定义在头文件linux/mutex.h中;

互斥体(mutex)是Linux系统提供的另外一种互斥机制;在Linux内核中是真实存在的;

1).定义互斥体

struct mutex my_mutex;    //定义互斥体

mutex_init(&my_mutex);    //初始化互斥体

2).获取和释放互斥体:

void mutex_lock(struct mutex* lock);               //获取互斥体,不可被信号中断

void mutex_lock_interruptible(struct mutex* lock); //获取互斥体,可被信号打断

int mutex_trylock(struct mutex* lock);             //尝试获取互斥体

void mutex_unlock(struct mutex* lock);             //释放互斥体

3).其它函数:

int mutex_is_locked(struct mutex* lock):

该函数检查互斥锁lock是否处于锁定状态;返回1,表示已锁定;返回0,表示未锁定;

int mutex_lock_interruptible(struct mutex* lock);  //该函数可被信号打断

int mutex_lock_killable(struct mutex* lock);       //该函数可被kill信号打断

4).互斥体的使用模式:

struct mutex my_mutex;   //定义互斥体

mutex_init(&my_mutex);   //初始化互斥体

mutex_lock(&my_mutex);   //获取互斥体

......                   //临界区代码

mutex_unlock(&my_mutex); //释放互斥体

例子:

#include

#include

#include

#include

#include

#include

//这三个头文件与内核线程的使用有关;

#include

#include

#include

//互斥量相关

#include

MODULE_LICENSE("GPL");

MODULE_AUTHOR("*************");

MODULE_VERSION("2.6.35.000");

static int sleep_time = (1*10*HZ);

static int shared_res = 0;

//STEP1:定义互斥量

struct mutex my_mutex;

//STEP5:实现线程函数

static int thread_process1(void* param)

{

//int val = 0, ret = 0;

while(1)

{

set_current_state(TASK_UNINTERRUPTIBLE);

if(kthread_should_stop())

{

printk("kernel thread '%s' should stop;file:%s;line:%d\n", __FUNCTION__, __FILE__, __LINE__);

break;

}

//STEP3:对临界区加锁

mutex_lock(&my_mutex);

shared_res++;

//STEP4:对临界区解锁

mutex_unlock(&my_mutex);

mdelay(sleep_time);

}

return 12;

};

static int thread_process2(void* param)

{

//int val = 0, ret = 0;

while(1)

{

set_current_state(TASK_UNINTERRUPTIBLE);

if(kthread_should_stop())

{

printk("kernel thread '%s' should stop;file:%s;line:%d\n", __FUNCTION__, __FILE__, __LINE__);

break;

}

//STEP3:对临界区加锁

mutex_lock(&my_mutex);

shared_res++;

//STEP4:对临界区解锁

mutex_unlock(&my_mutex);

msleep(sleep_time);

}

return 34;

};

static int thread_process3(void* param)

{

int val = 0;//, ret = 0;

while(1)

{

set_current_state(TASK_UNINTERRUPTIBLE);

if(kthread_should_stop())

{

printk("kernel thread '%s' should stop;file:%s;line:%d\n", __FUNCTION__, __FILE__, __LINE__);

break;

}

//STEP3:对临界区加锁

mutex_lock(&my_mutex);

val = shared_res;

printk("%s: shared resource = %d;\n%s", __FUNCTION__, val, ((val % 3) ? "" : "\n"));

//STEP4:对临界区解锁

mutex_unlock(&my_mutex);

msleep(sleep_time);

}

return 56;

};

static int thread_process4(void* param)

{

int val = 0;//, ret = 0;

while(1)

{

set_current_state(TASK_UNINTERRUPTIBLE);

if(kthread_should_stop())

{

printk("kernel thread '%s' should stop;file:%s;line:%d\n", __FUNCTION__, __FILE__, __LINE__);

break;

}

//STEP3:对临界区加锁

mutex_lock(&my_mutex);

val = shared_res;

printk("%s: shared resource = %d;\n%s", __FUNCTION__, val, ((val % 3) ? "" : "\n"));

//STEP4:对临界区解锁

mutex_unlock(&my_mutex);

msleep(sleep_time);

}

return 78;

};

static struct task_struct* my_thread1 = NULL;

static struct task_struct* my_thread2 = NULL;

static struct task_struct* my_thread3 = NULL;

static struct task_struct* my_thread4 = NULL;

static int __init study_init(void)

{

int err = 0;

printk("%s\n", __PRETTY_FUNCTION__);

//STEP2:初始化互斥量

mutex_init(&my_mutex);

printk("init mutex ok\n");

my_thread1 = kthread_create(thread_process1, NULL, "my_thread1");

if(IS_ERR(my_thread1))

{

err = PTR_ERR(my_thread1);

my_thread1 = NULL;

printk(KERN_ERR "unable to start kernel thread1:%d\n", err);

return err;

}

my_thread2 = kthread_create(thread_process2, NULL, "my_thread2");

if(IS_ERR(my_thread2))

{

err = PTR_ERR(my_thread2);

my_thread2 = NULL;

printk(KERN_ERR "unable to start kernel thread2:%d\n", err);

return err;

}

my_thread3 = kthread_create(thread_process3, NULL, "my_thread3");

if(IS_ERR(my_thread3))

{

err = PTR_ERR(my_thread3);

my_thread3 = NULL;

printk(KERN_ERR "unable to start kernel thread3:%d\n", err);

return err;

}

my_thread4 = kthread_create(thread_process4, NULL, "my_thread4");

if(IS_ERR(my_thread4))

{

err = PTR_ERR(my_thread4);

my_thread4 = NULL;

printk(KERN_ERR "unable to start kernel thread4:%d\n", err);

return err;

}

wake_up_process(my_thread1);

wake_up_process(my_thread2);

wake_up_process(my_thread3);

wake_up_process(my_thread4);

printk("%s:all kernel thread start;\n", __FUNCTION__);

return 0;

}

static void __exit study_exit(void)

{

int ret = -1;

printk("%s\n",__PRETTY_FUNCTION__);

if(my_thread1)

{

ret = kthread_stop(my_thread1);

my_thread1 = NULL;

printk("kernel thread1 stop,exit code is %d;\n",ret);

}

if(my_thread2)

{

ret = kthread_stop(my_thread2);

my_thread2 = NULL;

printk("kernel thread2 stop,exit code is %d;\n",ret);

}

if(my_thread3)

{

ret = kthread_stop(my_thread3);

my_thread3 = NULL;

printk("kernel thread3 stop,exit code is %d;\n",ret);

}

if(my_thread4)

{

ret = kthread_stop(my_thread4);

my_thread4 = NULL;

printk("kernel thread4 stop,exit code is %d;\n",ret);

}

printk("%s:all kernel thread stop;\n", __FUNCTION__);

}

module_init(study_init);

module_exit(study_exit);