Messages in this thread | | | Date | Tue, 24 Jun 2008 09:59:24 +0200 | From | Mikael Pettersson <> | Subject | Re: Any lightweight way for one thread to force another thread to suspend execution? |
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Eric Smith writes: > Andi wrote about my inquire regarding a way to synchronously stop > another thread: > > Any such mechanism will need a syscall, and it's unlikely that > > any syscall will get much cheaper than a kill(SIGSTOP) > > Unfortunately, as Bart pointed out, this stops ALL the threads > in a process (required for POSIX conformance). However, it appears that > I may be able to do it by creating my threads using clone() with appropriate > parameters rather than pthread_create(). > > The next question, which I haven't yet been able to answer for myself > from staring at the kernel sources, is whether sending SIGSTOP is > synchronous. In other words, when the kill() returns, is the target > thread already stopped? Even on an SMP system where the thread may have > been executing concurrently on another processor? > > If not, the next question will be whether there's a more efficient way > to wait for a process to enter the "T" state than busy-polling a file > in /proc.
SIGSTOP is unreliable since some other process may wake the target up with a SIGCONT.
man ptrace(), see the PTRACE_ATTACH request.
(Presumably it will DTRT if you give it a tid not just a pid, but I haven't tested that.)
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