Debouncer

Debouncer module to reduce frequency of function calls to alerts, updates and similar. It supports four different modes:

• apply() - For delayed triggers, e.g. to trigger an autocomplete action
• immediate() - For reducing frequency of events, the first event per interval is delivered immediately, e.g. trigger data processing tasks
• immediate2() - Similiar to immediate but never delays events, either forwards them or ignores them, e.g. to trigger alert emails
• delay() - Only triggers an event after the timeout period, any further event delays the trigger. E.g. to detect data streams that ended actvitiy

Usage Example

  Debouncer.apply(SomeKey, fn() -> 
    IO.puts("Hello World, debounced will appear in 5 seconds") 
  end)

  Debouncer.immediate(OtherKey, fn() -> 
    IO.puts("Hello World, will appear immediate, but not again within 5 seconds") 
  end)

Behaviour Graph

EVENT        X1---X2------X3-------X4----------
TIMEOUT      ----------|----------|----------|-
===============================================
apply()      ----------X2---------X3---------X4
immediate()  X1--------X2---------X3---------X4
immediate2() X1-----------X3-------------------
delay()      --------------------------------X4

This graph represents when the different variants fire an event respectively on a timeline. In code the first line would look like this:

fn ->
  Debouncer.apply(SomeKey, fn() -> IO.puts("X1") end, 1000)
  Process.sleep(500)
  Debouncer.apply(SomeKey, fn() -> IO.puts("X2") end, 1000)
  Process.sleep(800)
  Debouncer.apply(SomeKey, fn() -> IO.puts("X3") end, 1000)
  Process.sleep(900)
  Debouncer.apply(SomeKey, fn() -> IO.puts("X4") end, 1000)
  Process.sleep(1200)
end.()

> X2
> X3
> X4

Shorthands

When using Module-Function-Argument tuples as callbacks (aka mfa) it can be convenient to skip the key and use the mfa itself as key:

# Call later() function immediately with the default 5 second debounce:
Debouncer.immediate({__MODULE__, :later, []})

# Call later() function immediately with 1 second debounce:
Debouncer.immediate({__MODULE__, :later, []}, 1_000)

# Same but in using method binding
Debouncer.immediate(&later/0, 1_000)

WARNING

Don't use in-place fun definitions in the shorthand, as those not work as unique-key because each call will be a different instance. So the debounce counting won't work.

Example:

# Because (`fn -> 1 end != fn -> 1 end`) don't do this:
Debouncer.immediate(fn -> later() end, 1_000)

Installation

The debouncer can be installed by adding debouncer to your list of dependencies in mix.exs:

def deps do
  [
    {:debouncer, "~> 0.1"}
  ]
end

The debouncer is an application and will start a GenServer to trigger the events. To include the Application in your release add it to your extra applications:

  def application do
    [
      mod: {Your.Application, []},
      extra_applications: [:debouncer]
    ]
  end

If it's not started it will try to start itself on usage.

The docs can be found at https://hexdocs.pm/debouncer.

Remarks

The delay() behaviour should be the same as in Michal Muskalas Debounce implementation https://github.com/michalmuskala/debounce