Questions on Runtime.exec

Currently i need to backup a file from the current directory to a Archive directory. So to rename the file in the current directory then move it or copy it into the Archive directory.
My question is can Runtime.exec () run 2 commands
first will be "cmd /c start rename A*.zip A_01.zip"
second will be "cmd /c copy A_01.zip newfolder\A_01.zip" ?
Reason why i dun wan to run 2 .exec() statement is that i dun wan too many popout screens.
Hope I can get my solution here.
Thanks

don't know whether it works on windoze too, but on unix you can execute several commands seperated by an ";". perhaps this works for exec() too (?)
so far,
stefan g.

Similar Messages

Question about Runtime.exec

Rob,
Thanks for your help.
I asked a question about a weird Exception on Nov 14, and you told me that I am
using Runtime.exec to start an external process, and that process is crashing.
I am a green-hand on Weblogic, and I am trying to enhancing a project developped
by another person, so I am not familiar with some concepts yet.
Could you please give me some simple explanation about Runtime.exec and external
process?
I found two methods that uses "Runtime" from two classes as following, could you
help me to see whether or not there is something wrong with the usage of Runtime?
Thank you very much.
private int runShellCommand(String command) {
int exitVal = -1;
try {
File runDir = new File(runDirectory);
String[] env = new String[0];
Runtime rt = Runtime.getRuntime();
               double start = System.currentTimeMillis();
Process proc = rt.exec(command, env, runDir);
// Capture output in separate thread
ThreadedStreamReader error = new ThreadedStreamReader(proc.getErrorStream(),
"ERROR");
ThreadedStreamReader output = new ThreadedStreamReader(proc.getInputStream(),
"OUTPUT");
error.start();
output.start();
exitVal = proc.waitFor();
if (logger.isDebugEnabled()) {
     double runtime = (System.currentTimeMillis() - start) / 1000.0;
     logger.info("run " + runId + " " + command + " finished in " + runtime
+ " seconds");
} catch (IOException e) {
logger.fatal("DOE-2 failed \n" + e.getMessage());
} catch (InterruptedException e) {
e.printStackTrace();
return exitVal;
public static void main(String[] args) throws Exception, InterruptedException
final Doe2MessageServer server = new Doe2MessageServer();
while(!connected) {
Thread.sleep(1000);
logger.info("Attempting to start JMS service ...");
               try {
          server.init();
               } catch (Exception ex) {
// shutdown hook to close JMS connection
Runtime.getRuntime().addShutdownHook(
new Thread() {
public void run() {
server.finalize();
server.receiveMessage();

Runtime.exec is a J2SE API. It's not really specific to WLS.
You can read about it here:
http://java.sun.com/j2se/1.4.1/docs/api/java/lang/Runtime.html
It looks like you are starting a JMS Server in a separate process and
that process is crashing.
(You could of course just use WLS's JMS Server instead :>)
-- Rob
Iris Qu wrote:
Rob,
Thanks for your help.
I asked a question about a weird Exception on Nov 14, and you told me that I am
using Runtime.exec to start an external process, and that process is crashing.
I am a green-hand on Weblogic, and I am trying to enhancing a project developped
by another person, so I am not familiar with some concepts yet.
Could you please give me some simple explanation about Runtime.exec and external
process?
I found two methods that uses "Runtime" from two classes as following, could you
help me to see whether or not there is something wrong with the usage of Runtime?
Thank you very much.
private int runShellCommand(String command) {
int exitVal = -1;
try {
File runDir = new File(runDirectory);
String[] env = new String[0];
Runtime rt = Runtime.getRuntime();
               double start = System.currentTimeMillis();
Process proc = rt.exec(command, env, runDir);
// Capture output in separate thread
ThreadedStreamReader error = new ThreadedStreamReader(proc.getErrorStream(),
"ERROR");
ThreadedStreamReader output = new ThreadedStreamReader(proc.getInputStream(),
"OUTPUT");
error.start();
output.start();
exitVal = proc.waitFor();
if (logger.isDebugEnabled()) {
     double runtime = (System.currentTimeMillis() - start) / 1000.0;
     logger.info("run " + runId + " " + command + " finished in " + runtime
+ " seconds");
} catch (IOException e) {
logger.fatal("DOE-2 failed \n" + e.getMessage());
} catch (InterruptedException e) {
e.printStackTrace();
return exitVal;
public static void main(String[] args) throws Exception, InterruptedException
final Doe2MessageServer server = new Doe2MessageServer();
while(!connected) {
Thread.sleep(1000);
logger.info("Attempting to start JMS service ...");
               try {
          server.init();
               } catch (Exception ex) {
// shutdown hook to close JMS connection
Runtime.getRuntime().addShutdownHook(
new Thread() {
public void run() {
server.finalize();
server.receiveMessage();

