got incorrect result with gevent

[torpedoallen]

import time
import gevent.monkey
gevent.monkey.patch_all()

a = time.time()
mc.set('a', 1)

def add(key):
    #with lock:
    mc.incr(key)

jobs = []
for i in xrange(1000):
    jobs.append(gevent.spawn(add, 'a'))
gevent.joinall(jobs)
print mc.get('a')
mc.delete('a')
print time.time() - a

just like the code above, It gives 995 but 1001 as suppose to be. Is there any idea about this issue?

Thanks in advance.

[jaysonsantos]

Hey @torpedoallen I guess it is because it is because you are having a race condition, imagine you have 10 threads trying to increment on the same value (and if there is no value, it will start as 0 I think), it is not predicable which will be the outcome.