一般我们在程序设计的时候，我们使用wait来获取子进程的退出状态，但是wait将会阻塞等到子进程结束。对于waitpid来说：
pid_t waitpid(pid_t pid, int *statloc, int options);
我们可以通过设置第3个参数options为WNOHANG来使waitpid为非阻塞，但这样的话，我们就需要不断的调用waitpid来探测子进程是否结束。
signal中有一个SIGCHLD，当一个进程终止或停止时，将SIGCHLD信号发送给其父进程。按照系统默认情况，这个信号是被忽略的。如果父进程希望被告知其子进程的这种状态的变化，则应该设置捕获这个信号。在信号处理函数里面，通常要调用一种wait来获取子进程的ID和其退出状态。
#include
<
sys
/
types.h
>
#include < unistd.h >
#include < stdio.h >
#include < string .h >
#include < sys / wait.h >
#include < signal.h >
sig_atomic_t child_exit_state;
void clean_child_process( int sig_number){
int status;
wait( & status);
child_exit_state = status;
}
int main( int argc, char ** argv){
pid_t pid;
struct sigaction action;
memset( & action, 0 , sizeof (action));
action.sa_handler =& clean_child_process;
sigaction( SIGCHLD, & action,NULL);
pid = fork();
}
int main( int argc, char ** argv){
pid_t pid;
struct sigaction action;
memset( & action, 0 , sizeof (action));
action.sa_handler =& clean_child_process;
sigaction( SIGCHLD, & action,NULL);
pid = fork();
if (pid == 0 ) {
printf( " Child process...\n " );
sleep( 5 );
printf( " Child terminated.\n " );
}
else {
printf( " Parent process...\n " );
sleep( 6 );
printf( " Child status: %d\n " , child_exit_state);
}
return 0 ;
}
#include < unistd.h >
#include < stdio.h >
#include < string .h >
#include < sys / wait.h >
#include < signal.h >
sig_atomic_t child_exit_state;
void clean_child_process( int sig_number){
int status;
wait( & status);
child_exit_state = status;
}
int main( int argc, char ** argv){
pid_t pid;
struct sigaction action;
memset( & action, 0 , sizeof (action));
action.sa_handler =& clean_child_process;
sigaction( SIGCHLD, & action,NULL);
pid = fork();
}
int main( int argc, char ** argv){
pid_t pid;
struct sigaction action;
memset( & action, 0 , sizeof (action));
action.sa_handler =& clean_child_process;
sigaction( SIGCHLD, & action,NULL);
pid = fork();
if (pid == 0 ) {
printf( " Child process...\n " );
sleep( 5 );
printf( " Child terminated.\n " );
}
else {
printf( " Parent process...\n " );
sleep( 6 );
printf( " Child status: %d\n " , child_exit_state);
}
return 0 ;
}
