synchronizing using completion function

essential linux device dirver:

 

In the following example,  'my_release' is called when module is removed.

But before the module's unloaded, you have to make sure that 'my_thread'

has finished some very important task which will incur harmful effective to

our system if not properly handled. When 'my_thread' has finished the critical

task,  call 'complete_and_exit' to signal 'my_release' . In the 'my_releas'  side,

it can call 'wait_for_completion' to wait for 'my_thread' to exit. When 'my_release'

return from 'wait_for_completion' call,  the module can safely unloaded.

 

sample code:

 

#include <linux/module.h>#include <linux/sched.h>#include <linux/kthread.h>#include <linux/wait.h>static DECLARE_COMPLETION(my_thread_exit); // Completionstatic DECLARE_WAIT_QUEUE_HEAD(my_thread_wait); // Wait queueint pink_slip = 0; // exit flag for my_thread// Helper threadstatic int my_thread(void *unused){DECLARE_WAITQUEUE(wait, current);daemonize("my_thread");add_wait_queue(&my_thread_wait, &wait);while (1) {// Relinquish processor until event occursset_current_state(TASK_INTERRUPTIBLE);schedule();/* Control gets here when the thread is woken up from the my_threa_wait wait queue */// quit if let goif (pink_slip){break;}// do the real work}// Here you can do somethingprintk("you can do some important work./n");printk("Hi, This is %s. I am ready to die./n", __func__);set_current_state(TASK_RUNNING);remove_wait_queue(&my_thread_wait, &wait);// Atomatically signal completion and exitcomplete_and_exit(&my_thread_exit, 0);}static int __init my_init(void){printk("Hello, my dear!/n");// Kick start the threadkernel_thread(my_thread, NULL,CLONE_FS | CLONE_FILES | CLONE_SIGHAND | SIGCHLD);return 0;}static void __exit my_release(void){printk("Bye, my dear!/n Cruel world!/n");pink_slip = 1; // set the exit flag of my_threadprintk("Hi, I am %s. The module will be unloaded, Please ready!/n", __func__);wake_up(&my_thread_wait); // activate my_threadwait_for_completion(&my_thread_exit);// Wait until my_thread quits}module_init(my_init);module_exit(my_release);MODULE_LICENSE("Dual BSD/GPL");