yield 异步 并行 Promise await async

yield方式转移执行权的协程之间不是调用者与被调用者的关系，而是彼此对称、平等的

http://www.geeksforgeeks.org/use-yield-keyword-instead-return-keyword-python/

def simpleGeneratorFun():
    yield 1
    yield 2
    yield 3

for value in simpleGeneratorFun():
    print(value)

print('-----')

def nextSquare():
    i = 1
    while True:
        yield i * i
        i += 1

for num in nextSquare():
    if num > 100:
        break
    print(num)

Python yield 使用浅析 https://www.ibm.com/developerworks/cn/opensource/os-cn-python-yield/

 

GitHub - gevent/gevent: Coroutine-based concurrency library for Python https://github.com/gevent/gevent

gevent - 廖雪峰的官方网站 https://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/001407503089986d175822da68d4d6685fbe849a0e0ca35000

Python通过yield提供了对协程的基本支持，但是不完全。而第三方的gevent为Python提供了比较完善的协程支持。

gevent是第三方库，通过greenlet实现协程，其基本思想是：

当一个greenlet遇到IO操作时，比如访问网络，就自动切换到其他的greenlet，等到IO操作完成，再在适当的时候切换回来继续执行。由于IO操作非常耗时，经常使程序处于等待状态，有了gevent为我们自动切换协程，就保证总有greenlet在运行，而不是等待IO。

version = 3.7.4

协程创建 任务执行
Coroutines and Tasks — Python 3.7.4 documentation https://docs.python.org/3/library/asyncio-task.html#creating-tasks

# 协程通过 async/await 语法进行声明，是编写异步应用的推荐方式。
# Coroutines declared with async/await syntax is the preferred way of writing asyncio applications.

import asyncio
import time, random

def taskPool():
    '''
    任务池
    一个任务一个协程
    :return:
    '''
    return [i for i in range(random.randint(0, 32))]

# 协程通过 async/await 语法进行声明，是编写异步应用的推荐方式。
# Coroutines declared with async/await syntax is the preferred way of writing asyncio applications.
async def executeSingleTask(taskId, delay=10):
    print(f'taskId {taskId} started at {time.strftime("%X")}')
    await asyncio.sleep(delay)
    print(f'taskId {taskId} finished at {time.strftime("%X")}')

async def executeAllTask():
    # 获取任务
    taskList, awaitList = taskPool(), []

    # 异步任务创建
    for taskId in taskList:
        task = asyncio.create_task(executeSingleTask(taskId))
        awaitList.append(task)
    # 异步任务执行
    for a in awaitList:
        await a

asyncio.run(executeAllTask())

　　

D:\pyCGlang\venv\异步\Scripts\python.exe D:/pyCGlang/异步/a.py
taskId 0 started at 00:11:36
taskId 1 started at 00:11:36
taskId 2 started at 00:11:36
taskId 3 started at 00:11:36
taskId 4 started at 00:11:36
taskId 5 started at 00:11:36
taskId 6 started at 00:11:36
taskId 7 started at 00:11:36
taskId 8 started at 00:11:36
taskId 9 started at 00:11:36
taskId 10 started at 00:11:36
taskId 11 started at 00:11:36
taskId 12 started at 00:11:36
taskId 13 started at 00:11:36
taskId 14 started at 00:11:36
taskId 15 started at 00:11:36
taskId 16 started at 00:11:36
taskId 17 started at 00:11:36
taskId 18 started at 00:11:36
taskId 19 started at 00:11:36
taskId 20 started at 00:11:36
taskId 21 started at 00:11:36
taskId 22 started at 00:11:36
taskId 0 finished at 00:11:46
taskId 2 finished at 00:11:46
taskId 6 finished at 00:11:46
taskId 14 finished at 00:11:46
taskId 22 finished at 00:11:46
taskId 21 finished at 00:11:46
taskId 20 finished at 00:11:46
taskId 19 finished at 00:11:46
taskId 18 finished at 00:11:46
taskId 17 finished at 00:11:46
taskId 16 finished at 00:11:46
taskId 13 finished at 00:11:46
taskId 15 finished at 00:11:46
taskId 12 finished at 00:11:46
taskId 11 finished at 00:11:46
taskId 10 finished at 00:11:46
taskId 9 finished at 00:11:46
taskId 8 finished at 00:11:46
taskId 5 finished at 00:11:46
taskId 7 finished at 00:11:46
taskId 4 finished at 00:11:46
taskId 1 finished at 00:11:46
taskId 3 finished at 00:11:46

