Executing process with ProcessBuilder causes hang on waitFor

Question

I'm having problems with running an exernal application out of Java. I'm aware of the problem with the input and output streams, and I'm trying to read them as follows:

    ProcessBuilder pb = new ProcessBuilder(args);
    args[args.length - 1] += "<NUL";

    pb.redirectErrorStream(true);
    Process p = pb.start();

    InputStreamReader isr = new InputStreamReader(p.getInputStream());
    BufferedReader input = new BufferedReader(isr);
    while (input.readLine() != null) {
    }       

    p.waitFor();
    input.close();
    isr.close();

The command I'm executing is xdg-open for an URL, so it shouldn't wait for input.

This works nine times out of ten on my machine, but sometimes it simply hangs at pb.start(); and the command isn't executed.

The java thread is waiting on the process to return. Here's the stack trace:

Name: LinkHandlerExec
State: WAITING on java.lang.UNIXProcess$Gate@356122dc
Total blocked: 0  Total waited: 1

Stack trace: 
java.lang.Object.wait(Native Method)
java.lang.Object.wait(Object.java:502)
java.lang.UNIXProcess$Gate.waitForExit(UNIXProcess.java:80)
java.lang.UNIXProcess.<init>(UNIXProcess.java:161)
java.lang.ProcessImpl.start(ProcessImpl.java:81)
java.lang.ProcessBuilder.start(ProcessBuilder.java:468)

Here's what strace tells me:

$ sudo strace -p 13255
Process 13255 attached - interrupt to quit
futex(0x7fbb673e49d0, FUTEX_WAIT, 13262, NULL

Is this related?: http://stackoverflow.com/questions/1043611/failure-to-start-program-from-java-using-processbuilder?rq=1 — Baz, Aug 01 '12 at 09:25
while (input.readLine() != null) {} // empty while is this like this only in your original code — Harmeet Singh, Aug 01 '12 at 09:25
http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=2 — LiuYan 刘研, Aug 01 '12 at 09:40
@Baz, yes, it's related. I've tried moving the closing of the strims after the wait, as suggested there, but that didn't have an effect. — alexsb, Aug 01 '12 at 09:46
@LiuYan - I've read the Java World Article and am aware of the problems. The code there is from 2000 and ProcessBuilder is a better choice in my opinion. I've tried it to, but had similar problems — alexsb, Aug 01 '12 at 09:46
Can you confirm that it hangs at `p.waitFor()`, not at `input.readLine()`? And, print the result of `input.readLine()` may help debugging. — LiuYan 刘研, Aug 01 '12 at 11:33
I checked again, and it does not hang at waitFor() (I corrected that in the original answer) but at pb.start(); Thanks for the hint! There is nothing read in any situation, but it never geht's there when it hangs. — alexsb, Aug 01 '12 at 11:42
What OS are you on? If you are on linux, you might want to use `strace` to see what syscalls the processes are currently executing. Might or might not be helpful, but worth a try. — MvG, Aug 01 '12 at 12:04
Thanks @MvG I'm on linux. The output seems to not be very helpful: $ sudo strace -p 13255 [sudo] password for alexsb: Process 13255 attached - interrupt to quit futex(0x7fbb673e49d0, FUTEX_WAIT, 13262, NULL — alexsb, Aug 01 '12 at 15:46
@alexsb, I feared that futex thing might happen. But what about the child process? Has that started yet, and if so, where is it blocked? — MvG, Aug 01 '12 at 18:26

score 0 · Answer 1 · answered May 23 '13 at 16:29

We also observed such problem on CentOS 6.3 JDK 1.6.0_33-b03. Investigation showed that this happens after OutOfMemoryError has happened in this Java process.

Looking to the code of class java.lang.UNIXProcess I suppose that such problem may happen when a non-IO Exception (e.g. an Error) gets thrown in the separate thread run within the UNIXProcess constructor, somewhere between lines 109 and 130. This code would better be organized as

try {
  .....
} finally {
  gate.exit();
}

, but instead it is organized as

try {
  ...
} catch (IOException e) {
  gate.setException(e); /*remember to rethrow later*/
  gate.exit();
  return;
}
...
gate.exit();

, so a non-IO exception may cause gate.exit() not to be called, what causes the main caller thread to hang up forever in method gate.waitForExit() (line 145).

Executing process with ProcessBuilder causes hang on waitFor

1 Answers1