[R] Global counter in library

[Pascal A. Niklaus]

Thanks for the hint. I think I will use a big.matrix [with 1 element 
only ;-) ] and a mutex to ensure access is thread-safe.

Pascal


On 12.03.19 17:35, Duncan Murdoch wrote:
> On 11/03/2019 2:57 p.m., Pascal A. Niklaus wrote:
>> I am trying to implement a global counter in a library. This counter
>> resides in an environment local to that package, and is incremented by
>> calling a function within this package.
>>
>> Problems arise when I use parallelization. I protected the increment
>> operation with a lock so that this operation effectively should be
>> atomic. However, the environment local to the package seems not to be
>> shared among the threads that use the functions in that package (not in
>> the sense that a change would be visible in the other threads).
>>
>> How is such a global counter best implemented?
>
> Use the Rdsm package.  See ?Rdsm::Rdsm for help.
>
> Duncan Murdoch
>
>>
>> Here is a basic sketch of what I tried:
>>
>>
>> library(parallel)
>>
>> library(flock)
>>
>> ## begin of code in package
>>
>> tmp <- tempfile()
>> .localstuff <- new.env()
>> .localstuff$N <- 0
>> .localstuff$tmp <- tempfile()
>>
>> incr <- function()
>> {
>>       h <- lock(.localstuff$tmp)
>>       .localstuff$N <- .localstuff$N + 1
>>       unlock(h)
>> }
>>
>> ## end code in library
>>
>> invisible(mclapply(1:10, function(i) incr()))
>>
>> cat("N =", .localstuff$N)