On Mar 14, 2014, at 8:09 AM, Kirill Müller <kirill.muel...@ivt.baug.ethz.ch>
wrote:
> Hi
>
> Is there a way to detect that the process that corresponds to a pipe has
> ended? On my system (Ubuntu 13.04), I see
>
> > p <- pipe("true", "w"); Sys.sleep(1); system("ps -elf | grep true | grep -v
> > grep"); isOpen(p)
> [1] TRUE
>
> The "true" process has long ended (as the filtered ps system call emits no
> output), still R believes that the pipe p is open.
>
As far as R is concerned, the connection is open. In addition, pipes exist even
without the process - you can close one end of a pipe and it will still exist
(that’s what makes pipes useful, actually, because you can choose to close
arbitrary combination of the R/W ends). Detecting that the other end of the
pipe has closed is generally done by sending/receiving data to/from the end of
interest - i.e. reading from a pipe that has closed the write end on the other
side will yield 0 bytes read. Writing to a pipe that has closed the read end on
the other side will yield SIGPIPE error (note that for text connections you
have to call flush() to send the buffer):
> p=pipe("true","r")
> readLines(p)
character(0)
> close(p)
> p=pipe("true","w")
> writeLines("", p)
> flush(p)
Error in flush.connection(p) : ignoring SIGPIPE signal
> close(p)
Cheers,
Simon
> Thanks for your input.
>
>
> Best regards
>
> Kirill
>
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