Linux kernel 中的的等待队列(阻塞式)

等待队列在Linux内核中用来阻塞或唤醒一个进程，也可以用来同步对系统资源的访问，还可以实现延迟功能

等待队列接口函数介绍：

#include <linux/wait.h> //头文件包含

1.定义、初始化等待队列（指向等待队列链表）

定义一个等待队列头

wait_queue_head_t my_queue;

初始一个等待队列头

init_waitqueue_head(&my_queue);

定义并初始化一个等待队列头

DECLARE_WAIT_QUEUE_HEAD(my_queue);

2.进程的睡眠操作——条件睡眠

判断condition条件，决定是否将当前进程推入等待队列

wait_event(wait_queue_head_t wq, int condition);

wait_event_interruptible /*可以被系统消息打断*/

(wait_queue_head_t wq,int condition);

wait_event_timeout(wait_queue_head_t wq, int

condition, long timeout)；

wait_event_interruptiblble_timeout(wait_queue_head_t wq,

int condition, long timeout);

参数wq:表示等待队列头

参数condition:阻塞条件，为假(0)则进入休眠直到wake_up且condition为真条件成立才退出

参数timeout：表示睡眠指定时长（时钟滴答度量，eg.延时2秒=2*HZ）后，自动转入唤醒状态

进程的睡眠操作——无条件睡眠

//将当前进程推入等待队列将其睡眠，wake_up唤醒

sleep_on(wait_queue_head_t *q);

interruptible_sleep_on(wait_queue_head_t *q);

long sleep_on_timeout(wait_queue_head_t *q, long timeout)；

long interruptible_sleep_on_timeout(wait_queue_head_t *q, long timeout)；

参数wq:表示等待队列头

参数timeout：表示睡眠指定时长后，自动转入唤醒状态

3.进程唤醒函数

wake_up(wait_queue_head_t *wq);

wake_up_interruptible(wait_queue_head_t *wq);

注意事项:

1.唤醒函数和导致睡眠函数要配对使用，如果导致睡眠函数使用带interruptible的，则唤醒函数也要使用interruptible的。

2.在使用wake_up唤醒进程之前要将wait_event中的condition变量的值赋为真，否则该进程被唤醒后会立即再次进入睡眠

等待队列应用实例：

代码实例：

应用层代码：

#include <stdio.h>#include <stdlib.h>#include <fcntl.h>#include <unistd.h>int main(){char *devname = "/dev/key1_eint";int fd;unsigned char key;fd = open(devname, O_RDWR);while(1){read(fd, &key, sizeof(key)); printf("the key = %d\n",key);}close(fd);}

驱动层：

#include <linux/device.h>#include <linux/interrupt.h>#include <linux/module.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/init.h>#include <linux/delay.h>#include <linux/irq.h>#include <asm/uaccess.h>#include <asm/irq.h>#include <asm/io.h>#include <mach/gpio.h>#include <mach/regs-gpio.h>  #define EINT_DEVICE_ID1#define DRIVER_NAME"key1_eint"#define err(msg) printk(KERN_ERR "%s: " msg "\n", DRIVER_NAME)#define __debug(fmt, arg...)printk(KERN_DEBUG fmt, ##arg)#define GPH3CON(unsigned long)(S5PV210_GPH3_BASE+ 0x00)#define GPH3DAT(unsigned long)(S5PV210_GPH3_BASE + 0x04)#define GPH2UP(unsigned long)(S5PV210_GPH2_BASE + 0x08)static int major = 0;static int minor = 0;struct class *key_class;static struct device *key_device;/*定义等待队列头，该等待队列头属于该驱动程序*/static wait_queue_head_t wait_queue;static unsigned char key;irqreturn_t buttons_interrupt(int irq, void *dev_id){key = (unsigned int)dev_id;wake_up_interruptible(&wait_queue);//唤醒等待队列return IRQ_HANDLED;}static void key_io_port_init(void){unsigned long reg_val;reg_val = readl(GPH3CON);reg_val &= ~((0x0f<<0) | (0x0f<<4));reg_val |= ((0x01<<0) | (0x01<<4));writel(reg_val, GPH3CON);reg_val = readl(GPH3DAT);reg_val &= ~((0x01<<0) | (0x01<<1));writel(reg_val, GPH3DAT);reg_val = readl(GPH2UP);reg_val &= ~(0x03<<8);reg_val |= 0x02<<8;writel(reg_val, GPH2UP);}static ssize_t key_read(struct file *filp, char *buf, size_t count, loff_t *f_pos){int key_num;int cpy_len;int retval;/* 该函数体内部会定义struct wait_queue结构体变量，并将将当前进程 * 添加到队列中睡眠，(wait_queue_head_t为等待队列链表的头，struct  * wait_queue记录着链表节点信息) */interruptible_sleep_on(&wait_queue);key_num = key;//读取键值cpy_len = min(sizeof(key_num), count);retval = copy_to_user(buf, &key_num, cpy_len);return (cpy_len - retval);}/* Driver Operation structure */static struct file_operations key_fops = {.owner = THIS_MODULE,.read = key_read,};static int __init key_eint_init(void){int retval;key_io_port_init();init_waitqueue_head(&wait_queue);//初始化等待队列头retval = set_irq_type(IRQ_EINT(20),IRQ_TYPE_EDGE_FALLING);if(retval){err("IRQ_EINT20 set irq type failed");goto error;}retval = request_irq(IRQ_EINT(20), buttons_interrupt, IRQF_DISABLED, "KEY1", (void *)EINT_DEVICE_ID);if(retval){err("request eint20 failed");goto error;}major = register_chrdev(major, DRIVER_NAME, &key_fops);if(major < 0){err("register char device fail");retval = major;goto error_register;}key_class=class_create(THIS_MODULE,DRIVER_NAME);if(IS_ERR(key_class)){err("class create failed!");retval =  PTR_ERR(key_class);goto error_class;}key_device=device_create(key_class,NULL, MKDEV(major, minor), NULL,DRIVER_NAME);if(IS_ERR(key_device)){err("device create failed!");retval = PTR_ERR(key_device);goto error_device;}__debug("register myDriver OK! Major = %d\n", major);return 0;error_device:class_destroy(key_class);error_class:unregister_chrdev(major, DRIVER_NAME);error_register:free_irq(IRQ_EINT(20), (void *)EINT_DEVICE_ID);error:return retval;}static void __exit key_eint_exit(void){free_irq(IRQ_EINT(20), (void *)EINT_DEVICE_ID);unregister_chrdev(major, DRIVER_NAME);device_destroy(key_class,MKDEV(major, minor));class_destroy(key_class);return;}module_init(key_eint_init);module_exit(key_eint_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("eric");