Add initial impl of TaskExecutor

packages/tasq/src/LinkedList.test.ts

@@ -10,16 +10,65 @@ describe('LinkedList', () => {
     })
   })
 
-  describe('push', () => {
+  describe('clear', () => {
+    it('clears the array and sets length to 0', () => {
+      const array = [0, 1, 2, 3, 4, 5]
+      const ll = LinkedList.fromArray(array)
+      expect(ll.length).toBe(6)
+      ll.clear()
+      expect(ll.length).toBe(0)
+      expect(ll.toArray()).toEqual([])
+    })
+  })
 
+  describe('push', () => {
+    it('pushes a new element to the end', () => {
+      const ll = new LinkedList()
+      ll.push(0)
+      expect(ll.length).toBe(1)
+      ll.push(1)
+      expect(ll.length).toBe(2)
+      ll.push(2, 3)
+      expect(ll.length).toBe(4)
+      ll.push(4, 5, 6)
+      expect(ll.length).toBe(7)
+      expect(ll.toArray()).toEqual([0, 1, 2, 3, 4, 5, 6])
+    })
   })
 
   describe('peek', () => {
-
+    it('returns the next element', () => {
+      const ll = new LinkedList()
+      expect(ll.peek()).toEqual(undefined)
+      expect(ll.peek()).toEqual(undefined)
+      ll.push(1)
+      expect(ll.peek()).toEqual(1)
+      expect(ll.peek()).toEqual(1)
+      ll.push(2)
+      expect(ll.peek()).toEqual(1)
+      expect(ll.peek()).toEqual(1)
+      ll.clear()
+      expect(ll.peek()).toEqual(undefined)
+    })
   })
 
-  describe('pop', () => {
-
+  describe('shift', () => {
+    it('returns the first element and shifts the linked list', () => {
+      const ll = LinkedList.fromArray([0, 1, 2, 3])
+      expect(ll.length).toBe(4)
+      expect(ll.shift()).toEqual(0)
+      expect(ll.length).toBe(3)
+      expect(ll.shift()).toEqual(1)
+      expect(ll.length).toBe(2)
+      expect(ll.shift()).toEqual(2)
+      expect(ll.length).toBe(1)
+      expect(ll.shift()).toEqual(3)
+      expect(ll.length).toBe(0)
+      expect(ll.shift()).toEqual(undefined)
+      expect(ll.length).toBe(0)
+      expect(ll.shift()).toEqual(undefined)
+      expect(ll.length).toBe(0)
+    })
   })
 
 })

packages/tasq/src/LinkedList.ts

@@ -1,6 +1,6 @@
 export interface IQueue<T> {
   push(...t: T[]): void
-  pop(): T | undefined
+  shift(): T | undefined
   peek(): T | undefined
   toArray(): T[]
 }
@@ -10,6 +10,28 @@ interface INode<T> {
   next?: INode<T>
 }
 
+export interface IIterator<T> {
+  hasNext(): boolean
+  next(): T | undefined
+}
+
+export class LinkedListIterator<T> implements IIterator<T> {
+  constructor(protected node: INode<T> | undefined) {
+  }
+  hasNext() {
+    return this.node !== undefined
+  }
+  next(): T | undefined {
+    if (this.node === undefined) {
+      return undefined
+    }
+    const node = this.node
+    const {value} = node
+    this.node = node.next
+    return value
+  }
+}
+
 export class LinkedList<T> implements IQueue<T> {
   length = 0
 
@@ -34,22 +56,21 @@ export class LinkedList<T> implements IQueue<T> {
     return this.head && this.head.value
   }
 
-  pop(): T | undefined {
+  shift(): T | undefined {
     if (!this.length) {
       return undefined
     }
-    if (this.length === 1) {
-      const value = this.head!.value
-      this.head = this.tail = undefined
-      this.length = 0
-      return value
-    }
     const head = this.head!
     this.head = head.next
     this.length--
     return head.value
   }
 
+  clear() {
+    this.head = this.tail = undefined
+    this.length = 0
+  }
+
   toArray(): T[] {
     const array: T[] = []
     for (let h = this.head; h !== undefined; h = h.next) {
@@ -58,6 +79,10 @@ export class LinkedList<T> implements IQueue<T> {
     return array
   }
 
