scheduler_priorities.cpp

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/******************************************************************************
** Copyright © 2019 by J.M.McGuiness, coder@hussar.me.uk
**
** This library is free software; you can redistribute it and/or
** modify it under the terms of the GNU Lesser General Public
** License as published by the Free Software Foundation; either
** version 2.1 of the License, or (at your option) any later version.
**
** This library is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
** Lesser General Public License for more details.
**
** You should have received a copy of the GNU Lesser General Public
** License along with this library; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
 
#include "../core/application.hpp"
 
#include <boost/exception/diagnostic_information.hpp>
#include <boost/program_options.hpp>
 
#include <filesystem>
#include <fstream>
#include <iostream>
 
#include <sys/time.h>
#include <sys/resource.h>
 
constexpr const char copyright[]=
"/******************************************************************************\n"
"** Copyright © 2019 by J.M.McGuiness, coder@hussar.me.uk\n"
"**\n"
"** This library is free software; you can redistribute it and/or\n"
"** modify it under the terms of the GNU Lesser General Public\n"
"** License as published by the Free Software Foundation; either\n"
"** version 2.1 of the License, or (at your option) any later version.\n"
"**\n"
"** This library is distributed in the hope that it will be useful,\n"
"** but WITHOUT ANY WARRANTY; without even the implied warranty of\n"
"** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n"
"** Lesser General Public License for more details.\n"
"**\n"
"** You should have received a copy of the GNU Lesser General Public\n"
"** License along with this library; if not, write to the Free Software\n"
"** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA\n"
"*/\n";
constexpr const char header_guard_postfix[]="#endif\n";
 
/**
   \todo This cannot be set unless CAP_SYS_RESOURCE is applied.
 
      const int schedule_policy=SCHED_FIFO;
 
   This may be done thus:
 
      sudo setcap 'CAP_SYS_RESOURCE=+ep' /path/to/executable
 
   If SCHED_OTHER is used then basically one cannot set the priority, as the min & max are both set to zero.
*/
const int schedule_policy=SCHED_OTHER;
 
using namespace jmmcg::LIBJMMCG_VER_NAMESPACE;
 
struct header_guard_t {
   std::ostream &os;
 
      header_guard_t(std::string const &exe, std::string const &fname, std::ostream &s) noexcept(false)
   : os(s) {
      os
         <<"#ifndef LIBJMMCG_UNIX_"<<std::filesystem::path(fname).stem().string()<<"_HPP\n"
            "#define LIBJMMCG_UNIX_"<<std::filesystem::path(fname).stem().string()<<"_HPP\n"
         <<copyright
         <<"// Auto-generated header file.\n"
            "// DO NOT EDIT. IT WILL BE OVERWRITTEN.\n"
            "// Version: " LIBJMMCG_VERSION_NUMBER "\n"
            "// O/S info: '" LIBJMMCG_SYSTEM_NAME << "', specifically: '" LIBJMMCG_SYSTEM "'\n"
            "/**\n"
            "\t\\file The constants created in this file are used in api_threading_traits::set_kernel_priority(), so must not be manually doctored! To re-generate this file for your O/S, run '"<<exe<<"' in the installation directory as a suitable user.\n"
            "*/\n"
            "namespace jmmcg { namespace LIBJMMCG_VER_NAMESPACE { namespace ppd { namespace private_ {\n";
   }
   ~header_guard_t() noexcept(false) {
      os<<"} } } }\n"
         <<header_guard_postfix;
   }
};
 
auto get_sched_min_max() noexcept(false) {
   rlimit lim{};
   int err=::getrlimit(RLIMIT_NICE, &lim);
   if (err==-1) {
      throw std::runtime_error("Failed to get the rlimit of the priorities.");
   }
   lim.rlim_cur=lim.rlim_max;
   err=::setrlimit(RLIMIT_NICE, &lim);
   if (err==-1) {
      throw std::runtime_error("Failed to update the rlimit of the priorities.");
   }
   const int max_priority=sched_get_priority_max(schedule_policy);
   const int min_priority=sched_get_priority_min(schedule_policy);
   if ((max_priority!=-1) && (min_priority!=-1)) {
      return std::make_pair(min_priority, max_priority);
   } else {
      throw std::runtime_error("Failed to get the max & min priorities of the scheduler.");
   }
}
 
/// Discover the minimum and maximum scheduler-priorities on the current system.
int
main(int argc, char const * const *argv) noexcept(true) {
   try {
      boost::program_options::options_description general(
         "A program to discover the minimum and maximum scheduler-priorities on the current system and put them into a C++ header-file. For details regarding the properties of this program, see the documentation that came with the distribution. Copyright © J.M.McGuiness, coder@hussar.me.uk. http://libjmmcg.sf.net/ Distributed under the terms of the GPL v2.1.\n"+exit_codes::to_string()+"Arguments"
      );
      general.add_options()
         ("help", "Print this help message.")
         ("version", "Print the build number of this program.")
      ;
      boost::program_options::options_description prog_opts("Program options.");
      prog_opts.add_options()
         ("cpp_header", boost::program_options::value<std::string>()->required(), "The file-path of the output C++ header-file.")
      ;
      boost::program_options::options_description all("All options.");
      all.add(general).add(prog_opts);
      boost::program_options::variables_map vm;
      boost::program_options::store(boost::program_options::parse_command_line(argc, argv, all), vm);
      if (vm.count("help")) {
         std::cout<<all<<std::endl;
         return exit_codes::exit_print_help;
      }
      if (vm.count("version")) {
         std::cout<<LIBJMMCG_DETAILED_VERSION_INFO<<std::endl;
         return exit_codes::exit_print_version;
      }
      boost::program_options::notify(vm);
 
      std::ofstream cpp_header(vm["cpp_header"].as<std::string>().c_str());
      const header_guard_t header_guard(std::filesystem::path(argv[0]).filename().string(), vm["cpp_header"].as<std::string>(), cpp_header);
      auto const &sched_min_max=get_sched_min_max();
      cpp_header
         <<"\nenum scheduler_policy : int {\n"
         <<"\tschedule_policy="<<schedule_policy<<"\n"
         "};\n"
         "\nenum scheduler_min_max_priorities : int {\n"
         "\tscheduler_min_priority="<<sched_min_max.first<<",\n"
         "\tscheduler_max_priority="<<sched_min_max.second<<"\n"
         "};\n\n";
 
      return exit_codes::exit_success;
   } catch (std::exception const &ex) {
      std::cerr<<"STL-derived exception. Details: "<<boost::diagnostic_information(ex)<<std::endl;
      return exit_codes::exit_stl_exception;
   } catch (...) {
      std::cerr<<"Unknown exception."<<std::endl;
      return exit_codes::exit_unknown_exception;
   }
   return exit_codes::exit_unknown_failure;
}