[bug #15719] Test suite not reliable for parallel build support

[Michael Haubenwallner]

Follow-up Comment #9, bug #15719 (project make):

With cvs HEAD (as of 2012-12-09), I've seen TEST #11 ("thing1,thing2
start,end") sometimes failing, even without so much load on the Linux build
machine, where the diff output shows /missing/ lines.

Extracting this test and running in a loop with strace (test script attached)
shows the situation when output lines get lost:

When those two shells running the "echo thingX start; sleep 1; echo thingX
end" command do the write(1, "thingX ...") syscall (because echo being a
shell-builtin) at the same time (on different cores), one of the line is
overwritten by the other one.
However, I've seen this happening when the output is redirected to a file
only.

So indeed the tests seem fragile, for these two reasons:
1) It does expect the output lines from concurrent processes in a particular
order.
2) It does expect the output lines from concurrent processes redirected to one
stream to not overwrite each other.

But I've failed to find a spec about how the content is expected to be merged
when multiple processes concurrently write to a single file descriptor...

(file #27084)
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Additional Item Attachment:

File name: makebug-15719-test11.sh        Size:0 KB


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