[llvm-bugs] [Bug 50129] New: omp cancel parallel not working as expected

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50129

            Bug ID: 50129
           Summary: omp cancel parallel not working as expected
           Product: clang
           Version: trunk
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: OpenMP
          Assignee: unassignedclangbugs at nondot.org
          Reporter: michael.p.rice at intel.com
                CC: llvm-bugs at lists.llvm.org

The following test shows 'omp cancel' is not working as expected.  Run with:

OMP_CANCELLATION=true  ./a.out

It should quickly print:

Cancel happened as you would expect!

Clang will not cancel.

#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>

// Run with environment variable: OMP_CANCELLATION=true

int main(int argc, char **argv) {
  int* array;
  int nthreads, i, j;

  #pragma omp parallel
  #pragma omp single nowait
  nthreads = omp_get_num_threads();

  array = (int*)malloc(sizeof(int)*nthreads);
  for (i = 0; i < nthreads; ++i)
    array[i] = 0;

  assert(omp_get_cancellation() && "Need to set OMP_CANCELLATION=true");

  #pragma omp parallel
  {
    int tid = omp_get_thread_num();
    if (tid == 0) {
      // Master signals other threads that cancellation is in order
      // This thread will go to end of parallel right here
      // not at the cancellation point below
      #pragma omp cancel parallel
    }
    // Have worker threads sleep here for "long enough"
    usleep(1000000);
    #pragma omp barrier
    array[tid] = 1;
  }

  int errors = 0;
  for (i = 0; i < nthreads; ++i) {
    if (array[i] != 0) {
      printf("Thread %d made it through unexpectedly!\n", i);
      errors++;
    }
  }

  if (errors) {
    printf("%d errors occurred!\n", errors);
    exit(1);
  }

  printf("Cancel happened as you would expect!\n");

  return 0;
}

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