Shared Memory Atomic Operations • semaphore

The goal of semaphore is to enable synchronization of concurrent R processes.

Implements named semaphores from the Boost C++ library. Semaphores are managed by the operating system, which is responsible for ensuring that this integer value can be safely incremented or decremented by multiple processes. Processes can also wait (blocking) for the value to become non-zero.

Works cross-platform, including Windows, MacOS, and Linux.

Installation

# Install the latest stable version from CRAN:
install.packages("semaphore")

# Or the development version from GitHub:
install.packages("pak")
pak::pak("cmmr/semaphore")

Usage

library(semaphore)

s <- create_semaphore()
print(s)
#> [1] "uUkKpNMbTVgaborHG4rH"

increment_semaphore(s)

decrement_semaphore(s, wait = FALSE)
#> [1] TRUE
decrement_semaphore(s, wait = FALSE)
#> [1] FALSE

remove_semaphore(s)
#> [1] TRUE

Example: Producer/Consumer

Open two separate R sessions on the same machine.

Session 1 - Producer

library(semaphore)
s <- 'mySemaphore'

create_semaphore(s)

# enable session 2 to output 'unblocked!' three times
increment_semaphore(s)
increment_semaphore(s)
increment_semaphore(s)

remove_semaphore(s)

Session 2 - Consumer

library(semaphore)
s <- 'mySemaphore'

for (i in 1:3) {

  # Block until session 1 increments the semaphore
  decrement_semaphore(s)
  
  # Do some work
  message('unblocked!')
}

message('finished')