Detect a terminated pipe

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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