Hello,
The point is that I do not use tcltk, it gets loaded probably as a
dependency of a dependency of a package.
When I unload it all work perfectly fine. I just found it because one
of my computer did not have tk8.5 installed, and did not exhibit the
mentioned bug. So I really think something should be done about this.
Maybe the "gui loop" should not be run a the the loading of the tcltk
package, but
at the first function ran, or something like this.
As you can see in my example code, the in-memory database is opened in
the parallel code...
Best,
Karl
On Mon, Dec 31, 2012 at 10:58 PM, Simon Urbanek
<simon.urba...@r-project.org> wrote:
>
> On Dec 31, 2012, at 1:08 PM, Karl Forner wrote:
>
>> Hello,
>>
>> I spent a lot of a time on a weird bug, and I just managed to narrow it down.
>>
>
> First, tcltk and multicore don't mix well, see the warning in the
> documentation (it mentions GUIs and AFAIR tcltk fires up a GUI event loop
> even if you don't actually create GUI elements). Second, using any kind of
> descriptors in parallel code is asking for trouble since those will be owned
> by multiple processes. If you use databases files, etc. they must be opened
> in the parallel code, they cannot be shared by multiple workers. The latter
> is ok in your code so you're probably bitten by the former.
>
> Cheers,
> Simon
>
>
>
>> In parallel code (here with parallel::mclappy, but I got it
>> doMC/multicore too), if the library(tcltk) is loaded, R hangs when
>> trying to open a DB connection.
>> I got the same behaviour on two different computers, one dual-core,
>> and one 2 xeon quad-core.
>>
>> Here's the code:
>>
>> library(parallel)
>> library(RSQLite)
>> library(tcltk)
>> #unloadNamespace("tcltk")
>>
>> res <- mclapply(1:2, function(x) {
>> db <- DBI::dbConnect("SQLite", ":memory:")
>> }, mc.cores=2)
>> print("Done")
>>
>> When I execute it (R --vanilla < test_parallel_db.R), it hangs
>> forever, and I have to type several times CTRL+C to interrupt it. I
>> then get this message:
>>
>> Warning messages:
>> 1: In selectChildren(ac, 1) : error 'Interrupted system call' in select
>> 2: In selectChildren(ac, 1) : error 'Interrupted system call' in select
>>
>> Then, just remove library(tcltk), or uncomment
>> unloadNamespace("tcltk"), and it works fine again.
>>
>> I guess there's a bug somewhere, but where exactly ?
>>
>> Best,
>>
>> Karl Forner
>>
>> Further info:
>>
>>
>> R version 2.15.1 (2012-06-22) -- "Roasted Marshmallows"
>> Copyright (C) 2012 The R Foundation for Statistical Computing
>> ISBN 3-900051-07-0
>> Platform: x86_64-unknown-linux-gnu (64-bit)
>>
>> ubuntu 12.04 and 12.10
>>
>> ubuntu package tk8.5
>>
>> ______________________________________________
>> R-devel@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>
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