Fang

Background task processing library for Rust. It uses Postgres DB as a task queue.

Installation

1. Add this to your Cargo.toml

[dependencies]
fang = "0.6"
serde = { version = "1.0", features = ["derive"] }

Supports rustc 1.62+

2. Create fang_tasks table in the Postgres database. The migration can be found in the migrations directory.

Usage

Defining a task

Every task should implement fang::Runnable trait which is used by fang to execute it.

use fang::Error;
use fang::Runnable;
use fang::typetag;
use fang::PgConnection;
use serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize)]
struct MyTask {
    pub number: u16,
}

#[typetag::serde]
impl Runnable for MyTask {
    fn run(&self, _connection: &PgConnection) -> Result<(), Error> {
        println!("the number is {}", self.number);

        Ok(())
    }
}

As you can see from the example above, the trait implementation has #[typetag::serde] attribute which is used to deserialize the task.

The second parameter of the run function is diesel's PgConnection, You can re-use it to manipulate the task queue, for example, to add a new job during the current job's execution. Or you can just re-use it in your own queries if you're using diesel. If you don't need it, just ignore it.

Enqueuing a task

To enqueue a task use Queue::enqueue_task

use fang::Queue;

...

Queue::enqueue_task(&MyTask { number: 10 }).unwrap();

The example above creates a new postgres connection on every call. If you want to reuse the same postgres connection to enqueue several tasks use Postgres struct instance:

let queue = Queue::new();

for id in &unsynced_feed_ids {
    queue.push_task(&SyncFeedMyTask { feed_id: *id }).unwrap();
}

Or you can use PgConnection struct:

Queue::push_task_query(pg_connection, &new_task).unwrap();

Starting workers

Every worker runs in a separate thread. In case of panic, they are always restarted.

Use WorkerPool to start workers. WorkerPool::new accepts one parameter - the number of workers.

use fang::WorkerPool;

WorkerPool::new(10).start();

Use shutdown to stop worker threads, they will try to finish in-progress tasks.

use fang::WorkerPool;

worker_pool = WorkerPool::new(10).start().unwrap;

worker_pool.shutdown()

Using a library like signal-hook, it's possible to gracefully shutdown a worker. See the Simple Worker for an example implementation.

Check out:

• Simple Worker Example - simple worker example
• El Monitorro - telegram feed reader. It uses Fang to synchronize feeds and deliver updates to users.

Configuration

To configure workers, instead of WorkerPool::new which uses default values, use WorkerPool.new_with_params. It accepts two parameters - the number of workers and WorkerParams struct.

Configuring the type of workers

You can start workers for a specific types of tasks. These workers will be executing only tasks of the specified type.

Add task_type method to the Runnable trait implementation:

...

#[typetag::serde]
impl Runnable for MyTask {
    fn run(&self) -> Result<(), Error> {
        println!("the number is {}", self.number);

        Ok(())
    }

    fn task_type(&self) -> String {
        "number".to_string()
    }
}

Set task_type to the WorkerParamas:

let mut worker_params = WorkerParams::new();
worker_params.set_task_type("number".to_string());

WorkerPool::new_with_params(10, worker_params).start();

Without setting task_type workers will be executing any type of task.

Configuring retention mode

By default, all successfully finished tasks are removed from the DB, failed tasks aren't.

There are three retention modes you can use:

pub enum RetentionMode {
    KeepAll,        \\ doesn't remove tasks
    RemoveAll,      \\ removes all tasks
    RemoveFinished, \\ default value
}

Set retention mode with set_retention_mode:

let mut worker_params = WorkerParams::new();
worker_params.set_retention_mode(RetentionMode::RemoveAll);

WorkerPool::new_with_params(10, worker_params).start();

Configuring sleep values

You can use use SleepParams to confugure sleep values:

pub struct SleepParams {
    pub sleep_period: u64,     \\ default value is 5
    pub max_sleep_period: u64, \\ default value is 15
    pub min_sleep_period: u64, \\ default value is 5
    pub sleep_step: u64,       \\ default value is 5
}p

If there are no tasks in the DB, a worker sleeps for sleep_period and each time this value increases by sleep_step until it reaches max_sleep_period. min_sleep_period is the initial value for sleep_period. All values are in seconds.

Use set_sleep_params to set it:

let sleep_params = SleepParams {
    sleep_period: 2,
    max_sleep_period: 6,
    min_sleep_period: 2,
    sleep_step: 1,
};
let mut worker_params = WorkerParams::new();
worker_params.set_sleep_params(sleep_params);

WorkerPool::new_with_params(10, worker_params).start();

Periodic Tasks

Fang can add tasks to fang_tasks periodically. To use this feature first run the migration with fang_periodic_tasks table.

Usage example:

use fang::Scheduler;
use fang::Queue;

let queue = Queue::new();

queue
     .push_periodic_task(&SyncMyTask::default(), 120)
     .unwrap();

queue
     .push_periodic_task(&DeliverMyTask::default(), 60)
     .unwrap();

Scheduler::start(10, 5);

In the example above, push_periodic_task is used to save the specified task to the fang_periodic_tasks table which will be enqueued (saved to fang_tasks table) every specied number of seconds.

Scheduler::start(10, 5) starts scheduler. It accepts two parameters:

• Db check period in seconds
• Acceptable error limit in seconds - |current_time - scheduled_time| < error

Contributing

1. Fork it!
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Running tests locally

cargo install diesel_cli

docker run --rm -d --name postgres -p 5432:5432 \
  -e POSTGRES_DB=fang \
  -e POSTGRES_USER=postgres \
  -e POSTGRES_PASSWORD=postgres \
  postgres:latest

DATABASE_URL=postgres://postgres:postgres@localhost/fang diesel migration run

// Run regular tests
cargo test --all-features

// Run dirty/long tests, DB must be recreated afterwards
cargo test --all-features -- --ignored --test-threads=1

docker kill postgres

Author

Ayrat Badykov (@ayrat555)