com.sun.akuma

Class Daemon

java.lang.Object

com.sun.akuma.Daemon

Direct Known Subclasses:

Daemon.WithoutChdir, NetworkServer

public class Daemon
extends 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 and Description
static class	Daemon.WithoutChdir Flavor of Daemon that doesn't change the current directory.

Constructor Summary

Constructors

Constructor and Description
Daemon()

Method Summary

Methods

Modifier and Type	Method and 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 String	getCurrentExecutable() Gets the current executable name.
void	init() Prepares the current process to act as a daemon.
void	init(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(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 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:

Exception

isDaemonized

public boolean isDaemonized()

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

daemonize

public void daemonize()
               throws IOException

Relaunches the JVM with the exact same arguments into the daemon.

Throws:

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 Exception

Prepares the current process to act as a daemon. The daemon's PID is written to the file /var/run/daemon.pid.

Throws:

Exception

init

public void init(String pidFile)
          throws 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:

Exception

closeDescriptors

protected void closeDescriptors()
                         throws 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:

IOException

chdirToRoot

protected void chdirToRoot()

change directory to '/' to avoid locking directories.

writePidFile

protected void writePidFile(String pidFile)
                     throws IOException

Writes out the PID of the current process to the specified file.

Parameters:

pidFile - the filename to write the PID to.

Throws:

IOException

getCurrentExecutable

public static String getCurrentExecutable()

Gets the current executable name.