T13701 fails sporadically

T13701 fails sporadically, comments in D3586 indicate that it happens while the system is under load.

I reproduced this issue by duplicating T13701 7 times, making tests T13701[A-H], then running

make test TEST="T13701A T13701B T13701C T13701D T13701E T13701F T13701G T13701H THREADS=8"

on my box with 4 cpus.

Comparing profiling reports of the test under and not under load, I found the additional allocations to be in SysTools.builderMainLoop.loop. This function busy-waits from when 2 EOFs are received until getProcessExitCode returns a Just. That this is the cause was verified by changing

| otherwise -> loop chan hProcess t p exitcode

to

| otherwise -> threadDelay 10000 >> loop chan hProcess t p exitcode

Trac metadata

Trac field	Value
Version	8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Test Suite
Test case
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