Problem executing file through Runtime.exec

Hi,
i am trying to execute a java programem using the the following line
Runtime.exec("java Myclass");
But no response for it.
Anybody help me.
Jossy

As required by forum protocol for people who ask questions about Runtime.exec I am posting the standard link:
http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html

The Runtime.exec methods doesn't work well on Solaris ???

I have two threads and I set the different running time.
I use Runtime.exec to a run the command and use Process to get the process.
It works properly in the windows2000 platform.
However, when I transfer the platform to Solaris...and run the program...
Two threads always at the same time....It is very wired....I always debug
for 2 days....
(at first I run "vmstat 1 2" command, later I change to "ls","rmdir"....etc,
all of them don't work.....
If I close the Runtime.exec..........Everything works well......)
And I study the API. I found this message...
The Runtime.exec methods may not work well for special processes on certain
native platforms, such as native windowing processes, daemon processes,
Win16/DOS processes on Win32, or shell scripts. The created subprocess does
not have its own terminal or console.
Could someone share her/his experience.....:(
And if any other way I can run command inside java code instead of
Runtime.exec.....???
Please reply my mail to [email protected] I do appreciate your kindly &
great help!!!!!!!!
This is my code.......
import java.io.*;
import java.lang.*;
import java.util.*;
* <p>ServerThread1</p>
* <p>??�X???��?�D???�X???, "Vmstat 1 2".</p>
class ServerThread1 extends Thread{
private ServerAgent Sa;
public ServerThread1 (String Name, ServerAgent Sa){
super(Name);
this.Sa = Sa; file://Assign ServerAgent reference Sa
public void run(){
while(true){
try{
Thread.sleep(5000);
catch (Exception e){
System.out.println("ServerThread1 fails");
System.out.println("Thread1 is running.");
try {
Runtime rt1 = Runtime.getRuntime();
Process proc1 = rt1.exec("mkdir"); ------>If I close
rt1.exec , two threads works seperately...........:(
catch (Exception e) {
System.out.println("Thread1 Error");
class ServerThread2 extends Thread{
private ServerAgent Sa;
public ServerThread2 (String Name, ServerAgent Sa){
super(Name);
this.Sa = Sa;
public void run(){
while(true){
try{
Thread.sleep(15000);
catch (Exception e){
System.out.println("ServerThread2 fails");
System.out.println("Thread2 is running.");
try {
Runtime rt2 = Runtime.getRuntime();
Process proc2 = rt2.exec("vmstat 1 2"); ----->If I don't run
the rt2.exe, two threads work seperately....
catch (Exception e) {
System.out.println("Thread2 Error");
public class ServerAgent{
private Vector v1 = new Vector();
private Vector v2 = new Vector();
private Hashtable currentData = new Hashtable();
private static String startUpSwap = null;
private static String startUpMem = null;
public static void main(String[] arg) {
ServerAgent s = new ServerAgent();
ServerThread1 st1 = new ServerThread1("Thread1",s);
ServerThread2 st2 = new ServerThread2("Thread2",s);
st1.start();
st2.start();

If I close the Runtime.exec..........Everything works
well......)You don't empty the output of the command, that blocks the process.
A citation from
http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html
Why Runtime.exec() hangs
The JDK's Javadoc documentation provides the answer to this question:
Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.
Try out something like this:
String s;
try {
   Process myProcess =
   Runtime.getRuntime().exec("ls -l"));
   DataInputStream in = new DataInputStream(
          new BufferedInputStream(myProcess.getInputStream()));
    while ((s = in.readLine()) != null) {
        out.println(s);
catch (IOException e) {
    out.println("Error: " + e);
}Another source of trouble under Unix is not having the correct permission for that user that executes the Java VM, which will be the permissions for the spawned subprocess. But this probably not the case, as you see something after exit.
Regards,
Marc

How to capture output from Runtime.exec() ?

