In my code, I want to restart the program. For this i have used the following code in Windows:
if(System.getProperty("os.name").contains("Windows"))
{
//For Windows Builds use this
new ProcessBuilder("java", "Launcher").inheritIO().start();
System.exit(0);
}
For Linux Builds I used
else
{
//For Linux/Unix or Mac Builds use this
new ProcessBuilder("/bin/bash", "-c" ,"java Launcher").inheritIO().start();
}
So now, the implementation for Windows works just fine. It begins a new instance and exits the old.
But the Linux implementation is kinda a bit odd. I added System.exit(0); thinking that it will kill the current process right after creating the new one, but it seemed to exit the process itself. I cannot restart the program in anyway in Linux, although it was doable in Windows.
Would appreciate help and feedback!
EDIT: [28-July-2020]
So I did find that the new process is created, but the IO is not inherited to the new session. I tweaked a bit of code and now the program creates the new process, gets IO control and after entering a command, it exits.
if(System.getProperty("os.name").contains("Windows"))
{
//For Windows Builds use this
new ProcessBuilder("cmd", "/c", "java Launcher").inheritIO().start();
System.exit(0);
}
else
{
//For Linux/Unix or Mac Builds use this
long pid = ProcessHandle.current().pid();
System.out.println(pid);
String a=String.valueOf(pid);
Thread.sleep(10000);
System.out.println(new ProcessBuilder("/bin/bash", "-c", "java Launcher").inheritIO().start());
System.exit(1);
}
Without System.exit(1); the program continues with the newly created process, but with the old process still running in the background. When I try to kill the old process, both the processes are killed.
Here are the new screenshots, with the code specified above.
https://gofile.io/d/MAYLeJ
EDIT: [29-July-2020]
Been working more on why the code is not working. I did get an exception for the same code, which WSL didnt detect!
The Error Log
Update: I did find the right answer and it might be a bit complex, but I shall try to make it as simple as possible.
In this, we will require 2 separate classes: 1 class to monitor the child process, 1 class which is the main process.
For the sake of simplicity, I shall name the monitoring class as SessionManager and the main class as mainClass
In the SessionManager class, I've implemented the following code.
try
{
//A loop which will run infinitely to montior and start new processes
while(true)
{
//Create the process and listen to the exit code generated by the child process spawned.
ProcessBuilder session_monitor=new ProcessBuilder("java", "<classname>");
Process process_monitor= session_monitor.inheritIO().start();
//wait for the child process to end before proceeding
process_monitor.waitFor();
switch(process_monitor.exitValue())
{
//Implement the logic here
case 0: //do something
break;
case 1: //do something
break;
}
}
}
catch(Exception E)
{
E.printStackTrace();
}
And in the mainClass program, we shall have a main method to start the process running.
class mainClass
{
public static void main(String[] args)
{
System.out.println("Hello World");
//exit the process with a code for the SessionManager's logic to work
System.exit(0); //Using a normal exit code here
}
}
This has worked for me, and if you think this implementation can be improved, I'd love to hear it. Thank you for all your support :)
Related
I've had a bit of an issue, and I'm pretty new at Java. For context, I'm making a GUI in Javafx, with a Batch backend. The GUI only has to call the Batch script(core.bat) once, and know when it has ended after it has been called. Currently, I call the Batch script using the following code:
Runtime runtime = Runtime.getRuntime();
try {
Process p1 = runtime.exec("cmd /c start core.bat");
} catch(IOException ioException) {}
The issue comes into play when I need to know when the Batch script has ended. I would give examples of what I've tried so far, but I've tried so many things over the past three hours and overwritten my code so many times that I just don't know anymore.
Any solution will do. I just need some way to determine when the Batch script has ended, after which it will close itself. Due to this, knowing when the Batch script ends is not the only possible method.
Knowing when the instance of command prompt running the script ends is also an option.
Any solutions are helpful, thank you.
Take a look at Process#waitFor. It waits until the process has finished.
You might need to start a new Thread if you don't want to wait for it but only get notified/execute code when the program is finished(blocking seems not like a good idea in JavaFX):
Runtime runtime = Runtime.getRuntime();
try {
Process p1 = runtime.exec("core.bat");
Thread t=new Thread(()->{
try{
p1.waitFor();
//your code
}catch(InterruptedException e){
Thread.currentThread.interrupt();//not actually needed, but I think it is a good practise and...SonarLint :)
}
});
t.setDaemon(true);
t.start();
} catch(IOException ioException) {}
Also, you executed the cmd command start, that starts a new process that you cannot control that easily. Just execute core.bat or cmd /c core.bat
setDaemon(true); marks your Thread as a daemon Thread, that does not affect the end of the Program(ends if all Threads that are no daemon Threads finished).
