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puddle.gleam
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puddle.gleam
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import gleam/list
import gleam/result
import gleam/otp/actor
import gleam/erlang/process
pub opaque type ManagerMessage(resource_type, result_type) {
ManagerShutdown(fn(resource_type) -> Nil)
CheckIn(process.Subject(ResourceMessage(resource_type, result_type)))
CheckOut(
process.Subject(
Result(process.Subject(ResourceMessage(resource_type, result_type)), Nil),
),
)
}
pub opaque type ResourceMessage(resource_type, result_type) {
ResourceUsage(
fn(resource_type) -> result_type,
process.Subject(Result(result_type, Nil)),
)
ResourceShutdown(fn(resource_type) -> Nil)
}
type Puddle(resource_type, result_type) =
List(process.Subject(ResourceMessage(resource_type, result_type)))
pub fn start(
size: Int,
resource_creation_function: fn() -> Result(resource_type, Nil),
) -> Result(
process.Subject(ManagerMessage(resource_type, result_type)),
actor.StartError,
) {
use puddle <- result.then(
new(size, resource_creation_function)
|> result.map_error(fn(_) {
actor.InitFailed(process.Abnormal("Failed to create new resource"))
}),
)
actor.start(puddle, handle_manager_message)
}
/// checks-out a resource, applies the function and then checks-in the resource
pub fn apply(
manager: process.Subject(ManagerMessage(resource_type, result_type)),
fun: fn(resource_type) -> result_type,
timeout: Int,
rest,
) {
use subject <- result.then(
check_out(manager, timeout)
|> result.replace_error(Nil)
|> result.flatten,
)
let mine = process.new_subject()
utilize(subject, fun, mine)
let selector =
process.new_selector()
|> process.selecting(mine, fn(r) { r })
let result =
process.select(selector, timeout)
|> result.flatten
check_in(manager, subject)
rest(result)
}
pub fn shutdown(manager, resource_shutdown_function) {
process.send(manager, ManagerShutdown(resource_shutdown_function))
}
fn check_out(
manager: process.Subject(ManagerMessage(resource_type, result_type)),
timeout: Int,
) {
process.try_call(manager, CheckOut, timeout)
}
fn utilize(
subject: process.Subject(ResourceMessage(resource_type, result_type)),
fun: fn(resource_type) -> result_type,
mine: process.Subject(Result(result_type, Nil)),
) {
process.send(subject, ResourceUsage(fun, mine))
}
fn check_in(
manager: process.Subject(ManagerMessage(resource_type, result_type)),
subject: process.Subject(ResourceMessage(resource_type, result_type)),
) {
process.send(manager, CheckIn(subject))
}
fn new(
size: Int,
resource_creation_function: fn() -> Result(resource_type, Nil),
) -> Result(Puddle(resource_type, result_type), Nil) {
list.repeat("", size)
|> list.try_map(fn(_) {
case resource_creation_function() {
Ok(initial_state) -> {
actor.start(initial_state, handle_resource_message)
|> result.nil_error()
}
Error(Nil) -> Error(Nil)
}
})
}
fn handle_manager_message(
msg: ManagerMessage(resource_type, result_type),
puddle: Puddle(resource_type, result_type),
) {
case msg {
ManagerShutdown(resource_shutdown_function) -> {
list.each(
puddle,
fn(item) {
process.send(item, ResourceShutdown(resource_shutdown_function))
},
)
actor.Stop(process.Normal)
}
CheckIn(subject) -> {
actor.continue(list.prepend(puddle, subject))
}
CheckOut(client) -> {
case puddle {
[] -> {
actor.send(client, Error(Nil))
actor.continue(puddle)
}
[chosen, ..new_puddle] -> {
actor.send(client, Ok(chosen))
actor.continue(new_puddle)
}
}
}
}
}
fn handle_resource_message(
msg: ResourceMessage(resource_type, result_type),
resource: resource_type,
) {
case msg {
ResourceUsage(fun, client) -> {
let result = fun(resource)
actor.send(client, Ok(result))
actor.continue(resource)
}
ResourceShutdown(shutdown) -> {
shutdown(resource)
actor.Stop(process.Normal)
}
}
}