Write an R object into shared memory and return a version that other processes on the same machine can map without copying.
Value
For atomic vectors (including character vectors and those with
attributes such as names, dim, class, or levels) and lists or data
frames whose elements are such vectors, an ALTREP-backed object that
reads directly from shared memory. For any other object (environments,
closures, language objects, NULL), the input is returned
unchanged with no shared memory region created.
Details
Attributes are stored alongside the data in the shared memory region
and restored on the consumer side. Character vectors use a packed
layout and elements are materialised lazily on access. When serialised
(e.g. by serialize() or across a mirai() call), a
shared object is represented compactly by its SHM name (~30 bytes)
rather than by its contents.
The shared memory region is managed automatically. It stays alive as long as the returned object (or any element extracted from it) is referenced in R, and is freed by the garbage collector when no references remain.
share() is idempotent: calling it on an object that is already
backed by shared memory returns the input unchanged without
allocating a new region.
Important: always assign the result of share() to a
variable. The shared memory is kept alive by the R object reference —
if the result is used as a temporary (not assigned), the garbage
collector may free the shared memory before a consumer process has
mapped it.
See also
map_shared() to open a shared region by name,
shared_name() to extract the SHM name.