Java Process.waitFor() and IO streams
- by lynks
I have the following code;
String[] cmd = { "bash", "-c", "~/path/to/script.sh" };
Process p = Runtime.getRuntime().exec(cmd);
PipeThread a = new PipeThread(p.getInputStream(), System.out);
PipeThread b = new PipeThread(p.getErrorStream(), System.err);
p.waitFor();
a.die();
b.die();
The PipeThread class is quite simple so I will include it in full;
public class PipeThread implements Runnable {
private BufferedInputStream in;
private BufferedOutputStream out;
public Thread thread;
private boolean die = false;
public PipeThread(InputStream i, OutputStream o) {
in = new BufferedInputStream(i);
out = new BufferedOutputStream(o);
thread = new Thread(this);
thread.start();
}
public void die() { die = true; }
public void run() {
try {
byte[] b = new byte[1024];
while(!die) {
int x = in.read(b, 0, 1024);
if(x > 0) out.write(b, 0, x);
else die();
out.flush();
}
}
catch(Exception e) { e.printStackTrace(); }
try {
in.close();
out.close();
}
catch(Exception e) { }
}
}
My problem is this; p.waitFor() blocks endlessly, even after the subprocess has terminated. If I do not create the pair of PipeThread instances, then p.waitFor() works perfectly. What is it about the piping of io streams that is causing p.waitFor() to continue blocking?
I'm confused as I thought the IO streams would be passive, unable to keep a process alive, or to make Java think the process is still alive.