Process finished with exit code 0

　　

效果上实现了10个任务的并行执行

import asyncio
import time, random

def taskPool():
    '''
    任务池
    一个任务一个协程
    :return:
    '''
    return [i for i in range(random.randint(0, 32))]

# 协程通过 async/await 语法进行声明，是编写异步应用的推荐方式。
# Coroutines declared with async/await syntax is the preferred way of writing asyncio applications.
async def executeSingleTask(taskId, delay=10):
    print(f'taskId {taskId} started at {time.strftime("%X")}---{time.time()}')
    await asyncio.sleep(delay)
    print(f'taskId {taskId} finished at {time.strftime("%X")}---{time.time()}')

async def executeAllTask():
    # 获取任务
    taskList, awaitList = taskPool(), []

    # 异步任务创建
    for taskId in taskList:
        task = asyncio.create_task(executeSingleTask(taskId))
        awaitList.append(task)
    # 异步任务执行
    for a in awaitList:
        await a

asyncio.run(executeAllTask())

　　

D:\pyCGlang\venv\异步\Scripts\python.exe D:/pyCGlang/异步/a.py
taskId 0 started at 00:28:34---1567528114.565263
taskId 1 started at 00:28:34---1567528114.565263
taskId 2 started at 00:28:34---1567528114.565263
taskId 3 started at 00:28:34---1567528114.565263
taskId 4 started at 00:28:34---1567528114.565263
taskId 5 started at 00:28:34---1567528114.565263
taskId 6 started at 00:28:34---1567528114.565263
taskId 7 started at 00:28:34---1567528114.566263
taskId 8 started at 00:28:34---1567528114.566263
taskId 9 started at 00:28:34---1567528114.566263
taskId 10 started at 00:28:34---1567528114.566263
taskId 11 started at 00:28:34---1567528114.566263
taskId 12 started at 00:28:34---1567528114.566263
taskId 0 finished at 00:28:44---1567528124.5508342
taskId 2 finished at 00:28:44---1567528124.5508342
taskId 5 finished at 00:28:44---1567528124.5508342
taskId 1 finished at 00:28:44---1567528124.5508342
taskId 4 finished at 00:28:44---1567528124.5508342
taskId 3 finished at 00:28:44---1567528124.5508342
taskId 6 finished at 00:28:44---1567528124.566835
taskId 12 finished at 00:28:44---1567528124.566835
taskId 11 finished at 00:28:44---1567528124.566835
taskId 7 finished at 00:28:44---1567528124.566835
taskId 10 finished at 00:28:44---1567528124.566835
taskId 9 finished at 00:28:44---1567528124.566835
taskId 8 finished at 00:28:44---1567528124.566835

Process finished with exit code 0

　　

https://developers.google.com/web/fundamentals/primers/async-functions

function now(){
  const c=(new Date()) +(new Date().getMilliseconds());
  console.log(c);
}
function wait(ms) {
  now();
  return new Promise(r => setTimeout(r, ms));
}
async function parallel() {
  console.log("start!--->");
  now();
  const wait1 = wait(6000); // Start a 6000ms timer asynchronously…
  const wait2 = wait(6000); // …meaning this timer happens in parallel.
  await wait1; // Wait 6000ms for the first timer…
  await wait2; // …by which time this timer has already finished.
  console.log("<---done!");
  now();
  return "done!";
}
parallel();

　　

start!--->
VM125:4 Thu Sep 05 2019 20:19:24 GMT+0800 (新加坡标准时间)110
VM125:4 Thu Sep 05 2019 20:19:24 GMT+0800 (新加坡标准时间)110
VM125:4 Thu Sep 05 2019 20:19:24 GMT+0800 (新加坡标准时间)110
Promise {<pending>}__proto__: Promise[[PromiseStatus]]: "resolved"[[PromiseValue]]: "done!"
VM125:17 <---done!
VM125:4 Thu Sep 05 2019 20:19:30 GMT+0800 (新加坡标准时间)112

　　

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide/Using_promises

在 ECMAScript 2017 标准的 async/await 语法糖中，这种同步形式代码的对称性得到了极致的体现：

async function foo() {
  try {
    let result = await doSomething();
    let newResult = await doSomethingElse(result);
    let finalResult = await doThirdThing(newResult);
    console.log(`Got the final result: ${finalResult}`);
  } catch(error) {
    failureCallback(error);
  }
}