This has got to be one of the strangest things I have ever observed. Consider the following Java program:
import java.io.IOException;
public class StrangeError {
public static void main(String[] args) {
try {
Process process = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\" amd64 && set"
).start();
process.waitFor();
} catch (IOException|InterruptedException e) {
System.out.println(e.getMessage());
}
}
}
I compiled it with javac StrangeError.java, copied it to my server running Windows Server 2012 R2, and ran it with java StrangeError.
Here's where things start to get weird. The program hangs, waiting for the process it spawned to finish. This is not the expected behavior, since the vcvarsall.bat script should complete immediately as well as set.
So I started playing around and discovered the following:
Removing set causes vcvarsall.bat to terminate
Removing vcvarsall.bat causes set to terminate
Replacing && with || causes everything to terminate correctly
Copying vcvarsall.bat to a location on the desktop and changing the path causes everything to terminate correctly
A nearly equivalent program works fine in Go using the same commands
I get this output if I run everything in WinDbg and interrupt the process after it hangs
This does not appear to be reproducible with vcvarsall.bat from MSVC2013 but is also reproducible with MSVC2015 on Windows 10
What on earth is wrong with the original program? If I copy and paste the entire command (cmd /c "C:\...) into Start->Run, it immediately launches cmd and terminates, as expected.
Is this a bug with Java? Is this a bug with Windows?
Is this a bug with Java? Is this a bug with Windows?
It's a bug in your code. :-)
By default, a child process created using a ProcessBuilder object has output redirected to a pipe, the parent end of which can be obtained using Process.getInputStream() and which is not automatically drained if your code does not make use of it.
Since your code simply calls .waitFor without making any provision to drain the pipe, it will deadlock as soon as the pipe's buffer overflows. I believe the default buffer size is 4,096 bytes. On my machine, the output of the command you're running is 5,192 bytes, but this will vary depending on the original contents of the environment block. (From the sounds of it, the output length in your environment is borderline, only just above the limit, so that even small changes like changing the version of VS make a difference.)
One of the many possible solutions, depending on what you're actually trying to do, is to tell Java not to pipe the child's output:
import java.io.IOException;
public class StrangeError {
public static void main(String[] args) {
try {
ProcessBuilder processb = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\" amd64 && set"
);
processb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
Process process = processb.start();
process.waitFor();
} catch (IOException|InterruptedException e) {
System.out.println(e.getMessage());
}
}
}
Not possible to read standard input and output error inside the same ProcessBuilder.
So you need to create two ProcessBuilder
Process process1 = new ProcessBuilder(
"cmd",
"/c",
"\"C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\vcvarsall.bat\",
"amd64");
Process process2 = new ProcessBuilder(
"cmd",
"/c",
"set");
process1.start();
if (process1.waitFor() == 0) {
process2.start();
if (process2.waitFor() == 0) {
// Successfull execution
}
}
And one thing : I don't think it is a good practice to do shell/batch launches with Java (or another language). Maybe you should use a script (shell, batch, python, perl...) to control standard input/output streams.
[NB. This is related to How do I launch a completely independent process from a Java program? but different]
I want to be able to spawn external processes (shell scripts) from a "manager" Java process that should keep running when the JVM is killed - but it seems that when I kill the parent Java program the child is killed too (note, the behaviour is different if the JVM exits naturally). The simplest test program I have is:
public class Runit {
public static void main(String args[]) throws IOException, InterruptedException {
Runtime.getRuntime().exec(args[0]);
// doesn't work this way either
// ProcessBuilder pb = new ProcessBuilder(args[0]);
// pb.start();
while (true) {
System.out.println("Kill me");
Thread.sleep(2000);
}
}
}
and external script:
#!/bin/sh
while [ 1 ] ; do
ls
sleep 1
done
run as
java -classpath jar-with-dependencies.jar temp.exec.Runit runit.sh
If the manager simply exits (i.e. take out the "while" loop in the Java program) then the spawned process keeps running, but when I Ctrl+c the Java program the external program is killed too which is not what I want.
I'm using OpenJDK 1.6 on Ubuntu.
