[RFC] Fix PosixProcess by porting VMProcess from Classpath...

Wed Jul 14 18:42:00 GMT 2004

Andrew Haley wrote:
>David Daney writes:
> > Andrew Haley wrote:
> > > 
> > > So, we wait either to be notified or until one second has passed.
> > > That doesn't seem like such a great scheme, altho' it's better than
> > > what we do at present. 
> > > 
> > > I suppose the right thing to do is call wait(2) instead of waiting on
> > > workList -- when we add a process to that list we can send the
> > > reaper/initiator thread a signal to wake it up.
> > > 
> > That is exactly what I was/am thinking.
> > 
> > What signal to send to wake it up?
> > 
> > SIGHUP, some "real time" signal, something else?
>>Hmmm. Tricky. :-)
>>Maybe SIGALRM ? SIGPOLL?
>Perhaps sigwait() should be used rather than wait(). With wait() and 
signals, it may be tricky to avoid race conditions - what happens if the 
thread is signaled (by another thread wanting to start a process), 
immediately before entering the wait() call?
As for what signal to use, anything should be ok provided we don't 
conflict with the GC's signals. posix-threads.cc defines a signal to 
implement interrupt(), perhaps we could use that. The sigwait() would 
handle both SIGCHLD and the "wake up" signal.
This ought to work so long as SIGCHLD is guaranteed to be delivered to 
the same thread which spawned the process? I'm not sure if this is 
guaranteed by the POSIX spec or not.
Regards
Bryce