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Zero-Copy Shared Objects

Source: R/share.R
share.Rd

Create shared memory representations of R objects for efficient parallel access without duplication.

Creates a shared memory representation of an R object. The object is serialized once and can be accessed by multiple worker processes without copying.

Usage

share(
  x,
  backing = c("auto", "mmap", "shm"),
  readonly = TRUE,
  name = NULL,
  deep = FALSE,
  min_bytes = 64 * 1024 * 1024,
  cycle = c("error", "skip"),
  mode = c("balanced", "strict")
)

Arguments

x

An R object to share. Supports vectors, matrices, arrays, lists, data frames, and any object that can be serialized with serialize().

backing

Backing type: "auto" (default), "mmap", or "shm".

  • "auto": Let the system choose the best option.

  • "mmap": File-backed memory mapping. Most portable.

  • "shm": POSIX shared memory or Windows named mapping.

readonly

Logical. If TRUE (default), the segment is protected after writing, making it read-only. Set to FALSE only if you need to modify the shared data (advanced use case).

name

Optional name for the shared object. If NULL (default), a unique name is generated. Named shares can be opened by name in other processes.

deep

Logical. If TRUE, recursively traverse lists and data.frames, sharing individual components that meet the size threshold. When FALSE (default), the entire object is serialized as one unit.

min_bytes

Minimum size in bytes for an object to be shared when deep=TRUE. Objects smaller than this threshold are kept in-place. Default is 64MB (64 * 1024 * 1024).

cycle

How to handle cyclic references when deep=TRUE. Either "error" (default) to stop with an error, or "skip" to skip cyclic references.

mode

Sharing mode when deep=TRUE. Either "balanced" (default) to continue on hook errors and non-shareable types, or "strict" to error.

Value

A shard_shared object (when deep=FALSE) or shard_deep_shared object (when deep=TRUE) containing:

  • path: The path or name of the shared segment

  • backing: The backing type used

  • size: Total size in bytes

  • readonly: Whether the segment is protected

  • class_info: Original class information

Details

The share() function is the primary high-level API for creating zero-copy shared inputs. When you share an object:

  1. The object is serialized into a shared memory segment

  2. The segment is marked read-only (protected)

  3. A lightweight handle is returned that can be passed to workers

  4. Workers attach to the segment and deserialize on demand

This approach eliminates per-worker duplication of large inputs. The data exists once in shared memory, and all workers read from the same location.

Immutability Contract: Shared objects are immutable by design. Any attempt to modify shared data in a worker will fail. This guarantees deterministic behavior and prevents accidental copy-on-write.

See also

segment_create for low-level segment operations, pool_create for worker pool management.

Examples

# \donttest{
mat <- matrix(rnorm(1e4), nrow = 100)
shared_mat <- share(mat)
recovered <- fetch(shared_mat)
identical(mat, recovered)
#> [1] FALSE
close(shared_mat)
# }