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# Used by "mix format" | ||
[ | ||
inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"] | ||
] |
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name: CI | ||
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on: [push, pull_request] | ||
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jobs: | ||
build: | ||
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name: Build and test | ||
runs-on: ubuntu-latest | ||
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env: | ||
MIX_ENV: test | ||
GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} | ||
steps: | ||
- uses: actions/checkout@v2 | ||
- name: Set up Elixir | ||
uses: erlef/setup-beam@988e02bfe678367a02564f65ca2e37726dc0268f | ||
with: | ||
elixir-version: '1.12.3' # Define the elixir version [required] | ||
otp-version: '24.1' # Define the OTP version [required] | ||
- name: Restore dependencies cache | ||
uses: actions/cache@v2 | ||
with: | ||
path: deps | ||
key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }} | ||
restore-keys: ${{ runner.os }}-mix- | ||
- name: Install dependencies | ||
run: mix deps.get | ||
- name: Run tests | ||
run: mix coveralls.github |
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name: Release | ||
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on: workflow_dispatch | ||
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jobs: | ||
build: | ||
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name: Publish hex package | ||
runs-on: ubuntu-latest | ||
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env: | ||
GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} | ||
HEX_API_KEY: ${{ secrets.HEX_API_KEY }} | ||
steps: | ||
- uses: actions/checkout@v2 | ||
- name: Set up Elixir | ||
uses: erlef/setup-beam@988e02bfe678367a02564f65ca2e37726dc0268f | ||
with: | ||
elixir-version: '1.12.3' # Define the elixir version [required] | ||
otp-version: '24.1' # Define the OTP version [required] | ||
- name: Restore dependencies cache | ||
uses: actions/cache@v2 | ||
with: | ||
path: deps | ||
key: ${{ runner.os }}-mix-${{ hashFiles('**/mix.lock') }} | ||
restore-keys: ${{ runner.os }}-mix- | ||
- name: Install dependencies | ||
run: mix deps.get | ||
- name: Compile | ||
run: mix compile | ||
- name: Build hex package | ||
run: mix hex.build | ||
- name: Publish hex package | ||
run: mix hex.publish --yes |
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# The directory Mix will write compiled artifacts to. | ||
/_build/ | ||
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# If you run "mix test --cover", coverage assets end up here. | ||
/cover/ | ||
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# The directory Mix downloads your dependencies sources to. | ||
/deps/ | ||
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# Where third-party dependencies like ExDoc output generated docs. | ||
/doc/ | ||
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# Ignore .fetch files in case you like to edit your project deps locally. | ||
/.fetch | ||
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# If the VM crashes, it generates a dump, let's ignore it too. | ||
erl_crash.dump | ||
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# Also ignore archive artifacts (built via "mix archive.build"). | ||
*.ez | ||
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# Ignore package tarball (built via "mix hex.build"). | ||
stagger-*.tar | ||
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# Temporary files, for example, from tests. | ||
/tmp/ | ||
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# LSP | ||
.elixir_ls |
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# Changelog | ||
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## 0.1.0 (2022-01-26) - Initial revision | ||
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# MIT License | ||
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Copyright (c) 2022 Nick Gunn | ||
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Permission is hereby granted, free of charge, to any person obtaining | ||
a copy of this software and associated documentation files (the | ||
"Software"), to deal in the Software without restriction, including | ||
without limitation the rights to use, copy, modify, merge, publish, | ||
distribute, sublicense, and/or sell copies of the Software, and to | ||
permit persons to whom the Software is furnished to do so, subject to | ||
the following conditions: | ||
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The above copyright notice and this permission notice shall be | ||
included in all copies or substantial portions of the Software. | ||
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, | ||
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | ||
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | ||
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE | ||
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION | ||
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION | ||
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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# Stagger | ||
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[![Build Status](https://github.com/ausimian/stagger/actions/workflows/elixir.yml/badge.svg)](https://github.com/ausimian/stagger/actions?query=workflow%3A%22CI%22) | ||
[![Coverage Status](https://coveralls.io/repos/github/ausimian/stagger/badge.svg?branch=main)](https://coveralls.io/github/ausimian/stagger?branch=main) | ||
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Point-to-point, durable message-queues as GenStage producers. | ||
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Stagger enables the creation of GenStage processes that enqueue terms to simple, | ||
file-backed message-queues, allowing the producer and consumer to run independently | ||
of each other, possibly at different times. | ||
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+----------+ +----------+ +----------+ +------------+ | ||
| Upstream | | MsgQueue | | MsgQueue | | Downstream | | ||
| | -> | | <- | | <---> | | | ||
| Client | | Producer | | Consumer | | Processing | | ||
+----------+ +----------+ +----------+ +------------+ | ||
| | read | ||
write | | | ||
+------+ | ||
| FILE | | ||
| | | ||
| | | ||
+------+ | ||
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Your upstream client writes its events into the message-queue (provided by | ||
Stagger), which persists them to local storage. Your (GenStage) consumer, subscribes | ||
to the producer and receives events, via this local storage. | ||
## Installation | ||
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The package can be installed by adding `stagger` to your list of dependencies in `mix.exs`: | ||
