Linux completion理解
来源:互联网 发布:照片装饰软件下载 编辑:程序博客网 时间:2024/04/29 20:07
completion是一种轻量级的机制,它允许一个线程告诉另一个线程工作已经完成。可以利用下面的宏静态创建completion:
DECLARE_COMPLETION(my_completion);
如果运行时创建completion,则必须采用以下方法动态创建和初始化:
struct compltion my_completion;
init_completion(&my_completion);
completion的相关定义包含在kernel/include/linux/completion.h中:
struct completion {
unsigned int done;
wait_queue_head_t wait;
};
#define COMPLETION_INITIALIZER(work)
{ 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
#define DECLARE_COMPLETION(work)
struct completion work = COMPLETION_INITIALIZER(work)
static inline void init_completion(struct completion *x)
{
x->done = 0;
init_waitqueue_head(&x->wait);
}
要等待completion,可进行如下调用:
void wait_for_completion(struct completion *c);
触发completion事件,调用:
void complete(struct completion *c); //唤醒一个等待线程
void complete_all(struct completion *c); //唤醒所有的等待线程
为说明completion的使用方法,将<<Linux设备驱动程序>>一书中的complete模块的代码摘抄如下:
/** complete.c -- the writers awake the readers*/------------------------------------------------------------#include <linux/module.h>#include <linux/init.h>#include <linux/sched.h> /* current and everything */#include <linux/kernel.h> /* printk() */#include <linux/fs.h> /* everything... */#include <linux/types.h> /* size_t */#include <linux/completion.h>MODULE_LICENSE("Dual BSD/GPL");static int complete_major = 253; //指定主设备号DECLARE_COMPLETION(comp);ssize_t complete_read ( struct file *filp, char __user *buf, size_t count, loff_t *pos){ printk(KERN_DEBUG "process %i (%s) going to sleepn", current->pid, current->comm); wait_for_completion(&comp); printk(KERN_DEBUG "awoken %i (%s)n", current->pid, current->comm); return 0;}ssize_t complete_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); complete(&comp); return count;}struct file_operations complete_fops = { .owner = THIS_MODULE, .read = complete_read, .write = complete_write,};int complete_init(void){ int result; result = register_chrdev(complete_major, "completion", &complete_fops); if (result < 0) return result; if (complete_major == 0) complete_major = result; return 0;}void complete_cleanup(void){ unregister_chrdev(complete_major, "completion");}module_init(complete_init);module_exit(complete_cleanup);
该模块定义了一个简单的completion设备:任何试图从该设备中读取的进程都将等待,直到其他设备写入该设备为止。编译此模块的Makefile如下:
obj-m := complete.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
rm -f *.ko *.o *.mod.c
在linux终端中执行以下命令,编译生成模块,并进行动态加载
# make
# mknod completion c 253 0
# insmod complete.ko
再打开三个终端,一个用于读进程:
# cat completion
一个用于写进程:
# echo >completion
另一个查看系统日志:
# tail -f /var/log/messages
值得注意的是,当我们使用的complete_all接口时,如果要重复使用一个completion结构,则必须执行INIT_COMPLETION (struct completion c)来重新初始化它。可以在kernel/include/linux/completion.h中找到这个宏的定义:
#define INIT_COMPLETION(x) ((x).done = 0)
以下代码对书中原有的代码进行了一番变动,将唤醒接口由原来的complete换成了complete_all,并且为了重复利用completion结构,所有读进程都结束后就重新初始化completion结构,具体代码如下:
#include <linux/module.h>#include <linux/init.h>#include <linux/sched.h>#include <linux/kernel.h>#include <linux/fs.h>#include <linux/types.h>#include <linux/completion.h>MODULE_LICENSE("Dual BSD/GPL");#undef KERN_DEBUG#define KERN_DEBUG "<1>"static int complete_major=253;static int reader_count = 0;DECLARE_COMPLETION(comp);ssize_t complete_read (struct file *filp,char __user *buf,size_t count,loff_t *pos){ printk(KERN_DEBUG "process %i (%s) going to sleep,waiting for writern",current->pid,current->comm); reader_count++; printk(KERN_DEBUG "In read ,before comletion: reader count = %d n",reader_count); wait_for_completion(&comp); reader_count--; printk(KERN_DEBUG "awoken %s (%i) n",current->comm,current->pid); printk(KERN_DEBUG "In read,after completion : reader count = %d n",reader_count); /*如果使用complete_all,则completion结构只能用一次,再次使用它时必须调用此宏进行重新初始化*/ if(reader_count == 0) INIT_COMPLETION(comp); return 0;}ssize_t complete_write(struct file *filp,const char __user *buf,size_t count,loff_t *pos){ printk(KERN_DEBUG "process %i (%s) awoking the readers...n",current->pid,current->comm); printk(KERN_DEBUG "In write ,before do complete_all : reader count = %d n",reader_count); if(reader_count != 0) complete_all(&comp); printk(KERN_DEBUG "In write ,after do complete_all : reader count = %d n",reader_count); return count;}struct file_operations complete_fops={ .owner = THIS_MODULE, .read = complete_read, .write = complete_write,};int complete_init(void){ int result; result=register_chrdev(complete_major,"complete",&complete_fops); if(result<0) return result; if(complete_major==0) complete_major =result; printk(KERN_DEBUG "complete driver test init! complete_major=%dn",complete_major); printk(KERN_DEBUG "静态初始化completionn"); return 0;}void complete_exit(void){ unregister_chrdev(complete_major,"complete"); printk(KERN_DEBUG "complete driver is removedn");}module_init(complete_init);module_exit(complete_exit);
这里测试步骤和上述一样,只不过需要多打开几个终端来执行多个进程同时读操作。
- Linux completion理解
- linux completion
- Linux Completion
- Linux 的 completion机制
- Linux中的completion
- linux completion接口
- Linux中的completion
- linux kernel completion
- linux completion接口
- linux bash-completion
- Linux 的 completion机制
- Linux 的 completion机制
- linux completion 笔记
- Linux中的completion使用
- Linux同步(一)-------completion
- Linux 的 completion机制
- Linux completion机制
- Linux completion 使用例子
- php安装gd(freetype、jpeg、png、zlib)
- getClass()
- android图像处理系列之四--给图片添加边框(上)
- thinkcentre 主机从光盘重装系统
- C#base关键字
- Linux completion理解
- cocos2d-x:动作 Actions
- android图像处理系列之五--给图片添加边框(中)
- 百度Geocoding接口(可用于地理编码和逆地理编码)
- loadrunner 脚本录制问题之 ie
- MFC分割窗口防止用户改变窗格的大小
- tar、zip 、unzip 打包与压缩
- java 从零开始,学习笔记之基础入门<线程及实例分析>(十九)
- 改写linux窗口程序设计的Qt例子(4)