flock-package {flock}

Process synchronization using file locks.

Description

Enables synchronization between R processes using a file lock. Supports both exclusive (writer) and shared (readers) locks.

On UNIX, the implementation relies on the fcntl system call. While on Windows, the LockFileEx/UnlockFileEx APIs are used.

Details

Package:	flock
Type:	Package
Version:	0.6
Date:	2014-11-24
License:	Apache License 2.0

Author(s)

Ivan Popivanov

Maintainer: Ivan Popivanov <[e-mail]>

Examples

## Not run: 
require(DBI)
require(flock)
require(RSQLite)
require(parallel)

dbpath <- tempfile()
con <- dbConnect(RSQLite::SQLite(), dbname=dbpath)
df <- data.frame(value = 0)
dbWriteTable(con, "test", df)
dbDisconnect(con)

write.one.value <- function(val, lock.name=NULL) {
   if(!is.null(lock.name)) {
      file.lock = lock(lock.name)
   }
   
   # The three lines below are the "critical section"
   con <- dbConnect(RSQLite::SQLite(), dbname = dbpath)
   dbWriteTable(con, "test", data.frame(value = val), append = TRUE)
   dbDisconnect(con)
   
   if(!is.null(lock.name)) {
      unlock(file.lock)
   }
}

lock.name = tempfile()

# Run the parallel database updates with two cores
mclapply(1:100, write.one.value, mc.cores=2, lock.name=lock.name)

# To see the failing scenario, run (on a multi-core system):
# mclapply(1:100, write.one.value, mc.cores=2)

## End(Not run)