Hi,
Well, the question is in the subject ...
I'd like to capture the output of a process ran by Runtime.exec() in order to process it.
thanks,
ionel

Okay ...
Sorry for the post !
I found the solution : Runtime.exec().getOutputStream()
Thanks however
ionel

Java.lang.Runtime.exec problem in ubuntu 9.10

Hi:
I tried to run some command in the java code , for example "grass64 -text /home/data/location", this command works well in the terminal, however when I call it in the java code I got some excepetions.
My code is :
public class Grass {
     public static String grassBatJob="GRASS_BATCH_JOB";
     public void run(String cmd,String jobPath) {
          //set the environments variables
          Map<String, String> env=new HashMap<String, String>();
          env.put(grassBatJob, jobPath);
          String gisDataBase="/home/kk/grass/GrassDataBase";
          String location="spearfish60";
          String mapset="PERMANENT";
          cmd=cmd+" "+gisDataBase+"/"+location+"/"+mapset;
          CommandLine line=new CommandLine(cmd);
          //the real cmd should be >>grass64 -text /home/kk/grass/GrassDataBase/spearfish60/PERMANENT
          System.out.println("start line=="+line.toString());
          DefaultExecutor de=new DefaultExecutor();
          try {
               int index=de.execute(line,env);
               System.out.println(index);
          } catch (ExecuteException e) {
               e.printStackTrace();
          } catch (IOException e) {
               e.printStackTrace();
     public static void main(String[] args) {
          String jobPath=Grass.class.getResource("grass.sh").getFile();
          new Grass().run("grass64 -text", jobPath);
The real cmd I want to execute is "grass64 -text /home/kk/grass/GrassDataBase/spearfish60/PERMANENT" with the envrionment variable "GRASS_BATCH_JOB=jobPath",it works well in the ternimal ,however in my application I got the exception"
java.io.IOException: Cannot run program "grass64 -text /home/kk/grass/GrassDataBase/spearfish60/PERMANENT": java.io.IOException: error=2, No such file or directory
     at java.lang.ProcessBuilder.start(ProcessBuilder.java:459)
     at java.lang.Runtime.exec(Runtime.java:593)
     at org.apache.commons.exec.launcher.Java13CommandLauncher.exec(Java13CommandLauncher.java:58)
     at org.apache.commons.exec.DefaultExecutor.launch(DefaultExecutor.java:246)
     at org.apache.commons.exec.DefaultExecutor.executeInternal(DefaultExecutor.java:302)
     at org.apache.commons.exec.DefaultExecutor.execute(DefaultExecutor.java:149)
     at org.kingxip.Grass.run(Grass.java:27)
     at org.kingxip.Grass.main(Grass.java:38)
Caused by: java.io.IOException: java.io.IOException: error=2, No such file or directory
     at java.lang.UNIXProcess.<init>(UNIXProcess.java:148)
     at java.lang.ProcessImpl.start(ProcessImpl.java:65)
     at java.lang.ProcessBuilder.start(ProcessBuilder.java:452)
     ... 7 more
I wonder why?

