R help - Dec 2012 - Making fifo work (Linux)

Friends

I need to get R reading from a fifo. I want it to block till there is some
data in the fifo, consume what input it gets there, do some thing with it
then loop back and block again.

Very simple.  Yes?  No.

The example in the documentation works OK..

       zz <- fifo("foo-fifo", "w+")
       writeLines("abc", zz)
       print(readLines(zz))
       close(zz)
       unlink("foo-fifo")

But when I tryu my code to *read* and *block*, id does not work.

P <- "Myfoofifo"
C <- fifo(P, "r", blocking=TRUE)

If Myfoofifo does not exist this has an error:
> C <- fifo(P, "r", blocking=TRUE)
Error in fifo(P, "r", blocking = TRUE) : cannot open the connection
In addition: Warning message:
In fifo(P, "r", blocking = TRUE) : cannot open fifo
'Myfoofifo'
>
> C <- fifo(P, "w+", blocking=TRUE)
succeeds but a read...
> Z <- readLines(C)
hangs.  Writing to Myfoofifo from other programmes, opening closing even
deleting it makes no difference.

I am stuck.  I can find no pertinent  examples.  What can I do?

Worik

	[[alternative HTML version deleted]]

Your problem seems to be unfamiliarity with this operating-system-specific
feature. You should be reading the OS documentation (e.g. "man fifo"
and learning how to use the feature in general before using it in R. (Hint:
off-topic here.)

Some words to the wise: Make sure you test with two processes, one for reading,
one for writing (this is not a storage medium, it is an inter-process
communication mechanism). Make sure you define a specific number of lines (e.g.
1) when you read unless you want to wait until the writing process closes the
fifo.
---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
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--------------------------------------------------------------------------- 
Sent from my phone. Please excuse my brevity.

Worik R <worikr at gmail.com> wrote:
>Friends
>
>I need to get R reading from a fifo. I want it to block till there is
>some
>data in the fifo, consume what input it gets there, do some thing with
>it
>then loop back and block again.
>
>Very simple.  Yes?  No.
>
>The example in the documentation works OK..
>
>       zz <- fifo("foo-fifo", "w+")
>       writeLines("abc", zz)
>       print(readLines(zz))
>       close(zz)
>       unlink("foo-fifo")
>
>But when I tryu my code to *read* and *block*, id does not work.
>
>P <- "Myfoofifo"
>C <- fifo(P, "r", blocking=TRUE)
>
>If Myfoofifo does not exist this has an error:
>
>> C <- fifo(P, "r", blocking=TRUE)
>Error in fifo(P, "r", blocking = TRUE) : cannot open the
connection
>In addition: Warning message:
>In fifo(P, "r", blocking = TRUE) : cannot open fifo
'Myfoofifo'
>>
>
>> C <- fifo(P, "w+", blocking=TRUE)
>
>succeeds but a read...
>
>> Z <- readLines(C)
>
>hangs.  Writing to Myfoofifo from other programmes, opening closing
>even
>deleting it makes no difference.
>
>I am stuck.  I can find no pertinent  examples.  What can I do?
>
>Worik
>
>	[[alternative HTML version deleted]]
>
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