[Numpy-discussion] Non-deterministic test failure in master

[David Cournapeau]

On Thu, Jun 28, 2012 at 8:06 PM, Nathaniel Smith <njs at pobox.com> wrote:
> On Thu, Jun 28, 2012 at 7:13 AM, Pierre Haessig
> <pierre.haessig at crans.org> wrote:
>> Hi Nathaniel,
>> Le 27/06/2012 20:22, Nathaniel Smith a écrit :
>>> According to the Travis-CI build logs, this code produces
>>> non-deterministic behaviour in master:
>> You mean non-deterministic across different builds, not across different
>> executions on the same build, right ?
>>
>> I just ran a small loop :
>>
>> N = 10000
>> N_good = 0
>> for i in range(N):
>>    a = np.arange(5)
>>    a[:3] = a[2:]
>>    if (a == [2,3,4,3,4]).all():
>>        N_good += 1
>> print 'good result : %d/%d' % (N_good, N)
>>
>> and got 100 % good replication.
>
> Yes, the current hypothesis is that there is one particular Travis-CI
> machine on which memcpy goes backwards, and so the test fails whenever
> the build gets assigned to that machine. (Apparently this is actually
> faster on some CPUs, and new versions of glibc are known to exploit
> this.)

see also this: https://bugzilla.redhat.com/show_bug.cgi?id=638477

David