Linux kernel Process Management ～Supplement（updating)

Author: Harold Wang 
http://blog.csdn.net/hero7935

 

1.Task state:

struct task_struct* task;              

/*

* This is OK even in SMP system, because it can involve Memory Barrier if necessary.

*/

set_task_state(task,state);  

set_task_state(current,state)=set_current_state(state)

 /*

 * We can simply use this instead if not in SMP environment;

 */       

 task->state=state;

 

 2.Iterate all processes:

 

struct task_struct* task;

for_each_process(task)

{

    printk("%s[%d]/n",task->comm,task->pid);

}

// if we want get the Init process(PID=1)

for(task=current;task!=init_task;task=task->parent);

 

//The relationship between process family:

3. Process Creation:

 

Modern Unix kernels involve three mechnisms to create process with less overhead, at least, do their best.

• Copy On Write Tech
• Lightweight process
• vfork() system call(deprecated, see Advanced Unix Programming 2rd edition)
  

   IN LINUX:

   fork() :

--copy all the resources the parent has-->generate process

--clone(SIGCHLD,0)

  vfork():

--copy works as fork() except the task_struct and kernel stack-->generate thread.

--clone(CLONE_VFORK|CLONE-VM|SIGCHLD,0)

NOTE: we can specify the resources that we want the "clone" to share with its parent.

           like : CLONE_FS   CLONE_FILES  CLONE_VM CLONE_SIGHAND et  al.

 

//In fact, fork/vfork/clone, they all call do_fork at last to achieve their goals.

 

Author: Harold Wang 
http://blog.csdn.net/hero7935

 

//if this is still not clear, please look at this picture to see if any better:

4. Process Switch see x86 or amd64

5. Process Termination:

    two methods to teminate process---->

exit_group()：corresponding main kernel function is do_group_exit()

_exit()：corresponding main kernel function is do_exit()

 

    note: do_exit() only mean that the thread is in the state of EXIT_ZOMBIE, when all objects associated with the task are freed, the task is not runnable(no longer has an address space in which to run) . The only memory it occupies is its kernel stack, the thread_info structure,and the task_struct structure. YES, the final work will be fixed by its parent who call the wait() function. YES, may be his original parent has left him, so forget_orginal_parent() will give a hand. YES, it nobody like this orphan, init thread will do.

 

Author: Harold Wang 
http://blog.csdn.net/hero7935

  

    when we can do_exit