[Bug c/50675] New: master and single OpenMP constructs broken

[Bug c/50675] New: master and single OpenMP constructs broken

[markflorisson88 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50675

             Bug #: 50675
           Summary: master and single OpenMP constructs broken
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: markflorisson88@gmail.com


single and master do not work properly in loops. They are either not executed
as often as they should, or the program deadlocks entirely:

#include <stdio.h>

int main(int argc, char **argv) {
    int i;
    #pragma omp parallel
    {
        for (i = 0; i < 10; i++) {
            #pragma omp single
            puts("hello");
        }
    }
    return 0;
}

This program deadlocks in gcc 4.4 and 4.6, whereas in 4.2 is is only executed 4
times (which is the number of cores on my machine). The same goes for the
master construct.

[Bug c/50675] master and single OpenMP constructs broken

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50675

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-10-09 13:41:54 UTC ---
User error.  The i variable is shared in your testcase, thus different threads
may encounter #pragma omp single different number of times, which is invalid.
Just use #pragma omp parallel private (i) or declare i inside of the #pragma
omp parallel block instead.

[Bug c/50675] master and single OpenMP constructs broken

[markflorisson88 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50675

--- Comment #2 from markflorisson88 <markflorisson88 at gmail dot com> 2011-10-09 13:46:27 UTC ---
Indeed, you are right. My apologies, I should teach myself to use
default(none).