Gevent rawlink(callback) are executed before gevent.join() return

Gevent can spawn a co-routine: g1 = gevent.spawn(function)
After the function is been called, g1 has its return value: g1.value
If we want to have a callback with g1.value: g1.rawlink(callback)
This callback will be called before join: gevent.joinall([g1])

Here is the expirement about this conclusion:

Python语言: 

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Author: Yuande Liu
# gevent's rawlink(callback) are executed before gevent.join() return

from __future__ import print_function
import gevent
from gevent.pool import Pool
p = Pool(100)

alist = []

def return_self(x):
   return x

def callback(greenlet):
   """
   If we call `gevent.sleep(0)` in this callback:
       AssertionError: Impossible to call blocking function in the event loop callback
   """
   global alist
   alist.append( greenlet.value )
   2**2**20 # about 2s in Intel i5 2.4GHz

def run():
   for x in xrange(10000):
       b = p.spawn(return_self, x)
       b.rawlink(callback)

   global alist
   print('before join alist: {}'.format(len(alist)))
   p.join()
   print('after join alist: {}'.format(len(alist)))

run()
print('alist: {}'.format(len(alist)))

结果：

before join alist: 9900

after join alist: 10000

alist: 10000

阅读之后，发现确实是这样。