[lldb-dev] [Bug 25019] New: race in process return code collection in python test runner

[via lldb-dev]

https://llvm.org/bugs/show_bug.cgi?id=25019

            Bug ID: 25019
           Summary: race in process return code collection in python test
                    runner
           Product: lldb
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: lldb-dev at lists.llvm.org
          Reporter: todd.fiala at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

I have noticed that roughly 1 in 5 times, one of the process control child
process return code tests is failing.  It is receiving a 0 return code from the
process that was definitely returning a 10 value (verified in multiple ways).

This looks like it maybe similar to what was posted here:
http://stackoverflow.com/questions/31539749/python-subprocess-read-returncode-is-sometimes-different-from-returned-code

It looks like the root of it is that subprocess.Popen.communicate() indirectly
sets the return code, and wait() does as well.  And the mechanism by which this
happens is not thread safe.

Since this code is happening in two different threads of execution
(intentionally), this is going to be problematic.

I had initially torn out the communicate() call and replaced it with an
asyncore loop, which we can easily work in our own poll() check to manage
lifetime of the process.  There's a simple state flow that needs to happen
here.

I yanked that out since we didn't have the asyncore.file_dispatcher on the
Windows side.

I think we may need a simple stdout/stderr pipe pump that essentially does what
asyncore did, in a pure-python manner, so that we can make sure poll() happens
in a thread-safe manner.

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