Killing a Child Thread


 
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# 1  
Old 05-29-2012
Killing a Child Thread

What is the best way for a parent to kill a child thread that has blocked on a command it cannot finish and will never read another line of its code? Will pthread_cancel() work with a thread that will never stop processing its current line of code? Thanks.
# 2  
Old 05-30-2012
Read cancellation point and then you will know if you can use pthread_cancel.
Threads The read system call is one of a lot of cancellation points.

BTW - threads are very different from a child process.

You can also invoke pthread_kill but other threads and the main thread can be affected unless threads all have enabled per-thread signal handling.
# 3  
Old 05-30-2012
Thanks, but what do you mean by "read cancellation point?"

One other matter, my tests show that if, by chance, the thread no longer exists when I call pthread_cancel, the parent will abend with a segfault. What signal might I trap with signal() to prevent this?
# 4  
Old 05-30-2012
Quote:
Originally Posted by Brandon9000
Thanks, but what do you mean by "read cancellation point?"
As in reading, reading which you do, not the computer. Specifically, reading about cancellation points on the link he posted.
# 5  
Old 05-30-2012
I see. Thanks. I will.

One other thing, if I cancel a thread, I have to consider the possibility that there could be an unanticipated scenario in which the thread no longer exists at the instant when I cancel it, even if thought I was doing appropriate checking for existence. In a test I did, cancelling a non-existent thread caused a segfault which caused the parent to exit. I tried to trap signals to prevent the parent from abending using SIG_IGN, but it abended anyway. Do you know if such a thing is possible. I did work up a scheme which should prevent ever cancelling a non-existent thread, but I would feel more comfortable if that situation were covered.
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