Re: System.out and System.err

From:

=?ISO-8859-1?Q?Jan_Thom=E4?= <janthomae@janthomae.de>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 2 Oct 2008 08:26:33 +0200

Message-ID:

<6kj7spF86252U1@mid.individual.net>

On 2008-10-02 00:09:52 +0200, "Mike Schilling"
<mscottschilling@hotmail.com> said:

I think we all assume that access to System.out and System.err is
thread-safe; if we write to them from more than one threads, the worst
that will happen is output getting interleaved but not lost, nor will
exceptions be caused by unsynchronized access (e.g., we don't expect
internal bufferr-copying routines to get confused.) Looking, though,
I can't find this guarnteed anywhere. Can anyone point to an offical
statement about it?

Well the only "official" statement I have found looking at the
implementation of PrintStream which System.out and System.err are
internally. The write( .... ) methods are all internally synchronized,
so they will not produce weird results when multiple threads access
them:

public void write(int b) {
    try {
        synchronized (this) {
        ensureOpen();
        out.write(b);
        if ((b == '\n') && autoFlush)
            out.flush();
        }
    }
    catch (InterruptedIOException x) {
        Thread.currentThread().interrupt();
    }
    catch (IOException x) {
        trouble = true;
    }
    }