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Example of using Poolboy in Elixir to limit concurrency (e.g. of HTTP requests).
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defmodule HttpRequester do | |
use GenServer | |
def start_link(_) do | |
GenServer.start_link(__MODULE__, nil, []) | |
end | |
def fetch(server, url) do | |
# Don't use cast: http://blog.elixirsips.com/2014/07/16/errata-dont-use-cast-in-a-poolboy-transaction/ | |
timeout_ms = 10_000 | |
GenServer.call(server, {:fetch, url}, timeout_ms) | |
end | |
def handle_call({:fetch, url}, _from, state) do | |
IO.puts "fetching #{url}" | |
:timer.sleep 5000 | |
IO.puts "fetched #{url}" | |
{:reply, "whatever", state} | |
end | |
end | |
defmodule PoolboyDemo do | |
def run do | |
transaction_timeout_ms = 10_000 | |
await_timeout_ms = 100_000 | |
{:ok, pool} = :poolboy.start_link( | |
[worker_module: HttpRequester, size: 5, max_overflow: 0] | |
) | |
tasks = Enum.map 1..20, fn(n) -> | |
Task.async fn -> | |
:poolboy.transaction pool, fn(http_requester_pid) -> | |
HttpRequester.fetch(http_requester_pid, "url #{n}") | |
end, transaction_timeout_ms | |
end | |
end | |
tasks |> Enum.each &Task.await(&1, await_timeout_ms) | |
end | |
end |
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Yes, this looks good and the changes make sense.
I suggest using
GenServer.*
instead of:gen_server.*
:infinity
timeout is almost never a good idea, so I suggest using some finite value. Otherwise, you risk deadlocks and total blockages of your system.