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A hunky Erlang worker pool factory
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README.md

Poolboy - A hunky Erlang worker pool factory

Usage

Worker = poolboy:checkout(PoolName),
Reply = gen_server:call(Worker, WorkerFun),
poolboy:checkin(PoolName, Worker),
Reply.

Example

This is an example application showcasing database connection pools using Poolboy and Will Glozer's epgsql.

example.app

{application, example, [
    {description, "An example application"},
    {vsn, "0.1"},
    {applications, [kernel, stdlib, sasl, crypto, ssl]},
    {modules, [example, example_worker]},
    {registered, [example]},
    {mod, {example, []}},
    {env, [
        {pools, [
            {pool1, [
                {size, 10},
                {max_overflow, 20},
                {hostname, "127.0.0.1"},
                {database, "db1"},
                {username, "db1"},
                {password, "abc123"}
            ]},
            {pool2, [
                {size, 5},
                {max_overflow, 10},
                {hostname, "127.0.0.1"},
                {database, "db2"},
                {username, "db2"},
                {password, "abc123"}
            ]}
        ]}
    ]}
]}.

example.erl

-module(example).
-behaviour(application).
-behaviour(supervisor).

-export([start/0, stop/0, query/2, query/3]).
-export([start/2, stop/1]).
-export([init/1]).

start() ->
    application:start(?MODULE).

stop() ->
    application:stop(?MODULE).

start(_Type, _Args) ->
    supervisor:start_link({local, example_sup}, ?MODULE, []).

stop(_State) ->
    ok.

init([]) ->
    {ok, Pools} = application:get_env(example, pools),
    PoolSpecs = lists:map(fun({PoolName, PoolConfig}) ->
        Args = [{name, {local, PoolName}},
                {worker_module, example_worker}]
                ++ PoolConfig,
        {PoolName, {poolboy, start_link, [Args]},
                    permanent, 5000, worker, [poolboy]}
    end, Pools),
    {ok, {{one_for_one, 10, 10}, PoolSpecs}}.

query(PoolName, Sql) ->
    Worker = poolboy:checkout(PoolName),
    Reply = gen_server:call(Worker, {query, Sql}),
    poolboy:checkin(PoolName, Worker),
    Reply.

query(PoolName, Stmt, Params) ->
    Worker = poolboy:checkout(PoolName),
    Reply = gen_server:call(Worker, {query, Stmt, Params}),
    poolboy:checkin(PoolName, Worker),
    Reply.

example_worker.erl

-module(example_worker).
-behaviour(gen_server).
-behaviour(poolboy_worker).

-export([start_link/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
         code_change/3]).

-record(state, {conn}).

start_link(Args) ->
    gen_server:start_link(?MODULE, Args, []).

init(Args) ->
    process_flag(trap_exit, true),
    Hostname = proplists:get_value(hostname, Args),
    Database = proplists:get_value(database, Args),
    Username = proplists:get_value(username, Args),
    Password = proplists:get_value(password, Args),
    {ok, Conn} = pgsql:connect(Hostname, Username, Password, [
        {database, Database}
    ]),
    {ok, #state{conn=Conn}}.

handle_call({query, Sql}, _From, #state{conn=Conn}=State) ->
    {reply, pgsql:squery(Conn, Sql), State};
handle_call({query, Stmt, Params}, _From, #state{conn=Conn}=State) ->
    {reply, pgsql:equery(Conn, Stmt, Params), State};
handle_call(_Request, _From, State) ->
    {reply, ok, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(stop, State) ->
    {stop, shutdown, State};
handle_info({'EXIT', _, _}, State) ->
    {stop, shutdown, State};
handle_info(_Info, State) ->
    {noreply, State}.

terminate(_Reason, #state{conn=Conn}) ->
    pgsql:close(Conn),
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

Options

  • name: the pool name
  • worker_module: the module that represents the workers
  • size: maximum pool size
  • max_overflow: maximum number of workers created if pool is empty

Authors

License

Poolboy is available in the public domain (see UNLICENSE). Poolboy is also optionally available under the Apache License (see LICENSE), meant especially for jurisdictions that do not recognize public domain works.

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