#include <stdio.h>
#include <pthread.h>
void* func(void* args) {
  printf("hello world from tid = %ld\n", pthread_self());
  return NULL;
}
int main() {
  pthread_t threads[4];
  for(int i = 0; i < 4; i++) {
    pthread_create(&threads[i], NULL, func, NULL);
  }
  for(int i = 0; i < 4; i++) {
    pthread_join(threads[i], NULL);
  }
  return 0;
}

#include <thread>
#include <iostream>
void* func() {
  printf("hello world from %ld\n", std::this_thread::get_id());
  return 0;
}
int main() {
  std::thread threads[4];
  for(auto &t : threads) {
    t = std::thread(func);
  }
  for(auto &t : threads) {
    t.join();
  }
  return EXIT_SUCCESS;
}

#include <stdio.h>
#include <omp.h>
int main() {
  // #pragma 表示這是編譯指導(dǎo)語(yǔ)句 表示編譯器需要對(duì)下面的并行域進(jìn)行特殊處理 omp parallel 表示下面的代碼區(qū)域 {} 是一個(gè)并行域 num_threads(4) 表示一共有 4 個(gè)線程執(zhí)行 {} 內(nèi)的代碼 因此實(shí)現(xiàn)的效果和上面的效果是一致的
  #pragma omp parallel num_threads(4)
  {
    printf("hello world from tid = %d\n", omp_get_thread_num()); // omp_get_thread_num 表示得到線程的線程 id
  }
  return 0;
}

#include <stdio.h>
#include <omp.h>
#include <unistd.h>
int main() {
  #pragma omp parallel num_threads(4)
  {
    printf("parallel region 1 thread id = %d\n", omp_get_thread_num());
    sleep(1);
  }
  printf("after parallel region 1 thread id = %d\n", omp_get_thread_num());
  #pragma omp parallel num_threads(4)
  {
    printf("parallel region 2 thread id = %d\n", omp_get_thread_num());
    sleep(1);
  }
  printf("after parallel region 2 thread id = %d\n", omp_get_thread_num());
  #pragma omp parallel num_threads(4)
  {
    printf("parallel region 3 thread id = %d\n", omp_get_thread_num());
    sleep(1);
  }
  printf("after parallel region 3 thread id = %d\n", omp_get_thread_num());
  return 0;
}

parallel region 1 thread id = 0
parallel region 1 thread id = 3
parallel region 1 thread id = 1
parallel region 1 thread id = 2
after parallel region 1 thread id = 0
parallel region 2 thread id = 0
parallel region 2 thread id = 2
parallel region 2 thread id = 3
parallel region 2 thread id = 1
after parallel region 2 thread id = 0
parallel region 3 thread id = 0
parallel region 3 thread id = 1
parallel region 3 thread id = 3
parallel region 3 thread id = 2
after parallel region 3 thread id = 0

#include <stdio.h>
#include <omp.h>
#include <math.h>
/// @brief 計(jì)算 x^2 一部分的面積
/// @param start 線程開(kāi)始計(jì)算的位置
/// @param end   線程結(jié)束計(jì)算的位置
/// @param delta 長(zhǎng)方形的邊長(zhǎng)
/// @return 計(jì)算出來(lái)的面積
double x_square_partial_integral(double start, double end, double delta) {
  double s = 0;
  for(double i = start; i < end; i += delta) {
    s += pow(i, 2) * delta;
  }
  return s;
}
int main() {
  int s = 0;
  int e = 10;
  double sum = 0;
  #pragma omp parallel num_threads(32) reduction(+:sum)
  {
    // 根據(jù)線程號(hào)進(jìn)行計(jì)算區(qū)間的分配
    // omp_get_thread_num() 返回的線程 id 從 0 開(kāi)始計(jì)數(shù) ：0, 1, 2, 3, 4, ..., 31
    double start = (double)(e - s) / 32 * omp_get_thread_num();
    double end   = (double)(e - s) / 32 * (omp_get_thread_num() + 1);
    sum = x_square_partial_integral(start, end, 0.0000001);
  }
  printf("sum = %lf\n", sum);
  return 0;
}