Type: Package
Title: Process Synchronization Using File Locks
Version: 0.7
Date: 2016-11-10
Author: Ivan Popivanov
Maintainer: Ivan Popivanov <ivan.popivanov@gmail.com>
Description: Implements synchronization between R processes (spawned by using the "parallel" package for instance) using file locks. Supports both exclusive and shared locking.
License: Apache License 2.0
Imports: Rcpp (≥ 0.11.3), methods
LinkingTo: Rcpp
NeedsCompilation: yes
Packaged: 2016-11-12 06:59:02 UTC; ivpop
Repository: CRAN
Date/Publication: 2016-11-12 16:23:32

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 <ivan.popivanov@gmail.com>

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)

Locking/Unlocking

Description

Checks whether a lock has been obtained.

Usage

is.locked(file.lock)

Arguments

file.lock

The lock as an object of type FileLock.

Author(s)

Ivan Popivanov

Examples

## Not run: 
require(flock)

file.lock = lock("~/file.lock")
# Critical section code goes between here and the unlock call
if(is.locked(file.lock)) {
   print("Got the lock!")
}
unlock(file.lock)

## End(Not run)

Locking/Unlocking

Description

Locks a file in exclusive or shared mode.

Usage

lock(path, exclusive = TRUE)

Arguments

path

Character. The path.

exclusive

Logical. The lock type, exclusive or shared.

Details

The file is created if it doesn't exist.

Value

Returns an object of type FileLock, which is to be used for the unlock call.

Author(s)

Ivan Popivanov

Examples

## Not run: 
require(flock)

file.lock = lock("~/file.lock")
# Critical section code goes here
unlock(file.lock)

## End(Not run)

Locking/Unlocking

Description

Unlocks a file previously locked via lock.

Usage

unlock(file.lock)

Arguments

file.lock

The FileLock object returned by lock.

Author(s)

Ivan Popivanov

See Also

lock

Examples

## Not run: 
require(flock)

file.lock = lock("~/file.lock")
# Critical section code goes here
unlock(file.lock)

## End(Not run)