flock (version 0.7)

flock-package: 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

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)