[New-bugs-announce] [issue13812] multiprocessing package doesn't flush stderr on child exception

[Jon Brandvein]

New submission from Jon Brandvein <jon.brandvein at gmail.com>:

When a child process exits due to an exception, a traceback is written, but stderr is not flushed. Thus I see a header like "Process 1:\n", but no traceback.

I don't have a development environment or any experience with Mecurial, so I'm afraid there's no patch, but it's a one-liner.

In   /Lib/multiprocess/process.py :: Process._bootstrap

    except:
        exitcode = 1
        import traceback
        sys.stderr.write('Process %s:\n' % self.name)
        sys.stderr.flush()
        traceback.print_exc()

Append a "sys.stderr.flush()" to the suite.

It surprised me that flushing was even necessary. I would've thought that the standard streams would all be closed just before the process terminated, regardless of exit status. But I observe that unless I explicitly flush stdout and stderr before terminating, the output is lost entirely, even if the exit is not abnormal. This isn't the desired behavior, is it?

----------
components: Library (Lib)
messages: 151508
nosy: brandj
priority: normal
severity: normal
status: open
title: multiprocessing package doesn't flush stderr on child exception
type: behavior
versions: Python 3.2, Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue13812>
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