Fix #1667 Potential crash for the OpenMP multi-thread running.

Initialize the omp_partitions vector with the number of points, skip the for loop if the last partition has been calculated. A light-weight checker is added to verify the validation of the partition vector.

Author: Liang-N1

Common/src/linear_algebra/CSysMatrix.cpp

@@ -190,6 +190,7 @@ void CSysMatrix<ScalarType>::Initialize(unsigned long npoint, unsigned long npoi
 
   /*--- This is akin to the row_ptr. ---*/
   omp_partitions = new unsigned long [omp_num_parts+1];
+  for (unsigned long i = 0; i <= omp_num_parts; ++i) omp_partitions[i] = nPointDomain;
 
   /*--- Work estimate based on non-zeros to produce balanced partitions. ---*/
 
@@ -202,7 +203,17 @@ void CSysMatrix<ScalarType>::Initialize(unsigned long npoint, unsigned long npoi
     if (row_ptr_prec[iPoint] >= part*nnz_per_part)
       omp_partitions[part++] = iPoint;
   }
-  omp_partitions[omp_num_parts] = nPointDomain;
+
+  for (unsigned long thread = 0; thread < omp_num_parts; ++thread) {
+    const unsigned long begin = omp_partitions[thread];
+    const unsigned long end = omp_partitions[thread + 1];
+    if (begin > end) {
+      SU2_MPI::Error("Invalid nodes are distributed in the thread " + to_string(thread) + ".", CURRENT_FUNCTION);
+    } else if (begin == end) {
+      cout << "WARNING: Redundent thread has been detected. Performance could be impacted." << endl;
+      break;
+    }
+  }
 
   /*--- Generate MKL Kernels ---*/
 
@@ -707,6 +718,7 @@ void CSysMatrix<ScalarType>::BuildILUPreconditioner() {
   {
     const auto begin = omp_partitions[thread];
     const auto end = omp_partitions[thread+1];
+    if (begin == end) continue;
 
     /*--- Each thread will work on the submatrix defined from row/col "begin"
      *    to row/col "end-1" (i.e. the range [begin,end[). Which is exactly
@@ -784,6 +796,7 @@ void CSysMatrix<ScalarType>::ComputeILUPreconditioner(const CSysVector<ScalarTyp
   {
     const auto begin = omp_partitions[thread];
     const auto end = omp_partitions[thread+1];
+    if (begin == end) continue;
 
     ScalarType aux_vec[MAXNVAR];
 
@@ -846,6 +859,7 @@ void CSysMatrix<ScalarType>::ComputeLU_SGSPreconditioner(const CSysVector<Scalar
   {
     const auto begin = omp_partitions[thread];
     const auto end = omp_partitions[thread+1];
+    if (begin == end) continue;
 
     /*--- Each thread will work on the submatrix defined from row/col "begin"
      *    to row/col "end-1", except the last thread that also considers halos.
@@ -876,6 +890,8 @@ void CSysMatrix<ScalarType>::ComputeLU_SGSPreconditioner(const CSysVector<Scalar
   {
     const auto begin = omp_partitions[thread];
     const auto row_end = omp_partitions[thread+1];
+    if (begin == row_end) continue;
+
     /*--- On the last thread partition the upper
      *    product should consider halo columns. ---*/
     const auto col_end = (row_end==nPointDomain)? nPoint : row_end;