#include "../common/common.h"
int main(void)
{
  pid_t pid;

  if ((pid = fork()) < 0) {
    perror("fork error");
    return EXIT_FAILURE;
  } else if (0 == pid) {
    printf("[%ld] child process is running...\n", (long)getpid());
    _exit(0);
  }

  //sleep(15);

  if (waitpid(pid, NULL, 0) < 0) {
    perror("waitpid error");
    return EXIT_FAILURE;
  }

  for (; ;) {
    pause();
  }
  return EXIT_SUCCESS;
}

#include <sys/wait.h>
#include "../common/common.h"
int main(void)
{
  pid_t pid;

  if ((pid = fork()) < 0) {
    perror("fork error");
    return EXIT_FAILURE;
  } else if (0 == pid) {
    printf("first child is running..\n"); 
    /**在第一个子进程中再次fork***/
    if ((pid = fork()) < 0) {
      perror("fork error");
      return EXIT_FAILURE;
    } else if (pid > 0) {/**父进程退出**/
      printf("[%ld] first child is exit...\n", (long)getpid());
      _exit(0);
    }

    sleep(2);/**确保父进程先运行**/
    printf("second process pid: %ld, second process's parent pid: %ld\n", (long)getpid(), (long)getppid()); 
    //sleep(15);
    printf("[%ld] is exit..\n", (long)getpid());
    _exit(0);
  }

  /***获得第一个子进程的退出状态***/
  if (waitpid(pid, NULL, 0) < 0) {
    perror("waitpid error");
    return EXIT_FAILURE;
  }

  for(;;)
    pause();
  return EXIT_SUCCESS;
}

#include <signal.h>
#include "../common/common.h"
int main(void)
{
  /***显示忽略SIGCHLD信号****/
  if (signal(SIGCHLD, SIG_IGN) == SIG_ERR) {
    perror("signal error");
    return EXIT_SUCCESS;
  }

  pid_t pid;
  int i;
  /**产生10个子进程***/
  for (i=0; i<10; ++i) {
    if ((pid = fork()) < 0) {
      perror("fork error");
      return EXIT_FAILURE;
    } else if (0 == pid) {
      _exit(0);
    }
    sleep(2);
    continue;
  }

  for (; ;)
    pause();
  return EXIT_SUCCESS;
}

#include <signal.h>
#include <sys/wait.h>
#include "../common/common.h"
void sig_chld(int signo);
int main(void)
{
  /**捕获此信号, 此刻系统会立刻检测是否有次信号产生**/
  if (signal(SIGCHLD, sig_chld) == SIG_ERR) {
    handler_err("signal error to SIGCHLD");
  }

  pid_t pid;
  int i;
  for (i=0; i<10; i++) {

    if ((pid = fork()) < 0) {
      handler_err("fork error");
    } else if (0 == pid) {
      printf("child pid: %d\n", getpid());
      _exit(0);
    } 

    sleep(1);
    continue;
  }

  for (; ;) {
    pause();
  }  
  return EXIT_SUCCESS;
}

/**捕获到信号后会立刻执行此段代码***/
void sig_chld(int signo)
{
  printf("receive child signal\n");
  if (waitpid(-1, NULL, 0) < 0) {
    perror("waitpid error");
  }

  if (signal(SIGCHLD, sig_chld) == SIG_ERR) {
    perror("signal error to SIGCHLD");
  }
}