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# Poolboy - A hunky Erlang worker pool factory
[](https://travis-ci.org/devinus/poolboy)
[](https://gratipay.com/devinus/)
Poolboy is a **lightweight**, **generic** pooling library for Erlang with a
focus on **simplicity**, **performance**, and **rock-solid** disaster recovery.
## Usage
```erl-sh
1> Worker = poolboy:checkout(PoolName).
<0.9001.0>
2> gen_server:call(Worker, Request).
ok
3> poolboy:checkin(PoolName, Worker).
ok
```
## Example
This is an example application showcasing database connection pools using
Poolboy and [epgsql](https://github.com/epgsql/epgsql).
### example.app
```erlang
{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
```erlang
-module(example).
-behaviour(application).
-behaviour(supervisor).
-export([start/0, stop/0, squery/2, equery/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({Name, SizeArgs, WorkerArgs}) ->
PoolArgs = [{name, {local, Name}},
{worker_module, example_worker}] ++ SizeArgs,
poolboy:child_spec(Name, PoolArgs, WorkerArgs)
end, Pools),
{ok, {{one_for_one, 10, 10}, PoolSpecs}}.
squery(PoolName, Sql) ->
poolboy:transaction(PoolName, fun(Worker) ->
gen_server:call(Worker, {squery, Sql})
end).
equery(PoolName, Stmt, Params) ->
poolboy:transaction(PoolName, fun(Worker) ->
gen_server:call(Worker, {equery, Stmt, Params})
end).
```
### example_worker.erl
```erlang
-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} = epgsql:connect(Hostname, Username, Password, [
{database, Database}
]),
{ok, #state{conn=Conn}}.
handle_call({squery, Sql}, _From, #state{conn=Conn}=State) ->
{reply, epgsql:squery(Conn, Sql), State};
handle_call({equery, Stmt, Params}, _From, #state{conn=Conn}=State) ->
{reply, epgsql:equery(Conn, Stmt, Params), State};
handle_call(_Request, _From, State) ->
{reply, ok, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, #state{conn=Conn}) ->
ok = epgsql: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
- `strategy`: `lifo` or `fifo`, determines whether checked in workers should be
placed first or last in the line of available workers. So, `lifo` operates like a traditional stack; `fifo` like a queue. Default is `lifo`.
## Authors
- Devin Torres (devinus) <devin@devintorres.com>
- Andrew Thompson (Vagabond) <andrew@hijacked.us>
- Kurt Williams (onkel-dirtus) <kurt.r.williams@gmail.com>
## License
Poolboy is available in the public domain (see `UNLICENSE`).
Poolboy is also optionally available under the ISC license (see `LICENSE`),
meant especially for jurisdictions that do not recognize public domain works.
|
