Java – Signal Handling
By admin on Feb 6, 2008 in Java, Programming
In my earlier article, I talked about how to do a graceful shutdown your of Java application when Ctr-C, or the termination signal is intercepted. Now I am going to roughly show you how to do it using Java signal handling.
JVM signal handling is slightly different across different platforms, e.g. across Linux, HP-UX and Windows. So the signal handling program you write in Windows may not work in Linux or HP-UX. Unlike the previous article which is using shutdown hook, which is platform independent, if you want to use signal handling in Java, you have to know which signal(s) you want to handle.
E.g. for Unix/Linux based platform the signals are SEGV, ILL, FPE, BUS, SYS, CPU, FSZ, ABRT, INT, TERM, HUP, USR1, QUIT, BREAK, TRAP, PIPE.
For Windows based platform, the signals are SEGV, ILL, FPE, ABRT, INT, TERM, BREAK.
However, to really determine which signal can be handled in your target platform, you have to test it yourself.
Here is a simple program that you can use to test out signal handling in Java.
import sun.misc.Signal;
import sun.misc.SignalHandler;
public class SignalHandlerExample implements SignalHandler {
private SignalHandler oldHandler;
public static SignalHandler install(String signalName) {
Signal diagSignal = new Signal(signalName);
SignalHandlerExample instance = new SignalHandlerExample();
instance.oldHandler = Signal.handle(diagSignal, instance);
return instance;
}
public void handle(Signal signal) {
System.out.println("Signal handler called for signal "
+ signal);
try {
signalAction(signal);
// Chain back to previous handler, if one exists
if (oldHandler != SIG_DFL && oldHandler != SIG_IGN) {
oldHandler.handle(signal);
}
} catch (Exception e) {
System.out.println("handle|Signal handler
failed, reason " + e.getMessage());
e.printStackTrace();
}
}
public void signalAction(Signal signal) {
System.out.println("Handling " + signal.getName());
System.out.println("Just sleep for 5 seconds.");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
System.out.println("Interrupted: "
+ e.getMessage());
}
}
public static void main(String[] args) {
SignalHandlerExample.install("TERM");
SignalHandlerExample.install("INT");
SignalHandlerExample.install("ABRT");
System.out.println("Signal handling example.");
try {
Thread.sleep(50000);
} catch (InterruptedException e) {
System.out.println("Interrupted: " + e.getMessage());
}
}
}
This program handles the TERM, INT, and ABRT signals. When it starts up, it will just sleep. During this time, if you press Ctr-C, the INT signal is triggered and signalAction is called.
Here is the sample output.
C:\>java -cp . SignalHandlerExample Signal handling example. Signal handler called for signal SIGINT Handling INT Just sleep for 5 seconds.
joe | Feb 9, 2009 | Reply
Hi,
neat trick:) I used it in my database console tool, http://sf.net/projects/jdbcon
Thanks!
Arslan | Nov 26, 2009 | Reply
Thank you for this article. It is quite cool. I simplified it for my particular use in handling a SIGPIPE.
private void setupPipeSignalHandler()
{
Signal.handle(new Signal(“PIPE”), new SignalHandler()
{
public void handle(Signal signal)
{
System.exit(2);
}
});
}
Just a question regarding the static method install. Why not have this method as the constructor of the class. It just looks like it is doing the job of a conventional constructor.
Karanth Srihari | Dec 10, 2009 | Reply
Hi,
This one exits after handling the signal.
If i modify the try catch sleep in main like this
try {
for(int i=0;i <10;i++)
{
System.out.println(“Sleeping in Main for index i = ” + i);
Thread.sleep(5000);
}
} catch (InterruptedException e) {
System.out.println(“Interrupted: ” + e.getMessage());
}
and when i run this code, i get the following output:
——————————–
Signal handling example.
Sleeping in Main for index i = 0
Sleeping in Main for index i = 1
Sleeping in Main for index i = 2
Sleeping in Main for index i = 3
Sleeping in Main for index i = 4
Sleeping in Main for index i = 5
Sleeping in Main for index i = 6
Signal handler called for signal SIGINT
Handling INT
Just sleep for 5 seconds in signalAction method.
Sleeping in Main for index i = 7
——————————
The program exists after 7!! it didnt continue till 10. What could be the reason? i gave “kill -INT pid”
Thanks.