Add GetNumProc util helper (#533)

- add `GetNumProc` helper to util library
- test `GetNumProc`
- document new helper in env variables guide

Author: aobolensk

docs/user_guide/environment_variables.rst

@@ -5,6 +5,7 @@ The following environment variables can be used to configure the project's runti
 
 - ``PPC_NUM_PROC``: Specifies the number of processes to launch.
   Default: ``1``
+  Can be queried from C++ with ``ppc::util::GetNumProc()``.
 
 - ``PPC_NUM_THREADS``: Specifies the number of threads to use.
   Default: ``1``

modules/util/include/util.hpp

@@ -52,6 +52,7 @@ enum GTestParamIndex : uint8_t { kTaskGetter, kNameTest, kTestParams };
 
 std::string GetAbsoluteTaskPath(const std::string& id_path, const std::string& relative_path);
 int GetNumThreads();
+int GetNumProc();
 double GetTaskMaxTime();
 double GetPerfMaxTime();
 

modules/util/src/util.cpp

@@ -28,6 +28,14 @@ int ppc::util::GetNumThreads() {
   return 1;
 }
 
+int ppc::util::GetNumProc() {
+  const auto num_proc = env::get<int>("PPC_NUM_PROC");
+  if (num_proc.has_value()) {
+    return num_proc.value();
+  }
+  return 1;
+}
+
 double ppc::util::GetTaskMaxTime() {
   const auto val = env::get<double>("PPC_TASK_MAX_TIME");
   if (val.has_value()) {

modules/util/tests/util.cpp

@@ -108,3 +108,19 @@ TEST(GetPerfMaxTime, ReadsFromEnvironment) {
   env::detail::set_scoped_environment_variable scoped("PPC_PERF_MAX_TIME", "12.5");
   EXPECT_DOUBLE_EQ(ppc::util::GetPerfMaxTime(), 12.5);
 }
+
+TEST(GetNumProc, ReturnsDefaultWhenUnset) {
+  const auto old = env::get<int>("PPC_NUM_PROC");
+  if (old.has_value()) {
+    env::detail::delete_environment_variable("PPC_NUM_PROC");
+  }
+  EXPECT_EQ(ppc::util::GetNumProc(), 1);
+  if (old.has_value()) {
+    env::detail::set_environment_variable("PPC_NUM_PROC", std::to_string(*old));
+  }
+}
+
+TEST(GetNumProc, ReadsFromEnvironment) {
+  env::detail::set_scoped_environment_variable scoped("PPC_NUM_PROC", "4");
+  EXPECT_EQ(ppc::util::GetNumProc(), 4);
+}