Merge branch 'warning-parallel-papilo' into 'master'

add warning if PaPILO runs not sequential

See merge request integer/scip!3874

Author: ambros-gleixner

src/scip/presol_milp.cpp

@@ -532,7 +532,9 @@ SCIP_RETCODE performRationalPresolving(
 
    /* call presolving (without storing information for dual postsolve) */
    SCIPverbMessage(scip, SCIP_VERBLEVEL_HIGH, NULL,
-               "   (%.1fs) running MILP presolver\n", SCIPgetSolvingTime(scip));
+      "   (%.1fs) running MILP presolver%s\n", SCIPgetSolvingTime(scip),
+      presolve.getPresolveOptions().threads == 1 ? "" : " on multiple threads");
+
    int oldnnz = problem.getConstraintMatrix().getNnz();
 
 #if (PAPILO_VERSION_MAJOR >= 2)
@@ -1084,7 +1086,8 @@ SCIP_RETCODE performRealPresolving(
 
    /* call the presolving */
    SCIPverbMessage(scip, SCIP_VERBLEVEL_HIGH, NULL,
-               "   (%.1fs) running MILP presolver\n", SCIPgetSolvingTime(scip));
+      "   (%.1fs) running MILP presolver%s\n", SCIPgetSolvingTime(scip),
+      presolve.getPresolveOptions().threads == 1 ? "" : " on multiple threads");
 
    /* call presolving without storing information for dual postsolve */
 #if (PAPILO_VERSION_MAJOR >= 2)
@@ -1752,7 +1755,7 @@ SCIP_RETCODE SCIPincludePresolMILP(
          "maximum number of threads presolving may use (0: automatic)",
          &presoldata->threads, FALSE, DEFAULT_THREADS, 0, INT_MAX, NULL, NULL) );
 #else
-   presoldata->threads = DEFAULT_THREADS;
+   presoldata->threads = 1;
 #endif
 
    SCIP_CALL( SCIPaddIntParam(scip,