Edit1: Changing the exec to
Runtime.getRuntime().exec("/usr/bin/nohup " + args[0]);
doesn't help.
Edit2: Adding a shutdown hook as described in How to gracefully handle the SIGKILL signal in Java doesn't stop the Ctrl+c being propagated to the child.
Vladimir gave the hint we needed! (Sorry, beat Lukasz to it)
Add another script spawn_protect.sh
#!/bin/sh
LOG=$1
shift
nohup $* > $LOG 2>&1 &
And change the manager to:
public class Runit {
public static void main(String args[]) throws IOException, InterruptedException {
Runtime.getRuntime().exec(args);
while (true) {
System.out.println("Kill me");
Thread.sleep(5000);
}
}
}
Then run as:
java -classpath jar-with-dependencies.jar temp.exec.Runit spawn_protect.sh /tmp/runit.log runit.sh
Now runit.sh is really detached from the JVM process!
In Linux, if you start another process, it is your child and you are his parent. If parent gets killed, all children get killed, and their children too (what a terrible atrocity).
What you need, is to start a process that won't be killed when you exit your program. So, you need to give birth to not your own child. The methods to do that are described for example here: Linux: Prevent a background process from being stopped after closing SSH client for example use screen utility.
You've got to make it a daemon. Don't be afraid it's not a horror movie. Simply you'll need to detach your processes from controlling terminal session. I've always do it in a oposite way: shell script that launches Java.
Here is an explanation:
http://en.wikipedia.org/wiki/Daemon_(computing)
You can also you "jvm shutdown hooks", but they will not work in some situations.
I start another application from within my Java app using runtime.exec. That child program starts no problems but when I call system.exit(0); from the parent app the parents JVM keeps running until the child program is terminated.
Here is a simple example:
public class Test {
public static void main(String[] args) {
try{
Runtime runtime = Runtime.getRuntime();
Process p=runtime.exec("cmd /c \"client.exe\"");
Thread.sleep(10000);
System.exit(0);
}
catch(Exception e){}
}
}
I want the child app to continue running after System.exit is called and for Test apps JVM to shutdown completely.
In eclipse I get this behavior:
After the Test app starts, client.exe starts up immediately. After the 10 second sleep the app exits but from the eclipse console the Test app is still running. More strange hitting the red terminate button at this point does nothing. Yet as soon as client.exe is closed the parent Test app finally terminates.
However even more strange if I hit the red terminate button in the eclipse console BEFORE the 10 second sleep elapses then the Test App closes and the client.exe keeps on running. This is the behavior I want but I can't figure out. Any ideas?
This is the default behaviour of most OS's, that a parent process can't terminate until all child processes have terminated.
Now, there is a "funky" way to create a "parentless" process, so that the parent process can terminate and the child process will continue running, but this becomes OS dependent, which you already have any way...
Basically, the command lines becomes something like...
cmd /C start /B /NORMAL cmd /c "client.exe"
Now. I would recommend that you use the Runtime#exec(String[]) variant, as this deals with spaces within commands better
String[] cmd = {"cmd", "/C", "start", "/B", "/NORMAL", "cmd", "/c", "client.exe"};
runtime.exec(cmd);
Normally, I would recommend ProcessBuilder over Runtime#exec, as it allows you to, amongst other things, change the working directory for the process...
I am working on a program written in Java which, for some actions, launches external programs using user-configured command lines. Currently it uses Runtime.exec() and does not retain the Process reference (the launched programs are either a text editor or archive utility, so no need for the system in/out/err streams).
There is a minor problem with this though, in that when the Java program exits, it doesn't really quit until all the launched programs are exited.
I would greatly prefer it if the launched programs were completely independent of the JVM which launched them.
The target operating system is multiple, with Windows, Linux and Mac being the minimum, but any GUI system with a JVM is really what is desired (hence the user configurability of the actual command lines).
Does anyone know how to make the launched program execute completely independently of the JVM?
Edit in response to a comment
The launch code is as follows. The code may launch an editor positioned at a specific line and column, or it may launch an archive viewer. Quoted values in the configured command line are treated as ECMA-262 encoded, and are decoded and the quotes stripped to form the desired exec parameter.
