linux下多线程C++运行时间统计

CMakeLists.txt

• 下面所有的代码的CMakeLists.txt如下

• cmake_minimum_required(VERSION 2.8)
  
  list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake/Modules)
  
  # else can not fin nullptr and so on.
  set (CMAKE_CXX_STANDARD 11)
  
  #project name
  project(thread_test)
  
  #debug
  set(CMAKE_BUILD_TYPE debug )
  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC -march=native -fopenmp -g2 -ggdb -lpthread")
  
  # thread_create
  set( EXE_NAME thread_create_test )
  set(APP_SRC thread_create.cpp)
  add_executable(${EXE_NAME} ${APP_SRC} )
  target_link_libraries(${EXE_NAME})
  

  clock

  • clock函数在ctime中，用于统计cpu时钟时间，在程序是单线程时，相对准确，但是如果开启多线程，则会出现很大误差。如下面的程序

    #include <iostream>
    #include <pthread.h>
    #include <unistd.h>
    
    #include <ctime>
    #include <unistd.h>
    #include <vector>
    
    using namespace std;
    
    void* thread_1(void*)
    {
        // clock_t t;
        // t = clock();
        for (int i = 0; i < 20000; ++i)
        {
            for (int j = 0; j < 20000; ++j)
            {
                int m = 2*3*4*5*6;
            }
        }
        // t = clock() - t;
        // cout << (unsigned int)pthread_self() << ", time : " << ((double)t)/CLOCKS_PER_SEC << "s" << endl;
    }
    
    
    // the two thread will run arandom order(simutaneously).
    int main()
    {
        cout << "pthread create test" << endl;
    
        int ret = 0;
        pthread_t th_id_1, th_id_2;
    
        clock_t t;
        t = clock();
        std::vector<pthread_t> vec_thread(10);
        for (int i = 0; i < vec_thread.size(); ++i)
        {
            ret = pthread_create( &vec_thread[i], NULL, thread_1, NULL );
            if( ret )
            {
                cout << "create thread 1 failed..." << endl;
                return -1;
            }
        }
    
        for (int i = 0; i < vec_thread.size(); ++i)
        {
            pthread_join( vec_thread[i], NULL );
        }
    
        t = clock() - t;
        cout << "all time : " << ((double)t)/CLOCKS_PER_SEC << "s" << endl;
    
        return 0;
    }

    运行需要1s左右，但是会记录10s左右的时间，因为每个线程中，cpu的clock都在计数，因此这个时间是不准确的。

  • time

    • time也在ctime中，它是记录系统时间，以s为最小单位，如下面的程序

    • #include <iostream>
      #include <pthread.h>
      #include <unistd.h>
      
      #include <ctime>
      #include <unistd.h>
      #include <vector>
      
      using namespace std;
      
      void* thread_1(void*)
      {
          // clock_t t;
          // t = clock();
          for (int i = 0; i < 20000; ++i)
          {
              for (int j = 0; j < 20000; ++j)
              {
                  int m = 2*3*4*5*6;
              }
          }
          // t = clock() - t;
          // cout << (unsigned int)pthread_self() << ", time : " << ((double)t)/CLOCKS_PER_SEC << "s" << endl;
      }
      
      
      // the two thread will run arandom order(simutaneously).
      int main()
      {
          cout << "pthread create test" << endl;
      
          int ret = 0;
          pthread_t th_id_1, th_id_2;
      
          time_t t;
          t = time(NULL);
          std::vector<pthread_t> vec_thread(10);
          for (int i = 0; i < vec_thread.size(); ++i)
          {
              ret = pthread_create( &vec_thread[i], NULL, thread_1, NULL );
              if( ret )
              {
                  cout << "create thread 1 failed..." << endl;
                  return -1;
              }
          }
      
          for (int i = 0; i < vec_thread.size(); ++i)
          {
              pthread_join( vec_thread[i], NULL );
          }
      
          double cost_t = time(NULL) - t;
          cout << "all time : " << cost_t  << "s" << endl;
      
          return 0;
      }