Thanks for all of your reply, and now I can run the command, however I met some problems when I tried to get the result of the exec.
The core codes are shown below:
String cmd="g.version";
String[] exe={"bash","-c",cmd};
Process p1=Runtime.getRuntime.exec(exe,env); // the env has been set
GrassThread outThread=new GrassThread("out", p1.getInputStream());
outThread.start();
GrassThread errorThread=new GrassThread("error", p1.getErrorStream());
errorThread.start();
int exitVal = p1.waitFor();
String resu=outThread.sb.toString();
System.out.println("==========the output start========");
System.out.println(resu);
System.out.println("==========the output end========");
System.out.println("ExitValue: " + exitVal); //------------------> line one
public class GrassThread extends Thread{
     public StringBuffer sb=new StringBuffer();
     public GrassThread(String type,InputStream is) {
          this.type=type;
          this.is=is;
     public void run() {
          try {
               InputStreamReader isr = new InputStreamReader(is);
               BufferedReader br = new BufferedReader(isr);
               String line = null;
               while ((line = br.readLine()) != null) {
                    System.out.println(type + ">" + line);
                    sb.append(line).append("\r"); // ----------------------------> line two
}I define a StringBuffer in the GrassThread to save the output (see the code where I marked by "line two"), and when the process complete, I check the StringBuffer to get the output (see code where I marked by "line one"), however the output in the console of the IDE are :
----------- output in the console of the IDE start -------------
==========the output start========
==========the output end========
ExitValue: 0
out>GRASS 6.4.0RC5 (2009)
----------output in the console of the IDE end--------------------
I can not understand, in the code "line one", I first get the output using "System.out.println(resu);",then I print the exitvalue,but why the order of the output in the console is not what I expected?
Another question, the code above assume the output can be got from the Process's getInputStream, however sometimes the output maybe come from the Process's getErrorStream, so how to handle it?
Edited by: apachemaven on 2010-3-5 ??5:38

Using runtime.exec,process streams

Hi all,
I am using runtime.exec to execute a batch file(rmdir /s/q directoryname) which deletes all the files in a certain directory(including subdirectories). However, some of the files are not deleted since they are being used by other processes.
I have closed all file references but still the batch file says they are being used by other processes. The File.canWrite() method however, returns true for all the files. I have also tried to delete the files using file.delete but it does not work.
So I have 2 questions.
1. Can I forcibly delete these files some other way.
2. If i call a batch file to delete the files and it fails on some files, the command window displays "cannot delete files". How can I write out thse messages into a text file which i can use as a log file.Do I have to use Process.getInputstream()/Process.getInputstream() ? If so, how?
Thanks for your help.
Vinny

I tried the following before but the string i get is always empty, but i can see there are messages in the command window. Please let me now if i am doing something wrong.
try{
Process p = rt.exec("cmd.exe /c start deletefiles.bat");
InputStream ins = p.getInputStream();
byte[] bytearray = new byte[1024];
int bytecount;
String dos_string="";
BufferedInputStream bis = new BufferedInputStream(ins);
while ((bytecount = bis.read(bytearray, 0, 1024)) > -1) {
String str = new String(bytearray,0,bytecount);
dos_string += str;
System.out.println("dos string is" +dos_string);
catch (Exception e) {
System.out.println("Error: " + e);

Using Runtime.exec to execute a C++ executable

Hello,
I would like to know if it possible to execute a C++ executable using Runtime.exec() and wait for it to complete and how do I read back the output file created by the C++ executable into the Java Code?
TIA.
RHP

When I execute the code with Runtime.exec(), and read
from the Process's inputStream I am ablt to view the
cout from the C++ code. But the output file that has
to be created by the C++ code is not created,Then this is maybe an error in the C++ code? Maybe you don't have permissions to create that file where you want to.
where
would the output from the C++ code go to when I use a
ofstream in my C++ code andIf you create the file stream in C++ with an absolute file name then the output goes into that file. If it's a relative file name, then the basis is most likely the current working directory (found in the system property "user.dir" if you used one of Runtime's methods without the File argument, otherwise it's the directory you provide.
How do I read both streams
from the Java Code?You create an FileInputStream and - if you want to read character instead of binary data - on top of that an InputStreamReader. You might add a BufferedReader on top of that if you want to read line by line.
does that answer your questions?
robert

Need info about Runtime.exec

Hello, I have a non program specific question about how Runtime.exec works. First off assume that I handle all my input streams and output streams correctly, and I am not worried about inter process communication. The question is, when I use Runtime.getRuntime().exec(cmd[],pth[],dir) does the JVM that is running the code that calls it live until the spawned process dies, or can it die without waiting for the execed process to die? I am trying to write an app that can spawn a new copy of itself that is completely independent from the original process, and may live on long after the original is no longer needed. To ensure proper resource management I need to know that the JVM that launches the new process does not have to wait for the new process to die prior to completely cleaning itself up.
Does that make sense?
Any suggestions, ideas, questions?
Thanks in advance for the help.
Message was edited by:
elixic

