[Bug libgomp/40494] New: omp for loop with guided schedule fails to terminate in certain cases

[Bug libgomp/40494] New: omp for loop with guided schedule fails to terminate in certain cases

[per at bitempire dot com]

The following loop, which seems valid according to the OpenMP specification
v2.5 and 3.0 fails to terminate:

int x;
#pragma omp parallel for schedule(guided)
for(x = 3; x < 478; x += 2) {
  ...
}

I've tested with two and eight threads and different chunksizes, with the same
non-termination result. Changing the upper bound to 477, however, makes the
loop terminate, which leads me to belive this is an issue in the GNU OpenMP
runtime library.

I have confirmed that the problems exists in 4.2, 4.3 and 4.5 (trunk,
19-06-09). To me,  bug 35625 seems somewhat similar but was supposedly fixed in
4.3.

/Per


-- 
           Summary: omp for loop with guided schedule fails to terminate in
                    certain cases
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: per at bitempire dot com
 GCC build triplet: i686-pc-linux
  GCC host triplet: i686-pc-linux
GCC target triplet: i686-pc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40494

[Bug libgomp/40494] omp for loop with guided schedule fails to terminate in certain cases

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2009-07-10 10:43 -------
Sorry, can't reproduce this.

extern void abort (void);

int
main (void)
{
  int x, y = 0;
  #pragma omp parallel for schedule(guided) reduction(+:y)
  for (x = 3; x < 478; x += 2)
    y++;
  if (y != 238)
    abort ();
  return 0;
}

works just fine with current 4.4 or trunk, both x86_64-linux -m32 and -m64,
OMP_NUM_THREADS={1,2,4,8,16,32,64}.  Are you sure you were not testing
everything against gcc 4.2 libgomp.so?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40494

[Bug libgomp/40494] omp for loop with guided schedule fails to terminate in certain cases

[per at bitempire dot com]

------- Comment #2 from per at bitempire dot com  2009-07-28 11:23 -------
Sorry, you're right - it works fine with gcc 4.3 and later. I must have
accidentally linked to libgomp 4.2 which is a part of llvm-gcc.

I apologize for the inconvenience.


-- 

per at bitempire dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40494