feat: pool.cancelPendingTasks method

[AriPerkkio]

• Fixes Feature: pool.cancelPendingTasks method for gracefully cancelling all tasks that have not started #52

Here is the same test case with signal usage to demonstrate the issue clearly:

import EventEmitter from 'events'

test('queued tasks can be aborted', async () => {
  const pool = new Tinypool({
    filename: resolve(__dirname, 'fixtures/sleep.js'),
    minThreads: 0,
    maxThreads: 1,
  })

  const signal = new EventEmitter()

  const time = 500
  const promises = []
  let finishedTasks = 0
  let cancelledTasks = 0

  for (const _ of Array(10).fill(0)) {
    const promise = pool
      .run({ time }, { signal })
      .then(() => {
        finishedTasks++
      })
      .catch((error) => {
        if (error.message !== 'The task has been aborted') {
          throw error
        }
        cancelledTasks++
      })
    promises.push(promise)
  }

  // Wait for task to start
  await new Promise((resolve) => setTimeout(resolve, time / 2))
  expect(pool.queueSize).toBe(9)

  // One task is running, cancel the pending ones
  signal.emit('abort')

  // The first task should still be on-going, pending ones should be cancelled
  expect(finishedTasks).toBe(0)
  expect(pool.queueSize).toBe(0)

  await Promise.all(promises)

  expect({ finishedTasks, cancelledTasks }).toEqual({
    finishedTasks: 1,
    cancelledTasks: 9,
  })
})

[Aslemammad]

Nice! Please try adding a documentation.

[AriPerkkio]

Documentation added. I did some refactoring to the old ones to make sure constructor options, pool methods and package exports are in their own sections.

[Aslemammad]

Thank you so much.