[Rd] tempdir() may be deleted during long-running R session

[Martin Maechler]

>>>>> Dirk Eddelbuettel <edd at debian.org>
>>>>>     on Sun, 23 Apr 2017 09:15:18 -0500 writes:

    > On 21 April 2017 at 10:34, frederik at ofb.net wrote:
    > | Hi Mikko,
    > | 
    > | I was bitten by this recently and I think some of the replies are
    > | missing the point. As I understand it, the problem consists of these
    > | elements:
    > | 
    > | 1. When R starts, it creates a directory like /tmp/RtmpVIeFj4
    > | 
    > | 2. Right after R starts I can create files in this directory with no
    > |    error
    > | 
    > | 3. After some hours or days I can no longer create files in this
    > |    directory, because it has been deleted

    > Nope. That is local to your system. 

Correct.  OTOH, Mikko and Frederik have a point in my view (below).

    > Witness eg at my workstation:

    > /tmp$ ls -ltGd Rtmp* 
    > drwx------ 3 edd 4096 Apr 21 16:12 Rtmp9K6bSN
    > drwx------ 3 edd 4096 Apr 21 11:48 RtmpRRbaMP
    > drwx------ 3 edd 4096 Apr 21 11:28 RtmpFlguFy
    > drwx------ 3 edd 4096 Apr 20 13:06 RtmpWJDF3U
    > drwx------ 3 edd 4096 Apr 18 15:58 RtmpY7ZIS1
    > drwx------ 3 edd 4096 Apr 18 12:12 Rtmpzr9W0v
    > drwx------ 2 edd 4096 Apr 16 16:02 RtmpeD27El
    > drwx------ 2 edd 4096 Apr 16 15:57 Rtmp572FHk
    > drwx------ 3 edd 4096 Apr 13 11:08 RtmpqP0JSf
    > drwx------ 3 edd 4096 Apr 10 18:47 RtmpzRzyFb
    > drwx------ 3 edd 4096 Apr  6 15:21 RtmpQhvAUb
    > drwx------ 3 edd 4096 Apr  6 11:24 Rtmp2lFKPz
    > drwx------ 3 edd 4096 Apr  5 20:57 RtmprCeWUS
    > drwx------ 2 edd 4096 Apr  3 15:12 Rtmp8xviDl
    > drwx------ 3 edd 4096 Mar 30 16:50 Rtmp8w9n5h
    > drwx------ 3 edd 4096 Mar 28 11:33 RtmpjAg6iY
    > drwx------ 2 edd 4096 Mar 28 09:26 RtmpYHSgZG
    > drwx------ 2 edd 4096 Mar 27 11:21 Rtmp0gSV4e
    > drwx------ 2 edd 4096 Mar 27 11:21 RtmpOnneiY
    > drwx------ 2 edd 4096 Mar 27 11:17 RtmpIWeiTJ
    > drwx------ 3 edd 4096 Mar 22 08:51 RtmpJkVsSJ
    > drwx------ 3 edd 4096 Mar 21 10:33 Rtmp9a5KxL
    > /tmp$ 

    > Clearly still there after a month. I tend to have some longer-running R
    > sessions in either Emacs/ESS or RStudio.

    > So what I wrote in my last message here *clearly* applies to you: a local
    > issue for which you have to take local action as R cannot know.  You also
    > have a choice of setting variables to affect this.

Thank you Dirk (and Brian).  That is all true, and of course I
have known about this myself "forever" as well.
 
    > | If R expected the directory to be deleted at random, and if we expect
    > | users to call dir.create every time they access tempdir, then why did
    > | R create the directory for us at the beginning of the session? That's
    > | just setting people up to get weird bugs, which only appear in
    > | difficult-to-reproduce situations (i.e. after the session has been
    > | open for a long time).

    > I disagree. R has been doing this many years, possibly two decades.

Yes, R has been doing this for a long time, including all the
configuration options with environment variables, and yes this
is sufficient "in principle".
 
    > | I think before we dismiss this we should think about possible in-R
    > | solutions and why they are not feasible. 

Here Mikko and Frederik do have a point I think.

    > | Are there any packages which
    > | would break if a call to 'tempdir' automatically recreated this
    > | directory? (Or would it be too much of a performance hit to have
    > | 'tempdir' check and even just issue a warning when the directory is
    > | found not to exist?)

    > | Should we have a timer which periodically updates
    > | the modification time of tempdir()? What do other long-running
    > | programs do (e.g. screen, emacs)?

Valid questions, in my view.  Before answering, let's try to see
how hard it would be to make the tempdir() function in R more versatile.

As I've found it is not at all hard to add an option which
checks the existence and if the directory is no longer "valid",
tries to recreate it (and if it fails doing that it calls the
famous R_Suicide(), as it does when R starts up and tempdir()
cannot be initialized correctly).

The proposed entry in NEWS is

   • tempdir(check=TRUE) recreates the tmpdir() if it is no longer valid.

and of course the default would be status quo, i.e.,  check = FALSE,
and once this is in R-devel, we (those who install R-devel) can
experiment with it.

Martin