How to check if a process is waiting due to call to wait() or waitpid()?

Question

I see that in sys_wait4 (that is reached through calls to wait() or waitpid()) we insert the current process into a special queue that is saved in its struct task:

DECLARE_WAITQUEUE(wait, current);    
add_wait_queue(&current->wait_chldexit,&wait);

So if I want to check if a certain process is waiting due to call to wait() or waitpid() I need to check if it's in its own (???) wait_chldexit queue?

So only the process itself could be inserted into its own wait_chldexit queue?

Did I get it right?

This is linux kernel 2.4.

score 1 · Accepted Answer · answered Nov 07 '16 at 12:01

Yes, waitqueue current->wait_chldexit may contain either single element for current process or non elements at all.

No one wakes up given waitqueue, instead waiting is broken by a signal arised from the child thread.

By checking this waitqueue for some thread, you may detect whether that the thread is blocked in wait() or waitpid() call.

How to check if a process is waiting due to call to wait() or waitpid()?

1 Answers1