Problem in "Process.waitFor()" in multithreaded application (UNIX OS)

Question

Hello all
This is very urgent for me.
I am using the follwing code to invoke the child process which calls a shell script in the unix OS,and it is going fine when runs in single thread. But if i run it as the multhreaded appln, anyone of the thread hangs in the 'Process.waitfor()' call. But sometimes all the threads are returning successfully. I am calling this code from the one or more threads. This is tested in the java1.2 and 1.3. so can u suggest me how to change the code or any way to fix up the problem.
// the code starts
String s[] = new String[3];
s[0] = "/bin/sh";
s[1] = "-c";
s[2] = "encrypt.sh"; //some .sh filename to do the task
Runtime runtime = Runtime.getRuntime();
Process proc;
proc = runtime.exec(s);
InputStream is = proc.getInputStream();
byte buf[] = new byte[256];
int len;
while( (len=is.read(buf)) != -1) {
String s1 = new String(buf,0,len);
System.out.println(s1);
InputStream es = proc.getErrorStream();
buf = new byte[256];
while( (len=es.read(buf)) != -1) {
String s1 = new String(buf,0,len);
System.out.println("Error Stream : " + s1);
// place where it hang
retValue = proc.waitFor();
//code ends
i am handling the errorstream and output stream and not getting any error stream output and not printing any messages in the child process. When i synchronize the whole function, it went fine, but spoils the speed performance. I tried all the option but i could not solve the problem.
thanks

Answer 1

You're first reading all of the standard output, then reading all of the standard error. What if the process generates too much output to standard error and hangs while it waits for your program to read it? I would suggest having two threads, one which reads the standard output and the other which reads standard error.