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https://github.com/whitfin/sleeplocks

BEAM friendly spinlocks for Elixir/Erlang
https://github.com/whitfin/sleeplocks

concurrency concurrent-data-structure parallel-programming

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BEAM friendly spinlocks for Elixir/Erlang

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README 

        
# sleeplocks

[![Build Status](https://img.shields.io/github/actions/workflow/status/whitfin/sleeplocks/ci.yml?branch=main)](https://github.com/whitfin/sleeplocks/actions) [![Hex.pm Version](https://img.shields.io/hexpm/v/sleeplocks.svg)](https://hex.pm/packages/sleeplocks) [![Documentation](https://img.shields.io/badge/docs-latest-blue.svg)](https://hexdocs.pm/sleeplocks/)



This library is designed to provide simple locking mechanisms in Erlang/Elixir, similar to

how spinlocks work in other languages - except using messages to communicate locking.



This is useful for libraries which require lock synchronization, without having to roll your

own (however simple). Locks can be held by arbitrary numbers of process, making it possible

to implement various throttling mechanisms.



Best of all, this library is tiny! It builds upon basic OTP principles to implement lock

behaviour via simple processes and message passing.



## Installation



### Rebar



Follow the instructons found [here](https://hex.pm/docs/rebar3_usage) to configure your

Rebar setup to use Hex as a dependency source, then you can grab it directly:



```erlang

{deps,[

  % pulls the latest version

  sleeplocks,

  % to pull the latest version from github

  {sleeplocks, {git, "git://github.com/whitfin/sleeplocks.git"}}

]}.

```



### Mix



To install it for your project, you can pull it directly from Hex. Rather

than use the version shown below, you can use the latest version from

Hex (shown at the top of this README).



```elixir

def deps do

  [{:sleeplocks, "~> 1.0"}]

end

```



## Usage



Snippets below contain sample usage in both Erlang and Elixir, and cover most of the small

API space offered by `sleeplocks`. For a more complete example, scroll down!



### Erlang



```erlang

% create a new single lock (with a name)

1> sleeplocks:new(1, [{name, {local, my_lock}}]).

{ok,<0.179.0>}



% take ownership of the lock

2> sleeplocks:acquire(my_lock).

ok



% release the current hold on a lock

3> sleeplocks:release(my_lock).

ok



% attempt to acquire a lock (which will succeed)

4> sleeplocks:attempt(my_lock).

ok



% now that it's taken, other attempts will fail

5> sleeplocks:attempt(my_lock).

{error,unavailable}



% release the lock again

6> sleeplocks:release(my_lock).

ok



% handle acquisition and locking automatically

7> sleeplocks:execute(my_lock, fun() ->

7>   3

7> end).

3

```



### Elixir



```elixir

# create a new single lock (with a name)

iex(1)> :sleeplocks.new(1, [ name: :my_lock ])

{:ok, #PID<0.179.0>}



# take ownership of the lock

iex(2)> :sleeplocks.acquire(:my_lock)

:ok



# release the current hold on a lock

iex(3)> :sleeplocks.release(:my_lock)

:ok



# attempt to acquire a lock (which will succeed)

iex(4)> :sleeplocks.attempt(:my_lock)

:ok



# now that it's taken, other attempts will fail

iex(5)> :sleeplocks.attempt(:my_lock)

{:error, :unavailable}



# release the lock again

iex(6)> :sleeplocks.release(:my_lock)

:ok



# handle acquisition and locking automatically

iex(7)> :sleeplocks.execute(:my_lock, fn ->

iex(7)>   3

iex(7)> end)

3

```



## Examples



This example is in Elixir, but it should be fairly understandable for those coming from

both languages. It simply spawns 6 processes which each attempt to hold a lock for 10

seconds. As the lock is created with only 2 slots, this runs for 30 seconds and 2 of our

spawned tasks can hold the lock at any given time.



```elixir

# First create a new lock, with 2 slots only

{:ok, ref} = :sleeplocks.new(2)



# Then spawn 6 tasks, which each just sleep for 10 seconds

# after acquiring the lock. This means that 2 processes will

# acquire a lock and then release after 10 seconds. This

# will repeat 3 times (6 / 2) until 30 seconds are up.

for idx <- 1..6 do

  Task.start(fn ->

    :sleeplocks.execute(ref, fn ->

      IO.puts("Locked #{idx}")

      Process.sleep(10_000)

      IO.puts("Releasing #{idx}")

    end)

  end)

end

```