Thank you all who gave useful input. I had done some reading on this already and could not find a definite answer on weather or not the calling JVM can properly dispose of itself prior to the process it called being disposed of.
The answer it seems is dependent on context. In windows, and from a GUI app, it looks like the calling JVM can die any time it wants too. A command line app on the other hand seems to have to wait for the app it called to die first. I have not tested it on other OS's but I am sure it varies by OS as well. I would not even be surprised if it varies by JVM.
So the short answer to my question that you all helped me find is this, It varies by context.
Thanks again for the help.
Isaac

Runtime.exec() hangs with 1.4.1

Hello altogether,
I am trying to execute a command with Runtime.getRuntime.exec()
I have already taken care of capturing the output and I observe that depending of the program I try to execute the process hangs.
I am using JRE 1.4.1_02 under Redhat 7.2 with kernel 2.4.18-26
Executing the same program under JRE 1.3.1 the program does not hang.
Executing 'top -bn0q' hangs, executing 'ls -als' it hangs.
Here is my sample code:
<code>
import java.io.*;
public class Exec
/** catches the output in a parallel thread */
class StreamReader extends Thread
String category = null;
InputStream is;
StreamReader(String category, InputStream is)
this.category = category;
this.is = is;
public void run()
try
System.out.println(this.category+": reader runs");
InputStreamReader isr = new InputStreamReader(this.is);
BufferedReader br = new BufferedReader(isr);
String line = null;
while (br.ready() && (line = br.readLine())!=null)
System.out.println(this.category+':'+line);
catch (Exception e)
e.printStackTrace();
public void run(String[] cmd)
StringBuffer outStrBuf = new StringBuffer();
try
Runtime rt = Runtime.getRuntime();
System.out.println("got runtime");
Process process = rt.exec(cmd);
System.out.println("fired cmd");
// any errors
System.out.println("prepare error stream");
StreamReader errSr = new StreamReader("ERR",process.getErrorStream());
// any output
System.out.println("prepare output stream");
StreamReader outSr = new StreamReader("OUT",process.getInputStream());
// start the readers to read
System.out.println("start readers");
errSr.start();
outSr.start();
System.out.println("waiting for process to end");
process.waitFor(); //Waits for the subprocess to complete.
catch (Exception e)
System.err.println("Error while executing cmd: " + cmd);
e.printStackTrace();
System.out.println(outStrBuf);
     public static void main(String[] args)
String [] cmd = {"top","-bn0q"};
if (args.length >= 1)
cmd = args;
System.out.println(args[0]);
Exec exec = new Exec();
exec.run(cmd);
</code>
The output of java Exec is:
[user]$ java Exec
got runtime
fired cmd
prepare error stream
prepare output stream
start readers
waiting for process to end
OUT: reader runs
ERR: reader runs
...and there it hangs. Interesting is, that when I use ls -als as command, I get the directory listing.
Do you have any ideas what I am doing wrong? Is there any difference in the Runtime.exec() between 1.3 and 1.4 version?

Unbelievable and what a shame. I was hacking 2 days on several variations of this problem and the solution and I finally found one difference:
while (br.ready() && (line = br.readLine())!=null)
I assume that when executing the command, the output streams are not ready and my Output gobbler threads end.
...however the command is still executing and starts to write its output. And as we all know this will overflow the buffer and the process hangs.
So the final solution is:
/** catches the output in a parallel thread */
class StreamReader extends Thread
String category = null;
InputStream is;
StreamReader(String category, InputStream is)
    this.category = category;
    this.is = is;
public void run()
    try
      System.out.println(this.category+": reader runs");
      InputStreamReader isr = new InputStreamReader(this.is);
      BufferedReader br = new BufferedReader(isr);
      String line = null;
      while (/**br.ready() &&*/ (line = br.readLine())!=null)
        System.out.println(this.category+':'+line);
    catch (Exception e)
      e.printStackTrace();
}So the only question that I have open: Why does this makes no problem with 1.3 but with 1.4 ?

Why is Runtime.Exec not perfekct?