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```elixir | ||
def deps do | ||
[ | ||
{:stagger, "~> 0.1.0"} | ||
] | ||
end | ||
``` | ||
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The docs can be found at <https://hexdocs.pm/stagger>. | ||
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## Copyright and License | ||
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Copyright (c) 2022, Nick Gunn | ||
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Stagger runtime source code is licensed under the [MIT License](LICENSE.md). | ||
Stagger test source code is licensed under the [GPL3 License](test/LICENSE). | ||
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defmodule Stagger do | ||
@moduledoc ~S""" | ||
Point-to-point, durable message-queues as GenStage producers. | ||
Stagger enables the creation of GenStage processes that enqueue terms to simple, | ||
file-backed message-queues, allowing the producer and consumer to run independently | ||
of each other, possibly at different times. | ||
+----------+ +----------+ +----------+ +------------+ | ||
| Upstream | | MsgQueue | | MsgQueue | | Downstream | | ||
| | -> | | <- | | <---> | | | ||
| Client | | Producer | | Consumer | | Processing | | ||
+----------+ +----------+ +----------+ +------------+ | ||
| | read | ||
write | | | ||
+------+ | ||
| FILE | | ||
| | | ||
| | | ||
+------+ | ||
Your upstream client writes its events into the message-queue (provided by | ||
Stagger), which persists them to local storage. Your (GenStage) consumer, subscribes | ||
to the producer and receives events, via this local storage. | ||
## Producers | ||
Upstream clients must first open their message-queue, via `open/1`, and then use the | ||
resulting process to enqueue writes, via `write/2`. | ||
{:ok, pid} = Stagger.open("/path/to/msg/queue") | ||
... | ||
:ok = Stagger.write(pid, "foo") | ||
:ok = Stagger.write(pid, "bar") | ||
:ok = Stagger.write(pid, "baz") | ||
The process created via `open/1` is the GenStage MsgQueue - by writing entries to it, | ||
it will satisfy demand from a downstream consumer. | ||
## Consumers | ||
Downstream clients are GenStage consumers. They must also open the message-queue, via | ||
`open/1` and then subscribe use existing GenStage subscription facilities: | ||
def init(args) do | ||
{:ok, pid} = Stagger.open("/path/to/msg/queue") | ||
{:ok, sub} = GenStage.sync_subscribe(self(), to: pid, ack: last_processed()) | ||
... | ||
end | ||
def handle_events(events, _from, stage) do | ||
... | ||
end | ||
## Sequence numbers | ||
Sequence numbers are used to control the events seen by a subscriber. Every event | ||
delivered to a consumer is a 2-tuple of `{seqno, msg}` and it is the consumer's | ||
responsibility to successfully record this sequence number as having been | ||
processed. | ||
A consumer must indicate its last-processed sequence number by passing `ack: N` in | ||
the subscription options (pass `ack: 0` when no such number exists) whenever it | ||
(re)subscribes. Event delivery will resume from the Nth + 1 event. | ||
Every message _written_ to the message-queue is assigned an incrementing sequence number | ||
by the Stagger process. When an existing message queue is re-opened, the process will | ||
first recover the last written number, using that as the base for any subsequent writes. | ||
## Purging | ||
In order to prevent unconstrained growth of the message-queue file, a consumer may | ||
periodically purge the queue of old entries by passing a `purge: N` option when it | ||
(re)subscribes e.g: | ||
last = last_processed() | ||
{:ok, sub} = GenStage.sync_subscribe(self(), to: pid, ack: last, purge: last) | ||
All entries _up to and including_ N are removed from the head of message-queue file. | ||
The value of N will be capped to no more than the value of the last ack'd message. | ||
To summarize: | ||
- `ack: N` determines that the next delivered message will have a seqno of N + 1 | ||
- `purge: M` is a hint to the producer to remove messages 1..M from the head of | ||
the message queue. | ||
## Why not RabbitMQ? | ||
If you think you need something like RabbitMQ, you probably do :-). Stagger is | ||
intended to be a lightweight durable message queue with minimal dependencies. | ||
""" | ||
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@doc """ | ||
Open a message-queue file, returning the pid responsible for managing it. | ||
The resulting pid can be used by upstream clients to enqueue messages via `write/2`, or | ||
may be used as the target of a GenStage subscribe operation. | ||
The following option may be passed to the function: | ||
* `hibernate_after: N` - After a period of _N_ milliseconds, the returned process will | ||
hibernate. If unspecified, defaults to 15 seconds. Pass `hibernate_after: :infinite` | ||
to inhibit this behaviour. This option only takes effect if the process managing the | ||
queue is created by the call to `open/2`. | ||
""" | ||
@spec open(binary, Keyword.t) :: :ignore | {:error, any} | {:ok, any} | {:ok, pid, any} | ||
def open(path, opts \\ []) when is_binary(path) do | ||
args = Map.new(opts) |> Map.put(:path, path) | ||
case DynamicSupervisor.start_child(Stagger.MsgQueueSupervisor, {Stagger.MsgQueue, args}) do | ||
{:ok, pid} -> | ||
{:ok, pid} | ||
{:error, {:already_started, pid}} -> | ||
{:ok, pid} | ||
error -> | ||
error | ||
end | ||
end | ||
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@doc """ | ||
Write a term to the message-queue. | ||
""" | ||
@spec write(pid :: atom | pid | {atom, any} | {:via, atom, any}, term :: any, timeout :: :infinite | non_neg_integer()) :: :ok | {:error, any} | ||
def write(pid, term, timeout \\ 5000) do | ||
Stagger.MsgQueue.write(pid, term, timeout) | ||
end | ||
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end |
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defmodule Stagger.Application do | ||
@moduledoc false | ||
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use Application | ||
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@impl true | ||
def start(_type, _args) do | ||
children = [ | ||
# A registry used to hold each MsgQueue, keyed by the path of the MsgQueue file | ||
%{id: Stagger.MsgQueueRegistry, start: {Registry, :start_link, [[keys: :unique, name: Stagger.MsgQueueRegistry]]}}, | ||
# The supervisor for the MsgQueue processes | ||
{DynamicSupervisor, strategy: :one_for_one, name: Stagger.MsgQueueSupervisor}, | ||
] | ||
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opts = [strategy: :one_for_one, name: Stagger.Supervisor] | ||
Supervisor.start_link(children, opts) | ||
end | ||
end |
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