dplR (version 1.5.3)

uuid.gen: UUID Generator

Description

Initializes and returns a generator of universally unique identifiers. Use the returned function repeatedly for creating one or more UUIDs, one per function call.

Usage

uuid.gen(more.state = "")

Arguments

more.state

A character string for altering the state of the generator

Value

• A parameterless function which returns a single UUID (character string)

Details

This function returns a function (closure) which generates UUIDs. The state of that anonymous function is set when uuid.gen is called. The state consists of the following:

• System and user information (Sys.info)
• Rversion (R.version)
• Platform information (.Platform)
• Working directory
• ProcessIDof theRsession
• Time whenuuid.genwas called (precision of seconds or finer)
• The text in parametermore.state

The Pseudo Random Number Generator of R(see .Random.seed) is used in the generation of UUIDs. No initialization of the PRNG is done. Tampering with the state of the RPRNG while using a given UUID generator causes a risk of non-unique identifiers. Particularly, setting the state of the PRNG to the same value before two calls to the UUID generator guarantees two identical identifiers. If two UUID generators have a different state, it is not a problem to have the PRNG going through or starting from the same state with both generators.

The user is responsible for selecting a PRNG with a reasonable number of randomness. Usually, this doesn't require any action. For example, any PRNG algorithm available in Rworks fine. However, the uniqueness of UUIDs can be destroyed by using a bad user-supplied PRNG.

The UUIDs produced by uuid.gen generators are Version 4 (random) with 122 random bits and 6 fixed bits. The UUID is presented as a character string of 32 hexadecimal digits and 4 hyphens:

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

where x is any hexadecimal digit and y is one of "8", "9", "a", or "b". Each x and y in the example is an independent variables (for all practical purposes); subscripts are omitted for clarity. The UUID generator gets 32 hex digits from the MD5 message digest algorithm by feeding it a string consisting of the constant generator state and 5 (pseudo) random numbers. After that, the 6 bits are fixed and the hyphens are added to form the final UUID.

References

Leach, P., Mealling, M. and Salz, R. (July 2005) A Universally Unique IDentifier (UUID) URN Namespace, RFC 4122. [Online]. Available: http://tools.ietf.org/html/rfc4122

See Also

digest, Random

Examples

## Normal use
ug <- uuid.gen()
uuids <- character(100)
for(i in 1:100){
  uuids[i] <- ug()
}
length(unique(uuids)) == 100 # TRUE, UUIDs are unique with high probability

## Do NOT do the following unless you want non-unique IDs
rs <- .Random.seed
set.seed(0L)
id1 <- ug()
set.seed(0L)
id2 <- ug()
id1 != id2 # FALSE, The UUIDs are the same
.Random.seed <- rs

## Strange usage pattern, but will probably produce unique IDs
ug1 <- uuid.gen("1")
set.seed(0L)
id1 <- ug1()
ug2 <- uuid.gen("2")
set.seed(0L)
id2 <- ug2()
id1 != id2 # TRUE, The UUIDs are different with high probability
.Random.seed <- rs