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5 wait和waitpid函数
当一个进程正常或异常终止时，内核就向其父进程发送SIGCHLD信号。
5.1调用wait或waitpid的进程可能会：
阻塞（如果其子进程都还在运行）
带子进程的终止状态立即返回
出错立即返回
5.2wait和waitpid的区别：
在一个子进程终止前， wait 使其调用者阻塞，而 waitpid 有一选择项，可使调用者不阻塞。
waitpid并不等待第一个终止的子进程—它有若干个选择项，可以控制它所等待的进程。
代码示例：
#include "ourhdr.h"
#include <sys/wait.h>
void pr_exit(int status)
{
if (WIFEXITED(status))
printf("normal termination, exit status = %d\n",
WEXITSTATUS(status));
else if (WIFSIGNALED(status))
printf("abnormal termination, signal number = %d%s\n",
WTERMSIG(status),
#ifdef WCOREDUMP
WCOREDUMP(status) ? " (core file generated)" : "");
#else
"");
#endif
else if (WIFSTOPPED(status))
printf("child stopped, signal number = %d\n",
WSTOPSIG(status));
}
int main(void)
{
pid_t pid;
int status;
if ((pid = fork()) < 0)
err_sys("fork error");
else if (pid == 0) /* child */
exit(7);
if (wait(&status) != pid) /* wait for child */
err_sys("wait error");
pr_exit(status); /* and print its status */
if ((pid = fork()) < 0)
err_sys("fork error");
else if (pid == 0) /* child */
abort(); /* generates SIGABRT */
if (wait(&status) != pid) /* wait for child */
err_sys("wait error");
pr_exit(status); /* and print its status */
if ((pid = fork()) < 0)
err_sys("fork error");
else if (pid == 0) /* child */
status /= 0; /* divide by 0 generates SIGFPE */
if (wait(&status) != pid) /* wait for child */
err_sys("wait error");
pr_exit(status); /* and print its status */
exit(0);
}
打印结果：
[root@rac1 fork]# gcc wait.c wait.c: In function ‘main’: wait.c:48: warning: division by zero [root@rac1 fork]# ./a.out normal termination, exit status = 7 abnormal termination, signal number = 6 abnormal termination, signal number = 8
5.3如果一个进程要 f o r k一个子进程，但不要求它等待子进程终止，也不希望子进程处于僵死状态直到父进程终止，实现这一要求的诀窍是调用 f o r k两次。
代码示例：
#include "ourhdr.h"
#include <sys/wait.h>
#include <sys/types.h>
int
main(void)
{
pid_t pid;
if ((pid = fork()) < 0) {
err_sys("fork error");
} else if (pid == 0) { /* first child */
if ((pid = fork()) < 0)
err_sys("fork error");
else if (pid > 0)
exit(0); /* parent from second fork == first child */
/*
* We‘re the second child; our parent becomes init as soon
* as our real parent calls exit() in the statement above.
* Here‘s where we‘d continue executing, knowing that when
* we‘re done, init will reap our status.
*/
sleep(2);
printf("second child, parent pid = %d\n", getppid());
exit(0);
}
if (waitpid(pid, NULL, 0) != pid) /* wait for first child */
err_sys("waitpid error");
/*
* We‘re the parent (the original process); we continue executing,
* knowing that we‘re not the parent of the second child.
*/
exit(0);
}
打印结果：
[root@rac1 fork]# ./a.out [root@rac1 fork]# second child, parent pid = 1
6 wait3 和wait4函数
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原文地址：http://www.cnblogs.com/huanhuanang/p/4440660.html
