进程休眠之sleepy不懂的地方

最新推荐文章于 2023-08-29 13:53:19 发布

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本文探讨了Linux中通过sleepy_read和sleepy_write函数实现的进程间通信机制。具体分析了当多个进程调用sleepy_read进入等待状态时，如何通过调用sleepy_write来唤醒这些进程，并解释了唤醒顺序及重复唤醒时的行为。

无法理解：

ssize_t sleepy_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
{
printk(KERN_DEBUG "process %i (%s) going to sleep\n",
current->pid, current->comm);
wait_event_interruptible(wq, flag != 0);
flag = 0;
printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);
return 0; /* EOF */
}

ssize_t sleepy_write (struct file *filp, const char __user *buf, size_t count,
loff_t *pos)
{
printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",
current->pid, current->comm);
flag = 1;
wake_up_interruptible(&wq);

return count; /* succeed, to avoid retrial */

}

假设有两个进程在等待时调用了sleepy_write函数，具体的过程是怎么样的？
为什么说第二个被唤醒的进程马上又会进入休眠呢？

等待是什么意思啊？是休眠了，是不是调用read休眠了，如果是那为什么还可以调用sleepy_write。

写的测试程序：

//testsleepy.c
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
int fd;
char* filename;
char buf[1] ={0x54};
if (argc != 3){
return 0;
}

filename = argv[1];

fd = open(filename, O_RDWR);

if (fd < 0){
printf("error, can't open %s\n", filename);
   return 0;
}
if (!strcmp("read", argv[2])){
read(fd, buf, 1);
}

else if(!strcmp("write", argv[2])){
write(fd, buf, 1);
}
return 0;
}

terminal1：
$ ./testsleepy /dev/sleepy read

terminal2：
$ ./testsleepy /dev/sleepy read

ternimal1 && terminal2 running testsleepy is sleepy

How can the testsleepy to wake_up throught calling write function ？

When I open another terminal and run ./testsleepy /dev/sleepy write。

Please guess the result which the terminal will wake up。

The result is that the second terminal program will wake up.

when I run ./testsleepy /dev/sleepy write again.
The first terminal will wake up

user four terminal to read
cat /var/log/kern.log
Oct 16 23:52:15 ubuntu kernel: [19326.544325] process 7211 (testsleep) going to sleep //terminal1
Oct 16 23:52:18 ubuntu kernel: [19329.207916] process 7212 (testsleep) going to sleep //terminal2
Oct 16 23:52:19 ubuntu kernel: [19331.122049] process 7213 (testsleep) going to sleep //terminal3
Oct 16 23:52:23 ubuntu kernel: [19334.319102] process 7214 (testsleep) going to sleep //terminal4
Oct 16 23:52:26 ubuntu kernel: [19337.326668] process 7216 (testsleep) awakening the readers... //terminal write
Oct 16 23:52:26 ubuntu kernel: [19337.326801] awoken 7214 (testsleep)
Oct 16 23:52:28 ubuntu kernel: [19339.622754] process 7217 (testsleep) awakening the readers... //terminal write
Oct 16 23:52:28 ubuntu kernel: [19339.622837] awoken 7211 (testsleep)
Oct 16 23:52:34 ubuntu kernel: [19345.777920] process 7218 (testsleep) awakening the readers... //terminal write
Oct 16 23:52:34 ubuntu kernel: [19345.778015] awoken 7213 (testsleep)
Oct 16 23:52:36 ubuntu kernel: [19347.477079] process 7219 (testsleep) awakening the readers... //terminal write
Oct 16 23:52:36 ubuntu kernel: [19347.477159] awoken 7212 (testsleep)

I don't know why the results will look like this !

PS：尚待我去理解的地方！有时间在去慢慢理解吧！