# Background Jobs

This crate provides tooling required to run some processes asynchronously from a usually
synchronous application. The standard example of this is Web Services, where certain things
need to be processed, but processing them while a user is waiting for their browser to respond
might not be the best experience.

### Usage
#### Add Background Jobs to your project
```toml
[dependencies]
actix = "0.8"
background-jobs = "0.5.1"
failure = "0.1"
futures = "0.1"
serde = "1.0"
serde_drive = "1.0"
sled = "0.24"
```

#### To get started with Background Jobs, first you should define a job.
Jobs are a combination of the data required to perform an operation, and the logic of that
operation. They implment the `Job`, `serde::Serialize`, and `serde::DeserializeOwned`.

```rust
use background_jobs::Job;
use serde_derive::{Deserialize, Serialize};

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct MyJob {
    some_usize: usize,
    other_usize: usize,
}

impl MyJob {
    pub fn new(some_usize: usize, other_usize: usize) -> Self {
        MyJob {
            some_usize,
            other_usize,
        }
    }
}

impl Job for MyJob {
    fn run(self, _: ()) -> Box<dyn Future<Item = (), Error = Error> + Send> {
        info!("args: {:?}", self);

        Box::new(Ok(()).into_future())
    }
}
```

The run method for a job takes an additional argument, which is the state the job expects to
use. The state for all jobs defined in an application must be the same. By default, the state
is an empty tuple, but it's likely you'll want to pass in some Actix address, or something
else.

Let's re-define the job to care about some application state.

```rust
#[derive(Clone, Debug)]
pub struct MyState {
    pub app_name: String,
}

impl MyState {
    pub fn new(app_name: &str) -> Self {
        MyState {
            app_name: app_name.to_owned(),
        }
    }
}

impl Job<MyState> for MyJob {
    fn run(self, state: MyState) -> Box<dyn Future<Item = (), Error = Error> + Send> {
        info!("{}: args, {:?}", state.app_name, self);

        Box::new(Ok(()).into_future())
    }
}
```

#### Next, define a Processor.
Processors are types that define default attributes for jobs, as well as containing some logic
used internally to perform the job. Processors must implement `Proccessor` and `Clone`.

```rust
use background_jobs::{Backoff, MaxRetries, Processor};

const DEFAULT_QUEUE: &'static str = "default";

#[derive(Clone, Debug)]
pub struct MyProcessor;

impl Processor<MyState> for MyProcessor {
    // The kind of job this processor should execute
    type Job = MyJob;

    // The name of the processor. It is super important that each processor has a unique name,
    // because otherwise one processor will overwrite another processor when they're being
    // registered.
    const NAME: &'static str = "MyProcessor";

    // The queue that this processor belongs to
    //
    // Workers have the option to subscribe to specific queues, so this is important to
    // determine which worker will call the processor
    //
    // Jobs can optionally override the queue they're spawned on
    const QUEUE: &'static str = DEFAULT_QUEUE;

    // The number of times background-jobs should try to retry a job before giving up
    //
    // Jobs can optionally override this value
    const MAX_RETRIES: MaxRetries = MaxRetries::Count(1);

    // The logic to determine how often to retry this job if it fails
    //
    // Jobs can optionally override this value
    const BACKOFF_STRATEGY: Backoff = Backoff::Exponential(2);
}
```

#### Running jobs
By default, this crate ships with the `background-jobs-actix` feature enabled. This uses the
`background-jobs-actix` crate to spin up a Server and Workers, and provides a mechanism for
spawning new jobs.

`background-jobs-actix` on it's own doesn't have a mechanism for storing worker state. This
can be implemented manually by implementing the `Storage` trait from `background-jobs-core`,
or the `background-jobs-sled-storage` crate can be used to provide a
[Sled](https://github.com/spacejam/sled)-backed jobs store.

With that out of the way, back to the examples:

##### Main
```rust
use actix::System;
use background_jobs::{ServerConfig, SledStorage, WorkerConfig};
use failure::Error;

fn main() -> Result<(), Error> {
    // First set up the Actix System to ensure we have a runtime to spawn jobs on.
    let sys = System::new("my-actix-system");

    // Set up our Storage
    let db = Db::start_default("my-sled-db")?;
    let storage = SledStorage::new(db)?;

    // Start the application server. This guards access to to the jobs store
    let queue_handle = ServerConfig::new(storage).start();

    // Configure and start our workers
    let mut worker_config = WorkerConfig::new(move || MyState::new("My App"));
    worker_config.register(MyProcessor);
    worker_config.set_processor_count(DEFAULT_QUEUE, 16);
    worker_config.start(queue_handle.clone());

    // Queue our jobs
    queue_handle.queue::<MyProcessor>(MyJob::new(1, 2))?;
    queue_handle.queue::<MyProcessor>(MyJob::new(3, 4))?;
    queue_handle.queue::<MyProcessor>(MyJob::new(5, 6))?;

    // Block on Actix
    sys.run()?;
    Ok(())
}
```

##### Complete Example
For the complete example project, see [the examples folder](https://git.asonix.dog/Aardwolf/background-jobs/src/branch/master/examples/actix-example)

#### Bringing your own server/worker implementation
If you want to create your own jobs processor based on this idea, you can depend on the
`background-jobs-core` crate, which provides the Processor and Job traits, as well as some
other useful types for implementing a jobs processor and job store.

### Contributing
Feel free to open issues for anything you find an issue with. Please note that any contributed code will be licensed under the GPLv3.

### License

Copyright © 2019 Riley Trautman

Background Jobs is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Background Jobs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. This file is part of Background Jobs.

You should have received a copy of the GNU General Public License along with Background Jobs. If not, see [http://www.gnu.org/licenses/](http://www.gnu.org/licenses/).