Re: ptrace.2: BUGS (missing WIFEXITED notification)

[Denys Vlasenko <dvlasenk-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 05/14/2015 06:50 PM, Quentin Casasnovas wrote:
>>> The only way for us to work-around this behaviour was to have
>>> PTRACE_O_TRACEEXIT and detach from the threads when we were notified of a
>>> thread termination, without PTRACE_O_TRACEEXIT I don't think one can be
>>> notified in way, leading to hangs almost certainly when tracing multiple
>>> threads and some are in ptrace-stop.
>>
>> Why do you do that waitpid on thread group leader?
>>
>> strace is the user of ptrace, and it has no problem with this behavior.
>> It simply waits for all tracees via waitpid(-1). Whichever sends the next
>> notification is processed.
>>
> 
> That's because strace has all threads running; in our use-case, we attach
> to all threads of a group and restart a single thread to do some work.  In
> this particular case, waitpid(-1, ...) does not help because to exit, the
> other threads need to be PTRACE_CONT'ed.

Can you be more specific?
IF you have thread(s) which "do some work", then waitpid(-1) would work
for you - presumably, you wait for them to finish doing work,
or otherwise terminate, get a signal, whatever?
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