How is Java Process.getOutputStream() Implemented?

Question

I know the answer depends on the particular JVM, but I would like to understand how it is usually implemented? Is it in terms of popen (posix)? In terms of efficiency do I need to keep something in mind (other than using a Buffered stream as suggested by the javadoc). I would be interested to know if there is a general reference about implementations of JVMs which answers such questions.

Answer 1

Look at the source of JDK.

In this case, for Unix, look at UnixProcess class.it does a fork and exec and wraps file and buffer streams around native file descriptors.

pid = forkAndExec(prog,
              argBlock, argc,
      envBlock, envc,
      dir,
      redirectErrorStream,
      stdin_fd, stdout_fd, stderr_fd);
stdin_stream = new BufferedOutputStream(new FileOutputStream(stdin_fd));

For native code look at: native/java/lang/UNIXProcess_md.c

It does something interesting! it opens pipes and give them as STDIN, STDOUT, STDERR to child and other side of pipes are used by parent!

In short IPC mechanism is pipes.