Restart task

This is the way to create a restartable task.

This will cancel the oldest instance of the task and start a new instance of it. You can also provide a max that will only restart the oldest task instance if the threshold is exceeded.

Usage

To specify a task as restartable, you can either use the dot notation or the options notation.

Dot notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task.restart(async () => {
    // your code
  });
</script>

Options notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task(
    async () => {
      // your code
    },
    { kind: 'restart' },
  );
</script>

Caution

If you invoke perform multiple times in the same microtask, only the last instance will actually run because by the time the function is invoked the previous invocations would’ve been already canceled.

Max concurrency

This is how you can specify the maximum number of concurrent instances. The default is 1, here we’re setting it to 5.

Dot notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task.restart(
    async () => {
      // your code
    },
    { max: 5 },
  );
</script>

Options notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task(
    async () => {
      // your code
    },
    { kind: 'restart', max: 5 },
  );
</script>

The task class

The return value of the task function will be a svelte stateful class where you can access state from all the instances running and eventually cancel them with cancelAll.

Task structure Take a look at the Task structure documentation in our Getting started

Passing props

While defining a task, if the function that you pass in has some arguments, those will be required by the perform function (and it will be strongly typed too).

Caution

If you need to pass multiple props you should use an object because the second parameter will always be the SheepdogUtils.

Dot notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task.restart(async (id: string) => {
    // your code
  });
</script>

<button
  on:click={() => {
    restartTask.perform('42');
  }}>perform</button
>

Options notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task(
    async (id: string) => {
      // your code
    },
    { kind: 'restart' },
  );
</script>

<button
  on:click={() => {
    restartTask.perform('42');
  }}>perform</button
>

Getting the return value

If you return something from your task you can access the return value by awaiting the perform function.

Dot notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task.restart(async () => {
    return 42;
  });
</script>

<button
  on:click={() => {
    const number = await restartTask.perform();
    console.log(number); // 42
  }}>perform</button
>

Options notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task(
    async () => {
      return 42;
    },
    { kind: 'restart' },
  );
</script>

<button
  on:click={() => {
    const number = await restartTask.perform();
    console.log(number); // 42
  }}>perform</button
>

Getting the TaskInstance

If you don’t await the perform function, then you’ll get back the task instance that you can use either to cancel it or to get its current state. The TaskInstance is also a svelte stateful class and you can access the current value.

Dot notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task.restart(async () => {
    // your code
  });
</script>

<button
  on:click={() => {
    const lastRun = restartTask.perform();
    console.log(lastRun); // { isRunning: true, hasStarted: true, ... }
    lastRun.cancel();
  }}>perform</button
>

Options notation

<script lang="ts">
  import { task } from '@sheepdog/svelte';

  const restartTask = task(
    async () => {
      // your code
    },
    { kind: 'restart' },
  );
</script>

<button
  on:click={() => {
    lastRun = restartTask.perform();
    console.log(lastRun); // { isRunning: true, hasStarted: true, ... }
    lastRun.cancel();
  }}>perform</button
>