jomarbueyes@[EMAIL PROTECTED]
writes:
> On Apr 27, 5:14 pm, Charles Coldwell <coldw...@[EMAIL PROTECTED]
> wrote:
>>
>> IIUC, the problem was in a section of code that looks something like
>> this:
>>
>> !$omp parallel do private(wk, i2, i1) shared(x, z)
>> do i2 = 1, N2
>> do i1 = 1, N1
>> wk(i1) = x(i1, i2)
>> end do
>> call <NetLibSubroutine>(wk, z, <other stuff>)
>> do i1 = 1, N1
>> x(i1, i2) = wk(i1)
>> end do
>> !$omp end parallel do
>>
>> The problem here is most likely coming in the second DO loop.
>> Although wk is private, x is shared, and all the threads are executing
>> the same iterations over i1, and therefore clobbering each other's
>> lvalues.
>
> Thank you for your answer. I am a bit puzzled about your explanation
> that the threads are clobbering each other's lvalues in the second
> loop. I might be missing something in the way that OpenMP works. As I
> understand, the parallel do directive before the outer loop will make
> sure that different threads use different non-overlaping sets of
> values of i2. Thus I'd expect that at a given time each thread is
> working on a different column of x, thus the memory location x(i1, i2)
> written too in the second inner loop is different for each thread
> (that is, even though all threads write to the same set of rows, they
> are writing different columns). Am I correct in this assumption or am
> I missing something fundamental about OpenMP?
No, you are correct. Sorry for the red herring. However, "z" is
shared in the example above. So if several threads are calling
"<NetLibSubroutine>(wk, z, <other stuff>)" simultaneously, could that
be the problem?
Chip
--
Charles M. "Chip" Coldwell
"Turn on, log in, tune out"
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