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Reputation: 17131

Erlang - Random Number gen with Makeref

I am trying to generate a random enough number quickly.

Right Now I am using the following:

uniqueID() ->   C = random:uniform(9999) ,   %%%DO SPEED TEST
    random:seed(C,random:uniform(99),random:uniform(99)),
    {_, {H, Min, S}}  = calendar:universal_time(),
    {A, B} = statistics(wall_clock),
    (A*B) +((H + C + Min) * S).

It takes too long compared to something like make_ref().

6> make_ref().
#Ref<0.0.0.74>

How can I take the unique ref and parse it to become an integer?

such as 00074

Thanks for the help.

Upvotes: 5

Views: 1843

Answers (3)

toraritte
toraritte

Reputation: 8303

From Erlang/OTP release 18.0 this is supported out of the box using erlang:unique_integer/{0,1}.

Called without options it returns unique values and with modifiers it produces strictly monotonic results albeit these calls are more expensive.

erlang:unique_integer() -> integer()
erlang:unique_integer(ModList) -> integer()     Modlist = [Modifier]
    Modifier = positive | monotonic

Generates and returns an integer unique on current runtime system instance. The integer is unique in the sense that this BIF, using the same set of modifiers, will not return the same integer more than once on the current runtime system instance. Each integer value can of course be constructed by other means.

Currently valid Modifiers:

positive
    Return only positive integers.

monotonic
    Return strictly monotonically increasing integers corresponding to creation time.

As erlang:now/0 became deprecated, a few things are suggested to be implemented with erlang:unique_integer/{0,1}.

Upvotes: 0

probsolver
probsolver

Reputation: 926

{A,B,C} = now(), A * 1000000000000 + B * 1000000 + C.

Upvotes: 1

archaelus
archaelus

Reputation: 7129

Are you really sure you want to use erlang:make_ref/0 for unique numbers? Refs are only unique for one launch of one erlang vm - they are repeatable, predictable, and make lousy unique identifiers if you plan to use them for anything other than tags in erlang messages to match up requests and replies.

You could do it by formatting the ref as a string (erlang:ref_to_list/1) and then parsing that.

However, I think the best idea would be to use crypto:rand_bytes/1 to get yourself an N byte binary of random bytes, or crypto:rand_uniform/2 if you need a random integer in some range. This method at least gives you some guarantees as to the quality of the random integers you produce (see the openssl rand_bytes documentation).

Upvotes: 8

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