From 3d794d2d80339b2be1e22baad13f99b2b81d91e5 Mon Sep 17 00:00:00 2001
From: Kai Bao <kai.bao@sintef.no>
Date: Thu, 8 Aug 2024 16:10:27 +0200
Subject: [PATCH] using std::from_chars instead of std::stoi

---
 opm/simulators/flow/FlowMain.hpp | 29 +++++++++++++-------------
 opm/simulators/flow/Main.hpp     | 35 ++++++++++++++++----------------
 2 files changed, 32 insertions(+), 32 deletions(-)

diff --git a/opm/simulators/flow/FlowMain.hpp b/opm/simulators/flow/FlowMain.hpp
index db2251599..8d1d72ac9 100644
--- a/opm/simulators/flow/FlowMain.hpp
+++ b/opm/simulators/flow/FlowMain.hpp
@@ -38,6 +38,7 @@
 #include <dune/common/parallel/mpihelper.hh>
 #endif
 
+#include <charconv>
 #include <cstddef>
 #include <memory>
 
@@ -376,28 +377,26 @@ namespace Opm {
             // OMP_NUM_THREADS is set or command line --threads-per-process used.
             // Issue a warning if both OMP_NUM_THREADS and --threads-per-process are set,
             // but let the environment variable take precedence.
-            const int default_threads = 2;
+            constexpr int default_threads = 2;
             const int requested_threads = Parameters::get<TypeTag, Parameters::ThreadsPerProcess>();
             int threads = requested_threads > 0 ? requested_threads : default_threads;
 
             const char* env_var = getenv("OMP_NUM_THREADS");
-            int omp_num_threads = -1;
-            try {
-                if (env_var) {
-                    omp_num_threads = std::stoi(env_var);
+            if (env_var) {
+                int omp_num_threads = -1;
+                auto result = std::from_chars(env_var, env_var + std::strlen(env_var), omp_num_threads);
+                if (result.ec == std::errc() && omp_num_threads > 0) {
+                    // Set threads to omp_num_threads if it was successfully parsed and is positive
+                    threads = omp_num_threads;
+                    // Warning in 'Main.hpp', where this code is duplicated
+                    // if (requested_threads > 0) {
+                    //     OpmLog::warning("Environment variable OMP_NUM_THREADS takes precedence over the --threads-per-process cmdline argument.");
+                    // }
+                } else {
+                    OpmLog::warning("Invalid value for OMP_NUM_THREADS environment variable.");
                 }
-            } catch (const std::invalid_argument& e) {
-                // Do nothing if an invalid_argument exception is caught
             }
 
-            // Set threads to omp_num_threads if it was successfully parsed and is positive
-            if (omp_num_threads > 0) {
-                threads = omp_num_threads;
-                // Warning in 'Main.hpp', where this code is duplicated
-                // if (requested_threads > 0) {
-                //     OpmLog::warning("Environment variable OMP_NUM_THREADS takes precedence over the --threads-per-process cmdline argument.");
-                // }
-            }
             // We are not limiting this to the number of processes
             // reported by OpenMP as on some hardware (and some OpenMPI
             // versions) this will be 1 when run with mpirun
diff --git a/opm/simulators/flow/Main.hpp b/opm/simulators/flow/Main.hpp
index 991320833..cd1e460cb 100644
--- a/opm/simulators/flow/Main.hpp
+++ b/opm/simulators/flow/Main.hpp
@@ -77,6 +77,7 @@
 #endif
 
 #include <cassert>
+#include <charconv>
 #include <cstdlib>
 #include <filesystem>
 #include <iostream>
@@ -713,28 +714,28 @@ private:
         // This function is called before the parallel OpenMP stuff gets initialized.
         // That initialization happens after the deck is read and we want this message.
         // Hence we duplicate the code of setupParallelism to get the number of threads.
-        static bool first_time = true;        
-        const int default_threads = 2;
+        static bool first_time = true;
+        constexpr int default_threads = 2;
         const int requested_threads = Parameters::get<TypeTag, Parameters::ThreadsPerProcess>();
         threads = requested_threads > 0 ? requested_threads : default_threads;
 
         const char* env_var = getenv("OMP_NUM_THREADS");
-        int omp_num_threads = -1;
-        try {
-            if (env_var) {
-                omp_num_threads = std::stoi(env_var);
+        if (env_var) {
+            int omp_num_threads = -1;
+            auto result = std::from_chars(env_var, env_var + std::strlen(env_var), omp_num_threads);
+            const bool can_output = first_time && FlowGenericVanguard::comm().rank() == 0;
+            if (result.ec == std::errc() && omp_num_threads > 0) {
+                // Set threads to omp_num_threads if it was successfully parsed and is positive
+                threads = omp_num_threads;
+                if (can_output && requested_threads > 0) {
+                    std::cout << "Warning: Environment variable OMP_NUM_THREADS takes precedence over the --threads-per-process cmdline argument."
+                              << std::endl;
+                }
+            } else {
+                if (can_output) {
+                    std::cout << ("Warning: Invalid value for OMP_NUM_THREADS environment variable.") << std::endl;
+                }
             }
-        } catch (const std::invalid_argument&) {
-            // Do nothing if an invalid_argument exception is caught
-        }
-
-        // Set threads to omp_num_threads if it was successfully parsed and is positive
-        if (omp_num_threads > 0) {
-            if (first_time && FlowGenericVanguard::comm().rank() == 0 && requested_threads > 0) {
-                std::cout << "Warning: Environment variable OMP_NUM_THREADS takes precedence over the --threads-per-process cmdline argument."
-                          << std::endl;
-            }
-            threads = omp_num_threads;
         }
 
         first_time = false;