Python Eventlet派生不并发执行
Python Eventlet派生不并发执行
提问于 2016-08-09 16:51:29
我使用eventlet编写了以下两个版本的代码。预期2个spawn_n调用将并发执行，但事实并非如此。执行是串行进行的。
import eventlet
import threading
import datetime
from eventlet.green import urllib2
def hello(name):
print eventlet.greenthread.getcurrent(), threading.current_thread()
print datetime.datetime.now()
print " %s hello !!" % name
urllib2.urlopen("http://www.google.com/intl/en_ALL/images/logo.gif").read()
eventlet.spawn(hello, 'abc')
eventlet.spawn(hello, 'xyz')
eventlet.sleep(0)O/P：<_MainThread(MainThread，启动140365670881088)>
2016-08-09 14:04:57.782866
abc你好!！
<_MainThread(MainThread，启动140365670881088)>
2016-08-09 14:05:02.929903
xyz你好!！
import eventlet
import threading
import datetime
from eventlet.green import urllib2
def hello(name):
print eventlet.greenthread.getcurrent(), threading.current_thread()
print datetime.datetime.now()
print " %s hello !!" % name
urllib2.urlopen("http://www.google.com/intl/en_ALL/images/logo.gif").read()
pool = eventlet.GreenPool(size=4)
pool.spawn_n(hello, 'pqr')
pool.spawn_n(hello, 'lmn')
pool.waitall()O/P：<_MainThread(MainThread，启动139897149990720)>
2016-08-09 14:05:25.613546
pqr你好!！
<_MainThread(MainThread，启动139897149990720)>
2016-08-09 14:05:30.699473
lmn你好!！
在这两个版本的代码中，调用都是按顺序进行的。
回答 1
Stack Overflow用户
发布于 2016-08-10 17:58:26
def fun(tag):
print('{0} begin'.format(tag))
eventlet.sleep(0.1) # pretty much the same as running HTTP request and throwing results away
print('{0} end'.format(tag))
t1 = time.time()
pool.spawn(fun, 'Turtle')
pool.spawn(fun, 'Achilles')
pool.waitall()
tt = time.time() - t1
print('Total time: {0:.2f}'.format(tt))您将看到类似于以下内容的输出：
Turtle begin
Achilles begin
Turtle end
Achilles end
Total time: 0.10这表明函数的执行是在IO等待点处交错执行的(休眠)，这接近于协作并发的定义。还要注意，总时间不是两个睡眠的总和，而是最大+基础设施开销(在这个合成测试中应该接近于零)。
有问题的代码无法显示这一点，因为在IO之前只有print(它不会在Eventlet中创建IO等待)，在IO之后没有。所以你实际要执行的是：
main: pool.waitall() begin, switch to Eventlet loop
loop: oh, there are greenthreads scheduled to run now, switch to 1
1: print this
1: print that
1: urllib... start network IO, switch to loop
loop: there is another green thread scheduled, switch to 2
2: print this
2: print that
2: urllib... start network IO, switch to Eventlet loop
loop: wait for any event that should wake greenthread,
suppose that would be thread 1 urllib that is finished first
1: HTTP request finished, thread 1 finished, but no code to prove it
loop: wait for any event...
2: HTTP request finished, thread 2 finished
main: pool.waitall() finished页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/38846147
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