关于进程间通信的Linux小程序

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <signal.h>

const int key = 0x12345678;
static int pfd1[2], pfd2[2];

#define SHM_LEN (10*1024)
#define VAL_NUM 5

int init_shm() {
 int shmid = -1;

 shmid = shmget((key_t)key, SHM_LEN, 0666 | IPC_CREAT);
 if (shmid < 0) {
  printf("shmget failed!\n");
  exit(-1);
 }

 return shmid;
}

void cancel_shm(int shmid) {
 if (shmctl(shmid, IPC_RMID, 0) == -1) {
  printf("shmctl failed!\n");
  exit(-1);
 } 
 printf("cancel_shm successfully!\n");
}

void *shm_get(int shmid) {
 void *mem = NULL;

 mem = shmat(shmid, 0, 0);
 if (mem == (void *)-1) {
  printf("shmat failed!\n");
  exit(-1);
 }

 return mem;
}

int get_val(int *val, int num) {
 int i;
 for (i = 0; i < num; i++) {
  printf("please input a num:");
  scanf("%d", val + i);
 }
}
void show_val (int *val, int num) {
 int i;
 for (i = 0; i < num; i++) {
  printf("%d\t", *(val + i));
 }
 printf("\n");
}

int add_val (int *val, int num) {
 int result = 0;
 int i;
 
 for (i = 0; i < num; i++) {
  result += *(val + i);
 }

 return result;
}

int square_val (int *val, int num) {
 int result = 0;
 int i, tmp;

 for (i = 0; i < num; i++) {
  tmp = *(val + i);
  result += (tmp * tmp);
 }

 return result;
}

void TELL_WAIT (void) {
 if (pipe(pfd1) < 0 || pipe(pfd2) < 0) {
  printf("pipe error!\n");
  exit(-1);
 }
}

void TELL_PARENT (pid_t pid) {
 if (write(pfd2[1], "c", 1) != 1) {
  printf("write error!\n");
  exit(-1);
 }
}

void WAIT_PARENT (void) {
 char c;

 if (read(pfd1[0], &c, 1) != 1) {
  printf("read error!\n");
  exit(-1);
 }
}

void TELL_CHILD (pid_t pid) {
 if (write(pfd1[1], "p", 1) != 1) {
  printf("write error!\n");
  exit(-1);
 }
}

void WAIT_CHILD (void) {
 char c;

 if (read(pfd2[0], &c, 1) != 1) {
  printf("read error!\n");
  exit(-1);
 }
}

int main(int argc, char *argv[]) {
 void *mem = NULL;
 int shmid = -1;
 pid_t pid = -1;
 int val[VAL_NUM];
 int result = 0;

 shmid = init_shm();
 
 TELL_WAIT();
 if ((pid = fork()) < 0) {  //error
  printf("fork error!\n"); 
  exit(-1);
 } else if (pid == 0) {   //child
  int result = 0;

  WAIT_PARENT();

  mem = shm_get(shmid);  //get share memery

  memcpy(val, mem, sizeof(int) * VAL_NUM);
  result = square_val(val, VAL_NUM); 

  *(int *)((void *)mem + SHM_LEN - 4) = result;

  TELL_PARENT(pid);

  exit(1);
 } else {      //parent
  int child_result = 0;

  mem = shm_get(shmid);  //get share memery
  get_val(val, VAL_NUM);  //get user input
  memcpy(mem, val, sizeof(int) * VAL_NUM); //copy user input to share memery

  TELL_CHILD(pid);

  result = add_val(val, VAL_NUM);

  WAIT_CHILD();
  child_result = *(int *)((void *)mem + SHM_LEN - 4);
  printf("result:%d, child_result:%d, all:%d\n", result, child_result, result + child_result);
 }

 cancel_shm(shmid);

 return 0;
}