Data race within write intrinsic with output into a character variable

[Tobias Burnus]

Hi Martin,

On 10.03.21 21:40, mscfd via Fortran wrote:
> Using helgrind on a simple omp do loop with write to
> a character variable, I get some possible data races
> in libgfortran/io/unit.c.

[...]

Thanks for digging. I have filled https://gcc.gnu.org/PR99529

> There global array newunits is
> allocated and possibly reallocated in
> "newunit_alloc". According to the lock outputs from
> helgrind I see that this routine is called even if
> output is into a character variable. [...]
Concur - I don't know why this is needed (it is clearly done in
purpose), but I only know libgfortran's I/O superficially.
> Could it be that the corresponding write routine in
> transfer.c which calls newunit_free does not obtain
> the necessary lock. I cannot find it (which does not
> count for much).

Glancing at the code, I came to the same conclusion (see patch in the
linked PR). But I have not tried whether it helps. But at least it compiles.

Thus, if you could test whether it helps on your side? Otherwise, I hope
that Jerry chimes in.

Tobias

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