TASK_INTERRUPTIBLE 和TASK_UNINTERRUPTIBLE

TASK_INTERRUPTIBLE 和TASK_UNINTERRUPTIBLE 的区别
TASK_INTERRUPTIBLE是可以被信号和wake_up()唤醒的,当信号到来时,进程会被设置为可运行。
而TASK_UNINTERRUPTIBLE只能被wake_up()唤醒。

信号本质

信号是在软件层次上对中断机制的一种模拟,软中断

信号来源

信号事件的发生有两个来源:

硬件来源:(比如我们按下了键盘或者其它硬件故障);

软件来源:最常用发送信号的系统函数是kill, raise,
alarm和setitimer以及sigqueue函数,软件来源还包括一些非法运算等操作。

区分是什么原因唤醒进程,用signal_pending( current
);

检查当前进程是否有信号处理,返回不为0表示有信号需要处理。-ERESTARTSYS
表示信号函数处理完毕后重新执行信号函数前的某个系统调用。也就是说,如果信号函数前有发生系统调用,在调度用户信号函数之前,内核会检查系统调用的返回
值,看看是不是因为这个信号而中断了系统调用.如果返回值-ERESTARTSYS,并且当前调度的信号具备-ERESTARTSYS属性,系统就会在用
户信号函数返回之后再执行该系统调用。

实例:

186 static int inet_csk_wait_for_connect(struct sock *sk, long timeo)
187 {
188 struct inet_connection_sock *icsk = inet_csk(sk);
189 DEFINE_WAIT(wait);
190 int err;
191
192 /*
193 * True wake-one mechanism for incoming connections: only
194 * one process gets woken up, not the 'whole herd'.
195 * Since we do not 'race & poll' for established sockets
196 * anymore, the common case will execute the loop only once.
197 *
198 * Subtle issue: "add_wait_queue_exclusive()" will be added
199 * after any current non-exclusive waiters, and we know that
200 * it will always _stay_ after any new non-exclusive waiters
201 * because all non-exclusive waiters are added at the
202 * beginning of the wait-queue. As such, it's ok to "drop"
203 * our exclusiveness temporarily when we get woken up without
204 * having to remove and re-insert us on the wait queue.
205 */
206 for (;;) {
207 prepare_to_wait_exclusive(sk->sk_sleep, &wait,
208 TASK_INTERRUPTIBLE);
209 release_sock(sk);
210 if (reqsk_queue_empty(&icsk->icsk_accept_queue))
211 timeo = schedule_timeout(timeo);
212 lock_sock(sk);
213 err = 0;
214 if (!reqsk_queue_empty(&icsk->icsk_accept_queue))
215 break;
216 err = -EINVAL;
217 if (sk->sk_state != TCP_LISTEN)
218 break;
219 err = sock_intr_errno(timeo);
220 if (signal_pending(current))
221 break;
222 err = -EAGAIN;
223 if (!timeo)
224 break;
225 }
226 finish_wait(sk->sk_sleep, &wait);
227 return err;
228 }
05-11 16:27