On Fri, 31 Aug 2018, Gábor Csárdi wrote:
On Fri, Aug 31, 2018 at 3:35 PM Tomas Kalibera <tomas.kalib...@gmail.com> wrote:
On 08/31/2018 03:13 PM, Gábor Csárdi wrote:
On Fri, Aug 31, 2018 at 2:51 PM Tomas Kalibera <tomas.kalib...@gmail.com> wrote:
[...]
kill(sig=0) is specified by POSIX but indeed as you say there is a race
condition due to PID-reuse. In principle, detecting that a worker
process is still alive cannot be done correctly outside base R.
I am not sure why you think so.
To avoid the race with PID re-use one needs access to signal handling,
to blocking signals, to handling sigchld. system/system2 and
mcparallel/mccollect in base R use these features and the interaction is
still safe given the specific use in system/system2 and
mcparallel/mccollect, yet would have to be re-visited if either of the
two uses change. These features cannot be safely used outside of base R
in contributed packages.
Yes, _in theory_ this is right, and of course this only works for
child processes.
_In practice_, you do not need signal handling. The startup time stamp
method is
completely fine, because it is practically impossible to have two
processes with the
same pid and the same (high precision) startup time. This method also
works for any
process (not just child processes), so for PSOCK clusters as well.
PSOCK workers may not be running on the same host as the master process.
Best,
luke
Gabor
[...]
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Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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