Question

I am encountering some weird behavior when calling a shell script from a Java process.

Process p = Runtime.getRuntime().exec("mybashscript.sh");
(new StreamGobblerThread(p.getInputStream())).start();
(new StreamGobblerThread(p.getErrorStream())).start();
p.waitFor();
returnValue = p.exitValue();

The StreamGobblerThread just has a run() method that does a

while(((inputStream.available>0) { inputStream.skip(available); }

About 20% of the time this works, but mostly the script fails with a return code of 141 right away.

From what I found on google, 141 is a return code when a SIGPIPE was received.

Any ideas?

Answer 1

I’m not 100% sure what the problem, but first of all:

while(((inputStream.available>0) { inputStream.skip(available); }

isn’t valid.

This is because inputStream.available() isn’t blocking, so if it doesn’t have anything to read immediately, it’s not going to read anything at all.

You’re better off having something like this:

byte[] buf = new byte[8192];
int next;
try {
    while ((next = in.read(buf)) != -1) {}
} catch (IOException e) {
    throw new GroovyRuntimeException("exception while dumping process stream", e);
}

read() is blocking so, this way it actually will continue reading until the stream is properly closed.

(Note: This code is from Groovy’s implementation of consumeProcessOutput()