Hi, On Tue, Nov 25, 2008 at 6:35 AM, Andrej van der Zee <[EMAIL PROTECTED]> wrote: > Hi, > > Probably a very basic question, but unfortunately not for me: When a > parent process attaches to a forked child it finally can access the > pfm-context after the parent is finished waiting for the child to > exit. At this point, is the child task still in kernel memory? And if > so, at which point does the kernel know it can release it? > I think your question is orthogonal to perfmon2. What happens between a child and its parent is not modified in anyway by perfmon2.
You need to have the thread stopped when you attach a perfmon2 context. This is accomplished today via ptrace (PTRACE_ATTACH). Then, you can detach the thread and let it run to completion. Should you need to read out some counts before it dies, you'd have to stop the thread again via ptrace. When the thread eventually terminates, monitoring stops and the context is automatically detached. Death of a process is a two-step process, there is a signal (SIGCHLD) and then you need to reclaim the remaining resources via wait(). A key point to understand is that a thread can never reclaim all of its resources, this is always accomplished by the thread calling wait(), could be the parent or the init process. As for the perfmon2 context, it remains available after the signal and after the wait. The reason for this and this is a key design choice, is that the "owner" of the perfmon2 context is not the monitored thread, it is whichever process has a file descriptor open on it. Now you see why the perfmon2 context can survive the death of the monitored thread (except for self-monitoring, of course). If your question was more along the lines of: can I peek at the child's memory when I get the SIGCHLD? I think the answer is no because the memory resource has already been freed by then (do_exit). ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
