exit和wait一起可以彻底清除子进程的资源

#include<stdio.h> #include<unistd.h> #include<sys/types.h> #include<stdlib.h> #include <errno.h> 

int main() { pid_t p1,p2,pr; int i; for(i=0;i<=2;i++) { if((p1=fork())==0) { printf("parent process%d child process%d\n",getppid(),getpid()); exit(0); //我发现把return 0替换为exit(0)也可以的！，不过编译器这两种的处理区别很大，以后再做解释

 } else{ pr=wait(NULL); //如果成功，wait会返回被收集的子进程的进程ID， //如果调用进程没有子进程，调用就会失败，此时wait返回-1，同时errno被置为ECHILD。

  if( pr>0) printf("I catched a child process with pid of %d\n", pr); else printf("error: %s\n.\n", strerror(errno)); } } return 0; } 输出结果如下： parent process4595 child process4596 I catched a child process with pid of 4596 parent process4595 child process4597 I catched a child process with pid of 4597 parent process4595 child process4598 I catched a child process with pid of 4598 当把exit注释后输出结果如下： parent process4642 child process4643 parent process4643 child process4644 parent process4644 child process4645 I catched a child process with pid of 4645 I catched a child process with pid of 4644 parent process4643 child process4646 I catched a child process with pid of 4646 I catched a child process with pid of 4643 parent process4642 child process4647 parent process4647 child process4648 I catched a child process with pid of 4648 I catched a child process with pid of 4647 parent process4642 child process4649 I catched a child process with pid of 4649

//重新执行一边的结果

parent process4657 child process4658 parent process4658 child process4659 parent process4659 child process4660 I catched a child process with pid of 4660 I catched a child process with pid of 4659 parent process4658 child process4661 I catched a child process with pid of 4661 I catched a child process with pid of 4658 parent process4657 child process4662 parent process4662 child process4663 I catched a child process with pid of 4663 I catched a child process with pid of 4662 parent process4657 child process4664 I catched a child process with pid of 4664 从上面的输出结果可以得出：exit可以用来释放进程的资源，必须加上，当注释掉时，可能因为子进程的资源没有 及时清理掉，所以导致wait阻塞住，不能及时清理掉子进程！ 总结：当进程发出exit该调用时，内核会释放进程占有的资源，释放进程上下文所占的内存空间，保留 进程表项，将进程表项中记录进程状态的关键字设为僵死状态。内核在进程收到不可扑捉的信号时，会从内核内部调用exit ，使得进程退出。父进程通过wait，并释放进程表项。