The launch occurs on the EDT.
static Throwable launch(String cmd, File fil, int lin, int col) throws Throwable {
String frs[][]={
{ "$FILE$" ,fil.getAbsolutePath().replace('\\','/') },
{ "$LINE$" ,(lin>0 ? Integer.toString(lin) : "") },
{ "$COLUMN$",(col>0 ? Integer.toString(col) : "") },
};
String[] arr; // array of parsed tokens (exec(cmd) does not handle quoted values)
cmd=TextUtil.replace(cmd,frs,true,"$$","$");
arr=(String[])ArrayUtil.removeNulls(TextUtil.stringComponents(cmd,' ',-1,true,true,true));
for(int xa=0; xa<arr.length; xa++) {
if(TextUtil.isQuoted(arr[xa],true)) {
arr[xa]=TextDecode.ecma262(TextUtil.stripQuotes(arr[xa]));
}
}
log.println("Launching: "+cmd);
Runtime.getRuntime().exec(arr);
return null;
}
This appears to be happening only when the program is launched from my IDE. I am closing this question since the problem exists only in my development environment; it is not a problem in production. From the test program in one of the answers, and further testing I have conducted I am satisfied that it is not a problem that will be seen by any user of the program on any platform.
There is a parent child relation between your processes and you have to break that.
For Windows you can try:
Runtime.getRuntime().exec("cmd /c start editor.exe");
For Linux the process seem to run detached anyway, no nohup necessary.
I tried it with gvim, midori and acroread.
import java.io.IOException;
public class Exec {
public static void main(String[] args) {
try {
Runtime.getRuntime().exec("/usr/bin/acroread");
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("Finished");
}
}
I think it is not possible to to it with Runtime.exec in a platform independent way.
for POSIX-Compatible system:
Runtime.getRuntime().exec(new String[]{"/bin/sh", "-c", "your command"}).waitFor();
I have some observations that may help other people facing similar issue.
When you use Runtime.getRuntime().exec() and then you ignore the java.lang.Process handle you get back (like in the code from original poster), there is a chance that the launched process may hang.
I have faced this issue in Windows environment and traced the problem to the stdout and stderr streams. If the launched application is writing to these streams, and the buffer for these stream fills up then the launched application may appear to hang when it tries to write to the streams. The solutions are:
Capture the Process handle and empty out the streams continually - but if you want to terminate the java application right after launching the process then this is not a feasible solution
Execute the process call as cmd /c <<process>> (this is only for Windows environment).
Suffix the process command and redirect the stdout and stderr streams to nul using 'command > nul 2>&1'
It may help if you post a test section of minimal code needed to reproduce the problem. I tested the following code on Windows and a Linux system.
public class Main {
/**
* #param args the command line arguments
*/
public static void main(String[] args) throws Exception {
Runtime.getRuntime().exec(args[0]);
}
}
And tested with the following on Linux:
java -jar JustForTesting.jar /home/monceaux/Desktop/__TMP/test.sh
where test.sh looks like:
#!/bin/bash
ping -i 20 localhost
as well as this on Linux:
java -jar JustForTesting.jar gedit
And tested this on Windows:
java -jar JustForTesting.jar notepad.exe
All of these launched their intended programs, but the Java application had no problems exiting. I have the following versions of Sun's JVM as reported by java -version :
Windows: 1.6.0_13-b03
Linux: 1.6.0_10-b33
I have not had a chance to test on my Mac yet. Perhaps there is some interaction occuring with other code in your project that may not be clear. You may want to try this test app and see what the results are.
You want to launch the program in the background, and separate it from the parent. I'd consider nohup(1).
I suspect this would require a actual process fork. Basically, the C equivalent of what you want is:
pid_t id = fork();
if(id == 0)
system(command_line);
The problem is you can't do a fork() in pure Java. What I would do is:
Thread t = new Thread(new Runnable()
{
public void run()
{
try
{
Runtime.getRuntime().exec(command);
}
catch(IOException e)
{
// Handle error.
e.printStackTrace();
}
}
});
t.start();
That way the JVM still won't exit, but no GUI and only a limited memory footprint will remain.
I tried everything mentioned here but without success. Main parent Java process can't quit until the quit of subthread even with cmd /c start and redirecting streams tu nul.
Only one reliable solution for me is this:
try {
Runtime.getRuntime().exec("psexec -i cmd /c start cmd.cmd");
}
catch (Exception e) {
// handle it
}
I know that this is not clear, but this small utility from SysInternals is very helpful and proven. Here is the link.
One way I can think of is to use Runtime.addShutdownHook to register a thread that kills off all the processes (you'd need to retain the process objects somewhere of course).
The shutdown hook is only called when the JVM exits so it should work fine.
A little bit of a hack but effective.