R devel - Jun 2011 - doMC - compiler - concatenate an expression vector into a single expression?

Hi,

this post is about foreach operators, the compiler package and the last 
update of doMC that includes support for the compiler functionality.

I am using a home-made %dopar%-like operator that adds some custom 
expression to be executed before the foreach loop expression itself (see 
sample code below).
It used to work perfectly with doMC 1.2.1, but with the introduction of 
the compiler functionality, things do not work properly.
The change in the doMC package consists in evaluating a compiled 
expression instead of the original R expression:

# from doMC:::doMC ...
c.expr <- comp(expr, env = envir, options = list(suppressUndefined = TRUE))

and for R >= 2.13.0 comp is defined as compiler::compile:
function (e, env = .GlobalEnv, options = NULL)
{
     cenv <- makeCenv(env)
     cntxt <- make.toplevelContext(cenv, options)
     cntxt$env <- addCenvVars(cenv, findLocals(e, cntxt))
     genCode(e, cntxt)
}
<environment: namespace:compiler>

My guess is that the function findLocals or genCode can not handle a 
2-length expression vector.

Maybe somebody who knows the internals of these functions could explain 
better this behaviour?
How can I concatenate two expressions into a single one?

Thank you,
Renaud


##################################################
# Sample code
##################################################

`%dopar2%` <- function(obj, ex){

     # append custom code to the expression
     ex <- c(expression({ a <- i; message("Custom ", a);}),
substitute(ex))

     # call the standard %dopar% operator
     do.call(`%dopar%`, list(obj, ex), envir=parent.frame() )
}
res <- foreach(i=1:3) %dopar2% { print(i); i*2; }
res


#########################
# Output with doSEQ or doMC 1.2.1
#########################
Custom 1
[1] 1
Custom 2
[1] 2
Custom 3
[1] 3
 > res
[[1]]
[1] 2

[[2]]
[1] 4

[[3]]
[1] 6


#########################
# Output with doMC 1.2.2
#########################

[[1]]
expression({
     a <- i
     message("Custom ", a)
}, {
     print(i)
     i * 2
})

[[2]]
expression({
     a <- i
     message("Custom ", a)
}, {
     print(i)
     i * 2
})

[[3]]
expression({
     a <- i
     message("Custom ", a)
}, {
     print(i)
     i * 2
})



-- 
Renaud Gaujoux
Computational Biology - University of Cape Town
South Africa


 

###
UNIVERSITY OF CAPE TOWN 

This e-mail is subject to the UCT ICT policies and e-mai...{{dropped:5}}

Dear Renaud,

Thank you for the report. I see that Steve Weston has responded to your
cross-posting on r-sig-hpc; I hope this helps with your immediate problem.
We will investigate whether changes to doMC are warranted.

Regards,
Rich Calaway

On Tue, Jun 28, 2011 at 2:58 AM, Renaud Gaujoux
<renaud@cbio.uct.ac.za>wrote:
> Hi,
>
> this post is about foreach operators, the compiler package and the last
> update of doMC that includes support for the compiler functionality.
>
> I am using a home-made %dopar%-like operator that adds some custom
> expression to be executed before the foreach loop expression itself (see
> sample code below).
> It used to work perfectly with doMC 1.2.1, but with the introduction of the
> compiler functionality, things do not work properly.
> The change in the doMC package consists in evaluating a compiled expression
> instead of the original R expression:
>
> # from doMC:::doMC ...
> c.expr <- comp(expr, env = envir, options = list(suppressUndefined =
TRUE))
>
> and for R >= 2.13.0 comp is defined as compiler::compile:
> function (e, env = .GlobalEnv, options = NULL)
> {
>    cenv <- makeCenv(env)
>    cntxt <- make.toplevelContext(cenv, options)
>    cntxt$env <- addCenvVars(cenv, findLocals(e, cntxt))
>    genCode(e, cntxt)
> }
> <environment: namespace:compiler>
>
> My guess is that the function findLocals or genCode can not handle a
> 2-length expression vector.
>
> Maybe somebody who knows the internals of these functions could explain
> better this behaviour?
> How can I concatenate two expressions into a single one?
>
> Thank you,
> Renaud
>
>
> ##############################**####################
> # Sample code
> ##############################**####################
>
> `%dopar2%` <- function(obj, ex){
>
>    # append custom code to the expression
>    ex <- c(expression({ a <- i; message("Custom ", a);}),
substitute(ex))
>
>    # call the standard %dopar% operator
>    do.call(`%dopar%`, list(obj, ex), envir=parent.frame() )
> }
> res <- foreach(i=1:3) %dopar2% { print(i); i*2; }
> res
>
>
> #########################
> # Output with doSEQ or doMC 1.2.1
> #########################
> Custom 1
> [1] 1
> Custom 2
> [1] 2
> Custom 3
> [1] 3
> > res
> [[1]]
> [1] 2
>
> [[2]]
> [1] 4
>
> [[3]]
> [1] 6
>
>
> #########################
> # Output with doMC 1.2.2
> #########################
>
> [[1]]
> expression({
>    a <- i
>    message("Custom ", a)
> }, {
>    print(i)
>    i * 2
> })
>
> [[2]]
> expression({
>    a <- i
>    message("Custom ", a)
> }, {
>    print(i)
>    i * 2
> })
>
> [[3]]
> expression({
>    a <- i
>    message("Custom ", a)
> }, {
>    print(i)
>    i * 2
> })
>
>
>
> --
> Renaud Gaujoux
> Computational Biology - University of Cape Town
> South Africa
>
>
>
>
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-- 
Rich Calaway
Documentation Manager
Revolution Analytics, Inc.
1505 Westlake Ave North Suite 300
Seattle, WA 98109
richcalaway@revolutionanalytics.com
206-456-6086 (Direct Phone)
855-GET-REVO x6086 (Toll-free)

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