gen_server stands for "generic server", a module behaviour in Erlang.
Questions tagged [gen-server]
315 questions
37
votes
4 answers
How to perform actions periodically with Erlang's gen_server?
I want to start a gen_server that additionally, will perform one action every minute.
What is the best way to schedule that?
Piotr Usewicz
- 620
- 2
- 6
- 13
27
votes
1 answer
Does Elixir provide an easier way to get a GenServer process's current state?
Given a simple GenServer process.
defmodule KVServer do
use GenServer
def start do
GenServer.start(__MODULE__, %{}, name: :kv_server)
end
def store(k, v) do
GenServer.cast(:kv_server, {:store, k, v})
end
def…
sbs
- 4,102
- 5
- 40
- 54
26
votes
3 answers
Graceful shutdown of GenServer
I writing an Elixir app with GenServer that starts an external application on boot and shuts it down and does other clean-up on exit. I've added bootup functionality in the init/1 callback and cleanup code in the terminate/2 callback.
The init code…
Sheharyar
- 73,588
- 21
- 168
- 215
16
votes
4 answers
What's the benefit of registering name using {:via, module, term} in GenServer.start_link/3?
In GenServer.start_link/3 I can register a name locally using an atom for a process like this:
defmodule Worker do
use GenServer
def start_link do
GenServer.start_link(__MODULE__, nil, name: :worker)
end
end
Then I can start a supervisor…
sbs
- 4,102
- 5
- 40
- 54
14
votes
2 answers
Erlang: difference between using gen_server:cast/2 and standard message passing
I was working though a problem and noticed some code where a previous programmer was passing messages using the standard convention of PID ! Message. I have been using gen_server:cast/2. I was wondering if somebody could explain to me the critical…
RockyMountainHigh
- 2,871
- 5
- 34
- 68
13
votes
2 answers
Getting gen_server/gen_fsm state for debugging
Is it possible to obtain the current state of a gen_server process (presumably by sending some system message)? It could be useful when debugging.
Of course, I can add a message which returns the current state to handle_call:
get_state(Server) ->…
Alexey Romanov
- 167,066
- 35
- 309
- 487
13
votes
1 answer
gen_server with a dict vs mnesia table vs ets
I'm building an erlang server.
Users sends http requests to the server to update their status.
The http request process on the server saves the user status message in memory.
Every minute the server sends all messages to a remote server and clear…
pablo
- 2,719
- 11
- 49
- 67
12
votes
1 answer
How to handle timeouts in poolboy?
I have a problem with a long-time consuming migration, which I desired to run in the parallel (it can be runned in the parallel). Actually migration is about taking all records in the database and implement time- and resource- consuming operations…
Alex Antonov
- 14,134
- 7
- 65
- 142
11
votes
2 answers
In Erlang, what's the difference between gen_server:start() and gen_server:start_link()?
Can someone explain what's the difference between gen_server:start() and gen_server:start_link()?
I've been told that it's something about multi threading stuff.
EDIT:
If my gen_server is called from multiple threads, will it execute them all at…
Guga Melkadze
- 275
- 2
- 12
10
votes
1 answer
when to use Gen_Fsm and when to use Gen_Server?
After checking out Gen_Fsm and Gen_Server documents, I found that, more or less, they act as similar behavior. In my opinion, if there is one loop function for sending broadcast or listening tcp sock, it is better to use Gen_Fsm, or else to use…
why
- 23,923
- 29
- 97
- 142
10
votes
2 answers
Proper way to structure GenServer calls to self
I know it's pretty much impossible to have a GenServer process call itself because you essentially hit a deadlock. But, I'm curious if there's a preferred way to do this kind of thing.
Assume the following scenario: I've got a queue that I'm popping…
Micah
- 17,584
- 8
- 40
- 46
10
votes
3 answers
erlang OTP Supervisor crashing
I'm working through the Erlang documentation, trying to understand the basics of setting up an OTP gen_server and supervisor. Whenever my gen_server crashes, my supervisor crashes as well. In fact, whenever I have an error on the command line, my…
drfloob
- 3,154
- 1
- 24
- 31
10
votes
1 answer
My supervisor crashes when I try to start it from eshell?
I'm very new to OTP, I'm trying to create simple example to understand supervisor behaviour:
Here is simple increment server
-module( inc_serv ).
-behaviour( gen_server ).
-export( [ start/0, inc/1, stop/0 ] ).
-export( [ init/1, handle_call/3,…
stemm
- 5,960
- 2
- 34
- 64
8
votes
3 answers
What kind of types can be sent on an Erlang message?
Mainly I want to know if I can send a function in a message in a distributed Erlang setup.
On Machine 1:
F1 = Fun()-> hey end,
gen_server:call(on_other_machine,F1)
On Machine 2:
handler_call(Function,From,State) ->
{reply,Function(),State)
Does…
Federico
- 5,438
- 5
- 39
- 47
8
votes
2 answers
How to implement a resetable countdown timer with a GenServer in Elixir or Erlang
How do we implement a reset-able countdown timer with a GenServer?
1) perform a task after fixed amount of time, say every 60 seconds
2) have a way to reset the countdown back to 60 seconds before the timer elapses
I have looked at How to perform…
Charles Okwuagwu
- 10,538
- 16
- 87
- 157