Parallelisation in R: Using parLapply with pointer to C object - c

Question

I'm trying to parallelise an R function that conducts some arithmetic in C.
A C object is constructed once from an R dataset using some function, which I'll call InitializeCObject, that returns a pointer to the object. I want to create an instance of this object on each worker that I can reuse many times.
This is where I've got so far:
nCores <- 2
cluster <- makeCluster(nCores)
on.exit(stopCluster(cluster))
clusterEvalQ(cluster, {library(pkgName); NULL})
The simplest solution is to make a new C object on each call:
x <- list(val1, val2) # list of length `nCores`
parLapply(cluster, x, function (x_i) pkgName::MakeObjectAndCalc(x_i, dataset))
But the time spent initializing the C object on every single call outweighs the benefits of parallelization.
I've tried creating nCores C objects and exporting all of them to each worker, then making worker n use local object n:
cPointer <- lapply(seq_len(nCores), function(xx) InitializeCObject(dataset))
on.exit(DestroyCObject(cPointer), add=TRUE)
clusterExport(cluster, 'cPointer')
parLapply(cluster, seq_len(nCores), function (i) Calculate(x[[i]], cPointer[[i]]))
But this doesn't work; the objects on the workers seem not to be initialized.
So I tried creating a separate C object locally on each worker:
clusterExport(cluster, 'dataset')
clusterEvalQ(cluster, {
localPointer <- InitializeCObject(dataset)
LocalCalc <- function (x) Calculate(x, localPointer)
on.exit(DestroyCObject(localPointer))
}
parLapply(cluster, x, LocalCalc)
But this causes the workers to crash. Any suggestions as to how I might move forwards would be appreciated.
edit: minimal C example
Here's my attempt to provide a minimal example of the associated C code. I'm far from fluent in C structures but hopefully this code is sufficient to demonstrate my problem.
// Define object structure
typedef struct CObject_t {
int data;
} CObject_t *CObject;
// Allocate memory to new (empty) object and return pointer to it
CObject new_object_t(void) {
CObject new = (CObject)calloc(1, sizeof(CObject_t));
return new;
}
int initialize_object(const int *dataset, CObject cObj) {
cObj->data = *dataset;
}
int use_object_to_calculate(int *x, CObject cObj) {
*x = *x + cObj->data;
return x;
}