求100000个浮点数的和。要求：
（1）随机生成100000个浮点数（父进程）；
（2）然后创建4个后代进程，分别求25000个浮点数的和；
（3）父进程对4个后代进程的结果求和；
（4）进程间用共享内存进行通信，用信号量实现同步和互斥。要求在创建子进程之后，由父进程创建共享缓冲区和信号量。

#include <stdio.h>
#include <sys/mman.h>   //共享内存
#include <semaphore.h>  //信号量
#include <fcntl.h>      //O_* 宏定义
#include <stdlib.h>
#include <unistd.h>
#include <time.h>double num[5][25000];//放随机数double sum_calculate(int i)
{int k;double totalsum=0;for(k=1; k<=25000; k++)totalsum += num[i][k];return totalsum;
}int main()
{//数组从1开始double sum[5] = {0.0};//放四个进程的计算和srand((unsigned int)time(0));//初始化种子为随机值//随机生成100000浮点数int i,j,k;for(i=1; i<=4; i++)for(j=1; j<=25000; j++)num[i][j] = (double)rand()/(double)RAND_MAX;//随机数转换为double类型//父进程//创建共享内存,调整大小后，并将其映射到进程的地址空间int shmem_fd = shm_open("data_buffer", O_RDWR|O_CREAT, 0666);ftruncate(shmem_fd, sizeof(double)*4+sizeof(int)*2);double *ptr = mmap(NULL, sizeof(double)*4+sizeof(int)*2, PROT_READ | PROT_WRITE, MAP_SHARED, shmem_fd, 0);//利用信号量实现父进程与子进程的同步/互斥sem_t *w = sem_open("lock", O_CREAT, 0666, 1);sem_t *s = sem_open("lock",O_CREAT,0666,0);pid_t pid;int ret;for(i=1; i<=4; i++){pid = fork();if(pid < 0){printf("fork error");exit(1);}else if(pid == 0)//子进程{//实现同步sem_wait(s);int shmem_fd = shm_open("data_buffer", O_RDWR | O_CREAT, 0666);ftruncate(shmem_fd, sizeof(double)*4+sizeof(int)*2);double *ptr = mmap(NULL, sizeof(double)*4+sizeof(int)*2, PROT_READ | PROT_WRITE, MAP_SHARED, shmem_fd, 0);sum[i] = sum_calculate(i);printf("(%d)Child_%d sum:%.3f\n",getpid(),i,sum[i]);//利用信号量实现互斥，将数据写入sem_wait(w);*(ptr+i) = sum[i];sem_post(w);//解除地址映射ret = munmap(ptr, sizeof(double)+sizeof(int)*2);if(ret<0){perror("munmap");}exit(1);}else{sem_post(s);}}double totalsum_1=0,totalsum_2=0;for(j=1; j<=4; j++){for(k=1; k<=25000; k++)totalsum_1 += num[j][k];}sem_wait(w);for(int j = 1; j <= 4; j++){totalsum_2 += ptr[j];}sem_post(w);printf("(%d)Parent direct sum:%.3f,sum from chilren:%.3f\n",getpid(),totalsum_1,totalsum_2);//释放ret = shm_unlink("data_buffer");if(ret < 0){perror("shm_unlink");exit(-1);}ret = munmap(ptr, sizeof(double)*4+sizeof(int)*2);if(ret < 0){perror("munmap");}ret = sem_unlink("lock");if(ret < 0){perror("sem_unlink");exit(-1);}return 0;
}

运行结果：