize(...);
             System.exit(0);
         }
     }

     // your normal main code follows
     // this part can be executed in two ways
     // 1) the user runs your process in the foreground
     // 2) you decided to daemonize yourself, in which case the newly forked daemon will execute this code,
     //    while the originally executed foreground Java process exits before it gets here.
     ...
 }

    Alternatively, your main class can extend from Daemon, so that you can customize some of the behaviors.

    Author:
    Kohsuke Kawaguchi

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static class  Daemon.WithoutChdir
      Flavor of Daemon that doesn't change the current directory.

    • Constructor Summary

      Constructors 
      Constructor Description
      Daemon()  

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void all​(boolean daemonize)
      Do all the necessary steps in one go.
      protected void chdirToRoot()
      change directory to '/' to avoid locking directories.
      protected void closeDescriptors()
      Closes inherited file descriptors.
      void daemonize()
      Relaunches the JVM with the exact same arguments into the daemon.
      void daemonize​(JavaVMArguments args)
      Relaunches the JVM with the given arguments into the daemon.
      static java.lang.String getCurrentExecutable()
      Gets the current executable name.
      void init()
      Prepares the current process to act as a daemon.
      void init​(java.lang.String pidFile)
      Prepares the current process to act as a daemon.
      boolean isDaemonized()
      Returns true if the current process is already launched as a daemon via daemonize().
      static void selfExec​(JavaVMArguments args)
      Overwrites the current process with a new Java VM with the given JVM arguments.
      protected void writePidFile​(java.lang.String pidFile)
      Writes out the PID of the current process to the specified file.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • Daemon

        public Daemon()

    • Method Detail

      • all

        public void all​(boolean daemonize)
         throws java.lang.Exception
        Do all the necessary steps in one go.
        Parameters:
        daemonize - Parse the command line arguments and if the application should be daemonized, pass in true.
        Throws:
        java.lang.Exception

      • isDaemonized

        public boolean isDaemonized()
        Returns true if the current process is already launched as a daemon via daemonize().

      • daemonize

        public void daemonize()
               throws java.io.IOException
        Relaunches the JVM with the exact same arguments into the daemon.
        Throws:
        java.io.IOException

      • daemonize

        public void daemonize​(JavaVMArguments args)
        Relaunches the JVM with the given arguments into the daemon.

      • selfExec

        public static void selfExec​(JavaVMArguments args)
        Overwrites the current process with a new Java VM with the given JVM arguments.

      • init

        public void init()
          throws java.lang.Exception
        Prepares the current process to act as a daemon. The daemon's PID is written to the file /var/run/daemon.pid.
        Throws:
        java.lang.Exception

      • init

        public void init​(java.lang.String pidFile)
          throws java.lang.Exception
        Prepares the current process to act as a daemon.
        Parameters:
        pidFile - the filename to which the daemon's PID is written; or, null to skip writing a PID file.
        Throws:
        java.lang.Exception

      • closeDescriptors

        protected void closeDescriptors()
                         throws java.io.IOException
        Closes inherited file descriptors.

        This method can be overridden to no-op in a subtype. Useful for debugging daemon processes when they don't work correctly.

        Throws:
        java.io.IOException

      • chdirToRoot

        protected void chdirToRoot()
        change directory to '/' to avoid locking directories.

      • writePidFile

        protected void writePidFile​(java.lang.String pidFile)
                     throws java.io.IOException
        Writes out the PID of the current process to the specified file.
        Parameters:
        pidFile - the filename to write the PID to.
        Throws:
        java.io.IOException

      • getCurrentExecutable

        public static java.lang.String getCurrentExecutable()
        Gets the current executable name.