linux内核同步机制之完成量
定义在头文件linux/completion.h中;
完成量(completion)是Linux系统提供的一种比信号量更好的同步机制,是对信号量的一种补充;它用于一个执行单元等待另一个执行单元完成某事;使用完成量等待时,调用进程是以独占睡眠方式进行等待的;不是忙等待;
1).定义完成量:
struct completion my_completion; //定义完成量my_completion2).初始化完成量:
init_completion(&my_completion); //初始化完成量my_completion
DECLARE_COMPLETION(my_completion); //初始化完成量my_completion的快捷方式3).等待完成量:
void wait_for_completion(struct completion* comp):
该函数等待一个完成量被唤醒;该函数会阻塞调用进程,如果所等待的完成量没有被唤醒,那就一直阻塞下去,而且不会被信号打断;
int wait_for_completion_interruptible(struct completion* comp):
该函数等待一个完成量被唤醒;但是它可以被外部信号打断;
int wait_for_completion_killable(struct completion* comp):
该函数等待一个完成量被唤醒;但是它可以被kill信号打断;
unsigned long wait_for_completion_timeout(struct completion* comp, unsigned long timeout):
该函数等待一个完成量被唤醒;该函数会阻塞调用进程,如果所等待的完成量没有被唤醒,调用进程也不会一直阻塞下去,而是等待一个指定的超时时间timeout,当超时时间到达时,如果所等待的完成量仍然没有被唤醒,那就返回;超时时间timeout以系统的时钟滴答次数jiffies计算;
bool try_wait_for_completion(struct completion* comp):
该函数尝试等待一个完成量被唤醒;不管所等待的完成量是否被唤醒,该函数都会立即返回;
bool completion_done(struct completion* comp):
该函数用于检查是否有执行单元阻塞在完成量comp上(是否已经完成),返回0,表示有执行单元被完成量comp阻塞;相当于wait_for_completion_timeout()中的timeout=0;
注意:这几个函数都会把进程添加到等待队列中,进程在等待队列中以独占睡眠方式进行等待,直到请求被内核中的某些部分处理;4).唤醒完成量:
void complete(struct completion* comp):
该函数只唤醒一个正在等待完成量comp的执行单元;
void complete_all(struct completion* comp):
该函数唤醒所有正在等待同一个完成量comp的执行单元;
NORET_TYPE void complete_and_exit(struct completion* comp, long code):
该函数唤醒一个正在等待完成量comp的执行单元,并退出,code为退出码;注意:在内核处理完请求之后,必须调用这三个函数中的一个,来唤醒其它正在等待的进程;
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
//完成量相关
#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:定义完成量
struct completion my_comp;
//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
wait_for_completion(&my_comp);
shared_res++;
//STEP4:对临界区解锁
complete(&my_comp);
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
wait_for_completion(&my_comp);
shared_res++;
//STEP4:对临界区解锁
complete(&my_comp);
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
wait_for_completion(&my_comp);
val = shared_res;
printk("%s: shared resource = %d;\n%s", __FUNCTION__, val, ((val % 3) ? "" : "\n"));
//STEP4:对临界区解锁
complete(&my_comp);
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
wait_for_completion(&my_comp);
val = shared_res;
printk("%s: shared resource = %d;\n%s", __FUNCTION__, val, ((val % 3) ? "" : "\n"));
//STEP4:对临界区解锁
complete(&my_comp);
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:初始化完成量
init_completion(&my_comp);
printk("init completion ok\n");
complete_all(&my_comp);
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__);
//complete_all(&my_comp);
complete(&my_comp);
if(my_thread1)
{
ret = kthread_stop(my_thread1);
my_thread1 = NULL;
printk("kernel thread1 stop,exit code is %d;\n",ret);
}
//complete_all(&my_comp);
complete(&my_comp);
if(my_thread2)
{
ret = kthread_stop(my_thread2);
my_thread2 = NULL;
printk("kernel thread2 stop,exit code is %d;\n",ret);
}
//complete_all(&my_comp);
complete(&my_comp);
if(my_thread3)
{
ret = kthread_stop(my_thread3);
my_thread3 = NULL;
printk("kernel thread3 stop,exit code is %d;\n",ret);
}
//complete_all(&my_comp);
complete(&my_comp);
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);