process - Java hangs when trying to close a ProcessBuilder OutputStream

Question

I have the following Java code to start a ProcessBuilder, open an OutputStream, have the process write a string to an OutputStream, and then close the OutputStream. The whole thing hangs indefinitely when I try to close the OutputStream. This only happens on Windows, never on Mac or Linux.

Some of the related questions seem to be close to the same problem I'm having, but I haven't been able to figure out how to apply the answers to my problem, as I am a relative newbie with Java. Here is the code. You can see I have put in a lot of println statements to try to isolate the problem.

    System.out.println("GenMic trying to get the input file now");
    System.out.flush();
    OutputStream out = child.getOutputStream();
    try {
        System.out.println("GenMic getting ready to write the input file to out");
        System.out.flush();
        out.write(intext.getBytes());  // intext is a string previously created
        System.out.println("GenMic finished writing to out");
        System.out.flush();
        out.close();
        System.out.println("GenMic closed OutputStream");
        System.out.flush();
    } catch (IOException iox) {
        System.out.println("GenMic caught IOException 2");
        System.out.flush();
        String detailedMessage = iox.getMessage();
        System.out.println("Exception: " + detailedMessage);
        System.out.flush();
        throw new RuntimeException(iox);
    }

And here is the output when this chunk is executed:

GenMic trying to get the input file now

GenMic getting ready to write the input file to out

GenMic finished writing to out

Answer 1

When that happened to me it was because I hadn't read everything from the stream being written to by the process.

The API docs for the java.lang.Process class say:

The created subprocess does not have its own terminal or console. All its standard io (i.e. stdin, stdout, stderr) operations will be redirected to the parent process through three streams (getOutputStream(), getInputStream(), getErrorStream()). The parent process uses these streams to feed input to and get output from the subprocess. 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 would try calling getInputStream() on the Process instance and writing a loop to read one byte at a time until it reaches EOF. And I'd do the same thing with getErrorStream() just in case the process is writing to stderr.