npm package: @microsoft/task-scheduler
Description: Schedule tasks in a monorepo
Author: Vincent Bailly
Latest version: 2.7.1

# @microsoft/task-scheduler

Run a sequence of steps across all the packages of a monorepo.

# Why

- This tool does not assume any workspace/package manager so it can be used on any JavaScript repository.
- The steps run on the main thread, sparing the cost of spawning one process per step. If parallelization is needed, the implementation of the steps can spawn processes.
- This tool optimizes CI builds performance by avoiding unnecessary waiting (see example below).
- This tool has no dependencies and is very small.
- Its interface makes it easy to compose with other tools to get fancy pipelines (eg. parallelization, profiling, throttling...)
- Running the tasks on the main node process allows for cross-step in-memory memoization

# Usage

```js
const { createPipeline } = require("@microsoft/task-scheduler");

// this graph describes a topological graph
// e.g. {foo: {location: 'packages/foo', dependencies: ['bar']}, bar: { ... }}
const graph = getDependencyGraph();

const pipeline = await createPipeline(graph)
  // defining a task with NO task dependencies
  .addTask({
    name: "prepare",
    run: prepare
  })
  // defining a task with task dependencies as well as the topological deps
  .addTask({
    name: "build",
    run: build,
    deps: ["prepare"],
    topoDeps: ["build"]
  })
  .addTask({
    name: "test",
    run: test,
    deps: ["build"]
  })
  .addTask({
    name: "bundle",
    run: bundle,
    deps: ["build"]
  })
  // you can call go() with no parameters to target everything, or specify which packages or tasks to target
  .go({
    packages: ["foo", "bar"],
    tasks: ["test", "bundle"]
  });

async function prepare(cwd, stdout, stderr) {
...
}

async function build(cwd, stdout, stderr) {
...
}

async function test(cwd, stdout, stderr) {
...
}

async function bundle(cwd, stdout, stderr) {
...
}

```

A `Task` is described by this:

```ts
type Task = {
  /** name of the task */
  name: string;

  /** a function that gets invoked by the task-scheduler */
  run: (cwd: string, stdout: Writable, stderr: Writable) => Promise<boolean>;

  /** dependencies between tasks within the same package (e.g. `build` -> `test`) */
  deps?: string[];

  /** dependencies across packages within the same topological graph (e.g. parent `build` -> child `build`) */
  topoDeps?: string[];

  /** An optional priority to set for packages that have this task. Unblocked tasks with a higher priority will be scheduled before lower priority tasks. */
  priorities?: {
    [packageName: string]: number;
  };
};
```

Here is how the tasks defined above would run on a repo which has two packages A and B, A depending on B:

```

A:            [-prepare-]         [------build------] [----test----]
                                                      [-----bundle-----]
B: [-prepare-] [------build------] [----test----]
                                   [-----bundle-----]
----------> time
```

Here is how the same workflow would be executed by using lerna:

```

A:            [-prepare-]                   [------build------] [----test----][-----bundle-----]

B: [-prepare-]           [------build------]                    [----test----][-----bundle-----]

----------> time
```

# Contributing

## Development

This repo uses `beachball` for automated releases and semver. Please include a change file by running:

```
$ yarn change
```

## CLA

This project welcomes contributions and suggestions. Most contributions require you to agree to a
Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us
the rights to use your contribution. For details, visit https://cla.opensource.microsoft.com.

When you submit a pull request, a CLA bot will automatically determine whether you need to provide
a CLA and decorate the PR appropriately (e.g., status check, comment). Simply follow the instructions
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This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.