[erlang-questions] Timer implementation models

[Nathaniel Waisbrot]

Well for one, send_after/3 and send_interval/3 will produce slightly different timing.

Suppose your do_something/0 takes 50ms to run. Then in "Model 2", ignoring any complexities of scheduling, your function will be invoked at

t+1000, t+2050, t+3100, t+4150, t+5200, t+6250, ...

While "Model 3", under the same simplifying assumption would be invoked at

t+1000, t+2000, t+3000, t+4000, t+5000, t+6000, ...


To give you a few more choices:

- When using gen_server, I prefer to call timer:apply_after/4 and timer:apply_interval/4. I either have them call gen_server:cast/2 or a local function that calls cast.
- When using gen_server, you can give a timeout in your callback response. This works quite differently from the timer module, but might be useful for some things
- When using gen_statem, you can give a timeouts like gen_server, but a wider variety of behavior is available



> On Oct 30, 2017, at 6:35 PM, Chaitanya Chalasani <cchalasani@REDACTED> wrote:
> 
> Hi,
> 
> I have hundred’s of processes each running its own timers.
> I can think of the following models. Wanted to know the pros and cons of each model.
> 
> ** Model 1 **
> loop1(State) ->
>  receive
>  after 1000 ->
>      do_someting()
>  end.
> 
> ** Model 2 **
> loop2(State) ->
>  erlang:send_after(1000, self(), timeout),
>  receive
>    timeout ->
>      do_someting(),
>      erlang:send_after(1000, self(), timeout)
>  end.
> 
> ** Model 3 **
> loop3(State) ->
>  timer:send_interval(1000, self(), timeout),
>  loop3a(State).
> 
> loop3a(State) ->
>  receive
>    timeout ->
>      do_someting()
>  end.
> 
> The above three models using the gen_server -
> 
> ** Model 1 **
> init(_Args) ->
>  {ok, State, 1000}.
> 
> handle_info(timeout, State) ->
>  do_someting(),
>  {noreply, State, 1000}
> 
> ** Model 2 **
> init(_Args) ->
>  erlang:send_after(1000, self(), timeout),
>  {ok, State}.
> 
> handle_info(timeout, State) ->
>  do_someting(),
>  erlang:send_after(1000, self(), timeout),
>  {noreply, State}
> 
> ** Model 3 **
> init(_Args) ->
>  timer:send_interval(1000, self(), timeout),
>  {ok, State}.
> 
> handle_info(timeout, State) ->
>  do_someting(),
>  {noreply, State}
> 
> /Chaitanya
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