cel()
consumer_2.cancel()
await asyncio.gather(consumer_1, consumer_2, producer_1, producer_2, return_exceptions=True)
%time asyncio.run(main())
########## 输出 ##########
producer_1 put a val: 5
producer_2 put a val: 3
consumer_1 get a val: 5
consumer_2 get a val: 3
producer_1 put a val: 1
producer_2 put a val: 3
consumer_2 get a val: 1
consumer_1 get a val: 3
producer_1 put a val: 6
producer_2 put a val: 10
consumer_1 get a val: 6
consumer_2 get a val: 10
producer_1 put a val: 4
producer_2 put a val: 5
consumer_2 get a val: 4
consumer_1 get a val: 5
producer_1 put a val: 2
producer_2 put a val: 8
consumer_1 get a val: 2
consumer_2 get a val: 8
Wall time: 10 s
并发编程之 Futures
区别并发和并行
- 并发通常应用与 I/O 操作频繁的场景，比如你要从网站上下载多个文件， I/O 操作的时间可能比 CPU 运行处理的时间长得多，通过线程和任务之间互相切换的方式实现，但同一时刻，只允许有一个线程或任务执行
- 并行更多应用于 CPU heavy 的场景，比如 MapReduce 中的并行计算，为了加快运算速度，一般会用多台机器，多个处理器来完成。可以让多个进程完全同步同时的执行
Python 中之所以同一时刻只运行一个线程运行，其实是由于全局解释锁的存在。但对 I/O 操作而言，当其被 block 的时候，全局解释器锁便会被释放，使气体线程继续执行。
import concurrent.futures
import requests
import threading
import time
def download_one(url):
resp = requests.get(url)
print('Read {} from {}'.format(len(resp.content), url))
# 版本 1
def download_all(sites):
with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
executor.map(download_one, sites)
# 版本 2
def download_all(sites):
with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
to_do = []
for site in sites:
future = executor.submit(download_one, site)
to_do.append(future)
for future in concurrent.futures.as_completed(to_do):
future.result()
def main():
sites = [
'https://en.wikipedia.org/wiki/Portal:Arts',
'https://en.wikipedia.org/wiki/Portal:History',
'https://en.wikipedia.org/wiki/Portal:Society',
'https://en.wikipedia.org/wiki/Portal:Biography',
'https://en.wikipedia.org/wiki/Portal:Mathematics',
'https://en.wikipedia.org/wiki/Portal:Technology',
'https://en.wikipedia.org/wiki/Portal:Geography',
'https://en.wikipedia.org/wiki/Portal:Science',
'https://en.wikipedia.org/wiki/Computer_science',
'https://en.wikipedia.org/wiki/Python_(programming_language)',
'https://en.wikipedia.org/wiki/Java_(programming_language)',
'https://en.wikipedia.org/wiki/PHP',
'https://en.wikipedia.org/wiki/Node.js',
'https://en.wikipedia.org/wiki/The_C_Programming_Language',
'https://en.wikipedia.org/wiki/Go_(programming_language)'
]
start_time = time.perf_counter()
download_all(sites)
end_time = time.perf_counter()
print('Download {} sites in {} seconds'.format(len(sites), end_time - start_time))
if __name__ == '__main__':
main()
## 输出
Read 151021 from https://en.wikipedia.org/wiki/Portal:Mathematics
Read 129886 from https://en.wikipedia.org/wiki/Portal:Arts
Read 107637 from https://en.wikipedia.org/wiki/Portal:Biography
Read 224118 from https://en.wikipedia.org/wiki/Portal:Society
Read 184343 from https://en.wikipedia.org/wiki/Portal:History
Read 167923 from https://en.wikipedia.org/wiki/Portal:Geography
Read 157811 from https://en.wikipedia.org/wiki/Portal:Technology
Read 91533 from https://en.wikipedia.org/wiki/Portal:Science
Read 321352 from https://en.wikipedia.org/wiki/Computer_science
Read 391905 from https://en.wikipedia.org/wiki/Python_(programming_la