+  iterator(): LinkedListIterator<T> {
+    return new LinkedListIterator(this.head)
+  }
+
   static fromArray<T>(t: T[]): LinkedList<T> {
     const list = new LinkedList<T>()
     list.push(...t)

packages/tasq/src/TaskExecutor.test.ts

@@ -0,0 +1,42 @@
+import {TaskExecutor} from './TaskExecutor'
+
+describe('TaskExecutor', () => {
+
+  function delay(ms: number): Promise<void> {
+    return new Promise(resolve => setTimeout(resolve, ms))
+  }
+
+  describe('post', () => {
+    it('posts new tasks and executes asynchronously', async () => {
+      const results: number[] = []
+      const te = new TaskExecutor<number>(1, async task => {
+        await delay(task)
+        results.push(task)
+      })
+      te.post(10)
+      te.post(5)
+      te.post(7)
+      await te.wait()
+      expect(results).toEqual([10, 5, 7])
+    })
+    it.only('executes tasks in different order', async () => {
+      const results: number[] = []
+      const te = new TaskExecutor<number>(2, async task => {
+        await delay(task)
+        results.push(task)
+      })
+      te.post(100) // worker1
+      te.post(50) // worker2
+      te.post(85) // worker2
+      te.post(10) // worker1
+      await te.wait()
+      expect(results).toEqual([50, 100, 10, 85])
+    })
+
+  })
+
+  describe('error handling', () => {
+
+  })
+
+})

packages/tasq/src/TaskExecutor.ts

@@ -1,25 +1,80 @@
-export interface ITaskExecutor<T> {
-  post(task: T)
-  start()
-  stop()
+import {EventEmitter} from 'events'
+import {LinkedList} from './LinkedList'
+
+export interface ITask<T> {
+  execute(): Promise<void>
 }
 
-export class Queue<T> {
-  pop()
+interface ITaskEvents {
+  success: void
+  failure: Error
 }
 
+export interface ITaskExecutor<T> {
+  post(task: T): void
+
+  wait(): Promise<void>
+
+  addListener<E extends keyof ITaskEvents>(
+    event: E, listener: (value: ITaskEvents[E]) => void): void
+  removeListener<E extends keyof ITaskEvents>(
+    event: E, listener: (value: ITaskEvents[E]) => void): void
+}
+
+let counter = 0
+
 export class TaskExecutor<T> implements ITaskExecutor<T> {
-  protected queue: T[] = []
+  protected taskQueue = new LinkedList<T>()
+  protected workers: Set<Promise<void>> = new Set()
+  protected events = new EventEmitter()
+
+  constructor(
+    readonly n: number = 1,
+    readonly processTask: (task: T) => Promise<void>,
+  ) {
+  }
+
+  addListener<E extends keyof ITaskEvents>(
+    event: E, listener: (value: ITaskEvents[E]) => void): void {
+    this.events.addListener(event, listener)
+  }
+  removeListener<E extends keyof ITaskEvents>(
+    event: E, listener: (value: ITaskEvents[E]) => void): void {
+    this.events.removeListener(event, listener)
+  }
 
   post(task: T) {
-    this.queue.push(task)
+    this.taskQueue.push(task)
+    if (this.workers.size < this.n) {
+      const worker = this.startWorker()
+    }
   }
 
-  start() {
-
+  protected async startWorker() {
+    counter++
+    const promise = this._startWorker(counter)
+    this.workers.add(promise)
+    await promise
+    this.workers.delete(promise)
   }
 
-  stop() {
+  protected async _startWorker(id: number) {
+    let task = this.taskQueue.shift()
+    while (task !== undefined) {
+      try {
+        await this.processTask(task)
+        this.events.emit('success')
+      } catch (err) {
+        this.events.emit('failure', err)
+      }
+      task = this.taskQueue.shift()
+    }
+  }
 
+  async wait() {
+    const workers = Array.from(this.workers)
+    for (const worker of workers) {
+      await worker
+    }
   }
 }