Hi!
I need to execute a program from java using Runtime.Exec(). I have done everything right with redirection the output stream and read it from a seperate thread. This works for most of the programs I tried, but not for all. Sometimes I miss some of the output.
But if I use redirection to a file from the shell it works perfect.
(i.e. /bin/pramsim > outfil)
Why is this? Why isn't Runtime.exec as good as shell redirection?
/Karl

Ok sorry, here is some more detalis.
The program( pramsim) prints to both standard output and standard error. Output written to stderr does always work. But output so stout fails quite often. After some research I found out that pramsim is using the function printf(...) which is bufferd by default. So I only get the output when the program prints alot, so the buffer gets full.
Can I in some way turn buffering off from java? Found a C function called setbuf(1,null) which turns buffering off. But this means I have to changes the code to pramsim, and I want to avoid that!
I also wonder: How does redirection in the shell make this work. I guess buffering is turned off when I redirect to a file using 'pramsim > outfil'. (maybe this is more a C question but I hope that I can get some help here)
/Karl

Opening a new browser using Runtime.exec()...

I am trying to open a new IE browser window (from Windows) using Runtime.exec( ) command. The problem is that it uses the existing browser window instead of opening a new window. (opens a new window only if there isn't any other browser window)
Here is the snippet of code that I am using to do this:
String WIN_PATH = "rundll32";
String WIN_FLAG = "url.dll,FileProtocolHandler";
String url = "http://www.cnn.com";
String cmd = WIN_PATH + " " + WIN_FLAG + " " + url;
Process p = Runtime.getRuntime().exec(cmd);
Thanks in advance.
-Kishore

>
opening browser window seems to be easy task, >Even easier with [Desktop.browse(URI)|http://java.sun.com/javase/6/docs/api/java/awt/Desktop.html#browse(java.net.URI)].
>
..can someone help me with closing browser window from java?>Which browser window?
If you're app. opens a page that you control, it can be done from the web page. See [Have a Java button close the browser window|http://www.rgagnon.com/javadetails/java-0282.html] or the JS based [Close the browser|http://www.rgagnon.com/jsdetails/js-0079.html].
If you do not control the page, don't close it - the user knows where the little 'x' button is.
As an aside, despite being opposite ends of the one question, I do not consider this question to be 'part' of the current thread. I think you would have been better off starting a dedicated thread and explaining more fully what the use case is (and adding lots of Dukes).

Why cant I Runtime.exec(file.getAbsolutePath()) ???

I want to run custom file (not directory!) using Runtime.exec() (or you know other way? :) )
Here is what i get::
java.io.IOException: CreateProcess: C:\Documents and Settings\Sugar.SERVER\jbproject\test\theFileICannotOpen.txt error=2
     at java.lang.Win32Process.create(Native Method)
     at java.lang.Win32Process.<init>(Win32Process.java:66)
     at java.lang.Runtime.execInternal(Native Method)
     at java.lang.Runtime.exec(Runtime.java:566)
     at java.lang.Runtime.exec(Runtime.java:428)
     at java.lang.Runtime.exec(Runtime.java:364)
     at java.lang.Runtime.exec(Runtime.java:326)
     at NotWorkingRuntimeClass.main(NotWorkingRuntimeClass.java:27)P.S. 1) the file i want to open EXISTS.
2) I can get also the 193 error code.
P.P.S. It WORKS on *.exe files. How to make all type-files to open? (allow the system to decide which application to use for opening the fie, of course...)
Please help!
THANK YOU!!!

Well, then i've got another question.
How to open the specified file using the system's default program for such file types?
Thanks again, Boris.

Runtime.exec() for different Windows versions ?

Hello all.
I'm currently developing a Java program that uses Runtime.exec() to launch a MS-DOS application (the old MS-Kermit). It works fine under Windows ME and Java 1.3.1 but the very same code fails to work under Windows 2000. That's very bad for me, since my program should work on all windows platforms from 95 up to XP (and NT).
My question is : can I trust Runtime.exec() or am I damned to write different versions of the same command for different operating systems ?
Thanks.

Runtime is not os independent, so yes, it has to accomodate the os differences. There is an enhancement request on the subject, tho.
Search the forums, there is code that handles the differences posted.

