Task.Supervisor

A task supervisor.

This module defines a supervisor which can be used to dynamically supervise tasks. Behind the scenes, this module is implemented as a :simple_one_for_one supervisor where the workers are temporary by default (that is, they are not restarted after they die; read the docs for start_link/1 for more information on choosing the restart strategy).

See the Task module for more information.

Name registration

A Task.Supervisor is bound to the same name registration rules as a GenServer. Read more about them in the GenServer docs.

Summary

Functions

async(supervisor, fun): Starts a task that can be awaited on
async(supervisor, module, fun, args): Starts a task that can be awaited on
async_nolink(supervisor, fun): Starts a task that can be awaited on
async_nolink(supervisor, module, fun, args): Starts a task that can be awaited on
async_stream(supervisor, enumerable, fun, options \\ []): Returns a stream that runs the given function concurrently on each item in enumerable
async_stream(supervisor, enumerable, module, function, args, options \\ []): Returns a stream that runs the given module, function and args concurrently on each item in enumerable
async_stream_nolink(supervisor, enumerable, fun, options \\ []): Returns a stream that runs the given function concurrently on each item in enumerable
async_stream_nolink(supervisor, enumerable, module, function, args, options \\ []): Returns a stream that runs the given module, function and args concurrently on each item in enumerable
children(supervisor): Returns all children PIDs
start_child(supervisor, fun): Starts a task as a child of the given supervisor
start_child(supervisor, module, fun, args): Starts a task as a child of the given supervisor
start_link(opts \\ []): Starts a new supervisor
terminate_child(supervisor, pid): Terminates the child with the given pid

Functions

async(supervisor, fun)

async(Supervisor.supervisor(), (... -> any())) :: Task.t()

Starts a task that can be awaited on.

The supervisor must be a reference as defined in Task.Supervisor. The task will still be linked to the caller, see Task.async/3 for more information and async_nolink/2 for a non-linked variant.

async(supervisor, module, fun, args)

async(Supervisor.supervisor(), module(), atom(), [term()]) :: Task.t()

Starts a task that can be awaited on.

async_nolink(supervisor, fun)

async_nolink(Supervisor.supervisor(), (... -> any())) :: Task.t()

Starts a task that can be awaited on.

The supervisor must be a reference as defined in Task.Supervisor. The task won’t be linked to the caller, see Task.async/3 for more information.

Compatibility with OTP behaviours

If you create a task using async_nolink inside an OTP behaviour like GenServer, you should match on the message coming from the task inside your GenServer.handle_info/2 callback.

The reply sent by the task will be in the format {ref, result}, where ref is the monitor reference held by the task struct and result is the return value of the task function.

Keep in mind that, regardless of how the task created with async_nolink terminates, the caller’s process will always receive a :DOWN message with the same ref value that is held by the task struct. If the task terminates normally, the reason in the :DOWN message will be :normal.

async_nolink(supervisor, module, fun, args)

async_nolink(Supervisor.supervisor(), module(), atom(), [term()]) :: Task.t()

Starts a task that can be awaited on.

The supervisor must be a reference as defined in Task.Supervisor. The task won’t be linked to the caller, see Task.async/3 for more information.

async_stream(supervisor, enumerable, fun, options \\ [])

async_stream(Supervisor.supervisor(), Enumerable.t(), (term() -> term()), Keyword.t()) :: Enumerable.t()

Returns a stream that runs the given function concurrently on each item in enumerable.

Each item will be appended to the given args and processed by its own task. The tasks will be spawned under the given supervisor and are linked to the current process, similar to async/2.

See async_stream/6 for discussion and examples.

async_stream(supervisor, enumerable, module, function, args, options \\ [])

async_stream(Supervisor.supervisor(), Enumerable.t(), module(), atom(), [term()], Keyword.t()) :: Enumerable.t()

Returns a stream that runs the given module, function and args concurrently on each item in enumerable.

Each item will be appended to the given args and processed by its own task. The tasks will be spawned under the given supervisor and linked to the current process, similar to async/4.

When streamed, each task will emit {:ok, val} upon successful completion or {:exit, val} if the caller is trapping exits. Results are emitted in the same order as the original enumerable.

The level of concurrency can be controlled via the :max_concurrency option and defaults to System.schedulers_online/0. The timeout can also be given as option and defaults to 5000 and it defaults to the maximum amount of time to wait without a task reply.

Finally, if you find yourself trapping exits to handle exits inside the async stream, consider using async_stream_nolink/6 to start tasks that are not linked to the current process.

Options

:max_concurrency - sets the maximum number of tasks to run at the same time. Defaults to System.schedulers_online/0.
:timeout - the maximum amount of time to wait without receiving a task reply (across all running tasks). Defaults to 5000.

Examples

Let’s build a stream and then enumerate it:

stream = Task.Supervisor.async_stream(MySupervisor, collection, Mod, :expensive_fun, [])
Enum.to_list(stream)

async_stream_nolink(supervisor, enumerable, fun, options \\ [])

async_stream_nolink(Supervisor.supervisor(), Enumerable.t(), (term() -> term()), Keyword.t()) :: Enumerable.t()

Returns a stream that runs the given function concurrently on each item in enumerable.

Each item will be appended to the given args and processed by its own task. The tasks will be spawned under the given supervisor and are not linked to the current process, similar to async_nolink/2.

See async_stream/6 for discussion and examples.

async_stream_nolink(supervisor, enumerable, module, function, args, options \\ [])

async_stream_nolink(Supervisor.supervisor(), Enumerable.t(), module(), atom(), [term()], Keyword.t()) :: Enumerable.t()

Returns a stream that runs the given module, function and args concurrently on each item in enumerable.

See async_stream/6 for discussion and examples.

children(supervisor)

children(Supervisor.supervisor()) :: [pid()]

Returns all children PIDs.

start_child(supervisor, fun)

start_child(Supervisor.supervisor(), (... -> any())) :: {:ok, pid()}

Starts a task as a child of the given supervisor.

Note that the spawned process is not linked to the caller, but only to the supervisor. This command is useful in case the task needs to perform side-effects (like I/O) and does not need to report back to the caller.

start_child(supervisor, module, fun, args)

start_child(Supervisor.supervisor(), module(), atom(), [term()]) :: {:ok, pid()}

Starts a task as a child of the given supervisor.

Similar to start_child/2 except the task is specified by the given module, fun and args.

start_link(opts \\ [])

start_link(Supervisor.options()) :: Supervisor.on_start()

Starts a new supervisor.

The supported options are:

:name - used to register a supervisor name, the supported values are described under the Name Registration section in the GenServer module docs;
:restart - the restart strategy, may be :temporary (the default), :transient or :permanent. Check Supervisor.Spec for more info. Defaults to :temporary so tasks aren’t automatically restarted when they complete nor in case of crashes;
:shutdown - :brutal_kill if the tasks must be killed directly on shutdown or an integer indicating the timeout value, defaults to 5000 milliseconds;
:max_restarts and :max_seconds - as specified in Supervisor.Spec.supervise/2;

terminate_child(supervisor, pid)

terminate_child(Supervisor.supervisor(), pid()) :: :ok

Terminates the child with the given pid.

© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/elixir/1.4.5/Task.Supervisor.html