Properly closing Java Process InputStream from getInputStream

Question

I could not find clarification of this in the documentation. But when we have a Process object and call getInputStream(),

Do we get a new stream that we should explicitly close when we are done with it? or do we get the stream that is already there, associated with the Process, that we should not close, but the Process would take care of closing it?

Basically, how should we interact with the stream we get from Process.getInputStream()? close or not to close?

Answer 1

From reading UNIXProcess.java, this is what happens:

We need to distinguish between two states: either process is still alive, or it is dead.

If the process is alive, by closing OutputStream (goes to stdin of the process), you are telling the process that there is no more input for it. By closing InputStreams (stdout, stderr of the process), process is no longer to write to these (it will get SIGPIPE if it tries).

When process dies, Java will buffer remaining data from stdout/stderr, and close all three streams for you (it is running "process reaper" thread, which is notified on process death). Any attempt to write to OutputStream will fail. Reading from InputStream will return buffered data, if any. Closing any of them has no benefit, but also causes no harm. (Underlying file descriptors are closed by this time).