Re: Data race within write intrinsic with output into a character variable

[Kay Diederichs <kay.diederichs@uni-konstanz.de>]

On 3/10/21 12:35 PM, Martin Stein via Fortran wrote:
> Hi,
> 
> I am seeing rare but reproducible memory corruptions which I can trace back to lines like
> 
> write(out,'(a,i8)') 'short string', k
> 
> where out is a (sufficiently large) character(len=...) variable and k some small integer. The line itself occurs in a subroutine called from within an openmp region.
> 
> I have seen this in two rather different circumstances. If I change the line to
> 
> out = 'short string' // toStr(k)
> 
> and write my own small toStr function, which translates an integer to its string representation, then the memory corruption (usually occuring shortly afterwards but on seemingly unrelated code) disappears.
> As out is usually not even used (it is a routine for debugging which only uses the output in case something goes wrong), I am pretty sure that the problem is within the write code.
> 
> Unfortunately I cannot create a small reproducer. As I have already seen data races/memory corruption with write (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88899 and https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88768) I am inclined to conclude that the write intrinsic is at fault here.
> 
> Any idea on how this can be further investigated? If write is indeed at fault, that would be pretty bad.
> 
> Best regards
> Martin
> 
> 

which version of gfortran, and which operating system?

Kay