Running java process in a while loop using Runtime.exec() hangs on solaris

I'm writting a multithreaded application in which I'll be starting multiple instances of "AppStartThread" class (given below). If I start only one instance of "AppStartThread", it is working fine. But if I start more than one instance of "AppStartThread", one of the threads hangs after some time (occasionaly). But other threads are working fine.
I have the following questions:
1. Is there any problem with starting a Thread inside another thread?. Here I'm executing the process in a while loop.
2. Other thing i noticed is the Thread is hanging after completing the process ("java ExecuteProcess"). But the P.waitFor() is not coming out.
3. Is it bcoz of the same problem as given in Bug ID : 4098442 ?.
4. Also java 1.2.2 documentation says:
"Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock. "
I'm running this on sun Solaris/java 1.2.2 standard edition. If any of you have experienced the same problem please help me out.
Will the same problem can happen on java 1.2.2 enterprise edition.?
class AppStartThread implements Runnable
public void run()
while(true)
try
Process P=Runtime.getRuntime().exec("java ExecuteProcess");
P.waitFor();
System.out.println("after executing application.");
P.destroy();
P = null;
System.gc();
catch(java.io.IOException io)
System.out.println("Could not execute application - IOException " + io);
catch(java.lang.InterruptedException ip)
System.out.println("Could not execute application - InterruptedException" + ip);
catch (Exception e)
System.out.println("Could not execute application -" + e.getMessage());

I'm writting a multithreaded application in which I'll
be starting multiple instances of "AppStartThread"
class (given below). If I start only one instance of
"AppStartThread", it is working fine. But if I start
more than one instance of "AppStartThread", one of the
threads hangs after some time (occasionaly). But other
threads are working fine.
I have the following questions:
1. Is there any problem with starting a Thread inside
another thread?. Here I'm executing the process in a
while loop.Of course this is OK, as your code is always being run by one thread or another. And no, it doesn't depend on which thread is starting threads.
2. Other thing i noticed is the Thread is hanging
after completing the process ("java ExecuteProcess").
But the P.waitFor() is not coming out.This is a vital clue. Is the process started by the Runtime.exec() actually completing or does the ps command still show that it is running?
3. Is it bcoz of the same problem as given in Bug ID :
4098442 ?.
4. Also java 1.2.2 documentation says:
"Because some native platforms only provide limited
ed buffer size for standard input and output streams,
failure to promptly write the input stream or read the
output stream of the subprocess may cause the
subprocess to block, and even deadlock. "These two are really the same thing (4098442 is not really a bug due to the reasons explained in the doc). If the program that you are exec'ing produces very much output, it is possible that the buffers to stdout and stderr are filling preventing your program from continuing. On Windows platforms, this buffer size is quite small (hundreds of characters) while (if I recall) on Solaris it is somewhat larger. However, I have seent his behavior causing problem on Solaris 8 in my own systems.
I once hit this problem when I was 'sure' that I was emitting no output due to an exception being thrown that I wasn't even aware of - the stack trace was more than enough to fill the output buffer and cause the deadlock.
You have several options. One, you could replace the System.out and System.err with PrintStream's backed up by (ie. on top of) BufferedOutputStream's that have large buffers (multi-K) that in turn are backed up by the original out and err PrintStream's. You would use System.setErr() and System.setOut() very early (static initializer block) in the startup of your class. The problem is that you are still at the mercy of code that may call flush() on these streams. I suppose you could implement your own FilterOutputStream to eat any flush requests...
Another solution if you just don't care about the output is to replace System.out and System.err with PrintStreams that write to /dev/nul. This is really easy and efficient.
The other tried and true approach is to start two threads in the main process each time you start a process. These will simply consume anything that is emitted through the stdout and stderr pipes. These would die when the streams close (i.e. when the process exits). Not pretty, but it works. I'd be worried about the overhead of two additional threads per external process except that processes have such huge overhead (considering you are starting a JVM) that it just won't matter. And it's not like the CPU is going to get hit much.
If you do this frequently in your program you might consider using a worker thread pool (see Doug Lea's Executor class) to avoid creating a lot of fairly short-lived threads. But this is probably over-optimizing.
Chuck

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