EDIT: New version of rslurm makes the solution very easy. See my answer below.
Apologies for the somewhat longer than desired MWE, and a title that I realize after submitting the question may be needlessly complicated. I believe the real issue is getting the environment of a RefClass object into rslurm::slurm_apply.
Here I define a toy reference class called BankAccount. It has two fields and two methods.
The fields are transactions, a list of all transactions associated with the account and suspicion_threshold the value above which the bank will investigate the transaction.
The two methods are is_suspicious which compares the transactions with the suspicion_threshold on the local machine and is_suspicious_slurm, which uses rslurm::slurm_apply to spread many calls to is_suspicious over a cluster of computers managed by SLURM. You can imagine if there were many transactions or if the is_suspicious function were more complex, this might be necessary.
So, here's the setup
BankAccount <- setRefClass(
Class = 'BankAccount',
fields = list(
transactions = 'numeric',
suspicion_threshold = 'numeric'
)
)
BankAccount$methods(
is_suspicious = function(start_idx = 1, stop_idx = length(transactions)) {
return(start_idx + which(transactions[start_idx:stop_idx] > suspicion_threshold) - 1)
}
)
BankAccount$methods(
is_suspicious_slurm = function(num_nodes) {
usingMethods(is_suspicious)
t <- length(transactions)
t_per_n <- floor(t/num_nodes)
starts <- seq(from = 1, length.out = num_nodes, by = t_per_n)
stops <- seq(from = t_per_n, length.out = num_nodes, by = t_per_n)
stops[num_nodes] <- t
sjob <- rslurm::slurm_apply(f = is_suspicious,
params = data.frame(start_idx = starts,
stop_idx = stops),
nodes = num_nodes,
add_objects = .self)
results_list <- rslurm::get_slurm_out(slr_job = sjob,
outtype = "raw",
wait = TRUE)
return(unlist(results_list))
}
)
Now, on my local machine I can run:
library(RCexampleforSE)
set.seed(27599)
b <- BankAccount$new()
b$transactions <- rnorm(n = 500)
b$suspicion_threshold <- 2
b$is_suspicious()
b$is_suspicious_slurm(num_nodes = 3)
and it works as expected:
62 103 155 171 182 188 297 398 493 499
If I run:
b$is_suspicious_slurm(num_nodes = 3)
I get an error, since my personal computer is not connected to a SLURM cluster.
sh: squeue: command not found Cannot submit; no SLURM workload manager on path Submission scripts output in directory _rslurm_13ba46e3c70b0 Error in rslurm::get_slurm_out(slr_job = sjob, outtype = "raw", wait = TRUE): slr_job has not been submitted
If I logon to my university cluster, which uses SLURM, and run the same script, the setup and local methods work just as they did on my personal computer. When I run:
b$is_suspicious_slurm(num_nodes = 3)
it sends jobs to the cluster, as hoped for:
Submitted batch job 6363868
But these jobs error immediately with the following error message in slurm_0.out, slurm_1.out, and slurm_2.out:
Error in attr(, "mayCall") : argument 1 is empty Execution halted
I figure the job probably needs, but doesn't have available, the BankAccount object. So I tried passing it in as add_objects parameter to rslurm::slurm_apply:
sjob <- rslurm::slurm_apply(f = is_suspicious,
params = data.frame(start_idx = starts,
stop_idx = stops),
nodes = num_nodes,
add_objects = .self)
I also tried it in quotes and inside eval(), neither of which worked.
How can I make the object accessible to the worker jobs created with rslurm::slurm_apply?
Version 0.4.0 of rslurm completely solved this problem.
Define is_suspicious_slurm() as:
BankAccount$methods(
is_suspicious_slurm = function(num_nodes) {
usingMethods(is_suspicious)
t <- length(transactions)
t_per_n <- floor(t/num_nodes)
starts <- seq(from = 1, length.out = num_nodes, by = t_per_n)
stops <- seq(from = t_per_n, length.out = num_nodes, by = t_per_n)
stops[num_nodes] <- t
sjob <- rslurm::slurm_apply(f = is_suspicious,
params = data.frame(start_idx = starts,
stop_idx = stops),
nodes = num_nodes)
results_list <- rslurm::get_slurm_out(slr_job = sjob,
outtype = "raw",
wait = TRUE)
return(unlist(results_list))
}
)
The only change is that in the call to rslurm::slurm_apply, the add_objects parameter is not specified. It does not need to be specified because as @Ian pointed out:
"...you don't need to pass self at all when slurm_apply sends the serialized function, which appears to include both ".self" and "transactions" in the enclosing environment."